Differential Pulse Voltammetry Signal Research Articles

A fluorescence-electrochemical dual-mode aptasensor based on novel DNA-dependent PBNFs@PtPd for highly selective and sensitive detection of procymidone through hybridization chain reaction

Herein, a study for the first application of a hybridization chain reaction, a 1,8-naphthalimides-DNA (NDs) intercalator, and DNA-dependent Prussian blue nanoflowers@PtPd materials (PBNFs@PtPd) in the development of a fluorescence-electrochemical (FL-EC) aptasensor. This construction establishes an efficient sensing platform for the detection of procymidone (PCM). In the context of the described experiment, dual-mode detection is achieved through the generation of FL signals by an aptamer labeled with a Cy5 moiety and the formation of DPV signals by the modification of a thionine-appended 1,8-naphthalimide (Thi-NDs). In the presence of PCM, specific recognition occurs, followed by the utilization of magnetic separation technology to release DNA1 (S1) and aptamer-Cy5 (Apt-Cy5), subsequently introducing them onto both fluorescence and EC platforms. The presence of S1 effectively activates hybridization chain reaction (HCR) for the electrode surface, thereby significantly increasing the binding sites for Thi-NDs and consequently greatly amplifying the response signal of differential pulse voltammetry (DPV). The developed FL-EC dual-mode sensing platform demonstrates high sensitivity in the detection of PCM, with the detection limits of 0.173 μg·ml−1 (within the detection range of 500 pg·ml−1 to 500 ng·ml−1) and 0.074 ng·ml−1 (within the detection range of 100 pg·ml−1 to 100 ng·ml−1), respectively. The designed dual-mode sensor exhibits notable characteristics, including high selectivity, reproducibility, synergy, and reliable monitoring/capability for PCM in real samples.

Electrochemical genosensor based on RNA-responsive human telomeric G-quadruplex DNA: A proof-of-concept with SARS-CoV-2 RNA

In this report, a facile and label-free electrochemical RNA biosensor is developed by exploiting methylene blue (MB) as an electroactive positive ligand of G-quadruplex. The electrochemical response mechanism of the nucleic acid assay was based on the change in differential pulse voltammetry (DPV) signal of adsorbed MB on the immobilized human telomeric G-quadruplex DNA with a loop that is complementary to the target RNA. Hybridization between synthetic positive control RNA and G-quadruplex DNA probe on the transducer platform rendered a conformational change of G-quadruplex to double-stranded DNA (dsDNA), and increased the redox current of cationic MB π planar ligand at the sensing interface, thereby the electrochemical signal of the MB-adsorbed duplex is proportional to the concentration of target RNA, with SARS-CoV-2 (COVID-19) RNA as the model. Under optimal conditions, the target RNA can be detected in a linear range from 1 zM to 1 μM with a limit of detection (LOD) obtained at 0.59 zM for synthetic target RNA and as low as 1.4 copy number for positive control plasmid. This genosensor exhibited high selectivity towards SARS-CoV-2 RNA over other RNA nucleotides, such as SARS-CoV and MERS-CoV. The electrochemical RNA biosensor showed DPV signal, which was proportional to the 2019-nCoV_N_positive control plasmid from 2 to 200000 copies (R2 = 0.978). A good correlation between the genosensor and qRT-PCR gold standard was attained for the detection of SARS-CoV-2 RNA in terms of viral copy number in clinical samples from upper respiratory specimens.

Toward Remote Detection of Chemical Warfare Simulants Using a Miniature Potentiostat

A miniaturized electrochemical sensor was developed for the remote detection of chemical warfare agent (CWA) simulants. To facilitate drone-based remote sensing, this present study focuses on advancing the miniaturized and compact electrochemical sensor for monitoring two CWA simulants, diisopropyl fluorophosphate (DFP) and O,S-diethylmethylphosphonothioate (O,S-DEMPT). The differential pulse voltammetry (DPV) signal was processed, and the DPV signature features were extracted on the basis of the redox properties associated with the absence and the presence of DFP and O,S-DEMPT. Upon the addition of 0.10 equivalence of DFP or O,S-DEMPT, a shift in potential (E) of ~0.13 V was recorded. The limit of detection (LOD) was calculated to be 0.25 µM (0.046 ppm) and 0.10 µM (0.017 ppm) for DFP and O,S-DEMPT, respectively. These results were validated using a portable Palmsens Emstat HR potentiostat, which corroborated the results obtained using a lab benchtop potentiostat. Additionally, Boolean logic (“AND” operation) was implemented for future drone technology deployment. This advancement enables the fabrication of a networked device capable of autonomously executing tasks without constant oversight.

