Disposable electrochemical immunosensor diagnosis device based on nanoparticle probe and immunochromatographic strip

We describe a disposable electrochemical immunosensor diagnosis device that integrates the immunochromatographic strip technique with an electrochemical immunoassay and exploits quantum dot (QD, CdS@ZnS) as labels for amplifying signal output. The device takes advantage of the speed and low cost of the conventional immunochromatographic strip test and the high sensitivity of the nanoparticle-based electrochemical immunoassay. A sandwich immunoreaction was performed on the immunochromatographic strip, and the captured QD labels in the test zone were determined by highly sensitive stripping voltammetric measurement of the dissolved metallic component (cadmium) with a disposable screen-printed electrode, which is embedded underneath the membrane on the test zone. The new device coupled with a portable electrochemical analyzer shows great promise for in-field and point-of-care quantitative testing of disease-related protein biomarkers. The parameters (e.g., voltammetric measurement of QD labels, antibody immobilization, the loading amount of QD-antibody, and the immunoreaction time) that govern the sensitivity and reproducibility of the device were optimized with IgG model analyte. The voltammetric response of the optimized device is highly linear over the range of 0.1-10 ng mL(-1) IgG, and the limit of detection is estimated to be 30 pg mL(-1) in association with a 7-min immunoreaction time. The detection limit was improved to 10 pg mL(-1) using a 20-min immunoreaction time. The device has been successfully applied for the detection of prostate-specific antigen (PSA) in human serum sample with a detection limit of 20 pg mL(-1). The results were validated by using the commercial PSA enzyme-linked immunosorbent assay kit and showed high consistency. The new disposable electrochemical diagnosis device thus provides a rapid, clinically accurate, and quantitative tool for protein biomarker detection.     

Electrochemical sensor for organophosphate pesticides and nerve agents using zirconia nanoparticles as selective sorbents

An electrochemical sensor for detection of organophosphate (OP) pesticides and nerve agents using zirconia (ZrO2) nanoparticles as selective sorbents is presented. Zirconia nanoparticles were electrodynamically deposited onto the polycrystalline gold electrode by cyclic voltammetry. Because of the strong affinity of zirconia for the phosphoric group, nitroaromatic OPs strongly bind to the ZrO2 nanoparticle surface. The electrochemical characterization and anodic stripping voltammetric performance of bound OPs were evaluated using cyclic voltammetric and square-wave voltammetric (SWV) analysis. SWV was used to monitor the amount of bound OPs and provide simple, fast, and facile quantitative methods for nitroaromatic OP compounds. The sensor surface can be regenerated by successively running SWV scanning. Operational parameters, including the amount of nanoparticles, adsorption time, and pH of the reaction medium have been optimized. The stripping voltammetric response is highly linear over the 5-100 ng/mL (ppb) methyl parathion range examined (2-min adsorption), with a detection limit of 3 ng/mL and good precision (RSD = 5.3%, n = 10). The detection limit was improved to 1 ng/mL by using 10-min adsorption time. The promising stripping voltammetric performances open new opportunities for fast, simple, and sensitive analysis of OPs in environmental and biological samples. These findings can lead to a widespread use of electrochemical sensors to detect OP contaminates.     

Preconcentration and Voltammetric Determination of Mercury(II) at a Chemically Modified Glassy Carbon Electrode

In this work, the organic compound 2-mercaptobenzimidazole was covalently bound on the surface of a glassy carbon rod, via silanization, yielding a material capable of selectively complexing Hg(2+) ions. This material was applied as an electrode for voltammetric determination of mercury(II) following its nonelectrolytic preconcentration. After exchanging the medium, the voltammetric measurements were carried out by anodic stripping in the differential pulse mode (pulse amplitude, 50 mV; scan rate, 1.25 mV s(-)(1)) using 10(-)(2) mol L(-)(1) NaSCN solution as supporting electrolyte. An anodic stripping peak was obtained at 0.06 V (vs SCE) by scanning the potential from -0.3 to +0.3 V. After a 5 min preconcentration period in a pH 4.0 Hg(2+) solution, this electrode shows increasing voltammetric response in the range 0.1-2.2 μg mL(-)(1), with a relative standard deviation of 5% and a practical detection limit of 0.1 μg mL(-)(1) (5.0 × 10(-)(7) mol dm(-)(3)). Compared with the conventional stripping approach, this chemically modified glassy carbon electrode procedure presented good discrimination against interference from Cu(II) in up to 10-fold molar excess.     

