Surface Of Screen-printed Electrode Research Articles

Effect of Aspect Ratio of a Gold-Nanorod-Modified Screen-Printed Carbon Electrode for Carbaryl Detection in Three Different Samples of Vegetables.

In this study, three different sizes of gold nanorods (AuNRs) were synthesized using the seed-growth method by adding various volumes of AgNO3 as 400, 600, and 800 μL into the growth solution of gold nanoparticles. Three different sizes of AuNRs were then characterized using UV-vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns, and atomic force microscopy (AFM) to investigate the surface morphology, topography, and aspect ratios of each synthesized AuNR. The aspect ratios from the histogram of size distributions of three AuNRs as 2.21, 2.53, and 2.85 can be calculated corresponding to the addition of AgNO3 volumes of 400, 600, and 800 μL. Moreover, each AuNR in three different aspect ratios was drop-cast onto the surface of a commercial screen-printed carbon electrode (SPCE) to obtain three different SPCE-modified AuNRs (SPCE-A400, SPCE-A600, and SPCE-A800, respectively). All SPCE-modified AuNRs were then evaluated for their electrochemical behavior using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques and the highest electrochemical performance was shown as the order of magnitude of SPCE-A400 > SPCE-A600/SPCE-A800. The reason for the highest electrocatalytic activity of SPCE-A400 might be due to the smallest particle size and uniform distribution of AuNRs ∼ 2.2, which enhanced the charge transfer, thus providing the highest electroactive surface area (0.6685 cm2) compared to other electrodes. These results also confirm that the sensing mechanism for all SPCE-modified AuNRs is controlled by diffusion phenomena. In addition, the optimum pH was obtained as 4 for carbaryl detection for all SPCE-modified AuNRs with the highest current shown by SPCE-A400. Furthermore, SPCE-A400 has the highest fundamental parameters (surface coverage, catalytic rate constant, electron transfer rate constant, and adsorption capacity) for carbaryl detection, which were investigated using cyclic voltammetry and chronoamperometric techniques. The electroanalytical performances of all SPCE-modified AuNRs for carbaryl detection were also investigated with SPCE-A400 displaying the best performance among other electrodes in terms of its linearity (0.2-100 μM), limit of detection (LOD) ∼ 0.07 μM, and limit of quantification (LOQ) ∼ 0.2 μM. All SPCE-modified AuNRs were also subsequently evaluated for their stability, reproducibility, and selectivity in the presence of interfering species such as NaNO2, NH4NO3, Zn(CH3CO2)2, FeSO4, diazinon, and glucose and show reliable results as depicted from %RSD values less than 3%. At last, all SPCE-modified AuNRs have been employed for carbaryl detection using a standard addition technique in three different samples of vegetables (cabbage, cucumber, and Chinese cabbage) with its results (%recovery ≈ 100%) within the acceptable analytical range. In conclusion, this work demonstrates the great potential of a disposable device based on an AuNR-modified SPCE for rapid detection and high sensitivity in monitoring the concentration of carbaryl as a residual pesticide in vegetable samples.

Redox probe-free electrochemical immunosensor utilizing electropolymerized melamine on reduced graphene oxide for the point-of-care diagnosis of gastric cancer

Pepsinogen I (PG I) is a biomarker that plays a crucial role in the diagnosis of gastric cancer. The development of biosensor to monitor PG I overexpression in serum is crucial for early gastric cancer diagnosis, offering a less invasive alternative to the costly and uncomfortable gastroscopy procedure. This study presents a cost-efficient, scalable and disposable label-free biosensing strategy for detecting PG I, utilizing a redox-active polymelamine electrodeposited on a reduced graphene oxide screen-printed electrode surface (PM-rGO/SPE). Under optimized conditions, the conducting polymer PM was deposited on the rGO/SPE via a potentiodynamic method. The structural and morphological features of PM-rGO/SPE were analyzed with the assistance of Raman and Scanning Electron Microscopy analysis. Specific monoclonal anti-PG I antibodies were immobilized on the in situ prepared redox-active layer via EDC/NHS chemistry to develop a novel electrochemical immunosensor. Unlike the traditional immunosensing strategies which utilizes external redox probe solution for measuring the signal, the developed configuration allowed for redox-probe free monitoring of current changes of the redox active PM resulting from the formation of the immunocomplex on the electrode surface. Utilizing this method, PG I detection spanned a clinically relevant concentration range of 0.01–200 ng/mL, with a low limit of detection at 9.1 pg/mL. The electrochemical immunosensor demonstrated specificity against other biomarkers such as PDCD1, ErBb2, and CD28 with negligible interference. The immunosensor exhibited excellent recovery capabilities for PG I detection in serum samples. These findings underscore the potential of the PM-rGO/SPE immunosensor as a point-of-care diagnostic tool for gastric cancer.

