Homocysteine-Mediated Reactivity and Assembly of Gold Nanoparticles

Abstract

This paper reports the findings of an investigation of the reactivity and assembly of gold nanoparticles mediated by homocysteine (Hcys), a thiol-containing amino acid found in plasma. The aim is to gain insight into the interparticle interaction and reactivity, which has potential application for the detection of thiol-containing amino acids. By monitoring the evolution of the surface plasmon resonance absorption and the dynamic light scattering of gold nanoparticles in the presence of Hcys, the assembly was shown to be dependent on the nature and concentration of the electrolytes, reflecting an effective screening of the diffuse layer around the initial citrate-capped nanoparticles that decreases the barrier to the Hcys adsorption onto the surface, and around the subsequent Hcys-capped nanoparticles that facilitate the zwitterion-type electrostatic interactions between amino acid groups of Hcys bound to different nanoparticles. A key element of the finding is that the interparticle zwitterion interaction of the Hcys-Au system is much stronger than the expectation for a simple Hcys or Au solution, a new phenomenon originating from the unique nanoscale interparticle interaction. The strength and reversibility of the interparticle zwitterion-type electrostatic interactions between amino acid groups are evidenced by the slow disassembly upon increasing pH at ambient temperatures and its acceleration at elevated temperature. These findings provide new insight into the precise control of interfacial interactions and reactivities between amino acids anchored to nanoparticles and have broad implications in the development of colorimetric nanoprobes for amino acids.

Detection of Oxidative Stress Biomarkers Using Novel Nanostructured Biosensors

“…Large increase of the RELS signal was reported for both GSH and Hcys confirming the assembly process (Stobiecka et al, 2010a, Stobiecka et al, 2010b. While in the Hcys-induced assembly, the main forces are Hbonding, in the case of GSH-induced assembly, the zwitterionic forces are dominant, although the H-bonding plays also a role (Lim et al, 2007, Lim et al, 2008. No aggregation of nanoparticles has been found in the presence of nitrotyrosine.…”

“…At the pH =6.0, homocysteine exists as a zwitterion with -amino group protonated (-NH 3 + ) and carboxylic group dissociated (COO − ). Therefore, the zwitterionic interparticle binding between Hcys-capped AuNP is playing a predominant role, as recently discussed by Zhong et al (Lim et al, 2007). The bathochromic shift of the surface plasmon peak (Δ max = 36 nm, for 16 M Hcys) corresponds to the formation of small Hcys-linked AuNP ensembles.…”

“…replacing short-chain citrate molecules in the nanoparticle shell with longer-chain GSH molecules) and interparticle interactions leading to AuNP assembly. In contrast to the behavior of NT, Hcys and GSH, replace nonthiolated AuNP shell and in the proper pH range induce assembly of gold nanoparticles ( Figure 5) (Lim et al, 2007, Lim et al, 2008, Stobiecka et al, 2010a, Stobiecka et al, 2010b. Large increase of the RELS signal was reported for both GSH and Hcys confirming the assembly process (Stobiecka et al, 2010a, Stobiecka et al, 2010b.…”

“…The aggregation of AuNP may also be caused by other factors, such as the addition of higher salt concentrations or injection of small amounts of multivalent metal cations able to coordinate to the ligands of nanoparticle shells, however, neither the salt or metal cations have any chance to replace a SAM film that protects AuNP. The affinity of thiols to a Au surface (Whitesides et al, 2005) enables such thiols as GSH and homocysteine to readily replace citrates from the nanoparticle shell (Lim et al, 2007, Lim et al, 2008, Stobiecka et al, 2010b. While GSH can form intermittently some weakly bound intermediate interparticle linking structures (Stobiecka et al, 2010a), these only help to isolate a citrate ion from its neighbors and remove that citrate from the film.…”

Colorimetric Assay of Aminopeptidase N Activity Based on Inhibition of the Disassembly of Gold Nano-composites Conjugated with a Thermo-responsive Copolymer

“…The spontaneous assembly is responsible for an interparticle interaction between cysteine adhered on AuNPs through the formation of hydrogen bonds. 33,34 Contrarily, as shown in Fig. 2b cysteinylglycine causes a very small change in the extinction spectra of AuNPs, indicating that gold nano-particles with cysteinylglycine still possess high dispersibility.…”