Poly-L-lysine-modified with ferrocene to obtain a redox polymer for mediated glucose biosensor application.

Ferrocene-based polymers as redox mediators are considered versatile and important in the study of glucose biosensors. Poly-L-lysine (PLL), as a cationic polymer, possesses good properties including biocompatibility, biodegradation and water solubility. In this work, PLL was modified with ferrocene carboxylate in a very simple way by activating the carboxyl group of Fc, which reacted with the amino groups of the polymer. The resulting product was analysed by FTIR. Performance as a redox mediator (Fc-PLL) with the enzyme glucose oxidase was tested by cyclic voltammetry and showed an increase in the oxidation current in the presence of glucose in PBS pH 7.4. Additionally, performance as a biosensor was evaluated by amperometry and gave a linear range of 0-10 mM, a limit of detection of 23 µM, a sensitivity of 6.55 µA/cm2 mM and high selectivity. To evaluate the charged regions of Fc-PLL/GOx on the electrode surface, analysis by scanning electrochemical microscopy showed remarkable activity. The Fc-PLL redox polymer as a glucose biosensor has been well accepted as this kind of material, and the results showed remarkable activity as an electron transfer mediator between the redox polymer and the GOx enzyme.

Use of a Thermophile Desiccation-Tolerant Cyanobacterial Culture and Os Redox Polymer for the Preparation of Photocurrent Producing Anodes.

Oxygenic photosynthesis conducted by cyanobacteria has dramatically transformed the geochemistry of our planet. These organisms have colonized most habitats, including extreme environments such as the driest warm desert on Earth: the Atacama Desert. In particular, cyanobacteria highly tolerant to desiccation are of particular interest for clean energy production. These microorganisms are promising candidates for designing bioelectrodes for photocurrent generation owing to their ability to perform oxygenic photosynthesis and to withstand long periods of desiccation. Here, we present bioelectrochemical assays in which graphite electrodes were modified with the extremophile cyanobacterium Gloeocapsopsis sp. UTEXB3054 for photocurrent generation. Optimum working conditions for photocurrent generation were determined by modifying directly graphite electrode with the cyanobacterial culture (direct electron transfer), as well as using an Os polymer redox mediator (mediated electron transfer). Besides showing outstanding photocurrent production for Gloeocapsopsis sp. UTEXB3054, both in direct and mediated electron transfer, our results provide new insights into the metabolic basis of photocurrent generation and the potential applications of such an assisted bioelectrochemical system in a worldwide scenario in which clean energies are imperative for sustainable development.

Online self-powered Cr(VI) monitoring with autochthonous Pseudomonas and a bio-inspired redox polymer.

The assessment of water quality is critical to implement preventive and emergency interventions aimed to limit/avoid environmental contamination and human exposure to toxic compounds. While established high-resolution techniques allow quantitative and qualitative determination of contaminants, their widespread application is not feasible due to cost, time, and need for trained personnel. In this context, the development of easy-to-implement approaches for preliminary detection of contaminants is of the utmost importance. Herein, a portable self-powered microbial electrochemical sensor enabling online monitoring of Cr(VI) is reported. The biosensor employs a bio-inspired redox mediating system to allow extracellular electron transfer between a bacterial isolate from chromium-contaminated environments and the electrode, providing a clear response to Cr(VI) presence. The biosensor shows good linearity (R2 = 0.983) and a limit of detection of 2.4 mg L-1 Cr(VI), with a sensitivity of 0.31 ± 0.02 µA cm-2 mgCr(VI)-1 L. The presented microbial bioanode architecture enhanced biosensor performance thanks to the improved "electrical wiring" between biological entities and the abiotic electrode surface. This approach could be easily implemented in engineered electrode surfaces, such as paper-based multi-anodes that maximize bacterial colonization, further improving biosensor response. Graphical abstract.