Carbon Nanostructured Immunosensing of Anti-SARS-CoV-2 S-Protein Antibodies.

The rampant spread and death rate of the recent coronavirus pandemic related to the SARS-CoV-2 respiratory virus have underscored the critical need for affordable, portable virus diagnostics, particularly in resource-limited settings. Moreover, efficient and timely monitoring of vaccine efficacy is needed to prevent future widespread infections. Electrochemical immunosensing poses an effective alternative to conventional molecular spectroscopic approaches, offering rapid, cost-effective, sensitive, and portable electroanalysis of disease biomarkers and antibodies; however, efforts to improve binding efficiency and sensitivity are still being investigated. Graphene quantum dots (GQDs) in particular have shown promise in improving device sensitivity. This study reports the development of a GQD-functionalized point-of-contamination device leveraging the selective interactions between SARS-CoV-2-specific Spike (S) Protein receptor binding domain (RBD) antigens and IgG anti-SARS-CoV-2-specific S-protein antibodies at screen-printed carbon electrode (SPCE) surfaces. The immunocomplexes formed at the GQD surfaces result in the interruption of the redox reactions that take place in the presence of a redox probe, decreasing the current response. Increased active surface area, conductivity, and binding via EDC/NHS chemistry were achieved due to the nanomaterial inclusion, with 5 nm, blue luminescent GQDs offering the best results. GQD concentration, EDC/NHS ratio, and RBD S-protein incubation time and concentration were optimized for the biosensor, and inter- and intra-screen-printed carbon electrode detection was investigated by calibration studies on multiple and single electrodes. The single electrode used for the entire calibration provided the best results. The label-free immunosensor was able to selectively detect anti-SARS-CoV-2 IgG antibodies between 0.5 and 100 ng/mL in the presence of IgM and other coronavirus antibodies with an excellent regression of 0.9599. A LOD of 2.028 ng/mL was found, offering comparable findings to the literature-reported values. The detection sensitivity of the sensor is further compared to non-specific IgM antibodies. The developed GQD immunosensor was compared to other low-oxygen content carbon nanomaterials, namely (i) carbon quantum dot (CQD), (ii) electrochemically reduced graphene oxide, and (iii) carbon black-functionalized devices. The findings suggest that improved electron transfer kinetics and increased active surface area of the CNs, along with surface oxygen content, aid in the detection of anti-SARS-CoV-2 IgG antibodies. The novel immunosensor suggests a possible application toward monitoring of IgG antibody production in SARS-CoV-2-vaccinated patients to study immune responses, vaccine efficacy, and lifetime to meet the demands for POC analysis in resource-limited settings.

Electrochemical study of N-acetyl neuraminic acid at gold-modified screen-printed carbon electrodes for a glycoprotein sensor of SARS-CoV-2

