Progress of Polyaniline Glucose Sensors for Diabetes Mellitus Management Utilizing Enzymatic and Non-Enzymatic Detection.

Glucose measurement is a fundamental tool in the daily care of Diabetes Mellitus (DM) patients and healthcare professionals. While there is an established market for glucose sensors, the rising number of DM cases has promoted intensive research to provide accurate systems for glucose monitoring. Polyaniline (PAni) is a conductive polymer with a linear conjugated backbone with sequences of single C-C and double C=C bonds. This unique structure produces attractive features for the design of sensing systems such as conductivity, biocompatibility, environmental stability, tunable electrochemical properties, and antibacterial activity. PAni-based glucose sensors (PBGS) were actively developed in past years, using either enzymatic or non-enzymatic principles. In these devices, PAni played roles as a conductive material for electron transfer, biocompatible matrix for enzymatic immobilization, or sensitive layer for detection. In this review, we covered the development of PBGS from 2015 to the present, and it is not even exhaustive; it provides an overview of advances and achievements for enzymatic and non-enzymatic PBGB PBGS for self-monitoring and continuous blood glucose monitoring. Additionally, the limitations of PBGB PBGS to advance into robust and stable technology and the challenges associated with their implementation are presented and discussed.

Simultaneous Detection of Dihydroxybenzene Isomers Using Electrochemically Reduced Graphene Oxide-Carboxylated Carbon Nanotubes/Gold Nanoparticles Nanocomposite.

An electrochemical sensor based on electrochemically reduced graphene oxide (ErGO), carboxylated carbon nanotubes (cMWCNT), and gold nanoparticles (AuNPs) (GCE/ErGO-cMWCNT/AuNPs) was developed for the simultaneous detection of dihidroxybenzen isomers (DHB) hydroquinone (HQ), catechol (CC), and resorcinol (RS) using differential pulse voltammetry (DPV). The fabrication and optimization of the system were evaluated with Raman Spectroscopy, SEM, cyclic voltammetry, and DPV. Under optimized conditions, the GCE/ErGO-cMWCNT/AuNPs sensor exhibited a linear concentration range of 1.2-170 µM for HQ and CC, and 2.4-400 µM for RS with a detection limit of 0.39 µM, 0.54 µM, and 0.61 µM, respectively. When evaluated in tap water and skin-lightening cream, DHB multianalyte detection showed an average recovery rate of 107.11% and 102.56%, respectively. The performance was attributed to the synergistic effects of the 3D network formed by the strong π-π stacking interaction between ErGO and cMWCNT, combined with the active catalytic sites of AuNPs. Additionally, the cMWCNT provided improved electrocatalytic properties associated with the carboxyl groups that facilitate the adsorption of the DHB and the greater amount of active edge planes. The proposed GCE/ErGO-cMWCNT/AuNPs sensor showed a great potential for the simultaneous, precise, and easy-to-handle detection of DHB in complex samples with high sensitivity.

Naked-Eye Detection of Glucose in Saliva with Bienzymatic Paper-Based Sensor.

The high incidence of Diabetes Mellitus in low-income regions has promoted the development of low-cost alternatives to replace blood-based procedures. In this work, we present a bienzymatic paper-based sensor suitable for the naked-eye detection of glucose in saliva samples. The sensor was obtained by a stamping procedure and modified with chitosan to improve the colorimetric readout. The bienzymatic reaction of GOx-HRP coupled with 2,4,6-tribromo-3-hydroxy benzoic acid was applied for the detection of glucose within a range from 0 to 180 mgdL-1 in buffer and artificial saliva solutions. The visual readout was perceived by the naked eye and registered with an office scanner to evaluate the analytical performance. The results showed a limit of detection of 0.37 mgdL-1 (S/N = 3) with an R.S.D. of 1.69% and a linear range from 1 to 22.5 mgdL-1 with an R² of 0.99235. The analysis of human saliva samples was performed without pre-processing, achieving recoveries from 92 to 114%. The naked-eye detection was evaluated under two different light settings, showing average recoveries of 108.58 and 90.65% for standard and low illumination. The proposed device showed potential for easy-to-use, sensitive, low-cost, fast, and device-free detection of salivary glucose suitable for untrained personnel operation and limited facilities.

The Evaluation of a Low-Cost Colorimeter for Glucose Detection in Salivary Samples.

