Application of cadmium sulfide nanoparticles as oligonucleotide labels for the electrochemical detection of NOS terminator gene sequences

A mercaptoacetic acid (MAA)-modified cadmium sulfide (CdS) nanoparticle was synthesized in aqueous solution and used as an oligonucleotide label for the electrochemical detection of nopaline synthase (NOS) terminator gene sequence. The carboxyl groups on the surface of the CdS nanoparticle can be easily covalently linked with NH₂-modified NOS oligonucleotide probe sequences. The target ssDNA sequence was fixed onto the electrode surface by covalently linking to a mercaptoethanol self-assembled gold electrode, and the DNA hybridization of target ssDNA with probe ssDNA was accomplished on the electrode surface. The CdS nanoparticles anchored on the hybrids were dissolved in the solution by the oxidation with HNO₃ and further detected by a sensitive differential pulse anodic stripping voltammetric method. The detection results can be used for monitoring the hybridization, and the NOS target sequence was satisfactorily detected in the approximate range from 8.0 × 10⁻¹² to 4.0 × 10⁻⁹ mol L⁻¹ with a detection limit of 2.75 × 10⁻¹² mol L⁻¹ (3σ). The established method extended the nanoparticle-labeled electrochemical DNA analysis to genetically modified organisms (GMOs) specific sequence samples with higher sensitivity and selectivity.     

Quartz Crystal Microbalance for Selenite Sensing Based on Growth of Cadmium Selenite Crystals Immobilized on a Monolayer of Phosphorylated 11-Mercapto-1-Undecanol

 A quartz crystal microbalance (QCM) sensor for selenite ions in aqueous solution was constructed based on crystal formation of cadmium selenite, immobilized with a self-assembly monolayer (SAM) of phosphorylated 11-mercapto-1-undecanol (MUD) on a QCM gold electrode surface. The mass change caused by the selective adsorption of selenite ions on the cadmium selenite crystals at the solid/solution interface was detected by the QCM. The response (−ΔF) of the modified QCM oscillator increased with increasing selenite ion concentrations in sample solutions, ranging from 9.7×10⁻⁵ to 9.0×10⁻⁴ M at pH 7.4. The synthetic process of anchoring cadmium selenite crystals on the phosphorylated MUD organic film was also followed by using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The atomic concentrations measured by XPS confirmed the crystal growth of cadmium selenite on the phosphorylated MUD SAM at the QCM gold electrode surface. From the AFM images, changes in surface topographic features were followed: the MUD SAM and phosphorylated MUD on the QCM gold electrode had similar surface roughness; however the difference for the cadmium selenite film on the phosphorylated MUD SAM was clearly seen. The observed QCM frequency change of the modified QCM oscillator per unit time was found to be proportional to the square of the supersaturation of cadmium selenite, indicating the crystal growth of cadmium selenite at the solid/solution interface. The modified QCM oscillator exhibited selectively strong QCM response to SeO₃ ²⁻ ion. In contrast, the responses to tested interfering anions were almost negligible. The order of anion selectivities of the present modified QCM sensor was SeO₃ ²⁻≫CO₃ ²⁻>SeO²⁻ ₄, SO₄ ²⁻, Br⁻, I⁻, NO₃ ⁻. These selectivities were basically attributable to the differences in solubility products and solubilities for the salts of each anion with cadmium (II) ion. Received May 12, 1998. Revision December 29, 1998.     

Preparation and electrorheological characteristic of CdS/Polystyrene composite particles

Cadmium sulfide/polystyrene (CdS/PS) hybrid particles were synthesized and their physical characteristics including electrorheology were examined. Monodisperse CdS/PS nanocomposite particles with diameters of 2 μm were obtained via dispersion polymerization. To form cadmium sulfide nanoparticles onto the PS surface, 2-(dimethylamino)ethyl methacrylate was used as a functional monomer for coordinating with Cd²⁺ ions. Finally, cadmium sulfide nanoparticles with size < 10 nm were formed with the release of S²⁻ ions from thioacetamide. The morphology of the as-prepared CdS/PS nanocomposite particles clearly showed that the CdS particles are present on the surface of the PS. The optical properties were also studied. In addition, their electrorheological characteristics were confirmed by using optical microscopy with applied electrical field. Recently, dielectric properties of CdS nanoparticles were already reported; however, electrorheological characteristics of CdS/PS nanocomposite particles were investigated for the first time.     

CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe<Superscript>−</Superscript> ions in aqueous solution

Water-soluble cadmium sulfide (CdS) quantum dots (QDs) capped by mercaptoacetic acid were synthesized by aqueous-phase arrested precipitation, and characterized by transmission electron microscopy, spectrofluorometry, and UV-Vis spectrophotometry. The prepared luminescent water-soluble CdS QDs were evaluated as fluorescence probes for the detection of highly reactive hydrogen selenide ions (HSe⁻ ions). The quenching of the fluorescence emission of CdS QDs with the addition of HSe⁻ ions is due to the elimination of the S²⁻ vacancies which are luminescence centers. Quantitative analysis based on chemical interaction between HSe⁻ ions and the surface of CdS QDs is very simple, easy to develop, and has demonstrated very high sensitivity and selectivity features. The effect of foreign ions (common anions and biologically relevant cations) on the fluorescence of the CdS QDs was examined to evaluate the selectivity. Only Cu²⁺ and S²⁻ ions exhibit significant effects on the fluorescence of CdS QDs. With the developed method, we are able to determine the concentration of HSe⁻ ions in the range from 0.10 to 4.80 μmol L⁻¹, and the limit of detection is 0.087 μmol L⁻¹. The proposed method was successfully applied to monitor the obtained HSe⁻ ions from the reaction of glutathione with selenite. To the best of our knowledge, this is the first report on fluorescence analysis of HSe⁻ ions in aqueous solution. Figure CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe- ions in aqueous solution     

Preparation of a novel composite particles and its application in the fluorescent detection of proteins

A new fluorescence method for the detection of proteins with novel composite nanoparticles (CdS/PPA) has been developed. The composite nanoparticles have been prepared through an in-situ polymerization method under ultrasonic irradiation. The surface of the composite nanoparticles was covered with functional groups (-COOH). These groups may play a major role in the improving the water solubility and biocompatibility of the nanoparticles. The composite particles is combined with proteins in NaAc-HCl buffer solution (pH=1.99), which can result in strong fluorescence, and the response is linearly proportional to the concentration of proteins. In λem/λex=650 nm/365 nm place (the stoke’ shift is 285 nm), its fluorescent strength reaches the maximum. Under the optimum conditions, the linear range is 0.10–20.0 μg·ml⁻¹ with the detection limit of 41 ng·ml⁻¹ for HSA, and 0.10–15.0 μg·ml⁻¹ with the detection limit of 35 ng·ml⁻¹ for Human γ-IgG . The method has been applied to the determination of the total protein in human serum samples collected from the hospital and the results are satisfactory.     

Characterization of gold nanoparticles electrochemically deposited on amine-functioned mesoporous silica films and electrocatalytic oxidation of glucose

This study reports the preparation and characterization of gold nanoparticles deposited on amine-functioned hexagonal mesoporous silica (NH₂–HSM) films and the electrocatalytic oxidation of glucose. Gold nanoparticles are fabricated by electrochemically reducing chloroauric acid on the surface of NH₂–HSM film, using potential step technology. The gold nanoparticles deposited have an average diameter of 80 nm and show high electroactivity. Prussian blue film can form easily on them while cycling the potential between −0.2 and 0.6 V (vs saturated calomel electrode) in single ferricyanide solution. The gold nanoparticles loading NH₂–HSM-film-coated glassy carbon electrode (Au–NH₂–HSM/GCE) shows strong catalysis to the oxidation of glucose, and according to the cathodic oxidation peak at about 0.16 V, the catalytic current is about 2.5 μA mM⁻¹. Under optimized conditions, the peak current of the cathodic oxidation peak is linear to the concentration of glucose in the range of 0.2 to 70 mM. The detection limit is estimated to be 0.1 mM. In addition, some electrochemical parameters about glucose oxidation are estimated.     