Abstract An electrochemical sensor of SARS-CoV-2 spike glycoprotein S1 has been developed using N-acetyl neuraminic acid (Neu5Ac) as the biosensing agent based on the interaction between Neu5Ac with the N-terminal domain of spike glycoprotein S1. Gold-modified screen-printed carbon electrodes (Au-SPCEs), prepared by electrochemical deposition of gold particles on a screen-printed carbon electrode surface, were used to detect the presence of the SARS-CoV-2 from the change in the electrochemical behavior of Neu5Ac. Cyclic voltammetry of Neu5Ac in phosphate buffer solution pH 7.6 using Au-SPCEs yielded a couple of oxidation and reduction peaks at potentials of +0.6 and 0.1 V (vs Ag/AgCl), respectively. The currents of both peaks linearly increased with the Neu5Ac concentrations in the range from 0 to 200 µM. A sensitivity of 0.77 mA/mM and 0.47 mA/mM for reduction and oxidation currents were observed, respectively, with estimated detection limits (LODs) of 51.05 µM and 35.77 µM. In the presence of SARS-CoV-2 spike glycoprotein S1, these current peaks decreased. At an optimum contact time of 30 min, a linear correlation to the current change of the reduction peaks was observed for the spike glycoprotein S1 over the concentration range 0 to 0.01 µg/mL. An estimated LOD of 0.7 ng/mL could be achieved with excellent stability (2.18% RSD value for n = 10), indicating that the sensor is promising for use in real applications of SARS-CoV-2 spike glycoprotein S1 detection.

The optimization of self-assembled monolayer of thiols on screen-printed gold electrode

<span>The activated gold-modified electrode surface for self-assembled monolayer (SAM) is suitable for N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC), 16-mercaptohexadecanoic acid (16-MDA), and N-hydroxysuccinimide (NHS). The various substrates could potentially be used for surface functionalization that binds to one another. Using modified screen-printed gold electrodes, 16-MDA, EDC, and NHS, we developed a self-assembling monolayer. Different 16-MDA concentrations were applied to the surface of a screen-printed electrode surface to enhance the sensitivity of the working electrode. The impact of different EDC, NHS, and 16-MDA concentrations (0.4 M, 0.8 M, 1 M, 1.2 M, 1.4 M, and 1.8 M) and incubation times between 5 and 30 minutes were examined and compared. The binding surface of the screen-printed gold electrode was characterized using the differential pulse voltammetry (DPV) technique. It has been demonstrated that the substrate concentrations at 5 minutes and 30 minutes of incubation time used to have the highest surface coverage and electron transfer rates. This concentration would be utilized in the subsequent experiment to evaluate the binding of various bacterial species. These findings suggest that the SAM in a modified screen-printed gold electrode may be functionalized to detect microorganisms.</span>

Development of an electrochemical biosensor utilizing a combined aptamer and MIP strategy for the detection of the food allergen lysozyme.

This study aims to develop a MIP-Apt-based electrochemical biosensor for the sensitive and selective determination of Lysozyme (Lyz), a food allergen. For the development of the sensor, in the first stage, modifications were made to the screen-printed electrode (SPE) surface with graphene oxide (GO) and gold nanoparticles (AuNPs) to increase conductivity and surface area. The advantages of using aptamer (Apt) and molecularly imprinted polymer (MIP) technology were combined in a single biointerface in the prepared sensing tool. Surface characterization of the biosensor was performed using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectrometry (XPS), contact angle measurements, cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). A wide linear range from 0.001 to 100pM was obtained under optimized conditions for the determination of Lyz detection usingthe proposed MIP-Apt sensing strategy. The limit of detection (LOD) and limit of quantification (LOQ) for Lyz were 3.67 fM and 12 fM, respectively. This biosensor displays high selectivity, repeatability, reproducibility, and long storage stability towards Lyz detection. The results show that a sensitive and selective sensor fabrication is achieved compared with existing methods.

