Modified Working Electrode Research Articles

Development of ultrasensitive genosensor targeting pathogenic Leptospira DNA detection in artificial urine

In the last decades, to access the stages of leptospirosis pathogenicity, site of infection, progression, monitor disease, and after-treatment were required especially non-invasive techniques. This becomes one of the significant goals for researchers. In this study, we developed a highly sensitive DNA-based electrochemical sensor to detect pathogenic leptospires in urine samples using a gold screen-printed electrode. The gold working electrode was electrodeposited with diazonium salt (CMA) with external carboxylic acid from the surface, and the specific Loa22 single-stranded DNA (ssDNA) probe to Leptospira interrogans was immobilized through a carbodiimide chemical reaction. The modified working electrode was characterized by contact angle measurement, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). After that, targeted DNA testing showed the EIS change in the range of 5 ag mL-1 - 16 fg mL-1 with a correlation R2 of 0.9638. The high sensitivity electrochemical sensor indicated a lower limit of detection to the attomolar level specifically 5 ag mL-1. Additionally, the developed genosensor exhibited high specificity without crossing other bacteria present in urine such as Escherichia coli, Staphylococcus aureus, and S. typhi as well as non-pathogenic leptospires L. biflexa serovar Patoc. Leptospires DNA was analyzed in both buffer solution and diluted artificial urine and detection in diluted artificial urine 1:1,000 was possible despite salt interferences. This study provides a highly sensitive lower detection platform for leptospirosis, offering potential for further development as a portable and point-of-care testing tool.

Sensitivity of chitosan/reduced graphene oxide/manganese dioxide modified electrodes for cholesterol detection using cyclic voltammetry

Cholesterol detection needs to be carried out to detect early symptoms of dangerous diseases such as heart disease. The process of detecting cholesterol in the human blood requires a sensitive detection tool in order to produce accurate values. This paper reports the performance of chitosan thin films modified with reduced graphene oxide (rGO) and manganese dioxide (MnO2) as the sensitive layer of working electrodes in detecting cholesterol. The electrode substrate is a copper-screen printed electrode (copper-SPE) which was patterned into 5 mm of sensitive area. The chitosan and chitosan-reduced graphene oxide (rGO) matrices were deposited on the top of working electrodes. The characterization of chitosan, chitosan/rGO, and chitosan/rGO/MnO2 thin films was performed using AFM, FE-SEM, and FTIR. The electrochemical sensing properties of modified working electrode were observed using an electrochemical method of cyclic voltammetry (CV). The novelty of this research is the utilization of chitosan/rGO/MnO2 thin film-based working electrode for detecting cholesterol. The testing results indicated that the sensitivity of the modified working electrodes increased when working electrodes based on chitosan/rGO/MnO2 thin film were used for cholesterol detection compared to the working electrodes based on the chitosan thin film. It was proven from the sensitivity of working electrodes based on chitosan/rGO/MnO2 thin film which gave the lowest value of 3.21 × 10−5 µA/µM as well as the ability of working electrodes based on chitosan/rGO/MnO2 thin film which worked at limit of detection (LoD) 0.26 µM/L and limit of quantification (LoQ) 0.87 µM/L. Based on the sensitivity, LoD, and LoQ values, the chitosan/rGO/MnO2 modified electrodes can be used as working electrodes to measure cholesterol concentration in blood.

Electrochemical performance of gold nanoparticles decorated on Multi-walled Carbon Nanotube (MWCNT) Screen-printed Electrode (SPE)

The modification of the multi-walled carbon nanotube screen-printed electrode (MWCNT/SPE) with gold nanoparticles (AuNP) was achieved through drop-casting method utilizing gold nanoparticles synthesized via the Turkevich method. The combination of nanomaterial based on carbon (multi-walled carbon nanotubes) and the noble metal (gold nanoparticles) aims to exploit the synergistic benefits of the two materials in electrochemical measurement. Electrochemical performance was evaluated through techniques including cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results indicated an increase in the electroactive surface area of the modified working electrodes compared to the unmodified ones. This increase in electroactive surface area can be attributed to the successful decoration of AuNP, which facilitates greater surface interactions and improved electron transfer kinetics, crucial for efficient catalytic reactions. The decoration of AuNP also makes sure that the electrode will have good biocompatibility for future bioanalytical applications. This investigation’s main goal was to determine the effects of the AuNP modification methods to the carbon electrode’s electroactive surface area for further contributing to the development of efficient label-free sensing platforms for diverse applications in biosensing.

