Detection of riboflavin by localized surface plasmon resonance biosensor with titanium nitride and nanostructure

Abstract

Surface plasmon resonance (SPR) is the oscillation of coherent delocalized electrons (plasmons) at the interface between a metal film and a dielectric medium excited by incident light. It is well known that plasmon resonance is very sensitive to the change of the medium in contact with the metal layer. Therefore, SPR has been adopted as biosensors in some applications such as protein detection owing to its high sensitivity as well as the label free and real time response. Typically, gold is chosen as the SPR material because it exhibits good plasmon resonance in the middle of the visible range and its excellent resistance to oxidation. Also, some nanostructures of SPR material have been found useful for plasmonic sensing. Recently, titanium nitride (TiN) has been considered as an alternative plasmon material for gold. In this dissertation, an inductive study was conducted to illustrate and understand the feasibility and effect of titanium nitride and nanostructures as an alternative material for plasmonic biosensing. Riboflavin, an essential vitamin for human, was proposed to be the biosubstance to be sensed in this dissertation due to the expected bioaffinity towards TiN. Traditionally, there are several methods for riboflavin detection. Yet, the majority of methods have drawbacks. In particular, many of these methods require extensive preparation before detection test, especially the requirement of bio-labelling. Therefore, a label-free, direct and simple plasmonic biosensing system of riboflavin with TiN and nanostructures was studied in this dissertation. The plasmonic material, TiN film, was synthesized by radio-frequency magnetron sputtering. Also, the fabrication of TiN nanostructures was done by a three-step method to understand the effect of nanostructures on the plasmonic sensing. Atomic force microscopy and ultraviolet–visible spectroscopy were performed to characterize the parameters and topographies of the plasmonic materials. A common path interference phase detection method was used to perform the whole sensing experiment. Direct adsorption tests of 10000 ppb riboflavin on different plasmonic substrates were firstly done. The results showed that there was adsorption of riboflavin on both TiN nanoholes and TiN film. This is the first time ever positive result of riboflavin detection with TiN and nanostructures. The response from the TiN nanoholes was higher than the response from TiN film due to signal amplification from the nanostructures. As TiN nanoholes provided significant response in direct adsorption, it was further tested with various concentrations of riboflavin solution. It was discovered that there was a concentration-dependent response of direct adsorption of riboflavin on TiN nanoholes from 100 ppb to 10000 ppb. The higher the concentration, the larger the response. Saturation test of riboflavin on TiN nanoholes was also conducted to understand the binding events between riboflavin and TiN. It was found that the phase responses reduced when testing with the same piece of TiN nanoholes chip. The binding sites on the surface were indicated to be saturated due to the reduction in adsorption response. Moreover, a novel functionalization method with biotinylated riboflavin binding protein on TiN film was introduced to improve the selectivity and detection response of riboflavin on TiN film. It was found that there was an improvement in the detection of functionalized TiN film for 10000 ppb riboflavin, compared with bare TiN film. In conclusion, an investigation in plasmonic detection system of riboflavin has been successfully designed and conducted. The discoveries in this dissertation have shown a great potential for the detection of riboflavin with TiN nanostructures. Moreover, by employing the biotinylation method, TiN film should be applicable for a broad range of plasmonic biosensing.