Deposition of Prussian blue on nanoporous gold film electrode and its electrocatalytic reduction of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

Prussian blue-modified nanoporous gold film (PB-NPGF) electrode was fabricated in this study. The fabrication was realized through electrodeposition of Prussian blue nanoparticles on the skeleton of a nanoporous gold film electrode without destroying the porous structure of NPGF electrode. The resulting PB-NPGF composite electrode showed very high electrocatalytic activity, repeatability, and stability to the reduction of H₂O₂. For instance, its activity was about twenty times that of the PB-modified polished gold electrode. More importantly, the sensitivity of the PB-NPGF composite electrode reaches as high as 10.6 μA μM⁻¹ cm⁻². This PB-NPGF composite electrode is very promising in the fields of catalysis, analysis, and so on.     

The amperometric determination of indole-3-acetic acid based on CeCl<Subscript>3</Subscript>-DHP film modified gold electrode

An amperometric sensor for the determination of indole-3-acetic acid (IAA) based on the CeCl₃-DHP film modified gold electrode was developed. CeCl₃ was dissolved into water in the presence of dihexadecyl hydrogen phosphate (DHP). The IAA sensor was prepared via evaporating solvent of the CeCl₃-DHP dispersion on the gold electrode surface. The amperometric response of IAA on the CeCl₃-DHP film modified gold electrode was investigated. The experimental results indicate that the passivation of the electrode due to the adsorption of the oxidation product of IAA decreases significantly at the CeCl₃-DHP film modified gold electrode, in contrast to that at the bare and the DHP modified gold electrode. The experimental parameters were optimized and an electrochemical method for the determination of IAA was established. The oxidation peak current is linearly with the concentration of IAA from 1 × 10⁻⁷ to 2 × 10⁻⁵ mol l⁻¹ and the detection limit is 3 × 10⁻⁸ mol l⁻¹. The relative standard deviation of eight measurements is 3.2% for 5 × 10⁻⁷ mol l⁻¹ IAA. The IAA in plant leaves were extracted and determined by the IAA sensor.     

Photochemical synthesis of cadmium sulfide nanoparticles

The formation of cadmium sulfide nanoparticles upon UV irradiation of aqueous solutions of cadmium thiosulfates was established on the basis of spectroscopic and macroscopic data. The yield and size of the cadmium sulfide nanoparticles depend on the ratio of cadmium to thiosulfate ions in solution, the concentration of the solution, and the irradiation duration. The cadmium sulfide nanoparticles with a diameter of 4 nm were obtained by the photolysis of solutions with a concentration of 10⁻³ mol L⁻¹ at the ratio S₂O₃ ²⁻: Cd²⁺ = 2: 1.     

New adsorptive square wave method for trace determination of prilocain in the flow injection system by a fast fourier analysis

The determination of prilocain, used to manage tonic-clonic seizures, has been carried out at micro gold electrode (Au UME) using continuous fast Fourier transform square wave voltammetry. The Au UME electrode exhibited an effective response towards prilocaine adsorption. The peak current was also found to be significantly increased. The determination was carried out in phosphate containing electrolyte in the pH of 2.0 and a well-defined change on the peak current were noticed. The peak current was found to be linearly dependent on concentration of prilocain in the concentration range 5.0 × 10⁻⁷–1.0 × 10⁻¹¹ M with a detection limit of 5.0 × 10⁻¹² M. This paper describes development of a new analysis system to determine of prilocain by a novel square wave voltammetry method to perform a very sensitive method. The method used for determination of prilocain by measuring the changes in admittance voltammogram of a gold ultramicroelectrode (in 0.05 M H₃PO₄ solution) caused by adsorption of the prilocain on the electrode surface. Variation of admittance in the detection process is created by inhibition of oxidation reaction of the electrode surface, by adsorbed of prilocain. Furthermore, signal-to-noise ratio has significantly increased by application of discrete Fast Fourier Transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. Also in this work some parameters such as SW frequency, eluent pH, and accumulation time were optimized. The relative standard deviation at concentration 5.0 × 10⁻⁸ M is 5.8% for 5 reported measurements.     

