In-situ label-free optofluidic DNA biosensor based on fiber-optic Michelson interferometer with vernier effect for microfluidic chip

A label-free fiber-optic optofluidic biosensor integrated into microfluidic chip based on vernier effect is proposed for the specific and high-sensitivity detection of DNA molecules, which is made up of a Michelson interferometer (MI) and a Fabry Perot interferometer (FPI) in parallel. The MI is prepared by a single-hole dual-core micro-structured fiber (MOF) with a suspended core attached to the hole serving as the sensing arm, and used as the sensing element. A micropore is etched directly above the microchannel of MI as the fluid inlet by femtosecond laser processing, and integrated into the microfluidic chip for sample replacement. The detection volume is only nanoliters and the sample can be quickly replaced within seconds. The experimental findings indicate that the proposed optofluidic sensor shows a high refractive index (RI) sensitivity of −8791 nm/RIU and has an ultra-low detection limit of 7.45 × 10 −6 RIU within the range of 1.3328–1.3370. By immobilizing probe DNA (pDNA) molecules on the suspended core through surface functionalization, the optofluidic sensor enables label-free detection of 1 μM complementary DNA (cDNA) solution and shows excellent specificity. The proposed fiber optofluidic biosensor has great development prospects in ultra-low volume and high-sensitivity detection of biomolecules.