Experimental and computational investigation of a DNA-shielded 3D metal–organic framework for the prompt dual sensing of Ag+ and S2−

We herein report an efficient Ag⁺ and S²⁻ dual sensing scenario by a three-dimensional (3D) Cu-based metal–organic framework [Cu(Cdcbp)(bpea)]_n (MOF 1, H₃CdcbpBr = 3-carboxyl-(3,5-dicarboxybenzyl)-pyridinium bromide, bpea = 1,2-di(4-pyridinyl)ethane) shielded with a 5-carboxytetramethylrhodamine (TAMRA)-labeled C-rich single-stranded DNA (ss-probe DNA, P-DNA) as a fluorescent probe. The formed MOF-DNA probe, denoted as P-DNA@1, is able to sequentially detect Ag⁺ and S²⁻ in one pot, with detection limits of 3.8 nM (for Ag⁺) and 5.5 nM (for S²⁻), which are much more lower than the allowable Ag⁺ (0.5 μM) and S²⁻ (0.6 μM) concentration in drinking water as regulated by World Health Organization (WHO). The detection method has been successfully applied to sense Ag⁺ and S²⁻ in domestic, lake, and mineral water with satisfactory recoveries ranging from 98.2 to 107.3%. The detection mechanism was further confirmed by molecular simulation studies.

We herein report an efficient Ag⁺ and S²⁻ dual sensing scenario by a three-dimensional Cu-based metal–organic framework shielded with a 5-carboxytetramethylrhodamine-labeled C-rich single-stranded DNA as a fluorescent probe.     

Reversible four-color electrochromism triggered by the electrochemical multi-step redox of Cr-based metallo-supramolecular polymers

Four color electrochromism (yellow, magenta, blue, and navy) has been achieved in Cr(iii)-based metallo-supramolecular polymers (polyCr), which were synthesized by 1 : 1 complexation of Cr ions and 1,4-di[[2,2′:6′,2′′-terpyridin]-4′-yl]benzene (L). The polymer structure was determined by X-ray absorption fine structure (XAFS) measurement and X-ray photoelectron spectroscopy (XPS). The molecular weight of polyCr was calculated as 3.2 × 10⁷ Da using right angle light scattering (RALS). The EXAFS fitting indicated that the bond distances of Cr–N are 2.020 Å and 2.208 Å. A film of polyCr shows multi-color electrochromism (EC) or absorption: a sharp peak at 380 nm at 0 V vs. Ag/Ag⁺ (yellow), a sharp peak at 510 nm and a broad peak at 800 nm at −0.6 V vs. Ag/Ag⁺ (magenta), a broad peak at 610 nm and between 700–900 nm at −1.2 V vs. Ag/Ag⁺ (blue), a broad peak between 450–900 nm at −1.8 V vs. Ag/Ag⁺ (navy). The transmittances change (ΔT), the switching times for coloring and bleaching (T_c, T_b) and the coloration efficiency (η_c, η_b): [ΔT, (T_c, T_b), (η_c, η_b)] were [39.2%, (5.56 s, 1.39 s), (169 cm² C⁻¹, 230 cm² C⁻¹)] at 510 nm between −0.6 and 0.2 V vs. Ag/Ag⁺, [67.0%, (6.93 s, 2.52 s), (138 cm² C⁻¹, 172 cm² C⁻¹)] at 610 nm between −1.2 and 0.2 V vs. Ag/Ag⁺, [86.1%, (6.80 s, 3.03 s), (167 cm² C⁻¹, 134 cm² C⁻¹)] at 780 nm between −1.8 and 0.2 V vs. Ag/Ag⁺, respectively, during the cycles. The durability experiment indicates that polyCr shows an EC property for at least 100 cycles.

Four color electrochromism (yellow, magenta, blue, and navy) has been achieved in Cr(iii)-based metallo-supramolecular polymers (polyCr), which were synthesized by 1 : 1 complexation of Cr ions and 1,4-di[[2,2′:6′,2′′-terpyridin]-4′-yl]benzene (L).     

BrCl+ elimination from Coulomb explosion of 1,2-bromochloroethane induced by intense femtosecond laser fields

By using a dc-slice imaging technique, photodissociation of 1,2-C₂H₄BrCl was investigated at 800 nm looking for heteronuclear unimolecular ion elimination of BrCl⁺ in an 80 fs laser field. The occurrence of fragment ion BrCl⁺ in the mass spectrum verified the existence of a unimolecular decomposition channel of BrCl⁺ in this experiment. The relative quantum yield of the BrCl⁺ channel was measured to be 0.8%. By processing and analyzing the velocity and angular distributions obtained from the corresponding sliced images of BrCl⁺ and its partner ion C₂H₄⁺, we concluded that BrCl⁺ came from Coulomb explosion of the 1,2-bromochloroethane dication 1,2-C₂H₄BrCl²⁺. With the aid of quantum chemical calculations at the M06-2X/def2-TZVP level, the potential energy surface for BrCl⁺ detachment from 1,2-C₂H₄BrCl²⁺ has been examined in detail. According to the ab initio calculations, two transition state structures tended to correlate with the reactant 1,2-C₂H₄BrCl²⁺ and the products BrCl⁺ + C₂H₄⁺. In this entire dissociation process, the C–Br and C–Cl bond lengths were observed to elongate asymmetrically, that is, the C–Br chemical bond broke firstly, and subsequently a new Br–Cl chemical bond started to emerge while the C–Cl bond continued to exist for a while. Hence, an asynchronous concerted elimination mechanism was favored for BrCl⁺ detachment.

Concerted elimination of the molecular ion BrCl⁺ from Coulomb explosion of 1,2-bromochloroethane was studied theoretically and experimentally.     

A Bi2WO6/Ag2S/ZnS Z-scheme heterojunction photocatalyst with enhanced visible-light photoactivity towards the degradation of multiple dye pollutants

A novel visible-light-driven Z-scheme heterojunction, Bi₂WO₆/Ag₂S/ZnS, was synthesized and its photocatalytic activity was evaluated for the treatment of a binary mixture of dyes, and its physicochemical properties were characterized using FT-IR, XRD, DRS and FE-SEM techniques. The Bi₂WO₆/Ag₂S/ZnS Z-scheme heterojunctions not only facilitate the charge separation and transfer, but also maintain the redox ability of their components. The superior photocatalytic activity demonstrated by the Z-scheme Bi₂WO₆/Ag₂S/ZnS attributes its unique properties such as the rapid generation of electron–hole pairs, slow recombination rate, and narrow bandgap. The performance of the Bi₂WO₆/Ag₂S/ZnS was evaluated for the simultaneous degradation of methyl green (MG) and auramine-O (AO) dyes, while the influences of the initial MG concentration (4–12 mg L⁻¹), initial AO concentration (2–6 mg L⁻¹), pH (3–9), irradiation time (60–120 min) and photocatalyst dosage (0.008–0.016 g L⁻¹) were investigated through the response surface methodology. The desirability function approach was applied to optimize the process and results revealed that maximum photocatalytic degradation efficiency was obtained at optimum conditions including 6.08 mg L⁻¹ of initial MG concentration, 4.04 mg L⁻¹ of initial AO concentration, 7.25 of pH, 90.58 min of irradiation time and 0.013 g L⁻¹ of photocatalyst dosage. In addition, a possible photocatalytic mechanism of the Bi₂WO₆/Ag₂S/ZnS heterojunction was proposed based on the photoinduced charge carriers.

A Z-scheme Bi₂WO₆/Ag₂S/ZnS heterojunction was successfully synthesized as a novel visible-light-driven photocatalyst for the degradation of multiple dye pollutants.     

