8-aminoquinoline functionalized silica nanoparticles: a fluorescent nanosensor for detection of divalent zinc in aqueous and in yeast cell suspension

Zinc is one of the most important transition metal of physiological importance, existing primarily as a divalent cation. A number of sensors have been developed for Zn(II) detection. Here, we present a novel fluorescent nanosensor for Zn(II) detection using a derivative of 8-aminoquinoline (N-(quinolin-8-yl)-2-(3 (triethoxysilyl)propylamino)acetamide (QTEPA) grafted on silica nanoparticles (SiNPs). These functionalized SiNPs were used to demonstrate specific detection of Zn(II) in tris-HCl buffer (pH 7.22), in yeast cell (Saccharomyces cerevisiae) suspension, and in tap water. The silane QTEPA, SiNPs and final product were characterized using solution and solid state nuclear magnetic resonance, Fourier transform infrared, ultraviolet-visible absorption spectroscopy, transmission electron microscopy, elemental analysis, thermogravimetric techniques, and fluorescence spectroscopy. The nanosensor shows almost 2.8-fold fluorescence emission enhancement and about 55 nm red-shift upon excitation with 330 ± 5 nm wavelength in presence of 1 μM Zn(II) ions in tris-HCl (pH 7.22). The presence of other metal ions has no observable effect on the sensitivity and selectivity of nanosensor. This sensor selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 μM. The sensor shows good applicability in the determination of Zn(II) in tris-HCl buffer and yeast cell environment. Further, it shows enhancement in fluorescence intensity in tap water samples.     

An optical fiber chemical sensor for mercury ions based on a porphyrin dimer

The synthesis of a novel fluoroionophore, 5-p-[[4-(10',15',20'-triphenyl-5'-porphinato) phenyloxyl]-1-butyloxyl]phenyl-10,15,20-triphenylporphine (DTPP), and its application for preparation of a Hg(II)-sensitive optical fiber chemical sensor are described. The response of the sensor is based on the fluorescence quenching of DTPP by coordination with Hg(II). The porphyrin dimer-based sensor shows a linear response toward Hg(II) in the concentration range 5.2 x 10(-7)-3.1 x 10(-4) mol x L(-1), with a working pH range from 2.4 to 8.0. The sensor shows excellent selectivity for Hg(II) over transition metal cations including Cd(II), Co(II), Cu(II), Ni(II), Pb(II), Zn(II), and Fe(III). As a sensing agent, the porphyrin dimer shows obviously better fluorescence response characteristics toward Hg(II) compared to porphyrin monomer or metalloporphyrin. The effect of the composition of the sensor membrane was studied, and the experimental conditions were optimized. The sensor has been used for determination of Hg(II) in water samples.     

Copper ion-selective fluorescent sensor based on the inner filter effect using a spiropyran derivative

A highly selective copper(II) ion fluorescent sensor has been designed based on the UV-visible absorption of a spiropyran derivative coupled with the use of a metal porphyrin operative on the fluorescence inner filter effect. Spiropyrans, which combine the characteristics of metal binding and signal transduction, have been widely utilized in cationic ion recognition by UV-visible spectroscopy. In the present work, the viability of converting the absorption signal of the spiropyran molecule into a fluorescence signal was explored. On account of overlap of the absorption band of the spiropyran (lambda(abs) = 547 nm) in the presence of copper ion with the Q-band of an added fluorophore, zinc meso-tetraphenylporphyrin (lambda(abs) = 556 nm), the effective light absorbed by the porphyrin and concomitantly the emitted light intensity vary as a result of varying absorption of the spiropyran via fluorescence inner filter effect. The metal binding characteristic of the spiropyran presents an excellent selectivity for copper ion in comparison with several other heavy or transition metal ions. Since the changes in the absorbance of the absorber translate into exponential changes in fluorescence of the fluorophore, the novelty of the present device is that the analytical signal is more sensitive over that of the absorptiometry or that of the fluorometry using one single dye. To realize a practical fluorescent sensor, both the absorber and fluorophore were immobilized in a plasticized poly(vinyl chloride) membrane, and the sensing characteristics of the membrane for copper ion were investigated. The sensor is useful for measuring Cu2+ at concentrations ranging from 7.5 x 10(-7) to 3.6 x 10(-5) M with a detection limit of 1.5 x 10(-7) M. The sensor is chemically reversible, the fluorescence was switched off by immersing the membrane in copper ion solution and switched on by washing it with EDTA solution.     

