Ultra-sensitive and label-free biosensors using surface plasmon resonance of nano-grating structure in nanofluidic preconcentrator

In this paper, we demonstrated a label-free biosensor with ultrahigh sensitivity by combining an electrokinetic trapping (EKT)-based nanofluidic preconcentrator with periodic metallic nanograting surface plasmon resonance (SPR) sensing chips. Label-free SPR sensing chips were patterned inside the concentration channel by e-beam lithography, e-gun evaporation followed by the lift-off process. The nanofluidic preconcentrator consisted of two microchannels (a concentration channel and a buffer channel) cast in PDMS and a porous membrane (Nafion). By collecting and trapping the biomolecules in the concentration channel, our nanofluidic preconcentrator generated a preconcentrated plug precisely on the SPR sensing chip. Through a custom-made optical system, the spectrum of the SPR sensing chip and the antibody-antigen binding is detected successfully. The wavelength sensitivity is 460nm/RIU for a SPR sensing chip with the nanograting of 90 nm in width with 550 nm in period. The preconcentration factor of our nanofluidic preconcentrator is approximately 10,000 folds. In our antibody-antigen binding test, anti-bovine serum albumin (BSA) in 1xPBS was preconcentrated from 20 ng/ml to 200 μg/ml. This device can be utilized in detecting low-abundance analytes by integrating the label-free preconcentration mechanism and a label-free SPR sensor.