Synthesis and Characterization of Tunable, pH-Responsive Nanoparticle–Microgel Composites for Surface-Enhanced Raman Scattering Detection

Abstract

The synthesis of microgels with pH-tunable swelling leads to adjustable and pH-responsive substrates for surface-enhanced Raman scattering (SERS)-active nanoparticles (NPs). Sterically stabilized and cross-linked latexes were synthesized from random copolymers of styrene (S) and 2-vinylpyridine (2VP). The pH-dependent latex-to-microgel transition and swellability were tuned based on their hydrophobic-to-hydrophilic content established by the S/2VP ratio. The electrostatic loading of polystyrene/poly(2-vinylpyridine) microgels [PS x P2VP y (M)] with anions such as tetrachloroaurate (AuCl 4 – ) and borate-capped Ag NPs was quantified. The PS x P2VP y (M) can load ∼0.3 equiv of AuCl 4 – and the subsequent photoreduction results in Au NP-loaded PS x P2VP y (M) with NPs located throughout the structure. Loading PS x P2VP y (M) with borate-capped Ag NPs produces PS x P2VP y (M) with NPs located on the surface of the microgels, where the Ag content is set by S/2VP. The pH-responsive SERS activity is also reported for these Ag NP-loaded microgels. Analytical enhancement factors for dissolved crystal violet are high (i.e., 10 9 to 10 10 ) and are set by S/2VP. The Ag NP-loaded microgels with ∼80 wt % 2VP exhibited the most stable pH dependent response.

Surface‐Bound Microgels for Separation, Sensing, and Biomedical Applications

“…[9,49,102,180,181] Curtis et al, for example, fabricated P(S-co-2VP) microgels modified with gold nanoparticles (AuNPs) for sensitive detection of crystal violet (CV) in solution. [48] The SERS capacity bestowed by the AuNPs, combined with the electrostatic localization of materials within the microgels, allowed the system to achieve an analytical enhancement factor (AEF) of 10 10 to detect CV in solution compared to 5 × 10 9 for nanoparticles alone. Islam et al developed light-sensitive etalons using thermosensitive microgels impregnated with AuNPs.…”

“…Specifically, controlled swelling has been leveraged to release physically bound molecules, [20,[34][35][36] adjust the surface stiffness, [5,25,[37][38][39] and enable sensing activity. [9,40,41] Furthermore, the monomers used to construct the microgels are often amenable to post-synthetic modification with (bio)macromolecules, [42][43][44][45][46] nanoparticles, [47][48][49] and small molecules, [50][51][52][53] thus expanding their technological potential.…”

Development and Application of Nanoparticle-Nanopolymer Composite Spheres for the Study of Environmental Processes

“…Single particle-based methods have recently been applied in monitoring polymeric degradation ( Barber et al, 2020 ) and also in tracking carboxylated microspheres ( Jiménez-Lamana et al, 2020 ), but has yet to be applied in an environmental context for MP analysis. The core polymeric material is a polystyrene-poly(2-vinylpyridine) co-polymer (PS-co-P2VP) which had been previously shown to be a suitable platform for the attachment and growth of metallic nanoparticles ( Curtis et al, 2018 ). These nanoscale polymer core particles were then overcoated with additional polymeric material (polystyrene or polymethylmethacrylate) to ensure that their behavior and interactions with environmental substrates mimicked that of ‘pristine’ MP particles.…”

Nanoscale uniformity in the active tuning of a plasmonic array by polymer gel volume change

“…However, the optimization of nanostructures on the hydrogels is very limited due to technical problems related to the preparation and observation of ordered metal nanoarrays on the hydrogels, although the precise control of ordered nanostructures is important to achieve better performance on active plasmonics. [41][42][43][44][45] In our previous study, we developed a method for preparing metal nanostructures on hydrogels. 46 In this method, ne gold structures prepared by lithographic techniques on a silicon substrate were transferred onto a poly(acrylic acid) (PAA) gel based on the moderate interactions between the gold and gel.…”