Two fold increase in synthesis of gold nanoparticles assisted by proteins and phenolic compounds in Pongamia seed cake extract: response surface methodology approach

The objective of the present study was to optimise the biosynthesis of gold nanoparticles using aqueous extract of Pongamia seed cake (PSC). Proteins, amino acids and phenolic compounds present in the PSC extract are responsible for reducing the metal precursor salt to nanoparticles. The levels of factors for optimisation of nanoparticles synthesis was evaluated using UV–Vis spectrophotometer by one factor at a time studies. Further factorial design was employed to study the significant effect of various parameters on the nanoparticles synthesis. The levels of two significant factors i.e. pH and concentration of PSC extract as obtained from factorial design were optimized further for maximum nanoparticle synthesis applying central composite design. The optimized conditions were found to be pH 3.6 and PSC extract concentration of 17.07% (w/v) at which an increase (OD at 530 nm = 1.3) in nanoparticle synthesis was observed as compared to un-optimized conditions (OD at 530 nm = 0.66). The model obtained on optimization was validated and it describes the nanoparticle synthesis aptly with an error between experimental and predicted values of just 1.15% with an R² of 0.985. It can be concluded that, RSM approach was found to be an efficient technique to optimize the reaction conditions, where a twofold increase in synthesis of small sized monodispersed gold nanoparticles was seen. Graphic abstract: [Figure not available: see fulltext.].