Developing highly sensitive, selective, and reproducible miniaturized bio-sensing platforms require reliable biointerface which should be compatible with microfabrication techniques. In this study, we have fabricated pyrolyzed carbon arrays with high surface area as a bio-sensing electrode, and developed the surface functionalization methods to increase biomolecules immobilization efficiency and further understand electrochemical phenomena at biointerfaces. The carbon microelectrode arrays with high aspect ratio have been fabricated by carbon microelectromechanical systems (C-MEMS) and nanomaterials such as graphene have been integrated to further increase surface area. To achieve the efficient covalent immobilization of biomolecules, various oxidation and reduction functionalization methods have been investigated. The oxidation treatment in this study includes vacuum ultraviolet, electrochemical activation, UV/Ozone and oxygen RIE. The reduction treatment includes direct amination and diazonium grafting. The developed bio-sensing platform was then applied for several applications, such as: DNA sensor; H2O2 sensor; aptamer sensor and HIV sensor.
Conventional electrochemical double-layer capacitors (EDLCs) are well suited as power sources for devices that require large bursts of energy in short time periods. However, when compared to their battery counterparts, EDLCs suffer from low energy densities. The low energy density of EDLCs hinders their applications in devices that require a simultaneous supply of high power and high energy. In order to improve the energy density of EDLCs, the concept of hybridization of lithium-ion batteries (LIBs) and EDLCs has gathered much attention in past years. Such a hybrid is typically referred to as “lithium-ion capacitor” (LIC) or “lithium capacitor” and essentially utilizes a lithium intercalating anode (such as graphite or Li4Ti5O12) and a fast charging-discharging EDLC electrode (such as activated carbon, carbon nanostructures) in a lithium-salt based electrolyte. Although such a system sounds quite ideal in theory, there are major challenges that need to be addressed in order to fully realize the benefits of LIB and EDLC electrodes in conjunction. Most of these challenges stem from the mismatch in capacity of the electrodes and also the charging-discharging times of the electrodes. For instance, the EDLC electrode acts as the limiting factor for the capacity of the system while the LIB electrode limits the power of the system. Here we have fabricated a hybrid capacitor that utilizes a Li4Ti5O12 (LTO) based anode and an activated carbon (AC) composite based cathode. Half-cell testing for both LTO and AC have been shown along with full cell evaluation.
Miniaturized enzymatic biofuel cells (EBFCs) that convert biological energy into electrical energy by using enzymemodified electrodes are considered as one of the promising candidates to power the implantable medical devices and portable electronics. However, their low power density and insufficient cell lifetime are two big obstacles to need to be tackled before EBFCs become viable for practical application. In this study, the theoretical simulation of this EBFC system is conducted using finite element analysis from COMSOL 4.3a in terms of cell performance, efficiency and optimum cell configurations. We optimized the electrodes design in steady state based on a three dimensional EBFC chip and studied the effect of orientation of the microelectrode arrays in blood artery. In the experimental part, we demonstrated an EBFC system that used 3D micropillar arrays integrated with graphene/enzyme composites. The fabrication process of this system combined top-down carbon microelectromechanical system (CMEMS) technology to fabricate the 3D micropillar arrays platform and bottom-up electrophoretic deposition (EPD) to deposit graphene/enzyme composite onto the 3D micropillar arrays. The amperometric response of the graphene based bioelectrodes exhibited excellent electrochemical performance and the 3D graphene/enzyme based EBFC generated a maximum power density of 136.3 μWcm-2 at 0.59 V, which is about 7 times of the maximum power density of the bare 3D carbon based EBFC.
Enzymatic biofuel cells (EBFCs) that oxidize biological fuels using enzyme-modified electrodes are considered a
promising candidate for implantable power sources. However, there are still challenges to overcome before biofuel cells
become competitive in any practical applications. Currently, the short lifespan of the catalytic enzymes and poor power
density are the most critical issues in developing EBFCs. In this paper, we will review the recent development of biofuel
cells and highlight the progress in Carbon-microelectromechanical system (C-MEMS) based micro biofuel cells by both
computational modeling and experimental work. Also, our effort on utilizing a covalent immobilization technique for the
attachment of enzymes onto the substrate which is expected to increase the enzyme loading efficiency and the power
density of devices is discussed in this paper.
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