Simultaneous preconcentration and determination of copper, nickel, cobalt and lead ions content by flame atomic absorption spectrometry

A sensitive and simple method for the simultaneous preconcentration of nutritionally important minerals in real samples has been reported. The method is based on the formation of metal complexes by 4,6-dihydroxy-2-mercaptopyrimidine (DHMP) loaded on activated carbon. The metals content on the complexes are then eluted using 5 mL 2M HNO(3) in acetone, which are detected by AAS at resonance line. In this procedure, minerals such as Cu, Ni, Pb and Co could be analyzed in one run by caring out the simultaneous separation and quantification of them. At optimum condition the response are linear over concentration range of 0.04-1.1 microg mL(-1) for Ni(2+) and 0.04-1.0 microg mL(-1) for Cu(2+), Pb(2+) and Co(2+). The detection limits of each element are expressed as the amount of analytes in ng mL(-1) giving a signal to noise ratio of 3 are equal to 3.5, 3.4, 2.9 and 8.4 for Ni(2+), Co(2+), Cu(2+) and Pb(2+). The sorption capacity was determined by saturating 0.5 g solid phase. The loading capacity are 0.54, 0.53, 0.63 and 0.45 mg g(-1) for Ni(2+), Co(2+), Cu(2+) and Pb(2+). The ability of method for repeatable recovery of trace ion are 99.0, 98.9, 99.2 and 98.8 with R.S.D. of 1.4, 1.3, 1.2 and 1.4 for Ni(2+), Co(2+), Cu(2+) and Pb(2+). The low detection limits of these elements in this technique make it a superior alternative to UV-vis and in several applications, also an alternative to ICP-MS techniques. The method has been successfully applied for these metals content evaluation in some real samples including natural water, leaves of spinach and cow liver.     

Metal ion (silver, cadmium and zinc ions) modified CdS quantum dots for ultrasensitive copper ion sensing

Metal ion (Ag(+), Cd(2+), Zn(2+)) modified CdS quantum dots (QDs) were synthesized and used for Cu(2+) sensing. Modification by these metal ions could enhance the PL intensity of CdS QDs with the extent of the PL enhancement being related to the concentration of the metal ions. Different metal ion (Ag(+), Cd(2+), Zn(2+)) modified CdS QDs also showed different analytical characteristics for Cu(2+) sensing. In particular, Ag( + ) modified CdS QDs showed greatly enhanced sensitivity for Cu(2+) determination than did the unmodified CdS QDs. A limit of detection (LOD) of 2.0 × 10(-10) M was obtained for Ag(+) modified CdS QDs, which is the lowest LOD obtained using QDs as fluorescence probes for Cu(2+) sensing. This study demonstrates the important role of surface state of QDs in fluorescence sensing.     

A nanoparticle autocatalytic sensor for Ag+ and Cu2+ ions in aqueous solution with high sensitivity and selectivity and its application in test paper

A novel nanoparticle autocatalytic sensor for the detection of Ag(+) and Cu(2+) has been constructed based on the oxidative ability of Ag(+) and Cu(2+) toward o-phenylenediamine (OPDA). Ag(+) and Cu(2+) can be reduced to zerovalent silver and copper, respectively, and then such zerovalent Ag and Cu species form silver and copper nanoparticles that can catalyze the reaction between OPDA and Ag(+) and Cu(2+). In the reaction, OPDA is oxidized to 2,3-diaminophenazine (OPDAox), which has a fluorescence emission at 568 nm. Under the optimal conditions, Ag(+) and Cu(2+) can be detected in the concentration ranges from 60 nM to 60 μM and from 2.5 nM to 25 μM, respectively. Through this facile approach, Ag(+) and Cu(2+) can be detected down to 60 nM and 2.5 nM, respectively. In addition, the sensor is utilized for the detection of Ag(+) and Cu(2+) in sewage, and we have obtained very good results that are consistent with those of inductively coupled plasma-mass spectroscopy (ICP-MS). Moreover, such a nanoparticle autocatalytic sensor is applied to test paper for the detection of Ag(+) and Cu(2+) with the naked eye. With such test paper, Ag(+) and Cu(2+) could be detected at levels as low as 0.06 nmol and 0.3 nmol, respectively, with detection ranges of 0.06-60 nmol for Ag(+) and 0.3-60 nmol for Cu(2+), under the irradiation of UV light (365 nm). The test paper could be potentially used in the rapid detection of Ag(+) and Cu(2+) in real samples.     