How to Perform Reliable IR Compensation in Electrocatalysis?

iR compensation is one of the most used techniques in electrochemical analysis, which is designed to correct the voltage loss between the working electrode and the reference electrode in the electrolyte (Rsolution).[1] It is conducted using two methods frequently, namely the after-the-scan and the on-the-fly methods. A factor is often engaged when performing the iR compensation, which is an empirical value (e.g., 80%~100%) chosen by researchers. After the compensation, the experimental data (mainly electrocatalytic indicators like overpotential and Tafel slope) can be greatly “improved”.[2] However, the abuse of iR compensation, especially in electrocatalysis studies, can generate misleading and exaggerated results.In this study, we present a detailed analysis of the applicability of the iR compensation technique in current electrocatalysis studies by revisiting the technical assumptions.[3] A few considerations are discussed. Firstly, it is pointed out that the resistance obtained from the electrochemical impedance spectroscopy is not always the resistance that needs to be compensated. The main reason is the involvement of the catalyst material resistance (Rcatalyst) and the contact resistance between the substrate and the catalyst material (Rcontact) (Figure 1). Depending on the types of activity (intrinsic activity, sample activity, electrode activity, and industrial activity) of interest, one should choose different resistance values. For example, only Rsolution should be compensated when studying the electrode activity, but both Rcontact and Rsolution should be compensated for sample activity analysis. Secondly, the resistance may be potential/time-dependent, meaning the value should be measured at the reaction condition, other than the often-used open circuit potential. Thirdly, the distribution of resistance on the catalyst surface sites is uneven, suggesting that one single value cannot be used for sites at different surface traits. Fourthly, most researchers use linear sweep voltammetry (LSV) where the current is always contributed by both the Faradic current and non-Faradic current. However, only the Faradic current should be compensated because non-Faradic current does not flow between the working and reference electrodes.Regarding these considerations and experimental methods, we further suggested a standard workflow to perform iR compensation in electrocatalysis studies.[3] Figure 1. Voltage loss across a three-electrode system with a modified working electrode and the corresponding equivalent circuit diagram. (1) surface of the substrate; (2) surface of the catalyst contacting the substrate; (3) surface of the catalyst contacting the electrolyte solution; (4) outer boundary of the diffuse layer; (5) junction of the reference electrode. Reference: Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications, 2nd ed.; John Wiley & Sons, Inc., 2001 Anantharaj, S.; Noda, S. J. Mater. Chem. A 2022, 10, 17, 9348– 9354 Zheng, W. ACS Energy Lett. 2023, 8, 4, 1952–1958 Figure 1

A Portable Integrated Electrochemical Sensing System for On-Site Nitrite Detection in Food.

Ensuring an appropriate nitrite level in food is essential to keep the body healthy. However, it still remains a huge challenge to offer a portable and low-cost on-site food nitrite analysis without any expensive equipment. Herein, a portable integrated electrochemical sensing system (IESS) is developed to achieve rapid on-site nitrite detection in food, which is composed of a low-cost disposable microfluidic electrochemical patch for few-shot nitrite detection, and a reusable smartphone-assisted electronic device based on self-designed circuit board for signal processing and wireless transmission. The electrochemical patch based on MXene-Ti3C2Tx/multiwalled carbon nanotubes-cyanocobalamin (MXene/MWCNTs-VB12)-modified working electrode achieves high sensitivity of 10.533µA mm-1 and low nitrite detection limit of 4.22µm owing to strong electron transfer ability of hybrid MXene/MWCNTs conductive matrix and high nitrite selectivity of VB12 bionic enzyme-based ion-selective layer. Moreover, the portable IESS can rapidly collect pending testing samples through a microfluidic electrochemical patch within 1.0s to conduct immediate nitrite analysis, and then wirelessly transmit data from a signal-processing electronic device to a smartphone via Bluetooth module. Consequently, this proposed portable IESS demonstrates rapid on-site nitrite analysis and wireless data transmission within one palm-sized electronic device, which would pave a new avenue in food safety and personal bespoke therapy.

