A Novel Nanowell Array Sensor for POC Measurement of Stress Hormones

The electrodes were stacked vertically above one another to minimize the electrode spacing. The electrodes were separated by a 40-nanometer insulator layer within the nanowells, meaning that the counter electrodes were actually integrated into the nanowell structure. This sensor geometry limited the exposed surface area of the electrodes, and, as a result, the amount of probe antibody molecules inside the nanowells, while also enhancing the sensitivity by focusing the electric field into the nanowells.

This functional geometry permitted rapid and low volume (less than five microliters) sensing through activation of the wells with antibodies and monitoring of real-time binding events. A 28-well plate biochip was built on a glass substrate by sequential deposition, patterning, and etching steps to create a stacked nanowell array sensor with an electrode gap of 40 nanometers. Sensor response for cortisol concentrations between one and 15 micrograms per deciliter in buffer solution was recorded, and a limit of detection of 0.5 micrograms per deciliter was achieved.

The nanowell array sensor was used to analyze 65 serum samples from patients with rheumatoid arthritis, and the results were compared to those obtained from the standard enzyme-linked immunosorbent assay (ELISA). The results confirmed that nanowell array sensors could be a promising platform for point-of-care testing, where real-time, laboratory-quality diagnostic results are essential.

"The use of nanosensors allowed us to detect cortisol molecules directly without the need for any other molecules or particles to act as labels," said first author Dr. Reza Mahmoodi, a postdoctoral researcher at Rutgers University. "Our new sensor produces an accurate and reliable response that allows a continuous readout of cortisol levels for real-time analysis. It has great potential to be adapted to non-invasive cortisol measurement in other fluids such as saliva and urine. The fact that molecular labels are not required eliminates the need for large bulky instruments like optical microscopes and plate readers, making the readout instrumentation something you can measure ultimately in a small pocket-sized box or even fit onto a wristband one day."

The nanowell array sensor was described in the June 30, 2021, online edition of the journal Science Advances.

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