Label-free, ultra-sensitive DNA biosensing using active two-mode microfiber ring laser functionalized by self-assembled DNA nanoprobes

A label-free, ultra-sensitive deoxyribonucleic acid (DNA) biosensor based on two-mode microfiber ring laser is proposed and demonstrated. A tapered two-mode fiber interferometer (TTMFI) is developed to excite strong evanescent waves and achieve single-longitudinal-mode laser mode-selection inside an active fiber ring laser cavity. Self-assembled tetrahedral DNA nanostructure probes are functionalized onto the TTMFI's surface, with increased DNA binding efficiency and enhanced light interaction. DNA hybridization detection with concentration ranging from 10 aM to 100 fM is achieved, with a limit of detection (LoD) of ∼0.1 aM and sensitivity of 1.626 nm/lg(aM). In addition, single-base mismatched detection of 20-base target DNA with high specificity is achieved. The proposed biosensor has the advantages of ultra-low LoD, high specificity, and real-time detection, having broad application prospects in fields such as disease diagnosis, microbial detection, and environmental science.