A universal CRISPR-Cas14a responsive triple-sensitized upconversion photoelectrochemical sensor

It has recently been discovered that, like other members of the Cas family (12a and 13a), the clustered regularly interspaced short palindrome repeat CRISPR-Cas14a system not only mediates high-sensitivity detection with exceptionally strong gene editing ability but is also generally useful for DNA detection via fluorescence. Photoelectrochemical (PEC) sensors have been widely applied as efficient analytical tools. Measuring electrical signals is more cost-effective and the necessary equipment is more easily portable than fluorescence signal detectors, but their stability still needs to be improved. The high base resolution of CRISPR-Cas14a can compensate for such shortcomings. Therefore, electrical signals and fluorescence signals were combined, and the development of a universal CRISPR-Cas14a-responsive ultrasensitive upconversion PEC sensor is described in this paper. Moreover, strand displacement amplification (SDA) and a near-infrared (NIR) light source were utilized to further improve the stability and sensitivity of the photoelectric signals. At the same time, the modified working electrode (UCNPs-ssDNA-CdS@Au/ITO) on the three-electrode disposable sensor was used as the reporter probe, which cooperates with the trans-cleavage activity of Cas14a endonuclease. To verify the universality of this sensor, the UCNPs-Cas14a-based PEC sensor was applied for the detection of the small-molecule toxin T2 and protein kinase PTK7. Here, we report that the limit of detection of this reagent was within the fg range, successfully applied to the detection of T2 in oats and PTK7 in human serum. We propose that by combining PEC and CRISPR-14a, UCNPs-Cas14a-based PEC sensors could become powerful drivers for the extensive development of ultrasensitive, accurate and cost-effective universal sensors for detection and diagnosis.

A three-dimensional metal hydroxide activated in an alkaline electrolyte used for electrochemical simultaneous detection of 5-hydroxytryptophan and tryptophan

An electrochemical sensor was designed for simultaneous detection of 5-Hydroxytryptophan (5-HTP) and tryptophan (L-Trp) based on a FeZnSn three-dimensional metal hydroxide activated in an alkaline electrolyte/ glassy carbon electrode (FeZnSn-TDHae/GCE). The results showed that the electrochemical activation method can effectively reduce the charge transfer resistance of FeZnSn three-dimensional metal hydroxide (FeZnSn-TDH) hardly affecting the electrochemical active surface areas, in which the charge transfer resistance of FeZnSn-TDHae was only one quarter of FeZnSn-TDH, and the DPV current response values of 5-HTP and L-Trp on FeZnSn-TDHae/GCE were 2.36 and 1.91 times that of on GCE. The modified working electrode had the wide linear response range of 1–800 μM and 3–800 μM for simultaneous detection of 5-HTP and L-Trp, and the detection limits of 5-HTP and L-Trp obtained in this work were 0.7398 μM and 1.2209 μM, respectively. Furthermore, the sensor was applied to the simultaneous detection of 5-HTP and L-Trp in human serum albumin samples by standard adding method.

Electrochemical DNA Sensor Designed Using the Pencil Graphite Electrode to Detect Listeria monocytogenes.

In the present work, a novel electrochemical DNA sensor was designed to detect L. monocytogenes. Two different gene fragments were selected for the sensor design. One is a 702bp long fragment of the hlyA gene, encoding the synthesis of listeriolysin O toxin, which is unique only to pathogenic strains of L. monocytogenes and is essential for pathogenicity. The other is a 209bp long fragment of the 16S RNA gene found in all species of the Listeria genus. As the working electrode, the pencil graphite electrode was modified in various ways (activated or covered with polypyrrole), and six different combinations were constituted using three types of the modified working electrode and two different gene fragments. The developed system is based on differential pulse voltammetric transduction of guanine oxidation after hybridization between the selected gene fragment (38µg/mL) and the selected fragment-specific inosine-modified probe (1.8 µmol/L) immobilized on a pencil graphite electrode surface. The comparison of all combinations demonstrates that the best results are obtained with the combination formed from a polypyrrole-coated pencil graphite electrode (prepared at 2 scans) and 702bp fragment of the hlyA gene. The analysis time is less than 1 hour, and the necessary DNA concentrations for the analysis have been determined as 8.2 × 10-11M DNA and 2.7 × 10-10M DNA respectively, for the hlyA gene and 16S RNA gene.

