Electrochemical Biosensor For Sensitive Detection Research Articles

An electrochemical biosensor for sensitive detection of live Salmonella in food via MXene amplified methylene blue signals and electrostatic immobilization of bacteriophages.

Anovel bacteriophage-targeted electrochemical biosensor designed for accurate and quantitative detection of live Salmonella in food samplesis presented. The biosensor is simply constructed by electrostatic immobilizing bacteriophages on MXene-nanostructured electrodes. MXene, renowned for its high surface area, biocompatibility, and conductivity, serves as an ideal platform for bacteriophage immobilization. This allows for a high-density immobilization of bacteriophage particles, achieving approximately 71 pcs μm-2. Remarkably, the bacteriophages immobilized MXene nanostructured electrodes still maintain their viability and functionality, ensuring their effectiveness in pathogen detection. Therefore, the proposed biosensor exhibited enhanced sensitivity with a low limit of detection (LOD) of 5CFUmL-1. Notably, the biosensor shows excellent specificity in the presence of other bacteria that commonly contaminate food and can distinguish live Salmonella from a mixed population. Furthermore, it is applicable in detecting live Salmonella in food samples, which highlights its potential in food safety monitoring. This biosensor offers simplicity, convenience, and suitability for resource-limited environments, making it a promising tool for on-site monitoring of foodborne pathogenic bacteria.

A Novel Enzyme-Based Electrochemical Biosensor for Sensitive Detection of Hydrogen Peroxide Based on the Fluorescent Peptide Self-Assembled Nanomaterials

A Novel Enzyme-Based Electrochemical Biosensor for Sensitive Detection of Hydrogen Peroxide Based on the Fluorescent Peptide Self-Assembled Nanomaterials

An electrochemical biosensor based on mild reduction-activated CRISPR/Cas12a system for sensitive detection of circulating tumor cells

Circulating tumor cell (CTC) has been a valuable biomarker for the diagnosis of breast cancer, while folate receptor is a kind of cell surface receptor glycoprotein which is overexpressed in breast cancer. In this work, we have designed and fabricated an electrochemical biosensor for sensitive detection of folate receptor-positive CTCs based on mild reduction assisted CRISPR/Cas system. Specifically, folate functionalized magnetic beads are firstly prepared to capture CTCs owing to the strong affinity between folate and the folate receptors on the surface of cells. Then, the cell membranes are treated by mild reduction so as to expose a large number of free sulfhydryl groups, which can be coupled with maleimide-DNA to introduce the signal amplified CRISPR/Cas12a system. After the trans-cleavage activity of CRISPR/Cas12a is activated, the long chain DNA modified with electroactive molecules methylene blue can be randomly cleaved into short DNA fragments, which are then captured on the graphite electrode through the host-guest recognition with cucurbit [7]uril, generating highly amplified electrochemical signal corresponding to the number of CTCs. The electrochemical biosensor not only demonstrates the sensitivity with a low detection limit of 2 cells/mL, but also highlights its excellent selectivity and stability in complex environment. Therefore, our biosensor may provide an alternative tool for the analysis of CTCs.

A sensitive electrochemical biosensor for detection of carbaryl based on hollow covalent-organic frameworks-gold nanoparticles nanospheres

Carbaryl as an important insecticide is always used in agricultures to achieve higher yields. So, rapid detection of carbaryl residues in agricultural products is very necessary due to its potential harm to human beings. Herein, a hollow covalent-organic frameworks (HCOFTFPB-DBD) gold nanoparticles (AuNPs) nanospheres was used to construct a sensitive electrochemical carbaryl biosensor. The surface of electrode modified by HCOFTFPB-DBD-AuNPs nanospheres was negatively charged and repelled the [Fe(CN)6]3-/4-. The acetylcholinesterase (AChE) immobilized on HCOFTFPB-DBD-AuNPs nanospheres catalyzed the hydrolysis of acetylcholine chloride to thiocholine (TCh). The obtained positively charged TCh was adsorbed on the electrode surface by Au-S, which made the electrode surface positively charged to adsorb the negatively charged [Fe(CN)6]3-/4-, showing enhanced oxidation current of [Fe(CN)6]3-/4-. After carbaryl was added, the oxidation current of [Fe(CN)6]3-/4- deceased because ChE activity were inhibited by carbaryl. So, the sensitive detection of carbaryl was achieved at a low potential, which resulted in a high selectivity. The biosensor had a detection limit of 0.38 μM, a linear range of 1.10 μM-40.0 μM, a sensitivity of 0.00863 mA μM−1 and better performance in actual sample.

