Photonic Crystal Enhanced Quantum Dot Biosensor for Cancer-associated miRNA Detection.

Nanoscale quantum emitters are useful tags for monitoring biomolecular interactions, but remain restricted by large numerical aperture objectives, blinking nature, and omnidirectional emission. Herein, using the multiplicative effects of amplified excitation, highly directed extraction, Purcell enhancement, and blinking suppression on a photonic crystal (PC) surface, we were able to boost the signal by over 3,000 times. Even with a low-NA lens (NA = 0.5, 50X) and an inexpensive optical setup, our platform provides single quantum dot (QD) sensitivity with a high signal-to-noise ratio (SNR = 59). By integrating the photonics enhancement with a newly designed bioassay, we achieved ultrasensitive detection with a detection limit up to 10 aM and an over 9-log linear dose-response range using simple steps, room temperature workflow. In addition, we observed distinct surface motion trajectories of QDs when their surface attachment stringency is affected by a single base mutation in a cancer-specific miRNA sequence[ 1].