Design and Verification of a Wearable Microcapacitance Test System for POC Biosensing

Nanofarad/picofarad scale ac microcapacitance as an electronic signal has advantages on sensitivity and resolution for high-precision biosensors, while its compact test system for wearable applications has not been commercially available. A precise test system for microcapacitance detection is designed and realized by combining a direct digital synthesizer (DDS) with impedance spectrum method. The system is of high integration, high portability, and low cost and can achieve data transmission with mobile terminals via wireless controlling. It has continuously variable frequency and amplitude modulations of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0\sim 100$ </tex-math></inline-formula> kHz and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0\sim 1.98$ </tex-math></inline-formula> V, respectively. A wide 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">$0\sim 100$ </tex-math></inline-formula> nF and a precision as low as 1 pF are realized simultaneously. Combining a sweat collection patch and a capacitive biosensor, this system is employed for hepatitis B surface antibody detection in sweat, with the target concentration in the range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{\mathbf {-12}}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{\mathbf {-16}}$ </tex-math></inline-formula> g/mL and a detection limit of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.905\times 10^{\mathbf {-17}}$ </tex-math></inline-formula> g/mL. The application case verifies the system function with high precision, high reliability, stable data communication, as well as excellent field operability. This system provides an executable solution for constructing smart wearable platforms for point-of-care (POC) biosensing based on microcapacitance detection.