Signal enhancement of optical immunosensing by gold nanoparticles

Optical signals, such as surface plasmon resonance (SPR) angle, fluorescence intensity and quantum yield are commonly measured in optical immunosensing when an immunological interaction takes place between analytes and the specific bio-recognizable interface. Extensive researches on have been therefore concentrated for decades to develop a more sensitive interface to lower the limit of detection. When the chromophores are in proximity to metal nanoparticles, gold nanoparticles (AuNPs) are capable of amplifying the signals by at least one order of magnitude. The enhancement factor is particularly dependent on the separation between the chromophores and surface of metallic nanoparticles, as well as the distribution of the electromagnetic field surrounding to the metallic nanoparticles. In this study, the fluorescence enhancement of Au-avidin-Texas Red conjugate was studied using multiple crosslinkers with different lengths. It was observed that in the presence of oligo-ethylene-glycol-based (OEG-based) crosslinkers not only was stability of gold nanoparticles against protein adsorption improved, but also fluorescence intensity was enhanced. The AuNPs intentionally capped with oligo ethylene glycol ligand will remain colloidal in high ionic strength up to 2mol/l. The fluorescence intensity was enhanced 3.8-fold when CT(PEG)7 was sandwiched at the length of 35.5A while 9-fold, in case that CT(PEG)12 was selected at specific length of 47.8A in the Au-avidin conjugate. It is predicted that such a multiplexing probe can be applied not only as a complementary substrate in SPR immunosensing but also as a fluorescence enhancer in the conventional fluorescence immunosensing.MASTER OF ENGINEERING (MSE