A novel ACE2-Based electrochemical biosensor for sensitive detection of SARS-CoV-2

SARS-CoV-2 emerged in late 2019 and quickly spread globally, resulting in significant morbidity, mortality, and socio-economic disruptions. As of now, collaborative global efforts in vaccination and the advent of novel diagnostic tools have considerably curbed the spread and impact of the virus in many regions. Despite this progress, the demand remains for low-cost, accurate, rapid and scalable diagnostic tools to reduce the influence of SARS-CoV-2. Herein, the angiotensin-converting enzyme 2 (ACE2), a receptor for SARS-CoV-2, was immobilized on two types of electrodes, a screen-printed gold electrode (SPGE) and a screen-printed carbon electrode (SPCE), to develop electrochemical biosensors for detecting SARS-CoV-2 with high sensitivity and selectivity. This was achieved by using 1H, 1H, 2H, 2H-perfluorodecanethiol (PFDT) and aryl diazonium salt serving as linkers for SPGEs and SPCEs, respectively. Once SARS-CoV-2 was anchored onto the ACE2, the interaction of the virus with the redox probe was analyzed using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Aryl diazonium salt was observed as a superior linker compared to PFDT due to its consistent performance in the modification of the SPCEs and effective ACE2 enzyme immobilization. A distinct pair of redox peaks in the cyclic voltammogram of the biosensor modified with aryl diazonium salt highlighted the redox reaction between the functional groups of SARS-CoV-2 and the redox probe. The sensor presented a linear relationship between the redox response and the logarithm of SARS-CoV-2 concentration, with a detection limit of 1.02 × 106 TCID50/mL (50% tissue culture infectious dose). Furthermore, the biosensor showed remarkable selectivity towards SARS-CoV-2 over H1N1virus.

A Multienzyme Reaction-Mediated Electrochemical Biosensor for Sensitive Detection of Organophosphorus Pesticides.

Ethephon (ETH), a commonly employed growth regulator, poses potential health risks due to its residue in fruits and vegetables, leading to both acute and subchronic toxicity. However, the detection accuracy of ETH is compromised by the color effects of the samples during the detection process. In this work, a multienzyme reaction-mediated electrochemical biosensor (MRMEC) was developed for the sensitive, rapid, and color-interference-resistant determination of ETH. Nanozymes Fe3O4@Au-Pt and graphene nanocomplexes (GN-Au NPs) were prepared as catalysts and signal amplifiers for MRMEC. Acetylcholinesterase (AChE), acetylcholine (ACh), and choline oxidase (CHOx) form a cascade enzyme reaction to produce H2O2 in an electrolytic cell. Fe3O4@Au-Pt has excellent peroxidase-like activity and can catalyze the oxidation of 3,3',5,5'-tetramethvlbenzidine (TMB) in the presence of H2O2, resulting in a decrease in the characteristic peak current of TMB. Based on the inhibitory effect of ETH on AChE, the differential pulse voltammetry (DPV) current signal of TMB was used to detect ETH, offering the limit of detection (LOD) of 2.01 nmol L-1. The MRMEC method effectively analyzed ETH levels in mangoes, showing satisfactory precision (coefficient of variations, 2.88-15.97%) and recovery rate (92.18-110.72%). This biosensor holds promise for detecting various organophosphorus pesticides in food samples.

Development of a regenerable dual-trigger tripedal DNA walker electrochemical biosensor for sensitive detection of microRNA-155

