Abstract
Screen printed electrodes were employed in a proof of concept determination of homocysteine and glutathione using electrochemically oxidized catechol via a 1,4-Michael addition reaction in the absence and presence of cysteine, and each other. Using cyclic voltammetry, the Michael reaction introduces a new adduct peak which is analytically useful in detecting thiols. The proposed procedure relies on the different rates of reaction of glutathione and homocysteine with oxidized catechol so that at fast voltage scan rates only homocysteine is detected in cyclic voltammetry. At slower scan rates, both glutathione and homocysteine are detected. The combination of the two sets of data provides quantification for homocysteine and glutathione. The presence of cysteine is shown not to interfere provided sufficient high concentrations of catechol are used. Calibration curves were determined for each homocysteine and glutathione detection; where the sensitivities are 0.019 μA·μM−1 and 0.0019 μA·μM−1 and limit of detections are ca. 1.2 μM and 0.11 μM for homocysteine and glutathione, respectively, within the linear range. This work presents results with potential and beneficial use in re-useable and/or disposable point-of-use sensors for biological and medical applications.
Highlights
Screen-printing technology is a well-known and established technology for mass producing electrodes [1,2,3]
This paper reports on the use of disposable screen-printed electrodes to facilitate the determination of homocysteine and glutathione in the presence of each other in a pure aqueous system by utilizing an ortho-quinone as the mediator
Shown in the Figure 6ib, the cyclic voltammetric response of electro-oxidized catechol when homocysteine is present in solution shows an increase in the forward peak, decrease in the back peak and the appearance of a new adduct peak; indicating a
Summary
Screen-printing technology is a well-known and established technology for mass producing electrodes [1,2,3]. To satisfy the growing technology of present and future applications, screen-printed electrodes are becoming more attractive and ideal for applications that require high throughput screening or do not require the need for complex and expensive equipment, such as bio-applications [1,2] Thiols such as homocysteine, HCys (Figure 1a), and glutathione, GSH (Figure 1b), are known to offer biological insight in respect of reflecting normal metabolism functions and homeostasis [6]. The glutathione content can be determined by subtracting the determined homocysteine value from the total adduct peak obtained at the slower scan rate This proof of concept work was further applied to pre-determined mixed solutions containing both analytes (glutathione and homocysteine) and later applied again with mixed solutions containing another added thiol compound, cysteine (Figure 1c) to further emphasize the value of this proposed procedure towards possible practical applications on physiological fluids (i.e., urine and/or plasma). The use of screen-printed electrodes continues to add upon the proposed idea of a possible portable sensor, whether it is for space-saving equipment in the lab or a point-of-care system for a medical facility
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