Disposable Polyaniline/m-Phenylenediamine-Based Electrochemical Lactate Biosensor for Early Sepsis Diagnosis

Lactate serves as a crucial biomarker that indicates sepsis assessment in critically ill patients. A rapid, accurate, and portable analytical device for lactate detection is required. This work developed a stepwise polyurethane-polyaniline-m-phenylenediamine via a layer-by-layer based electrochemical biosensor, using a screen-printed gold electrode for lactate determination in blood samples. The developed lactate biosensor was electrochemically fabricated with layers of m-phenylenediamine, polyaniline, a crosslinking of a small amount of lactate oxidase via glutaraldehyde, and polyurethane as an outer membrane. The lactate determination using amperometry revealed the biosensor's performance with a wide linear range of 0.20-5.0 mmol L-1, a sensitivity of 12.17 ± 0.02 µA·mmol-1·L·cm-2, and a detection limit of 7.9 µmol L-1. The developed biosensor exhibited a fast response time of 5 s, high selectivity, excellent long-term storage stability over 10 weeks, and good reproducibility with 3.74% RSD. Additionally, the determination of lactate in human blood plasma using the developed lactate biosensor was examined. The results were in agreement with the enzymatic colorimetric gold standard method (p > 0.05). Our developed biosensor provides efficiency, reliability, and is a great potential tool for advancing lactate point-of-care testing applications in the early diagnosis of sepsis.

Voltammetric sensor for an anti-cancer drug cisplatin based on bismuth nanoparticles/graphene modified glassy carbon electrode

A selective and sensitive voltammetric sensor for the measurement of the chemotherapy drug cisplatin was based on bismuth nanoparticles decorated on a graphene-modified glassy carbon electrode (BiNPs/Gr/GCE). The surface morphologies of electrode modifications were characterized using scanning electron microscopy (SEM). Electrochemical characteristics were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was employed to detect cisplatin oxidation. Under the optimal conditions, oxidation peak currents increased linearly with cisplatin concentration from 6.0 to 180 μM. The detection limit was calculated to be 4.4 μM and the limit of quantification was 14.7 μM. Analytical performance studies demonstrated the good electrode reproducibility and the selectivity of the BiNPs/Gr/GCE towards cisplatin detection. The developed cisplatin sensor was successfully utilized to measure cisplatin in samples of human serum. Recoveries ranged from 89 to 102% and the results from the developed sensor were concordant (P > 0.05) with the results of analysis by high-performance liquid chromatography coupled with ultraviolet detection.

A Novel Microfluidic-Based OMC-PEDOT-PSS Composite Electrochemical Sensor for Continuous Dopamine Monitoring

Fast and precise analysis techniques using small sample volumes are required for next-generation clinical monitoring at the patient's bedside, so as to provide the clinician with relevant chemical data in real-time. The integration of an electrochemical sensor into a microfluidic chip allows for the achievement of real-time chemical monitoring due to the low consumption of analytes, short analysis time, low cost, and compact size. In this work, dopamine, used as a model, is an important neurotransmitter responsible for controlling various vital life functions. The aim is to develop a novel serpentine microfluidic-based electrochemical sensor, using a screen-printed electrode for continuous dopamine detection. The developed sensor employed the composite of ordered mesoporous carbon (OMC) and poly (3,4 ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT-PSS). The performance of a microfluidic, integrated with the sensor, was amperometrically evaluated using a computer-controlled microfluidic platform. The microfluidic-based dopamine sensor exhibited a sensitivity of 20.2 ± 0.6 μA μmol L^-1, and a detection limit (LOD) of 21.6 ± 0.002 nmol L^-1, with high selectivity. This microfluidic-based electrochemical sensor was successfully employed to determine dopamine continuously, which could overcome the problem of sensor fouling with more than 90% stability for over 24 h. This novel microfluidic sensor platform provides a powerful tool for the development of a continuous dopamine detection system for human clinical application.

