A ratiometric electrochemical biosensor for sensitive detection of Hg based on thymine–Hg–thymine structure

In this paper, a simple, selective and reusable electrochemical biosensor for the sensitive detection of mercury ions (Hg²⁺) has been developed based on thymine (T)-rich stem–loop (hairpin) DNA probe and a dual-signaling electrochemical ratiometric strategy. The assay strategy includes both “signal-on” and “signal-off” elements. The thiolated methylene blue (MB)-modified T-rich hairpin DNA capture probe (MB-P) firstly self-assembled on the gold electrode surface via Au–S bond. In the presence of Hg²⁺, the ferrocene (Fc)-labeled T-rich DNA probe (Fc-P) hybridized with MB-P via the Hg²⁺-mediated coordination of T–Hg²⁺–T base pairs. As a result, the hairpin MB-P was opened, the MB tags were away from the gold electrode surface and the Fc tags closed to the gold electrode surface. These conformation changes led to the decrease of the oxidation peak current of MB (I_MB), accompanied with the increase of that of Fc (I_Fc). The logarithmic value of I_Fc/I_MB is linear with the logarithm of Hg²⁺ concentration in the range from 0.5 nM to 5000 nM, and the detection limit of 0.08 nM is much lower than 10 nM (the US Environmental Protection Agency (EPA) limit of Hg²⁺ in drinking water). What is more, the developed DNA-based electrochemical biosensor could be regenerated by adding cysteine and Mg²⁺. This strategy provides a simple and rapid approach for the detection of Hg²⁺, and has promising application in the detection of Hg²⁺ in real environmental samples.     

Electrochemical biosensor for amplified detection of Pb2+ based on perfect match of reduced graphene oxide–gold nanoparticles and single-stranded DNAzyme

Analytical and Bioanalytical Chemistry - In this study, a sensitive amplification strategy for Pb2+ detection using reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) was proposed....     

Study on an electrochemical biosensor for thrombin recognition based on aptamers and nano particles

This paper presents a high specific, sensitive electrochemical biosensor for recognition of protein such as thrombin based on aptamers and nano particles. Two different aptamers were chosen to construct a sandwich manner for detecting thrombin. Aptamer I was immobilized on nano magnetic particle for capturing thrombin, and aptamer II labled with nano gold was used for detection. The electrical current generated from gold after the formation of the complex of magnetic particle, thrombin and nano gold, and then an electrochemical cell designed by ourselves was used for separating, gathering, and electrochemical detecting. Through magnetic separation, high specific and sensitive detection of the target protein, thrombin, was achieved. Linear response was observed over the range 5.6×10-12―1.12×10-9 mol/L, with a detection limit of 1.42×10-12 mol/L. The presence of other protein as BSA did not affect the detection, which indicates that high selective recognition of thrombin can be achieved in complex biological samples such as human plasma.     

An electrochemical biosensor for α-fetoprotein based on carbon paste electrode constructed of room temperature ionic liquid and gold nanoparticles

A novel and effective electrochemical immunosensor for the rapid determination of α-fetoprotein (AFP) based on carbon paste electrode (CPE) consisting of room temperature ionic liquid (RTIL) N-butylpyridinium hexafluorophosphate (BPPF₆) and graphite. The surface of the CPE was modified with gold nanoparticles for the immobilization of the α-fetoprotein antibody (anti-AFP). By sandwiching the antigen between anti-AFP on the CPE modified with gold nanoparticles and the secondary antibody, polyclonal anti-human-AFP labeled with horseradish peroxidase (HRP-labeled anti-AFP), the immunoassay was established. The concentration of AFP was determined based on differential pulse voltammetry (DPV) signal, which was generated in the reaction between O-aminophenol (OAP) and H₂O₂ catalyzed by HRP labeled on the sandwich immunosensor. AFP concentration could be measured in a linear range of 0.50-80.00 ng mL⁻¹ with a detection limit of 0.25 ng mL⁻¹. The immunosensor exhibited high sensitivity and good stability, and would be valuable for clinical assay of AFP.     

An electrochemical signal switch–based (on–off) aptasensor for sensitive detection of insulin on gold-deposited screen-printed electrodes

Journal of Solid State Electrochemistry - Insulin hormone is of great importance for many diseases, especially for diabetes management. Therefore, different detection strategies have been used for...     