Since microRNAs (miRNAs) are valuable biomarkers for disease diagnosis and prognosis, the pursuit of enhanced detection sensitivity through signal amplification strategies has emerged as a prominent focus in low-abundance miRNA detection research. DNA walkers, as dynamic DNA nanodevice, have gained significant attention for their applications as signal amplification strategies. To overcome the limitations of unipedal DNA walkers with a restricted signal amplification efficiency, there is a great need for multi-pedal DNA walkers that offer improved walking and signal amplification capabilities. Here, we employed a combination of catalytic hairpin assembly (CHA) and APE1 enzymatic cleavage reactions to construct a tripedal DNA walker, driving its movement to establish a cascade signal amplification system for the electrochemical detection of miRNA-155. The biosensor utilizes tumor cell-endogenous microRNA-155 and APE1 as dual-trigger for DNA walker formation and walking movement, leading to highly efficient and controllable signal amplification. The biosensor exhibited high sensitivity, with a low detection limit of 10 pM for microRNA-155, and successfully differentiated and selectively detected microRNA-155 from other interfering RNAs. Successful detection in 20 % serum samples indicates its potential clinical application. In addition, we harnessed strand displacement reactions to create a gentle yet efficient electrode regeneration strategy, to addresses the time-consuming challenges during electrode modification processes. We have successfully demonstrated the stability of current signals even after multiple cycles of electrode regeneration. This study showcased the high-efficiency amplification potential of multi-pedal DNA walkers and the effectiveness and versatility of strand displacement in biosensing applications. It opens a promising path for developing regenerable electrochemical biosensors. This regenerable strategy for electrochemical biosensors is both label-free and cost-effective, and holds promise for detecting various disease-related RNA targets beyond its current application.

Wash- and Separation-Free Electrochemical Detection of Proteases

Proteases play crucial roles in biological systems, including digestion, catabolism, and cell signaling. Indirect detection of Porphyromonas gingivalis in saliva, based on proteolytic cleavage by an Arg-specific gingipain (Arg-gingipain) protease, has traditionally been used for simple, initial diagnosis of periodontitis. To accurately detect P. gingivalis using a point-of-care format, development of a simple biosensor that can measure the exact concentration of P. gingivalis is required. However, electrochemical detection in saliva is challenging due to the presence of various interfering electroactive species in different concentrations. Here, we report a washing- and separation-free electrochemical biosensor for sensitive detection of P. gingivalis in saliva. Glycine–proline–arginine conjugated with 4-aminophenol (AP) was used as an electrochemical substrate for a trypsin-like Arg-gingipain, and glycylglycine was used to increase the Arg-gingipain activity. The electrochemical signal of AP was increased using electrochemical–chemical (EC) redox cycling involving an electrode, AP, and tris(2-carboxyethyl)phosphine, and the electrochemical charge signal was corrected using the initial charge obtained before a 15 min incubation period. The EC redox cycling combined with the matrix-corrected signal facilitated a high and reproducible signal without requiring washing and separation steps. The proteolytic cleavage of the electrochemical substrate was specific to P. gingivalis. The calculated detection limit for P. gingivalis in artificial saliva was 5 × 105 colony-forming units/mL, and the concentration of P. gingivalis in human saliva could be measured. The developed biosensor can be used as an initial diagnosis method to distinguish between healthy people and patients with periodontal diseases.References S. Park, K. Park, H. S. Na, J. Jung, H. Yang, Anal. Chem. 93, 5644 (2021) S. Park, J. Shin, J. Kwon, W. Lee, J. Kim, G. Kim, J. M. Joo, H. Yang, ACS Sens. 6, 1305 (2021) S. Park, G. Kim, J. Seo, H. Yang, Anal. Chem. 88, 11995 (2016)S. Park, Y. M. Shin, J. Seo, J.-J. Song, H. Yang, Analyst 141, 2481 (2016)S. Park, Y. Shin, J.-J. Song, H. Yang, Biosens. Bioelectron. 72, 211 (2015)S. Park, H. Yang, Analyst, 139, 4051 (2014)

A dual-amplification mode and Cu-based metal-organic frameworks mediated electrochemical biosensor for sensitive detection of microRNA

