Differential Pulse Voltammetric Signal Research Articles

An Electrochemical Sensor for Sulfadiazine Determination Based on a Copper Nanoparticles/Molecularly Imprinted Overoxidized Polypyrrole Composite.

To protect consumers from risks related to overexposure to sulfadiazine, total residues of this antibacterial agent in animal-origin foodstuffs not exceed international regulations. To this end, a new electrochemical sensor based on a molecularly imprinted polymer nanocomposite using overoxidized polypyrrole and copper nanoparticles for the detection of sulfadiazine is elaborated. After optimization of the preparation of the electrochemical sensors, their differential pulse voltammetric signal exhibits an excellent stability and reproducibility at 1.05 V, with a large linear range between 10-9 and 10-5 mol L-1 and a low detection limit of 3.1 × 10-10 mol L-1. The produced sulfadiazine sensor was successfully tested in real milk samples. The combination of the properties of the electrical conduction of copper nanoparticles with the properties of the preconcentration of the molecularly imprinted overoxidized polypyrrole allows for the highly sensitive detection of sulfadiazine, even in real milk samples. This strategy is new and leads to the lowest detection limit yet achieved, compared to those of the previously published sulfadiazine electrochemical sensors.

Dopamine‐loaded Liposomes‐amplified Electrochemical Immunoassay Based on MXene (Ti3C2)−AuNPs

AbstractA simple and novel electrochemical immunoassay based on MXene (Ti3C2)−Au nanoparticles (AuNPs) was designed for sensitive screening of a disease‐related biomarker, prostate‐specific antigen (PSA), by using dopamine‐loaded liposomes (DLL) for signal amplification. The system involves two parts, namely, sandwich‐type immunoreaction to capture DLL and electrochemical measurement of dopamine. The target PSA can cause a specific antigen‐antibody reaction and DLL are enriched in the enzyme‐labeled pores. After Triton X‐100 is injected into the detection cell, the carried DLL was quickly cracked to release dopamine wrapped in the cavity. A nanocomposite consisting of MXene (Ti3C2) support to immobilize Au nanoparticles (Ti3C2−Au) was utilized to modify a glassy carbon electrode, which gives a strongly enhanced differential pulse voltammetric (DPV) signals for dopamine. In this case, the change of DPV signal depends on the amount of dopamine released by liposomes, which is further positively correlated with the concentration of the analyte PSA. Combining the of MXene (Ti3C2)−AuNPs nanomaterials (large specific surface area, excellent electrical conductivity, and good electrocatalytic properties) with the liposome signal amplification strategy, the electrochemical immunoassay exhibited excellent performance toward PSA determination with a broad linear range of 1 pg/mL to 50 ng/mL and limit of detection down to 0.31 pg/mL (S/N=3) under the optimized testing conditions. High specificity for PSA over other disease‐related biomarkers and acceptable nanocomposite/electrode stability were acquired. The excellent analytical performance shows that the current strategy provides an effective detection platform for clinical sample analysis.

Electrochemical detection of carbendazim with mulberry fruit-like gold nanocrystal/multiple graphene aerogel and DNA cycle amplification.

An aptasensor for electrochemical detection of carbendazim is reported with mulberry fruit-like gold nanocrystal (MF-Au)/multiple graphene aerogel (MGA) and DNA cycle amplification. HAuCl4 was reduced by ascorbic acid in a CTAC solution containing KBr and KI and formed trioctahedron gold nanocrystal. The gold nanocrystal underwent structural evolution under enantioselective direction of l-cysteine. The resulting MF-Au shows a mulberry fruit-like nanostructure composed of gold nanocrystals of about 200 nm as the core and many irregular gold nanoparticles of about 30 nm as the shell. The exposure of high-index facets improves the catalytic activity of MF-Au. MF-Au/MGA was used for the construction of an aptasensor for electrochemical detection of carbendazim. The aptamer hybridizes with assistant strand DNA to form duplex DNA. Carbendazim binds with the formed duplex DNA to release assistant strand DNA, triggering one three-cascade DNA cycle. The utilization of a DNA cycle allows one carbendazim molecule to bring many methylene blue–labeled DNA fragments to the electrode surface. This promotes significant signal amplification due to the redox reaction of methylene blue. The detection signal is further enhanced by the catalysis of MF-Au and MGA towards the redox of methylene blue. A differential pulse voltammetric signal, best measured at − 0.32 V vs. Ag/AgCl, increases linearly with the carbendazim concentration ranging from 1.0 × 10−16 to 1.0 × 10−11 M with a detection limit of 4.4 × 10−17 M. The method provides ultrahigh sensitivity and selectivity and was successfully applied to the electrochemical detection of carbendazim in cucumber.Graphical abstract This study reports on an ultrasensitive aptasensor for electrochemical detection of carbendazim in cucumber based on mulberry fruit–like gold nanocrystal–multiple graphene aerogel and DNA cycle double amplification.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00604-021-04886-y.