Immobilization of flavine adenine dinucleotide onto nickel oxide nanostructures modified glassy carbon electrode: fabrication of highly sensitive persulfate sensor

A simple method was used to fabricate flavin adenine dinucleotide (FAD)/NiOx nanocomposite on the surface of glassy carbon (GC) electrode. Cyclic voltammetry technique was applied for deposition nickel oxide nanostructures onto GC surface. Owing to its high biocompatibility and large surface area of nickel oxide nanomaterials with immersing the GC/NiOx-modified electrode into FAD solution for a short period of time, 10–140 s, a stable thin layer of the FAD molecules immobilized onto electrode surface. The FAD/NiOx films exhibited a pair of well-defined, stable, and nearly reversible CV peaks at wide pH range (2–10). The formal potential of adsorbed FAD onto nickel oxide nanoparticles film, E ^o′ vs. Ag/AgCl reference electrode is −0.44 V in pH 7 buffer solutions was similar to dissolved FAD and changed linearly with a slope of 58.6 mV/pH in the pH range 2–10. The surface coverage and heterogeneous electron transfer rate constant (k _s ) of FAD immobilized on NiOx film glassy carbon electrode are 4.66 × 10⁻¹¹ mol cm⁻² and 63 ± 0.1 s⁻¹, indicating the high loading ability of the nickel oxide nanoparticles and great facilitation of the electron transfer between FAD and nickel oxide nanoparticles. FAD/NiOx nanocomposite-modified GC electrode shows excellent electrocatalytic activity toward S₂O₈²⁻ reduction at reduced overpotential. Furthermore, rotated modified electrode illustrates good analytical performance for amperometric detection of S₂O₈²⁻. Under optimized condition, the concentration calibration range, detection limit, and sensitivity were 3 μM–1.5 mM, 0.38 μM and 16.6 nA/μM, respectively.     

Electrochemical detection of arsenic on a gold nanoparticle array

The detection of As(III) was investigated on a gold nanoparticle array. At the first stage, gold nanoparticles were synthesized on glassy carbon microspheres. The resulting hybrid material was characterized by SEM and the sizes of the nanoparticles were found to be in the range 20–200 nm. At the second stage, glassy carbon microspheres decorated with Au nanoparticles were abrasively attached to the surface of a basal-plane pyrolytic electrode. The resulting gold nanoarray was characterized by the reduction of surface gold oxides. Furthermore, it was found to have good characteristics for the sensing of arsenic via anodic stripping voltammetry with a limit of detection of 0.8 μM and a sensitivity of 0.91 C M⁻¹. The text was submitted by the authors in English.     

Electrochemiluminescence DNA sensor based on Ru(bpy) 3 2+ -doped silica nanoparticle labeling and proximity-dependent surface hybridization assay

A new electrochemiluminescence (ECL) method based on the proximity-dependent surface hybridization assay and Ru(bpy)₃²⁺-doped silica nanoparticles (Ru-DSNPs) as labels were proposed for detecting DNA. The hybridization process involves two steps: firstly, the 3′ thiolated capture probe was self-assembled on the gold electrode. Secondly, the proximity-dependent surface hybridization assay was carried out. This proximity-dependent surface hybridization assay depended on the simultaneous recognition of a target DNA by a capture probe and Ru-DSNP-labeled probe and the formation of a duplex complex, which results in the luminophor approach to the electrode surface. Thus, sensitive ECL signals were obtained. Under optimum conditions, the intensity of the ECL of Ru-DSNPs was linearly related to the concentration of the target sequence in the range of 2.0 × 10⁻¹⁵ to 2.0 × 10⁻¹¹ mol/L. The detection limit was 1.0 × 10⁻¹⁵ mol/L (S/N = 3).     