Construction of electrochemical biosensor based on magnetic Fe3O4/α-Fe2O3 heterogeneous nanorods for the sensitive detection of MUC1 mucoprotein

Magnetic Fe3O4/α-Fe2O3 heterogeneous nanorods with the saturation magnetization of 69.5 emu/g were prepared via the hydrothermal and calcination-reduction process using β-FeOOH nanorods as precursor and galactose as the reducing agent. The average length and diameter of the nanorods were 81.6 nm and 23.9 nm, respectively. The surfaces of the heterogeneous nanorods were modified with PEI and HAuCl4, resulting in magnetic rod-like Fe3O4/α-Fe2O3@Au nanocomposites. By utilizing the Au–S effect, Apt/ssDNA hybrid double-strands were loaded onto Fe3O4/α-Fe2O3@Au nanocomposites to form Fe3O4/α-Fe2O3@Au-Apt/ssDNA biosensors capable of recognizing mucoprotein-1 (MUC1) mucoprotein. These biosensors could be magnetically assembled onto a magnetic glassy carbon electrode to create a "Turn off" type electrochemical biosensor. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV) techniques were used to evaluate the detection performance. Based on the change in DPV signals, the optimal concentrations of magnetic Fe3O4/α-Fe2O3@Au nanocomposites and Apt/ssDNA double-stranded probes were 12 mg/mL and 9 μM, respectively, while the optimal incubation time was 2 h. Under these conditions, the sensor exhibited a linear detection range of 0.1 pg/mL to 1500 pg/mL (R2 = 0.9988), with a limit of detection (LOD) of 0.1 pM and a limit of quantitation (LOQ) of 0.34 pM. The biosensor demonstrated excellent performance in terms of selectivity, reproducibility (RSD = 2.9 %), and stability. When actual serum samples diluted by a factor of 20 in PBS were tested, the recovery rate ranged from 95.65 % to 103.40 %, indicating that this approach for sensitive detection of MUC1 holds promising prospects.

Sensitive electrochemical detection of l-tryptophan using a glassy carbon electrode modified with pectin extracted from Arthrocnemum indicum leaves

Pectin from Arthrocnemum indicum leaves (PAI) extracted from plants, harvested in the Tunisian Sahel, was used for the first time as a sensitive matrix for the design of an electrochemical sensor of l-tryptophan via differential pulse voltammetry (DPV). A glassy carbon electrode (GCE) was modified by a PAI layer through simple adsorption, leading to a DPV signal of l-tryptophan that was increased by a factor of 15. The PAI-modified electrode exhibited a good analytical performance towards the detection of l-tryptophan with a wide linear range between 9.10−5 mM to 2.10−2 mM, a detection limit of 0.09 µM, and a sensitivity of 90.15 µA. mM−1. Compared to other reported electrochemical sensors, PAI/GCE presents a lower detection limit, even without the use of nanomaterials. In addition, the PAI/GCE showed good reproducibility and good selectivity towards the determination of l-tryptophan versus other amino acids, uric acid, and ascorbic acid, making it suitable for the determination of l-tryptophan in biological fluids.

An electrochemical biosensor based on phage-encoded protein RBP 41 for rapid and sensitive detection of Salmonella

Salmonellosis caused by Salmonella contaminated food poses a serious threat to human health. The rapid and accurate detection of Salmonella is critical for preventing foodborne illness outbreaks. In this study, an electrochemical biosensor was developed using a newly identified biorecognition element, RBP 41, which is capable of specifically recognizing and binding to Salmonella. The biosensor was constructed through a layer-by-layer assembly of graphene oxide (GO), gold nanoparticles (GNPs), and RBP 41 on a glassy carbon electrode (GCE), with the GNPs amplifying the detection signal. The established biosensor was able to detect Salmonella in concentrations ranging from 3 to 106 CFU/mL within approximately 30 min by using differential pulse voltammetry (DPV) signal, and the estimated detection limit was to be 0.2984 Log10 CFU/mL. The biosensor demonstrated excellent specificity and was effective in detecting Salmonella in food matrices, such as skim milk and lettuce. Overall, this study highlights the potential of phage tail receptor binding proteins in biosensing and the proposed biosensor as a promising alternative for rapid and sensitive Salmonella detection in various samples.