The green synthesis of a palm empty fruit bunch-derived sulfonated carbon acid catalyst and its performance for cassava peel starch hydrolysis

A sulfonated carbon acid catalyst (C–SO₃H) was successfully generated from palm empty fruit bunch (PEFB) carbon via hydrothermal sulfonation via the addition of hydroxyethylsulfonic acid and citric acid. The C–SO₃H catalyst was identified as containing 1.75 mmol g⁻¹ of acid and 40.2% sulphur. The surface morphology of C–SO₃H shows pores on its surface and the crystalline index (CrI) of PEFB was decreased to 63.8% due to the change structure as it became carbon. The surface area of the carbon was increased significantly from 11.5 to 239.65 m² g⁻¹ after sulfonation via hydrothermal treatment. The identification of –SO₃H, COOH and –OH functional groups was achieved using Fourier-transform infrared spectroscopy. The optimal catalytic activity of C–SO₃H was achieved via hydrolysis reaction with a yield of 60.4% of total reducing sugar (TRS) using concentrations of 5% (w/v) of both C–SO₃H and cassava peel starch at 100 °C for 1 h. The stability of C–SO₃H shows good performance over five repeated uses, making it a good potential candidate as a green and sulfonated solid acid catalyst for use in a wide range of applications.

A sulfonated carbon acid catalyst (C–SO₃H) was successfully generated from palm empty fruit bunch (PEFB) carbon via hydrothermal sulfonation via the addition of hydroxyethylsulfonic acid and citric acid.     

Theoretical study on molecular mechanism of aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformyfuran catalyzed by VO2+ with counterpart anion in N,N-dimethylacetamide solution

Vanadium-containing catalysts exhibit good catalytic activity toward the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformyfuran (DFF). The aerobic oxidation mechanism of HMF to DFF catalyzed by VO₂⁺ with counterpart anion in N,N-dimethylacetamide (DMA) solution have been theoretically investigated. In DMA solution, the stable VO₂⁺-containing complex is the four-coordinated [V(O)₂(DMA)₂]⁺ species. For the gross reaction of 2HMF + O₂ → 2DFF + 2H₂O, there are three main reaction stages, i.e., the oxidation of the first HMF to DFF with the reduction of [V(O)₂(DMA)₂]⁺ to [V(OH)₂(DMA)]⁺, the aerobic oxidation of [V(OH)₂(DMA)]⁺ to the peroxide [V(O)₃(DMA)]⁺, and the oxidation of the second HMF to DFF with the reduction of [V(O)₃(DMA)]⁺ to [V(O)₂(DMA)₂]⁺. The rate-determining reaction step is associated with the C–H bond cleavage of –CH₂ group of the first HMF molecule. The peroxide [V(O)₃(DMA)]⁺ species exhibits better oxidative activity than the initial [V(O)₂(DMA)₂]⁺ species, which originates from its narrower HOMO–LUMO gap. The counteranion Cl⁻ exerts promotive effect on the aerobic oxidation of HMF to DFF catalyzed by [V(O)₂(DMA)₂]⁺ species.

The rate-determining reaction step is associated with the C–H bond cleavage of –CH₂ group of the first HMF molecule oxidized by [V(O)₂(DMA)₂]⁺ species, while counteranion Cl⁻ exhibits catalytically promotive effect.     

Direct cyanidation of silver sulfide by heterolytic C–CN bond cleavage of acetonitrile

Extraction of silver as silver cyanide from silver sulfide was made possible using acetonitrile as the source of cyanide. The process of cyanidation took place through the oxidation of sulfide to sulfur oxides and cleavage of the C–CN bond of acetonitrile. The reaction was found to be catalyzed by vanadium pentoxide and hydrogen peroxide. The different species involved in the cyanidation process were duly characterized using FTIR, ESI-MS, HRMS, XPS and UV-vis spectroscopic analysis. The mechanism of the cyanidation process was confirmed through in situ FTIR analysis.

Herein, we report the cleavage of the C–CN bond of acetonitrile, catalyzed by vanadium pentoxide, for the direct cyanidation of silver sulfide.

Silver (Ag) is a precious noble metal that has found applications in photography, nanocatalysis, antibacterial agents and jewelry.^1–3 Most importantly, it contributes to the economic growth of numerous countries. Silver metal extracted from its main ores contributes to a high percentage (∼30%) of the total world production of Ag. Silver sulfide (Ag₂S) is the most common ore from which it is extracted.^4,5 However, the traditional way of extracting Ag from Ag₂S ore has many disadvantages, as it involves the use of poisonous sodium cyanide (NaCN) or potassium cyanide (KCN), which are also used in gold (Au) extraction.^4,5 The use of cyanide to achieve Ag leaching has led to great public concern, due to the damage it can cause to both human health and the environment. Because of the high toxicity of cyanide salts, strict regulation has been imposed to regulate or to ban the leaching of cyanide into the environment.⁶ It has been reported that the use of such cyanide salts in Au mining industries has led to the death of people working in those industries.⁷ Because of the devastating impacts of cyanide poisoning, researchers are constantly searching for alternative methods and new lixiviants to replace cyanide salt in silver extraction from Ag₂S. So far, researchers have adopted various alternative methods for silver extraction, such as leaching of Ag₂S using ferricyanide-cyanide solution.^8,9 Some have also used the precipitation method using high pressure and so on.¹⁰ Recently, the use of thiosulfate solution with buffer solution, most commonly ammonium acetate buffer at pH = 4, has drawn great attention, and has been found to be a potential candidate for Ag extraction from its ores.¹¹ Although the method is cheaper, it consumes a high concentration of the reagent and also depends on different conditions such as pH and the kinetics of oxygen reduction.^11,12 The reaction of silver ions (Ag⁺) with thiosulfate solution in the presence of a base (NH₃) is thermodynamically favorable, but the slow oxygen reduction process leads to deliberate leaching of Ag as silver thiosulfate complex, Ag(S₂O₃)₃⁵⁻.¹² Hence, the search for an alternative method is still an ongoing research process.Apart from alkali cyanides, alkyl nitriles such as acetonitrile (CH₃CN) are much less toxic and can be used as a source of cyanide ions (CN⁻).¹³ However, the thermodynamic stability and high bond energy associated with the C–CN bond restrict the application of this green solvent as a source of cyanide (CN⁻) in the silver extraction process.¹⁴ Literature reports suggest that organometallic catalysts can scissor the C–CN bond very effectively.^15–17 However, to the best of our knowledge, there is no such report that applies CH₃CN as a lixiviant in silver extraction as AgCN from Ag₂S. Recently, we reported that CH₃CN can be a suitable solvent to act as a cyanide source for the direct cyanidation of silver nitrates (AgNO₃) in the presence of vanadium pentoxide (V₂O₅) and hydrogen peroxide (H₂O₂).¹⁸ However, Ag is mostly extracted from Ag₂S in mining industries. Therefore, with our growing interest in finding a solution to replace cyanide salt, herein we demonstrate a highly effective method that allows for the direct precipitation of AgCN from Ag₂S within a very short period of time.Initially, to achieve the cyanidation of Ag₂S and obtain silver (Ag) as silver cyanide (AgCN), silver sulfide (Ag₂S) and vanadium pentoxide (V₂O₅) were mixed in a 1 : 1 ratio using a mortar and pestle. The mixture was ground for few minutes and then dried in oven at 100 °C. The process of grinding and heating was continued for 2 h by making a paste using an ethanol/water mixture as a solvent. The whole solid mixture was transferred to a 25 mL round bottom flask, followed by dropwise addition of 2 mL of hydrogen peroxide (30% w/v) in 10 mL CH₃CN as a solvent. The reaction mixture was then stirred for 90 min at room temperature. The solid material became completely dissolved and formed a homogeneous mixture, and the color of the solution was found to transform from black to yellow and finally to red, as shown in Scheme 1. Along with the change in color, white particles also began to precipitate from the solution, and this precipitation process was completed upon allowing the solution to stand overnight. The white precipitate was obtained by filtration using Whatmann filter paper, and was washed several times with double deionized water, and collected for further characterization. The obtained red filtrate was also kept for further analysis.Open in a separate windowScheme 1Synthesis of AgCN by cyanidation of Ag₂S.The formation of AgCN was found to be dependent on the amounts of V₂O₅ and the oxidant H₂O₂. The optimization values for these are depicted in ​and2.2. From

Microstructure–mechanical properties of Ag0/Au0 doped K–Mg–Al–Si–O–F glass-ceramics