Highly sensitive amperometric food sensor for Sudan-I dye using nanocomposites modified working electrode

Sudan-I dye (1-phenyl azo-2-naphthol) is commonly used as a coloring agent in the food and textile industries. The excessive use of Sudan-I dye has ill effects on human health. A sensitive and selective electrochemical detection is required for sensing Sudan-I dye in food products. An electrochemical sensor based on a modified working electrode using ternary mixed metal oxide (Ti/Fe/CuO) nanocomposites was developed for sensing Sudan-I dye. Using a modified Sol-gel technique, Ti/Fe/CuO mixed metal nanocomposites were synthesized. FT-IR, UV–Visible, SEM, and XRD techniques were used to characterize the Ti/Fe/CuO nanocomposites. Different voltammetric techniques, such as Cyclic voltammetry (CV), Differential Pulse Voltammetry (DPV), and Linear Sweep Voltammetric (LSV) were used for qualitative and quantitative estimation of Sudan-I dye. Electrochemical Impedance Spectroscopy (EIS) was used for structural information of interface. The specially designed working electrode acted as a sensor and shows good sensing ability toward Sudan-I dye in real food samples. A linear range of 0–160 µM and 0–200 µM for red chili sauce and powder (real samples), respectively was observed. Under the optimized condition, the current response was linear with a detection limit of 0.02 µM/L. A characteristic oxidation peak of 7263.36 µA at 0.2606 V and a reductive peak of − 1465 μA at − 0.3714 V are the characteristic peaks for Sudan-I dye. The effect of change in pH, scan rate, storage, stability behavior, and concentration of Sudan-I dye was evaluated. A comparative study was done between glassy carbon electrodes, bare Copper metal, and ternary metal oxide NCs modified electrodes. The developed electrochemical sensor demonstrated reliability, reproducibility, stability, speed, and non-specificity, making it suitable for both quantitative and qualitative analysis of food additives, preservatives, coloring agents, and flavoring agents.

Molecularly imprinted polymer dual electrochemical sensor for the one-step determination of albuminuria to creatinine ratio (ACR)

The urinary albumin to creatinine ratio (ACR) is a convenient and accurate biomarker of chronic kidney disease (CKD). An electrochemical sensor for the quantification of ACR was developed based on a dual screen-printed carbon electrode (SPdCE). The SPdCE was modified with carboxylated multiwalled carbon nanotubes (f-MWCNTs) and redox probes of polymethylene blue (PMB) for creatinine and ferrocene (Fc) for albumin. The modified working electrodes were then molecularly imprinted with coated with polymerized poly-o-phenylenediamine (PoPD) to form surfaces that could be separately imprinted with creatinine and albumin template molecules. The seeded polymer layers were polymerized with a second coating of PoPD and the templates were removed to form two different molecularly imprinted polymer (MIP) layers. The dual sensor presented recognition sites for creatinine and albumin on different working electrodes, enabling the measurement of each analyte in one potential scan of square wave voltammetry (SWV). The proposed sensor produced linear ranges of 5.0–100 ng mL−1 and 100–2500 ng mL−1 for creatinine, and 5.0–100 ng mL−1 for albumin. LODs were 1.5 ± 0.2 ng mL−1 and 1.5 ± 0.3 ng mL−1, respectively. The dual MIP sensor was highly selective and stable for seven weeks at room temperature. The ACRs obtained using the proposed sensor compared well (P > 0.05) with the results from immunoturbidimetric and enzymatic methods.

Enhancement of the Catalytic Effect on the Electrochemical Conversion of CO2 to Formic Acid Using MXene (Ti3C2Tx)-Modified Boron-Doped Diamond Electrode

The rising concentration of carbon dioxide (CO2) as one of the greenhouse gases in the atmosphere is a major source of worry. Electrochemical reduction of CO2 is one of many ways to convert CO2 gas into usable compounds. An electrochemical technique was applied in this study to reduce CO2 using a boron-doped diamond (BDD) working electrode modified with MXene (Ti3C2Tx) material to improve electrode performance. MXene concentrations of 0.5 mg/mL (MXene-BDD 0.5), 1.0 mg/mL (MXene-BDD 1.0), and 2.0 mg/mL (MXene-BDD 2.0) were drop-casted onto the BDD surface. MXene was effectively deposited on top of the BDD surface, with Ti weight loads of 0.12%, 4.06%, and 7.14% on MXene-BDD 0.5, MXene-BDD 1.0, and MXene-BDD 2.0, respectively. The modified working electrode was employed for CO2 electroreduction with optimal CO2 gas aeration. The existence of the MXene substance in BDD reduced the electroreduction overpotential of CO2. For the final result, we found that the MXene-BDD 2.0 electrode effectively generated the most formic acid product with a maximum reduction potential as low as −1.3 V (vs. Ag/AgCl).

