Electrochemical study of methylene blue incorporated into mordenite type zeolite and its application for amperometric determination of ascorbic acid in real samples

Electrophoresis on a polyester thread coupled with an end-channel pencil electrode detector

We present the design and characterization of a low cost, thread-based electrophoretic device with integrated electrochemical detection. The device has an end-channel pencil graphite electrode placement system for performing electrochemical detection on the thread electrophoresis platform with direct sample pipetting onto the thread. We also established the use of methylene blue and neutral red as a pair of reference migration markers for separation techniques coupled with electrochemical detection, as they have different colors for visual analysis and are both electroactive. Importantly, neutral red was also found to migrate at a similar rate to the EOF, indicating that it can be used as a visual identifier of EOF. The utility of our system was demonstrated by electrophoretic separation and electrochemical detection of physiologically relevant concentrations of pyocyanin in a solution containing multiple electroactive compounds. Pyocyanin is a biomarker for the detection of pathogenic Pseudomonas aeruginosa and has a redox potential that is similar to that of methylene blue. The system was able to effectively resolve methylene blue, neutral red, and pyocyanin in less than 7 min of electrophoretic separation. The theoretical limit of detection for pyocyanin was determined to be 559 nM. The electrophoretic mobilities of methylene blue (0.0236 ± 0.0007 mm² /V·s), neutral red (0.0149 ± 0.0007 mm² /V·s), and pyocyanin (0.0107 ± 0.0003 mm² /V·s) were also determined.

Sandwich-structured nanoparticles-grafted functionalized graphene based 3D nanocomposites for high-performance biosensors to detect ascorbic acid biomolecule

We present a highly sensitive and selective nano-biosensor for rapid, stable and highly reproducible detection of ascorbic acid (AA) in the presence of dopamine, uric acid and other interferences by a three-layer sandwich arrangement of nitrogen-doped functionalized graphene (NFG), silver nanoparticles (AgNPs) and nanostructured polyaniline (PANI) nanocomposite. The enhanced AA electrochemical properties of the NFG/AgNPs/PANI electrode is attributed to the superior conductivity of the NFG-PANI and the excellent catalytic activity of AgNPs. The critical modification of the AgNPs-grafted NFG-PANI coated on very low-cost fluorine doped tin oxide electrode (FTOE) increased the charge transfer conductivity of the electrode (the resistance drops down from 11,000 Ω to 6 Ω). The nano-biosensor was used to accurately detect AA in vitamin C tablets with the recovery of 98%. The sensor demonstrated a low detection limit of 8 µM (S/N = 3) with a very wide linear detection range of 10–11,460 µM, good reproducibility and excellent selectivity performance for AA detection. The results demonstrate that this nanocomposite is a promising candidate for rapid and selective detection of AA in practical clinical samples.

A novel electrochemical analysis of the legal psychoactive drug caffeine using a zeolite/MWCNT modified carbon paste sensor

Caffeine (Caf) is a natural central nervous system stimulant categorized by the US Food and Drug Administration as a safe drug and its maximal amount in soft drinks has been approximately determined to be lower than 200 mg L⁻¹.

A blood-serum sulfide selective electrochemical sensor based on a 9,10-phenanthrenequinone-tethered graphene oxide modified electrode

The sulfide ion and its associated species (H₂S and HS^-) are widely referred to as toxic chemicals. However, at concentrations of ∼10-100 μM, it serves as a neurotransmitter and signaling agent in biological systems. Abnormalities in blood serum sulfide can be an indication of several diseases, including diabetes, wherein there is a significant reduction in the sulfide ion concentration (<10 μM). Herein, we wish report a 9,10-phenanthrenequinone (PQn) tethered graphene oxide (GO) modified glassy carbon electrode (GCE/GO@PQn) for the highly selective and stable electrocatalytic oxidation and flow injection analysis (FIA) of sulfide ions. The electrode exhibits a detection range of 1-100 μM, and is suitable for the common biochemical interference-free detection of blood serum sulfide in pH 7 phosphate buffer solution. The modified electrode was found to be tolerant of interfering chemicals such as cysteine, uric acid, ascorbic acid, nitrate, glucose, hydrogen peroxide, nitrate, nitrite and dissolved oxygen. This is unlike conventional redox mediator modified electrodes, which all show marked interference with the above-mentioned chemicals during sulfide detection. A constructed FIA calibration plot (applied potential, E_app = 0.15 V vs. Ag/AgCl) was linear in the sulfide concentration ranges of 1-100 μM (1^st region) and 300 μM-5 mM (2^nd region) with a detection limit value of 700 nM. The selective and quick FIA of sulfide ions in three diabetic patient blood samples along with a control was demonstrated as a proof of concept.

Ascorbic acid sensor using a PVA/laccase-Au-NPs/Pt electrode

A surface-modified electrode, PVA/laccase-Au-NPs/Pt, was prepared to sense ascorbic acid (H₂A) in this study.

Properties of methylene blue in the presence of zeolite nanoparticles

Properties of methylene blue modified by incorporation in the large pores of LTL and BEA type zeolites, and stabilization on the external surface of small pore LTA type zeolite.

Methylene blue incorporated mesoporous silica microsphere based sensing scaffold for the selective voltammetric determination of riboflavin

Methylene blue incorporated sulfonic acid functionalized mesoporous silica microspheres is synthesized and utilized as effective sensing scaffold for electrochemical determination of nanomolar levels of riboflavin.

Simultaneous Chronoamperometric Sensing of Ascorbic Acid and Acetaminophen at a Boron-Doped Diamond Electrode

Cyclic voltammetry (CV) and chronoamperometry (CA) have been used to sense and determine simultaneously L-ascorbic acid (AA) and acetaminophen (AC) at a boron-doped diamond electrode (BDDE) in a Britton-Robinson buffer solution. The calibration plots of anodic current peak versus concentration obtained from CV and CA data for both investigated compounds in single and di-component solutions over the concentration range 0.01 mM – 0.1 mM proved to be linear, with very good correlation parameters. Sensitivity values and RSD of 2-3% were obtained for various situations, involving both individual and simultaneous presence of AA and AC. The chronoamperometric technique associated with standard addition in sequential one step and/or two successive and continuous chronoamperograms at two characteristic potential levels represented a feasible option for the simultaneous determination of AA and AC in real sample systems such as pharmaceutical formulations. The average values indicated by the supplier were confirmed to a very close approximation from chronoamperomgrams by using several additions with the application of suitable current correction factors.