Determination of terbutaline with ferrocene-gold colloid-1,4-benzenedimethanethiol layer-by-layer self-assembled gold electrode

Aminylferrocene is successfully immobilized on nanosized gold colloid particles associated with a 1,4-benzenedimethanethiol monolayer on a gold electrode surface and characterized by cyclic voltammograms and electrochemical impedance spectroscopy. In a pH 7.0 phosphate buffer solution, the formal potential (E ⁰’) of Fc is 0.432 V (SCE), and the apparent surface electron-transfer rate constant is 0.89 s⁻. The immobilized Fc gives an excellent electrocatalytic response to the terbutaline oxidation. The catalytic-current response of differential pulse voltammograms increases linearly with the terbutaline concentration from 1.75 × 10⁻⁷ to 5.62 × 10⁻⁴ mol/l. The detection limit is 2.30 × 10⁻⁸ mol/l. The determination of terbutaline in a tablet dosage is satisfactory. The method is simple, quick, and sensitive. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 8, pp. 969–974. The text was submitted by the authors in English.     

Simultaneous determination of uric acid and ascorbic acid at a ferrocenium–thioglycollate modified electrode

Self-assembled monolayers (SAMS) of chemisorbed thioglycollate on a gold electrode surface have been used as a base interface for the electrostatic adsorption of ferrocenium ion. Electrochemical impedance spectra (EIS) and cyclic voltammetry (CV) were used to evaluate the electrochemical properties of the supramolecular film. The bare gold electrode failed to distinguish the oxidation peaks of ascorbic acid (AA) and uric acid (UA) in phosphate buffer solution (PBS, pH 7.0), while the ferricinium–thioglycollate modified electrode could separate them efficiently. In differiential pulse voltammetric measurements, the prepared gold electrode could separate AA and UA signals, allowing the simultaneous determination of AA and UA. Under optimal conditions and within the linear range of 1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ M, the detection limits of AA and UA achieved were 2.0 × 10⁻⁷ and 1.0 × 10⁻⁷ M, respectively. The applicability of the prepared electrode was demonstrated by measuring AA and UA in human urine without any pretreatment. Figure Fabrication process for the modified electrode     

Determination of cocaine on banknotes through an aptamer-based electrochemiluminescence biosensor

A novel electrochemiluminescence (ECL) “sandwich” biosensor has been developed to detect cocaine. The sandwich biosensor was fabricated on the basis of the fact that a single aptamer could be split into two fragments and the two dissociated parts could form a folded, associated complex in the presence of targets. One of these (capture probe), which had hexane–thiol at its 5′-terminus, was immobilized on a gold electrode via thiol–gold binding. The other one (detection probe) was labeled with the ECL reagent tris(2,2′-bipyridyl)ruthenium(II)-doped silica nanoparticles (RuSiNPs) at its 3′-terminus. Owing to the weak interaction between the two fragments, the sensor exhibited a low ECL signal in the absence of cocaine. After the target cocaine had been added to the solution, it induced association of the two fragments and stabilized the associated complexes, leading to immobilization of RuSiNPs on the electrode surface, and the ECL detected on the electrode surface was enhanced. The enhanced ECL intensity was directly proportional to the logarithm of the cocaine concentration in the range from 1.0 × 10⁻⁹ to1.0 × 10⁻¹¹ mol/L, with a detection limit of 3.7 × 10⁻¹² mol/L. The biosensor was applied to detect trace amounts of cocaine on banknotes with satisfactory results.     

Preparation, characterization, and electrocatalytic properties of hybrid coatings of hexacyanometalate-doped-cationic films

Electrochemically active hybrid coatings based on cationic films, didodecyldimethylammonium bromide (DDAB), and poly(diallyldimethylammonium chloride) (PDDAC) are prepared on electrode surface by cycling the film-covered electrode repetitively in a pH 6.5 solution containing Fe(CN)₆ ³⁻ and Ru(CN)₆ ⁴⁻ anions. Modified electrodes exhibited stable and reversible voltammetric responses corresponding to characteristics of Fe(CN)₆ ^3−/4− and Ru(CN)₆ ^4−/3− redox couples. The cyclic voltammetric features of hybrid coatings resemble that of electron transfer process of surface-confined redox couple. Electrochemical quartz crystal microbalance results show that more amounts of electroactive anionic complexes partitioned into DDAB coating than those doped into PDDAC coating from the same doping solution. Peak potentials of hybrid film-bound redox couples showed a negative shift compared to those at bare electrode and this shift was more pronounced in the case of DDAB. Finally, the advantages of hybrid coatings in electrocatalysis are demonstrated with sulfur oxoanions.     

