Anthracene-Modified Multi-Walled Carbon Nanotubes as Direct Electron Transfer Scaffolds for Enzymatic Oxygen Reduction

The development of new methods to facilitate direct electron transfer (DET) between enzymes and electrodes is of much interest because of the desire for stable biofuel cells that produce significant amounts of power. In this study, hydroxylated multiwalled carbon nanotubes (MWCNTs) were covalently modified with anthracene groups to help orient the active sites of laccase to allow for DET. The onset of the catalytic oxygen reduction current for these biocathodes occurred near the potential of the T1 active site of laccase, and optimized biocathodes produced background-subtracted current densities up to 140 μA/cm². Potentiostatic and galvanostatic stability measurements of the biocathodes revealed losses of 25% and 30%, respectively, after 24 h of constant operation. Finally, the novel biocathodes were utilized in biofuel cells employing two different anodic enzymes. A compartmentalized cell using a mediated glucose oxidase anode produced an open circuit voltage of 0.819 ± 0.022 V, a maximum power density of 56.8 (±1.8) μW/cm², and a maximum current density of 205.7 (±7.8) μA/cm². A compartment-less cell using a DET fructose dehydrogenase anode produced an open circuit voltage of 0.707 ± 0.005 V, a maximum power density of 34.4 (±2.7) μW/cm², and a maximum current density of 201.7 (±14.4) μA/cm²

Zero-Dimensional Hybrid Organic-Inorganic Indium Bromide with Blue Emission

Low-dimensional hybrid organic-inorganic metal halides have received increased attention because of their outstanding optical and electronic properties. However, the most studied hybrid compounds contain lead and have long-term stability issues, which must be addressed for their use in practical applications. Here, we report a new zero-dimensional hybrid organic-inorganic halide, RInBr4, featuring photoemissive trimethyl(4-stilbenyl)methylammonium (R+) cations and nonemissive InBr4- tetrahedral anions. The crystal structure of RInBr4 is composed of alternating layers of inorganic anions and organic cations along the crystallographic a axis. The resultant hybrid demonstrates bright-blue emission with Commission Internationale de l'Eclairage color coordinates of (0.19, 0.20) and a high photoluminescence quantum yield (PLQY) of 16.36% at room temperature, a 2-fold increase compared to the PLQY of 8.15% measured for the precursor organic salt RBr. On the basis of our optical spectroscopy and computational work, the organic component is responsible for the observed blue emission of the hybrid material. In addition to the enhanced light emission efficiency, the novel hybrid indium bromide demonstrates significantly improved environmental stability. These findings may pave the way for the consideration of hybrid organic In(III) halides for light emission applications

Enzyme Cascade for Catalyzing Sucrose Oxidation in a Biofuel Cell

Biofuel cells provide a safe and renewable means of powering small electronic devices. In this work, we demonstrate a bioanode that is capable of extracting four electrons from a single molecule of sucrose by way of a three-enzyme cascade. Invertase, fructose dehydrogenase and glucose oxidase are immobilized in a ferrocene-modified linear poly­(ethylenimine) (LPEI) hydrogel onto the surface of a carbon electrode. Fuel sources are generated in the polymer film by (1) hydrolyzing sucrose into fructose and glucose and then (2) electroenzymatically oxidizing fructose and glucose to produce a current response. A previously unreported synergistic effect is observed between glucose oxidase and fructose dehydrogenase that results in a current response that is considerably higher than expected. The newly described enzyme cascade generated 302 ± 57 μA/cm² at 25 °C and 602 ± 62 μA/cm² at 37 °C and when poised against an air breathing platinum cathode in a biofuel cell, the multienzyme-containing film generated 42 ± 15 μW/cm² at 172 mV with a maximum current density of 344 ± 25 μA/cm² in 100 mmol/L sucrose at 25 °C. This is the first example of an enzymatic biofuel cell that utilizes both fructose and glucose as oxidation fuel sources