Highly sensitive, colorimetric detection of mercury(II) in aqueous media by quaternary ammonium group-capped gold nanoparticles at room temperature

We provide a highly sensitive and selective assay to detect Hg(2+) in aqueous solutions using gold nanoparticles modified with quaternary ammonium group-terminated thiols at room temperature. The mechanism is the abstraction of thiols by Hg(2+) that led to the aggregation of nanoparticles. With the assistance of solar light irradiation, the detection limit can be as low as 30 nM, which satisfies the guideline concentration of Hg(2+) in drinking water set by the WHO. In addition, the dynamic range of detection is wide (3 × 10(-8)-1 × 10(-2) M). This range, to our best knowledge, is the widest one that has been reported so far in gold nanoparticle (AuNP)-based assays for Hg(2+).     

Hierarchically Nanostructured Hybrid Platform for Tumor Delineation and Image‐Guided Surgery via NIR‐II Fluorescence and PET Bimodal Imaging

Bimodal imaging with fluorescence in the second near infrared window (NIR‐II) and positron emission tomography (PET) has important significance for tumor diagnosis and management because of complementary advantages. It remains challenging to develop NIR‐II/PET bimodal probes with high fluorescent brightness. Herein, bioinspired nanomaterials (melanin dot, mesoporous silica nanoparticle, and supported lipid bilayer), NIR‐II dye CH‐4T, and PET radionuclide ⁶⁴Cu are integrated into a hybrid NIR‐II/PET bimodal nanoprobe. The resultant nanoprobe exhibits attractive properties such as highly uniform tunable size, effective payload encapsulation, high stability, dispersibility, and biocompatibility. Interestingly, the incorporation of CH‐4T into the nanoparticle leads to 4.27‐fold fluorescence enhancement, resulting in brighter NIR‐II imaging for phantoms in vitro and in situ. Benefiting from the fluorescence enhancement, NIR‐II imaging with the nanoprobe is carried out to precisely delineate and resect tumors. Additionally, the nanoprobe is successfully applied in tumor PET imaging, showing the accumulation of the nanoprobe in a tumor with a clear contrast from 2 to 24 h postinjection. Overall, this hierarchically nanostructured platform is able to dramatically enhance fluorescent brightness of NIR‐II dye, detect tumors with NIR‐II/PET imaging, and guide intraoperative resection. The NIR‐II/PET bimodal nanoprobe has high potential for sensitive preoperative tumor diagnosis and precise intraoperative image‐guided surgery.     

Efficient fluorescence turn-on probe for zirconium via a target-triggered DNA molecular beacon strategy

It is well-known that Zr(4+) could selectively bind with two phosphate-functionalized molecules through a coordinate covalent interaction to form a sandwich-structured complex (-PO(3)(2-)-Zr(4+)-PO(3)(2-)-). In this paper, we for the first time converted such interaction into fluorescence sensing systems for Zr(4+) via a target-triggered DNA molecular beacon strategy. In the new designed sensing system, two phosphorylated and pyrene-labeled oligonucleotides were chosen as both recognition and reporter units, which will be linked by target Zr(4+) to form a hairpin structure and bring the two labeled pyrene molecules into close proximity, resulting in a "turn-on" excimer fluorescence signal. Moreover, γ-cyclodextrin was introduced to afford an amplified fluorescence signal and, therefore, provided an improved sensitivity for the target Zr(4+). This allows detection of Zr(4+) with high sensitivity (limit of detection, LOD = 200 nM) and excellent selectivity. The proposed sensing system has also been used for detection of Zr(4+) in river water samples with satisfactory result.     

