Raman Spectroscopy as an Assay to Disentangle Zinc Oxide Carbon Nanotube Composites for Optimized Uric Acid Detection

Abstract

Refluxed zinc oxide (ZnO) nanoparticles (NPs) were prepared and attached to carboxylic acid functionalized multi-walled carbon nanotubes (COOH-MWNTs) via sonication. Practical optimization of electrocatalysts using sonication to disentangle a carbon nanotube composite for monitoring uric acid (UA) is shown. Monitoring UA is important for the management of medical disorders. Selection of sonication time is a crucial step in producing the desired composite. We report, for the first time, the practical use of Raman spectroscopy to tune the sonication involved in tethering ZnO NPs to the multi-walled carbon nanotube (MWNT) surface. Maximum current for detecting UA, using chronoamperometry and cyclic voltammetry, correlated with the highest sp2-hybridized carbon signal, as seen in the integrated Raman G band peak areas denoting maximum COOH-MWNT disentanglement. An array of ZnO/COOH-MWNT composites were prepared ranging from 60 to 240 min sonication times. Optimum sonication (150 min) corresponded with both maximum measured current and MWNT disentanglement. The sensor was able to quantitatively and selectively measure UA at clinically relevant concentrations (100–900 μM) with rapid current response time (< 5 s).

A Cobalt (II) Oxide Carbon Nanotube Composite to Assay Dopamine

“…that more of the particulate surface area can be exposed and thereby increase electrocatalytic activity of ZnO/COOH-MWNTs [28]. However, this same effect was not observed for CoO/COOH-MWNTs for the detection of DA; the degree of disentanglement of the underlying carbon nanotube surface had no effect on the sensitivity of the composite.…”

“…Hence, the sonication time needed to produce the optimized dispersion of the composite needs to be experimentally determined prior to its use as a sensor. We have recently discovered that sonication can disentangle the COOH-MWNT support such that more of the particulate surface area can be exposed and thereby increase electrocatalytic activity of ZnO/COOH-MWNTs [28]. However, this same effect was not observed for CoO/COOH-MWNTs for the detection of DA; the degree of disentanglement of the underlying carbon nanotube surface had no effect on the sensitivity of the composite.…”

“…A drop casting method was used to modify the GCE surface using CoO/COOH-MWNT composite suspension. This approach has been effective for attaching metal oxide nanoparticles to the COOH-MWNT sidewalls using the cavitation process offered by sonication to tether them to the COOH functional groups [26][27][28]. The GCE surface was polished using 1.0 and 0.05 µm diameter alumina slurries, successively, with 10 min of sonication in between to obtain a mirror-like finish.…”

“…We observe an electrocatalytic activity dependence with sonication time ( Figure 1B). Sonication was used to attach the particles to the underlying COOH-MWNT surface, as demonstrated previously in our laboratory [26][27][28]. Sonication periods that are too brief are known to result in a sparse density of attached particles while excessively prolonged times damages the stable carboxylate -COO-structures needed to create a fine dispersion of them, often resulting in agglomeration and reduced electroactive surface area [31].…”

Carbon Nanotubes, Graphene, and Carbon Dots as Electrochemical Biosensing Composites

“…Pt nanoparticles have successfully been attached to functionalized MWCNTs using this sonication procedure [33]. This sonication approach has been used to attach zinc oxide (ZnO) NPs to the COOH-functionalized MWCNT sidewalls, useful for uric-acid sensing [34]. Sonication was also used to combine CoO NPs with MWCNTs for assaying dopamine using CV [35].…”