A 380-μW Electrochemical Impedance Measurement System for Protein Sensing

Abstract

Diagnostic testing plays an important role in modern medicine, helping physicians make informed decisions regarding disease diagnosis and treatment. Proteins’ biomarkers are utilized to detect disease onset, progression, efficacy of medicines, and patient susceptibility to get a specific kind of disease. Electrochemical impedance spectroscopy (EIS) is likely to underpin the progressive drive toward sensitive, miniaturized, and portable biomarker detection practices. The EIS is a highly sensitive detection method adopted to find the electrical response of chemical samples by applying low amplitude ac voltages/currents with tunable frequency. Conventional EIS systems use mixers and lock-in amplifiers to find both the real and imaginary components of the complex impedance. In this article, we present a partially integrated EIS measurement system to find the impedance of a biological sample. It includes a programmable sine-wave synthesizer (SWS) block with a frequency range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500 \mu $ </tex-math></inline-formula> Hz to 100 kHz. The implementation is based on switched-capacitor filters that adjust the cutoff frequency by changing the clock. The sample impedance is measured through mostly digital magnitude and phase-detection blocks. The proposed EIS system is realized using a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> technology with a 0.35-mm2 active area and 380- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> power consumption. The proposed magnitude detection archives a differential nonlinearity (DNL) performance of −0.34/+0.3 LSB and an integral nonlinearity (INL) of −0.75/+2 LSB. The system is used to measure the impedance of biological samples containing tumor necrosis factor alpha (TNF- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha$ </tex-math></inline-formula> ) protein at variable concentrations.