In understanding the catalytic efficacy of silver (Ag⁰) and gold (Au⁰) nanoparticles (NPs) on glass-ceramic (GC) crystallization, the microstructure–machinability correlation of a SiO₂–MgO–Al₂O₃–B₂O₃–K₂O–MgF₂ system is studied. The thermal parameters viz., glass transition temperature (T_g) and crystallization temperature (T_c) were extensively changed by varying NPs (in situ or ex situ). Tc was found to be increased (T_c = 870–875 °C) by 90–110 °C when ex situ NPs were present in the glass system. Under controlled heat-treatment at 950 ± 10 °C, the glasses were converted into glass-ceramics with the predominant presence of crystalline phase (XRD) fluorophlogopite mica, [KMg₃(AlSi₃O₁₀)F₂]. Along with the secondary phase enstatite (MgSiO₃), the presence of Ag and Au particles (FCC system) were identified by XRD. A microstructure containing spherical crystallite precipitates (∼50–400 nm) has been observed through FESEM in in situ doped GCs. An ex situ Ag doped GC matrix composed of rock-like and plate-like crystallites mostly of size 1–3 μm ensured its superior machinability. Vicker''s and Knoop microhardness of in situ doped GCs were estimated within the range 4.45–4.61 GPa which is reduced to 4.21–4.34 GPa in the ex situ Ag system. Machinability of GCs was found to be in the order, ex situ Ag > ex situ Au ∼ in situ Ag > in situ Au. Thus, the ex situ Ag/Au doped SiO₂–MgO–Al₂O₃–B₂O₃–K₂O–MgF₂ GC has potential for use as a machinable glass-ceramic.

In understanding the catalytic efficacy of silver (Ag⁰) and gold (Au⁰) nanoparticles (NPs) on glass-ceramic (GC) crystallization, the microstructure–machinability correlation of a SiO₂–MgO–Al₂O₃–B₂O₃–K₂O–MgF₂ system is studied.     

Reduction of silver ions in molybdates: elucidation of framework acidity as the factor controlling charge balance mechanisms in aqueous zinc-ion electrolyte

A percolating network of high electrical conductivity needed to operate electrodes at a fast rate can be formed by in situ reduction of Ag⁺ originating from mixed metal oxide lattices, but few studies have elucidated trends in this mechanism as a function of Ag⁺ concentration and structure. Candidates compared for the first time here are spinel Ag₂MoO₄, monoclinic and triclinic Ag₂Mo₂O₇, and Ag₂Mo₃O₁₀·2H₂O, which have reduction potentials for Ag⁺ and Mo⁶⁺ strongly decoupled by up to ∼600 mV in aqueous zinc-ion electrolyte. Under these conditions, Ag⁰ is the first reduction product and a decrease of charge transfer resistance by ∼100× is observed within 2.5% consumption of total Ag⁺ independent of initial structure. However, resistance metrics alone poorly describe materials which are robust to reducing silver with high energy at faster rates. Instead, after accounting for crystallinity and morphology differences, we find that the acidity of the molybdate framework is responsible for a switch in charge balance mechanism from the bulk formation of a mixed ZnMoO_x to pseudocapacitive Zn²⁺ precipitation, and that this mechanism switch is associated with minimized losses to rate, voltage and capacity yields as carbon/binder free electrodes relative to composites. The location of this acidity cutoff near the pH of the ZnSO₄ electrolyte may suggest a design principle for future low-carbon electrodes beyond molybdate framework structures.

Across four molybdates, reduction of silver ions in aqueous zinc electrolyte is more facile with increasing acidity.     

MoS42− intercalated NiFeTi LDH as an efficient and selective adsorbent for elimination of heavy metals

The enormous increase of heavy metal pollution has led to a rise in demand for synthesizing efficient and stable adsorbents for its treatment. Therefore, we have designed a novel adsorbent by introducing (MoS₄)²⁻ moieties within the layers of NiFeTi LDH-NO₃, via an ion exchange mechanism, as a stable and efficient adsorbent to deal with the increasing water pollution due to heavy metals. Characterization techniques such as XRD, FTIR, TGA, SEM, TEM, and Raman spectroscopy were used to confirm the formation of (MoS₄)²⁻ intercalated NiFeTi LDH and structural changes after the adsorption process. The efficiency of the material was tested with six heavy metal ions, among which it was found to be effective for toxic Pb²⁺ and Ag⁺ ions. When selectivity was studied with all six of the metal ions copresent in one solution, the material showed greater selectivity for Pb²⁺ and Ag⁺ ions with the selectivity order of Ni²⁺ < Cu²⁺ < Zn²⁺ < Fe³⁺ < Pb²⁺ < Ag⁺, with great adsorption capacities of 653 mg g⁻¹ for Pb²⁺ and 856 mg g⁻¹ for Ag⁺ metal ions. Further, the kinetics adsorption study for both the metal ions had a great correlation with the pseudo-second-order model and supported the chemisorption process via the formation of M–S bonding. The adsorption process obeyed the Langmuir model. Therefore, the MoS₄-LDH material could be a promising adsorbent for the removal of heavy metals.

Elimination of the heavy metals by using the MoS₄-LDH adsorbent.     

Synthesis of Mg and Zn diolates and their use in metal oxide deposition

The synthesis of complexes [M(OCHMeCH₂NMeCH₂)₂] (5, M = Mg; 7, M = Zn) is described. Treatment of MeHNCH₂CH₂NMeH (1) with 2-methyloxirane (2) gave diol (HOCHMeCH₂NMeCH₂)₂ (3), which upon reaction with equimolar amounts of MR₂ (4, M = Mg, R = Bu; 6, M = Zn, R = Et) gave 5 and 7. The thermal behavior and vapor pressure of 5 and 7 were investigated to show whether they are suited as CVD (= chemical vapor deposition) and/or spin-coating precursors for MgO or ZnO layer formation. Thermogravimetric (TG) studies revealed that 5 and 7 decompose between 80–530 °C forming MgO and ZnO as evidenced by PXRD studies. In addition, TG-MS-coupled experiments were carried out with 7 proving that decomposition occurs by M–O, C–O, C–N and C–C bond cleavages, as evidenced from the detection of fragments such as CH₄N⁺, C₂H₄N⁺, C₂H₅N⁺, CH₂O⁺, C₂H₂O⁺ and C₂H₃O⁺. The vapor pressure of 7 was measured at 10.4 mbar at 160 °C, while 5 is non-volatile. The layers obtained by CVD are dense and conformal with a somewhat granulated surface morphology as evidenced by SEM studies. In addition, spin–coating experiments using 5 and 7 as precursors were applied. The corresponding MO layer thicknesses are between 7–140 nm (CVD) or 80 nm and 65 nm (5, 7; spin-coating). EDX and XPS measurements confirm the formation of MgO and ZnO films, however, containing 12–24 mol% (CVD) or 5–9 mol% (spin-coating) carbon. GIXRD studies verify the crystalline character of the deposited layers obtained by CVD and the spin-coating processes.

Mg and Zn containing precursors for the generation of metal oxide layers by CVD and/or spin-coating are described.     

Synthesis and spectroscopic investigation of a novel sensitive and selective fluorescent chemosensor for Ag+ based on a BINOL–glucose derivative

Based on a versatile 2,2′-binaphthol (BINOL) backbone, a novel BINOL–glucose derivative fluorescent sensor was synthesized using a click reaction. The fluorescence responses of the BINOL–glucose derivative (S,β-d)-1 conclude that it can be used as a specific fluorescent chemical sensor for Ag⁺ in the presence of a large number of competing metal ions without any obvious interference from other metal ions. Mass spectrometric and NMR spectroscopic data were used to study the mechanism, and implied the formation of a 1 + 1 complex between BINOL–glucose 1 and Ag⁺. Both the oxygen atoms of S-BINOL and two nitrogen atoms of triazole were involved in coordinating the silver ion.

A BINOL–glucose derivative fluorescent sensor was synthesized to detect only Ag⁺ with high selectivity and sensitivity in a 1 + 1 formation.     

