Graduation Year

2013

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Electrical Engineering

Major Professor

Sylvia Thomas

Co-Major Professor

Stephen Saddow

Keywords

biocompatability, biofunctionalization, glucose sensor, implantable, silicon carbide

Abstract

A continuous glucose sensor employing radio frequency (RF) signals is presented using the biocompatible material Silicon Carbide (SiC). Unlike biosensors that require direct contact with interstitial fluids to trigger chemical reactions to operate, this biocompatible SiC sensor does not require a direct interface. The sensing mechanism for this SiC sensor is based upon a shift in resonant frequency, as a function of change in glucose levels, which electrically manifests itself as a change in blood permittivity and

conductivity. For in vivo applications the antenna sensor needs to operate inside the body environment, and it has been found that the best operational location of this biocompatible SiC sensor is within fatty tissue in close proximity to blood vessels. To test glucose levels, measurements using synthetic body fluid (SBF), which is electrically equivalent to blood plasma, were performed. Changes in sensor performance to varying glucose levels were measured and a shift in resonant frequency to lower values observed with increasing glucose level. In vitro sensor performance demonstrated that the sensor showed a dose dependent response to glucose concentration from 120 mg/dl to 530 mg/dl. A shift of 40 MHz was observed corresponding to a 97 kHz shift per 1 mg/dl change in blood glucose. Similarly the blood glucose levels were measured in pig blood using the same SiC based antenna sensor. The dependence of glucose concentration on resonance frequency observed with pig blood followed the same trend as the bloodviii

mimicking experiment discussed earlier. The sensor performance was linear with the frequency shift being a direct function of glucose concentration.

An in vivo experiment for foreign body response to subcutaneously-implanted antenna has been conducted using a pig/swine animal model. Tissue histology analysis showed that all-SiC antenna and poly ethylene glycol (PEG) coated Ti/Au antenna did not have any inflammatory immune response for 30 days. However, some inflammatory signs were found on bare Ti/Au antenna. The histological tissue analysis on a-SiC coated and single crystal 3C-SiC samples did not show any significant inflammatory response.

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