Development of gold nanorod-based localized surface plasmon resonance optical fiber biosensor

Abstract

ABSTRACT A localized surface plasmon resonance (LSPR) based optical fiber biosensor using gold nano rods has been developed. The LSPR optical fiber sensor was fabricated by immobilizing gold nanorods at the distal end of a multimode fiber. The surface of gold nanorods was further functio nalized with human IgG to create a bios ensor to detect anti-human IgG. The peak shift of the longitudinal plasmon wavelength of gold nanorod was monitored as a function of the refractive index change. The results show that refractive index sensitivity of th is sensor is 506 nm/RIU, and the limit of detection for anti-human IgG is 3 nM. Keywords: localized surface plasmon resonance, gold nanorods, optical fiber sensor, biosensor 1. INTRODUCTION Biosensors have been continuing to play an important role in many areas such as in biochemistry, medicine developments, disease detection and health monitoring. However, most of these types of biosensors need to be used in a laboratory environment, where expensive and bulk instruments are often required, and detection by employing these conventional biosensors is often time-consuming. Therefore, a fast, real-time, sensitive, portable and economical technique for developing biosensors is urgently required. Localized surface plasmon resonance (LSPR) is an advanced sensing technology that can be applied to this problem due to the fact that it is highly sensitive to the refractive index change caused by the interactions between small biomolecules, which makes it an ideal candidate for label-free biosensing applications. LSPR is normally generated on the surface of localized metallic nanoparticles when the frequency of incident light is resonant with the collective oscillation of conductive electrons in the metallic nanoparticles [1]. The optical properties of metallic nanoparticles are known to be highly dependent on the materials and their shapes and sizes [2]. Gold nanoparticle s are commonly employed to fabr icate LSPR biosensors due to the close affinity between gold and biomolecules. Among the various types of gold particles, gold nanorods (GNRs) have attracted much attention in recent years due to th eir unique shape and optical pr operties. Being different from the conventional gold nanospheres which have only one plasmon band, GNRs possess two plasmon bands, namely the transverse plasmon wavelength (TPW) and the longitudinal plasmon wavelength (LPW). The LPW is tunable with the aspect ratio of the GNRs and is much more sensitive to the refractive index change than TPW and the plasmon band of gold nanospheres. Fiber-optic based sensor devices, on the other hand, have shown advantages such as small sample volume requirements, a miniaturized and simplified optical design, immunity to el ectromagnetic interference and ca pability for remote sensing. Taking the advantages of both LSPR and optical fiber sensors, LSPR-based optical fiber biosensors offer an alternative solution which would be able to overcome many of the disadvantages of conventional biosensors discussed above. Several studies of LSPR based optical fiber sensors using gold nanospheres have been reported and shown their capability of being biosensors [3]. However, only few resear ch studies into GNRs-based LSPR optical fiber biosensors have been explored so far. In our previous study, a LPSR based optical fiber sensor using GNRs was successfully developed. The results have shown that the device created was highly sensitive to a bulk refractive index change. In this work, a similar GNRs-based LSPR optical fiber sensor has been fabricated based on our previous study. The refractive index sensitivity of the sensor has been investigated under conditions where the sensor was subjected to bulk refractive index change. The sensor was further functionalized with human IgG in order to make a label-free biosensor which is specific to anti-human IgG. The positive results obtained from this work show that the LSPR optical fiber sensor developed has the capability of being a labe l-free biosensor. This shows the poten tial that, based on the same principle demonstrated in this work, biosensors for detecting different targets could be developed effectively.