A target-triggered ultra-sensitive aptasensor for simultaneous detection of Cd2+ and Hg2+ using MWCNTs-Au NPs modified electrode

A sensitive electrochemical assay for simultaneously detecting cadmium ion (Cd2+) and mercury ion (Hg2+) with the aptamer as recognition unit was established, in which methylene blue (MB) and target-triggered in-situ generated Ag nanoclusters (Ag NCs) were identified as signal reporters. Multi-walled carbon nanotubes and gold nanoparticles composites were prepared with polyethyleneimine to amplify electrical signals of screen-printed electrodes. Due to the particular base sequences, MB labeled Cd2+ aptamer paired with ssDNA through T-Hg-T structure with Hg2+. Notably, the C-rich structure in ssDNA acted as a template for the generation of Ag NCs, which could induce differential pulse voltammetry signals corresponding to Hg2+ concentrations. This electrochemical aptasensor exhibited detection limits of 94.01 pg/mL and 15.74 pg/mL for Cd2+ and Hg2+, respectively. The developed aptasensor allowed for practical application to tea and vegetable samples with satisfactory accuracy. This work possesses potential in developing biosensing technologies for simultaneous determination of multiple heavy metals.

Highly sensitive electrochemical peptide-based biosensor for marine biotoxin detection using a bimetallic platinum and ruthenium nanoparticle-tethered metal-organic framework modified electrode.

Saxitoxin (STX) is a highly toxic small-molecule cyanotoxin that is water-soluble, stable in acidic media, and thermostable. STX is hazardous to human health and the environment in ocean, thus it is an important to detect it at very low concentrations. Herein, we developed an electrochemical peptide-based biosensor for the trace detection of STX in different sample matrix utilizing differential pulse voltammetry (DPV) signal. We synthesized the nanocomposite of zeolitic imidazolate framework-67 (ZIF-67) decorated bimetallic platinum (Pt) and ruthenium (Ru) nanoparticles (Pt-Ru@C/ZIF-67) using impregnation method. The nanocomposite modified with screen-printed electrode (SPE) was subsequently used to detect STX in the range of 1-1,000ngmL-1, with a detection limit (LOD) of 26.7pgmL-1. The developed peptide-based biosensor is highly selective and sensitive towards STX detection, thus it represents a promising strategy for the development of novel portable bioassay for monitoring various hazardous molecules in aquatic food chains.

Tetrahedral DNA Nanostructure-Engineered Paper-Based Electrochemical Aptasensor for Fumonisin B1 Detection Coupled with Au@Pt Nanocrystals as an Amplification Label.

Fumonisin B1 (FB1), as one of the highest toxicity mycotoxins, poses a serious threat to animal and human health, even at low concentrations. It is significant and challenging to develop a sensitive and reliable analytical device. Herein, a paper-based electrochemical aptasensor was designed utilizing tetrahedral DNA nanostructures (TDNs) to controllably anchor an aptamer (Apt), improving the recognition efficiency of Apt to its target. First, gold nanoparticles (AuNPs)@MXenes were used as a sensing substrate with good conductivity and modified on the electrode for immobilization of complementary DNA-TDNs (cDNA-TDNs). In the absence of FB1, numerous Apt-Au@Pt nanocrystals (NCs) was hybridized with cDNA and assembled on the sensing interface, which accelerated the oxidation of TMB with H2O2 and produced a highly amplified differential pulse voltammetry (DPV) signal. When the target FB1 specifically bound to its Apt, the electrochemical signal was decreased by releasing the Apt-Au@Pt NCs from double-stranded DNA (dsDNA). On account of the strand displacement reaction by FB1 triggering, the aptasensor had a wider dynamic linear range (from 50 fg/mL to 100 ng/mL) with a lower limit of detection (21 fg/mL) under the optimized conditions. More impressively, the designed FB1 aptasensor exhibited satisfactory performance in corn and wheat samples. Therefore, the TDN-engineered sensing platform opens an effective approach for sensitive and accurate analysis of FB1, holding strong potential in food safety and public health.