Nanomolar detection of essential amino acid in dairy products using a novel electrochemical sensor based on zinc cobaltite nanoflowers embedded porous 3D reduced graphene oxide

L-tryptophan (L-Trp) is a vital amino acid that sways neuronal function, immunity, and gut homeostasis, and its accurate detection in food samples is crucial. The aim of this study is to integrate zinc cobaltite (ZCO) nanoparticles and 3D porous reduced graphene oxide (rGO) on a screen-printed carbon electrode (SPCE) surface for building a novel electrochemical sensor to sensitively detect L-Trp in food products. A low-temperature aqueous solution method was employed in ZCO nanoflower synthesis and a hydrothermal approach was utilized to prepare 3D rGO. SEM, elemental mapping, XRD, Raman spectroscopy, XPS, and EIS characterizations were performed on the prepared nanocomposite, ZCO/3DrGO. Electrochemical experiments conducted with the cyclic and differential pulse voltammetric techniques were used for effectively assessing the catalytic power of ZCO/3DrGO/SPCE. With a low detection limit of 3 nM, high sensitivity of 19.53 μAμM−1cm−2, and a broad linear range of 0.08–5.93; 5.93–87.18 μM, the sensor demonstrated promising electrocatalytic activity towards L-Trp. Further, the reliability of the sensor was proved by analyzing its stability, repeatability, reproducibility, and selectivity towards L-Trp. The successful detection of L-Trp in dairy products (yogurt, milk, and cottage cheese) using the proposed sensor evinced its practical feasibility with high recovery of 98.16%–101.16% and low RSD of 2.8%.

G-Quadruplex/Hemin-Mediated Polarity-Switchable and Photocurrent-Amplified System for Escherichia coli O157:H7 Detection.

The contamination of food by pathogens is a serious problem in global food safety, and current methods of detection are costly, time-consuming, and cumbersome. Therefore, it is necessary to develop rapid, portable, and sensitive assays for foodborne pathogens. In addition, assays for foodborne pathogens must be resistant to interference resulting from the complex food matrix to prevent false positives and negatives. In this study, hemin and reduced graphene oxide-MoS2 sheets (GMS) were used to design a near-infrared (NIR)-responsive photoelectrochemical (PEC) aptasensor with target-induced photocurrent polarity switching based on a hairpin aptamer (Hp) with a G-quadruplex motif. A ready-to-use analytical device was developed by immobilizing GMS on the surface of a commercial screen-printed electrode, followed by the attachment of the aptamer. In the presence of Escherichia coli O157:H7, the binding sites of Hp with the G-quadruplex motif were opened and exposed to hemin, leading to the formation of a G-quadruplex/hemin DNAzyme. Crucially, after binding to hemin, the charge transfer pathway of GMS changes, resulting in a switch of the photocurrent polarity. Further, G-quadruplex/hemin DNAzyme enhanced the cathodic photocurrent, and the proposed sensor exhibited a wide linear range ((25.0-1.0) × 107 CFU/mL), a low limit of detection (2.0 CFU/mL), and good anti-interference performance. These findings expand the applications of NIR-responsive PEC materials and provide versatile PEC methods for detecting biological analytes, especially for food safety testing.

Electrochemically synthesized polyanine@Cu-BTC MOF as a bifunctional matrix for aptasensing of tetracycline in aquatic products

The development of new method for the rapid and facile screening of antibiotics residues in food is of great importance in food safety. Herein, a nanocompisite of polyaniline@copper-1,3,5-benzenetricarboxylic acid (PAN@Cu-BTC) with excellent electrochemical activity was directly prepared on the screen-printed electrode surface by a two-step electrochemical synthesis method. Then the tetracycline aptamer (TC-Apt) was assembled onto the electrode surface through the coordination between 5′-PO43- on the aptamer and Cu2+ on the MOF, achieving a novel electrochemical aptasensor for tetracycline (TC). The PAN@Cu-BTC has two functions in the aptasensors, namely the immobilization matrix of the aptamer probe and the internal signal source for target recognition. The electrochemical sensing assays showed that the capture of TC-Apt to the target on the electrode surface could cause the decrease of the electrochemical signal of PAN@Cu-BTC. Based on this, the TC can be analyzed in a wide range from 10 pM to 1 µM, with a low detection limit of 0.32 pM. The recoveries of the aptasensor for the detection of TC from Ctenopharyngodon idella meat were 90.0 %∼102.0 %, indicating that the constructed aptasensor is applicable for the detection of TC residues in fresh aquatic products.