Electrochemical biosensor for detection of MON89788 gene fragments with spiny trisoctahedron gold nanocrystal and target DNA recycling amplification.

Theshape-controlled synthesis of gold nanocrystals via shape induction of hexadecyltrimethylammonium chloride, potassium bromide, and potassium iodide and enantioselective direction of L-cysteineis reported. The resulting gold nanocrystals (STO-Au) offer spiny trisoctahedron nanostructures with good monodispersity and enhanced exposed high-index facets and high catalytic activity. Construction of the electrochemical sensing platform for MON89788 gene involves the modification of STO-Au, thionine (Thi), and labeled bipedal DNA probe 1 or 2 (P1 or P2) for target DNA-induced recycling amplification. In the detection, two surface DNA probes were immobilized on gold electrode via the Au-S bond. Then, hairpin DNA 1 (H1), Thi-STO-Au-P1, and Thi-STO-Au-P2 self-assemble into two-dimensional DNA nanopores (DNPs) on the electrode surface. Target DNA hybridizes with hairpin DNA 2 (H2) to open hairpin structure of H2. The opened H2 binds with H1 in the DNPs to release Thi-STO-Au-P1, Thi-STO-Au-P2, and target DNA by toehold-mediated strand-displacement. The utilization of target DNA-induced recycling allows one target DNA to release 2N STO-Au-labeled DNA strands, promoting significant signal amplification. The detection signal is further enhanced by the catalyzed redox reaction of Thi with STO-Au. The differential pulse voltammetric signal, best measured at - 0.18V vs. Ag/AgCl, decreases linearly with increasing concentration of MON89788 in the range 0.02-8 × 104 fM, and the detection limit is 0.0048 fM (S/N= 3). The proposed method was successfully applied for electrochemical detection of MON89788 gene fragments in the PCR products from genetically modified soybean. Graphical Abstract We develop l-cysteine controlled synthesis of spiny trisoctahedron gold nanocrystals with good monodispersity and highly exposed high-index facets. The architecture achieves to ultrahigh catalytic activity. The electrochemical biosensor based on gold nanocrystals and target DNA recycling amplification provides advantage of sensitivity, repeatability, and regeneration-free.

Assessment of the use of boron-doped diamond electrode for highly sensitive voltammetric determination of the azo-dye carmoisine E−122 in food and environmental matrices

A new protocol for the analysis of the azo-dye carmoisine (CMS) is presented by coupling differential pulse voltammetry (DPV) with a cathodically pretreated boron-doped diamond electrode (CPT-BDDE), in phosphate buffer solution (pH 2.0). The CMS presented diffusion-controlled oxidation and reduction peaks at +0.88 and −0.15 V vs Ag/AgCl, respectively. The effect of the pretreatment conditions, pH, and supporting electrolytes were evaluated to the voltammetric determination of CMS. Under optimized conditions, the differential pulse voltammetric signals for CMS were linear over the concentration range of 0.059–1.31 μmol L−1 and 0.010–0.079 μmol L−1 with limits of detection of 7.0 and 3.0 nmol L−1, for the anodic and cathodic processes respectively. The method was precise for CMS determination (RSD < 5.0%) and selective against other dyes. The developed protocol was successfully applied in the analysis of CMS in surface water and foodstuffs with accurate results in comparison with those obtained using a validated spectrophotometric method.

