An Audio Jack-Based Electrochemical Impedance Spectroscopy Sensor for Point-of-Care Diagnostics

Abstract

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 (mHealth) immunoassay platform based on audio jack embedded devices, such as smartphones and laptops, that uses electrochemical impedance spectroscopy (EIS) to detect binding of target biomolecules. Compared to other biomolecular detection tools, 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 comparably to laboratory grade instrumentation with 0.3% and 0.5° magnitude and phase error, respectively, over a 17 Hz to 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 (SAM) on a gold electrode demonstrating the potential for POC diagnostics.

Point‐of‐Care Smartphone‐based Electrochemical Biosensing

“…As is demonstrated in prior art, an output sinusoid from the audio channel can be rectified with a MOSFET H‐Bridge and Schottky diode to obtain a 1.2–4 V signal that can be further regulated and filtered . However, since various makes and models of smartphones use different drivers, the output characteristics of the headphone jacks can vary.…”

“…Even with this improvement, however, the power consumption of biosensors that use the audio port must still be low enough in order to remain compatible with most smartphones. As a result, all the peripherals in this space consume the least power (2.5–6.9 mW) when compared to other smartphone‐based biosensors, aside from those that use NFC .…”

“…This design is able to independently set the voltage range and scan rate, while still consuming low enough power to be powered off of the audio jack. Jiang et al., similar to Wang et al., completely does away with using a microprocessor, instead relying on frequency and voltage modulation of the audio output channel along with frequency and amplitude detection circuits to control the impedance biosensor . This design allows the peripheral to achieve a low 2.5 mW maximum power consumption and power itself directly from the audio port.…”

“…Custom EIS circuits have been created to obtain more accurate results that use on‐board ADCs, DACs, and microcontrollers relying on separate batteries to provide enough power . However, Jiang et al., as illustrated in Figure (B), shifts the generation of the stimulus signal and quantization to the smartphone through the headphone jack, negating the need for a microcontroller and mixed‐signal circuits allowing for a very low power (2.5 mW) EIS peripheral, which is mostly analog, albeit with a frequency range limited to the audio band .…”

Low-Cost, Compact, and Rapid Bio-Impedance Spectrometer with Real-Time Bode and Nyquist Plots

“…First is an AC current source, which must be stable within working frequency range; second is a data acquisition system to record voltage, current, and their phase difference; and third is software for computing and displaying the impedance dispersion curves, which is commonly in the Bode plot or Nyquist plot.Furthermore, in an effort to provide a BIS instrumentation system in good performance, some researchers have offered the new design. Starting from precision AC current sources [26], the high accuracy data acquisition system [27,28], even the whole system device [29][30][31][32][33]. Commonly, the offered BIS instrumentation system is arranged in modular and work separately.…”