An enzymatic histamine biosensor based on a screen-printed carbon electrode modified with a chitosan-gold nanoparticles composite cryogel on Prussian blue-coated multi-walled carbon nanotubes

A histamine biosensor was developed based on a screen-printed carbon electrode modified with Prussian blue (PB) electrodeposited on multi-walled carbon nanotubes covered with a macroporous layer of chitosan-gold nanoparticles composite cryogel (CS-AuNPs Cry). With its high specific surface area and conductivity, CS-AuNPs Cry proved an excellent supporting material for diamine oxidase (DAO) immobilization. PB acted as a redox mediator to promote electron transfer between hydrogen peroxide and the electrode surface. The PB reduction current was measured during the hydrogen peroxide-releasing oxidation of histamine catalyzed by DAO. The proposed biosensor displayed two linear ranges: 2.50-125.0 µmol L^-1 and 125.0-400.0 µmol L^-1. The limit of detection was 1.81 µmol L^-1. Reproducibility was good (RSD = 5.46%), operational stability high, long-term stability excellent, and selectivity good. The biosensor determined histamine levels in fish and shrimps with satisfactory recoveries, and the obtained results agreed with those obtained by ELISA.

A highly sensitive flow injection amperometric glucose biosensor using a gold nanoparticles/polytyramine/Prussian blue modified screen-printed carbon electrode

A novel oxidase enzyme sensor was fabricated based on the chemisorption of highly active glucose oxidase (GOx) on gold nanoparticles that were adsorbed on a polytyramine layer (AuNPs/Pty). The GOx/AuNPs/Pty assembly was coated on a Prussian blue (PB)-modified screen-printed carbon electrode (SPCE) to produce the GOx/AuNPs/Pty/PB/SPCE biosensor. The amperometric glucose biosensor response was measured at -0.10 V using a Ag pseudo-reference electrode through the reduction current of the PB mediator in a flow injection analysis system. Under optimised experimental conditions, the developed biosensor displayed linearity over the 1.0 μM-1.0 mM glucose concentration range and a limit of detection of 1.0 μM (S/N ≥ 3). A low value for the Michaelis constant of 0.21 mM indicated that the immobilised GOx had high affinity for glucose. The developed biosensor exhibited excellent operational stability over 374 injections, long-term stability over 3 weeks, good reproducibility (relative standard deviations = 1.9%-4.3%) and high selectivity. The results obtained analysing glucose in blood plasma samples were satisfactory when compared with the corresponding results recorded implementing the standard hexokinase-spectrophotometric method (P > 0.05).

Simultaneous Detection of Ammonium and Nitrate in Environmental Samples Using on Ion-Selective Electrode and Comparison with Portable Colorimetric Assays

Simple, robust, and low-cost nitrate- and ammonium-selective electrodes were made using substrate prepared from household materials. We explored phosphonium-based ILs and poly (methyl methacrylate)/poly(decyl methacrylate)(MMA-DMA) copolymer as matrix materials alternative to classical PVC-based membranes. IL-based membranes showed suitability only for nitrate-selective electrode exhibiting linear concentration range between 5.0 × 10^-6 and 2.5 × 10^-3 M with a detection limit of 5.5 × 10^-7 M. On the other hand, MMA-DMA-based membranes showed suitability for both ammonium- and nitrate-selective electrodes, and were successfully applied to detect NO₃^- and NH₄⁺ in water and soil samples. The proposed ISEs exhibited near-Nernstian potentiometric responses to NO₃^- and NH₄⁺ with the linear range concentration between 5.0 × 10^-5 and 5.0 × 10^-2 M (LOD = 11.3 µM) and 5.0 × 10^-6 and 1.0 × 10^-3 M (LOD = 1.2 µM), respectively. The power of ISEs to detect NO₃^- and NH₄⁺ in water and soils was tested by comparison with traditional, portable colorimetric techniques. Procedures required for analysis by each technique from the perspective of a non-trained person (e.g., farmer) and the convenience of the use on the field are compared and contrasted.