Voltammetric Measurement of Antioxidant Activity by Prevention of Cu(II)-Induced Oxidative Damage on DNA Bases Using a Modified Electrode.

The protective effect of antioxidants using electrochemical techniques can be evaluated by examining the oxidative changes in deoxyribonucleic acid (DNA) nucleobases. In this study, a gold nanoparticle (AuNP)-decorated and multiwalled carbon nanotube (MWCNT)-Nafion-modified glassy carbon electrode (GCE/AuNP/MWCNT-Nafion) was developed to evaluate the preventive ability of antioxidants on oxidative DNA damage. A modified working electrode was prepared and characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The developed electrochemical method relies on two phenomena: (i) reactive species (RS) produced by dissolved oxygen in the presence of copper(II) partially damage the DNA immobilized on the electrode surface and (ii) antioxidant compounds prevent this damage by scavenging the formed RS. Changes in guanine, adenine, and cytosine oxidation signals resulting from DNA damage were measured using differential pulse stripping voltammetry before/after the interaction of dsDNA with Cu(II) while antioxidants were absent or present. The DNA protective ability of antioxidants was assessed for a number of antioxidant compounds (i.e., ascorbic acid, gallic acid, epicatechin, catechin, epicatechin gallate, glutathione, chlorogenic acid, N-acetyl cysteine, rosmarinic acid, quercetin, and rutin). Quercetin was found to show the highest antioxidant effect, and its limit of detection was determined as 1 μM. The manufactured biosensor was put in an application for the determination of antioxidant activity of herbal teas.

A Novel Voltammetric Electronic Tongue Based on Nanocomposites Modified Electrodes for the Discrimination of Red Wines from Different Geographical Origins

A novel voltammetric electronic tongue (VE-tongue) system based on three nanocomposites modified working electrodes was used for the discrimination of red wine from different geographical origins. The three types of modified working electrodes were fabricated to detect glucose (Glu), tartaric acid (TA), and non-specific flavor information in a red wine sample, respectively. The electrochemical properties of three electrodes were tested by cyclic voltammetric method, and pH, accumulation time, and scan rates were optimized for Glu and TA sensors. Scanning electron microscopy (SEM), X-ray proton spectrum (XPS), and X-ray diffraction (XRD) were used for the characterization of modified materials. This sensor array was then applied to identify four kinds of red wines from different geographical origins, and the multi-frequency and potential steps (STEP) method was used to obtain flavor information regarding rice wines. The classification ability of this VE-tongue system was evaluated by using partial least squares (PLS) regression and principal component analysis (PCA), while back propagation neural network (BPNN), random forest (RF), support vector machines (SVM), deep neural network (DNN), and K-nearest neighbor (KNN) were used for the prediction. The results showed that PCA could explain about the 95.7% of the total variance, and BPNN performed best in the prediction work (the prediction accuracy was 95.8%). Therefore, the VE-tongue system with BPNN was chosen to effectively discriminate red wines from different geographical origins, and the novel VE-tongue aiming at red wine discrimination with high accuracy and lower cost was established.

Fabrication of Au/Fe3O4/RGO based aptasensor for measurement of miRNA-128, a biomarker for acute lymphoblastic leukemia (ALL).

Due to their high sensitivity, simplicity, portability, self‐contained, and low cost, the development of electrochemical biosensors is a beneficial way to diagnose and anticipate many types of cancers. An electrochemical nanocomposite‐based aptasensor is fabricated for the determination of miRNA‐128 concentration as the acute lymphoblastic leukemia (ALL) biomarker for the first time. The aptamer chains were immobilized on the surface of the glassy carbon electrode (GCE) through gold nanoparticles/magnetite/reduced graphene oxide (AuNPs/Fe3O4/RGO). Fast Fourier transform infrared (FTIR), X‐ray diffraction (XRD), vibrating sample magnetometer (VSM), and transmission electron microscopy (TEM) were used to characterize synthesized nanomaterials. Cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) were used to characterize the modified GCE in both label‐free and labeled methods. The results indicate that the modified working electrode has high selectivity and for miRNA‐128 over other biomolecules. The hexacyanoferrate redox system typically operated at around 0.3 V (vs. Ag/AgCl), and the methylene blue redox system ran at about 0 V, were used as an electrochemical probe. The detection limit and linear detection range for hexacyanoferrate and methylene blue are 0.05346 fM, 0.1–0.9 fM, and 0.005483 fM, 0.01–0.09 fM, respectively. The stability and diffusion control analyses were performed as well. In both label‐free and labeled methods, the modified electron showed high selectivity for miRNA‐128. The use of methylene blue as a safer redox mediator caused miRNA‐128 to be detected with greater accuracy at low potentials in PBS media. The findings also show the substantial improvement in detection limit and linearity by using reduced graphene oxide‐magnetite‐gold nanoparticles that can be verified by comparing with previous studies on the detection of other miRNAs.