Analysis of Gag-specific Cytotoxic T Lymphocytes in Simian Immunodeficiency Virus–infected Rhesus Monkeys by Cell Staining with a Tetrameric Major Histocompatibility Complex Class I–Peptide Complex

A tetrameric recombinant major histocompatibility complex (MHC) class I–peptide complex was used as a staining reagent in flow cytometric analyses to quantitate and define the phenotype of Gag-specific cytotoxic T lymphocytes (CTLs) in the peripheral blood of simian immunodeficiency virus macaque (SIVmac)-infected rhesus monkeys. The heavy chain of the rhesus monkey MHC class I molecule Mamu-A*01 and β₂-microglobulin were refolded in the presence of an SIVmac Gag synthetic peptide (p11C, C–M) representing the optimal nine–amino acid peptide of Mamu-A*01–restricted predominant CTL epitope to create a tetrameric Mamu-A*01/p11C, C–M complex. Tetrameric Mamu-A*01/p11C, C–M complex bound to T cells of SIVmac-infected, Mamu-A*01⁺, but not uninfected, Mamu-A*01⁺, or infected, Mamu-A*01⁻ rhesus monkeys. Specific staining of peripheral blood mononuclear cells (PBMC) from SIVmac-infected, Mamu-A*01⁺ rhesus monkeys was only found in the cluster of differentiation (CD)8α/β⁺ T lymphocyte subset and the percentage of CD8α/β⁺ T cells in the peripheral blood of four SIVmac-infected, Mamu-A*01⁺ rhesus monkeys staining with this complex ranged from 0.7 to 10.3%. Importantly, functional SIVmac Gag p11C-specific CTL activity was seen in sorted and expanded tetrameric Mamu-A*01/p11C, C–M complex–binding, but not nonbinding, CD8α/β⁺ T cells. Furthermore, the percentage of CD8α/β⁺ T cells binding this tetrameric Mamu-A*01/p11C, C–M complex correlated well with p11C-specific cytotoxic activity as measured in both bulk and limiting dilution effector frequency assays. Finally, phenotypic characterization of the cells binding this tetrameric complex indicated that this lymphocyte population is heterogeneous. These studies indicate the power of this approach for examining virus-specific CTLs in in vivo settings.Cytotoxic T lymphocytes (CTLs) play an important role in containing virus spread in many viral infections. However, the activity of this cell population in vivo has proven difficult to study because its evaluation has relied on cumbersome, functional assays that require extensive cell manipulation and lengthy in vitro periods of cell cultivation. Altman et al. have recently reported that fluorescence dye-coupled tetrameric MHC class I–peptide complexes can specifically bind to subpopulations of epitope-specific cluster of differentiation (CD)¹8⁺ T cells, raising the possibility that CTLs might be studied using flow cytometric technology (1).There is accumulating evidence for the importance of CTLs in controlling HIV-1 and simian immunodeficiency virus replication in both primary and chronic infections (2– 6). We have been studying the role of this cellular immune response in AIDS immunopathogenesis in the simian immunodeficiency virus (SIV)/macaque model of AIDS. Much of this work has focused on the evaluation of SIVmac Gag recognition by CTL in rhesus monkeys expressing the HLA-A homologue molecule Mamu-A*01. In fact, we have shown that CTL recognition of Gag in SIVmac-infected or vaccinated Mamu-A*01⁺ rhesus monkeys is restricted to a single epitope, 12–amino acid fragment of SIVmac 251 Gag (amino acid 179–190) (p11C), bound to Mamu-A*01 (7). Through studying the monkeys'' response to this dominant CTL epitope, we have been able to evaluate efficiently a variety of novel vaccine strategies for eliciting SIVmac-specific CTL responses and assess the role of CTLs in containing the replication of SIVmac during primary and chronic infections (8–11).In these studies, we have generated tetrameric Mamu-A*01/p11C, C–M complex using the optimal nine–amino acid fragment of SIVmac (amino acids 181–189) p11C, C-M (12) and evaluated its binding specificity in PBMCs of SIVmac-infected, Mamu-A*01⁺ rhesus monkeys. We demonstrate that the enumeration of CD8⁺ T cells that bind this complex in flow cytometric analyses correlates quantitatively with functional CTL activity and that this cell population is phenotypically heterogeneous.     

Alumina-promoted oxodefluorination

A simple protocol for the clean preparation of heterocyclic compounds containing dibenzofuran''s core via oxodefluorination of fluoroarenes on activated γ-Al₂O₃ is reported. Alumina can be considered as a reliable oxygen source enabling one-pot substitution of fluorine atoms and yielding benzoannulated furan derivatives. The corresponding C–F bond activation is selective towards less stable C–Br/C–I and occurs under metal- and solvent-free conditions.

A simple protocol for the clean preparation of heterocyclic compounds containing dibenzofuran''s core via oxodefluorination of fluoroarenes on activated γ-Al₂O₃ is reported.

Dibenzo[b,d]furan is an important moiety as its derivatives constitute a long list of natural products.^1,2 Moreover, multiple synthetic compounds bearing such a fragment also show biological activity^3–5e.g. mimic fragments of complex biological structures.^6,7 Due to its rigidity, dibenzofuran is oftentimes used as a bridge fixing fragment of the molecule at a desired distance giving rise to various chelating ligands,^8–13 cryptands,¹⁴ and other supramolecular hosts.^15–19 Furthermore, the stable dibenzofuran core enables different patterns of substitution. These features, in combination with appropriate electronic properties, make dibenzofuran and its derivatives potentially valuable components of phosphorescent OLEDs^20–22 thermally activated delayed fluorescence emitters,^23–25 perovskite solar cells²⁶etc. Thus, functionalized dibenzofurans appear to be important building blocks.Despite numerous synthetic approaches to this class of compounds, the construction of functionalized dibenzofurans is far from being trivial since all existing methods are generally reduced to either C–O or C–C coupling (Fig. 1). This is mainly connected to the fact that oxygen has to be present in the precursor''s structure because there is no reliable oxygen source that would enable double C–O bond incorporation. The majority of the available methods are based on Pd-catalysis,^27–34 while others exploit strong bases/acids and toxic solvent.^35–38 In addition, these methods rarely tolerate C–Br and C–I functionalities, which could have been used for further modifications.Open in a separate windowFig. 1Synthesis of dibenzofuran. Existing approaches vs. oxodefluorination.Herein, we report a transformation of fluorinated biphenyls into dibenzofuran''s derivatives. The reaction occurs on the surface of activated γ-Al₂O₃ and does not require other reagents. The scope and limitations of the reactions are considered: the technique is compatible with C–Br and C–I functionalities, enables double oxodefluorination and incorporation of hexagons, thus yielding ladder-type π-conjugated heteroacenes and xanthene''s derivatives, respectively.As a part of our ongoing research on alumina mediated C–F activation,^39,40 we have observed an interesting competition between C(aryl)–C(aryl) coupling and formation of oxygen-containing side products.⁴¹ In certain cases (i.e. when two fluorine atoms are dislocated in bay-region) the side products turned out to contain dibenzofuran''s moiety.⁴² Some additional data on this competition are briefly discussed in ESI.^†To investigate the formation of dibenzofuran''s core in more details, we have excluded one of the competitors i.e. the possibility for intramolecular C(aryl)–C(aryl) coupling. The simplest model meeting the requirements is 2,2′-difluorobiphenyl (1a), which upon exposure to activated alumina transforms into dibenzofuran 1 in 65% yield. As a matter of fact, the desired 1 is the only product that can be extracted from the reactionary mixture with aprotic solvent such as toluene (Fig. 2). Thus, flash chromatography is not required, since reactionary alumina already plays the role of a plug enabling effective separation from intermediate and side products, which can be extracted with methanol afterwards (see ESI^†). Notably, eliminated fluorine atoms are most likely to be bound to alumina in the form of extremely strong and naturally occurring Al–F bond yielding partially fluorinated alumina, which is of interest in multiple fields including catalysis.^43,44Open in a separate windowFig. 2(A) Synthesis of dibenzofuran and suggested mechanism of the reaction. (B) ¹H NMR of the reactionary mixture as obtained after extraction with toluene.As any other heterogeneous process, this reaction is quite likely to have a complicated manner. However, some pieces of evidence on C(aryl)–F polarization^41,45,46 allow us to suggest the key steps of the transformation. Alumina induces a partial positive charge on carbon generating incipient phenyl cation species,⁴⁷ which are to interact with proximal moieties. In the case of 2,2′-difluorobiphenyl, no aryl functionalities are available for intramolecular C(aryl)–C(aryl) coupling; therefore oxygen on alumina surface serves as an alternative nucleophile interacting with cation-like species. Such hydrolysis of C–F bond has already been observed as a side process.⁴¹ Unlike the reported transformation, the current precursor contains two fluorine atoms, whereas the polarization of the second C(aryl)–F bond induces the second C–O coupling, this time intramolecular, and subsequent covalent detachment of the product. Some other possible mechanisms occurring via aryne-particles or dehydration were excluded (see ESI^†). Noteworthy, the outcome of the reaction resembles double S_NAr, which can be generally achieved in activated arenes i.e. containing multiple electron-withdrawing groups. Such restriction does not apply to the alumina-promoted oxodefluorination due to its cationic nature.An interesting aspect of C(aryl)–F bond is that it can be used as both directing and functional groups, although it is seldom considered as the latter. In accordance with Open in a separate windowWhile tolerance to methyl group comes as no surprise, selective C–F activation in presence of C–Br and more interestingly C–I is a quite notable feature since fluorine forms stronger bonds with carbon in comparison to other halogens. At the same time, the reaction has a rather poor selectivity to C(aryl)–F bonds since only traces of 5 were extracted, whereas the rest of the precursor has remained on the surface in forms of hydrolyzed side products. A similar, although anticipated, outcome was observed in the case of 6, where nothing could be extracted with toluene due to the rapid hydrolysis of CF₃ groups.⁴⁸ As of methoxy groups, the corresponding toluene extract revealed no desired product 7. Presumably, it is connected to the fact that OCH₃ occupies reactive sites of alumina more rapidly than C–F polarization takes place.This observation is especially interesting in light of the following evidence. Oligophenylenes 8a, 9a, and 10a synthesized in one step via Suzuki coupling undergo double annulation yielding respective ladder-type π-conjugated compounds 8–10, which are promising candidates as organic semiconductors (Scheme 1).³⁷ Here, the formation of the first dibenzofuran''s moiety, apparently, does not prevent the second region from annulation.Open in a separate windowScheme 1Synthesis of ladder-type π-conjugated compounds, benzo[kl]xanthene and incorporation of oxygen into cove region.To investigate whether the approach is applicable to the synthesis of xanthene''s derivatives such as benzo[kl]xanthene (11), we have designed the corresponding precursor 11a having a choice between C–F and C–C couplings. Due to this competition, several products were extracted with toluene in this particular case. Therefore, toluene and methanol extracts were combined and separated by means of flash chromatography to reveal three major products 11b, 11c, and 11. To preclude the variability, we have synthesized rigid precursor 12a with two fluorine atoms in cove region. Thus, 12a transforms into 12 in considerable 75% yield enabling the synthesis of elusive naphtho[2,1,8,7-klmn]xanthene''s core.⁴⁹     