Dual-mode transfer response based on electrochemical and fluorescence signals for the detection of amyloid-beta oligomers (AβO).

An aptamer sensor has been developedutilizing a dual-mode and stimuli-responsive strategy for quantitative detection of AβO (amyloid-beta oligomers) through simultaneous electrochemical and fluorescence detection. To achieve this, we employed UIO-66-NH2 as a carrier container to load MB (Methylene Blue), and Fe3O4 MNPs (iron oxide magnetic nanoparticles) with aptamer (ssDNA-Fe3O4 MNPs) fixed on their surface for biological gating. The ssDNA-Fe3O4 MNPs were immobilized onto the surface of UIO-66-NH2 through hydrogen bonding between the aptamer and the -NH2 group on the surface of UIO-66-NH2, thereby encapsulating MB and forming ssDNA-Fe3O4@MB@UIO-66-NH2. During the detection of AβO, the aptamer selectively reacted with AβO to form the AβO-ssDNA-Fe3O4 complex, leading to its detachment from the surface of UIO-66-NH2. This detachment facilitated the release of MB, enabling its electrochemical detection. Simultaneously, the AβO-ssDNA-Fe3O4 complex was efficiently collected and separated using a magnet after leaving the container's surface. Furthermore, the addition of NaOH facilitated the disconnection of biotin modifications at the 3' end of the aptamer from the avidin modifications on the Fe3O4 MNPs. Consequently, the aptamer detached from the surface of Fe3O4 MNPs, resulting in the restoration of fluorescence intensity of FAM (fluorescein-5'-carboxamidite) modified at its 5' end for fluorescence detection. The dual-mode sensor exhibited significantly enhanced differential pulse voltammetry signals and fluorescence intensity compared to those in the absence of AβO. The sensor demonstrated a wide detection range of 10 fM to 10 μM, with a detection limit of 3.4 fM. It displayed excellent performance in detecting actual samples and holds promising prospects for early diagnosis of Alzheimer's disease.

Competitive electrochemical immunosensors by immobilization of hexahistidine-rich recombinant proteins on the signal labels

Most of proteins in the commercial ELISA kits are recombinant with hexahistidine (His6) tags. Based on this fact, we proposed a simple procedure for the preparation of signal labels and the design of competitive immunosensors. The signal labels were fabricated through the high-affinity interaction between the His6 tails on the surface of recombinant proteins and the coordinatively unsaturated copper ions on the surface of pristine Cu-based metal organic framework (Cu-MOF). The recombinant protein-modified MOF could be captured by the sensor electrode, thus producing a strong differential pulse voltammetry signal through the electrochemical reduction of Cu2+ ions in MOF. However, the target protein in sample solution could compete with the His6-tagged protein on the surface of Cu-MOF to bind the antibody attached on the electrode, thus leading to the decrease in the electrochemical signal. The peak current showed an inversely relationship with the concentration of target protein. The competitive immunosensor exhibited a linear range of 1 pg/mL to 1 ng/mL with SARS-CoV-2 nucleocapsid protein (N-protein) as the target analyte. We believe that the method can be used to detect other proteins by utilizing the characteristic of recombinant proteins in commercial kits.

Designing a label-free electrochemical aptasensor based on polypyrrole-l-cysteine-reduced graphene oxide nanocomposite for detection of 25-hydroxyvitamin D3.

