Kinetics of Fluorophore Formation in Bovine Serum Albumin–Gold Complexes

Abstract

We revisit the prevailing hypothesis that the red fluorophore (λem = 640 nm) in the bovine serum albumin (BSA)–gold (Au) compound is a Au25 nanocluster. To examine the hypothesis, we investigated the kinetics of Au binding in this compound. In addition to the specific Au­(III) binding sites in BSA, we found a significant degree of nonspecific Au­(III) binding on the BSA surface. Time-course of the emergence of the red fluorescence was measured in detail for a range of pH, temperature, and concentration of Au­(III) with respect to BSA. The red fluorophore formation was a slow yet dynamic process, which was consistent with the pH-induced equilibrium transition in the conformation of BSA. Notably, the kinetic rate of the fluorophore formation was not strongly dependent on the concentration of Au­(III). Incorporating the existence of multiple specific and nonspecific binding sites, we propose a new model of the red fluorophore formation mechanism based on Langmuir-type adsorption of Au to BSA, as an alternative to the single-site nucleation model of Au25 nanoclusters.

Stochastic DNA Dual-Walkers for Ultrafast Colorimetric Bacteria Detection

“…In the case that the target is in low concentration (<10 3 CFU/mL), a high concentration of nontarget bacteria would interfere with detection, which yet would not hamper the determination of high concentration target bacteria (≥10 3 CFU/mL). To address this issue, the competing adsorption could potentially be suppressed by modifying the probes with bovine serum albumin or 6-mercapto-1-hexanol as sealing agent. − To sum up, all of these results disclose that this dual-walker-based colorimetric method holds great potential for practical applications in complex biological samples under a given condition.…”

Potassium-Induced Emission Enhancement of Bovine Serum Albumin-Stabilized Red-Emitting Au Nanoclusters: Mechanism and Application to Blood Plasma

“…Their studies revealed that the onset of the red emission occurs at pH = 9.7, which is below pKa of tyrosine. In another paper, the same authors have debated assignment of the red emission to Au 25 NCs, nucleated at the single-site [25]. This assignment to Au 25 NCs was based on results obtained using the matrix-assisted laser desorption ionization time-of-ight (MALDI-TOF) technique [19].…”

Enzymatic digestion of luminescent albumin-stabilized gold nanoclusters under anaerobic conditions: clues to the quenching mechanism

“…[10][11][12][13][14][15][16] Surprisingly, while the perspective of the real-life applications of albuminconjugated AuNCs is becoming increasingly clear, the underlying mechanisms through which the complexes are formed and the luminescence intensity is affected by changing environmental factors are not understood in sufficient detail. [17][18][19][20] In the case of the protocol by Xie involving an alkaline pH, BSA acts as both a reducing agent for chloroauric(III) acid and a macromolecular ligand, subsequently enveloping the formed AuNCs. The latter function is essential as the bare AuNCs are unstable and prone to self-assembly into larger metallic and therefore non-luminescent nanoparticles (AuNPs).…”