Coupling fiber optics to a permeation liquid membrane for heavy metal sensor development

We present the first sensing system for metal ions based on the combination of separation/preconcentration by a permeation liquid membrane (PLM) and fluorescence detection with an optical fiber. As a model, a system for the detection of Cu(II) ions was developed. The wall of a polypropylene hollow fiber serves as support for the permeable liquid membrane. The lumen of the fiber contains the strip solution in which Cu(II) is accumulated. Calcein, a fluorochromic dye, acts as stripping agent and at the same time as metal indicator. The quenching of the calcein fluorescence upon metal accumulation in the strip phase is detected with a multimode optical fiber, which is incorporated into the lumen. Fluorescence is excited with a blue LED and detected with a photon counter. Taking advantage of the high selectivity and sensitivity of PLM preconcentration, a detection limit for Cu(II) of approximately 50 nM was achieved. Among five tested heavy metal ions, Pb(II) was the only major interfering species. The incorporation of small silica optical fibers into the polypropylene capillary allows for real-time monitoring of the Cu(II) accumulation process.     

Real-time determination of picomolar free Cu(II) in seawater using a fluorescence-based fiber optic biosensor

We report real-time, in situ determination of free copper ion at picomolar levels in seawater using a fluorescence-based fiber optic biosensor. The sensor transducer is a protein molecule, site-specifically labeled with a fluorophore that is attached to the distal end of an optical fiber, which binds free Cu(II) with high affinity and selectivity. The transducer reports the metal's concentration as a change in fluorescence intensity or lifetime, using a frequency domain approach. The transducer's response time is diffusion-limited, with a typical measurement requiring 30 s. The sensor demonstrates a detection limit of 0.1 pM free Cu(II) in a seawater model. Accuracy and precision of the sensor were at least comparable to cathodic ligand exchange/adsorptive cathodic stripping voltammetry. Measurements of tidal flushing of a copper-contaminated inlet are shown.     

对Cu~(2+)兼具检测及分离功能的聚氨酯泡沫的制备与性能

制备了对Cu~(2+)具有高灵敏检测及分离回收功能的聚氨酯泡沫。首先采用荧光前驱体4-溴-1,8-萘二甲酸酐、乙醇胺和2-氨基-4-噻唑乙酸作为原料合成含有羟基和噻唑乙酸基团的小分子传感器N-乙醇-4-(4-噻唑乙酸)-1,8-萘二甲酰亚胺(ETN);再通过其上的羟基与甲苯-2,4-二异氰酸酯(TDI)的-NCO基团反应将小分子感应器化学链接到多孔的聚氨酯泡沫上。荧光分析表明接有小分子感应器ETN的聚氨酯泡沫吸附Cu~(2+)离子后会发出荧光,荧光强度随Cu~(2+)离子浓度增加而变强。当Cu~(2+)离子的浓度低到10-7 mol/L数量级时也可检测到荧光。而且,多孔聚氨酯泡沫(当含1%的ETN)便具有37.66mg/g回收Cu~(2+)离子的能力,这使其具有在诸如废水和污水检测和分离Cu~(2+)的潜能和价值。     

Silicon-nanowire-based CMOS-compatible field-effect transistor nanosensors for ultrasensitive electrical detection of nucleic acids

We herein report the design of a novel semiconducting silicon nanowire field-effect transistor (SiNW-FET) biosensor array for ultrasensitive label-free and real-time detection of nucleic acids. Highly responsive SiNWs with narrow sizes and high surface-to-volume-ratios were "top-down" fabricated with a complementary metal oxide semiconductor compatible anisotropic self-stop etching technique. When SiNWs were covalently modified with DNA probes, the nanosensor showed highly sensitive concentration-dependent conductance change in response to specific target DNA sequences. This SiNW-FET nanosensor revealed ultrahigh sensitivity for rapid and reliable detection of 1 fM of target DNA and high specificity single-nucleotide polymorphism discrimination. As a proof-of-concept for multiplex detection with this small-size and mass producible sensor array, we demonstrated simultaneous selective detection of two pathogenic strain virus DNA sequences (H1N1 and H5N1) of avian influenza.     

