Ultra-sensitive electrochemical DNA biosensor based on signal amplification using gold nanoparticles modified with molybdenum disulfide,graphene and horseradish peroxidase

We have developed an ultra-sensitive electrochemical DNA biosensor by assembling probe ssDNA on a glassy carbon electrode modified with a composite made from molybdenum disulfide, graphene, chitosan and gold nanoparticles. A thiol-tagged DNA strand coupled to horseradish peroxidase conjugated to AuNP served as a tracer. The nanocomposite on the surface acts as relatively good electrical conductor for accelerating the electron transfer, while the enzyme tagged gold nanoparticles provide signal amplification. Hybridization with the target DNA was studied by measuring the electrochemical signal response of horseradish peroxidase using differential pulse voltammetry. The calibration plot is linear in the 5.0?×?10^?14 and 5.0?×?10^?9 M concentration range, and the limit of detection is 2.2?×?10^?15 M. The biosensor displays high selectivity and can differentiate between single-base mismatched and three-base mismatched sequences of DNA. The approach is deemed to provide a sensitive and reliable tool for highly specific detection of DNA.

The electrochemistry of uric acid at a gold electrode modified with L-cysteine, and its application to sensing uric urine

The electrochemistry of uric acid at a gold electrode modified with a self-assembled film of L-cysteine was studied by cyclic voltammetry and differential pulse voltammetry. Compared to the bare gold electrode, uric acid showed better electrochemical response in that the anodic peak current is stronger and the peak potential is negatively shifted by about 100 mV. The effects of experimental conditions on the oxidation of uric acid were tested and a calibration plot was established. The differential pulse response to uric acid is linear in the concentration range from 1.0?×?10^?6 to ~?1.0?×?10^?4 mol?L^?1 (r?=?0.9995) and from 1.0?×?10^?4 to ~?5.0?×?10^?4 mol?L^?1 (r?=?0.9990), the detection limit being 1.0?×?10^?7 mol?L^?1 (at S/N?=?3). The high sensitivity and good selectivity of the electrode was demonstrated by its practical application to the determination of uric acid in urine samples.

Highly Sensitive Electrogenerated Chemiluminescence Isoniazid with NiO Nanoparticles‐modified Graphite Electrode

Abstract

NiO nanoparticles (NiO NPs) were prepared with chemical precipitation method and modified on the surface of vaseline‐impregnated graphite electrode with chitosan. It was found that, based on the catalysis of the NiO NPs for the chemiluminescent reaction of the ECL process, the enhancing effect of isoniazid on the weak electrogenerated chemiluminescence (ECL) signal of luminol at a NiO NPs‐chitosan modified electrode was stronger than that at a bare graphite electrode. Under the optimum experimental conditions, the relative ECL intensity was linear with isoniazid concentration over the range 3.0×10^?10～1.0×10^?6 g/ml at the NiO NPs‐chitosan modified electrode with a detection limit of 1.0×10^?10 g/ml.     

Enhanced electrochemiluminescence of luminol at the gold nanoparticle/carbon nanotube/electropolymerised molecular imprinting composite membrane interface for selective recognition of triazophos

This paper reports a surface molecular self-assembly strategy for imprinting triazophos in the electropolymerised poly(aminthiophenol) (PATP) membranes at the surface of gold nanoparticle (AuNP)/carbon nanotube (CNT) composites modified glassy (GC) electrode for electrochemiluminescent (ECL) detection of pesticide triazophos. The electrochemical and ECL behaviours of luminol at the imprinted PATP/AuNP/CNT/GC electrode were investigated before and after the rebinding of triazophos. It was also found that the ECL intensity was strikingly enhanced by the adsorbed triazophos molecules in the imprinted PATP/AuNP/CNT composite membranes, which was about 5.2-fold as compared with the blank ECL intensity. On this basis, the molecularly imprinted polymer (MIP)-ECL sensor is established for high sensitive and selective detection of triazophos residues in vegetable samples. The resulting MIP-ECL sensor shows wide linear ranges from 3.1 × 10^?8 to 3.1 × 10^?5 g L^?1 with lower detection limit of 3.1 × 10^?9 g L^?1 for triazophos. Moreover, the MIP-ECL sensor has the advantages of high sensitivity, speed, specificity, stability and can become a promising technique for organophosphate pesticide detection.     

