Instrumentation For Reverse Iontophoresis And Biosensor Capacitance Measurement
Kumar, K Pavan
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Iontophoresis is a method to enhance and regulate the transdermal drug delivery by application of an electric field to the skin. Application of small electric current (µ A) enhances transport of both charged and neutral molecules across the skin. Reverse of this process enables extraction of analytes across the skin for noninvasive sensing and diagnosis. Hence it is planned to conduct detailed studies on Reverse Iontophoresis. An invitro model is developed to study the extraction of glucose across the skin. Effects of magnitude of electric current, time of application, pH etc. on the extraction of glucose are studied. It is observed that extraction of glucose at the cathode is higher than at the anode. Advantage of invitro model is the possibility of varying parameters to an extent which is impossible invivo. Instrumentation suitable for continuous monitoring of reverse iontophoresis invivo in human subjects is developed. It supplies the required current and acquires the potential profile of the skin during reverse iontophoresis. Potential profiles showed that skin resistance decreases with the application of current. Experimental results revealed that the application of pulsed DC tends to make the reverse iontophoresis more effective by enhancing the flow of analytes which is proved by the fact that skin resistance decreases and stabilizes faster in comparison to the one with direct current reverse iontophoresis. Present work emphasizes the importance of selecting an appropriate duty cycle and frequency for reverse iontophoresis. Duty cycle around 95% and frequency of 250 mHz are good for low frequency reverse iontophoresis. Effect of reverse iontophoresis on the skin recovery is observed by monitoring the potential profiles at the end of the process. In all the reverse iontophoresis experiments, safety of the patient is ensured by fixing a compliance voltage level. Finally, Instrumentation to measure the capacitance of biosensors is developed based on frequency domain technique with a sinusoidal input. Accuracy in capacitance measurements is ±5%. Glucose measurement is demonstrated with the developed instrument using a capacitance type biosensor. The obtained results are in good agreement with the standard UV-Visible spectroscopic measurements based on phenol-sulphuric acid assay method.