Portable and easy-to-use point-of-care (POC) diagnostic devices hold high promise for dramatically improving public health and wellness. In this paper, we present a mobile health immunoassay platform based on audio jack-embedded devices, such as smartphones and laptops, that uses electrochemical impedance spectroscopy to detect binding of target biomolecules. This platform is intended to be used as a plug-and-play peripheral that reuses existing hardware in the mobile device, and does not require an external battery, thereby improving upon its convenience and portability. Experimental data using a passive circuit network to mimic an electrochemical cell demonstrate that the device performs comparable to laboratory grade instrumentation with 0.3% and 0.5? magnitude and phase error, respectively, over a 17 Hz-17 kHz frequency range. The measured power consumption is 2.5 mW with a dynamic range of 60 dB. This platform was verified by monitoring the real-time formation of a NeutrAvidin self-assembled monolayer on a gold electrode demonstrating the potential for POC diagnostics.