Reversible Assembly and Disassembly of Gold Nanoparticles Directed by a Zwitterionic Polymer

Abstract

Herein, we have successfully introduced the stimuli-response concept into the controllable synthesis of gold nanoparticles (AuNPs) with designed properties. We used a pH-responsive zwitterionic polymer that acted as a template and a stabilizer. Gold colloids prepared in situ from the polymer solution have a narrow size distribution of about 5 nm. The assembly and disassembly of AuNPs can be finely tuned by modulating the net charges of the zwitterionic polymer so that they are either positive or negative as a function of the solution pH. Different aggregates and colors appear on altering the solution pH. In acidic solutions, gold colloids form large symmetrical aggregates, while the AuNPs disperse in solutions with a pH approximately 9.6. However, as the solution pH increases (>9.6), needle-like aggregates with a small interparticle distances are formed. On the basis of TEM, SEM, 1H NMR and UV/Vis measurements, we attribute pH-triggered aggregation and color changes of the gold colloids to the ionization process and conformational change of the polymer. The ionization process governs the choice of ligand anchored on the surface of AuNPs, and the conformational change of the polymer modulates the interspaces between AuNPs. The present approach, which is based on a rational design of the physicochemical properties of the template used in the synthesis process, provides a powerful means to control the properties of the nanomaterial. Furthermore, the colorimetric readout can be visualized and applied to future studies on nanoscale switches and sensors.

Optic and catalytic properties of gold nanoparticles tuned by homopolymers

“…This is also in agreement with that described in eq. (1) and has been found in many other systems [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] . In a previous report, we studied the catalytic activity of GNs supported by core-shell micelles with polystyrene (PS) as core and poly(4-vinylpyrydine) (P4VP) as shell and found that since the GNs on the surface of the micelle were wrapped by collapsed P4VP, their catalytic efficiency decreased with the decrease of GNs on the surface [15] .…”

“…The catalyst of GNs used in this system is so little that its effect on absorbance intensity at 400 nm could be ignored. In addition, since the added sodium borohydride largely exceeds the content of p-nitrophenol, the kinetics of the reduction can be treated as the first-order function of p-nitrophenol concentration [32,33] .…”

“…At the same time, the intensity of the absorption bands continuously decreases during the process of raising temperature from 40 to 65℃. The change of surface plasmon resonance is closely corresponding to the state of the PDMAEMA and can be explained by the distance changes among neighboring GNs under different conditions, which causes absorption change in the long-wavelength region [3,32] . At pH 2, since PDMAEMA keeps its stretch state, the GNs are widely separated by PDMAEMA and hence no obvious changes of the surface plasmon resonance are found under different temperature conditions.…”

Incorporation of Functionalized Palladium Nanoparticles within Ultrathin Nafion Films: A Nanostructured Composite for Electrolytic and Redox‐Mediated Hydrogen Evolution

“…The shift of the peak for the film towards the red region by about 20 nm, compared to the aqueous solution, is a common effect due to aggregation when a chromophore is incorporated within a polymeric film. [60] Unfortunately, UV-visible spectroscopy cannot directly detect the incorporation of palladium nanoparticles unambiguously as they do not display a strong surface plasmon band absorbance. [61] However, AFM, CV, and SECM data, reported in the following sections, confirmed the successful incorporation of Pd-DMAP nanoparticles.…”

Gold nanoparticle-based colorimetric assays for coagulation-related proteins and their inhibition reactions

“…As a result, the long-chain polymer structure of fibrin induces the aggregation of the Au NPs (Scheme 1A). The polymers assemble around each particle, thereby keeping them apart or holding them together, depending on the relative sizes of the polymers to particles, the radius of the effective repulsion between the particles, and the initial conformation of the polymers (Aubouy and Raphaël, 1998;Boyer et al, 2010;Ding et al, 2007;Huang et al, 2004;Polavarapu and Xu, 2008;Rahme et al, 2007;Skirtach et al, 2007). The polymer size and concentration play crucial roles in determining the stability of the particles (Chaplain et al, 1995;Mayer, 2001).…”