Reliable and precise quantification of 25-hydroxyvitamin D3 in clinical samples is vital because vitamin D3 deficiency lead to several disorders, such as mental illness, osteoporosis, and coronavirus disease. Herein, we report the fabrication of a novel electrochemical aptasensor using a nanocomposite, including reduced graphene oxide, pyrrole, and l-cysteine, for the sensitive detection of 25-hydroxyvitamin D3 . Subsequently, the aptamer of 25-hydroxyvitamin D3 was immobilized on the surface of the modified electrode. Differential pulse voltammetry signals were utilized for studying the binding and measurement of 25-hydroxyvitamin D3 based on the oxidation peak. Under the optimum conditions, the designed electrochemical aptasensor exhibited a linear detection range of 0.001-150nM, with a limit of detection of 0.006nM. Furthermore, the proposed aptasensor selectively detected 25-hydroxyvitamin D3 compared to other analogs. Moreover, this aptasensor was successfully applied for the detection of 25-hydroxyvitamin D3 in human serum samples, which were quantified by the enzyme-linked immunosorbent assay method. The acceptable recoveries of 82.67%-111.07% demonstrated that this proposed electrochemical aptasensor can be a promising alternative for clinical methods of vitamin D determination.

An Ultrasensitive Voltammetric Genosensor for the Detection of Bacteria Vibrio cholerae in Vegetable and Environmental Water Samples.

In view of the presence of pathogenic Vibrio cholerae (V. cholerae) bacteria in environmental waters, including drinking water, which may pose a potential health risk to humans, an ultrasensitive electrochemical DNA biosensor for rapid detection of V. cholerae DNA in the environmental sample was developed. Silica nanospheres were functionalized with 3-aminopropyltriethoxysilane (APTS) for effective immobilization of the capture probe, and gold nanoparticles were used for acceleration of electron transfer to the electrode surface. The aminated capture probe was immobilized onto the Si-Au nanocomposite-modified carbon screen printed electrode (Si-Au-SPE) via an imine covalent bond with glutaraldehyde (GA), which served as the bifunctional cross-linking agent. The targeted DNA sequence of V. cholerae was monitored via a sandwich DNA hybridization strategy with a pair of DNA probes, which included the capture probe and reporter probe that flanked the complementary DNA (cDNA), and evaluated by differential pulse voltammetry (DPV) in the presence of an anthraquninone redox label. Under optimum sandwich hybridization conditions, the voltammetric genosensor could detect the targeted V. cholerae gene from 1.0 × 10-17-1.0 × 10-7 M cDNA with a limit of detection (LOD) of 1.25 × 10-18 M (i.e., 1.1513 × 10-13 µg/µL) and long-term stability of the DNA biosensor up to 55 days. The electrochemical DNA biosensor was capable of giving a reproducible DPV signal with a relative standard deviation (RSD) of <5.0% (n = 5). Satisfactory recoveries of V. cholerae cDNA concentration from different bacterial strains, river water, and cabbage samples were obtained between 96.5% and 101.6% with the proposed DNA sandwich biosensing procedure. The V. cholerae DNA concentrations determined by the sandwich-type electrochemical genosensor in the environmental samples were correlated to the number of bacterial colonies obtained from standard microbiological procedures (bacterial colony count reference method).

A graphene oxide/Zn-metal organic framework electrochemical sensor for acetaminophen detection

In this study, an electrochemical sensor based on graphene oxide (GO)/Zn-metal organic framework (ZIF-8) composite electrode was used to detect acetaminophen (APAP). GO/ZIF-8 was characterized by X-ray diffraction, transmission electron microscope, and X-ray photoelectron spectroscopy. The electrochemical behavior of APAP on GO/ZIF-8 modified glassy carbon electrode (GCE) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The DPV signal of GO/ZIF-8 for APAP detection is 4.3 times higher than pure ZIF-8, and the efficient electrochemical performance was attributed to that introduction of GO can effectively enhance the electron transport capacity of ZIF-8. The sensor exhibits a linear range of 0.05–1.3 µM and a low detection limit of 0.014 µM. It shows excellent selectivity, repeatability and also can be used to determine APAP in human urine samples and drug tablets.