Adsorptive stripping voltammetry of hen-egg-white-lysozyme via adsorption-desorption at an array of liquid-liquid microinterfaces

Electrochemical adsorption and voltammetry of hen-egg-white-lysozyme (HEWL) was studied at an array of microinterfaces between two immiscible electrolyte solutions (μITIES). Adsorption of the protein was achieved at an optimal applied potential of 0.95 V, after which it was desorbed by a voltammetric scan to lower potentials. The voltammetric peak recorded during the desorption scan was dependent on the adsorption time and on the aqueous phase concentration of HEWL. The slow approach to saturation or equilibrium indicated that protein reorganization at the interface was the rate-determining step and not diffusion to the interface. For higher concentrations and longer adsorption times, a HEWL multilayer surface coverage of 550 pmol cm(-2) was formed, on the basis of the assumption that a single monolayer corresponded to a surface coverage of 13 pmol cm(-2). Implementation of adsorption followed by voltammetric detection as an adsorptive stripping voltammetric approach to HEWL detection demonstrated a linear dynamic range of 0.05-1 μM and a limit of detection of 0.03 μM, for 5 min preconcentration in unstirred solution; this is a more than 10-fold improvement over previous HEWL detection methods at the ITIES. These results provide the basis for a new analytical approach for label-free protein detection based on adsorptive stripping voltammetry.     

Electronic transport through ruthenium-based redox-active molecules in metal-molecule-metal nanogap junctions

Electronic transport through ruthenium-based redox-active organometallic molecules is measured by self-assembling diruthenium(III) tetra(2-anilinopyridinate)-di(4-thiolphenylethynyl) (trans-Ru2(ap)4(C'CC6H4S-)2 (A) and trans- Ru2(ap)4((C'CC6H4)2S-)2 (B) molecules in nanogap molecular junctions. Voltage sweeps at a high scan rate show low bias current peaks (at +/-0.35 +/- 0.05 V for A and +/-0.27 +/- 0.05 V for B), which change to plateaus in slow bias scans and a second conductance peak at approximately +/-1.05 +/- 0.15 V. The peaks/plateaus are not observed in the return bias sweeps, possibly due to charge storage in the molecules. The energy states for the molecular orbitals of these molecules as estimated from the conductance peaks are in close agreement with the respective energy values from voltammetric measurements in solution.     

Cathodic Stripping Voltammetry of Selenium(IV) at a Silver Disk Electrode

A new, simple, and reproducible method is described for the determination of selenium(IV) based on differential pulse cathodic stripping voltammetry. The optimized experimental conditions are as follows: selenium(IV) ions in an acidic medium (0.06 M HCl-0.07 M HNO(3)) are electrodeposited on a rotating silver disk electrode as silver selenide at -0.4 V vs SCE for 30 min; the deposit is then cathodically stripped in another solution (2 M NaOH) at a scan rate of 50 mV s(-1) to -1.2 V vs SCE. The cathodic stripping results in only a single well-defined peak at about -0.95 V vs SCE. The calibration (peak height vs selenium concentration) graph is linear up to at least 40 ng mL(-1) of selenium(IV) and passes through the origin, with a relative standard deviation of 2.7% for 20 ng mL(-1) (n = 5). The detection limit (3σ) is 0.20 ng mL(-1). The possible interferences have been evaluated. Dissolved oxygen does not affect the peak height of selenium. The electrode can be used repeatedly at least 20 times with excellent reproducibility without further polishing. The proposed method is an improvement over the existing cathodic stripping techniques.     