Magnetic perlite based molecularly imprinted polymer on screen printed carbon electrode as a new tyramine electrochemical sensor

This paper describes the design and fabrication of a sensitive electrochemical sensor using a new magnetic pearlite-based molecularly imprinted polymer (MPt/MIP) for the voltammetric determination of tyramine (Tyr). MPt/MIP nanocomposite was synthesized by direct surface-based imprinting procedure using methacrylic acid (MAA) as monomer for MIP and also functional group for magnetic perlite (MPt). The structural properties of MPt/MIP nanocomposite were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), FT-IR spectroscopy, vibrating sample magnetometry (VSM) and via adsorption kinetics and adsorption isotherms. The integrated analytical procedure consists of dispersion of synthesized MPt/MIPs for selective separation of target analyte from sample and their subsequent localization on the surface of a magnetic screen-printed carbon electrode (MSPCE) as a platform for determination of Tyr by differential pulse voltammetry (DPV). The experimental parameters which affect separation efficiency and electrochemical determination were optimized. The developed method provided a linear calibration range of 8.0 to 380.0 ng mL−1 (R2 = 0.998), and a detection limit of 3.8 ng mL−1. The intra-day and inter-day precision (%RSD) were in the range 3.1–4.4 %. The method was successfully applied to the determination of Tyr in real samples with recoveries ranging from 94.2 to 105.2 %.

Electrochemical aptasensor based on 3D graphene aerogel for prostate specific antigen detection

Prostatic cancer threatens the lives and health of numerous male patients all over the world. As a single-chain glycoprotein, prostate specific antigen (PSA) can be used to perform prostate cancer screening. At present, there are still problems such as time-consuming and low sensitivity in hospital detection. At the same time, electrochemical immunosensor technology has received a lot of attention due to its benefits, including high sensitivity, good selectivity, low usage and cost, and so on. Electrocatalysts are typically used to build electrochemical immunosensors for signal amplification in the recent years to realize sensitive detection of cancer biomarkers such as PSA. In recent years, three-dimensional nanomaterials have been widely used in the study of electrocatalysts, but the study of the sensitivity for PSA detection is still very scarce. The present work reported the application of a 3D graphene aerogel(GA)/AuNPs/Nafion electrochemical platform for highly sensitive PSA quantification. The electrochemical immunosensor has been designed by immobilizing aptamers on the screen-printed electrode (SPE) surface modified by GA/AuNPs/Nafion. Scanning electron microscopy (SEM), Raman spectra, and electrochemical characterization demonstrated the successful combination of GA/AuNPs/Nafion/SPE. Based on electrochemical impedance spectroscopy (EIS), the proposed immunosensor has demonstrated excellent electrochemical performance, exhibiting sensitive and stable responses for electrochemical detection of PSA ranging from 0.05 to 50 ng∙mL−1 with a limit of detection (LOD) of 0.0306 ng∙mL−1. This study has great potential application in PSA detection and provides a valuable reference for point-of-care testing (POCT) of prostate cancer.

Synergistic enhancement of electrochemiluminescence through hybridization of α-Ge nanolayers and gold nanoparticles for highly sensitive detection of tyramine

This work presents a novel approach for detecting biogenic amine tyramine using a sensitive and disposable electrochemiluminescent sensor. The sensor is fabricated by modifying a screen-printed carbon electrode surface with two nanomaterials, α-Ge nanolayers and AuNP, which synergistically enhance the electrochemiluminescence response. The sensor was characterized using various techniques such as SEM-EDX, EIS, Raman, and AFM. The principle of the biosensor relays on the fact that tyramine molecule acts as an analyte and co-reactant, which interacts with the luminophore [Ru(bpy)3]2+ on the sensor surface. The proposed sensor shows a linear response to tyramine concentration, with a detection limit of 2.28 µM. The sensor successfully detected tyramine in avocado samples, demonstrating its potential for practical applications.

Screen-Printed Carbon Electrodes with Cationic Cyclodextrin Carbon Nanotubes and Ferrocenyl-Carnosine for Electrochemical Sensing of Hg(II).

