DNA Sensing With Printed Circuit Board Electrode: Non-Faradaic Electrochemical Impedance Spectroscopy Analysis

Printed circuit boards (PCBs) provide a versatile platform for developing point-of-use electrochemical biosensors. Low-cost surface finish, such as electroless nickel immersion gold, on such PCBs offers several advantages over traditional electrochemical sensor substrates, such as cost-effectiveness, scalability, miniaturization, and ease of fabrication. For DNA sensing application of these electrodes, it is necessary to understand the optimal parameter space for error-free operation. In this work, we aim to characterize the double-layer capacitance (DLC) formed at electrode/electrolyte interface for DNA sensing using PCB electrodes. This study investigates the electrochemical behavior of the DLC formed over PCB electrodes in phosphate-buffered saline (PBS) electrolyte using non-Faradaic electrochemical impedance spectroscopy. By varying the electrolyte concentrations ( $\text{1 mM}$ , $\text{5 mM}$ , and $\text{10 mM}$ ) and the ac excitation potential amplitudes (5-100 mV), we analyze DLC formation at the electrode/electrolyte interface. The study examines ionic arrangement transitions at the open circuit potential (OCP), and their impact on DLC retention and distortion. $\text{5 mM}$ PBS electrolyte solution is found to best assist DLC formation as it has the highest capacitive contribution in impedance. In addition, the DLC formation is further examined with dilutions of $\text{20 bp}$ DNA fragments prepared in 1 and $\text{5 mM}$ PBS, ranging from $\text{1 ng}/\upmu \text{l}$ to $\text{20 ng}/\upmu \text{l}$ DNA. The dilutions prepared using $\text{5 mM}$ PBS show sequential change in constant phase element (CPE) parameters of the impedance up to $\text{10 ng}/\upmu \text{l}$ with OCP found to be maintained at a constant value of $\text{40 mV}$ . Higher DNA concentrations show decrease in OCP values, and thus this study presents optimal parameter space for DLC formation with proper ionic arrangement for accurate DNA detection using PCB electrodes.