Modulation of the Dual Resonant Peaks of a Long-Period Fiber Grating Towards Highly Sensitive Sensing by Means of Polymeric Nanocoatings for Biosensing Applications

The dual resonant peaks of a long-period fiber grating (LPFG) have been prepared by depositing the polyelectrolyte multilayer films composed of salt-containing poly(diallyldimethyl- ammonium chloride) (PDDA) and salt-containing poly(sodium-p- styrenesulfonate) (PSS). The multilayered polyelectrolyte films of PDDA/PSS were alternately assembled on the surface of the LPFG via electrostatic layer-by-layer (LBL) self-assembly approach. The sensing performance of the dual resonant peaks of the LPFG to nanofilms has been further evaluated. The experimental results demonstrated that the optimal sensitivities of the left resonant peak and the right resonant peak in the dual resonant peaks were as high as 52.79 nm/bilayer and 56.09 nm/bilayer, respectively, which were approximately 128 times and 136 times that of another single resonant peak in sequence. Finally, the reason for the emergence of the dual resonant peaks and the corresponding response mechanism to nanofilms were further analyzed and discussed theoretically. These findings are very beneficial for exploring the application of LPFGs in many fields such as biochemical sensing, drug screening, food detection and so on.