Aggregation of Gold Nanoparticles Caused in Two Different Ways Involved in 4-Mercaptophenylboronic Acidand Hydrogen Peroxide

Abstract

The difference in gold nanoparticle (AuNPs) aggregation caused by different mixing orders of AuNPs, 4-mercaptophenylboronic acid (4-MPBA), and hydrogen peroxide (H2O2) has been scarcely reported. We have found that the color change of a ((4-MPBA + AuNPs) + H2O2) mixture caused by H2O2 is more sensitive than that of a ((4-MPBA + H2O2) + AuNPs) mixture. For the former mixture, the color changes obviously with H2O2 concentrations in the range of 0~0.025%. However, for the latter mixture, the corresponding H2O2 concentration is in the range of 0~1.93%. The mechanisms on the color change originating from the aggregation of AuNPs occurring in the two mixtures were investigated in detail. For the ((4-MPBA + H2O2) + AuNPs) mixture, free 4-MPBA is oxidized by H2O2 to form bis(4-hydroxyphenyl) disulfide (BHPD) and peroxoboric acid. However, for the ((4-MPBA+AuNPs) + H2O2) mixture, immobilized 4-MPBA is oxidized by H2O2 to form 4-hydroxythiophenol (4-HTP) and boric acid. The decrease in charge on the surface of AuNPs caused by BHPD, which has alarger steric hindrance, is poorer than that caused by -4-HTP, and this is mainly responsible for the difference in the aggregation of AuNPs in the two mixtures. The formation of boric acid and peroxoboric acid in the reaction between 4-MPBA and H2O2 can alter the pH of the medium, and the effect of the pH change on the aggregation of AuNPs should not be ignored. These findings not only offer a new strategy in colorimetric assays to expand the detection range of hydrogen peroxide concentrations but also assist in deepening the understanding of the aggregation of citrate-capped AuNPs involved in 4-MPBA and H2O2, as well as in developing other probes.

Magneto‐plasmonic heterodimers: Evaluation of different synthesis approaches

“…The very low (almost absent) absorption curve for the samples obtained without reducing agent (synthesis 1a and 1b), in particular for lower APTES functionalization (synthesis 1a) can be due both to the GNPs small size, undetected by STEM observation but visible by TEM observation on sample 1b, and to the low concentration of GNPs above the critical size to give plasmon signals: it is well known that for NPs smaller than 5 nm the plasmon oscillation is strongly damped, resulting in a broad and low intensity plasmon signal 36 . On the contrary, samples 2a, 3a, 2b, and 3b revealed high amounts of GNPs with size and distribution correlated to a more intense peak in the absorption spectra or a plateau 32,33,37–40 …”

“…36 On the contrary, samples 2a, 3a, 2b, and 3b revealed high amounts of GNPs with size and distribution correlated to a more intense peak in the absorption spectra or a plateau. 32,33,[37][38][39][40] The magnetic response measurements of nanoplatforms obtained with syntheses 1a, 2a, and 3a and those related to syntheses 1b, 2b, and 3b are reported in Figure 8A,B, respectively. In particular, in both images, the red curves are related to the syntheses in which the Au(OH) 3 seeds were directly added to the M-A NPs suspension without using TA as reducing agent; the green curves are related to the syntheses in which HAuCl 4 and TA solutions were pre-mixed together and then added to the M-A NPs suspension; the blue curves are related to the syntheses performed adding HAuCl 4 and TA in sequence to the M-A NPs suspension.…”

Magnetoliposomes Based on Magnetic/Plasmonic Nanoparticles Loaded with Tricyclic Lactones for Combined Cancer Therapy

“…The increase in the core refraction index results in a red shift of the plasmon resonance peak [43]. Thus, the absorption spectrum indicates a shell between 5 and 10 nm, while for the gold-decorated NPs, the spectrum is typical of clusters of gold spheres [45].…”

“…The increase in the core refraction index results in a red shift of the plasmon resonance peak [43]. Thus, the absorption spectrum indicates a shell between 5 and 10 nm, while for the gold-decorated NPs, the spectrum is typical of clusters of gold spheres [45]. The position of the plasmon absorption band of gold nanoshells varies with the shell thickness and the refraction index of both core and surrounding media [43].…”

Functional-Group Effect of Ligand Molecules on the Aggregation of Gold Nanoparticles: A Molecular Dynamics Simulation Study

“…Therefore, determining the factors affecting the aggregation/dispersion behaviors of gold NPs and controlling these behaviors are crucial. Many experimental − and molecular dynamics (MD) simulation studies − have been performed to understand the aggregation/dispersion behaviors of functionalized gold NPs. In these simulation studies, the coarse-grained (CG) model − and realistic atomistic model − are widely used.…”