Protein stabilized Au nanoclusters: spectral properties and photostability

Abstract

Bovine serum albumin stabilized gold nanoclusters (BSA-Au nanoclusters) have been widely studied due to their possible applications in biomedicine as sensors, fluorescent or multi-modality markers, and therapeutic agents. Synthesis and optical properties of these nanoclusters have been extensively investigated; however, there is still very little data on photostability of BSA-Au nanoclusters. Photostability of BSA-Au nanoclusters is of major importance for a variety of applications, such as material sensing and fluorescence imaging. Herein we demonstrate that after synthesis the BSA-Au solution has two photoluminescence (PL) bands peaking at 468 and 660 nm. Nevertheless, a different behaviour of the PL bands at 468 and 660 nm upon irradiation indicates that only band at 660 nm is related to PL of Au nanoclusters. BSA-Au nanoclusters exhibit great colloidal stability and do not undergo irreversible changes when heated up to 65 °C. However, irradiation of BSA-Au nanoclusters causes a wavelength dependent decrease of intensity and a hypsochromic shift of the PL band at 660 nm which is proportional to the delivered dose. The shift of the PL band at 660 nm could occur due to loss of several gold atoms in Au nanoclusters and/or due to deterioration of a nanoparticle coating layer. We have also demonstrated that the photostability of BSA-Au nanoclusters increases in the cell growth medium.

Photoluminescent Gold Nanoclusters in Cancer Cells: Cellular Uptake, Toxicity, and Generation of Reactive Oxygen Species

“…The shape of the spectrum coincides with the absorption spectrum of pure BSA [47]. Photoluminescence spectrum of BSA-Au NCs solution (λ ex = 405 nm) has a main peak with a maximum at 650 nm and another band of lower intensity at 468 nm (Figure 1, red solid line).…”

“…The absorption spectrum of BSA-Au NCs ( Figure 1 , dash-dot purple line) exhibited gradually increasing absorbance to the shorter wavelength spectral region with a distinct absorption band at 280 nm. The shape of the spectrum coincides with the absorption spectrum of pure BSA [ 47 ]. Photoluminescence spectrum of BSA-Au NCs solution (λ ex = 405 nm) has a main peak with a maximum at 650 nm and another band of lower intensity at 468 nm ( Figure 1 , red solid line).…”

“…Photoluminescence spectrum of BSA-Au NCs solution (λ ex = 405 nm) has a main peak with a maximum at 650 nm and another band of lower intensity at 468 nm ( Figure 1 , red solid line). Components used for the synthesis of BSA-Au NCs (HAuCl 4 , BSA) or the mixture of those two materials did not exhibit photoluminescence in red spectral region (600–700 nm) [ 47 ]. BSA-Au NC solution has a wide photoluminescence (PL) excitation spectrum (λ em = 650 nm) ( Figure 1 , orange dashed line) gradually increasing to the shorter wavelength spectral region with a distinctive band at around 510 nm wavelength.…”

“…BSA-Au NC solution has a wide photoluminescence (PL) excitation spectrum (λ em = 650 nm) ( Figure 1 , orange dashed line) gradually increasing to the shorter wavelength spectral region with a distinctive band at around 510 nm wavelength. The hydrodynamic size of BSA-Au NCs is 9.4 nm on average, the core Au NCs being composed of ~29 gold atoms as it was calculated using the free electron gas model in our previous report [ 47 ].…”

“…We have shown that photoluminescent BSA-Au NCs do not accumulate uniformly in both MCF-7 and MDA-MB-231 cells, only up to 73.5% of the MCF-7 cells and 68.8% of the MDA-MB-231 cells had internalized BSA-Au NCs after 24 h of incubation while BSA-Alexa 488 conjugate was observed accumulated in all MCF-7 and MDA-MB-231 cells after 24 h of incubation ( Figure 3 ). Previously, we have also shown that the hydrodynamic size of BSA-Au NCs after the synthesis increased by approximately 2.5 nm (to 9.4 nm on average) compared to pure BSA [ 47 ] which could be due to the modification of the secondary structure of the BSA after labelling [ 48 ]. This transformation of the BSA structure could have caused difference of accumulation of BSA-Au NCs and BSA-Alexa 488 conjugate.…”