Phage-based capacitive biosensor for Salmonella detection

This article reports the detection of Salmonella spp. based on M13 bacteriophage in a capacitive flow injection system. Salmonella-specific M13 bacteriophage was immobilized on a polytyramine/gold surface using glutaraldehyde as a crosslinker. The M13 bacteriophage modified electrode can specifically bind to Salmonella spp. via the amino acid groups on the filamentous phage. An alkaline solution was used to break the binding between the sensing surface and the analyte to allow renewable use up to 40 times. This capacitive system provided good reproducibility with a relative standard deviation (RSD) of 1.1%. A 75 µL min^-1 flow rate and a 300 µL sample volume provided a wide linear range, from 2.0 × 10² to 1.0 × 10⁷ cfu mL^-1, with a detection limit of 200 cfu mL^-1. Bacteria concentration can be analyzed within 40 min after the sample injection. When applied to test real samples (raw chicken meat) it provided good recoveries (100-111%). An enrichment process was also explored to increase the bacteria concentration, enabling a quantitative detection of Salmonella spp. This biosensor opens a new opportunity for the detection of pathogenic bacteria using bacteriophage.

Pyrrolidinyl PNA polypyrrole/silver nanofoam electrode as a novel label-free electrochemical miRNA-21 biosensor

A label-free electrochemical miRNA biosensor was developed based on a pyrrolidinyl peptide nucleic acid (acpcPNA)/polypyrrole (PPy)/silver nanofoam (AgNF) modified electrode. The AgNF was electrodeposited as redox indicator on a gold electrode, which was then functionalized with an electropolymerized layer of PPy, a conducting polymer, to immobilize the PNA probes. The fabrication process was investigated by electrochemical impedance spectroscopy. The biosensor was used to detect miRNA-21, a biomarker abnormally expressed in most cancers. The signal was monitored by the change in current of the AgNF redox reaction before and after hybridization using cyclic voltammetry. Two PNA probe lengths were investigated and the longer probe exhibited a better performance. Nucleotide overhangs on the electrode side affected the signal more than overhangs on the solution side due to the greater insulation of the sensing surface. Under optimal conditions, the electrochemical signal was proportional to miRNA-21 concentrations between 0.20fM and 1.0nM, with a very low detection limit of 0.20fM. The biosensor showed a high specificity which could discriminate between complementary, single-, doubled-base mismatched, and non-complementary targets. Three out of the seven tested plasma samples provided detectable concentrations (63 ± 4, 111 ± 4 and 164 ± 7fM). The sensor also showed good recoveries (81-119%). The results indicated the possibilities of this biosensor for analysis without RNA extraction and/or amplification, making the sensor potentially useful for both the prognosis and diagnosis of cancer in clinical application.

Enhancing capacitive DNA biosensor performance by target overhang with application on screening test of HLA-B*58:01 and HLA-B*57:01 genes

A highly sensitive label-free DNA biosensor based on PNA probes immobilized on a gold electrode was used to detect a hybridization event. The effect of a target DNA overhang on the hybridization efficiency was shown to enhance the detected signal and allowed detection at a very low concentration. The sensors performances were investigated with a complementary target that had the same length as the probe, and the signal was compared to the target DNAs with different lengths and overhangs. A longer target DNA overhang was found to provide a better response. When the overhang was on the electrode side the signal enhancement was greater than when the overhang was on the solution side due to the increased thickness of the sensing surface, hence produced a larger capacitance change. Using conformationally constrained acpcPNA probes, double stranded DNA was detected sensitively and specifically without any denaturing step. When two acpcPNA probes were applied for the screening test for the double stranded HLA-B*58:01 and HLA-B*57:01 genes that are highly similar, the method differentiated the two genes in all samples. Both purified and unpurified PCR products gave comparable results. This method would be potentially useful as a rapid screening test without the need for purification and denaturation of the PCR products.