Ultrasensitive electrochemiluminescent immunoassay for morphine using a gold electrode modified with CdS quantum dots, polyamidoamine, and gold nanoparticles

We report on a novel electrochemiluminescent (ECL) immunoassay for the ultrasensitive determination of morphine by making use of a gold electrode which was modified with a nanocomposite film containing self-assembled polyamidoamine (PAMAM) CdS quantum dots and electrodeposited gold nanoparticles (Au-NPs). The highly uniform and well-dispersed quantum dots were capped with PAMAM dendrimers. Due to the synergistic effect of the modified quantum dots and the electrodeposited Au-NPs, the ECL response is dramatically enhanced. Under optimal experimental conditions, the immunoreaction between morphine and anti-morphine antibody resulted in a decrease of the ECL signal because of steric hindrance. The calibration plot is linear in the morphine concentration range from 0.2 to 180 ng?mL^?1, with a detection limit as low as 67 pg?mL^?1. The sensor was successfully applied to the determination of morphine in blood plasma. This kind of assay is expected to pave new avenues in label-free drug assays.

Determination of organophosphate pesticides using an acetylcholinesterase-based biosensor based on a boron-doped diamond electrode modified with gold nanoparticles and carbon spheres

We report on a biosensor for organophosphate pesticides (OPs) by exploiting their inhibitory effect on the activity of acetylcholinesterase (AChE). A boron-doped diamond (BDD) electrode was modified with a nanocomposite prepared from carbon spheres (CSs; with an average diameter of 500 nm) that were synthesized from resorcinol and formaldehyde, and then were coated with gold nanoparticles (AuNPs) by chemically growing them of the CSs. Compared to a bare BDD electrode, the electron transfer resistance is lower on this new electrode. Compared to an electrode without Au-NPs, the peak potential is negatively shifted by 42 mV, and the peak current is increased by 55 %. This is ascribed to the larger surface in the AuNP-CS nanocomposite which improves the adsorption of AChE, enhances its activity, and facilitates electrocatalysis. Under optimum conditions, the inhibitory effect of chlorpyrifos is linearly related to the negative log of its concentration in the 10^?11 to 10^?7 M range, with a detection limit of 1.3?×?10^?13 M. For methyl parathion, the inhibition effect is linear in the 10^?12 to 10^?6 M range, and the detection limit is 4.9?×?10^?13 M. The biosensor exhibits good precision and acceptable operational and temporal stability.

Comparative studies on electrogenerated chemiluminescence of luminol on gold nanoparticle modified electrodes

Comparative studies on the electrogenerated chemiluminescence (ECL) behavior of luminol on various electrodes modified with gold nanoparticles of different size were carried out in neutral solution by conventional cyclic voltammetry (CV). The results demonstrated that the gold nanoparticle modified electrodes could generate strong luminol ECL in neutral pH conditions. The catalytic performance of gold nanoparticle modified electrodes on luminol ECL depended not only on the gold nanoparticles but also on the substrate. Gold electrode and glassy carbon electrode were the most suitable substrates for the self-assembly of gold nanoparticles. Moreover, the gold nanoparticle modified gold and glassy carbon electrode had satisfying stability and reproducibility and did not need tedious pretreatment of electrode surface before each measurement. It was also found that luminol ECL behavior depended on the size of gold nanoparticles. The most intense ECL signals were obtained on a 16-nm-diameter gold nanoparticle modified electrode. The modified electrode prepared by the self-assembly method exhibited much better catalytic effect on luminol ECL than that prepared by the electrically deposited method. The ECL behavior of luminol on a gold nanoparticle self-assembled gold electrode was also investigated by other transient-state electrochemical techniques, such as chronoamperometry, differential pulse voltammetry, normal pulse voltammetry, and square wave voltammetry. The strongest ECL intensity was obtained under square wave voltammetric condition.     

New method for preparation of polyoxometalate-capped gold nanoparticles, and their assembly on an indium-doped tin oxide electrode

