pH-responsive SERS substrates based on AgNP-polyMETAC composites on patterned self-assembled monolayers

Abstract

Patterned silver nanoparticle (NP)-poly[2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (AgNP-polyMETAC) composites were prepared by electrochemical lithography, surface-initiated atom-transfer radical polymerization (SI-ATRP) and NP growth inside the polymer brushes. For this purpose, polymer brushes of poly[2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (polyMETAC) were utilized as strong electrolyte brush system. These were introduced in form of patterned polymer brushes to create pH-responsive surface enhanced Raman scattering SERS substrates. It is well-known that the charges of strong polyelectrolyte chains are usually insensitive to pH changes, hence, rarely strong polyelectrolyte brushes have been utilized so far to study pH-responsive properties of such films. Here pH-insensitive polyMETAC brushes exhibit pH-sensitive properties and can be used as pH-responsive surfaces for SERS applications due to the embedding of AgNPs into the polymer brushes. When increasing the pH, the assembly of the AgNPs transfers from quasi two-dimensional (2D) aggregates, attaching mainly to the polymer surface, into a three-dimensional (3D) assembly, where the particles are penetrating into the brushes. These changes result in significant alterations of the SERS efficiency of the polymer brush composite. At pH 5, the enhancement of the Raman scattering approaches its maximum. The fabricated SERS substrates show a high sensitivity as well as good experimental reliability at different pH values. Moreover, electrochemical lithography was utilized to fabricate patterned SERS substrate, which allows an easy combination of multiple other functionalities in hierarchical structuring steps. In addition, the microstructure is in our studies beneficial because of a simplified and reliable characterization of the polymer brushes at defined sample areas. The introduction of the microstructured brush system is regarded moreover attractive for the development of high-throughput platforms for rapid, automated screening and analysis applications.

Guanidinium and Phosphonium Scaffolds Loaded with Silver Nanoparticles: Synthesis, Characterization, In Vitro Assessment of the Antibacterial Potential and Toxicity

“…Because of the relatively low stability of colloidal solutions, numerous reports are devoted to investigations of stabilized silver nanoparticles [15][16][17][18][19][20][21][22][23][24][25]. A suitable stabilizer should be used to limit the growth of the silver particles and their aggregation.…”

“…Unfortunately, as long as there are not so many ways to create materials from nanoparticles, since their aggregation leads to the loss of most of the unique characteristics [7,13,14]. To prevent aggregation, it is necessary to use stabilizing agents, such as self-assembled monolayers [15,16], surfactants [17][18][19], polymers [20][21][22][23] or dendrimers [24,25]. These stabilizers protect the nanoparticles from the environment and prevent their agglomeration, and moreover play an important role in controlling the size and shape of the particles.…”

Thermoresponsive SERS Nanocapsules Constructed by Linear-Dendritic Poly(urea/malonamide) for Tunable Biomolecule Detection

“…A series of stimuli-responsive SERS substrates were demonstrated in the literature using pH-, heat-, strain-, magnetic field-, or light-induced approaches. The pH-controlled spatial distribution of silver nanoparticles (AgNPs) embedded on polymer brushes of poly­[2-(methacryloyloxy)­ethyl] trimethyl ammonium chloride (polyMETAC) as well as pH-controlled reversible assembly of gold nanoparticles (AuNPs) and AgNPs decorated with penicillamine were proven to be feasible approaches for dynamic SERS substrates. In addition, Guo et al developed a noncontact approach using an external magnetic field to control the spacing of a 2-dimensional (2-D) monolayer film using Fe 3 O 4 @AuNPs.…”

Fabrication of antireflective silver-capped tin oxide nano-obelisk arrays as high sensitive SERS substrate

“…SERS is a powerful analytical method which provide 'finger print' information of analyte molecules and has been used in diverse fields including chemical and bio-sensing, environmental monitoring, forensic science, medical diagnostics, bio-imaging and food safety [16][17][18][19][20]. The magnitude of enhancement observed in the SERS process is contributed by two factors, namely EM enhancement and chemical enhancement (CE) [21,22].…”