Novel hydrophilic bis(1,2,3-triazolyl)fluorenyl probe for in vitro zinc ion sensing

A hydrophilic bis(1,2,3-triazolyl)fluorene derivative was synthesized as a multi-photon-absorbing, zinc-ion-sensing fluorescent probe. The fluorescence response was approximately five-fold greater in presence of Zn(2+), resulting in a large binding constant (1 × 10(9)) for a 1:2 ligand to zinc complex. A four-fold increase in the two-photon absorption cross section was achieved upon binding Zn(2+). In vitro two-photon fluorescence microscopy imaging revealed a significant fluorescence increase upon introduction of Zn(2+) into HeLa cells and reversible Zn(2+) binding, demonstrating the potential of this probe for zinc ion sensing.     

Graphene-DNAzyme based biosensor for amplified fluorescence "turn-on" detection of Pb2+ with a high selectivity

On the basis of the remarkable difference in affinity of graphene (GO) with ssDNA containing a different number of bases in length, we for the first time report a GO-DNAzyme based biosensor for amplified fluorescence "turn-on" detection of Pb(2+). A FAM-labeled DNAzyme-substrate hybrid acted as both a molecular recognition module and signal reporter and GO as a superquencher. By taking advantage of the super fluorescence quenching efficiency of GO, our proposed biosensor exhibits a high sensitivity toward the target with a detection limit of 300 pM for Pb(2+), which is lower than previously reported for catalytic beacons. Moreover, with the choice of a classic Pb(2+)-dependent GR-5 DNAzyme instead of 8-17 DNAzyme as the catalytic unit, the newly designed sensing system also shows an obviously improved selectivity than previously reported methods. Moreover, the sensing system was used for the determination of Pb(2+) in river water samples with satisfying results.     

Quinolino-triazole linked gold nanoparticles as sensitive 'turn-on' fluorescent Cd(2+) probes

Quinoline derivatives were brought into the surface of gold nanoparticles (Au NPs) through click chemistry. The fluorescence was quenched by Au NPs because of electron transfer between Au NPs and quinoline. However, upon addition of Cd(2+) to the quinoline-triazole Au NP solution, it exhibited an effective switch-on fluorescence response, owing to the coordination between quinoline and Cd(2+) which can efficiently block the electron transfer. What's more, the fluorescent sensor can effectively detect Cd(2+) in aqueous solution with a detection limit of 1.0 × 10(-5) M.     

Conjugated polyelectrolyte-based real-time fluorescence assay for alkaline phosphatase with pyrophosphate as substrate

The fluorescence of the anionic, carboxylate-substituted poly(phenylene ethynylene) polymer PPECO2 is quenched very efficiently via the addition of 1 equiv of Cu(2+). Addition of pyrophosphate (PPi) into the weakly fluorescent solution of PPECO2 and Cu(2+) induces recovery of the polymer's fluorescence; the recovery occurs because PPi complexes with Cu(2+), effectively sequestering the ion so it cannot bind to the carboxylate groups of the polymer. A calibration curve was developed that relates the extent of fluorescence recovery to [PPi], making the PPECO2-Cu(2+) system a sensitive and selective turn-on sensor for PPi. Using the PPECO2-Cu(2+) system as the signal transducer, a real-time fluorescence turn-off assay for the enzyme alkaline phosphatase (ALP) using PPi as the substrate is developed. The assay operates with [PPi] in the micromolar range, and it offers a straightforward and rapid detection of ALP activity with the enzyme present in the nanomolar concentration range, operating either in an end point or real-time format. Kinetic and product inhibition parameters are derived by converting time-dependent fluorescence intensity into PPi (substrate) concentration, thus allowing calculation of the initial reaction rates (v(o)). Weak, nonspecific fluorescence responses are observed concomitant to addition of other proteins to the assay solution; however, the signal response to ALP is demonstrated to arise from the ALP catalyzed hydrolysis of PPi to phosphate (Pi).     

