A Mechanistic View of the Light-Induced Synthesis of Silver Nanoparticles Using Extracellular Polymeric Substances of Chlamydomonas reinhardtii

• Published in: Molecules (Basel, Switzerland) Vol. 24; no. 19; p. 3506
• Main Authors: Rahman, Ashiqur, Kumar, Shishir, Bafana, Adarsh, Lin, Julia, Dahoumane, Si Amar, Jeffryes, Clayton
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 27-09-2019; MDPI
• Subjects: Acidification; Adsorption; agnps; algal synthesis; Biomolecules; Biopolymers - chemistry; Biosynthesis; bottom-up; Chlamydomonas reinhardtii; Chlamydomonas reinhardtii - chemistry; eps; Extracellular polymers; factorial design; Factorial experiments; Functional groups; Hydrogen-Ion Concentration; Infrared spectroscopy; Light; Light intensity; Luminous intensity; Metal Nanoparticles - chemistry; Metal Nanoparticles - ultrastructure; nanobiomaterials; Nanoparticles; Particle Size; photon; Photons; Reaction mechanisms; Silver; Silver - chemistry; Stabilization; photon; algal synthesis; nanobiomaterials; bottom-up; AgNPs; factorial design; EPS
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules24193506

In the current study, extracellular polymeric substances (EPS) of
and photon energy biosynthetically converted Ag
to silver nanoparticles (AgNPs). The reaction mechanism began with the non-photon-dependent adsorption of Ag
to EPS biomolecules. An electron from the EPS biomolecules was then donated to reduce Ag
to Ag
, while a simultaneous release of H
acidified the reaction mixture. The acidification of the media and production rate of AgNPs increased with increasing light intensity, indicating the light-dependent nature of the AgNP synthesis process. In addition, the extent of Ag
disappearance from the aqueous phase and the AgNP production rate were both dependent on the quantity of EPS in the reaction mixture, indicating Ag
adsorption to EPS as an important step in AgNP production. Following the reaction, stabilization of the NPs took place as a function of EPS concentration. The shifts in the intensities and positions of the functional groups, detected by Fourier-transform infrared spectroscopy (FTIR), indicated the potential functional groups in the EPS that reduced Ag
, capped Ag
, and produced stable AgNPs. Based on these findings, a hypothetic three-step, EPS-mediated biosynthesis mechanism, which includes a light-independent adsorption of Ag
, a light-dependent reduction of Ag
to Ag
, and an EPS concentration-dependent stabilization of Ag
to AgNPs, has been proposed.