Bismuth-coated carbon electrodes for anodic stripping voltammetry

Bismuth-coated carbon electrodes display an attractive stripping voltammetric performance which compares favorably with that of common mercury-film electrodes. These bismuth-film electrodes are prepared by adding 400 microg/L (ppb) bismuth(III) directly to the sample solution and simultanously depositing the bismuth and target metals on the glassy-carbon or carbon-fiber substrate. Stripping voltammetric measurements of microgram per liter levels of cadmium, lead, thallium, and zinc in nondeaerated solutions yielded well-defined peaks, along with a low background, following short deposition periods. Detection limit of 1.1 and 0.3 ppb lead are obtained following 2- and 10-min deposition, respectively. Changes in the peak potentials (compared to those observed at mercury electrodes) offer new selectivity dimensions. Scanning electron microscopy sheds useful insights into the different morphologies of the bismuth deposits on the carbon substrates. The in situ bismuth-plated electrodes exhibit a wide accessible potential window (-1.2 to -0.2 V) that permits quantitation of most metals measured at mercury electrodes (except of copper, antimony, and bismuth itself). Numerous key experimental variables have been characterized and optimized. High reproducibility was indicated from the relative standard deviations (2.4 and 4.4%) for 22 repetitive measurements of 80 microg/L cadmium and lead, respectively. Such an attractive use of "mercury-free", environmetally friendly electrodes (with a performance equivalent to that of mercury ones) offers great promise to centralized and decentralized testing of trace metals.     

Dynamics and performance of fast linear scan anodic stripping voltammetry of cd, pb, and cu using in situ-generated ultrathin mercury films

The dynamics of fast linear scan (LS) ASV for the simultaneous detection of Cd, Pb, and Cu was investigated at various scan rates (0.5-10 V/s) and at different metal ion concentrations (50-800 nM) utilizing ultrathin mercury films (9 nm) at a conventional size (d(0) = 1 mm) electrode. Results of the investigation show that when the thin films were utilized, diffusion of metals through the mercury film was not the rate-limiting step of the stripping process at moderate to fast scan rates (0.5-10 V/s). A fairly linear relationship between the peak height and scan rate was observed at scan rates (0.5-10 V/s) beyond the upper limit of the theoretical model for the behavior of LS-ASV. In addition, peak width at half-height (b(1/2)) as low as 33 mV was achieved at 0.5 V/s. The behavior of LS-ASV in terms of peak width at these scan rates is thus different from what the theoretical model of LS-ASV would have predicted. For the ultrathin mercury films, at least two additional factors, kinetics and concentration, have significant effects on practical LS-ASV. Experimental results show that the stripping process of Cu was primarily kinetic-controlled for fast scans, while those for Cd and Pb were dependent on both scan rates and concentrations. The ultrathin mercury film resulted in a significant enhancement of the ratio of signal-to-baseline slope (i(p)/Δi(b), a ratio used to measure the effectiveness of discrimination of the peak signal against the steep sloping baseline in LS-ASV) for Cd and Pb stripping peaks, but only a slight enhancement for Cu stripping peaks. The optimal performance of LS-ASV in terms of sensitivity, peak width, and enhancement of the i(p)/Δi(b) ratio for the three metals was achieved at 2 V/s. Because of the high reproducibility of the background currents of the stable in situ MTFs, background subtraction was carried out at 2 V/s with little hysteresis. This feature, combined with the enhancement of the i(p)/Δi(b) ratio at the fast scan rate of 2 V/s, allowed for the detection of sub-ppb levels of Cd, Pb, and Cu at a deposition time of 2 min.     

A novel photoelectrochemical sensor for the organophosphorus pesticide dichlofenthion based on nanometer-sized titania coupled with a screen-printed electrode

A novel photoelectrochemical sensor for detection of the organophosphorus pesticide (OP) dichlofenthion using nanometer-sized titania coupled with a screen-printed electrode is presented. Nonelectroactive dichlofenthion can be indirectly determined through the photocatalytical degradation of dichlofenthion with nanometer-sized titania. The electrochemical characterization and anodic stripping voltammetric performance of dichlofenthion were evaluated using cyclic voltammetric (CV) and differential pulse anode stripping voltammetric (DPASV) analysis, respectively. DPASV analysis was used to monitor the amount of dichlofenthion and provide a simple, fast, and facile quantitative method for dichlofenthion. Operational parameters, including the photocatalysis time, pH of buffer solution, deposition potential, and accumulation time have been optimized. The stripping voltammetric response is linear over the 0.02-0.1 and 0.2-1.0 μmol/L ranges with a detection limit of 2.0 nmol/L. The assay result of dichlofenthion in green vegetable with the proposed method was in acceptable agreement with that of the gas chromatograph-mass spectrometer (GC-MS) method. The promising sensor opens a new opportunity for fast, portable, and sensitive analysis of OPs in environmental samples.     

