The effect of pH and transition metal ions on cysteine-assisted gold aggregation for a distinct colorimetric response

Abstract

Divalent transition metal ions facilitated the aggregation of gold nanoparticles: Fe2+ < Ni2+ < Zn2+ < Co2+ ≪ Mn2+ < Cu2+ at pH 7. The optimized AuNPs-Cu2+ system produced the progressive color change upon the addition of cysteine (0.2–2.0 μM).

Colorimetric Systems for the Detection of Bacterial Contamination: Strategy and Applications

“…High salt levels can neutralize the stabilizing electrostatic forces on AuNPs, causing the van der Waals forces to drive the conversion of dispersion into aggregation [ 58 ]. Another strategy involves the ion-induced aggregation of AuNPs [ 51 , 55 , 59 ]. For example, Mn 2+ can interact with carboxyl groups on the AuNP surface and lead to the aggregation of AuNPs, resulting in a change in color from red to purple.…”

“…For example, Mn 2+ can interact with carboxyl groups on the AuNP surface and lead to the aggregation of AuNPs, resulting in a change in color from red to purple. A recent study reported that the addition of Mn 2+ and Cu 2+ facilitates the cysteine-induced aggregation of AuNPs [ 59 ]. The thiol group of cysteine strongly binds to the AuNP surface, forming a zwitterionic structure with carboxyl and ammonium groups [ 60 ].…”

Core–shell Au–Ag nanoparticles as colorimetric sensing probes for highly selective detection of a dopamine neurotransmitter under different pH conditions

“…In the field of biosensing, noble (Au and Ag) metallic nanoparticles (NMNPs) with their unique optical properties are of great interest given their importance in the development of colorimetric and surface plasmonic resonance (SPR) biosensors, as well as surface-enhanced Raman scattering (SERS)active materials. [8][9][10][11][12][13] Gold NPs (Au NPs) possess attractive features such as chemical stability and ease of surface modification, which are imperative for sensing applications. 10,[14][15][16][17][18][19] The plasmonic efficiency of silver nanoparticles (Ag NPs) is higher than that of Au NPs.…”

“…[8][9][10][11][12][13] Gold NPs (Au NPs) possess attractive features such as chemical stability and ease of surface modification, which are imperative for sensing applications. 10,[14][15][16][17][18][19] The plasmonic efficiency of silver nanoparticles (Ag NPs) is higher than that of Au NPs. [20][21][22] In addition, some studies have shown that Ag NPs can be used as colorimetric sensors for dopamine detection.…”

“…However, many developed plasmonic sensing systems did not show the selective detection of DA against various interfering components including similar catecholamine neurotransmitters (epinephrine and norepinephrine). 25,[28][29][30][31][32][33][34][35][36] Meanwhile, some studies pointed out that the pH condition is one of the most important parameters that can not only influence the optical and electronic properties of NMNPs (Au and Ag) 10,22,37 but also change the surface states of catecholamine molecules in the aqueous phase. 38,39 In practice, an increase of solution pH leads to an increase in the negative surface charge of NMNPs, and induces the step-wise loss of protons from DA molecules.…”