Polarization properties of fluorescent BSA protected Au25 nanoclusters

Abstract

BSA protected gold nanoclusters (Au25) are attracting great deal of attention due to their unique spectroscopic properties and possible use in biophysical applications. Although there are reports on synthetic strategies, spectroscopy and applications, little is known about their polarization behavior. In this study, we synthesized the BSA protected Au25 nanoclusters and studied their steady state and time resolved fluorescence properties including polarization behavior in different solvents: glycerol, propylene glycol and water. We demonstrated that the nanocluster absorption can be separated from the extinction spectrum by subtraction of Rayleigh scattering. The nanocluster absorption spectrum is well approximated by three Gaussian components. By a comparison of the emissions from BSA Au25 clusters and rhodamine B in water, we estimated the quantum yield of nanoclusters to be higher than 0.06. The fluorescence lifetime of the BSA Au25 cluster is long and heterogeneous with an average value of 1.84 μs. In glycerol at −20°C the anisotropy is high, reaching a value of 0.35. However, the excitation anisotropy strongly depends on the excitation wavelengths indicating a significant overlap of the different transition moments. The anisotropy decay in water reveals a correlation time below 0.2 μs. In propylene glycol the measured correlation time is longer and initial anisotropy depends on the excitation wavelength. The BSA Au25 cluster, due to long lifetime and high polarization, can potentially be used in studying large macromolecules such as protein complexes with large molecular weight.

Fluorescence analysis of 6-mercaptopurine with the use of a nano-composite consisting of BSA-capped Au nano-clusters and core–shell Fe3O4–SiO2 nanoparticles

“…The dimensions of AuNCs are comparable to the electronic Fermi wavelength, and thus, the movements of electrons are restricted in all dimensions. As a result, the continuous electronic bands associated with the bulk or largish gold nanoparticles (AuNPs) become discrete levels, and this leads to completely different luminescent and electrical properties as compared to the larger-size particle systems; also, these systems are unable to support Surface plasmon resonance (SPR) (Raut et al, 2013). Apart from the successful use of AuNCs as chemical sensors and catalysts, they have also been applied for bio-labeling, bio-imaging, and in bio-medicine because they are of suitable size and are also, non-toxic (Chen et al, 2009;Rosi et al, 2006).…”

Protein stabilized Au nanoclusters: spectral properties and photostability

“…Currently, considerable research efforts are directed towards investigation of Au NCs synthesis [4][5][6][7][8][9][10], structure [7,11,12], optical properties [4,[13][14][15][16], photostability [17][18][19][20][21] and possible applications for material sensing [5,[22][23][24] as fluorescence [25,26] and dual-modality imaging contrast agents [27,28]. However, colloidal stability, photostability, dependence of optical properties on temperature, interaction of BSA-Au NCs with biomolecules are still poorly investigated.…”

Human serum albumin encapsulated gold nanoclusters: effects of cluster synthesis on natural protein characteristics

“…AuNCs are small in size, consisting of roughly 25 atoms in size and are less than 2nm in diameter, comparing with gold nanoparticles which can have diameters between 12-100nm and possess widely different properties. Of all the protein encapsulated gold nanoclusters, Serum Albumin based AuNCs have been the most widely studied [9][10][11][12][13] . This is due to the relative low costs of the materials needed for synthesis and the ease of the synthesis method 14 .…”