A new composite electrode has been fabricated using multiwall carbon nanotubes (MWCNT) and the ionic liquid n-octylpyridinum hexafluorophosphate (OPFP). This electrode shows very attractive electrochemical performances compared to other conventional electrodes using graphite and mineral oil, notably improved sensitivity and stability. One major advantage of this electrode compared to other electrodes using carbon nanotubes and other ionic liquids is its extremely low capacitance and background currents. A 10% (w/w) loading of MWCNT was selected as the optimal composition based on voltammetric results, as well as the stability of the background response in solution. The new composite electrode showed good activity toward hydrogen peroxide and NADH, with the possibility of fabricating a sensitive biosensor for glucose and alcohol using glucose oxidase and alcohol dehydrogenase, respectively, by simply incorporating the specific enzyme within the composite matrix. The marked electrode stability and antifouling features toward NADH oxidation was much higher for this composite compared to a bare glassy carbon electrode. While a loading of 2% MWCNT showed very poor electrochemical behavior, a large enhancement was observed upon gentle heating to 70 degrees C, which gave a response similar to the optimum composition of 10%. The ease of preparation, low background current, high sensitivity, stability, and small loading of nanotubes using this composite can create new novel avenues and applications for fabricating robust sensors and biosensors for many important species.

A sensitive electroanalytical methodology for the determination of capsaicin using adsorptive stripping voltammetry (AdsSV) at a multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode (MWCNT-BPPGE) is presented. This analytical method is then further developed using a multiwalled carbon nanotube screen-printed electrode (MWCNT-SPE) demonstrating the proof-of-concept that this approach can easily be incorporated into a sensing device which is both facile to use and inexpensive to produce. Capsaicin is the chemical responsible for the hot taste of chilli peppers, and measuring the concentration of capsaicin is an indicator of how hot any given chilli pepper, hot sauce and other related foodstuffs are. Standard additions plots for AdsSV of capsaicin at open circuit potential at a MWCNT-BPPGE exhibits two linear ranges, from 0.5 to 15 microM and from 15 to 60 microM. Using the first range of calibration curve, a detection limit of 0.31 microM (based on 3sigma) is obtained. The plot of standard additions of capsaicin determined using the disposable MWCNT-SPE shows a linear range between 0.5 and 35 microM and a detection limit of 0.45 microM. MWCNT-BPPGE and MWCNT-SPE are successfully utilized for the determination of capsaicin in real samples, such as a few commercially available hot pepper sauces, and the determined values are in excellent agreement and correlation with the average Scoville unit values reported in the literature for these sauces. To the best of our knowledge, this is the first electroanalytical method using MWCNT-BPPGE or MWCNT-SPE reported for the determination of capsaicin. This method offers advantages such as precision and objectivity over the well-known but potentially subjective Scoville method (based on organoleptic testing by human tasting panels) and is facile and inexpensive compared to existing HPLC methods.

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A simple method using an unmodified edge plane pyrolytic graphite electrode (EPPGE) is reported for the simultaneous determination of dopamine (DA), serotonin (ST) and ascorbic acid (AA). The performance of this electrode is superior to other unmodified carbon-based electrodes and also to many modified electrodes in terms of detection limit, sensitivity and peak separation for determination of DA, ST and AA. Using this method, detection limits of 90 nM, 60 nM and 200 nM were obtained for DA, ST and AA respectively. No electrode fouling is observed during a set of experiments and good sensitivity is obtained for the simultaneous determination of DA, ST and AA. The peaks for the three species are well resolved from each other and the electrode is successfully utilised for their determination in standard and real samples.