Electrochemical detection of Mycobacterium tuberculosis IS6110 gene fragments based on the gold nanocrystals with uniform morphology and highly exposed high-index facets and target DNA-induced recycling amplification

This paper reports the synthesis of gold nanocrystals via the reduction of chloroauric acid using ascorbic acid in the mixed hexadecyltrimethylammonium chloride aqueous solution with potassium bromide and potassium iodide. The resulting gold nanocrystals have trioctahedral nanostructures with uniform morphology and highly exposed high-index facets. The nanocrystals unique structure promotes enhanced chemical activity and catalytic activity. Preparation of the electrochemical sensing platform for IS6110 gene involves the modification of gold nanocrystals on hairpin DNA 2 (H2) and thionine as the redox probe for target DNA-induced signal amplification. Target DNA (IS6110 gene) hybridizes with hairpin DNA 1 (H1) pre-modified on the gold electrode, which opens the hairpin structure of H1. This can hybridize with H2 to release target DNA, which is used in the next recycle. The utilization of target DNA-induced recycling allows one target DNA to transport many redox probes to the electrode surface promoting significant signal amplification. The detection signal is further enhanced by catalyzed redox reaction of thionine with gold nanocrystals. The differential pulse voltammetric signal increases with increasing concentration of target DNA in the range of 0.1-1.0 × 105 fM with detection limit of 0.031 fM. The method provides ultrahigh sensitivity, specificity and stability and was successfully applied in the detection of tuberculosis in human blood.

Electrochemical determination of Salmonella typhimurium by using aptamer-loaded gold nanoparticles and a composite prepared from a metal-organic framework (type UiO-67) and graphene.

An aptamer based assay is described for the determination of Salmonella typhimurium (S.typhimurium). A metal-organic framework-graphene composite of type UiO-67/GR is used as the substrate, and an aptamer-gold nanoparticles-horseradish peroxidase (Apt-AuNP-HRP) conjugate the signal amplification probe. A phosphate-terminal and partially complementary DNA (cDNA) of the aptamer is covalently bound to UiO-67/GR via the chemical complexation between phosphate and Zr-OH groups of UiO-67, and then S. typhimurium and cDNA will compete for the binding sites. The binding of Apt-AuNP-HRP to S.typhimurium leads to the formation of strong conjugates. The unbound signal probes then attach to the surface of a glassy carbon electrode via hybridization with cDNA. This generates a large current response (best measured at a potential as low as -0.02V vs. saturated calomel electrode) under the catalytic action of HRP on the H2O2-hydroquinone system. Under the optimal conditions, the differential pulse voltammetric signal decreases linearly in the 2 × 101 -2 × 108cfu·mL-1S.typhimurium concentration range, with a lower detection limit of 5cfu·mL-1 (based on S/N = 3). The method was successfully applied to the detection of S. typhimurium in spiked milk samples. Graphical abstract Schematic presentation of electrochemical determination of Salmonella typhimurium (S.typhimurium). A metal-organic framework (type UiO-67) and graphene (GR) composite were used as substrate, and gold nanoparticles carrying horseradish peroxidase (HRP) for signal amplification. HQ: hydroquinone; cDNA: complementary DNA of aptamer.

Electrochemical aptasensor for detection of acetamiprid in vegetables with graphene aerogel-glutamic acid functionalized graphene quantum dot/gold nanostars as redox probe with catalyst

Glutamic acid-functionalized graphene quantum dots (Glu-GQD) was prepared by pyrolysis of citric acid and glutamic acid and used as reducing agent and stabilizer to produce Glu-GQD/Au in the presence of tannic acid. The resulting Glu-GQD/Au was covalently connected with aptamer (Apt) of acetamiprid to obtain one redox probe with catalyst. The study shows that Glu-GQD/Au offers nanostar-like structure with average particle size of 102.5 nm, composing of several nanometer-sized gold nanocrystals with the rich of sharp edges and corners. The unique structure makes gold nanostars good electrocatalytic activity, which was further improved by combination with Glu-GQD. In the redox probe, Glu-GQD can carry out reversible redox reaction on the electrode surface due to its high electroactivity. Gold nanostars in-situ catalyzes redox reactions of Glu-GQD and leads to an improved electrochemical behavior. Aptamer can specifically bind with acetamiprid and produce sensitive and selective electrochemical response. The electrochemical aptasensor based on Glu-GQD/Au-Apt/graphene aerogel exhibits ultrahigh sensitivity and selectivity for detection of acetamiprid. The differential pulse voltammetric signal linearly decreases with increasing acetamiprid concentration in the range from 1.0 fM to 1 × 105 fM with detection limit of 0.37 fM (S/N = 3). The aptasensor has been successfully applied in electrochemical detection of acetamiprid in vegetables.

