Sodium Dithionite-Assisted Gold Nanoparticle Synthesis and BSA Conjugation

Abstract The wet chemical method has long been a widely accepted approach for synthesizing gold nanoparticles (AuNPs). Trisodium citrate (Na₃C₆H₅O₇) has traditionally served as a common reducing agent in the colloidal gold nanoparticle synthesis (known as the Turkevich method), effectively converting citrate ions into bulk AuCl₄ in ionic form. In contrast, sodium dithionite (Na₂S₂O₄), an inexpensive reducing agent, acts on precursor materials by reducing their functional groups. In our current investigation, we explored the reducing capacity of sodium ions within the dithionite compound, leading to the formation of unique-sized ionic gold nanoparticles. The synthesized gold nanoparticles exhibited a strong surface plasmon resonance (PR) band at 531 nm in UV spectroscopy at a concentration of 1 mM. Additionally, the Raman spectrum of sodium dithionite-derived gold nanoparticles displayed intense bands at 523.4, 547, 593.4, and 1027 cm-1. The FT-IR spectrum revealed a weak intensity peak at 3934.78 and 3838.34 cm-1, with medium intensity observed at 3390 and 3367.71 cm-1. Furthermore, high-resolution transmission electron microscopy (HR-TEM) analysis indicated that the gold nanoparticles exhibited anisotropic shapes, with average diameters of 3.24 nm and 8.5 nm, respectively. However, conjugated with bovine serum albumin (BSA), the gold nanoparticles demonstrated maximum absorbance at a concentration of 400 µg/ml. Notably, BSA-conjugated gold nanoparticles exhibited strong surface plasmon resonance peaks at 537 nm under acidic conditions. This proposed synthesis protocol, utilizing dithionite as a reducing agent and BSA protein conjugation, may yield uniform-sized colloidal Au nanoparticles suitable for biomedical applications.