Microneedle Array Electrode With Ag-PPS Modification for Superior Bio-Signal Recording on Skin

High-quality recording of human bio-signals is very important for biomedical engineering research and clinical medical diagnosis. However, with the most commonly used wet electrode in the clinic, it is always hard to avoid problems of skin irritation, allergic reactions, and time-consuming skin preparation. In comparison, the flat dry electrode is less stimulative to skin and more convenient to use, but exhibits higher interface impedance and sensitivity to human motion. In this work, the highly reliable and reusable microneedle array electrodes (MAEs) are fabricated by micromolding technology and modified by drop coating to solve the above problems. The effects of silver nanoparticles (Ag), poly(3,4-ethylenedioxythiophene) (PEDOT):poly(sodiumstyrenesulfonate) (PPS), and Ag-PPS (Ag with PPS bilayer) modifications on interface impedance and bio-signal quality of the Au-MAEs are studied. The results indicate that the bilayer Ag-PPS-modified MAEs exhibit the most significant decrease in impedance (251.95 ± 8.35 $\text{k}\Omega $ to 7.81 ± 0.65 $\text{k}\Omega $ at 10 Hz) and increase in signal-to-noise ratio (SNR) (4.10 ± 0.52 to 10.71 ± 0.16) than the conventional wet electrode owing to the impedance reduction mechanisms based on physical puncture and electrochemical reaction. A novel equivalent circuit model is proposed to explain the two kinds of impedance reduction mechanisms. In addition, the mechanical test results prove that the modified microneedles could effectively penetrate the skin under 4 N of penetration force without bending or peeling and there is no significant skin irritation and allergic reactions after recording for 6 h. This dry MAE provides an alternative for stable bio-signal recording on the skin, including electrocardiograph (ECG) and electromyography (EMG).