3D carbon nanosphereand gold nanoparticle-based voltammetric cytosensor for cell line A549 and forearly diagnosis of non-small cell lung cancer cells.

An electrochemical cytosensor for the detection of the non-small-cell lung cancer cell line A549 (NSCLC) had been developed. A microwave-hydrothermal method was employed to prepare monodisperse colloidal carbon nanospheres (CNSs). Gold nanoparticles (AuNPs) were placed on the surface of the colloidal CNSs by self-assembly to obtain 3D-structured microspheres of the type CNS@AuNP. The results of an MTT assay show the microspheres to possess good biocompatibility. The CNS@AuNP nanocomposite was then placed, in a chitosan film, on a glassy carbon electrode (GCE). The voltammetric signals and detection sensitivity are significantly enhanced owing to the synergistic effect of CNSs and AuNPs. A cytosensor was then obtained by immobilization of antibody against the carcinoembryonic antigen (which is a biomarker for NSCLC) on the GCE via crosslinking with glutaraldehyde. Hexacyanoferrate is used as an electrochemical probe, and the typical working voltage is 0.2V (vs. SCE). If exposed to A549 cells, the differential pulse voltammetric signal decreases in the 4.2 × 10-1 to 4.2 × 10-6 cells mL-1 concentration range, and the detection limit is 14 cells mL-1 (at S/N = 3). Graphical abstract Schematic presentation of design strategy and fabrication process of the electrochemical cytosensor for A549 cells. (CNS: carbon nanospheres; GA: glutaraldehyde; PEI: polyethyleneimine; AuNPs: gold nanoparticles; BSA: Bovine serum albumin).

A quantification strategy for DNA hybridization via measurement of adsorbed anthraquinone monosulphonic acid on silica nanospheres

An amperometric DNA biosensor was developed based on a DNA quantification concept involving the adsorption behavior of anthraquinone monosulphonic acid (AQMS). The biosensor was built from a carbon pasted screen-printed electrode coated with silica nanospheres and gold nanoparticles. Silica nanospheres of 65–84 nm were synthesized via sonication and its surface further modified with amine group. Aminated silica nanospheres immobilize amine-functionalized DNA probe covalently via glutaraldehyde linkers while gold nanoparticles used as an effective electron transfer agent. Anionic AQMS can physically adsorb onto cationic aminated silica nanospheres, and the total AQMS adsorption will be reduced if hybridization occurs. Hence, an increasing amount of hybridized DNA cause a declination in differential pulse voltammetric current signal of AQMS at −0.50 V. The biosensor yielded a linear response range of 10−9–0.5 μM (R2 = 0.97) towards DNA target and showed negligible response to mismatched and noncomplemetary DNA. The fabricated DNA biosensor as an early detection and possible noninvasive method for clinical and medical use was successfully performed; with the detection of synthetic DNA target and cDNA that were reverse-transcripted from dengue virus RNA.

Functionalized N-doped graphene quantum dots for electrochemical determination of cholesterol through host-guest inclusion.

Functionalized nitrogen-doped graphene quantum dots (N-GQD) with mean particle size of 8.5 ± 0.5nm were covalently linked to β-cyclodextrin (β-CD) to form a β-CD@N-GQD nanoprobe. The probe is shown to enable voltammetric determination of cholesterol via selective host-guest recognition and by using ferrocene (FC) as the redox indicator.FC is first included inβ-cyclodextrin. Cholesterol has ahigher affinity for β-CD (in comparison to FC). It forms a strong inclusion complex with β-CD and can replace FC from its cavities. The quantity of released FC is proportional to the concentration of cholesterol. The differential pulse voltammetric signal for FC (with a peak at typically 0.22V vs Ag/AgCl) increases linearly in the 0.5-100μM cholesterol concentration range, with a limit of detection as low as 80nM. The assay is found to be highly selective over 15 potentially interfering species. The method was successfully applied to the detection of cholesterol in spiked serum samples which gave recoveries between 96 and 101%. The probe can be stored for at least 28days after which the activity still is 87%. Graphical abstract This scheme illustrates the detection of cholesterol by differential pulse voltammetry (DPV) technique. The β-cyclodextrin functionalized nitrogen-doped graphene quantum dot (β-CD@N-GQD) probe was developed to enable voltammetric determination of cholesterol using selective host-guest recognition.