In this work, we developed a novel label-free and highly sensitive electrochemical (EC) biosensor for detection of microRNA (miRNA), which was based on the target-triggered and the Cu-based metal-organic frameworks (Cu-MOFs) mediated CHA-HCR dual-amplification process. Initially, the target miRNA triggered the catalytic hairpin assembly (CHA) process of hairpin DNA 1 (H1) and hairpin DNA 2 (H2) to produce massive double-stranded DNA (H1/H2) which could hybridize with the single-stranded DNA 1 (P1) to form capture probe (P1/H1/H2) on electrode surface, realizing the first amplification of input signals. Subsequently, hybridization chain reaction (HCR) between signal probe (H3-AuNPs/Cu-MOFs) and hairpin DNA 4 (H4) was activated by above capture probe (P1/H1/H2), leading to the second amplification of input signals. After the HCR process, numerous Cu-MOFs were immobilized on the electrode surface, which brought out the enhancement of electrochemical signals generating by Cu-MOFs. Herein, Cu-MOFs not only offered the lager surface area to decorate with gold nanoparticles (AuNPs) and hairpin DNA 3 (H3), but also served as the signal probe (H3-AuNPs/Cu-MOFs) to produce electrochemical signals by hybridizing with the capture probe on electrode surface. Therefore, the ingenious design of CHA-HCR-Cu-MOFs scheme enables the sensitive analysis of microRNA-21 (miR-21) with a broad linear range from 0.1 fM to 100 pM and a lower LOD of 0.02 fM. In addition, the outstanding specificity of this sensing strategy allows it successfully to be applied for determining miR-21 in real biological samples.

Ratiometric electrochemical biosensor based on silver nanoparticles coupled with walker amplification for sensitive detection of microRNA

A novel ratiometric electrochemical biosensor for sensitive detection of microRNA was developed by using walker amplification technique. Ag nanoparticles (NPs) and methylene blue (MB) were used as signal probe and as reference, respectively. Firstly, the present target (miR-155) hybridized with DNA2 to release walker (DNA1), and then the walker hybridized with DNA3 to form activated DNA enzyme, inducing cycling shearing of DNA3 in the presence of Mn2+, thus a large number of product chains (S1) were produced. Then, S1 opened hairpin DNA (HP1) labeled with MB on the electrode, initiating enzyme-assisted cyclic clipping to generate abundant capture DNA. Thus numerous signal probes (DNA HP2-Ag NPs) were linked for electrochemical detection of target. As the electrochemical signal of MB at capture DNA was constant, so it was used as internal reference. Thus the signal ratio of Ag NPs to MB was used for detection, which can greatly reduce the background. The relation between the IAg/IMB and the concentration of target was 10−13-10−6 M, showing wide linear detection range. The biosensor displayed simple design, excellent sensitivity and high specificity for microRNA, showing enormous application prospect in bioanalysis and disease diagnosis fields.

A novel electrochemical biosensor for sensitive detection of non-small cell lung cancer ctDNA using NG-PEI-COFTAPB-TFPB as sensing platform and Fe-MOF for signal enhancement

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer with poor survival, in part because that half of the cases are already in advanced stage when they are diagnosed. In response to this issue, the present work constructed a novel electrochemical biosensor for sensitive detection of circulating tumor DNA (ctDNA) related to NSCLC. Specifically, polyethyleneimine (PEI) and covalent organic framework (COFTAPB-TFPB) functionalized nitrogen-doped graphene (NG) nanocomposite (NG-PEI-COFTAPB-TFPB) was designed and employed as sensing platform for the first time. NG-PEI-COFTAPB-TFPB with porous structure and good conductivity showed a synergistic effect on promoting electron transfer, which could provide large specific surface area and active sites to increase the immobilization of capture probe (CP). In addition, gold nanoparticles (AuNPs) decorated Fe-based metal-organic framework (Fe-MOF) were labeled with signal probe (SP) to form tracer label, which would attach to the electrode surface by sandwich hybridization of target probe (TP) with CP and SP. Consequently, FeIII from Fe-MOF could react with K4[Fe(CN)6] to form electroactive prussian blue, generating a significantly amplified electrochemical detection signal. Under optimum conditions, the proposed DNA biosensor displayed a broad linear range for ctDNA determination from 100 fM to 100 nM with a detection limit of 7.65 fM. Moreover, the biosensor was successfully fabricated to assay ctDNA in human serum, indicating the potential for cancer diagnosis. More importantly, the high sensitivity and satisfactory stability of this biosensor make it a promising method to detect other biomolecules by changing the corresponding sequences of CP and SP.

Washing- and Separation-Free Electrochemical Detection of Porphyromonas gingivalis in Saliva for Initial Diagnosis of Periodontitis.

