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Detection of stress biomarkers molecules, non-invasively, through (non-induced) sweat sampling is an important research field since sweat is a potential diagnostic fluid for early and continuous human health monitoring, not only for stress-related conditions directly but also for other pathologies (e.g., associated with chronic diseases). The simultaneous detection of multiple potential biomarkers in sweat samples, using simple and low-cost electrochemical methods (detecting patterns or “electrochemical fingerprints”) requiring no sample preparation and its correlation with physiological conditions, is an attractive methodology but not readily achievable. Several of these potential biomarkers’ electrochemical response presents very close oxidation potentials, among other factors that hamper the detection, such as pH dependence of the electrochemical response or partial adsorption on electrode surfaces. Disposable screen-printed electrode materials, with relatively low-cost, could be useful to overcome the difficulties. A set of selected potential stress-related (non-protein) biomarkers (tyrosine, phenylalanine, dopamine, serotonin, and hydrocortisone) was used in the current study for qualitative electrochemical detection on different screen-printed carbon-based electrodes. The detection was attained in simulated sweat solutions and real sweat samples. The goal was to evaluate the electrochemical response on the different surfaces and determine the most suitable carbon-based screen-printed electrodes that may be used in future sensing devices.

Cytochrome b5 reductase is an enzyme with the ability to generate superoxide anion at the expenses of NADH consumption. Although this activity can be stimulated by cytochrome c and could participate in the bioenergetic failure accounting in apoptosis, very little is known about other molecules that may uncouple the function of the cytochrome b5 reductase. Naphthoquinones are redox active molecules with the ability to interact with electron transfer chains. In this work, we made an inhibitor screening against recombinant human cytochrome b5 reductase based on naphthoquinone properties. We found that 5-hydroxy-1,4-naphthoquinone (known as juglone), a natural naphthoquinone extracted from walnut trees and used historically in traditional medicine with ambiguous health and toxic outcomes, had the ability to uncouple the electron transfer from the reductase to cytochrome b5 and ferricyanide. Upon complex formation with cytochrome b5 reductase, juglone is able to act as an electron acceptor leading to a NADH consumption stimulation and an increase of superoxide anion production by the reductase. Our results suggest that cytochrome b5 reductase could contribute to the measured energetic failure in the erythrocyte apoptosis induced by juglone, that is concomitant with the reactive oxygen species produced by cytochrome b5 reductase.