The study reports the use of nanoassembly based on cationic cyclodextrin carbon nanotubes (CNT-CDs) and ferrocenylcarnosine (FcCAR) for electrochemical sensing of Hg(II) in aqueous solution. β-cyclodextrins (CDs) were grafted onto CNTs by a click chemistry reaction between heptakis-(6-azido-6-deoxy)-β-cyclodextrin and alkyne-terminated CNTs. The cationic amine groups on the CD units were produced by the subsequent reduction of the residual nitrogen groups. The chemical composition and morphology of CNT-CDs were analyzed by X-ray photoelectron spectroscopy, scanning electron microscopy, and thermogravimetric analysis. A N,N-dimethylformamide dispersion of CNT-CDs was cast on the surface of screen-printed carbon electrodes (SPCEs), and the electrochemical response was evaluated by cyclic voltammetry (CV) using [Fe(CN)6]3- as the redox probe. The ability of SPCE/CNT-CD to significantly enhance the electroactive properties of the redox probe was combined with a suitable recognition element (FcCAR) for Hg(II). The electrochemical response of the CNT-CD/FcCAR nanoassembly was evaluated by CV and electrochemical impedance spectroscopy. The analytical performance of the Hg(II) sensor was evaluated by differential pulsed voltammetry and chronoamperometry. The oxidative peak current showed a linear concentration dependence in the range of 1-100 nM, with a sensitivity of 0.12 μA/nM, a limit of detection of 0.50 nM, and a limit of quantification of 1 nM.

Disposable nanosensor for the electrochemical determination of the interaction between DNA, and a mycotoxin, patulin

Silicon dioxide nanoparticles were synthesized and disposable screen-printed electrodes were modified with these nanoparticles to electrochemically detect the interaction between DNA and patulin, a mycotoxin. Firstly, the synthesized silicon dioxide nanoparticles were chemically characterized by X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR). Microscopic characterization of the nanoparticles was performed by Transmission Electron Microscopy (TEM) and Energy-dispersive X-ray spectroscopy (EDX). The surface of the silicon dioxide nanoparticle-modified screen-printed electrode was characterized by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). SiNP modification resulted in a 2-fold increase in surface area and a 2.3-fold enhancement in the signal. The detection limit (LOD) for the electrochemical patulin determination was calculated as 1.15 µg/mL, and the linear concentration range was found to be 3.2–20 µg/mL. The mode of interaction between patulin and dsDNA was determined through a molecular docking study. After the interaction between patulin and dsDNA, approximately 86 % and 23 % decreases were observed in patulin and guanine oxidation signals, respectively. The S % value for patulin was calculated by utilizing the decrease in the guanine signal after the interaction.

Electrochemical immunosensor based on carbon nanofibers and gold nanoparticles for detecting anti-Toxoplasma gondii IgG antibodies.

Anelectrochemical immunosensor based on carbon nanofibers (CNFs) and gold nanoparticles (AuNPs) was developed for detectinganti-Toxoplasma gondii antibodies (anti-T. gondii) IgG in human serum. CNFs were produced using electrospinning and carbonization processes. Screen-printed carbon electrode (SPCE) surface was modified with CNFs and AuNPs which wereelectrodeposited onto the CNFs. Then, T. gondii antigen was immobilized onto the AuNPs/CNFs/SPCE. Afterward, anti-T. gondii IgG positive serum samples were coated on the modified electrode and assessed via adding anti-human IgG labeled with horseradish peroxidase (HRP) enzyme. The morphology of SPCE, CNFs, and AuNPs/CNFs/SPCE surface was characterized using field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS). Characterization of CNFs was evaluated by Raman spectroscopy and X-ray diffraction (XRD). Electrochemical characterization of the immunosensor was verified using cyclic voltammetry (CV), and electrochemical response of modified electrode for anti-T. gondii IgG was detected via differential pulse voltammetry (DPV). This immunosensor was detectedin the range 0-200 U mL-1 with a low detection limit (9 × 10-3 U mL-1). In addition, the proposed immunosensor was exhibited with high selectivity, strong stability, and acceptable reproducibility and repeatability. Furthermore, there was a strong correlation between results obtained via the designed immunosensor and enzyme-linked immunosorbent assay (ELISA) as gold standard. In conclusion, the developed immunosensor isa promising route for rapid and accurate clinical diagnosis of toxoplasmosis.