An electrochemical microRNAs biosensor with the signal amplification of alkaline phosphatase and electrochemical–chemical–chemical redox cycling

MicroRNAs (MiRNAs) have been regarded as clinically important biomarkers and drug discovery targets. In this work, we reported a simple and ultrasensitive electrochemical method for miRNAs detection based on single enzyme amplification and electrochemical–chemical–chemical (ECC) redox cycling. Specifically, upon contact with the target miRNAs, the hairpin structure of biotinylated DNA immobilized on gold electrode was destroyed and the biotin group in DNA was forced away from the electrode surface, allowing for the coupling of streptavidin-conjugated alkaline phosphatase (SA-ALP). Then, ascorbic acid (AA, the enzymatic product of ALP) triggered the ECC redox cycling with ferrocene methanol (FcM) and tris(2-carboxyethyl)phosphine (TCEP) as the redox mediator and the chemical reducing reagent, respectively. The method was more sensitive than that with horseradish peroxidase (HRP) or glucose oxidase (GOx) triggered recycling since one ALP molecule captured by one target miRNA molecule promoted the production of thousands of AA. Analytical merits (e.g., detection limit, dynamic range, specificity, regeneration and reproducibility) were evaluated. The feasibility of the method for analysis of miRNA-21 in human serum has also been demonstrated.     

CuS–MWCNT based electrochemical sensor for sensitive detection of bisphenol A

The rapid and simple detection of bisphenol A is very important for the safety and reproduction of organisms. Here, a sensitive and reliable electrochemical sensor was established for bisphenol A detection based on the high amplification effect of copper sulfide-multi-walled carbon nanotube (CuS–MWCNT) nanocomposites. The flower-like CuS–MWCNT were successfully synthesized by a simple hydrothermal method accompanied by polyvinylpyrrolidone (PVP). Compared with bare glassy carbon electrode (GCE), CuS–MWCNT modified GCE could amplify the electrochemical signals in about ten times, which was attributed to the synergistic effect of CuS and MWCNT. The MWCNT could increase the specific surface area of electrodes and improve the electrode activity. The integration of CuS could further enhance the electrode conductivity as well as accelerate the electron transfer rate. Raman spectra and transmission electron microscope (TEM) were used to characterize the successful fabrication of CuS–MWCNT nanocomposites and its uniform and monodispersed morphology. Under optimizing conditions, the oxidation currents of bisphenol A via the differential pulse voltammetric (DPV) showed a good linear relationship with its concentration in a wide range of 0.5–100 μM, with a detection limit of 50 nM. This electrochemical sensor of bisphenol A provided a convenient and economical platform with high sensitivity and reproducibility, which had great potential in environmental monitoring.     

A novel electrochemical DNA biosensor construction based on layered CuS–graphene composite and Au nanoparticles

A novel CuS–graphene (CuS-Gr) composite was synthesized to achieve excellent electrochemical properties for application as a DNA electrochemical biosensor. CuS-Gr composite was prepared by a hydrothermal method, in which two-dimensional graphene served as a two-dimensional conductive skeleton to support CuS nanoparticles. A sensitive electrochemical DNA biosensor was fabricated by immobilizing single-stranded DNA (ss-DNA) labeled at the 5′ end using 6-mercapto-1-hexane (HS-ssDNA) on the surface of Au nanoparticles (AuNPs) to form ssDNA-S–AuNPs/CuS-Gr, and hybridization sensing was done in phosphate buffer. Cyclic voltammetry and electrochemical impedance spectroscopy were performed for the characterization of the modified electrodes. Differential pulse voltammetry was applied to monitor the DNA hybridization using an [Fe(CN)₆]^3?/4? solution as a probe. Under optimum conditions, the biosensor developed exhibited a good linear relationship between the current and the logarithm of the target DNA concentration ranging from 0.001 to 1 nM, with a low detection limit of 0.1 pM (3σ/S). The biosensor exhibited high selectivity to differentiate one-base-mismatched DNA and three-base-mismatched DNA. The results indicated that the sensing platform based on CuS-Gr provides a stable and conductive interface for electrochemical detection of DNA hybridization, and could easily be extended to the detection of other nucleic acids. Graphical abstracts

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An electrochemical aptasensor based on cu2+-induced signal amplification strategy for the detection of ochratoxin aEI北大核心CSCD

