940-P: Toward a Novel Tiny Continuous Glucose Monitor (CGM): Step 3, Building an Enhanced Ratiometric Detector Using a Buried Dual Junction Diode (BDJ)

Continuous glucose monitors (CGM) improve overall glucose control in patients with diabetes, but have many disadvantages for users. We are developing a novel CGM that will be painless to insert and wear, and easy to use. Our goal is an on-body, wirelessly transmitting CGM device that extracts interstitial fluid with a dime-sized patch of microneedles and optically detects glucose from extremely small fluid volumes. Our first step in 2016 was developing an innovative method for fabricating silicon microneedles, sharp and small enough to penetrate skin without pain (160 µm in height, 50 µm in diameter, and 100 µm in width). The next year we not only demonstrated that our microneedle fabrication is repeatable and reliable but also developed an entirely new, stable, non-enzymatic glucose-sensing method based on a variation of the well-known fluorescent-based boronic acid sensor. Since then, we have further refined our sensor for conductivity sensing as well as demonstrated a novel integrated silicon buried dual-junction (BDJ) photodiode-based system with which to detect glucose with our sensor.

Specifically, we built a buried dual junction (BDJ) photodiode for color or ratiometric optical sensing. We employed a simple polycarbonate UV filter to block stray 380 nm pump light from reaching the BDJ detector, and the signal-to-background ratio is further enhanced by incorporating a yellow band filter between the LED and sample reservoir. To test the optical performance of our photosensor, cationic polymer PFP and fluorescein/coumarin are excited at 380 nm and measured at the peak 425 and 525 nm. These data prove that our device is capable of detecting ∼µM of fluorophores in a ∼7 µL of volume. Next, we demonstrated the diffusion of molecules via hollow silicon microneedles. These data show that integration if all components can enable for the first time, a compact, wearable optical biosensor.