Ethylene Diamine Functionalized Citrate-Capped Gold Nanoparticles for Metal-Enhanced Bioluminescence

Abstract

Metal-enhanced bioluminescence (MEB) is a complex photophysical event which manifests itself in manifold luminescence enhancement and depends on many parameters. The parameters include the distance between the luminescent source and the nanomaterial surface, the size and shape of nanoparticles, localized surface plasmon resonance (LSPR) peaks of the nanomaterial and the dielectric constant of the surrounding medium. Studying distance-dependent MEB in the presence of linkers of specified length may provide new insights into luminescence enhancement. In this regard, the present investigation is aimed to understand the role of ethylene diamine as a potential linker in model systems for distance-dependent metal-enhanced bioluminescence (MEB) with gold nanoparticles (AuNPs). Four different types of AuNPs (AuNP1, AuNP2, AuNP3, AuNP4) were synthesized by varying the trisodium citrate (TC) and silver nitrate (AgNO3) concentrations with maximum absorbance values of 0.99, 1.24, 1.21 and 1.38 respectively and the corresponding LSPR peaks (λmax) of 520 nm, 535 nm, 525 nm, and 525 nm. Luminescence enhancement up to 1.44-fold was observed when ethylene diamine (ED) was used as a linker in the presence of 1-N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC), ATP and AuNP1. The sample consisting of FMN, EDC and AuNP1 showed 1.3-fold luminescence enhancement. It was noted that AuNPs synthesized using AgNO3 as an additional component did not enhance luminescence in all the investigations. The suggested technique of using linkers of predetermined lengths may also prove fairly effective for studying other parameters which can influence MEB and cause sensitivity enhancement of luminescence-based biosensors