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

$0\sim 100$

kHz and

$0\sim 1.98$

V, respectively. A wide range of

$0\sim 100$

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

$10^{\mathbf {-12}}$

$10^{\mathbf {-16}}$

g/mL and a detection limit of

$5.905\times 10^{\mathbf {-17}}$

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.

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