Methionine-pyrene hybrid based fluorescent probe for trace level detection and estimation of Hg(II) in aqueous environmental samples: experimental and computational studies

A new fluorescent, Hg(2+) selective chemosensor, 4-methylsulfanyl-2-[(pyren-4-ylmethylene)-amino] butyric acid methyl ester (L, MP) was synthesized by blending methionine with pyrene. It was well characterized by different analytical techniques, viz. (1)H NMR, (13)C NMR, QTOF mass spectra, elemental analysis, FTIR and UV-vis spectroscopy. The reaction of this ligand with Hg(2+) was studied by steady state and time-resolved fluorescence spectroscopy. The Hg(2+) complexation process was confirmed by comparing FTIR, UV-vis, thermal, QTOF mass spectra and (1)H NMR data of the product with that of the free ligand values. The composition (Hg(2+):L=1:1) of the Hg(2+) complex in solution was evaluated by fluorescence titration method. Based on the chelation assisted fluorescence quenching, a highly sensitive spectrofluorometric method was developed for the determination of trace amounts of Hg(2+) in water. The ligand had an excitation and emission maxima at 360 nm and 455 nm, respectively. The fluorescence life times of the ligand and its Hg(2+) complex were 1.54 ns and 0.72 ns respectively. The binding constant of the ligand, L with Hg(2+) was calculated using Benesi-Hildebrand equation and was found to be 7.5630×10(4). The linear range of the method was from 0 to 16 μg L(-1) with a detection limit of 0.056 μg L(-1) for Hg(2+). The quantum yields of the ligand and its Hg(2+) complex were found to be 0.1206 and 0.0757 respectively. Both the ligand and its Hg(2+) complex have been studied computationally (Ab-initio, Hartree Fock method) to get their optimized structure and other related physical parameters, including bond lengths, bond angles, dipole moments, orbital interactions etc. The binding sites of the ligand to the Hg(2+) ion as obtained from the theoretical calculations were well supported by (1)H NMR titration. The interference of foreign ions was negligible. This method has been successfully applied to the determination of mercury(II) in industrial waste water.     

Polyamine-functionalized carbon quantum dots as fluorescent probes for selective and sensitive detection of copper ions

A novel sensing system has been designed for Cu(2+) ion detection based on the quenched fluorescence (FL) signal of branched poly(ethylenimine) (BPEI)-functionalized carbon quantum dots (CQDs). Cu(2+) ions can be captured by the amino groups of the BPEI-CQDs to form an absorbent complex at the surface of CQDs, resulting in a strong quenching of the CQDs' FL via an inner filter effect. Herein, we have demonstrated that this facile methodology can offer a rapid, reliable, and selective detection of Cu(2+) with a detection limit as low as 6 nM and a dynamic range from 10 to 1100 nM. Furthermore, the detection results for Cu(2+) ions in a river water sample obtained by this sensing system agreed well with that by inductively couple plasma mass spectrometry, suggesting the potential application of this sensing system.     

普鲁士蓝基HClO荧光纳米探针及其对肿瘤细胞的特异性检测（英文）

次氯酸(HClO)是一种活性氧(ROS),在许多生理和病理过程中起着至关重要的作用。然而,过量的HClO会导致组织损伤、动脉粥样硬化、神经退行性疾病甚至癌症。因此,实时检测肿瘤细胞中HCl O对于探索HClO在肿瘤进展以及免疫治疗中的作用具有重要意义。与目前常用的工艺复杂、水溶性差的有机分子探针不同,本工作简单地将异硫氰酸荧光素(FITC)与中空介孔普鲁士蓝纳米粒子(HMPB)相结合,构建了一种新型的无机亲水荧光纳米探针。由于内滤光效应,HMPB中FITC的荧光有一定程度的猝灭,但通过Fe²⁺-ClO^–氧化还原反应可恢复荧光。体外条件下,加入HClO后, FITC在发射峰(520 nm)处荧光逐渐增强, HClO在5×10^–6～50×10^–6 mol/L范围内呈良好的线性关系,检出限为2.01×10^–6mol/L。此外,在细胞水平上,该纳米探针对癌细胞中的HClO显示出良好的特异检测能力,且灵敏度高。     