Indirect detection of Porphyromonas gingivalis in saliva, based on proteolytic cleavage by an Arg-specific gingipain (Arg-gingipain), has traditionally been used for simple, initial diagnosis of periodontitis. To accurately detect P. gingivalis using a point-of-care format, development of a simple biosensor that can measure the exact concentration of P. gingivalis is required. However, electrochemical detection in saliva is challenging due to the presence of various interfering electroactive species in different concentrations. Here, we report a washing- and separation-free electrochemical biosensor for sensitive detection of P. gingivalis in saliva. Glycine-proline-arginine conjugated with 4-aminophenol (AP) was used as an electrochemical substrate for a trypsin-like Arg-gingipain, and glycylglycine was used to increase the Arg-gingipain activity. The electrochemical signal of AP was increased using electrochemical-chemical (EC) redox cycling involving an electrode, AP, and tris(2-carboxyethyl)phosphine, and the electrochemical charge signal was corrected using the initial charge obtained before a 15 min incubation period. The EC redox cycling combined with the matrix-corrected signal facilitated a high and reproducible signal without requiring washing and separation steps. The proteolytic cleavage of the electrochemical substrate was specific to P. gingivalis. The calculated detection limit for P. gingivalis in artificial saliva was 5 × 105 colony-forming units/mL, and the concentration of P. gingivalis in human saliva could be measured. The developed biosensor can be used as an initial diagnosis method to distinguish between healthy people and patients with periodontal diseases.

Construction of a ternary nano-architecture based graphene oxide sheets, toward electrocatalytic determination of tumor-associated anti-p53 autoantibodies in human serum

Almost 13% of all death in the world is related to cancer. One of the major reasons for failing cancer treatment is the late diagnosis of the tumors. Thus, diagnosis at the early stages could be vital for the treatment. Serum autoantibodies, as tumor markers, are becoming interesting targets due to their medical and biological relevance. Among them, anti-p53 autoantibody in human sera is found to be involved in a variety of cancers. Regarding this issue, a novel and sensitive electrochemical biosensor for detection of anti-p53 autoantibody has been developed. For this purpose, a nanocomposite including thionine (as an electron transfer mediator)/chitosan/nickel hydroxide nanoparticles/electrochemically reduced graphene oxide (Th-CS-Ni(OH)2NPs–ERGO) as a support platform was fabricated on the surface of glassy carbon electrode via a layer-by-layer manner and characterized through common electrochemical and imaging techniques. Then, p53-antigen was immobilized on the nanocomposite and used in an indirect immunoassay with horseradish peroxidase (HRP)-conjugated secondary antibody and H2O2 as the substrate, following the typical Michaelis–Menten kinetics. Under optimized condition, two techniques, including differential Pulse Voltammetry (DPV) and Electrochemical Impedance Spectroscopy (EIS) as a label free technique, applied for the biomarker detection. The linear ranges and LODs were obtained 0.1–500 pg mL−1 and 0.001 pg mL−1 using DPV and 5–150 pg mL−1 and 0.007 pg mL−1 using EIS, respectively. Furthermore, the proposed biosensor displayed satisfying stability, selectivity, and reproducibility. According to the results, the presented protocol is promising to develop other electrochemical biosensors.

Electrochemical biosensor for sensitive detection of Hg2+ baesd on clustered peonylike copper-based metal-organic frameworks and DNAzyme-driven DNA Walker dual amplification signal strategy

A sensitive electrochemical biosensor was constructed for Hg2+ detection based on peonylike Cu-MOFs in situ growth of PtPd NPs bimetallic label S1 and Mg2+-dependent DNAzyme-driven DNA Walker dual amplification signal strategy. The hairpin DNA (HP) and signal label Cu-MOFs@PtPd NPs/S1 were first used to self-assemble on the gold nanorods/poly (diallyldimethylammonium chloride) functionalized graphene (AuNRs/PDDA-Gr) modified electrode, at this time, Cu ions can undergo a valence change to produce a larger initial signal. Here, we designed S2 that can perform dual functions and contains two sequences, on was a substrate sequence of the Mg2+-dependent DNAzyme and the other was a sequence complementary to HP. In the presence of target Hg2+, HP was opened and hybridized with enzymatically sequenced DNA Walker (S2) to preferentially form thymine-Hg2+-thymine (T-Hg2+-T). Then, DNA Walker exhibited catalytic activity of DNAzyme in the presence of Mg2+ to continuously cleave Cu-MOFs@PtPd NPs/S1, resulting in a decrease of electrochemical signal. Under optimal conditions, the change of current was linearly related to the negative logarithm of the Hg2+ concentration in the detection range of 0.001–100 nM with a low detection limit of 0.52 pM. Moreover, the proposed aptasensor was successfully applied in detection of milk powder samples.