A simple fluorescent probe for detection of Ag+ and Cd2+ and its Cd2+ complex for sequential recognition of S2−

In this study, we designed and synthesized a simple probe 2-(8-((8-methoxyquinolin-2-yl)methoxy)quinolin-2-yl)benzo[d]thiazole (DQT) for detection of Ag⁺ and Cd²⁺ in a CH₃OH/HEPES (9 : 1 v/v, pH = 7.30) buffer system. Its structure was characterized by NMR, ESI-HR-MS and DFT calculations, and its fluorescence performance was also investigated. Probe DQT showed fluorescence quenching in response to Ag⁺ and Cd²⁺ with low detection limits of 0.42 μM and 0.26 μM, respectively. Importantly, the complexation of the probe with Cd²⁺ resulted in a red shift from blue to green, making it possible to detect Ag⁺ and Cd²⁺ by the naked eye under an ultraviolet lamp. The DQT-Cd²⁺ complex could be used for sequential recognition of S²⁻. The recovery response could be repeated 3 times by alternate addition of Cd²⁺ and S²⁻. A filter paper strip test further demonstrated the potential of probe DQT as a convenient and rapid assay.

A fluorescent probe for detection of Ag⁺ and Cd²⁺ and its Cd²⁺ complex for sequential recognition of S²⁻.     

Halogen bond triggered aggregation induced emission in an iodinated cyanine dye for ultra sensitive detection of Ag nanoparticles in tap water and agricultural wastewater

Aggregation induced emission (AIE) has emerged as a powerful method for sensing applications. Based on AIE triggered by halogen bond (XB) formation, an ultrasensitive and selective sensor for picomolar detection of Ag nanoparticles (Ag NPs) is reported. The dye (CyI) has an iodine atom in its skeleton which functions as a halogen bond acceptor, and aggregates on the Ag NP plasmonic surfaces as a halogen bond donor or forms halogen bonds with the vacant π orbitals of silver ions (Ag⁺). Formation of XB leads to fluorescence enhancement, which forms the basis of the Ag NPs or Ag⁺ sensor. The sensor response is linearly dependent on the Ag NP concentration over the range 1.0–8.2 pM with an LOD of 6.21 pM (σ = 3), while for Ag⁺ it was linear over the 1.0–10 μM range (LOD = 2.36 μM). The sensor shows a remarkable sensitivity for Ag NPs (pM), compared to that for Ag⁺ (μM). The sensor did not show any interference from different metal ions with 10-fold higher concentrations. This result indicates that the proposed sensor is inexpensive, simple, sensitive, and selective for the detection of Ag NPs in both tap and wastewater samples.

Based on AIE triggered by halogen bond (XB) formation, we established an ultrasensitive and selective sensor for picomolar detection of Ag nanoparticles (Ag NPs).     

Aerobically stable and substitutionally labile α-diimine rhenium dicarbonyl complexes

New synthetic routes to aerobically stable and substitutionally labile α-diimine rhenium(i) dicarbonyl complexes are described. The molecules are prepared in high yield from the cis–cis–trans-[Re(CO)₂(^tBu₂bpy)Br₂]⁻ anion (2, where ^tBu₂bpy is 4,4′-di-tert-butyl-2,2′-bipyridine), which can be isolated from the one electron reduction of the corresponding 17-electron complex (1). Compound 2 is stable in the solid state, but in solution it is oxidized by molecular oxygen back to 1. Replacement of a single bromide of 2 by σ-donor monodentate ligands (Ls) yields stable neutral 18-electron cis–cis–trans-[Re(CO)₂(^tBu₂bpy)Br(L)] species. In coordinating solvents like methanol the halide is replaced giving the corresponding solvated cations. [Re(CO)₂(^tBu₂bpy)Br(L)] species can be further reacted with Ls to prepare stable cis–cis–trans-[Re(CO)₂(^tBu₂bpy)(L)₂]⁺ complexes in good yield. Ligand substitution of Re(i) complexes proceeds via pentacoordinate intermediates capable of Berry pseudorotation. In addition to the cis–cis–trans-complexes, cis–cis–cis- (all cis) isomers are also formed. In particular, cis–cis–trans-[Re(CO)₂(^tBu₂bpy)(L)₂]⁺ complexes establish an equilibrium with all cis isomers in solution. The solid state crystal structure of nearly all molecules presented could be elucidated. The molecules adopt a slightly distorted octahedral geometry. In comparison to similar fac-[Re(CO)₃]⁺complexes, Re(i) diacarbonyl species are characterized by a bend (ca. 7°) of the axial ligands towards the α-diimine unit. [Re(CO)₂(^tBu₂bpy)Br₂]⁻ and [Re(CO)₂(^tBu₂bpy)Br(L)] complexes may be considered as synthons for the preparation of a variety of new stable diamagnetic dicarbonyl rhenium cis-[Re(CO)₂]⁺ complexes, offering a convenient entry in the chemistry of the core.

New synthetic routes to aerobically stable and substitutionally labile α-diimine rhenium(i) dicarbonyl complexes offer a convenient entry in the chemistry of the cis-[Re(CO)₂]⁺ core.     

Dual-signal lateral flow assay using vancomycin-modified nanotags for rapid and sensitive detection of Staphylococcus aureus

This paper reports a colorimetric-fluorescent dual-signal lateral flow assay (LFA) based on vancomycin (Van)-modified SiO₂–Au-QD tags for sensitive and quantitative detection of Staphylococcus aureus (S. aureus). The combination of high-performance Van-tags and detection antibodies integrated into the LFA system produced assays with high sensitivity and specificity. The visualization limit of the colorimetric signal and the detection limit of the fluorescence signal of the proposed method for S. aureus can reach 10⁴ and 100 cells mL⁻¹, respectively.