Spectroscopic Probing of Mixed-Mode Adsorption of Ru(bpy)(3)(2+) to Silica

Evanescent wave excitation of fluorescence was used to study the adsorption of Ru(bpy)(3)(2+) from aqueous solution to three types of surfaces: bare silica, a dimethylethylsiloxane (C(2)) monolayer on silica, and a dimethyloctadecylsiloxane (C(18)) monolayer on silica. The solution pH was varied to investigate the nonpolar and electrostatic contributions to the free energy of adsorption for each surface. The pH dependence of the adsorption showed that the pK(a) is the same for each of the three surfaces, consistent with earlier conclusions that the acidity of derivatized silica surfaces is due to areas of exposed silica. The free energies of adsorption for the bare silica surface, -26.2(±0.2) kJ/mol at pH 8, was attributed to electrostatic interactions alone. The free energy of adsorption for the C(2) and C(18) surfaces, -28.5(±0.1) and -31.5(±0.1) kJ/mol, respectively, were found to have both electrostatic and nonpolar contributions, with the latter being larger by 50% for the C(2) surface and 100% for the C(18) surface. Using Gouy-Chapman theory, the surface charge densities on each of the three surfaces, calculated from the electrostatic interaction energy of Ru(bpy)(3)(2+), were found to be within the range of literature values: 8.8(±0.1) × 10(-)(7) mol/m(2) for bare silica and 1.7(±0.1) × 10(-)(7) mol/m(2) for both the C(18) and C(2) surfaces. The results demonstrate that a cationic dye can be used to probe the silanol activity of chemically modified silica surfaces. The results support the picture that these chemically modified silica surfaces are acidic due to molecular-scale areas of contact between the bare silica substrate and the aqueous phase.     

Conjugated polymer microspheres for "turn-off"/"turn-on" fluorescence optosensing of inorganic ions in aqueous media

The synthesis and characterization of a novel water-compatible microsized material, based on fluorescent conjugated polymers (CPs), and its applicability for optical sensing of inorganic ions of environment interest (copper and cyanide) in water media is here described. Polyfluorene-based fluorescent CPs were synthesized and functionalized with imidazole moieties (selective recognition element) and a terminal double bond (covalently linked to an organic matrix) through a postfunctionalization strategy. Further, microspheres of the novel imidazole-functionalized fluorescent CPs, able to work in water media, were synthesized via a microemulsion and polymerization procedure. The synthesized imidazole-functionalized CP microspheres were then evaluated as fluorescence "turn-Off" sensing materials for Cu(2+) detection in aqueous media. Analyte detection was based on the quenching effect of the Cu(2+), selectively recognized by the imidazole group, on the polymer fluorescence emission. The developed optosensor exhibits a detection limit of 1 μg/L for the determination of Cu(2+) in water with a reproducibility of 4%. The synthesized microsized material was also evaluated for the "turn-on" optosensing of cyanide in water, measuring the recovery of the emission signal from the CP that has been previously deactivated by the presence of quencher species. The "turn-On" optosensor allows the selective determination of free cyanide in aqueous solution with high sensitivity (detection limit of 18 μg/L), obtaining a reproducibility of 2.9%. A high sample throughput (between 7 and 12 samples per hour) was achieved in both cases. Analytical applicability of the fluorescent CP microsphere materials has been successfully demonstrated by tap and mineral water analysis.     

A new Schiff's base ligand immobilized agarose membrane optical sensor for selective monitoring of mercury ion

A highly selective optical sensor was developed for the Hg(2+) determination by chemical immobilization of 2-[(2-sulfanylphenyl)ethanimidoyl]phenol (L), on an agarose membrane. Spectrophotometric studies of complex formation between the Schiff's base ligand L and Hg(2+), Sr(2+), Mn(2+), Cu(2+), Al(3+), Cd(2+), Zn(2+), Co(2+) and Ag(+) metal ions in methanol solution indicated a substantially larger stability constant for the mercury ion complex. Consequently, the Schiff's base L was used as an appropriate ionophore for the preparation of a selective Hg(2+) optical sensor, by its immobilization on a transparent agarose film. A distinct color change, from yellow to green-blue, was observed by contacting the sensing membrane with Hg(2+) ions at pH 4.5. The effects of pH, ionophore concentration, ionic strength and reaction time on the immobilization of L were studied. A linear relationship was observed between the membrane absorbance at 650 nm and Hg(2+) concentrations in a range from 1×10(-2) to 1×10(-5) mol L(-1) with a detection limit (3σ) of 1×10(-6) mol L(-1). No significant interference from 100 times concentrations of a number of potentially interfering ions was detected for the mercury ion determination. The optical sensor was successfully applied to the determination of mercury in amalgam alloy and spiked water samples.     