Determination of organophosphorus compounds in water and food samples using a non-enzymatic electrochemical sensor based on silver nanoparticles and carbon nanotubes nanocomposite coupled with batch injection analysis

This work presents, for the first time, a fast and highly sensitive electrochemical method for determination of three organophosphorus compounds (OPs), diazinon (DZN), malathion (MLT), and chlorpyrifos (CLPF), using a modified pyrolytic graphite electrode (PGE) coupled to batch injection analysis system with multiple pulse amperometric detection (BIA–MPA). The PGE was modified by a nanocomposite based on functionalized carbon nanotubes (CNTf) and silver nanoparticles (AgNPs). The OPs samples were directly analyzed on the modified working electrode surface by BIA-MPA system in Britton-Robinson (BR) buffer 0.15 mol L−1 at pH 6.0. The MPA detection of DZN, MLT and CLPF was performed using two potential pulses, which were sequentially applied on modified PGE at −1.3 V (100 ms) and +0.8 V (100 ms) for selective determination of these three OPs and working electrode cleaning, respectively. Under optimized conditions, the sensor presented a linear range of 0.1–20 μmol L−1 for DZN, 1.0–30 μmol L−1 for MLT and from 0.25 to 50 μmol L−1 for CLPF. The limits of detection (LOD) and quantification (LOQ) of 0.35 and 1.18 μmol L−1 for DZN, 0.89 and 2.98 μmol L−1 for MLT, and 0.53 and 1.78 μmol L−1 for CLPF were obtained. The proposed method exhibited high sensitivity of 0.068, 0.030 and 0.043 mA L μmol−1 for DZN, MLT and CLPF detection, respectively. Furthermore, the BIA-MPA system provided an analytical frequency of 71 determinations per hour for direct determination of these OPs in water and food samples. The modified PGE coupled to BIA-MPA system showed a high stability of electrochemical response for OPs detection with relative standard deviation (RSD) of 1.60% (n = 20). The addition-recovery studies of the proposed method were carried out in tap water, orange juice, and apple fruit real samples, which showed suitable recovery values between 77 and 124%. The analytical performance of the developed sensor provides an attractive alternative method for OPs determination with great potential for a fast and sensitive application in contaminated samples with these pesticides.

Electro fabrication of molecularly imprinted sensor based on Pd nanoparticles decorated poly-(3 thiophene acetic acid) for progesterone detection

In recent years, scientific community has witnessed substantial interest in the design and engineering of electrodes as sensing platforms towards sensitive and selective detection of hormones. An electrochemical strategy for the detection of progesterone was proposed by generating a composite film comprising of palladium nanoparticles with 3-thiophene acetic acid (3-TAA) coupled with molecular imprinting technology. Progesterone molecule was employed as the template while generating molecular imprints by electropolymerization on the surface of the Carbon Fibre Paper (CFP) electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry were used to analyse the various modified working electrodes (CV). Characterization methods included field emission scanning microscopy, energy dispersive X-ray spectrometry, optical profilometry, and X-ray photon electron spectroscopy. Pd nanoparticles resulted in enhanced sensitivity and molecular imprinting technology contributed to its specificity. Because of the molecular cavities created on the removal of the template molecule, Nyquist plots data showed that the MIP/Pd/CFP electrode had the lowest charge transfer resistance compared to other control electrodes.

