Highly sensitive and specific detection of urinary Aquaporin-2 using tilted fiber grating sensors with Plasmonic nanocoatings

Tilted fiber Bragg gratings (TFBGs), which eliminate the cross-sensitivity between environmental temperature and fiber deformation, can be designed as highly sensitive biosensors for bio-sample measurements. The miniaturized size together with the capability of remote operation makes the TFBG biosensors work in hard-to-reach places, even possible in vivo. In this work, a Plasmonic biosensor based on a TFBG coated by a 50-nm gold film for specific urinary protein (Aquaporin-2, AQP2) detection is reported. Since the biosensor is designed as a reflective probe with a length of only 10 - 20 mm (through coating a gold film as a reflection mirror in the cleaved end downstream of the grating), it is easy to insert into the media for in situ bio-sample measurement. Using this device, AQP2 concentrations in rat urine has been clearly discriminated between healthy samples and nephrotic syndrome samples, by monitoring spectral drift or intensity variation. Experimental results show that the urinary protein AQP2 can be unambiguously measured within only 15 minutes, with an intensity change of 0.3 dB.