Functionalized gold nanoparticles capped with polyoxometalates were prepared by a simple photoreduction technique where phosphododecamolybdates serve as reducing reagents, photocatalysts, and as stabilizers. TEM images of the resulting gold nanoparticles show the particles to have a relative narrow size distribution. Monolayer and multilayer structures of the negatively charged capped gold nanoparticles were deposited on a poly(vinyl pyridine)-derivatized indium-doped tin oxide (ITO) electrode via the layer-by-layer technique. The surface plasmon resonance band of the gold nanoparticles displays a blue shift on the surface of the ITO electrode. This is due to the substrate-induced charge redistribution in the gold nanoparticles and a change in the electromagnetic coupling between the assembled nanoparticles. The modified electrode exhibits the characteristic electrochemical behavior of surface-confined phosphododecamolybdate and excellent electrocatalytic activity. The catalysis of the modified electrode towards the model compound iodate was systematically studied. The heterogeneous catalytic rate constant for the electrochemical reduction of iodate was determined by chronoamperometry to be ca. 1.34?×?10⁵ mol^?1·L·s^?1. The amperometric method gave a linear range from 2.5?×?10^?6 to 1.5?×?10^?3 M and a detection limit of 1.0?×?10^?6 M. We believe that the functionalized gold nanoparticles prepared by this photoreduction technique are advantageous in terms of fabrication of sensitive and stable redox electrodes.

Electrochemical Behavior and Application of Pirarubicin at Gold Nanoparticles–Modified Indium Tin Oxide Electrode

Abstract

A new type of gold nanoparticles–attached indium tin oxide electrode was made. By SEM and EDS, the as‐prepared gold nanoparticles–modified ITO electrode was characterized. This modified electrode has been used for the determination of pirarubicin (THP) in urine by cyclic voltammetry. Compared to a bare ITO electrode, the modified electrode exhibited a marked enhancement in the current response. Liner calibration curves are obtained in the range 5×10^?9mol/L～1.5×10^?6 mol/L with a detection limit of 1×10^?9 mol/L. The percentage of the recoveries ranged from 99.3% to 106.3%. The practical analytic utility of the method is illustrated by quantitative determination of THP in urine.     

Electrocatalytic studies of covalently immobilized metal tetra-amino phthalocyanines onto derivatized screen-printed gold electrodes

Metal tetra-amino phthalocyanine complexes (MTAPc; where M is Co or Mn) were immobilized on screen-printed gold electrodes pre-modified with monolayers of benzylamino groups. The functionalized electrodes were then activated using benzene-1,4-dicarbaldehyde as a linker before MTAPc complexes were immobilized. The surface coverages for the modified electrodes confirmed the perpendicular orientation of the MTAPcs. The apparent electron transfer constant (k_app) for the electrodes is 2.2?×?10^?5 cm.s^?1 for both CoTAPc and MnTAPc modified electrodes as calculated with data from impedance measurements. The k_app values for the bare and benzylamino modified electrodes were found to be 1.2?×?10^?4 cm.s^?1 and 4.9?×?10^?6 cm.s^?1, respectively. The electrocatalysis of the modified electrodes towards detection of H₂O₂ gave significant peak current densities and electrocatalytic potentials at ?0.28 V and ?0.31 V for the MnTAPc and CoTAPc modified electrodes, respectively.     

Fabrication of a Sensitive Impedance Biosensor of DNA Hybridization Based on Gold Nanoparticles Modified Gold Electrode

In this work, we report on the preparation of a simple, sensitive DNA impedance sensor. Firstly gold nanoparticles were electrodeposited on the surface of a gold electrode, and then probe DNA was immobilized on the surface of gold nanoparticles through a 5′‐thiol‐linker. Electrochemical impedance spectroscopy (EIS) was used to investigate probe DNA immobilization and hybridization. Compared to the bare gold electrode, the gold nanoparticles modified electrode could improve the density of probe DNA attachment and the sensitivity of DNA sensor greatly. The difference of electron transfer resistance (ΔR_et) was linear with the logarithm of complementary oligonucleotides sequence concentrations in the range of 2.0×10^?12 to 9.0×10^?8 M, and the detection limit was 6.7×10^?13 M. In addition, the DNA sensor showed a fairly good reproducibility and stability during repeated regeneration and hybridization cycles.     

Highly sensitive electrochemiluminescence “turn-on” aptamer sensor for lead(II) ion based on the formation of a G-quadruplex on a graphene and gold nanoparticles modified electrode

We have developed a “turn on” model of an electrochemiluminescence (ECL) based assay for lead ions. It is based on the formation of a G-quadruplex from an aptamer labeled with quantum dots (QDs) and placed on an electrode modified with of graphene and gold nanoparticles (AuNPs). A hairpin capture probe was labeled with a thiol group at the 5′-end and with an amino group at the 3′-end. It was then self-assembled on the electrode modified with graphene and AuNPs. In the absence of Pb(II), the amino tag on one end of the hairpin probe is close to the surface of the electrode and therefore unable to interact with the QDs because of steric hindrance. The ECL signal is quite weak in this case. If, however, Pb(II) is added, the stem-loop of the aptamer unfolds to form a G-quadruplex. The amino group at the 3′-end will become exposed and can covalently link to a carboxy group on the surface of the CdTe QDs. This leads to strong ECL. Its intensity increases (“turns on”) with the concentration of Pb(II). Such a “turn-on” method does not suffer from the drawbacks of “turn-off” methods. ECL intensity is linearly related to the concentration of Pb(II) in the 10 p mol·L^?1 to 1 n mol·L^?1 range, with a 3.8 p mol·L^?1 detection limit. The sensor exhibits very low detection limits, good selectivity, satisfying stability, and good repeatability.

