Optimization of Layer-by-layer Electrostatic Self-Assembly Processing Parameters for Optical Biosensing

The effect of layer-by-layer electrostatic self-assembly processing parameters on resulting thin-film characteristics was determined in order to optimize the thin-film structure for optical biosensing. The use of long-period fiber gratings (LPFGs) requires careful control of the refractive index of the surrounding medium, which can be achieved by tuning the refractive index and thickness of an optical thin film deposited directly on the optical fiber surface. The high-sensitivity LPFG refractometry range falls in a window just below the effective index of the relevant cladding mode. We investigated five factors at two levels using variable-angle spectroscopic ellipsometry and analysis of variance. Salt concentration and pH were found to be critical parameters for refractive index control.