A novel electrochemical aptasensor based on a Cu2+-induced signal amplification strategy was constructed for the rapid, sensitive and specific detection of ochratoxin A （OTA）. The OTA aptamer with poly （T） was hybridized with the captured DNA probe on the electrode surface. In the presence of Cu2+ and ascorbic acid, the end of poly（T） was used as a template to in situ grow copper nanoclusters （Cu NCs）. In the absence of targeted OTA, the gold electrodes after decorating Cu NCs were immersed into an acidic environment to release Cu2+. After enriching Cu2+ at a potential of − 1.6 V, the strongest current value of copper was recorded by measuring differential pulse voltammetry （DPV）. In the presence of OTA, the OTA aptamer was tightly bound to the target OTA. The OTA aptamer broke away from the electrode to reduce the growth of Cu NCs, resulting in lower DPV current response. This proposed method was employed to detect OTA with linear range from 0.1 to 50.0 ng/mL, and the detection limit was 41.2 pg/mL. The Cu2+-induced electrochemical aptasensor can be further applied in the analysis of target OTA in coffee solution samples. © 2023, Youke Publishing Co.,Ltd. All rights reserved.     

A new electrochemical method for DNA sequence detection with homogeneous hybridization based on host–guest recognition technology

This communication reports on a new electrochemical method to detect the hybridization specificity by using host–guest recognition technique. A hairpin DNA with dabcyl-labeled at its 3′ and NH₂ group at 5′ terminal was combined with CdS nanoparticle to construct a double-labeled probe (DLP), which could selectively hybridize with its target DNA in homogeneous solution. A β-CD modified Poly(N-acetylaniline) glassy carbon electrode was used for capturing the dabcyl label in DLP. When without binding with target DNA, the DLP kept its stem-loop structure which shielded the dabcyl molecule due to the loop of the hairpin DNA and CdS nanoparticle blocking dabcyl enter into the cavity of these β-CD molecules on the electrode. However, in present of complementary sequence, the target-binding DLP was incorporated into double stranded DNA, causing the DLP’s loop-stem structure opened and then the dabcyl was easily captured by the β-CD modified electrode. During electrochemical measurement, the signal from the dissolved Cd²⁺ was used for target DNA quantitative analysis.     

Fluorescent probes for detection of biothiols based on “aromatic nucleophilic substitution-rearrangement” mechanism

Biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) play important roles in physiological processes, and the detection of thiol using fluorescent probes has attracted attention due to their high sensitivity and selectively and invasive on-time imaging. However, the similar structures and reactivity of these biothiols present great challenges for selective detection. This review focused on the the “aromatic nucleophilic substitution-rearrangement (S_NAr-rearrangement) mechanism”, which provided a powerful tool to design fluorescent probes for the discrimination between biothiols. We classify the fluorescent probes according to types of fluorophores, such as difluoroboron dipyrromethene (BODIPY), nitrobenzoxadiazole (NBD), cyanine, pyronin, naphthalimide, coumarin, and so on. We hope this review will inspire exploration of new fluorescent probes for biothiols and other relevant analytes.     

An electrochemical chiral sensor based on amino-functionalized graphene quantum dots/β-cyclodextrin modified glassy carbon electrode for enantioselective detection of tryptophan isomers

An electrochemical chiral sensing platform based on amino-functionalized graphene quantum dots/β-cyclodextrin modified glassy carbon electrode (NH₂-GQDs/β-CD/GCE) was developed for enantioselective detection of tryptophan (Trp) isomers. NH₂-GQDs/β-CD/GCE showed high electrocatalytic activity and good analytical behavior toward the oxidation of Trp isomers. The oxidation peak potentials and oxidation peak currents of Trp isomers at NH₂-GQDs/β-CD/GCE surface were observed by differential pulse voltammetry. NH₂-GQDs/β-CD nanocomposite exhibited different binding ability for two Trp isomers and selectively bonded with d-Trp, resulting in the higher oxidation peak current of d-Trp at NH₂-GQDs/β-CD/GCE surface. Trp isomers exhibited different oxidation peak potentials at NH₂-GQDs/β-CD/GCE surface, and the peak potential separation between l-Trp and d-Trp was around 0.022 V, which was used for the enantioselective detection of Trp isomers. Under the optimum experimental conditions, the oxidation peak currents were linearly dependent on the concentrations of Trp isomers. The linear ranges of l-Trp and d-Trp were all from 1.0 to 30.0 μM with correlation coefficients of 0.9886 and 0.9800, respectively. The detection limits of l-Trp and d-Trp were 0.65 and 0.12 μM (3σ/K), respectively. Such NH₂-GQDs/β-CD/GCE displayed high anti-interference against some physiological substances, good reproducibility and excellent long-term stability toward Trp isomers detection in biomedical applications.     