铜表面电化学制备黑陶质感转化膜的研究

对铜在无硒电化学发黑液中的行为进行了研究.首先通过试验选择NaOH-H3BO3作为缓冲溶液体系,研究了铜在含0.1 mol/L Na2S的缓冲溶液中的循环伏安行为.根据循环伏安曲线上氧化峰的位置,确定铜电化学发黑的适宜电势.然后在不同电势下通过恒电势氧化或循环氧化-还原等方法制备了发黑膜.采用目视和电化学阻抗谱测量等方法,对发黑膜的色度、均一性、致密性和腐蚀防护性能进行了比较.结果表明,循环氧化-还原不能形成性能优良的发黑膜.在-0.8 V和-0.6 V (vs SCE)下形成的发黑膜颜色不均匀,色泽不佳,而在-0.05 V(vs SCE)条件下进行恒电势氧化则可在铜金属表面形成均匀致密、具有黑陶质感的发黑膜.     

Direct construction of an open-sandwich enzyme immunoassay for one-step noncompetitive detection of thyroid hormone T4

To establish a sensitive noncompetitive immunoassay for thyroxine (T4), we attempted to isolate anti-T4 antibodies from a phage display library based on a phagemid pDong1 ( Dong et al. Anal. Biochem.2009, 36, 386 ), which was designed to enable open-sandwich enzyme-linked immunosorbent assay (OS-ELISA) after selection on immobilized antigen. After the Fab-displaying phage library made from the splenocytes of T4-KLH immunized mice was subjected to biopanning on T4-BSA, two T4-specific clones were obtained. When they were assayed by indirect competitive ELISA, both clones showed low IC(50) (5-13 ng/mL), indicating their high affinity to T4. When they were used for OS-ELISA that detects antigen-dependency of the interaction between variable domains V(H) and V(L), a clone successfully detected 1 ng/mL of T4 with a working range superior to that of competitive IA. OS-ELISA was also performed with maltose binding protein (MBP)-fused V(H)/V(L) of this clone, which showed a detection limit less than 0.1 ng/mL T4. Moreover, the assay showed cross-reactivity with T3 similar to that of competitive ELISA, and also gave a reasonable total serum T4 concentration (90 ng/mL) from ethanol-extracted sample serum using the recombinant proteins. This is the first direct construction of an OS-ELISA system bypassing hybridoma, which will be applicable to the detection of many other small molecule antigens.     

Triple signal amplification of graphene film, polybead carried gold nanoparticles as tracing tag and silver deposition for ultrasensitive electrochemical immunosensing

A triple signal amplification strategy was designed for ultrasensitive immunosensing of cancer biomarker. This strategy was achieved using graphene to modify immunosensor surface for accelerating electron transfer, poly(styrene-co-acrylic acid) microbead (PSA) carried gold nanoparticles (AuNPs) as tracing tag to label signal antibody (Ab(2)) and AuNPs induced silver deposition for anodic stripping analysis. The immunosensor was constructed by covalently immobilizing capture antibody on chitosan/electrochemically reduced graphene oxide film modified glass carbon electrode. The in situ synthesis of AuNPs led to the loading of numerous AuNPs on PSA surface and convenient labeling of the tag to Ab(2). With a sandwich-type immunoreaction, the AuNPs/PSA labeled Ab(2) was captured on the surface of an immunosensor to further induce a silver deposition process. The electrochemical stripping signal of the deposited silver nanoparticles in KCl was used to monitor the immunoreaction. The triple signal amplification greatly enhanced the sensitivity for biomarker detection. The proposed method could detect carcinoembryonic antigen with a linear range of 0.5 pg mL(-1) to 0.5 ng mL(-1) and a detection limit down to 0.12 pg mL(-1). The immunosensor exhibited good stability and acceptable reproducibility and accuracy, indicating potential applications in clinical diagnostics.     