Given the limited access to healthcare resources, low-income settings require the development of affordable technology. Here we present the design and evaluation of a low-cost colorimeter applied to the non-invasive monitoring of Diabetes Mellitus through the detection of glucose in salival fluid. Samples were processed by the glucose oxidase-peroxidase enzymatic system and analyzed with the development equipment. A light emission diode of 532.5 nm was used as an excitation source and a RGB module was used as a receptor. A calibration curve to quantify the concentration of salivary glucose (0 to 18 mg/dL) was carried out by relating the RGB components registered with glucose concentrations, achieving a limit of detection of 0.17 mg/dL with a CV of 5% (n = 3). Salivary samples of diabetic and healthy volunteers were processed with the equipment showing an average concentration of 1.5519 ± 0.4511 mg/dL for the first and 4.0479 ± 1.6103 mg/dL for the last, allowing a discrimination between both groups. Results were validated against a UV-Vis-NIR spectrophotometer with a correspondence of R² of 0.98194 between both instruments. Results suggest the potential application of the developed device to the sensitive detection of relevant analytes with a low-cost, user-friendly, low-power and portable instrumentation.

Automated flow-through amperometric immunosensor for highly sensitive and on-line detection of okadaic acid in mussel sample.

An electrochemical immunosensor for okadaic acid (OA) detection has been developed, and used in an indirect competitive immunoassay format under automated flow conditions. The biosensor was fabricated by injecting OA modified magnetic beads onto screen printed carbon electrode (SPCE) in the flow system. The OA present in the sample competed with the immobilized OA to bind with anti-okadaic acid monoclonal antibody (anti-OA-MAb). The secondary alkaline phosphatase labeled antibody was used to perform electrochemical detection. The current response obtained from the labeled alkaline phosphatase to 1-naphthyl phosphate decreased proportionally to the concentration of free OA in the sample. The calculated limit of detection (LOD) was 0.15 µg/L with a linear range of 0.19-25 µg/L. The good recoveries percentages validated the immunosensor application for real mussel samples. The developed system automatically controlled the incubation, washing and current measurement steps, showing its potential use for OA determination in field analysis.

A novel automated flow-based biosensor for the determination of organophosphate pesticides in milk.

This work describes the development of an automated flow-based biosensor that employs genetically modified acetylcholinesterase (AChE) enzymes B394, B4 and wild type B131. The biosensor was based on a screen printed carbon electrode (SPE) that was integrated into a flow cell. Enzymes were immobilised on cobalt (II) phthalocyanine (CoPC) modified electrodes by entrapment in a photocrosslinkable polymer (PVA-AWP). The automated flow-based biosensor was successfully used to quantify three organophosphate pesticides (OPs) in milk samples. The OPs used were chlorpyriphos-oxon (CPO), ethyl paraoxon (EPOx) and malaoxon (MOx). The total analysis time for the assay was less than 15 min. Initially, the biosensor performance was tested in phosphate buffer solution (PBS) using B394, B131 and B4 biosensors. The best detection limits were obtained with B394; therefore, this biosensor was used to produce calibration data in milk with three OPs in the concentration range of 5 × 10(-6)M to 5 × 10(-12)M. The limit of detection (LOD) obtained in milk for CPO, EPOx and MOx were 5 × 10(-12)M, 5 × 10(-9)M and 5 × 10(-10)M, respectively, with a correlation coefficient R(2)=0.9910. The automated flow-based biosensor successfully quantified the OPs in different fat-containing milk samples. There were no false positives or false negatives observed for the analytical figures of merit for the constructed biosensors. This method is inexpensive, sensitive, portable, non-invasive and provides real-time results. This analytical system can provide rapid detection of highly toxic OPs in food matrices such as milk.

An approach to an inhibition electronic tongue to detect on-line organophosphorus insecticides using a computer controlled multi-commuted flow system.

An approach to an inhibition bioelectronic tongue is presented. The work is focused on development of an automated flow system to carry out experimental assays, a custom potentiostat to measure the response from an enzymatic biosensor, and an inhibition protocol which allows on-line detections. A Multi-commuted Flow Analysis system (MCFA) was selected and developed to carry out assays with an improved inhibition method to detect the insecticides chlorpyrifos oxon (CPO), chlorfenvinfos (CFV) and azinphos methyl-oxon (AZMO). The system manifold comprised a peristaltic pump, a set of seven electronic valves controlled by a personal computer electronic interface and software based on LabView® to control the sample dilutions into the cell. The inhibition method consists in the injection of the insecticide when the enzyme activity has reached the plateau of the current; with this method the incubation time is avoided. A potentiostat was developed to measure the response from the enzymatic biosensor. Low limits of detection of 10 nM for CPO, CFV, and AZMO were achieved.