A colorimetric-fluorescent dual-signal lateral flow assay was proposed for the sensitive detection of S. aureus by using vancomycin-modified SiO₂–Au-QD tags.

Staphylococcus aureus (S. aureus) is one of the major iatrogenic and foodborne bacteria that cause a wide range of infectious diseases, such as skin infection, sepsis, pneumonia, and osteomyelitis.^1,2 Accurate detection of S. aureus in food samples and clinical specimens is crucial to guarantee food safety and guide effective treatment. Current diagnostic technologies, mainly conventional blood cultures or plate cultures, polymerase chain reaction (PCR), mass spectrometry, and DNA sequencing-based methods, require long testing time (several hours to several days), complicated equipment, and tedious procedures, thus limiting their applications to point-of-care testing (POCT).^3–5Lateral Flow Assay (LFA) has become the most mature and widely used POCT method in recent years because of its rapidity, portability, low cost, and simple operation.^6–9 However, utilizing LFA for sensitive detection of S. aureus in complex samples is still a challenge. Limited research on LFA-based methods for detection of S. aureus has been reported, and the difficulty lies in three aspects. First, traditional LFA strip is based on colloidal gold (Au NPs) as reporters to provide colorimetric signal, which result in limited sensitivity.¹⁰ Second, complex matrix interferences in real samples adversely affect the stability and practical application of LFA system for bacteria detection.¹¹ Third, a pair of antibodies to S. aureus with high affinity and no cross-reactivity is needed for LFA detection; such antibodies are difficult to screen and expensive with poor reproducibility.^12,13 To address these problems, scholars should focus on developing and integrating novel nanotags with high signal intensity and good stability and new biorecognition molecules integrated into LFA system for S. aureus detection.Vancomycin (Van) is a broad-spectrum glycopeptide antibiotic that can specifically bind to d-Ala–d-Ala moieties on the cell wall of most Gram-positive bacteria via five-point hydrogen bonds.^14,15 Due to its high stability, low cost, and easy preparation, vancomycin has attracted wide attention to construct biosensors for detection of Gram-positive bacteria.^16–18 Our previous works demonstrated that Van-modified magnetic nanoparticles (e.g., Fe₃O₄@Au, and Fe₃O₄@Ag) could rapidly recognize and capture S. aureus in complex samples.^19,20In this work, a sensitive colorimetric-fluorescent dual-signal LFA strip for S. aureus detection was proposed on the basis of rapid and strong binding capability between vancomycin molecule-modified nanotags and S. aureus. A novel Van-modified dual-signal tag (SiO₂–Au-QD–Van) was fabricated via polyethyleneimine (PEI)-mediated assembly strategy.^21–23 The tag consisted of a monodisperse SiO₂ core (∼200 nm) as supporter, a layer of Au NPs (3 nm) to provide colorimetric signal, a layer of carboxylated CdSe/ZnS QDs to provide strong and stable fluorescence signal, and surface-modified vancomycin to effectively bind to S. aureus (Scheme 1a). The high-performance SiO₂–Au-QD–Van tag was introduced into a simple LFA strip to rapidly capture S. aureus and provide two signal modes. A detection antibody for S. aureus was coated onto the test line of the strip to immobilize the formed Van-tags-S. aureus complexes. The colorimetric intensity and fluorescence intensity of test line supported the rapid detection and high-sensitivity quantitative analysis of S. aureus, respectively. As far as we know, this work is the first to construct LFA strip by using the combination of vancomycin and specific antibody for bacteria detection.Open in a separate windowScheme 1Schematic of (a) synthesis of vancomycin-modified dual-signal tag and (b) mechanisms for rapid detection of S. aureus based on dual-signal tag-based LFA strip. Scheme 1b shows a simple LFA strip designed for rapid detection of S. aureus. The strip consists of a sample pad for Van tags/bacterial sample loading, an absorbent pad to provide capillary force, and a test line to coat S. aureus detection antibody. In test samples containing target S. aureus, the added SiO₂–Au-QD–Van tags bind tightly to S. aureus due to the high affinity of vancomycin toward the target bacteria. The formed SiO₂–Au-QD–Van–S. aureus complexes migrate along the nitrocellulose (NC) membrane under the capillary forces of absorbent pad and are caught by the test line that coated the S. aureus antibody. Considering the high price of vancomycin antibody, we do not set a control zone on the LFA strip. Thus, only one test line shows colorimetric/fluorescence signal in the presence of S. aureus. The visible/fluorescence intensity of the LFA strip is derived from the amount of SiO₂–Au-QD–Van–S. aureus complexes immobilized on the test line. The amount is proportional to the bacterial concentrations in the samples. Finally, quantitative analysis is performed in fluorescence mode because the fluorescence intensity of the strip can be easily read.High-performance SiO₂–Au-QD–Van tags are the key to building dual-signal LFA strip. As illustrated in Scheme 1a, the dual-signal core of SiO₂–Au-QD–Van tag was fabricated through our previously reported LBL assembly method followed by modification of vancomycin on its surface. Firstly, monodispersed SiO₂ (∼200 nm) spheres were reacted with aqueous PEI solution under intense sonication to form PEI-coated SiO₂ NPs (SiO₂@PEI).²⁴ Secondly, the SiO₂–Au NPs were prepared by adsorbing numerous small Au NPs (∼3 nm) onto the SiO₂@PEI surface through electrostatic interaction between positively charged PEI layer and negatively charged Au NPs. Thirdly, the prepared SiO₂–Au NPs were vigorously interacted with PEI solution again to coat the second PEI layer, thereby forming SiO₂–Au–PEI nanostructure. Finally, SiO₂–Au-QD NPs were obtained by electrostatic adsorption of dense CdSe/ZnS–MPA QDs onto the SiO₂–Au–PEI surface. ESI S1^† shows the detailed fabrication process of dual-signal SiO₂–Au-QD NPs.Transmission Electron Microscopy (TEM) was employed to verify the morphology of the dual-signal tags. Fig. 1a, b, and c display the typical TEM images of 200 nm SiO₂ core, SiO₂–Au, and SiO₂–Au-QD NPs, respectively. All the prepared NPs show good dispersivity and homogeneous nanostructure. After the successive coating of 3 nm Au NPs layer and QDs layer, the diameter of SiO₂–Au-QD NPs increased to approximately 240 nm. The EDS elemental mapping results further demonstrated the dense and uniform distribution of Au NPs (red signal) on the SiO₂ surface (blue signal) and CdSe/ZnS QDs (azure and purple signal) on the SiO₂–Au surface (Fig. 1d). The abundant CdSe/ZnS-MPA QDs on the outermost layer of the dual-signal tags not only generated high luminescence for quantitative analysis but also provided numerous carboxyl groups for subsequent modification of vancomycin. The zeta potential of SiO₂, SiO₂@PEI, SiO₂–Au, SiO₂–Au–PEI, and SiO₂–Au-QD NPs were measured to be −34.4, +42.3, +10.6, +40.7, and +9.4 mV, respectively (Fig. 1e). The zeta potential of the products increased significantly when the PEI layer was formed and decreased after the adsorption of negatively charged Au NPs and QDs. This finding indicated that the formation of dual-signal tags was driven by electrostatic interaction.Open in a separate windowFig. 1Characterization of dual-signal SiO₂–Au-QD nanotags. TEM images of (a) SiO₂ NPs, (b) SiO₂–Au NPs, and (c) SiO₂–Au-QD NPs. (d) EDS elemental mapping images of SiO₂–Au-QD tags. Zeta potential results (e) and fluorescence emission spectra (f) of vancomycin-modified nanotags and their intermediate products. Inset images display the photographs of SiO₂–Au-QD–Van tags under visible (left) and UV light (right).Vancomycin molecules were modified onto the surface of SiO₂–Au-QD NPs according to our previously reported approach.²⁵Scheme 1a shows the binding of the surface carboxyl groups of SiO₂–Au-QD NPs to vancomycin molecules through carbodiimide activation to form SiO₂–Au-QD–Van NPs. Fig. 1e and S1a^† show that the zeta potential of SiO₂–Au-QD decreased to −5.5 mV after vancomycin modification. This finding demonstrated the successful preparation of SiO₂–Au-QD–Van tags. In addition, Fig. 1f (inset) presents the photographs of SiO₂–Au-QD–Van tags under visible and UV light, indicating the good colorimetric signal and luminescence of the dual-signal tags. The figure also shows the fluorescence spectra of SiO₂, SiO₂–Au, SiO₂–Au-QD, and SiO₂–Au-QD–Van tags. SiO₂–Au-QD–Van NPs as well as SiO₂–Au-QD NPs exhibited strong fluorescence signal at 625 nm by excitation with 360 nm UV light, indicating that fluorescence quenching did not occur after vancomycin modification. The SiO₂–Au-QD–Van tags showed excellent optical/chemical stability in the sample solution within a wide pH range of 4–13 due to the high stability of CdSe/ZnS core–shell QDs and SiO₂ core used (Fig. S1b^†). These results suggested the potential of SiO₂–Au-QD–Van tags for bacteria detection in complex samples.Vancomycin binds to the cell wall of S. aureus though hydrogen bonding in the terminal peptide unit (d-Ala–d-Ala) (Fig. 2a). The TEM study confirmed the effective binding of the fabricated SiO₂–Au-QD–Van tags to S. aureus in aqueous solution (Fig. 2b). The S. aureus used in this work was verified by PCR (Fig. S2^†), indicating the amplification of the specific gene of S. aureus.²⁶ To further study the bind ability of SiO₂–Au-QD–Van tags in complex samples, we spiked 50 μL of high-salt solution (0.1 M PBS), vegetable juice, and milk samples with S. aureus (10⁶ cells mL⁻¹) and mixed them with Van nanotags (2 μL). As shown in Fig. 2c, the Van-tags were dispersed well in these complex samples with stable fluorescence intensity. The three samples containing Van tags were mixed with 25 μL of PBST buffer (1% Tween) and then tested by S. aureus antibody-modified LFA strip. Fig. 2d reveals the photographs and fluorescence images of dual-signal LFA strips with the test line for S. aureus detection. All the test lines showed a distinct purple color band and bright fluorescence band at 10⁶ cells mL⁻¹ of S. aureus under visible light and UV light, respectively. The detailed fluorescence signal value of the test lines was measured by a commercial fluorescent reader (Fig. 2e). The fluorescence intensity only slightly differed among the three tested strips, indicating that the SiO₂–Au-QD–Van based LFA strip can work well in real samples.Open in a separate windowFig. 