Versatile immunosensor using CdTe quantum dots as electrochemical and fluorescent labels

A versatile immunosensor using CdTe quantum dots as electrochemical and fluorescent labels has been developed for sensitive protein detection. This sandwich-type sensor is fabricated on an indium tin oxide chip covered with a well-ordered gold nanoparticle monolayer. Gel imaging systems were successfully introduced to develop a novel high-efficient optical immunoassay, which could perform simultaneous detection for the samples with a series of different concentrations of a target analyte. The linear range of this assay was between 0.1 and 500 ng/mL, and the assay sensitivity could be further increased to 0.005 ng/mL with the linear range from 0.005 to 100 ng/mL by stripping voltammetric analysis. The immunosensor showed good precision, high sensitivity, acceptable stability, and reproducibility and could be used for the detection of real sample with consistent results in comparison with those obtained by the ELISA method.     

Polymer-functionalized silica nanosphere labels for ultrasensitive detection of tumor necrosis factor-alpha

A signal amplification strategy for sensitive detection of tumor necrosis factor-alpha (TNF-α) using quantum dots (QDs)-polymer-functionalized silica nanosphere as the label was proposed. In this approach, silica nanospheres with good monodispersity and uniform structure were employed as carriers for surface-initiated atom transfer radical polymerization of glycidyl methacrylate, which is readily available functional monomer that possessing easily transformable epoxy groups for subsequent CdTe QDs binding through ring-open reaction. Then, human anti rabbit TNF-α antibody (anti-TNF-α, Ab2, served as a model protein) was bonded to CdTe QDs-modified silica nanospheres coated with polymer to obtain QDs-polymer-functionalized silica nanosphere labels (Si/PGMA/QD/Ab2). The Si/PGMA/QD/Ab2 labels were attached onto a gold electrode surface through a subsequent "sandwich" immunoreaction. This reaction was confirmed by scanning electron microscopy (SEM) and fluorescence microscopic images. Enhanced sensitivity could be achieved by an increase of CdTe QD loading per immunoassay event, because of a large number of surface functional epoxy groups offered by the PGMA. As a result, the electrochemiluminescence (ECL) and square-wave voltammetry (SWV) measurements showed 10.0- and 5.5-fold increases in detection signals, respectively, in comparison with the unamplified method. The detection limits of 7.0 pg mL(-1) and 3.0 pg mL(-1) for TNF-α antibodies by ECL and SWV measurements, respectively, were achieved. The proposed strategy successfully demonstrated a simple, reproducible, specific, and potent method that can be expanded to detect other proteins and DNA.     

Zeptomole voltammetric detection and electron-transfer rate measurements using platinum electrodes of nanometer dimensions

The characterization of quasi-hemispherical Pt electrodes of nanometer dimensions (radius 2-150 nm), prepared by electrophoretic coating of etched Pt wires with poly-(acrylic acid), is described. The goals of these experiments are to estimate the accuracy of using steady-state voltammetric limiting currents (i(lim)) in determining the true electrode area and to develop new electrochemical methods for rapidly screening individual electrodes for non-ideal geometries. Electrochemical active areas were determined by measuring the electrical charge (Q) associated with oxidation of adsorbed bis(2,2'-bipyridine)chloro(4,4'-trimethylenedipyridine)osmium(II) in fast-scan voltammetric measurements (scan rate 1000 V/s). Voltammetric peaks corresponding to oxidation of as few as approximately 7000 molecules (approximately 11 zmol) at individual electrodes are reported, allowing precise measurement of electrode areas as small as approximately 10(-10) cm2. A plot of i(lim) (for a soluble redox species) versus Q1/2 (for an adsorbed redox species), constructed from i(lim)-Q1/2 data pairs obtained as a function of the electrode radius, is shown to be linear if the electrode geometry is independent of electrode radius; departure of experimental values from the straight-line plot is a diagnostic indicator of a nonideal electrode geometry. The results indicate that approximately 50% of the electrodes prepared by the electrophoretic polymer-coating procedure are quasi-hemispherical, the remaining being recessed slightly below the polymer coating. The heterogeneous electron-transfer rate constant for the oxidation of the ferrocenylmethyltrimethylammonium cation in H2O/ 0.2 M KCl was also determined from steady-state voltammetry using the method of Mirkin and Bard and found to be 4.(8) +/- 3.(2) cm/s with alpha = 0.6(4) +/- 0.1(5).     