Ultrasensitive Pb(II) potentiometric sensor based on copolyaniline nanoparticles in a plasticizer-free membrane with a long lifetime

A newly designed Pb(II) potentiometric sensor based on intrinsically conducting nanoparticles of solid poly(aniline-co-2-hydroxy-5-sulfonic aniline) possessing many ligating functional groups like -NH-, -N=, -OH, -SO(3)H, -NH(2) as ionophores in plasticizer-free vinyl resin solid membranes has been fabricated. A linear Nernstian response is obtained within a wide Pb(II) activity range from 1.0 × 10(-3) to 1.0 × 10(-10) M with a detection limit as low as 2.2 × 10(-11) M. The pH independent plateau ranges between 3.5 and 7.0. After 15 months' usage, the sensor maintains 95% performance parameters. Its anti-interference ability to Cu(II), Cd(II), Ag(I), and Hg(II) is much stronger than other sensors with a detection limit at (sub)nanomolar level. Electrochemical impedance spectroscopy reveals that the solid sensing membrane has a diffusion coefficient of around 5 × 10(-14) to 1 × 10(-13) cm(2) s(-1). The much lower diffusion coefficient for Pb(II) is highly beneficial for the elimination of Pb(II) flux across the membrane. The wide detection concentration range, low detection limit, high selectivity, extensive pH window, and long lifetime make for a robust sensor giving reliable measurement of Pb(II) content with potential application in real-world samples at trace levels.     

Fabrication,characterization and sensing properties of Cu(II) ion imprinted sol–gel thin film on QCM

Cu(II)-molecularly imprinted sol–gel films (Cu(II)-MISGF), coated on a quartz crystal microbalance (QCM) chip, were fabricated using a sol–gel procedure. Co-hydrolysis and co-condensation of Cu(II) (templates), 3-aminopropyltrimethoxysilane (APTS, functional monomer) and tetraethoxysilane (TEOS, cross-linking agent) were performed with acid and base catalysis. The properties of the Cu(II)-MISGF were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and the electrochemical methods of cyclic voltammetry (CV). Microstructural observations revealed that the acid-catalyzed system yielded more mechanically stable thin films. A combined Cu(II)-MISGF-QCM with flow injection analysis (FIA) method was utilized to investigate the sensing performance of the Cu(II)-MISGF, with special emphasis on the most important properties of sensitivity, selectivity and response time. The Cu(II)-MISGF-QCM sensor, at a TEOS/APTS molar ratio of 10, exhibited excellent selectivity and rapidly responded to Cu(II) ions.     

DNA hybridization on silicon nanowires

Nanowire-based detection strategies provide promising new routes to bioanalysis and indeed are attractive to conventional systems because of their small size, high surface-to-volume ratios, electronic, and optical properties. A sequence-specific detection of single-stranded oligonucleotides using silicon nanowires (SiNWs) is demonstrated. The surface of the SiNWs is functionalized with densely packed organic monolayer via hydrosilylation for covalent attachment. Subsequently, deoxyribonucleic acid (DNA) is immobilized to recognize the complementary target DNA. The biomolecular recognition properties of the nanowires are tested via hybridization with ^γP³² tagged complementary and non-complementary DNA oligonucleotides, showing good selectivity and reversibility. No significant non-specific binding to the incorrect sequences is observed. X-ray photoelectron spectroscopy, fluorescence imaging, and nanodrop techniques are used to characterize the modified SiNWs and covalent attachment with DNA. The results show that SiNWs are excellent substrates for the absorption, stabilization and detection of DNA sequences and could be used for DNA microarrays and micro fabricated SiNWs DNA sensors.     