Horseradish Peroxidase-Immobilized Graphene Oxide-Chitosan Gold Nanocomposites as Highly Sensitive Electrochemical Biosensor for Detection of Hydrogen Peroxide

The generation of fast electrochemical response with high sensitivity is a significant parameter for enzymatic biosensors. However, establishing nanocomposite based modified electrode with fast electron shuttling between enzymes and the electrode surface for determination of hydrogen peroxide (H2O2) is highly challenging. Herein, the present work aims to develop second generation horseradish peroxidase (HRP) biosensors using Au nanochains dropcasted over electrochemically reduced graphene oxide-chitosan (ERGO-CHIT), a bio-nanocomposite film modified glassy carbon electrode (GCE) for reduction of H2O2 is demonstrated. The experimental conditions including effect of pH, loading of enzyme on the electrode surface and concentration of redox mediator as electrolyte were optimized. As a result, the HRP/Au/ERGO-CHIT/GCE electrode shows a larger enhancement in cathodic current signal with sharp peak response for reduction of H2O2, which can be attributed to the presence of Au nanochains on the modified electrode which improves the electron transfer between heme (Fe2+/Fe3+) center of enzymes on the electrode and the redox mediator in the electrolyte solution. The presence of HQ redox mediator in the electrolyte solution have provided stable peak response and offered more beneficiary in lowering the operating potential for the detection of H2O2 (−0.1 V), thereby reducing the influence from interference species. From the amperometric measurements, the HRP/Au/ERGO-CHIT/GCE modified electrode revealed high sensitivity (368.01 μA mM−1 cm−2) and possesses wide linear range (0.01 to 6.31 mM) which is mainly due to the high surface area and conductivity offered by Au nanochains which are located between ERGO and HRP. The resultant HRP/Au/ERGO-CHIT/GCE was found to possess good operational stability, high reproducibility, repeatability with low detection limits (4 μM), and thus it could be applicable for sensitive and rapid responsive detection of H2O2 in biological, clinical and environmental samples.

Electrochemical biosensor for telomerase activity assay based on HCR and dual interaction of the poly-adenine DNA with Au electrode and Ce-Ti dioxide nanorods

Abstract A new electrochemical biosensor for sensitive detection of telomerase activity based on the hybridization chain reaction and the dual interaction of the poly-adenine (polyA) DNA with Au electrode and Ce-Ti dioxide nanorods (Ce-Ti NRs) has been constructed. Deoxynucleotide triphosphates (dNTPs) can be incorporated at the 3´-OH of TS primer by telomerase to generate the extension products with telomeric repeats (TTAGGG)n (TEP), which can hybridize with hairpin (HP) DNA and open it to form a duplex DNA with a short poly-adenine DNA single-stranded tail (s1). The duplex DNA can be recognized and selectively cleaved into single-stranded DNA fragment s1 and TEP by exonuclease III (Exo III). The released TEP can then hybridize with the HP again to initiate the s1 recycling process, which will result in the massive release of s1 fragments from HP. The s1 fragments can be immobilized on the Au electrode surface through the interaction between polyA and Au electrode on one hand. On the other hand, Ce-Ti NRs can be adsorbed on the Au electrode surface by the interaction between Ce-Ti NRs and the phosphate groups of s1, resulting in the decrease of the differential pulse voltammetry (DPV) current of the redox probe. The higher activity of telomerase, more HP can be hybridized and cleaved, more poly-adenine and Ce-Ti NRs can be immobilized on electrode surface, and remarkable decrease of the DPV signal can be observed. The biosensor exhibited good sensitivity toward telomerase activity in HeLa cells.

Amperometric lactate nanobiosensor based on reduced graphene oxide, carbon nanotube and gold nanoparticle nanocomposite.

