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Electrodeionization (EDI) technology combines the operation principle of both ion exchange and electrodialysis in one single unit and overcomes the disadvantages of either unit. This technology has been widely used in the production of ultrapure water due to its better performance and economical operation at low feed concentrations. As a result, there have been several studies that deal with application of this technology for the removal of ions from water. However, except for a few studies, most of the reported works deal with the experimental study of EDI. This study deals with the development of a mathematical model for deionization of electrolyte solutions containing more than one ion and ions that are multivalent in nature. The model validity is verified by comparing the results with a few experimental observations. This is followed by a sensitivity study of the EDI unit to explore the effect of various operating and system parameters on the ion removing ability of the EDI unit. Consequently, a systematic optimization exercise that can simultaneously handle more than one objective for superior system performance of the experimental unit is demonstrated. Due to the optimization study, it is shown that many times EDI is not operated at optimized conditions and decreasing the flow rate, among other variables, might have a significant effect on system performance.

Power supply is an important aspect of micronanobiomedical devices. Implantable devices are required to stay inside of the body for longer period of time to provide continuous monitoring, detection, and therapeutics. The constricted areas of the human body, accessed by these devices, imply that the power source should not increase the payload significantly. Conventional on-board power sources are big, as compared with the device themselves, or involve wire-outs. Both provisions are liable to develop complications for sensor/actuator implant packaging. A plausible approach can be innovative solutions for sustainable bio-energy harvesting. Research studies have reported feasibility of miniature power sources, running on redox reactions. The device design, reported in this study, is a combination of nano-engineered composites and flexible thin film processing to achieve high density packaging. Of which, the end goal is production of energy for sensor applications. Both the bio-electrodes were successfully functionalized by amide bond cross-linkage between the carbon nanotube surface and the enzyme molecules: catalase and glucose oxidase for cathode and anode, respectively. The nanocomposite based biopower cell was evaluated as a steady power supply across the physiological range of glucose concentration. The power cell was able to deliver a steady power of 3.2 nW at 85 mV for glucose concentrations between 3 mM and 8 mM. Electron microscopy scanning of the functionalized electrode surface and spectroscopic evaluation of nanotube surface were used for evaluation of the biofunctionalization technique. Cyclic voltametric (CV) scans were performed on the cathodic and anodic half cells to corroborate bioactivity and qualitatively evaluate the power cell output against the redox peaks on the CV scans. The importance of these results has been discussed and conclusions have been drawn pertaining to further miniaturization (scale down) of the cell.

No abstract

Over the years, implantable sensor technology has found many applications in healthcare. Research projects have aimed at improving power supply lifetime for longevity of an implanted sensor system. Miniature power sources, inspired from the biofuel cell principle, can utilize enzymes (proteins) as catalysts to produce energy from fuel(s) that are perennial in the human body. Bio-nanocatalytic hierarchical structures, clusters made of enzyme molecules, can be covalently linked to the electrode’s surface to provide better enzyme loading and sustained activity. Carbon nanotube base electrodes, with high surface area for direct electron transfer, and enzyme clusters can achieve efficient enzymatic redox reaction. A redox pair of such bioelectrodes can make up a power source with improved performance. In this study, we have investigated high throughput processes for coupling enzyme catalysts with power harvesting mechanisms via a screen printing process and solution processing. The process incorporates enzyme (glucosse oxidase and catalase) micro-/nanocluster immobilization on the surface of carboxylated (functionalized) carbon nanotubes with screen printed electrodes. The 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysulfosuccinimide amide linkage chemistries were used to bind the enzyme molecules to nanotube surface, and bis[sulfosuccinimidyl] suberate (BS3) was used as the cross-linker between enzymes. Optimized enzyme cross-linking was obtained after 25 min at room temperature with 0.07 mmol BS3/nmol of enzymes, with which 44% of enzymes were immobilized onto the surface of the bioelectrode with only 24% enzyme activity lost. A cell, redox pair of bioelectrodes, was tested under continuous operation. It was able to maintain most of the enzyme activity for 7 days before complete deactivation at 16 days. Thus, the power harvesting mechanism was able to produce power continuously for 7 days. The results were also analyzed to identify impeding factors such as competitive inhibition by reaction byproduct and cathode design, and methods to rectify them have been discussed. Coupling this new and improved nanobiopower cell with a product removal mechanism and enzyme mutagenesis should provide enzyme protection and longevity. This would bring the research one step closer to development of compatible implantable battery technology for medical applications.