Fluorescence sensing of zinc(II) using ordered mesoporous silica material (MCM-41) functionalized with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide

A novel fluorescent zinc sensor was designed and synthesized on ordered mesoporous silica material, MCM-41, with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide (QTEPA; 3) using a simple one-step molecular self-assembly of the silane. The solution and solid samples were characterized using solid-state nuclear magnetic resonance, transmission electron microscopy, diffuse-reflectance infrared Fourier transform, and thermogravimetric analysis techniques. The QTEPA-modified MCM-41 (4) shows 3-fold fluorescence emission enhancement and about a 55 nm red shift upon addition of 1 μM Zn(II) ions in a Tris-HCl (pH 7.22) aqueous buffer solution. The UV-vis absorption maximum is at 330 ± 5 nm, and the fluorescence emission maximum wavelength is at 468 nm, with an increase in quantum yield from 0.032 to 0.106 under the same conditions. The presence of other metal ions has no observable effect on the sensitivity and selectivity of 4. This system selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 μM. The MCM-41-based systems have the advantage that they can be employed in aqueous solutions without any aggregation.     

Photoelectrocatalytic oxidation of o-phenols on copper-plated screen-printed electrodes

A novel and sensitive detection method based on photoelectrocatalytic oxidation of o-diphenols was demonstrated on a copper-plated screen-printed carbon electrode (designated CuSPE) in pH 8 phosphate buffer solution. The o-diphenols can be detected amperometrically through electrochemical oxidation at a low applied potential of -0.1 V versus Ag/AgCl, where the CuSPE is much less subject to interfering reactions. The mechanism that induces good selectivity of the CuSPE is explained in terms of the formation of a cyclic five-member complex intermediate (Cu(II)-o-quinolate). A prototype homemade flow through cell design is described for incorporating the photoelectrode and light source. Electrode irradiation results in a large increase in anodic current. The oxidative photocurrents produced by irradiation increase with light intensity presumably because of the formation of semiconductor Cu(2)O. The principle used in this study has an opportunity to extend into various research applications.     

Detection of mercury ion by infrared fluorescent protein and its hydrogel-based paper assay

Mercury is a highly hazardous and widespread pollutant with bioaccumulative properties. Novel approaches that meet the criteria of desired selectivity, high sensitivity, good biocompatibility, and low background interference in natural settings are continuously being explored. We herein describe a new strategy utilizing the combination of infrared fluorescent protein (IFP) and its chromophore as an infrared fluorescence probe for mercury ion (Hg(II)) detection. Hg(II) has been validated to have specific binding affinity to a cysteine residue (C24) of IFP, thereby inhibiting the conjugation of IFP chromophore biliverdin (BV) to C24 and "turning off" the infrared emission of IFP. The IFP/BV sensor has high selectivity toward Hg(II) among other metal ions over a broad pH range. The in vitro detection limit was determined to be less than 50 nM. As a genetically encoded probe, we demonstrate the IFP/BV sensor can serve as a tool to detect Hg(II) in living organisms or tissues. Moreover, we have exploited a protein-agarose hydrogel-based paper assay to immobilize IFP for detection of Hg(II) in a portable and robust fashion.     

In-situ detection of C-reactive protein using silicon nanowire field effect transistor

Label-free, sensitive, and real-time c-reactive protein (CRP) sensor was fabricated using p-type silicon nanowire (SiNW) based structures configured as field effect transistors (FET) using the conventional 'top-down' semiconductor processes. The width of SiNWs were distributed 80 nm to 400 nm. Among them to improve signal-to-noise ratio and sensitivity of SiNW FET, 221 nm-SiNW was chosen for biosensing of CRP. Antibody of c-reactive protein (anti-CRP) was immobilized on the SiNW surface through polydimethylsiloxane (PDMS) microfluidic channel for detection of CRP. Specific binding of CRP with anti-CRP on the SiNW surface caused a conductance change of SiNW FET and various injections from 10 and 1 microg/ml to 100 ng/ml solutions of CRP resulted in the conductance changes from 39 and 25 to 16%, respectively. Label-free, in-situ and very sensitive electrical detection of CRP was demonstrated with the prepared SiNW FET.     