Polyethylene Glycol-Mediated Directional Conjugation of Biological Molecules for Enhanced Immunoassays at the Point-of-Care.

Rapid and reliable point-of-care (POC) diagnostic tests can have a significant impact on global health. One of the most common approaches for developing POC systems is the use of target-specific biomolecules. However, the conjugation of biomolecules can result in decreased activity, which may compromise the analytical performance and accuracy of the developed systems. To overcome this challenge, we present a polymer-based cross-linking protocol for controlled and directed conjugation of biological molecules. Our protocol utilizes a bifunctional thiol-polyethylene glycol (PEG)-hydrazide polymer to enable site-directed conjugation of IgG antibodies to the surface of screen-printed metal electrodes. The metal surface of the electrodes is first modified with thiolated PEG molecules, leaving the hydrazide groups available to react with the aldehyde group in the Fc fragments of the oxidized IgG antibodies. Using anti-Klebsiella pneumoniae carbapenemase-2 (KPC-2) antibody as a model antibody used for antimicrobial resistance (AMR) testing, our results demonstrate a ~10-fold increase in antibody coupling compared with the standard N-hydroxysuccinimide (NHS)-based conjugation chemistry and effective capture (>94%) of the target KPC-2 enzyme antigen on the surface of modified electrodes. This straightforward and easy-to-perform strategy of site-directed antibody conjugation can be engineered for coupling other protein- and non-protein-based biological molecules commonly used in POC testing and development, thus enhancing the potential for improved diagnostic accuracy and performance.

An ultrasensitive label-free electrochemical aptasensing platform for Golgi protein-73 detection based on RGO-Fc-Mn3O4 nanocomposites

Golgi protein-73(GP73) is one of the most common biomarkers with outstanding sensitivity and specificity in the diagnosis of hepatocellular carcinoma. Herein an ultrasensitive label-free electrochemical aptasensing platform was constructed for GP73 detection based on reduced graphene oxide-ferrocene formic acid-tripterythrine tetroxide nanocomposites (RGO-Fc-Mn3O4) and GP73 aptamer (GP73Apt). Gold@poly-o-phenylenediamine (Au@PoPD) was electrodeposited on the surface of screen-printed electrode (SPE) as the conductive substrate. RGO-Fc-Mn3O4 was then drop-coated on Au@PoPD/SPE as a signal probe to generate measurable redox peaks due to the electroactivity of Fc in RGO-Fc-Mn3O4. GP73Apt was anchored on the surface of RGO-Fc-Mn3O4 NPs/Au@PoPD/SPE to constitute an electrochemical aptasensing biosensor. When GP73 was captured via the specific affinity of GP73Apt and formed GP73-GP73Apt complex onto the aptasensing platform, the formation GP73-GP73Apt complex impeded the electron transfer on the electrode interface, resulting in a decrease in the peak current recorded by differential pulse voltammetry method. Thus, GP73 can be detected by measuring the change of Fc redox peak current in RGO-Fc-Mn3O4. Log-linear calibration curve for GP73 concentration (0.01–1000 ng/mL) was obtained with good correlation coefficients of 0.99485 and a lower limit of detection of 0.01 ng/mL. The human serum samples were tested by direct detection method, and the relative error and relative standard deviation are 4.21–9.87% and 3.28–9.40%, respectively. All these results demonstrate that the proposed aptasensor would be a promising tool for clinical analysis of GP73 in the diagnosis of hepatocellular carcinoma.

ZnO Hollow Quasi-Spheres Modified Screen-Printed Graphite Electrode for Determination of Carmoisine.

