Plasmonic tilted FBG biosensor read-out with a 512-pixel spectrometer

Plasmonic tilted fiber Bragg gratings (TFBGs) are well-suited for accurate, rapid and minimally-invasive biosensing. They present a very dense transmitted amplitude spectrum of narrowband cladding mode resonances (full width at half maximum < 1 nm). This response is commonly demodulated using highly-resolved interrogators (wavelength resolution < 10 pm). This work investigates the possibility of reading-out the amplitude spectrum of a gold-coated TFBG by using a coarsely resolved spectrometer (166 pm). A refractometric sensitivity of 2656 nm/RIU has been observed thanks to a refined analysis of the spectral content which has led to the development a more efficient signal processing. This value represents a fivefold enhancement compared to previously reported read-out methods. Biosensing has been successfully achieved with gold-coated TFBGs used in reflection mode for the detection of insulin, with specific antibodies grafted on the gold surface. Our experimental study is an advance towards an industrialization of the FBG technology, as it opens the way to rapid parallel biodetection, benefiting from the multiple sensing channels (up to 64) of the interrogator as well as its high processing speed (repetition rate up to 3 kHz).