Detection of mercury(II) by quantum dot/DNA/gold nanoparticle ensemble based nanosensor via nanometal surface energy transfer

An ultrasensitive fluorescent sensor based on the quantum dot/DNA/gold nanoparticle ensemble has been developed for detection of mercury(II). DNA hybridization occurs when Hg(II) ions are present in the aqueous solution containing the DNA-conjugated quantum dots (QDs) and Au nanoparticles. As a result, the QDs and the Au nanoparticles are brought into the close proximity, which enables the nanometal surface energy transfer (NSET) from the QDs to the Au nanoparticles, quenching the fluorescence emission of the QDs. This nanosensor exhibits a limit of detection of 0.4 and 1.2 ppb toward Hg(II) in the buffer solution and in the river water, respectively. The sensor also shows high selectivity toward the Hg(II) ions.     

An effective three-dimensional surface-enhanced Raman scattering substrate based on oblique Si nanowire arrays decorated with Ag nanoparticles

Silicon nanowire arrays (SiNWAs) decorated with metallic nanoparticle heterostructures feature promising applications in surface-enhanced Raman scattering (SERS). However, the densely arranged SiNWAs are usually inconvenient for the following decoration of metallic nanoparticles, and only the top area of silicon nanowires (SiNWs) contributes to the SERS detection. To improve the utilization of the heterostructure, herein, oblique SiNWAs were grown separately, and Ag nanoparticles (AgNPs) were uniformly deposited by magnetron sputtering to get the three-dimensional (3D) SiNWAs decorated with AgNPs (AgNPs-SiNWAs) SERS substrate. The large open surfaces of oblique SiNWs would create more surface area available for the formation of hotspots and improve the adsorption and excitation of analyte molecules on the wire. The optimized AgNPs-SiNWAs substrate exhibits high sensitivity in detecting chemical molecule Rhodamine 6G, and the detection limit can reach 1 × 10^?10 M. More importantly, the substrate also can be used as an effective DNA sensor for label-free DNA detection.     

Tuning sensitivity and selectivity of complementary metal oxide semiconductor-based capacitive chemical microsensors

New details on selectivity and sensitivity of fully integrated CMOS-based capacitive chemical microsensor systems are revealed. These microsystems have been developed to detect volatile organics in ambient air and rely on polymeric sensitive layers. The sensitivity and selectivity changes induced by thickness variation of the sensitive polymer layer allow for tuning of the layer parameters to achieve desired sensor features. Cross-sensitivity to interfering agents can be drastically reduced, as is shown for two important cases: (a). rendering the capacitive sensor insensitive to a low-dielectric-constant analyte (lower than that of the polymer) and (b). reducing the influence of a high-dielectric-constant analyte, such as water, on the sensor response. The second case is of vital importance for capacitive sensors, since water is omnipresent and evokes large capacitive sensor signals. The thickness-induced selectivity is explained as a combination of dielectric constant change and swelling and has been confirmed by measurements. Experimentally determined sensitivities qualitatively and quantitatively coincide with the calculated values implying understanding of the sensing mechanism.     

Double-strand DNA-templated formation of copper nanoparticles as fluorescent probe for label-free aptamer sensor

