Carbon nanotubes incorporated with sol–gel derived La(OH)3 nanorods as platform to simultaneously determine ascorbic acid, dopamine, uric acid and nitrite

La(OH)3 Multi-Walled Carbon Nanotube/Carbon Paste-Based Sensing Approach for the Detection of Uric Acid—A Product of Environmentally Stressed Cells

This paper aims to develop an amperometric, non-enzymatic sensor for detecting and quantifying UA as an alert signal induced by allergens with protease activity in human cell lines (HEK293 and HeLa). Uric acid (UA) has been classified as a damage-associated molecular pattern (DAMP) molecule that serves a physiological purpose inside the cell, while outside the cell it can be an indicator of cell damage. Cell damage or stress can be caused by different health problems or by environmental irritants, such as allergens. We can act and prevent the events that generate stress by determining the extent to which cells are under stress. Amperometric calibration measurements were performed with a carbon paste electrode modified with La(OH)₃@MWCNT, at the potential of 0.3 V. The calibration curve was constructed in a linear operating range from 0.67 μM to 121 μM UA. The proposed sensor displayed good reproducibility with an RSD of 3.65% calculated for five subsequent measurements, and a low detection limit of 64.28 nM, determined using the 3 S/m method. Interference studies and the real sample analysis of allergen-treated cell lines proved that the proposed sensing platform possesses excellent sensitivity, reproducibility, and stability. Therefore, it can potentially be used to evaluate stress factors in medical research and clinical practice.

Printed Combinatorial Sensors for Simultaneous Detection of Ascorbic Acid, Uric Acid, Dopamine, and Nitrite

In this study, an effective and simple direct printing method was developed to create sensing devices on screen-printed carbon electrodes (SPCEs) to detect multiple species simultaneously. Two sensing materials, graphene oxide nanoribbons (GONRs) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), were printed on one SPCE for detection of multiple biochemical substances. Printed layers of the GONRs and PEDOT:PSS mixture (GONRs & PEDOT:PSS) on SPCE showed embedment of GONRs in the PEDOT:PSS layer and diminished the electrochemical activity of GONRs. In contrast, by printing the GONRs and PEDOT:PSS at separate locations (GONRs + PEDOT:PSS) on the same SPCE, the electrochemical activities of both GONRs and PEDOT:PSS can be preserved. Thus, without synthesizing new materials, the modified electrode is able to simultaneously detect ascorbic acid (AA), uric acid (UA), dopamine (DA), and nitrite (NO₂^-), with high anodic oxidation currents and well-separated voltammetric peaks, in differential pulse voltammetry measurements. The detection limits for the four analytes are 41 nM (AA), 30 nM (DA), 11 nM (UA), and 18 nM (NO₂^-), respectively. The electrode can either detect single species separately or simultaneously determine specific concentrations of the four species in aqueous mixtures, and this can be further extended for many other electrochemical sensing applications.

Novel Modifications to Carbon-Based Electrodes to Improve the Electrochemical Detection of Dopamine

In this work, we describe three simple modifications to carbon electrodes that were found to improve the detection of an exemplar neurotransmitter (dopamine) in the presence of physiological interferents (ascorbic acid and/or uric acid). First, the electro-oxidation of ascorbic acid, as a pretreatment, at boron-doped diamond electrode (BDE) interfaces is studied. This treatment did suppress the detection of ascorbic acid oxidation signal, but only in a manner suitable for single-use detection of high concentrations of dopamine (i.e., > 1 μM). Second, the hydrogenation of BDE by electrochemical cathodic treatment and plasma hydrogenation was investigated. Large cathodic, applied potentials (i.e., > - 5 V) and hydrogen plasma pretreatment of BDE lead to the partial and complete oxidization of ascorbic acid before dopamine, respectively. The consequence at hydrogen-plasma treated BDE is the complete electrochemical separation of these two species without any typical catalytic reactions between the analytes. Third, the modification of glassy carbon electrodes with carbon black nanoparticles is explored. This modification enables the simultaneous detection of ascorbic acid, dopamine and uric acid, significantly enhancing the sensitivity of dopamine. Dopamine was best detected using the unconventional route of detecting 5,6-dihydroxyindole, which is made possible by use of carbon-black nanoparticles. The potential of all three studied modifications to be of electroanalytical use is highlighted throughout this work.

A Nicotinamide Adenine Dinucleotide Dispersed Multi-walled Carbon Nanotubes Electrode for Direct and Selective Electrochemical Detection of Uric Acid

A nanocomposite platform built with multi-walled carbon nanotubes (MWCNTs) and nicotinamide adenine dinucleotide (NAD(+)) via a noncovalent interaction between the large π systems in NAD(+) molecules and MWCNTs on a glassy carbon substrate was successfully developed for the sensitive and selective detection of uric acid (UA) in the presence of ascorbic acid (AA), dopamine (DA). NAD(+) has an adenine subunit and a nicotinamide subunit, which enabled interaction with the purine subunit of UA through a strong π-π interaction to enhance the specificity of UA. Compared with a bare glassy carbon electrode (GCE) and MWCNTs/GCE, the MWCNTs-NAD(+)/GCE showed a low background current and a remarkable enhancement of the oxidation peak current of UA. Using differential pulse voltammetry (DPV), a high sensitivity for the determination of UA was explored for the MWCNTs-NAD(+) modified electrode. A linear relationship between the DPV peak current of UA and its concentration could be obtained in the range of 0.05 - 10 μM with the detection limit as low as 10 nM (S/N = 3). This present strategy provides a novel and promising platform for the detection of UA in human urine and serum samples.

A new strategy for simultaneous determination of 4-aminophenol, uric acid and nitrite based on a graphene/hydroxyapatite composite modified glassy carbon electrode

A novel electrochemical sensor has been fabricated based on a graphene/hydroxyapatite composite modified GCE for the selective and simultaneous detection of 4-aminophenol, uric acid and nitrite ions (NO²⁻) by voltammetric method for the first time.