Chemical Sensing Using Transmission Surface Plasmon Resonance Spectroscopy (T-SPR)

Abstract

Surface plasmon resonance (SPR) technique has become widely used in chemical sensing. Generally, the surface plasmon resonance is measured by the incident light reflected from the surface of the metal at the critical angle, this involves “reflection detection mode”. To determine SPR signal, the instrument with high complexity of several optical accessories is required in order to obtain the accurate information. In this study, the development of transmission surface plasmon resonance spectroscopy (T-SPR) is proposed as the instrument installation is uncomplicated and it provides good quality of plasmon signals. The gratings made from optical storage discs such as CD-R, DVD and BD-R coated with 40nm gold were used as important substrates to acquire T-SPR signal. Their surface morphologies and grating parameters were investigated by Atomic Force Microscopy (AFM). The T-SPR signals of the prepared grating were acquired at wavelength of 450-750 nm. It was found that the BD-R grating provided the distinguished SPR spectra with the correlation of incident angle and λmax of T-SPR peak with R² of 0.9989 and 0.9978 using air and water medium respectively. Therefore, the BD-R grating was used in the further experiments to monitor the effect of reflective index on T-SPR spectra. Mixture of ethylene glycol solutions with 10-50 % w/w were used as a validation condition. The detected T-SPR peak is sensitive to the reflective index of the medium with R² = 0.8962