Electrochemical Determination of Phenylalanine in Biological, Food and Pharmaceutical Samples using a MnO2/N‐doped Reduced Graphene Oxide Nanocomposite

AbstractIn this study, the MnO2/N‐doped reduced graphene oxide (NRGO) nanocomposite was synthesized and applied for the glass‐carbon electrode coating as working electrode for electrochemical phenylalanine determination. The structure, morphology, and composition of materials were characterized using appropriate methods. Optimal pH was investigated by injecting different amounts of phenylalanine into phosphate buffer solution and differential pulse voltammetry signal studying. Under optimal conditions, the calibration curve was linear in the range of 15–220 μM and the detection limit was 3.59 μM. The method shows acceptable selectivity in the presence of common interfering species in biological fluids. The method was successfully applied for the determination of the amino acid phenylalanine in blood plasma, food, and pharmaceutical samples. The results were evaluated by studying the amount of spiked recovery and statistical test with comparison to the high‐performance liquid chromatography method results and the accuracy and precision of the method for phenylalanine determining in real samples were confirmed.

Dual-signal ratiometric electrochemical immunosensor constructed with snowflake-like FeSe2-AuNPs and PAA-ZIF@TB for sensitive detection of CYFRA21-1

In this study, a ratiometric electrochemical immunosensor has been developed to detect the cytokeratin 19 fragment 21–1 (CYFRA21-1) biomarker in a highly sensitive manner through a dual-signal output model. As one of signal indicators, snowflake-like FeSe2 loaded with AuNPs (FeSe2-AuNPs) as sensing substrate with good conductivity and large active sites provides a differential pulse voltammetry (DPV) signal at +0.4 V. Another signal indicator, toluidine blue (TB) with the water-solubility property is an excellent redox probe that can generate DPV signal at −0.3 V. To solve the water-solubility problem, the TB is absorbed with polyacrylic acid (PAA) functionalized ZIF-67 (PAA-ZIF-67), which retains the properties of ZIF-67 that are large specific surface area and strong adsorption properties. The ratio of signals, stemmed from PAA-ZIF@TB and FeSe2-AuNPs (IPAA-ZIF@TB/IFeSe2-AuNPs), increases with the CYFRA21-1 concentration. Under optimal experimental conditions, CYFRA21-1 was detected in a wide dynamic range from 0.1 pg/mL to 100 ng/mL, with a lower limit of detection of 0.02 pg/mL. Looking ahead, this ratio based strategy provides prospective clinical applications for detecting other biomarkers.

NH2-MIL-125(Ti)/Reduced Graphene Oxide Enhanced Electrochemical Detection of Fenitrothion in Agricultural Products.

The abuse of organophosphate pesticides causes serious threats to human health, which threatens approximately 3 million people and leads to more than 2000 deaths each year. Therefore, it is necessary to determine the residue of fenitrothion (FT) in environmental and food samples. Herein, we developed a non-enzymatic electrochemical sensor with differential pulse voltammetry signal output to determine FT in model solutions and spiked samples. Delicately, the sensor was designed based on the fabrication of hydrothermally synthesized titanium-based metal-organic frameworks (MOFs) material (NH2-MIL-125(Ti))/reduced graphene oxide (RGO) (NH2-MIL-125(Ti)/RGO) nanocomposites for better target enrichment and electron transfer. The peak response of differential pulse voltammetry for FT under optimized conditions was linear in the range of 0.072-18 μM with the logarithm of concentrations, and the detection limit was 0.0338 μM. The fabricated sensor also demonstrated high stability and reproducibility. Moreover, it exhibited excellent sensing performances for FT in spiked agricultural products. The convenient fabrication method of NH2-MIL-125(Ti)/RGO opens up a new approach for the rational design of non-enzymatic detection methods for pesticides.

Electrochemical biosensors based on conducting polymer composite and PAMAM dendrimer for the ultrasensitive detection of acetamiprid in vegetables

