Electrochemical Detection

As the most popular mobile devices in the world, the smartphone has high-speed computing capabilities and large-capacity data storage capabilities. Hence, recently, there has been a large influx of biosensing peripheral modules that attach to smartphones to take advantage of their widespread availability, computing power, network connectivity, battery, and camera to offload as much of the biosensor as possible onto the phone itself. Many of the smartphone-based biosensor ecosystem consists of optical-based sensing. Electrochemical measurement has the advantage of being mostly independent of the smartphone’s capabilities while still achieving a comparable or better formfactor than optical peripherals. And it could be used for continuous monitoring of DA and other various biochemical substances. Thus, smartphone-based electrochemical detection is great potential for real-time monitoring of biochemical substances in the point-of-care testing (POCT).

Fig.1 The device of electrochemical detection. (Sun, 2018)

Electrochemical Techniques

• Amperometry

For potential controlled current measurement techniques such as chronoamperometry, cyclic voltammetry and pulse voltammetry, most devices use an available AFE. The detectable current range for this chip is 5-750 mA, which is acceptable for applications such as blood glucose measurement where the analyte concentration is generally high. Instead, when power can be traded for lower noise and smaller input bias current, custom potentiostat circuits with resistive feedback transimpedance amplifiers are designed to obtain a higher current resolution.

• Potentiometry

Potentiometric measurement circuitry typically only requires an amplifier with a large input impedance to measure the voltage from an ion selective electrode known for its high resistance (10 MW-1 GW).

• Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) is typically measured by applying a small sinusoidal voltage stimulus between electrodes and measuring the magnitude and phase of the resulting current signal at multiple frequencies in order to calculate an impedance spectrum. Due to the typical frequency range 1-100 kHz and the low 5-mV peak amplitude of the stimulus signal, EIS tends to be the most power consumptive measurement technique since it needs to measure both magnitude and phase accurately from a small current signal at all frequencies within the spectrum. In most cases, EIS measurements need to be fitted to a linear impedance model. With a high stimulus amplitude, it can no longer be assumed that the data matches this linear model.

Fig.2 Point-of-care electrochemical impedance spectroscopy implementations. (Jiang, 2017)

• Multi-technique

Combining multiple techniques into a single platform allows users the versatility to run a variety of different assays all just by changing the type of electrode.Scientists successfully demonstrate a peripheral device that runs multiple amperometric and potentiometric techniques all with the same handheld-sized device paired with a mobile phone using the headphone jack for data transfer at a rate of 17 bps. It runs chronoamperometry for detection of glucose, cyclic voltammetry for measuring P. falciparum (PfHRP2), square-wave anodic stripping voltammetry for heavy metal detection, and potentiometry for sodium measurements in urine. The device also has a vibration motor to increase metal deposition during stripping voltammetry thereby amplifying the electrochemical signal.

References

1. Sun, A.C.; etal. Point-of-Care Smartphone-based electrochemical biosensing. Electroanalysis. 2018, 30:1-16.
2. Jiang, H.; et al. An audio jack-based electrochemical impedance spectroscopy sensor for point-of-care diagnostics. IEEE Sensors Journal. 2017, PP(3):589-597.

For Research Use Only.