A Novel Sensitive Biosensor for Ca2+ Ion Based on Gold Nanoparticles Modified Electrode by Pulsed Electrodeposition

The work demonstrates a simple method for sensitive detection of Ca²⁺ ion by electrochemical response of alizarin red S (ARS) and Ca-ARS at a gold nanoparticle modified glassy carbon electrode (GCE). In the 0.1 M KOH, a sensitive reduction peak was observed at ?0.795 V at the gold nanoparticles modified electrode. The peak currents were proportional to the concentrations of Ca²⁺ ion in the range of 2.0 × 10^?7 M–1.2 × 10^?4 M. For the different pulse voltammetry (DPV) methods, the detection limit was 2.57 × 10^?8 M. The reaction mechanism was primarily determined by cyclic voltammetry, and the experimental results showed that the electrode processes were quasireversible responses of ARS and irreversible responses of ARS-Ca. In addition, the method was simple, fast, precise, and was used in the determination of calcium in blood serum with satisfactory results.     

Generation of gold nanostructures at the surface of platinum electrode by electrodeposition for ECL detection for CE

In this paper, we report a sensitive method for ECL detection for CE based on generation of gold nanostructures at the surface of Pt electrode by electrodeposition. Difenidol hydrochloride was used as a model analyte. With the increase of electrodeposition amount, the morphology of gold nanostructures changed from discrete nanoflowers to dense nanoparticle array. Interestingly, the variation of deposition amount also greatly affected the ECL intensity of difenidol. The ECL intensity increased remarkably with deposition amount and reached the maximum value at the deposition amount of 7.0×10^?8C; further increasing the deposition amount, however, caused the ECL intensity to decrease. Other conditions, including applied potential, injection time and voltage, buffer pH, were also optimized in detail. Under the optimized conditions, the linear response range of difenidol is from 1.0×10^?8 to 5.0×10^?5 M, and the detection limit was 4.0×10^?9 M (S/N=3). The RSDs of ECL intensity and migration time were 2.0 and 1.6%, respectively (n=5, at 7.5 μM difenidol). Compared with using bare electrode, the detection sensitivity was significantly improved by ca. two orders of magnitude. Notably, the nanogold was prepared at the surface of electrode and no nanogold was added to the electrophoretic buffer or detection cell, thus causing no interference to the separation. Finally, the proposed method was successfully applied to the analysis of difenidol in tablets and urine samples. With high sensitivity and good reproducibility, this method provides a promising platform for the determination of pharmaceuticals that have a tertiary amine group such as difenidol.     

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.     

Developing a Nano‐Biosensor for DNA Hybridization Using a New Electroactive Label

Development of electrochemical DNA hybridization biosensors based on carbon paste electrode (CPE) and gold nanoparticle modified carbon paste electrode (NGMCPE) as transducers and ethyl green (EG) as a new electroactive label is described. Electrochemical impedance spectroscopy and cyclic voltammetry techniques were applied for the investigation and comparison of bare CPE and NGMCPE surfaces. Our voltammetric and spectroscopic studies showed gold nanoparticles are enable to facilitate electron transfer between the accumulated label on DNA probe modified electrode and electrode surface and enhance the electrical signals and lead to an improved detection limit. The immobilization of a 15‐mer single strand oligonucleotide probe on the working electrodes and hybridization event between the probe and its complementary sequence as a target were investigated by differential pulse voltammetry (DPV) responses of the EG accumulated on the electrodes. The effects of some experimental variables on the performance of the biosensors were investigated and optimum conditions were suggested. The selectivity of the biosensors was studied using some non‐complementary oligonucleotides. Finally the detection limits were calculated as 1.35×10^?10 mol/L and 5.16×10^?11 mol/L on the CPE and NEGCPE, respectively. In addition, the biosensors exhibited a good selectivity, reproducibility and stability for the determination of DNA sequences.     