Synthesis of gold-palladium nanowaxberries/dodecylamine-functionalized graphene quantum dots-graphene micro-aerogel for voltammetric determination of peanut allergen Ara h 1

The paper reports synthesis of gold-palladium nanowaxberries(AuPd NWs)/dodecylamine-functionalized graphene quantum dots(D-GQDs)-graphene micro-aerogel(GMA). D-GQDs was used as a solid particle surfactant for stabilizing Pickering emulsion of toluene-in-graphene oxide aqueous dispersion. Graphene oxide sheets in the aqueous phase are reduced by hydrazine hydrate, diffused into the toluene droplet and self-assembled into graphene oxide micro-gels. Followed by freeze-drying, thermal annealing and hybridized with AuPd NWs. The as-prepared AuPd NWs/D-GQDs-GMA shows an unique three-dimensional structure with the size of microns. The small size and strong polarity make it can be directly dispersed in ethanol to form stable dispersion for sensor preparation. The hybrid of GMA, D-GQDs and AuPd NWs greatly improves the electron transfer, electroactive surface area and ion diffusion. The architecture of conductor/semiconductor/conductor achieves to a significant amplification of detection signal. The DNA biosensor based on the AuPd NWs/D-GQDs-GMA exhibits ultrasensitive differential pulse voltammetric (DPV) response towards peanut allergen Ara h 1. The DPV signal linearly increases with increasing DNA concentration in the range of 1.0 × 10−22-1.0 × 10−17 M with the detection limit of 4.7 × 10−23 M (S/N = 3). The analytical method was successfully applied to voltammetric determination of peanut allergen Ara h 1 in peanut milk beverage.

Histidine-functionalized graphene quantum dot-graphene micro-aerogel based voltammetric sensing of dopamine

Histidine-functionalized graphene quantum dots (His-GQDs) made via thermal pyrolysis of citric acid and histidine are combined with Zn2+ ions to form Zn-His-GQD complex. The complex was employed as the solid surfactant for stabilizing toluene-in-graphene oxide aqueous dispersion emulsion. The graphene oxide in the Pickering emulsion was slowly reduced by addition of hydrazine hydrate and leads to the formation of graphene micro-gel. The micro-gel was treated by freeze-drying, acid washing and thermal annealing to obtain His-GQD-graphene micro-aerogel (His-GQD-GMA). The as-prepared hybrid offers a three-dimensional architecture with well-defined porous structures, in which the His-GQDs were well dispersed and fixed on the graphene sheets. The all-carbon hybrid provides excellent electron/ion conductivity, electro-catalytic activity and structural stability. The sensor based on the His-GQD-GMA exhibits ultrasensitive electrochemical response to dopamine. Its differential pulse voltammetric signal linearly increases with the increase of dopamine concentration in the range from 1.0×10−9M to 8.0×10−5M with the detection limit of 2.9×10−10M (at a S/N ratio of 3). The sensitivity is much better than that of the reported graphene sensors for dopamine. The analytical method has been successfully applied in the detection of dopamine in rat brain. The study also opens a window on the electronic properties of graphene aerogel and graphene quantum dots as well their hybrids to meet needs of further applications in sensors, catalysis and energy storage and conversion devices.

Covalently Anchored p‐Aminobenzene Sulfonate Multilayer on a Graphite Pencil Lead Electrode: A Highly Selective Electrochemical Sensor for Dopamine

AbstractAn electrochemical sensor for dopamine (DA) has been developed based on the electrografting of 4‐aminobenzene sulfonic acid (4‐ABSA) onto the graphite pencil lead electrode (GPLE). The process of covalent anchoring and presence of 4‐ABSA on the GPLE was studied using cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical behaviour of the sensor towards DA, ascorbic acid (AA), and uric acid (UA) was studied in detail in phosphate buffer of pH 7. After optimizing the various parameters that influence the differential pulse voltammetric (DPV) signal for DA, the sensor exhibited a linear response over the 0.5 – 10 μmol⋅L‐1concentration range with a limit of detection, 0.095 μmol⋅L‐1 (at an S/N of 3). The sensor can selectively quantify DA even in the presence of 1 mmol⋅L‐1 AA. Distinct DPV signals were obtained for DA (at 0.191 mV vs. Ag/AgCl) and for UA (at 0.343 mV vs. Ag/AgCl). The sensor is highly selective, sensitive and stable. It was applied to the quantification of DA in injections and urine. Recovery studies were done by spiking both the real samples with a known quantity of DA.