Reliable detection of Listeria monocytogenes by a portable paper-based multi-biocatalyst platform integrating three biomarkers: Gene hly, acetoin, and listeriolysin O protein

As biomarkers for pathogenic Listeria monocytogenes, the detection of gene hly, acetoin, and listeriolysin O (LLO) is of great significance for preventing L. monocytogenes infection and diagnosing Listeriosis. Here, a portable paper-based multi-biocatalyst platform was constructed to identify L. monocytogenes by detecting multiple biomarkers at different levels: gene hly (nucleic acid), acetoin (small molecule metabolite), and LLO (protein). The integrating detections of the three biomarkers were successfully performed by two different modified working electrodes on a single paper-based multi-biocatalyst platform. The sensitive and reliable identification of L. monocytogenes was achieved using the portable paper-based multi-biocatalyst platform with wider detection range (from 1.0 × 104 to 1.0 × 109 CFU mL−1) and lower detection limit (104 CFU mL−1). Additionally, the simpler detection procedure and shorter detection time (2 h) endows the portable platform a better detection performance compared with National Food Safety Standard Method (China-GB 4789.30-2016). Moreover, the results detected by the portable platform in spiked samples were consistent with that obtained by the real-time quantitative polymerase chain reaction method, indicating a good application potential. These unique characteristics suggest that the portable platform provides a reliable identification method for L. monocytogenes.

Use of voltammetric and chemometric tools to develop a sensor in forensic chemistry

The large number of drug seizures has required the development of electrochemical sensors and new analytical techniques involving portable sensors. Here, we have studied cocaine hydrochloride oxy-reduction on the surface of carbon paste electrodes chemically modified with [VIIO(salen)], and we have evaluated these electrodes as voltammetric sensors for forensic purposes. The modified working electrode for cocaine hydrochloride analysis presented the sensitivity was 1.2 µmol.L−1, and the mean limits of detection and quantification were 0.31 and 1.03 µmol.L−1, respectively. As for the possible interferents, the investigated analytes exhibited similar electrochemical activity, with different sensitivities. Supervised classification of the data for the detection of analytes by the SIMCA chemometric method revealed that the voltammetric methodology predicted cocaine in real samples seized by the police more effectively than the other analytes. Thus, the developed voltammetric sensor has potential use in forensic investigations.

Tin derived antimony/nitrogen-doped porous carbon (Sb/NPC) composite for electrochemical sensing of albumin from hepatocellular carcinoma patients.

Anelectrochemical sensor based on an antimony/nitrogen-doped porous carbon (Sb/NPC) composite has been developedfor the quantitative detection of albumin from hepatocellular carcinoma (HCC) patients. Sb/NPC is hydrothermally synthesized from Sn/NPC precursors. The synthesized precursor (Sn/NPC) and the product (Sb/NPC) are characterized by XRD, FTIR, TGA, UV/Vis, SEM, and AFM. Cyclic voltammetry, chronoamperometry, and electrochemical impedance studies are used to investigate the electrochemical performance of Sb/NPC-GCE. Sb/NPC-GCE detects albumin at physiological pH of 7.4 in the potential range 0.92V and 0.09V for oxidation and reduction, respectively. LOD and recovery of Sb/NPC-GCEfor the determination of albuminare 0.13ng.mL-1 and 66.6±0.97-100±2.73%, respectively. Chronoamperometry of the modified working electrode demonstrates its stability for 14h, indicating its reusability and reproducibility. Sb/NPC-GCE is a selective sensor for albumin detection in the presence of interfering species. The electrodehas beenapplied for albumin detection inhuman serum samples of HCC patients. A negative correlation of albumin with alpha-fetoprotein levels in HCC patients is observed by statistical analysis.

Selective Voltammetric Detection of Ascorbic Acid from Rosa Canina on a Modified Graphene Oxide Paste Electrode by a Manganese(II) Complex.

Voltammetric techniques have been considered as an important analytical tool applied to the determination of trace concentrations of many biological molecules including ascorbic acid. In this paper, ascorbic acid was detected by square wave voltammetry, using graphene oxide paste as a working electrode, modified by a film of a manganese(II) complex compound. Various factors, such as the effect of pH, affecting the response characteristics of the modified electrode were investigated. The relationship between the peak height and ascorbic acid concentration within the modified working electrode was investigated, using the calibration graph. The equation of the calibration graph was found to be: I = 0.0550γac + 0.155 with R2 = 0.9998, where I is the SWV current and γac is the mass concentration of ascorbic acid. The LOD and LOQ of the proposed method were determined to be 1.288 μg/L and 3.903 μg/L, respectively. Several compounds, such as riboflavin, biotin, and ions, such as Fe and Cu, were tested and it seemed that they did not interfere with the analytic signal. The proposed procedure was successfully applied in the determination of ascorbic acid in Rosa canina hips.