Nitrogen-doped Carbon Materials For Enzyme Biofuel Cell

Enzyme biofuel cells (EBFC) have attracted great attention because they can convert chemical or biochemical energy to electricity by making use of body fluids. Compared with conventional fuel cell, EBFC have many advantages, such as abundant fuel, environmental friendly, operation at ambient temperatures and neutral pH, etc. Particularly, EBFC have been well developed based nanomaterials due to their excellent conductivity, large surface areas, and good biocompatibility. Currently, the development of EBFC focuses on employing new materials to improve the cell performance as well as constructing novel devices to expand their potential applications. In this dissertation, we have explored the new carbon nanomaterals to fabricate the high power output EBFC and broadened a novel application in self-powered sensors as well. The main contents are as follows:1. NADH Dehydrogenase-like Behavior of Nitrogen-Doped Graphene and Its Application in NAD+-Dependent Dehydrogenase Biosensing and enzyme biofuel cell platformNitrogen-doped graphene (NG) has received remarkable attention from both experimental and theoretical scientific communities because NG exhibits much better electrocatalytic activity than graphene, since lone electron pairs of the nitrogen atoms can form a delocalized conjugated system with the sp2-hybridized carbon framework. We found that NG had redox properties similar to Col, which mimicked flavin mononucleotide (FMN) in Col and efficiently catalyzed NADH oxidation. NG also acted as an electron transport "bridge" from NADH to the electrode due to its excellent conductivity. In comparison with a bare gold electrode, an 800 mV decrease in the overpotential for NADH oxidation and CoZ-like behavior were observed at NG-modified electrode, which is the largest decrease in overpotential for NADH oxidation reported to date. Electrodes modified and NG/gold nanoparticals/formate dehydrogenase (NG/AuNPs/FDH) showed excellent analytical performance for the detection of formate. Moreover, based on the NG/AuNPs/FDH bioanode and NG/AuNPs/laccase biocathode, we also fabricated a high power output, membrane-less formic acid/O2 enzymatic biofuel cell, in which the bioanode was proven to be effective for recycling the NAD+/NADH cofactor in the catalytic oxidation of formic acid. This strategy could be used to create a universal biosensing platform for developing NAD+-dependent dehydrogenase biosensors and biofuel cells.2. Ternary Hybrid of Carbon Nanotubes-Graphitic Carbon Nitride Nanosheets-Gold Nanoparticles as Robust Substrate Electrodes in Enzyme Biofuel CellSince NG exhibited excellent properties in biosensor and EBFC, we explored a higher nitrogen content carbon materials, graphitic carbon nitride nanosheets. However, the poor conductivity of g-C3N4 NSs limited their performance in constructing electrochemical sensors. The combination of g-C3N4 NSs with conductive carbon materials could improve the conductivity of the g-C3N4 NSs. Herein, we developed a convenient strategy to synthesize ternary hybrid consisting of CNTs/g-C3N4 NSs/gold nanoparticles (CNTs/g-C3N4 NSs/Au NPs), and employed the ternary hybrid as substrate electrodes for EBFC. Compare with EBFC based on the CNTs/Au NPs hybrid in the same condition, the enzyme modified ternary hybrid electrodes showed better bioelectrochemical properties, which resulted in high power output and good stability for the developed EBFC. Therefore, introducing g-C3N4 NSs to CNTs/Au NPs hybrid was proven to be effective for the improvement of glucose/O2 EBFC.3. Ultrasensitive and reusable self-powered cytosensor based on EBFCWe developed an ultrasensitive and reusable self-powered cytosensor based on enzyme biofuel cells (EBFC) for the detection of acute leukemia CCRF-CEM cells. The core component of the EBFC cytosensor was composed of an aptamer (Sgc8c)-functionalized cathode and a nitrogen-doped graphene/gold nanoparticles/glucose oxidase (NG/AuNPs/GOD) anode, which generated a maximum power output density (Pmax) of 115 μW cm-2. Once the negatively charged CCRF-CEM cells were captured by the cathode via aptamer recognition, their dramatic steric hindrance and electrostatic repulsion to the redox probe [Fe(CN)6]3- efficiently blocked the electron transfer between the probe and the cathode surface, and thereby caused a remarkable decrease in power output of the EBFC, which could be used to sensitively detect the cells. Notably, the power output density of the EBFC cytosensors could be restored by altering the specific conformation of the aptamer on the cathode to release the captured CCRF-CEM cells. This strategy is expected to have potential application as a powerful point-of-care tool for the early detection of circulating tumor cells.