Development of a highly selective and sensitive electrochemical sensor for Bi3+ determination based on nano-structured bismuth-imprinted polymer modified carbon/carbon nanotube paste electrode

A new nano-structured bismuth(III)-imprinted polymer was prepared by copolymerization of Bi(III)-methylene succinate complex and ethylene glycol dimethacrylate in acetonitrile via precipitation polymerization technique. The polymeric nanoparticles were then used as the Bi3+ selective modifier of a carbon/carbon nanotube paste electrode. Bismuth ions were accumulated on the surface of the electrode, immersed in the Bi3+ solution for a definite time. Then, the anodic striping differential pulse voltammetric signal of the modified electrode was recorded as analytical signal which was significantly higher than that recorded by the non-imprinted polymer based electrode, at the same experimental conditions. Compared to the previously reported carbon paste electrodes, this sensor was more selective, regarding potential interfering species of Cu2+ and Ag+. The electrode exhibited a dynamic linear response range of 0.2–2μmolL−1 and detection limit of 8.9nmolL−1 for Bi3+ measurement. The sensitivity of the sensor was 112.25μAμM−1, indicating an excellent sensitivity of the developed sensor. The sensor was successfully applied for the electrochemical determination of Bi3+ ions in environmental, pharmaceutical and biological samples.

Synthesis of palladium@gold nanoalloys/nitrogen and sulphur-functionalized multiple graphene aerogel for electrochemical detection of dopamine

Integration of noble metal nanomaterials on graphene nanosheets potentially paves one way to improve their electronic, chemical and electrochemical properties. The study reported synthesis of palladium@gold nanoalloys/nitrogen and sulphur-functionalized multiple graphene aerogel composite (Pd@Au/N,S-MGA). The as-prepared composite offers a well-defined three-dimensional architecture with rich of mesopores. The Pd@Au nanoalloys were dispersed on the graphene framework networks and their active sites were fully exposed. The unique structure achieves to ultra high electron/ion conductivity, electrocatalytic activity and structural stability. The sensor based on the Pd@Au/N,S-MGA creates ultrasensitive electrochemical response towards dopamine due to significantly electrochemical synergy between Pd, Au and N,S-MGA. Its differential pulse voltammetric signal linearly increases with the increase of dopamine concentration in the range from 1.0 × 10−9 M to 4.0 × 10−5 M with the detection limit of 3.6 × 10−10 M (S/N = 3). The analytical method provides the advantage of sensitivity, reproducibility, rapidity and long-term stability. It has been successfully applied in the detection of trace dopamine in biological samples. The study also opens a window on the electronic properties of graphene aerogel and metal nanomaterials as well their nanohybrids to meet needs of further applications as nanoelectronics in diagnosis, bioanalysis and catalysis.

An electrochemical dopamine aptasensor incorporating silver nanoparticle, functionalized carbon nanotubes and graphene oxide for signal amplification

In this work, immobilization of a dopamine (DA) aptamer was performed at the surface of an amino functionalized silver nanoparticle-carbon nanotube graphene oxide (AgNPs/CNTs/GO) nanocomposite. A 58-mer DA-aptamer was immobilized through the formation of phosphoramidate bonds between the amino group of chitosan and the phosphate group of the aptamer at the 5′ end. An AgNPs/CNTs/GO nanocomposite was employed as a highly catalytic label for electrochemical detection of DA based on electrocatalytic activity of the nanocomposite toward hydrogen peroxide (H2O2). Interaction of DA with the aptamer caused conformational changes of the aptamer which, in turn, decreased H2O2 oxidation and reduction peak currents. On the other hand, the presumed folding of the DA–aptamer complexes on the sensing interface inhibited the electrocatalytic activity of AgNPs/CNTs/GO toward H2O2. Sensitive quantitative detection of DA was carried out by monitoring the decrease of differential pulse voltammetric (DPV) responses of AgNPs/CNTs/GO nanocomposite toward H2O2 oxidation. The DPV signal linearly decreased with increased concentration of DA from 3 to 110nmolL−1 with a detection limit of 700±19.23pmolL−1. Simple preparation, low operation cost, speed and validity are the decisive factors of this method motivating its application to biosensing investigation.

