Photomorphogenesis of γ-globulin: effect on sequential ordering and knock out of gold nanoparticles array

Abstract

Herein we describe the synthesis of monodisperse protein-gold nanoparticles (AuNPs), wherein γ-globulin, a blood plasma protein acts as a capping, reducing, as well as a templating agent. As analysed through various photophysical, biophysical and microscopic techniques such as TEM, AFM, C-AFM, SEM, DLS, OPM, CD, and FTIR, we observed that the initial photoactivation of γ-globulin at pH 12 for 3 h resulted in small protein fibres of ca. 20 ± 5 nm in size. Subsequently, these fibres found to assist in the alignment of the colloidal gold nanoparticles of average diameter of ca. 2–2.5 nm on the surface of protein. At this particular irradiation time, the nano-bioconjugate thus formed exhibited negligible surface plasmon resonance absorption but showed an intense photoluminescence at 680 nm. Further irradiation for 24 h, led to the formation of self-assembled long fibres of the protein of ca. 2 ± 0.5 μm in diameter and ca. 18 μm in length. Interestingly, such a morphological transformation resulted in the sequential knock out of the anchored gold nanoparticles resulting in the clustering of the nanoparticles of size ca. 5–6 nm and observation of surface plasmon resonance band at around 520 nm with the concomitant quenching of luminescence intensity at 680 nm. The observation of light triggered self-assembly of protein and its effect on ordering and knock out of metal nanoparticles offers an approach for the design of novel nano-biohybrid materials for medicinal and optoelectronic applications.