Green Synthesis of 10 nm Gold Nanoparticles via Seeded-Growth Method and its Conjugation Properties on Lateral Flow Immunoassay

Abstract

In this work, 10 nm gold nanoparticles (AuNPs) was successfully synthesized via seeded-growth method. The green chemically synthesis of this AuNPs becomes attractive because the growth process does not involve heat. Moreover, this technique has advantages of quick, simple, and low cost process. Sodium borohydrate (NaBH4) was used as a reducing agent while trisodium citrate was used as a source of OH- ions in the seed stage. Hydroxylamine hydrochloride (NH4.3H2O) was used as a slow reducing agent to enlarge 4 nm seeds to 10 nm AuNPs. A 4 ml AuNPs seed was the optimized volume to produce 10 nm AuNPs with great homogeneity and dispersity. A sharp peak of surface plasmon resonance (SPR) measurement at 517 nm proved that 10 nm AuNPs was successfully synthesized via this method. Optical properties of the seeds and grown AuNPs were analyzed using UV-Vis spectroscopy while size and surface morphology were observed using a transmission electron microscopy (TEM). Particle size distribution was measured using Zetasizer. 10 nm AuNPs was then conjugated with streptavidin and goat anti-human IgA. Depending on type of protein, 10 µg/ml of streptavidin and 11.2 µg/ml of goat anti-human IgA were required to conjugate with 10 nm AuNPs. The produced products had binding capability on lateral flow immunoassay (LFI). A few nanometer red-shifted absorption spectrum of 10 nm AuNPs conjugated protein revealed successful conjugation instead of agglomeration. 1% BSA was determined as the optimum concentration to stabilize 10 nm AuNPs conjugated biomolecules.