Ultradense Electrochemical Chips with Arrays of Nanostructured Microelectrodes to Enable Sensitive Diffusion-Limited Bioassays

Abstract

Nanostructured microelectrodes (NMEs) are an attractive alternative to yield sensitive bioassays in unprocessed samples. However, although valuable for different applications, nanoporous NMEs usually cannot boost the sensitivity of diffusion-limited analyses because of the enlarged Debye length within the nanopores, which reduces their accessibility. To circumvent this limitation, nanopore-free gold NMEs were electrodeposited from 45 μm SU-8 apertures, featuring nanoridged microspikes on a recessed surface of gold thin film while carrying interconnected crown-like and spiky structures along the edge of a SU-8 passivation layer. These structures were grown onto ultradense, vertical array chips that offer a promising strategy for translating reproducible, high-resolution, and cost-effective sensors into real-world applications. The NMEs yielded reproducible analyses, while machine learning allowed us to predict the analytical responses from NME electrodeposition data. By taking advantage of the high surface area and accessible structure of the NMEs, these structures provided a sensitivity for [Fe(CN)6]3–/4– that was 5.5× higher than that of bare WEs while also delivering a moderate antibiofouling property in undiluted human plasma. As a proof of concept, these electrodes were applied toward the fast (22 min) and simple determination of Staphylococcus aureus by monitoring the oxidation of [Fe(CN)6]4–, which acted as a cellular respiration rate redox reporter. The sensors also showed a wide dynamic range, spanning 5 orders of magnitude, and a calculated limit of detection of 0.2 CFU mL–1.

Ultradense Array of On-Chip Sensors for High-Throughput Electrochemical Analyses

“…As noted in two-electrode cells, a voltage was applied between the WE and QRE fingers while the electrical current between these electrodes was monitored. The currents produced on WE from either [Fe(CN) 6 ] 4– oxidation (CA assays) or [Fe(CN) 6 ] 3–/4– redox quasi-reversible reactions (SWV assays) were followed. , …”

“…An additional strategy to obtain microfabricated high-density arrays was recently described by our group. , This method relies on the vertical integration of grid-patterned, two-electrode arrays of Au thin-film fingers onto glass, notably decreasing the number of contact pads and enhancing the integration density. For example, our chip would only require 22 pads to operate 96 cells.…”

“…Thus, these chips can afford reproducible, high-resolution, and cheap sensors . To date, our previous efforts on this new sensing arrangement involved the duplexing of bioassays from a single square wave voltammetry (SWV) scan and the electrodeposition of nanostructured microelectrodes to boost the sensitivity of diffusion-limited tests …”

“…Building upon our prior works, , we report the possibility of individually addressing the various arrayed sensors on a compact, fully integrated MEC to yield high-throughput in a simple and inexpensive way. Although a number of cells as high as 870 could be obtained, MECs with 48 sensors (16 WEs × 3 QREs) were used here by allowing evaporation-free subsequent analyses of small droplets (i.e., 10 μL) at room conditions.…”

Artificial Intelligence in Point-of-Care Biosensing: Challenges and Opportunities

“…For example, Malkiel et al report a Deep Learning model capable of predicting plasmonic nanostructure geometries that produce optimal responses upon interaction with various biomarkers [ 155 ]. Similarly, machine learning models have been employed in the design of electrodeposited electrochemical sensors [ 156 ].…”