Electrochemical detection of the disease marker human chitinase-3-like protein 1 by matching antibody-modified gold electrodes as label-free immunosensors

Tissue inflammation, certain cardiovascular syndromes and the occurrence of some solid tumors are correlated with raised serum concentrations of human chitinase-3-like protein 1 (YKL-40), a mammalian chitinase-like glycoprotein, which has become the subject of current research. Here we report the construction and characterization of an electrochemical platform for label-free immunosensing of YKL-40. Details of the synthesis of YKL-40 and production of anti-YKL-40 immunoglobulin G (IgG) are provided and cross-reactivity tests presented. Polyclonal anti-YKL-40 IgG was immobilized on gold electrodes and the resulting immunosensors were operated in an electrochemical flow system with capacitive signal generation. The strategy offered a wide linear detection range (0.1μg/L to 1mg/L) with correlation coefficients (R(2)) above 0.99 and good sensitivity (12.28±0.27nF/cm(2) per decade of concentration change). Additionally, the detection limit of 0.07±0.01μg/L was well below that of optical enzyme-linked immunosorbent assays (ELISAs), which makes the proposed methodology a promising alternative for YKL-40 related disease studies.

Label-free capacitive DNA sensor using immobilized pyrrolidinyl PNA probe: effect of the length and terminating head group of the blocking thiols

This paper reports, for the first time, the influence of the length and the terminating head group of blocking thiols on the sensitivity and specificity of a label-free capacitive DNA detection system using immobilized pyrrolidinyl peptide nucleic acid (acpcPNA) probes. A C-terminal lysine-modified acpcPNA was immobilized through four different alkanethiol self-assembled monolayers (SAMs), i.e., 3-mercaptopropionic acid (MPA), thioctic acid (TA), thiourea (TU) and mercaptosuccinic acid (MSA). The hybridization between the acpcPNA probes and the target DNA was directly measured using the capacitive system. Five blocking thiols of various lengths (C=3, 6, 8, 9 and 11), with the -OH terminating head group, i.e., 3-mercapto-1-propanol (3-MPL), 6-mercapto-1-hexanol (6-MHL), 8-mercapto-1-octanol (8-MOL), 9-mercapto-1-nonanol (9-MNL), 11-mercapto-1-undecanol (11-MUL) and another blocking thiol (C=11) with a -CH(3) terminating head group, and 1-dodecanethiol (1-DDT) were investigated. The blocking thiol with the same length as the total spacer of the immobilized acpcPNA gave the highest sensitivity and specificity with the -OH terminating head group providing a slightly better signal than the -CH(3) group. Under the optimized conditions, the immobilized acpcPNA probes provided a wide linear range for DNA detection (1.0 × 10(-11)-1.0 × 10(-8)M) with a very low detection limit in the picomolar range. The modified acpcPNA electrode could be reused through at least 58 cycles. The high sensitivity and very low detection limits are potentially useful for the analysis of ultra-trace levels of DNA in samples. Preliminary studies were also performed to see the effect of probe concentration and target length.

Aptamer-based potentiometric measurements of proteins using ion-selective microelectrodes

We here report on the first example of an aptamer-based potentiometric sandwich assay of proteins. The measurements are based on CdS quantum dot labels of the secondary aptamer, which were determined with a novel solid-contact Cd2+-selective polymer membrane electrode after dissolution with hydrogen peroxide. The electrode exhibited cadmium ion detection limits of 100 pM in 100 mL samples and of 1 nM in 200 microL microwells, using a calcium-selective electrode as a pseudoreference electrode. As a prototype example, thrombin was measured in 200 microL samples with a lower detection limit of 0.14 nM corresponding to 28 fmol of analyte. The results show great promise for the potentiometric determination of proteins at very low concentrations in microliter samples.