Abstract
Investigation and optimization of lysozyme (Lys) adsorption onto gold nanoparticles, AuNPs, were carried out. The purpose of this study is to determine the magnitude of the AuNPs–lysozyme interaction in aqueous media by simple spectrophotometric means, and to obtain the free energy of binding of the system for the first time. In order to explore the possibilities of gold nanoparticles for sensing lysozyme in aqueous media, the stability of the samples and the influence of the gold and nanoparticle concentrations in the detection limit were studied. ζ potential measurements and the shift of the surface plasmon band showed a state of saturation with an average number of 55 Lys per gold nanoparticle. Lysozyme–AuNPs interactions induce aggregation of citrate-stabilized AuNPs at low concentrations by neutering the negative charges of citrate anions; from those aggregation data, the magnitude of the interactions has been measured by using Benesi–Hildebrand plots. However, at higher protein concentrations aggregation has been found to decrease. Although the nanocluster morphology remains unchanged in the presence of Lys, slight conformational changes of the protein occur. The influence of the size of the nanoclusters was also investigated for 5, 10, and 20 nm AuNPs, and 10 nm AuNPs was found the most appropriate.
Highlights
From the first preparation of gold colloids by Faraday in 1857, research on the use of gold nanoparticles has been an area of broad interest, a fact which is reflected by an exponential growth in the number of publications in the recent years
One stands out greatly: AuNPs possess unique optical properties in terms of extremely high extinction coefficients, distance–dependent color, and outstanding fluorescence quenching ability, popularizing them for biosensor development [8]. Owing to those inherent optical properties (AuNPs possess extinction coefficients which are over 1000 times larger than those of organic dyes) certain chemical interactions lead to aggregation-induced color changes allowing for visual detection and quantification of those interactions [9]
Aggregation occurs seconds, but it has been found that at high concentraAggregation occurs in seconds, but it has been found that at high protein concentrations tions the aggregation degree of the AuNPs markedly decreases, a fact confirmed by the the aggregation degree of the AuNPs markedly decreases, a fact confirmed by the blue blue shift of λmax, the observed color changes of AuNPs/Lysozyme solutions from purple shift of λmax, the observed color changes of AuNPs/Lysozyme solutions from purple to red, and by the changes of ζ-potential, going from a negative to a positive value as [Lys]
Summary
From the first preparation of gold colloids by Faraday in 1857, research on the use of gold nanoparticles has been an area of broad interest, a fact which is reflected by an exponential growth in the number of publications in the recent years They are considered largely nontoxic, even though this non-toxicity is strongly dependent on their size and recent publications have reported conflicting data [6]. They are stable, conductive, catalytically active, and electron dense [7] Among their many qualities, one stands out greatly: AuNPs possess unique optical properties in terms of extremely high extinction coefficients, distance–dependent color, and outstanding fluorescence quenching ability, popularizing them for biosensor development [8]. Works dealing with protein detection using AuNPs aggregation-based assays, where both label
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