Mechanisms of Aggregation of Cysteine Functionalized Gold Nanoparticles

Abstract

The interaction of gold nanoparticles (AuNPs) with cysteine and its derivatives is the basis of a number of bionanotechnologies, and for these, the most important process is aggregation (or antiaggregation), which enables an array of colorimetric detection methods. When AuNPs were functionalized with cysteine, its dimer cystine, or the cysteine-derived tripeptide, glutathione, three different mechanisms of aggregation were observed. Both cysteine and glutathione induced aggregation of AuNPs without further pH modification: the first by interparticle zwitterionic interaction and the second by interparticle hydrogen bonding. Cystine, however, did not induce aggregation, although it dissociated into two cysteinate moieties upon adsorption on the AuNPs, which appear to be chemically identical to cysteinate produced from cysteine adsorption. We show that the difference is due to the lower coverage of cysteinate from cystine and differences in charge states of the adsorbates. On modifying the pH to 1.5, the surface species become cationic (neutral COOH and protonated NH 3 + ), and aggregation of cystine/AuNPs occurs immediately by interparticle hydrogen bonding. Thus, cysteine may induce aggregation by neutral hydrogen bonding or zwitterionic interaction between nanoparticles, but the mechanism depends sensitively on a number of parameters.

Nonpolar Interface Composition in Cetyltrimethylammonium Bromide Reverse Micellar Environments to Control Size and Induce Anisotropy on Gold Nanoparticles

“…This can be due to the formation of bridges between the nanoparticles and induction aggregation. Therefore, the induced AuNP aggregation by addition of L–Cys was attributed to the formation of zwitterionic networks involving interaction of the deprotonated carboxylate (‐COO − ) and protonated amine (‐NH 3 + ) groups between AuNPs‐bound to L–Cys, with the opposite groups of L–Cys capped on neighboring particles, consistent with studies conducted using FTIR spectroscopy and other techniques . Figure B shows the corresponding histogram providing the size distribution of AuNPs, indicating a normal distribution with a progressive increment of size from 9 nm to 14 nm.…”

Cysteine-containing oligopeptide β-sheets as redispersants for agglomerated metal nanoparticles

“…This tendency is similar to the aggregation of AuNPs when cysteine was added to aqueous dispersion of AuNPs. 18 In contrast, when the total concentrations of Fmoc-VKVVC were increased to 0.125 and 0.25 mM, the absorbance of AuNPs at 530 nm was increased (Fig. 2g, inset).…”

“…11 On the other hand, the shorter Fmoc-peptides, Fmoc-KVVC, Fmoc-VVC, Fmoc-VC and Fmoc-KC, as well as Fmoc-amino acid, Fmoc-C, hardly disperse the agglomerated MNPs. 18 Nonpeptide compound such as 1-dodecanethiol hardly exhibited redispersive property of AuNPs as well. Figure 5 shows schematic representation of possible mechanism of how the β-sheet redisperses the agglomerated MNPs.…”

Tetrazine Click Chemistry for the Modification of 1‐Hydroxy‐1,1‐methylenebisphosphonic Acids: Towards Bio‐orthogonal Functionalization of Gold Nanoparticles

“…The peak position and FWHMs of N1 on NPs are in good correlation with the synthetic oxidized product without gold substrate and can be accordingly assigned to aromatic nitrogen atoms. Furthermore previous studies showed that N2 energy corresponds to zwitterionic/protonated amines, and in our case this suggests also the presence of tautomers. We noticed that the N s signal is, as expected, identical for both reaction conditions (RT and MW conditions), despite the pyTz stability differences.…”