A Low-Temperature-Processed, Soft-Fluidic OEGFET Saliva Aptasensor for Cortisol

Label-free, organic field-effect transistor (OFET)-based biosensors have often overlooked a key challenge to commercialization, i.e., process integration. Many promising literature point-of-care (PoC) prototypes are poor integration candidates due to short shelf life, rigid form factor, and reliance on specialized data collection. Our flexible organic electrolyte-gated FET (OEGFET) sensor device architecture is designed to mitigate some of these integration challenges using a novel low temperature, low-cost fabrication process. As a result of the new process, we observed significant improvements in sensor operating parameters over our previous OEGFETs printed using conventional materials, including a 75% reduction in operating voltage (<5 V), $10\times $ superior cortisol detection limit, preserved electrical characteristics (<20% reduction), and laboratory shelf life of over 15 days. We observed excellent repeatability and a predictable distinction between concentration versus output current responses for synthetic samples and complex media, such as spiked saliva supernatant. The device demonstrated a broad detection range of 0.276 pM–27.6 $\mu \text{M}$ for cortisol samples, encompassing the salivary cortisol physiological range. Device specificity to cortisol was observed with progesterone samples, with highly repeatable results and predictable distinctions between binding and nonbinding assays. The fully flexible OEGFET is the first example of an electrolyte-gated OFET biosensor device with integrated soft microfluidic channels, validated using both synthetic and spiked saliva samples.