Double-strand DNA (dsDNA) can act as an efficient template for the formation of copper nanoparticles (Cu NPs) at low concentration of CuSO(4), and the formed Cu NPs have excellent fluorescence, whereas a single-strand DNA (ssDNA) template does not support Cu NPs' formation. This property of dsDNA-Cu NPs makes it suitable for DNA sensing. However, exploration of dsDNA-Cu NPs applied in biological analysis is still at an early stage. In this regard, we report herein for the first time a sensitive, cost-effective, and simple aptamer sensor (aptasensor) using dsDNA-Cu NPs as fluorescent probe. The design consists of a dsDNA with reporter DNA (here, aptamer) as template for the formation of Cu NPs, and the formed dsDNA-Cu NPs show high fluorescence. Using adenosine triphosphate (ATP) as a model analyte, the introduction of ATP triggers the structure switching of reporter DNA to form aptamer-ATP complex, causing the destruction of the double helix and thus no formation of the Cu NPs, resulting in low fluorescence. The preferable linear range (0.05-500 μM), sensitivity (LOD 28 nM), and simplicity for the detection of ATP indicate that dsDNA-Cu NPs may have great prospects in the field of biological analysis. We also use this novel fluorescent probe to determine ATP in 1% human serum and human adenocarcinoma HeLa cells. The dsDNA-Cu NPs probes provide recovery of 104-108% in 1% human serum and a prominent fluorescent signal is obtained in cellular ATP assay, revealing the practicality of using dsDNA-Cu NPs for the determination of ATP in real samples. Besides, this design is simply based on nucleic acid hybridization, so it can be generally applied to other aptamers for label-free detection of a broad range of analytes. Successful detection of cocaine with detection limit of 0.1 μM demonstrates its potential to be a general method.     

Ligand exchange based paraoxon imprınted QCM sensor

In the present work, a paraoxon imprinted QCM sensor has been developed for the determination of paraoxon based on the modification of paraoxon imprinted film onto a quartz crystal combining the advantages of high selectivity of the piezoelectric microgravimetry using MIP film technique and high sensitivity of QCM detection. The paraoxon selective memories have formed on QCM electrode surface by using a new metal–chelate interaction based on pre-organized monomer and the paraoxon recognition activity of these molecular memories was investigated. Molecular imprinted polymer (MIP) film for the detection of paraoxon was developed and the analytical performance of paraoxon imprinted sensor was studied. The molecular imprinted polymer were characterized by FTIR measurements. Paraoxon imprinted sensor was characterized with AFM and ellipsometer. The study also includes the measurement of binding interaction of paraoxon imprinted quartz crystal microbalance (QCM) sensor, selectivity experiments and analytical performance of QCM electrode. The detection limit and the affinity constant (K_affinity) were found to be 0.06 μM and 2.25 × 10⁴ M^? 1 for paraoxon [MAAP–Cu(II)–paraoxon] based thin film, respectively. Also, it has been observed that the selectivity of the prepared paraoxon imprinted sensor is high compared to a similar chemical structure which is parathion.     

Selective determination of beryllium(II) ion at picomole per decimeter cubed levels by kinetic differentiation mode reversed-phase high-performance liquid chromatography with fluorometric detection using 2-(2'-hydroxyphenyl)-10-hydroxybenzo[H]quinoline as precolumn chelating reagent

A highly sensitive and selective method for the determination of the Be(II) ion has been developed by the use of reversed-phase high-performance liquid chromatography (HPLC) with fluorometric detection using 2-(2'-hydroxyphenyl)-10-hydroxybenzo[h]quinoline (HPHBQ) as a precolumn (off-line) chelating reagent. The reagent HPHBQ has been designed to form the kinetically inert Be chelate compatible with high fluorescence yield, which is appropriate to the HPLC-fluorometric detection system. The Be-HPHBQ chelate is efficiently separated on a LiChrospher 100 RP-18(e) column with a methanol (58.3 wt %)-water eluent containing 20 mmol kg(-1) of tartaric acid and is fluorometrically detected at 520 nm with the excitation at 420 nm. Under the conditions used, the concentration range of 20-8,000 pmol dm(-3) of Be(II) ion can be determined without interferences from 10 micromol dm(-3) each of common metal ions, typically Al(III), Cu(II), Fe(III), and Zn(II), and still more coexistence of Ca(II) and Mg(II) ions at 0.50 mmol dm(-3) and 5.0 mmol dm(-3), respectively, is tolerated. The detection limit (3a baseline fluctuation) is 4.3 pmol dm(-3) (39 fg cm(-3)). The extraordinarily high sensitivity with toughness toward the matrix influence was demonstrated with the successful application to environmental Be analyses, such as determination of Be in rainwater and tap water.