DNA-capped mesoporous silica nanoparticles as an ion-responsive release system to determine the presence of mercury in aqueous solutions

We have developed DNA-functionalized silica nanoparticles for the rapid, sensitive, and selective detection of mercuric ion (Hg(2+)) in aqueous solution. Two DNA strands were designed to cap the pore of dye-trapped silica nanoparticles. In the presence of ppb level Hg(2+), the two DNA strands are dehybridized to uncap the pore, releasing the dye cargo with detectable enhancements of fluorescence signal. This method enables rapid (less than 20 min) and sensitive (limit of detection, LOD, 4 ppb) detection, and it was also able to discriminate Hg(2+) from twelve other environmentally relevant metal ions. The superior properties of the as-designed DNA-functionalized silica nanoparticles can be attributed to the large loading capacity and highly ordered pore structure of mesoporous silica nanoparticles, as well as the selective binding of thymine-rich DNA with Hg(2+) . Our design serves as a new prototype for metal-ion sensing systems, and it also has promising potential for detection of various targets in stimulus-release systems.     

Mesoporous thin-film on highly-sensitive resonant chemical sensor for relative humidity and CO2 detection

Distributed sensing of gas-phase chemicals is a promising application for mesoporous materials when combined with highly sensitive miniaturized gas sensors. We present a direct application of a mesoporous silica thin film on a highly sensitive miniaturized resonant chemical sensor with a mass sensitivity at the zeptogram scale for relative humidity and CO(2) detection. Using mesoporous silica thin-film, we report one of the lowest volume resolutions and a sensitive detection of 5.1 × 10(-4)% RH/Hz to water vapor in N(2), which is 70 times higher than a device with a nontemplated silica layer. In addition, a mesoporous thin-film that is functionalized with an amino-group is directly applied on the resonant sensor, which exhibits a volume sensitivity of 1.6 × 10(-4)%/Hz and a volume resolution of 1.82 × 10(-4)% to CO(2) in N(2).     

Luminescent, freestanding composite films of Au15 for specific metal ion sensing

A highly luminescent freestanding film composed of the quantum cluster, Au(15), was prepared. We studied the utility of the material for specific metal ion detection. The sensitivity of the red emission of the cluster in the composite to Cu(2+) has been used to make a freestanding metal ion sensor, similar to pH paper. The luminescence of the film was stable when exposed to several other metal ions such as Hg(2+), As(3+), and As(5+). The composite film exhibited visual sensitivity to Cu(2+) up to 1 ppm, which is below the permissible limit (1.3 ppm) in drinking water set by the U.S. environmental protection agency (EPA). The specificity of the film for Cu(2+) sensing may be due to the reduction of Cu(2+) to Cu(1+)/Cu(0) by the glutathione ligand or the Au(15) core. Extended stability of the luminescence of the film makes it useful for practical applications.     

Resonance energy transfer-amplifying fluorescence quenching at the surface of silica nanoparticles toward ultrasensitive detection of TNT

This paper reports a resonance energy transfer-amplifying fluorescence quenching at the surface of silica nanoparticles for the ultrasensitive detection of 2,4,6-trinitrotoluene (TNT) in solution and vapor environments. Fluorescence dye and organic amine were covalently modified onto the surface of silica nanoparticles to form a hybrid monolayer of dye fluorophores and amine ligands. The fluorescent silica particles can specifically bind TNT species by the charge-transfer complexing interaction between electron-rich amine ligands and electron-deficient aromatic rings. The resultant TNT-amine complexes bound at the silica surface can strongly suppress the fluorescence emission of the chosen dye by the fluorescence resonance energy transfer (FRET) from dye donor to the irradiative TNT-amine acceptor through intermolecular polar-polar interactions at spatial proximity. The quenching efficiency of the hybrid nanoparticles with TNT is greatly amplified by at least 10-fold that of the corresponding pure dye. The nanoparticle-assembled arrays on silicon wafer can sensitively detect down to approximately 1 nM TNT with the use of only 10 microL of solution (approximately 2 pg TNT) and several ppb of TNT vapor in air. The simple FRET-based nanoparticle sensors reported here exhibit a high and stable fluorescence brightness, strong analyte affinity, and good assembly flexibility and can thus find many applications in the detection of ultratrace analytes.