Label-free colorimetric sensing of cobalt(ii) based on inducing aggregation of thiosulfate stabilized gold nanoparticles in the presence of ethylenediamine

Abstract

As a sensitive and selective analytical technique, gold nanoparticles-based colorimetric sensing was characterized by its simplicity and cost-effectiveness. Specific methods have been extensively developed for different targets in diverse samples. In this study, a label-free method for sensing Co 2+ in aqueous solutions was described. The target was achieved by the induced aggregation of thiosulfate (S 2 O 3 2À ) stabilized gold nanoparticles (AuNPs) in the presence of ethylenediamine (en). Co 2+ first reacted with en and formed complexes of Co(en) 3 2+ in aqueous solutions, which was followed by the oxidation of Co(en) 3 2+ to Co(en) 3 3+ by dissolved oxygen. Co(en) 3 3+ then attacked S 2 O 3 2À ligands adsorbed on the AuNPs' surfaces, forming positively charged (en) 2 CoS 2 O 3 + on the AuNPs' surfaces, which reduced the surface charges of AuNPs and induced the aggregation of AuNPs. The process was accompanied by a red-shift in the adsorption spectrum and a visible colour change from wine red to blue. Potential effects of relevant experimental conditions, including pH, concentrations of S 2 O 3 2À and en, and incubation time were evaluated for optimization of the method. The proposed method is sensitive (LOD ¼ 0.0 4 mM or 2.36 ppb) and selective (by at least 100-fold over other metal ions except for Cu 2+ ) toward Co 2+ with a linear range from 0.1 to 0.7 mM. The cost-effective method allows rapid and simple determination of the concentrations of Co 2+ ions in drinking water.

Synthesis and multifunctional properties of lignosulfonate-stabilized gold nanoparticles

“…Note that the gold concentration in the reacting mixture was 1.25 mg cm À 3 which is much higher than in other reported synthesis protocols of Au-NPs [16,17,22]. Therefore, it was difficult to see the color differences between such concentrated solutions.…”

“…When the external stimuli bring the nanoparticles close to each other, a color change from ruby red to blue-purple can be observed. This is accompanied by the red-shift of the λ max and/or the appearance of a second absorption band at much longer wave lengths [5,16,17].…”

PolyA-tailed and fluorophore-labeled aptamer-gold nanoparticle conjugate for fluorescence turn-on bioassay using iodide-induced ligand displacement

“…On one hand, such two anions have been demonstrated to be capable of absorbing very strongly on gold surface for the removal of the surface impurities or other analytical applications (Chen et al, 2009;Li et al, 2013;Shen et al, 2014;Zhang et al, 2012c). Also, the Au-A interaction is intrinsically weaker than the Au-S covalent interaction (Zhang et al, 2012b), it is thus likely that a ligand displacement strategy of divide-and-conquer is adopted to displace the multiple consecutive adenines (polyA) anchored onto AuNP surface by the deposition of these anions on the particles ( Fig.…”

“…2 ) that have strong affinity for Au (Chen et al, 2009;Pienpinijtham et al, 2011;Zhang et al, 2012c), were first proposed as the ligand displacing reagents to release the attached polyA-tailed DNA from AuNP surface. Based on this novel finding and the employment of polyA-tailed, fluorophore-labeled apt29-AuNP (Fapt29-polyA-AuNP) conjugate and Apt15-conjugated magnetic beads (Apt15-MBs), we developed a cost-effective and sandwichtype fluorescence turn-on aptasensing platform for highly sensitive and specific TB detection, which eliminated the use of thiolated aptamer and thiol-containing displacing reagents.…”

A highly sensitive fluorescence turn-on platform with silver nanoparticles aptasening for human platelet-derived growth factor-BB

“…This platform was an integrative platform that combined the fluorescence signal and protein recognized sequences in a single ligand, so it would be much convenient for the preparation of Ag-FAM-apt and also not influence the function of aptamer for recognition of the protein specifically. Moreover, AuNPs were popular as a fluorophore quencher, and in general, this fluorescence turn-on methods had been used mostly based on AuNPs, one of the most commonly used strategies was the displacement of the attached DNA by small thiol-containing compounds, including 2-mercaptoethanol (2-ME) and dithiothreitol (DTT)[39][40][41]. However, comparing with AuNPs, the quenching ability of AgNPs had not been employed in such fluorescence turn-on platform beforehand.…”