Food colorants are important in food selection because they improve the gastronomic appeal of foods by improving their aesthetic appeal. However, after prolonged use, many colorants turn toxic and cause medical problems. A synthetic azo-class dye called carmoisine gives meals a red color. Therefore, the carmoisine determination in food samples is of great importance from the human health control. The current work was developed to synthesis ZnO hollow quasi-spheres (ZnO HQSs) to prepare a new electrochemical carmoisine sensor that is sensitive. Field emission-scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) have been used to analyze the properties of prepared ZnO HQSs. A screen-printed graphite electrode (SPGE) surface was modified with ZnO HQSs to prepare the ZnO HQSs-SPGE sensor. For carmoisine detection, the ZnO HQSs-SPGE demonstrated an appropriate response and notable electrocatalytic activities. The carmoisine electro-oxidation signal was significantly stronger on the ZnO HQSs-SPGE surface compared to the bare SPGE. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CHA), and differential pulse voltammetry (DPV) have been utilized to investigate the suggested protocol. The DPV results revealed an extensive linear association between variable carmoisine concentrations and peak current that ranged from 0.08 to 190.0 µM, with a limit of detection (LOD) as narrow as 0.02 µM. The ZnO HQSs-SPGE's ability to detect carmoisine in real samples proved the sensor's practical application.

Smartphone-Based Electrochemical Biosensor for On-Site Nutritional Quality Assessment of Coffee Blends.

This work aimed to develop an easy-to-use smartphone-based electrochemical biosensor to quickly assess a coffee blend's total polyphenols (Phs) content at the industrial and individual levels. The device is based on a commercial carbon-based screen-printed electrode (SPE) modified with multi-walled carbon nanotubes (CNTs) and gold nanoparticles (GNPs). At the same time, the biological recognition element, Laccase from Trametes versicolor, TvLac, was immobilized on the sensor surface by using glutaraldehyde (GA) as a cross-linking agent. The platform was electrochemically characterized to ascertain the influence of the SPE surface modification on its performance. The working electrode (WE) surface morphology characterization was obtained by scanning electron microscopy (SEM) and Fourier-transform infrared (FT-IR) imaging. All the measurements were carried out with a micro-potentiostat, the Sensit Smart by PalmSens, connected to a smartphone. The developed biosensor provided a sensitivity of 0.12 μA/μM, a linear response ranging from 5 to 70 μM, and a lower detection limit (LOD) of 2.99 μM. Afterward, the biosensor was tested for quantifying the total Phs content in coffee blends, evaluating the influence of both the variety and the roasting degree. The smartphone-based electrochemical biosensor's performance was validated through the Folin-Ciocâlteu standard method.

Electrochemical sensor based on polydopamine-molecularly imprinted polymer for detection of 4-ethylphenyl sulfate “a novel gut metabolite”: Fabrication, characterization, and performance evaluation in human urine

The 4-ethylphenyl sulfate (4-EPS) is considered a well-known gut microbiota derived metabolite that is involved in various human diseases and ailments. Thus, in the present work, an electrochemical sensor was developed using a polydopamine (PDA) based molecularly imprinted polymer (MIP) for the detection of 4-EPS, a gut metabolite using cyclic voltammetry (CV) for the first time. The synthesized PDA-MIP was characterized by fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques. The PDA-MIP was drop casted on the surface of screen-printed carbon electrode (SPCE) to fabricate an electrochemical sensor. The developed PDA-MIP/SPCE sensor showed a broad linear detection range of 0.1–300 ng/mL (correlation, R2 = 0.982) with a high sensitivity of 153.88 μA (log ng/mL)−1cm−2 and a low limit of detection (LOD) of 0.018 ng/mL. The selectivity studies were also performed against the possible interfering compounds in human urine. The reproducibility of fabricated PDA-MIP/SPCE shows relative standard deviation (RSD) of 5.34%. For demonstrating the effectiveness of the sensor, the real sample analysis was performed in human urine and it shows the good recovery range of 98.1–121.8% with a RSD of 1.35–13.93%. Therefore, the MIP based electrochemical sensor is economically feasible, which may propose a new diagnostic method for identifying diseases associated with the concentration of 4-EPS in other body fluids.