2(a) Schematic of coupling interaction of the vancomycin molecule with SiO₂–Au-QD NPs and binding interaction of S. aureus. (b) TEM image of formed Van-nanotags-S. aureus complexes. (c) Photographs and fluorescence images of Van-nanotags in different samples (PBS, vegetable juice, and milk). Photographs (d) and corresponding fluorescence intensity (e) of SiO₂–Au-QD–Van based LFA strips in PBS, vegetable juice, and milk.After the feasibility of the proposed method was confirmed, some important experimental conditions were optimized to ensure the high performance of the LFA system. The NC membrane type of the LFA strip was first investigated, considering the big size of S. aureus (∼600 nm) and SiO₂–Au-QD–Van tags (∼250 nm). The suitable NC membrane allowed the good transport of S. aureus and nanotags, and generated the best immune binding efficiency on the test line.²⁷ As revealed in Fig. S3a,^† we achieved the highest signal-to-noise ratio (SNR) for S. aureus detection using CN95 membrane with 15 μm pore size. Our previous works systematically investigated the running buffer for big nanotags.^28–30 We made slight adjustments and found that the PBS solution (10 mM, pH 7.4)-based running buffer containing 1% Tween 20 and 1% BSA can reduce the nonspecific adsorption of SiO₂–Au-QD–Van tags on the NC membrane and generate the highest fluorescence intensity on the test line (Fig. S3b^†). In addition, 0.8 mg mL⁻¹ of the detection antibody coated on the test line is sufficient for S. aureus detection (Fig. S3c^†).In this study, SiO₂–Au-QD–Van tags were directly added into 50 μL of the test sample to bind to S. aureus. The mixture was then mixed with 25 μL of running buffer for LFA detection. As mentioned in ESI S1.3,^† the concentration of SiO₂–Au-QD–Van solution was fixed at 2 mg mL⁻¹. Notably, the concentration of SiO₂–Au-QD–Van tags used for LFA detection seriously influence the final fluorescence signal at the test line on the strip. As shown in Fig. S4,^† excessive amounts of SiO₂–Au-QD–Van tags (4 μL) used reduce the detection sensitivity and increase the fluorescence background of LFA strip. This phenomenon can be attributed to the dense SiO₂–Au-QD–Van tags attached on the bacterial surface will affect the formation of nanotags S. aureus-antibody sandwich complexes on the test line. Thus, the optimized dosage of SiO₂–Au-QD–Van tags was chosen 3 μL (2 mg mL⁻¹) for LFA-based S. aureus detection.The incubation time of SiO₂–Au-QD–Van tags (3 μL) with S. aureus was next optimized to achieve the highest sensitivity. The TEM images in Fig. S5a^† reveal that the number of SiO₂–Au-QD–Van tags bound to S. aureus increased with increasing incubation time (2–8 min). This finding suggested the high affinity of Van-tags toward S. aureus. However, we found that excessive Van-tags conjugated outside the bacterial surface had adverse effect on the immunoreaction between the bacteria and test line (Fig. S5b^†). Incubation for 2 min is suitable for Van-tags-based LFA detection. The proposed LFA strip only needs 12 min for one testing with the addition of 10 min for chromatography.After the optimization of the experimental details, the sensitivity of the SiO₂–Au-QD–Van tags-based LFA strip was verified. We tested a series of samples containing different concentrations (10⁷ to 0 cell mL⁻¹) of S. aureus. Fig. 3a shows the photographs (i) and fluorescence images (ii) of the test strips for S. aureus detection. The visible purple color band and red fluorescence band of the test line were observed at high bacteria concentrations, and their signal intensity decreased gradually with decreasing concentrations of S. aureus. As shown in Fig. 3a(i), the visible test line of the tested strips for S. aureus was observed at 10⁴ cells mL⁻¹ by the naked eye. Under UV light, the fluorescence signal of the SiO₂–Au-QD–Van tags can significantly improve the detection sensitivity of LFA strip and can be applied to quantitative analysis. Based on the fluorescence images in Fig. 3a(ii), the fluorescence signal on the test line was visible in as low as 500 cells mL⁻¹ of S. aureus. Fig. 3b shows the corresponding calibration curve of the recorded fluorescence intensity. The calibration curve is fitted by a four-parameter logistic equation as shown in inset of Fig. 3b, where y is the fluorescence intensity at test line, and x is the logarithmic concentration of S. aureus. We estimated the limit of detection (LOD) by the fluorescence signal for S. aureus to be 100 cells mL⁻¹ at an SNR of 3 by using the IUPAC protocol.^31,32 Thus, the fluorescence detection limit of our proposed dual-signal strip is 100 times more sensitive than that acquired from the colorimetric signal. Moreover, the detection performance (sensitivity and dynamic range) of SiO₂–Au-QD–Van tags based-LFA in PBS buffer and vegetable juice were equal to that of in milk samples (Fig. S6^†). These results indicated the good stability of the proposed method in different samples. We also employed traditional plate counting to verify the accuracy of our method. As shown in Fig. S7,^† the results of plate counting method are consistent with the those of Van-tags based LFA.Open in a separate windowFig. 3Detection performance of SiO₂–Au-QD–Van based LFA strip in milk sample. (a) Photographs (i) and fluorescence pictures (ii) of SiO₂–Au-QD–Van-based LFA strip for different concentrations (10⁷ to 0 cells mL⁻¹) of S. aureus in milk samples. (b) Corresponding calibration curves for S. aureus. Inset in (b) is the linear part of the calibration curve. Error bars indicating the standard deviation of three independent tests.We determined the reproducibility of our method by testing four batches of dual-signal LFA strips with 10⁶ and 10⁴ cells mL⁻¹S. aureus. As shown in Fig. S8,^† all the LFA strips exhibited homogeneous and stable visible/fluorescence signal on the test lines, with relative standard deviation (RSD) less than 6.8%. This finding demonstrated the good reproducibility of SiO₂–Au-QD–Van-based LFA. We further assessed the specificity of the proposed method by testing various common pathogenic bacteria including Escherichia coli (E. coli), Salmonella typhimurium (S. typhi), L. monocytogenes (L. mono), Acinetobacter baumannii (A. baumannii), Pseudomonas aeruginosa (P. aeruginosa), and Staphylococcus epidermidis (S. epidermidis) as interferents. All the bacterial samples were prepared at a concentration of 10⁵ cells mL⁻¹ and detected by SiO₂–Au-QD–Van-based LFA. As shown in Fig. 4, the positive group (S. aureus) exhibited distinct visible/fluorescence band on the tested strip, whereas no test line was observed for the six other bacteria. These results indicated the good specificity of our method. Notably, several previous studies have shown that the vancomycin-modified magnetic beads can effectively and electively capture multidrug-resistant S. aureus including methicillin-resistant S. aureus (MRSA) and vancomycin-resistant bacteria.^15,33,34 Theoretically speaking, the SiO₂–Au-QD–Van tags have the ability to bind multidrug-resistant S. aureus, including MRSA and vancomycin-resistant S. aureus. Hence, the combination of Van-nanotags and detection antibody-modified LFA strip allows the accurate detection of S. aureus between other common bacteria. In addition, the SiO₂–Au-QD–Van-based LFA strips exhibited no obvious fluorescence signal attenuation of the test zone after storage for 30 days (Fig. S9^†), which confirms the good stability of our proposed method.Open in a separate windowFig. 4Specificity of SiO₂–Au-QD–Van-based LFA. Photographs and fluorescence intensities of the test strips in the presence of S. aureus and six other common pathogenic bacteria. Error bars indicating the standard deviation of three independent tests.The excellent detection performance (e.g., sensitivity, stability, specificity) of the proposed method for S. aureus could be attributed to the high-powered SiO₂–Au-QD–Van used in this study. The proposed SiO₂–Au-QD–Van tags combined the advantages of the stable SiO₂^† core, a layer of Au NPs, and a layer of carboxylated QDs. The tags cannot only have monodispersity and excellent stability in complex solution but also provides strong colorimetric and luminescence signal for rapid and sensitive determination of S. aureus. Moreover, Van-modified tags with low price but high affinity and S. aureus antibody with specificity were conjunct to improve the application of our method in POCT. The successfully developed rapid and sensitive LFA strip can ensure the detection assay to be completed within 12 min. The proposed SiO₂–Au-QD–Van tag-based method exhibits better sensitivity and more functions than other LFA-based bacteria detection approaches (Detection methodBacteriaLOD (cells mL⁻¹)Assay time (min)ReferenceColorimetric LFA S. aureus 1 × 10⁶15Wiriyachaiporn, 2013 (ref. 35)Colorimetric LFA E. coli O1574.5 × 10³20Zhu, 2018 (ref. 36)Fluorescent LFA E. coli O1573 × 10³120Li, 2019 (ref. 37)Magnetic-QD LFA S. typhi 3.75 × 10³35Hu, 2019 (ref. 38)Magnetic-QD LFA E. coli O1572.39 × 10²74Huang, 2019 (ref. 39)Fluorescent LFA S. aureus 1.4 × 10³20Shi, 2019 (ref. 40)Fluorescent LFA S. typhi 5 × 10²15Zhang, 2020 (ref. 41)Fe₃O₄@CuS LFA E. coli O15710²15Zhang, 2020 (ref. 42)Nanozyme LFA E. coli O15710²25Wang, 2020 (ref. 43)Colorimetric LFA S. aureus 1 × 10³>20Zhao, 2021 (ref. 44)Dual-signal LFA S. aureus 100 by fluorescence signal12This work10⁴ by colorimetric signalOpen in a separate windowIn summary, we propose a simple and sensitive LFA method for S. aureus detection by using vancomycin-modified SiO₂–Au-QD NPs as dual-signal tags. We fabricated novel dual-signal tags by PEI-mediated electrostatic adsorption of a layer of 3 nm Au NPs and a layer of QDs on the 200 nm SiO₂ core. The tags possess excellent stability and high colorimetric/fluorescence signal. Vancomycin molecules were conjugated onto the surface of SiO₂–Au-QD NPs to rapidly bind to target S. aureus with high affinity. By introducing Van-tags into LFA strip, we were able to rapidly and sensitively detect S. aureus in complex samples within 12 min via observation of colorimetric or fluorescence signal. In fluorescence quantitative mode, the LOD of SiO₂–Au-QD–Van-based LFA for S. aureus is as low as 100 cells/mL. Considering the other advantages including high stability, specificity, low cost, and easy to operate, we believe that the proposed method will become a promising tool for S. aureus detection in the POCT field.     