Electrochemical nanogravimetric studies of sulfur/sulfide redox processes on gold surface

Electrochemical quartz crystal microbalance, combined with cyclic voltammetric, chronoamperometric, and potentiostatic measurements, was used to study electrodeposition/dissolution phenomena at a gold electrode in solutions containing Na₂S. Spontaneous, open-circuit deposition processes as well as dissolution of the deposits in sulfide-free solutions have also been investigated. The potential range, scan rate, sulfide concentration, and pH have been varied. The results of the piezoelectric nanogravimetric studies are elucidated by a rather complex scheme involving underpotential deposition of sulfur at approximately −0.85 V vs. sodium calomel electrode, reductive dissolution of the deposited sulfur-containing layer at potentials more negative than approximately −0.9 V, and formation of a sulfur-containing multilayer at potentials more positive than −0.2 V. During the reduction of sulfur deposited on Au, a mass increase due to the formation of polysulfide species in the surface layer, accompanied by incorporation of Na⁺ counterions, can be observed that starts at approximately −0.4 V. This is a reversible process, i.e., during the reoxidation, counterions leave the surface layers. Frequency excursions during the electroreduction and reoxidation processes reveal existence of several competitive dissolution–deposition steps. Spontaneous interaction between Au and HS⁻ species results in a surface mass increase at the open-circuit potential, and it also manifests itself in the substantial decrease of the open-circuit potential after addition of Na₂S to the supporting electrolyte.     

A comparative spectroelectrochemical study of the redox electrochemistry of nitroanilines

The oxidative and reductive electrochemistry of the three isomeric nitroanilines has been studied in neutral (0.1 mol L⁻¹ KClO₄) and acidic (0.1 mol L⁻¹ HClO₄) aqueous electrolyte solutions by cyclic voltammetry and surface enhanced Raman spectroscopy (SERS). The cyclic voltammograms recorded for o- and p-nitroanilines with a gold electrode in acidic solution, scanning toward negative potentials, revealed formation of phenylenediamine not observed in neutral solution. Similar behavior of nitroanilines and phenylenediamines was observed on gold and platinum electrodes. An oxygen–gold adsorbate stretching mode was detected between 400 and 430 cm⁻¹ in the SER-spectra of the three isomeric nitroanilines in both electrolyte solutions at positive electrode potentials, implying perpendicular adsorption via the nitro group.     

Aptamer-based electrochemical approach to the detection of thrombin by modification of gold nanoparticles

This paper presents a simple electrochemical approach for the detection of thrombin, using aptamer-modified electrodes. The use of gold nanoparticles results in significant signal enhancement for subsequent detection. 1,6-Hexanedithiol was used as the medium to link Au nanoparticles to a bare gold electrode. Anti-thrombin aptamers were immobilized on the gold nanoparticles’ surfaces by self-assembly. The packing density of aptamers was determined by cyclic voltammetric (CV) studies of redox cations (e.g., [Ru(NH₃)₆]³⁺) which were electrostatically bound to the DNA phosphate backbones. The results indicate that the total amount of aptamer probes immobilized on the gold nanoparticle surface is sixfold higher than that on the bare electrode, leading to increased sensitivity of the aptasensor and a detection limit of 1 pmol L⁻¹. Based on the Langmuir model, the sensor signal displayed an almost perfect linear relationship over the range of 1 pmol L⁻¹ to 30 nmol L⁻¹. Moreover, the proposed aptasensor is highly selective and stable. In summary, this biosensor is simple, highly sensitive, and selective, which is beneficial to the ever-growing interest in fabricating portable bio-analytical devices with simple electrical readout procedures.