A sensitive amperometric method is reported for the determination of lactate. A platinum electrode was modified with a composite prepared from reduced graphene oxide (rGO), carbon nanotubes (CNTs) and gold nanoparticles. The composite was synthesized by the in-situ reduction of gold(III) ions on the GO-CNT hybrid. Triple composite components showed synergistic effects on the enzyme loading, electrocatalytic activity and electron transfer between receptor and electrode surface. The amperometric lactate sensor was obtained by immobilization of lactate oxidase (LOx) on the modified electrode. LOx catalyzes the conversion of lactate into pyruvate and hydrogen peroxide. The generated hydrogen peroxide is simultaneously involved in the oxidation reaction, which is associated with the electron production. These electrons act as amperometric signal generators. At the low potential of 0.2V, the nanobiosensor shows a relatively wide linear analytical range (i.e., 0.05-100mM of lactate) with high electrochemical sensitivity (35.3μA mM-1 cm-2) and limit of detection of 2.3μM. The sensor is stable, repeatable and reproducible. It is a highly sensitive tool for the detection of lactate in biological samples under both normoxic and hypoxic conditions. Graphical abstract Schematic representation of an electrochemical biosensor for sensitive detection of lactate in biological and food samples based on reduced graphene oxide-carbon nanotube-gold nanocomposite, as a surface modifier, and lactate oxidase, as a bioreceptor.

A Highly Sensitive Electrochemical Biosensor Based on Carbon Black and Gold Nanoparticles Modified Pencil Graphite Electrode for microRNA-21 Detection

This work aims to develop cost-effective, simple and sensitive electrochemical biosensor for detection of microRNA-21. The combination of carbon black (CB) and gold nanoparticles (AuNPs) as nanohybrid was employed for the first time as a platform for microRNA-21 biosensor fabrication. The developed biosensor is based on the immobilization of thiolated capture probe (complementary sequence of microRNA-21) labeled with methylene blue on the surface of the pencil graphite electrode modified with CB/AuNPs nanohybrid. After hybridization with the target microRNA-21, the orientation of the labeled capture probe changed which causes a decrease of the response of methylene blue oxidation. Differential pulse voltammetry was used for monitoring the methylene blue response before and after hybridization. Under the optimal conditions, the developed biosensor was characterized using differential pulse voltammetry (DPV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The detection of microRNA-21 was carried out using a DPV. A wide linear range was obtained between 2.9 fM and 0.7 µM of microRNA-21. The calculated limit of detection was 1 fM of microRNA-21. This approach shows a good reproducibility, stability and an excellent selectivity. The proposed biosensor was used for microRNA-21 analysis in serum and a satisfactory result was obtained.

An electrochemical biosensor for prostate cancer biomarker detection using graphene oxide-gold nanostructures.

In this paper, a most sensitive electrochemical biosensor for detection of prostate-specific antigen (PSA) was designed. To reach the goal, a sandwich type electrode composed of reduced graphene oxide/ gold nanoparticles (GO/AuNPs), Anti-Total PSA monoclonal antibody, and anti-Free PSA antibody was assembled. The functionalized materials were thoroughly characterized by atomic force microscope spectroscopy, transmission electron microscopy, and X-ray diffraction techniques. The electrochemical properties of each of the modification step were evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The results presented that the proposed biosensor possesses high sensitivity toward total and free PSA. Furthermore, the fabricated biosensor revealed an excellent selectivity for PSAin comparison to the other tumor markers such as BHCG, Alb, CEA, CA125, and CA19-9. The limit of detection for the proposed electrochemical biosensor was estimated to be around 0.2 and 0.07ng/mL for total and free PSA antigen, respectively.

Highly Sensitive Electrochemical Detection of Hydrogen Peroxide Based on Polyethyleneimine-Au Nanoparticles-Zinc Protoporphyrin

A novel electrochemical biosensor for sensitive detection of hydrogen peroxide (H2O2) was developed on the basis of polyethyleneimine-Au nanoparticles-zinc protoporphyrin (PEI-AuNPs-ZnPP). In this approach, PEI-AuNPs-ZnPP was prepared by coupling carboxyl of ZnPP with amino of PEI-AuNPs. Transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR) were used to characterize the formation of PEI-AuNPs-ZnPP. Under optimal conditions, this strategy showed a good sensitivity for H2O2 detection with a low detection limit of 0.0861 pM. What's more, this biosensor can be successfully applied for the measurement of H2O2 in human serum samples. These results suggested that PEI-AuNPs-ZnPP could be a good candidate for H2O2 detection in complicated biological samples.