Magnetic nanomaterial–based electrochemical biosensors for the detection of diverse circulating cancer biomarkers

Electrochemical biosensors are highly compatible with modern advancements in magnetic nanomaterials. In particular, the versatile nature of magnetic nanomaterials as a universal platform for selective isolation of diverse forms of cancer biomarkers in body circulation, is highly synergistic with electrochemical biosensors for elevating biosensing performance to unprecedented levels. Such diverse circulating target biomolecules include cell surface proteins of circulating tumor cells and extracellular vesicles (EVs), as well as circulating tumor nucleic acids (i.e. ctDNA/ctRNA). This focussed review serves to discuss the latest work in the fields of magnetic nanomaterials and electrochemistry to tackle existing analysis challenges of diverse circulating biomarkers in cancer.     

Graphene quantum dot–based electrochemical biosensing for early cancer detection

Electrochemical biosensing systems coupled with graphene quantum dots (GQDs) have demonstrated suitability for cancer diagnostic strategies, particularly to identify the changes facilitating the early phases of tumorigenesis as well as to detect ultralow concentrations of biomarkers that distinguish between normal and malignant cells. GQDs, known as a novel class of zero-dimensional semiconductor nanocrystals, are tiny graphene particles arranged in a honeycomb structure with a size range of 1–50 nm. The size of these GQDs is comparable with the size of biomolecules, thereby providing an ideal platform to study biomolecules such as proteins, cells, and viruses. GQDs are a superior platform for specific and sensitive recognition of cancer biomarkers; they are highly synergistic with electrochemical sensors. This review will shed light on the recent advancements made in the field of GQD-based electrochemical sensors for early cancer detection, with the aim of highlighting the prospects for further development in cancer diagnostics.     

Portable biosensor for quantitative detection of melamine based on CRISPRCas12a and a personal glucose meterEI北大核心CSCD

A CRISPR-Cas system holds great promise as a next-generation biosensing technology for molecular diagnostics. In this paper, a portable biosensor based on the trans-cleavage activity of CRISPR-Cas12a and a personal glucose meter has been developed for quantitative, sensitive and specific detection of melamine. The presence of the target melamine binds to the aptamer, leading to the release of locker DNA. And then, the leasing locker DNA activates the trans-cleavage activity of CRISPR-Cas12a to cleave the single-strand DNA (ssDNA) linker on sucrase-ssDNA modified electrode, releasing a short DNA fragment labeled with sucrase in the resulting solution. The sucrase could further catalyze sucrose to glucose, which could be detected by the PGM. Under the optimized conditions, the increase of PGM signal was relative with the concentration of melamine ranging from 0.1 to 2.5 μmol/L and the limit of detection (LOD) was 37 nmol/L. Moreover, the portable biosensor has strong specificity and can be used for the quantitative detection of melamine in milk samples. © 2023, Youke Publishing Co.,Ltd. All rights reserved.     

Cerium oxide nanofiber–based electrochemical immunosensor for detection of sepsis in biological fluid

Sepsis causes life-threatening complications with the highest burden of death and medical expenses in hospitals worldwide. Despite the progression of targeted therapies for sepsis, the challenge of early diagnosis of sepsis-related biomarkers remains. The analysis of the TNF-α and sTREM-1 in biological fluids provides essential information for effective treatments. In this work, we report developing an electrochemical immunosensor for the rapid detection of TNF-α and sTREM-1 proteins in human plasma samples. First, using the electrospinning process, cerium oxide nanofibers were synthesized. Subsequently, the antibodies corresponding to the targeted proteins are immobilized onto the surface-functionalized working electrodes using NHS/EDC chemistry. The proposed immunosensor’s performance in a biological fluid was assessed using an analytical electrochemistry approach. The limit of detection for the electrochemical immunosensors was 0.51 and 0.41 pg/mL for TNF-α and sTREM-1, respectively, with high selectivity and sensitivity for the use as a point of care device.

     

Electrochemically modified piezoelectric crystal biosensor for detection of Staphylococcus aureus

Electropolymerized o-phenylenediamine film is used as a functional coating for the immobilization of anti-S. aureus antibody on the surface of a gold-plated piezoelectric crystal, and this piezoelectric immunosensor is applied to detect S. aureus. The frequency shift (F = F20s - F380s, Hz) between the frequency at the 20th second (after the addition of sample, F20s) and that at 380 seconds later (F380s) was introduced to construct a calibration graph, and shortening of assay time was achieved. The S. aureus concentrations in the range of 105-109 cells/mL can be detected by this system.     