The Influence of Gold Nanoparticles on Simultaneous Determination of Uric Acid and Ascorbic Acid

A three-dimensional L-cysteine (L-cys) monolayer assembled on gold nanoparticles (GNP) providing simultaneous detection of uric acid (UA) and ascorbic acid (AA) was studied in this work. The cyclic voltammetry demonstrated that, at a bare glassy carbon electrode (GCE) or planar gold electrode, the mixture of UA and AA showed one overlapped oxidation peak; whereas when the electrode was modified with GNP, the oxidation peaks for UA and AA were separated. While a GNP modified electrode was further modified with L-cys monolayer (L-cys/GNP/GCE), namely, three-dimensional L-cys monolayer, a better separation for UA and AA response was obtained. Interestingly, the L-cys monolayer-modified planar gold electrode presented a block effect on the oxidation of AA, which was facilitated by the three-dimensional L-cys monolayer attributed to its distinct structure. The pH of solution presented a noticeable effect on the separation of UA and AA at GNP modified electrodes with or without L-cys monolayer. Wide concentration ranges from 2 × 10^?6?1 × 10^?3 M to UA and 2 × 10^?6?8 × 10^?4 M to AA could be obtained at L-cys/GNP/GCE.     

Self-assembly of ultra-small gold nanoparticles on an indium tin oxide electrode for the enzyme-free detection of hydrogen peroxide

A novel enzyme-free electrochemical sensor for H₂O₂ was fabricated by modifying an indium tin oxide (ITO) support with (3-aminopropyl) trimethoxysilane to yield an interface for the assembly of colloidal gold. Gold nanoparticles (AuNPs) were then immobilized on the substrate via self-assembly. Atomic force microscopy showed the presence of a monolayer of well-dispersed AuNPs with an average size of ~4 nm. The electrochemical behavior of the resultant AuNP/ITO-modified electrode and its response to hydrogen peroxide were studied by cyclic voltammetry. This non-enzymatic and mediator-free electrode exhibits a linear response in the range from 3.0?×?10^?5 M to 1.0?×?10^?3 M (M?=?mol?·?L^?1) with a correlation coefficient of 0.999. The limit of detection is as low as 10 nM (for S/N?=?3). The sensor is stable, gives well reproducible results, and is deemed to represent a promising tool for electrochemical sensing.

Novel glucose biosensor based on a glassy carbon electrode modified with hollow gold nanoparticles and glucose oxidase

A novel glucose biosensor is presented as that based on a glassy carbon electrode modified with hollow gold nanoparticles (HGNs) and glucose oxidase. The sensor exhibits a better differential pulse voltammetric response towards glucose than the one based on conventional gold nanoparticles of the same size. This is attributed to the good biological conductivity and biocompatibility of HGNs. Under the optimal conditions, the sensor displays a linear range from 2.0?×?10^?6 to 4.6?×?10^?5?M of glucose, with a detection limit of 1.6?×?10^?6?M (S/N?=?3). Good reproducibility, stability and no interference make this biosensor applicable to the determination of glucose in samples such as sports drinks.

Sandwich electrochemical thrombin assay using a glassy carbon electrode modified with nitrogen- and sulfur-doped graphene oxide and gold nanoparticles

Graphene oxide doped with nitrogen and sulfur was decorated with gold nanoparticles (AuNP-SN-GO) and applied as a substrate to modify a glassy carbon electrode (GCE). An aptamer against the model protein thrombin was self-assembled on the modified GCE which then was exposed to thrombin. Following aptamer-thrombin interaction, biotin-labeled DNA and aptamer 2 are immobilized on another AuNP-SN-GO hybrid and then are reacted with the thrombin/AuNP-SN-GO/GCE to form a sandwich. The enzyme label horseradish peroxidase (HRP) was then attached to the electrode by biotin–avidin interaction. HRP catalyzes the oxidation of hydroquinone by hydrogen peroxide. This generates a strong electrochemical signal that increases linearly with the logarithm of thrombin concentration in the range from 1.0?×?10^?13 M to 1.0?×?10^?8 M with a detection limit of 2.5?×?10^?14 M (S/N?=?3). The assay is highly selective. It provides a promising strategy for signal amplification. In our perception, it has a large potential for sensitive and selective detection of analytes for which appropriate aptamers are available.

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Graphic abstract A sandwich-type electrochemical aptasensor is fabricated for detection of thrombin using a glassy carbon electrode modified with nitrogen- and sulfur-doped graphene oxide and gold nanoparticles.