Design and analysis of fiber optic SPR sensor under optimum radiation damping for the detection of Escherichia coli bacteria

This article presents a theoretical investigation of fiber based plasmonic biosensor for the detection of e-coli bacteria in water medium. The method involves systematic optimization of parameters under optimum radiation damping (ORD) in near infrared region of wavelength. The sensor design consists of a 13.1 % germanium doped silica core, perfluorinated homopolymer cladding and a heterostructure of gallium nitride (GaN), silver (Ag) and aluminum nitride (AlN). Poly-l-lysine homopolymer is used over AlN to improve the specificity of the sensor by immobilization of bacteria on fiber surface. The structure is optimized based on the thickness of layers and operating wavelength using 2D simulation technique on MATLAB software. The initial simulations provided a figure of merit (FOM) of 4219 RIU- 1 which enhanced up to 14,420 RIU- 1 after simultaneous optimization of thicknesses. We demonstrated that our sensing mechanism is extremely accurate and capable of reliable detection of e-coli with sensitivity of 201.86 deg./RIU, FWHM of 0.014 degrees and power loss ratio (PLR) of 3.09. The combined FOM for the sensor is 44255.58 mu m4/RIU which is way higher than previously reported designs. The chosen materials are easily available and cheap with well-established fabrication techniques. Due to its high FOM and selectivity, the sensor opens the possibility of successful device level implementation.