Kinetin Detection Enhancement Based on Photonic Nanojets and Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) technique can increase the Raman signals of the analytes owing to the electric field enhancements on the nanostructures. The strong light intensity, called photonic nanojet, can be formed at the backlight of the dielectric microstructures. Recently, some researchers have applied the photonic nanojets in SERS. In this paper, a layer of synthesized low-cost polystyrene microspheres with the average of small particle size of 4.26 μm and high refractive index 1.5875 was prepared by dispersion polymerization method and coating on metal nanopillars SERS substrates using air-water interfacial floating method, and it was applied to improve the Raman signal sensitivity of kinetin (6-furfurylaminopurine) which is one kind of plant growth regulators and can function an effective compound for improving plant stress tolerance. The Raman intensity increased from 841 to 4449 for the Raman shift at 1327 cm ^-1 , about 5.29 times stronger. The SERS experiments using the kinetin of ultralow concentrations are measured and it shows that femto Molar can be measured. The numerical simulations indicated that the enhancement factor was about 4 times for plane wave illumination and 3.1 times for focused Gaussian beam. It has considerable potential for different analytes in sensing applications.