In situ fabrication of hierarchical biomass carbon-supported Cu@CuO–Al2O3 composite materials: synthesis,properties and adsorption applications

Hierarchical Cu–Al₂O₃/biomass-activated carbon composites were successfully prepared by entrapping a biomass-activated carbon powder derived from green algae in the Cu–Al₂O₃ frame (H–Cu–Al/BC) for the removal of ammonium nitrogen (NH₄⁺-N) from aqueous solutions. The as-synthesized samples were characterized via XRD, SEM, BET and FTIR spectroscopy. The BET specific surface area of the synthesized H–Cu–Al/BC increased from 175.4 m² g⁻¹ to 302.3 m² g⁻¹ upon the incorporation of the Cu–Al oxide nanoparticles in the BC surface channels. The experimental data indicated that the adsorption isotherms were well described by the Langmuir equilibrium isotherm equation and the adsorption kinetics of NH₄⁺-N obeyed the pseudo-second-order kinetic model. The static maximum adsorption capacity of NH₄⁺-N on H–Cu–Al/BC was 81.54 mg g⁻¹, which was significantly higher than those of raw BC and H–Al/BC. In addition, the presence of K⁺, Na⁺, Ca²⁺, and Mg²⁺ ions had no significant impact on the NH₄⁺-N adsorption, but the presence of Al³⁺ and humic acid (NOM) obviously affected and inhibited the NH₄⁺-N adsorption. The thermodynamic analyses indicated that the adsorption process was endothermic and spontaneous in nature. H–Cu–Al/BC exhibited removal efficiency of more than 80% even after five consecutive cycles according to the recycle studies. These findings suggest that H–Cu–Al/BC can serve as a promising adsorbent for the removal of NH₄⁺-N from aqueous solutions.

Hierarchical Cu–Al₂O₃/biomass-activated carbon composites were successfully prepared by entrapping a biomass-activated carbon powder derived from green algae in the Cu–Al₂O₃ frame (H–Cu–Al/BC) for the removal of ammonium nitrogen (NH₄⁺-N) from aqueous solutions.     

Ag8SnS6: a new IR solar absorber material with a near optimal bandgap

We report the synthesis and photovoltaic properties of a new ternary solar absorber – Ag₈SnS₆ nanocrystals prepared by successive ionic layer adsorption reaction (SILAR) technique. The synthesized Ag₈SnS₆ nanocrystals have a bandgap E_g of 1.24–1.41 eV as revealed from UV-Vis and external quantum efficiency (EQE) measurements. Its photovoltaic properties were characterized by assembling a liquid-junction Ag₈SnS₆ sensitized solar cell for the first time. The best cell yielded a J_sc of 9.29 mA cm⁻², a V_oc of 0.23 V, an FF of 31.3% and a power conversion efficiency (PCE) of 0.64% under 100% incident light illumination using polysulfide electrolyte and Au counter electrode. The efficiency improved to 1.43% at a reduced light intensity of 10% sun. When the polysulfide was replaced by a cobalt electrolyte with a lower redox level, the V_oc increased to 0.54 V and PCE increased to 2.29% under 0.1 sun, a respectable efficiency for a new solar material. The EQE spectrum covers the spectral range of 300–1000 nm with a maximum EQE of 77% at λ = 600 nm. The near optimal E_g and the respectable photovoltaic performance suggest that Ag₈SnS₆ nanocrystals have potential to be an efficient IR solar absorber.

We report the synthesis and photovoltaic properties of a new ternary solar absorber – Ag₈SnS₆ nanocrystals prepared by successive ionic layer adsorption reaction (SILAR) technique.