Sensitive determination of 4,6-dinitro-o-cresol based on a glassy carbon electrode modified with Zr-UiO-66 metal-organic framework entrapped FMWCNTs.

A DNOC electrochemical sensor has been developed by using a composite of Zr-UiO-66 and FMWCNTs on a glassy carbon electrode (GCE) and using the differential pulse voltammetry technique. The synthesized materials were physico-chemically characterized by BET, PXRD, FTIR, TGA, EDX, and FESEM. Cyclic voltammetry showed that DNOC has three oxidation peaks at 0.03 V (RSD: 0.23%), 0.42 V (RSD: 0.21%), and 1.32 V (RSD: 0.32%) and three reduction peaks at - 0.20 V (RSD: 0.15%), - 0.82 V (RSD: 0.26%), and - 1.14 V (RSD: 0.19%) which follow a diffusion-controlled mechanism. Different parameters were optimized using differential pulse voltammetry and good linear ranges were found for the simultaneous detection of the three reduction peaks. For a specific concentration range of 0.1-50 µM, a limit of detection of 0.119 µM based on 3Sb/m was obtained. The interfering effects of five non-phenolic pesticides and five heavy metals were evaluated to highlight the selectivity of the developed sensor. It is the first report of an electrochemical DNOC sensor in which all three oxidation peaks are prominently visible. Ethion and chloropyriphos were found to inhibit the redox process of DNOC on the developed sensor platform Zr-UiO-66/FMWCNT/GCE. The sensor was successfully applied to DNOC determination in spiked potato samples and the results showed a standard deviation of less than 3%. The proposed method is expected to provide a novel platform for the quantitative determination of DNOC pesticides in vegetables.

An ultra-sensitive uric acid second generation biosensor based on chemical immobilization of uricase on functionalized multiwall carbon nanotube grafted palm oil fiber in the presence of a ferrocene mediator.

In this work, palm oil fiber (POF) grafted functionalized multiwall carbon nanotube (FMWCNT) decorated ferrocene (Fc) has been drop coated on a platinum electrode (Pt), in which uricase (UOx) has been chemically immobilized for sensitive and selective biosensing of uric acid (UA). Through the use of EDC/NHS, a stable bioelectrode (UOx/Fc/FMWCNT-POF/Pt) was obtained and characterized by FTIR/ATRIR, XRD, Raman, EA/EDX, TGA, SEM, TEM, CV, EIS, CA, and DPV. Results from DPV showed the rapid response of the developed bioelectrode towards UA (0.185 V) with high sensitivity (41.14 µA mM-1) and good limit of detection (19 µM) in the linear range 10-1000 µM. The low value of Michaelis-Menten constant (km = 31.364 µM) shows high affinity of the UA towards the enzyme at the electrode surface. The developed biosensor demonstrates good reproducibility, repeatability, and stability with a deviation of less than 2.5%, and was successfully applied for human blood sample analysis. The CA study revealed a fast response time (2 s) of the sensor. The work has pioneered a new addition to the class of tailorable chemical species for biosensor development and proven to be a promising new tool for point of care testing (POCT) applications.