Fenugreek hydrogel–agarose composite entrapped gold nanoparticles for acetylcholinesterase based biosensor for carbamates detection

A biosensor was fabricated to detect pesticides in food samples. Acetylcholinesterase was immobilized in a novel fenugreek hydrogel–agarose matrix with gold nanoparticles. Transparent thin films with superior mechanical strength and stability were obtained with 2% fenugreek hydrogel and 2% agarose. Immobilization of acetylcholinesterase on the membrane resulted in high enzyme retention efficiency (92%) and a significantly prolonged shelf life of the enzyme (half-life, 55 days). Transmission electron microscopy revealed that, gold nanoparticles (10–20 nm in diameter) were uniformly dispersed in the fenugreek hydrogel–agarose–acetylcholinesterase membrane. This immobilized enzyme-gold nanoparticle dip-strip system detected various carbamates, including carbofuran, oxamyl, methomyl, and carbaryl, with limits of detection of 2, 21, 113, and 236 nM (S/N = 3), respectively. Furthermore, the fabricated biosensor exhibited good testing capabilities when used to detect carbamates added to various fruit and vegetable samples.     

Electrochemiluminescence DNA biosensor based on the use of gold nanoparticle modified graphite-like carbon nitride

The authors describe an electrochemiluminescent (ECL) DNA biosensor that is based on the use of gold nanoparticles (AuNPs) modified with graphite-like carbon nitride nanosheets (g-C₃N₄ NSs) and carrying a DNA probe. In parallel, nanoparticles prepared from gold-platinum (Au/Pt) alloy and carbon nanotubes (CNTs) were placed on a glassy carbon electrode (GCE). Once the g-C₃N₄ NHs hybridize with DNA-modified AuNPs, they exhibit strong and stable cathodic ECL activity. The Au/Pt-CNTs were prepared by electrochemical deposition of Au/Pt on the surface of the CNTs in order to warrant good electrical conductivity. On hybridization of immobilized capture probe (S₁), target DNA (S₂) and labeled signal probe (S₃), a sandwich-type DNA complex is formed that produces a stable ECL emission at a typical applied voltage of ?1.18 V and in the presence of peroxodisulfate. Under optimized conditions, the method has a response to target DNA that is linearly related to the logarithm of its concentration in the range between 0.04 f. and 50 pM, with a 0.018 f. detection limit.

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Graphical abstract Schematic presentation of an electrochemiluminescent DNA biosensor based on two-dimensional graphite-like carbon nitride nanosheets (g-C₃N₄ NSs) hybridized with gold nanoparticles. Abbreviations: MCH: 6-mercapto-1-hexanol; S1: Capture probe; S2: target DNA. 

     

Development of a stable biosensor based on a SiO2 nanosheet–Nafion–modified glassy carbon electrode for sensitive detection of pesticides

SiO₂ nanosheets (SNS) have been prepared by a chemical method using montmorillonite as raw material and were characterized by scanning electron microscopy and X-ray diffraction. SiO₂ nanosheet–Nafion nanocomposites with excellent conductivity, catalytic activity, and biocompatibility provided an extremely hydrophilic surface for biomolecule adhesion. Chitosan was used as a cross-linker to immobilize acetylcholinesterase (AChE), and Nafion was used as a protective membrane to efficiently improve the stability of the AChE biosensor. The AChE biosensor showed favorable affinity for acetylthiocholine chloride and catalyzed the hydrolysis of acetylthiocholine chloride with an apparent Michaelis–Menten constant of 134 μM to form thiocholine, which was then oxidized to produce a detectable and fast response. Based on the inhibition by pesticides of the enzymatic activity of AChE, detection of the amperometric response from thiocholine on the biosensor is a simple and effective way to biomonitor exposure to pesticides. Under optimum conditions, the biosensor detected methyl parathion, chlorpyrifos, and carbofuran at concentrations ranging from 1.0?×?10^?12 to 1?×?10^?10?M and from 1.0?×?10^?10 to 1?×?10^?8?M. The detection limits for methyl parathion, chlorpyrifos, and carbofuran were 5?×?10^?13?M. The biosensor developed exhibited good sensitivity, stability, reproducibility, and low cost, thus providing a new promising tool for analysis of enzyme inhibitors.