The cumulative harm caused by pesticide residues to environmental safety and human health is enormous, and the sensitive and selective detection pesticide in very trace amounts is currently a challenge. Herein, the biosensors for the ultrasensitive detection of acetamiprid (ACE) were proposed. The conducting polymer composite of phaseoloidin doped poly(3,4-ethyloxythiophene) (PL/PEDOT) was prepared with high surface area, excellent conductivity and stability, which was followed by the functionalization with poly(amidoamine) of the third generation (PAMAM). ACE aptamers were immobilized onto the platforms (PL/PEDOT and PAMAM/PL/PEDOT) for the development of ACE aptasensors. The concentration of ACE can be measured through both the increase of differential pulse voltammetry (DPV) signal change and the increase of the chronoamperometry (CA) signal change from the reduction of hydrogen peroxide catalyzed by PL/PEDOT. The ACE aptasensor based on PAMAM/PL/PEDOT exhibited linear ranges of 0.1 pg mL−1-10 ng mL−1 and 0.1 fg-1.0 pg mL−1, the detection limits as low as 0.0117 pg mL−1 and 0.0355 fg mL−1 (S/N = 3) through DPV and CA, respectively. Significantly, the response sensitivity of DNA/PAMAM/PL/PEDOT/GCE was 3.11 times higher than that of DNA/PL/PEDOT/GCE (by CA mode), proving that the PAMAM dendrimer can greatly enhance the sensing performance.

Construction of a dual-mode biosensor for electrochemiluminescent and electrochemical sensing of alkaline phosphatase

We demonstrate the construction of a dual-mode biosensor based on fully-π conjugated covalent organic framework (COF) and cobalt oxyhydroxide (CoOOH) nanoflakes for electrochemiluminescent (ECL) and electrochemical sensing of alkaline phosphatase (ALP). The fully-π conjugated COF with sp2 carbon-linkage is synthesized through Knoevenagel polycondensation of 2, 5-dimethoxy-terephthalaldehyde (DMTA) and 1,3,5-tris(4-cynomethylphenyl)benzene (TCPB), and it acts as an efficient ECL emitter whose signal is 41 and 125-fold higher than those of TCPB and DMTA. The ECL signal of TCPB-DMTA-COF may be quenched by CoOOH nanoflakes through electrochemiluminescent resonance energy transfer, and meanwhile CoOOH promotes the oxidation of o-phenylenediamine (o-PD) to generate a high differential pulse voltammetry (DPV) signal. When ALP is present, it hydrolyzes L-ascorbic acid-2-phosphate (AAP) to produce L-ascorbic acid (AA). AA can reduce CoOOH to Co2+, resulting in the decomposition of the CoOOH nanoflakes and consequently the recovery of ECL signal and the decrease of DPV peak current. This dual-mode biosensor can efficiently eliminate the errors associated with personnel operation and experimental factors, leading to more reliability and accuracy than single-mode biosensor. Moreover, this dual-mode biosensor can be applied for specifically sensing ALP in human serums and screening the inhibitors, with potential applications in biomedical researches.

Electrochemical assay of acetamiprid in vegetables based on nitrogen-doped graphene/polypyrrole nanocomposites.

Dual-mode electrochemical aptasensor based on nitrogen-doped graphene (NG) doped with the conducting polymer polypyrrole (PPy) nanocomposite is proposed for the determination of acetamiprid. NG/PPy was electrodeposited onto the glassy carbon electrode (GCE) using cyclic voltammetry technique. NG/PPy/GCE showed outstanding electrocatalytic activity for the oxidation of nitrite due to "active region" induced by the charge redistribution of carbon atoms. The ultrasensitive dual-mode biosensor for acetamiprid could be easily developed by coupling acetamiprid aptamers with the NG/PPy hybrid. The specific binding between acetamiprid and the aptamers resulted in the increase of differential pulse voltammetry (DPV) signal change and the decrease of chronoamperometry (CA) signal, and the concentration of acetamiprid could be measured. The working potentials of DPV and CA were - 0.2 ~ 0.4V and - 0.4 ~ 0.4V (vs. SCE), respectively. The dual-mode acetamiprid biosensor showed a wide linear range from 10-12 to 10-7gmL-1, with low detection limits of 1.15 × 10-13gmL-1 and 7.32 × 10-13gmL-1 through DPV and CA modes, respectively. Moreover, owing to high active area and superior conductivity, as well as good electrocatalytic ability, the dual-sensing platform based on NG/PPy nanocomposite supported the quantification of acetamiprid in complex samples. A dual-mode electrochemical aptasensor based on NG/PPy nanocomposite for acetamiprid detection was proposed through both the increase of differential pulse voltammetry (DPV) signal change and the decrease of chronoamperometry (CA) signal of the nitrite oxidation electrocatalyzed by NG/PPyn in sensors and biosensors.