Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Sylvia Thomas, Ph.D.

Co-Major Professor

Arash Takshi, Ph.D.

Committee Member

Nasir Ghani, Ph.D.

Committee Member

Norma Alcantar, Ph.D.

Committee Member

Shamima Afroz, Ph.D.

Keywords

CMOS, TIA, ENFM, SCTF, Silicon Carbide Nanoparticles, Conductive Polymer, Low-power, Low-noise

Abstract

Although wearable and portable biomedical devices are the pillar of modern and smart societies, a large portion the device infrastructure is still under development, operates with poor monitoring and automation, and lacks sufficient communication among components. Moreover, demand for wearable bio-medical devices is expected to increase in the coming years. This situation presents a unique opportunity for electrical engineers to design novel strategies that allow point-of-care diagnostics to satisfy the increasing demand of wearable bio-medical devices. For example, in the medical field there is a rising diabetic population base, high demand for miniature and low-power diagnostic devices, and the need for rapid technological advancements driving the market growth. Among biosensors, glucose sensors have the largest market presence due to the increasing population of diabetic patients and the rising need for point-of-care diagnostics and detection. Glucose sensors are used to measure the glucose concentration in blood of a patient and are an important part of managing diabetes mellitus. However, to be truly beneficial, the glucose sensor must be able to function properly over a long time period. The critical issues of a glucose sensor are limits in the device longevity, power consumption, sensitivity and biocompatibility.

This continuous glucose monitoring system needs to be power efficient, compact, portable, sensitive, and have a linear response for targeted levels. This research focuses on three main components, each of which addresses a challenge central to the future 1) Fabrication and characterization of spin-coated-thin-film (SCTF) and electrospun nanofibrous membrane (ENFM) based electrochemical enzymatic glucose sensors; 2) Design and simulation of a proposed low-power, low-noise transimpedance amplifier (TIA) and voltage control unit (VCU) for glucose sensing system; and 3) Integration of proposed chronoamperometric potentiostat (TIA and VCU) with glucose sensors to use it later for implantable bio-medical devices and In-vivo applications.

Electrochemical enzymatic biosensors have become popular for point-of-care monitoring of glucose levels in the blood. The sensitivity, limit of detection and durability of these biosensors can be significantly enhanced by the utilization of nanostructures in sensor fabrication. More specifically, a conductive polymer (CP) PEDOT:PSS based electrospun-nanofibrous-membrane (ENFM) can increase sensitivity, provide larger surface-to-volume catalyst loading, and create platform for effective enzyme binding. ENFMs are easily fabricated, cost effective, and can be tailored to detect a wide range of biochemical reactions with the appropriate materials and functionalization.

This work represents an integrated glucose monitoring system with a complementary metal oxide semiconductor (CMOS) based low-power, low-noise chronoamperometric potentiostat and electrochemical enzymatic ENFM based glucose sensor. The sensing circuitry can detect electrochemical current ranging from nanoamps to microamps from the ENFM glucose sensor. The proposed chronoamperometric potentiostat was implemented in 180 nm CMOS process using multi-stage difference-differential telescopic cascode operational amplifier configuration. The configuration achieves low-noise, high gain, stability and a low-power. The integration of ENFM glucose sensor with chronoamperometric potentiostat provides the basis for future wearable and portable biosensors.

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