Formation of Fluorescent Metal (Au, Ag) Nanoclusters Capped in Bovine Serum Albumin Followed by Fluorescence and Spectroscopy

Abstract

Fluorescent noble metal (Au, Ag) nanoclusters have been biolabeled to bovine serum albumin (BSA) by wet chemistry. Spectroscopic and fluorescence investigations relate the role of the pH and the nature of the reducing agent to the size and the oxidation state of metal clusters. Blue-emitting (λ = 450 nm) small gold nanoclusters (eight atoms) prepared at pH 8 weakly bonded to BSA grow at higher pH to form red-emitting (λ = 690 nm) bigger clusters (25 atoms) covalently bonded to BSA via the sulfur group. X-ray photoelectron spectroscopy (XPS) measurements indicate the presence of Au(I) only for the big clusters. Small silver nanoclusters labeled to the protein with a fluorescence emission in the red region are synthesized in the presence of a strong reducing agent and present only Ag(0). Steady-state and lifetime measurements confirm the crucial impact of the size and the oxidation state of Au(I) on the stabilization of the metal core inside the protein and on the presence of a long lifetime component (τ > 170 ns).

Multivalent Glycosylation of Fluorescent Gold Nanoclusters Promotes Increased Human Dendritic Cell Targeting via Multiple Endocytic Pathways

“…The short nanosecond range lifetime is usually associated with singlet excited states originating from metal-metal interactions. On the other hand, the long microsecond range lifetime component is typical of triplet excited states 43,57 . This extended high energy state is of interest for analytical applications due to its high sensitivity to the local environment.…”

“…For instance, the Mattoussi lab reported the preparation of red-emitting Au NCs with a quantum yield of up to 14% when stabilised with bidentate thiolated ligands containing a zwitterionic group 40 . NC features such as tunable photoluminescence [41][42] , multiexponential fluorescence lifetime [43][44] , or aggregation induced enhancement 45 have been extensively studied with potential applications in the fields of sensing 46 , bioimaging 47 and optics 48 . Other interesting properties of NCs relevant for therapeutic applications rely on their ultra-small size, low toxicity and stability in physiological media.…”

Protein stabilized Au nanoclusters: spectral properties and photostability

“…Formation of such nanoparticle in a protein template or attached to protein should not cause increase in the BSA size by 2.5 nm. This indicates that the size increase after synthesis could be due to the transformation of the secondary structure of BSA induced by formation of a gold nanocluster inside the protein [30].…”

“…In literature it was reported that BSA-Au NCs fluoresce in the red spectral region [4, 14-16, 30, 37] and the PL band at 640-700 nm corresponds to the PL of Au NCs that are formed inside BSA. Some papers reported that during synthesis two types of photoluminescent BSA-Au NCs are formed: blue photoluminescent NCs (PL λ max ~ 470 nm) and red photoluminescent NCs (PL λ max ~ 660 nm) [4,30,38]. However, it should be noted that these authors used ascorbic acid as a reducing agent.…”

Ultrasensitive electrospun fluorescent nanofibrous membrane for rapid visual colorimetric detection of H2O2

“…As depicted in Fig. 6, the XPS spectrum in the absence of H 2 O 2 shows an Au 4f band at binding energies of 83.9 and 87.6 eV assigned to 4f 5/2 and 4f 7/2 , which could be attributed to Au(0)state [39]. When reacted with H 2 O 2 , the peak gradually shifts to a higher binding energy level, which can be ascribed to higher oxidation states of Au [33].…”