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

In this work, thermoresponsive core–shell micelle-embedded silver nanoparticles (AgNPs) were prepared from a series of monodisperse linear-dendritic poly(urea/malonamide). Through efficient iterative synthesis, well-defined dendritic amphiphiles bearing dual functionality provide nucleation sites as excellent templates for immobilizing AgNPs on one end, while oligoethers anchor water to stabilize these micelles in water as polymer dispersions. During the heating process, linear-dendritic poly(urea/malonamide) with various ratios of hydrophilic/hydrophobic segments resulted in the size-dependent lowest critical solution temperature (LCST), ranging from 72 to 54 °C in aqueous media. As a result, the gap distances between AgNPs could be manipulated, resulting in a stronger hot spot effect using thermoresponsive nanocapsules for surface-enhanced Raman scattering (SERS) analysis. Consequently, the signal was enhanced at temperatures over the LCST. For AgNPs@TD-G1.5 thermoresponsive SERS nanocapsules, an ∼33 times enhancement during the LCST transition was obtained. The high sensitivity and stability of the intelligent AgNPs@thermoresponsive SERS nanocapsules endow them with great potential in the rapid SERS detection of small-molecule analytes by adsorbing analytes at room temperature (below the LCST) and encapsulating the analytes into micelles at high temperatures (above the LCST) in the application of monitoring trace-level and diverse analytes.