Imaging of metal ion dissolution and electrodeposition by anodic stripping voltammetry-scanning electrochemical microscopy

We have developed a new imaging method for scanning electrochemical microscopy (SECM) employing fast-scan anodic stripping voltammetry (ASV) to provide sensitive and selective imaging of multiple chemical species at interfaces immersed in solution. A rapid cyclic voltammetry scan (100 V/s) is used along with a short preconcentration time (300-750 ms) to allow images to be acquired in a normal SECM time frame. A Hg-Pt film electrode is developed having an equivalent Hg thickness of 40 nm that has good sensitivity at short preconcentration times and also retains thin-film behavior with high-speed voltammetric stripping. Fast-scan anodic stripping currents are shown to be linear for 1-100 microM of Pb (2+) and Cd (2+) solutions using a preconcentration time of 300 ms. SECM images showing the presence of Pb (2+) and Cd (2+) at concentrations as low as 1 microM are presented. In addition, a single ASV-SECM image is shown to produce unique concentration maps indicating Cd (2+) and Pb (2+), generated in situ from a corroding sample, while simultaneously detecting the depletion of O 2 at this sample. The transient voltammetric response at the film electrode is simulated and shows good agreement with the experimental behavior. We discuss the behavior of images and concentration profiles obtained with different imaging conditions and show that mass-transport limitations in the tip-substrate gap can induce dissolution. ASV-SECM can thus be used to detect and study induced dissolution not only at bulk metal surfaces but also on underpotential deposition layers, in this case Cd and Pb on Pt. In addition, we discuss how surface diffusion phenomena may relate to the observed ASV-SECM behavior.     

Development of a method for total inorganic arsenic analysis using anodic stripping voltammetry and a Au-coated, diamond thin-film electrode

We demonstrate that a Au-coated, boron-doped, diamond thin-film electrode provides a sensitive, reproducible, and stable response for total inorganic arsenic (As(III) and As(V)) using differential pulse anodic stripping voltammetry (DPASV). As is preconcentrated with Au on the diamond surface during the deposition step and detected oxidatively during the stripping step. Au deposition was uniform over the electrode surface with a nominal particle size of 23 +/- 5 nm and a particle density of 109 cm-2. The electrode and method were used to measure the As(III) concentration in standard and river water samples. The detection figures of merit were compared with those obtained using conventional Au-coated glassy carbon and Au foil electrodes. The method was also used to determine the As(V) concentration in standard solutions after first being chemically reduced to As(III) with Na2SO3, followed by the normal DPASV determination of As(III). Sharp and symmetric stripping peaks were generally observed for the Au-coated diamond electrode. LODs were 0.005 ppb (S/N = 3) for As(III) and 0.08 ppb (S/N = 3) for As(V) in standard solutions. An As(III) concentration of 0.6 ppb was found in local river water. The relative standard deviation of the As stripping peak current for river water was 1.5% for 10 consecutive measurements and was less than 9.1% over a 10-h period. Excellent electrode response stability was observed even in the presence of up to 5 ppm of added humic acid. In summary, the Au-coated diamond electrode exhibited better performance for total inorganic As analysis than did Au-coated glassy carbon or Au foil electrodes. Clearly, the substrate on which the Au is supported influences the detection figures of merit.     