Dual immunosensor based on methylene blue-electroadsorbed graphene oxide for rapid detection of the influenza A virus antigen

Rapid detection of influenza viral infections in poultry facilities is advantageous in several aspects such as environmental/personal safety, food-security, and socio-economy. Herein, we report the development of an electrochemical-based dual-sensor platform composed of methylene blue-electroadsorbed graphene oxide nanostructures modified with monoclonal antibodies against the HA proteins of H5N1 and H1N1. Bio-functional layers comprised of chitosan and protein-A molecules were implemented at the interface of the sensor element and antibodies, which synergistically enriched the bio-activity of immobilized antibodies for the immune complex formation. The differential pulse voltammetric signals resulted from the developed immunosensor platform exhibited a good correlation (R2=0.9978 for H1N1 and R2=0.9997 for H5N1) for the wide range of target concentrations 25–500pM). Chronoamperometric study also revealed the amplified current sensitivity of the immunoelectrodes even at the picomolar level. The proposed immunosensor design not only provides rapid analytical response time (<1min) but simplicity in fabrication and instrumentation, which paves an attractive platform for on-farm monitoring of viral infections.

Amperometric aptasensor for saxitoxin using a gold electrode modified with carbon nanotubes on a self-assembled monolayer, and methylene blue as an electrochemical indicator probe

A label-free electrochemical aptasensor was developed for selective detection of saxitoxin (STX). It is taking advantage of target-induced conformational change of an STX-specific aptamer when it binds to the toxin. A monolayer of octadecanethiol was deposited on a gold electrode, and then coated with a film of multiwalled carbon nanotubes (MWCNTs) to which the aptamer was covalently conjugated. Methylene blue (MB) was electrostatically anchored on carboxylated MWCNTs and used as the electrochemical indicator that produced a strong differential pulse voltammetric signal in the absence of target (STX). If, however, STX binds to its aptamer, this triggers a conformational change of the aptamer and results in the establishment of a barrier for heterogeneous electron transfer. The oxidation peak current of MB, acquired at −0.27 V (vs. Ag/AgCl), linearly decreases with increasing concentrations of STX in the 0.9 and 30 nM concentration range. The detection limit is 0.38 nM. Marine toxins that maybe present along with STX do not interfere even if they have a similar chemical structure. The assay was applied to the determination of STX in mussels samples and was found to be acceptably accurate. Hence, the method introduced here provides a rapid and sensitive tool for monitoring red tide pollution.

Ultrasensitive direct detection of dsDNA using a glassy carbon electrode modified with thionin-functionalized multiple graphene aerogel and gold nanostars

The paper reports on the synthesis of a composite consisting of thionin-functionalized multiple graphene aerogel and gold nanostars (termed TF-MGA/GNSs). The composite displays an enhanced electrochemical performance compared to the classical graphene aerogel. The performance can be further improved by increasing number of the graphene oxide gelation cycles. The composite was deposited on a glassy carbon electrode to obtain a biosensor for the direct detection of dsDNA. The interaction of thionin with dsDNA causes a specific electrochemical response, best at a working voltage of −228 mV (vs. Ag/AgCl). The enhanced electrocatalytic activity of the composite strongly improves sensitivity. The differential pulse voltammetric signal linearly decreases with increasing dsDNA concentration in the range from 100 fg · mL−1 to 10 ng · mL−1, and the detection limit is 39 fg · mL−1 (at an S/N ratio of 3). The method is sensitive, selective and rapid. It was successfully applied to the detection of circulating free DNA in human serum. The study also provides an attractive approach towards graphene aerogel-based materials to meet the needs of nanoelectronics for molecule diagnosis, bioanalysis and catalysis.