NIR‐Emitting Quantum Dot‐Encoded Microbeads through Membrane Emulsification for Multiplexed Immunoassays

NIR‐emitting CdSeTe/CdS/ZnS core/shell/shell QD‐encoded microbeads are combined with common flow cytometry with one laser for multiplexed detection of hepatitis B virus (HBV). A facile one‐pot synthetic route is developed to prepare CdSeTe/CdS/ZnS core/shell/shell QDs with high photoluminescence quantum yield and excellent stability in liquid paraffin, and a Shirasu porous glass (SPG) membrane emulsification technique is applied to incorporate the QDs into polystyrene–maleic anhydride (PSMA) microbeads to obtain highly fluorescent QD‐encoded microbeads. The relatively wide NIR photoluminescence full width half maximum of the CdSeTe/CdS/ZnS QDs is used to develop a ‘single wavelength’ encoding method to obtain different optical codes by changing the wavelengh and emission intensity of the QDs incorporated into the microbeads. Moreover, a detection platform combining NIR‐emitting CdSeTe/CdS/ZnS QD‐encoded microbeads and Beckman Coulter FC 500 flow cytometry with one laser of 488 nm is successfully used to conduct a 2‐plex hybridization assay for hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), and a 3‐plex hybridization assay for hepatitis B surface antibody (HBsAb), hepatitis B e antibody (HBeAb), and hepatitis B core antibody (HBcAb), which suggests the promising application of NIR QD‐encoded microbeads for multiplex immunoassays.     

Quantum dot-aptamer conjugates for synchronous cancer imaging, therapy, and sensing of drug delivery based on bi-fluorescence resonance energy transfer

We report a novel quantum dot (QD)-aptamer(Apt)-doxorubicin (Dox) conjugate [QD-Apt(Dox)] as a targeted cancer imaging, therapy, and sensing system. By functionalizing the surface of fluorescent QD with the A10 RNA aptamer, which recognizes the extracellular domain of the prostate specific membrane antigen (PSMA), we developed a targeted QD imaging system (QD-Apt) that is capable of differential uptake and imaging of prostate cancer cells that express the PSMA protein. The intercalation of Dox, a widely used antineoplastic anthracycline drug with fluorescent properties, in the double-stranded stem of the A10 aptamer results in a targeted QD-Apt(Dox) conjugate with reversible self-quenching properties based on a Bi-FRET mechanism. A donor-acceptor model fluorescence resonance energy transfer (FRET) between QD and Dox and a donor-quencher model FRET between Dox and aptamer result when Dox intercalated within the A10 aptamer. This simple multifunctional nanoparticle system can deliver Dox to the targeted prostate cancer cells and sense the delivery of Dox by activating the fluorescence of QD, which concurrently images the cancer cells. We demonstrate the specificity and sensitivity of this nanoparticle conjugate as a cancer imaging, therapy and sensing system in vitro.     

Gold nanoelectrode ensembles for the simultaneous electrochemical detection of ultratrace arsenic, mercury, and copper

Simultaneous electrochemical detection of As(III), Hg(II), and Cu(II) using a highly sensitive platform based on gold nanoelectrode ensembles (GNEEs) is described. GNEEs were grown by colloidal chemical approach on thiol-functionalized solgel derived three-dimensional silicate network preassembled on a polycrystalline gold (Au) electrode. GNEEs on the silicate network have been characterized by field emission scanning electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, and electrochemical measurements. Square wave anodic stripping voltammetry (SWASV) has been used for the detection of As(III) and Hg(II) without any interference from Cu(II) at the potentials of 0.06 and 0.53 V, respectively. The GNEE electrode is highly sensitive, and it shows linear response for As(III) and Hg(II) up to 15 ppb. The detection limit (signal-to-noise ratio = 4) of the GNEE electrode toward As(III) and Hg(II) is 0.02 ppb, which is well below the guideline value given by the World Health Organization (WHO). The potential application of the GNEE electrode for the detection of As(III) in a real sample collected from the arsenic-contaminated water in 24 North Parganas, West Bengal is demonstrated. The GNEE electrode has been successfully used for the simultaneous detection of As(III), Cu(II), and Hg(II) at sub-part-per-billion level without any interference for the first time. The nanostructured electrode shows individual voltammetric peaks for As(III), Cu(II), and Hg(II) at 0.06, 0.35, and 0.53 V, respectively. The analytical performance of the GNEE electrode is superior to the existing electrodes.