Uniform Microgels Containing Agglomerates of Silver Nanocubes for Molecular Size‐Selectivity and High SERS Activity

Abstract

Surface-enhanced Raman scattering (SERS) is a promising technique for molecular analysis as the molecular fingerprints (Raman spectra) are amplified to detectable levels compared with common spectroscopy. Metal nanostructures localize electromagnetic field on their surfaces, which can lead to dramatic increase of Raman intensity of molecules adsorbed. However, the metal surfaces are prone to contamination, thereby requiring pretreatment of samples to remove adhesive molecules. To avoid the pretreatment and potentially achieve point-of-care (POC) analysis, we have developed SERS-active microgels using the droplet-microfluidic system. As the microgels are composed of water-swollen network with consistent mesh size, they selectively allow diffusion of molecules smaller than the mesh, thereby excluding large adhesives. To render the microgels highly SERS-active, we destabilize silver nanocubes to form agglomerates, which are embedded in the matrix of microgels. The nanogaps in the agglomerates provide high sensitivity in Raman measurement and size-selective permeability of the microgel matrix obviates the pretreatment of samples. To validate the functions, we demonstrate the direct detection of Aspirin dissolved in whole blood without any pretreatment.

Plasmonic molecular assays: Recent advances and applications for mobile health

“…12, the bacteria were captured by the antibodies immobilized in the microchannel with an Au-coated SPR chip, resulting in a local refractive index change due to the binding event. Applications of microfluidics for other plasmonic detections, such as LSPR [172], SERS [173][174][175][176], and SEF [177] have also been extensively studied. For example, Quidant et al reported a parallel LSPR-based immunoassay chip for the real-time detection of AFP and PSA down to concentrations of 500 pg/mL in 50% human serum [172].…”

SERS‐Active‐Charged Microgels for Size‐ and Charge‐Selective Molecular Analysis of Complex Biological Samples

“…However, the liposomes and hydrogel‐shelled nanoparticles are difficult to separate and concentrate in practical uses due to small size and a lack of nanogaps provides limited sensitivity. To overcome the limitations of the nanocapsules, nanoparticles or their agglomerates are loaded in microgels using a microfluidic strategy . As the microgels with limiting mesh size allow the infusion of small molecules while excluding large protein, small molecules can be directly detected without pretreatment of the complex biological samples, such as blood; the mesh size is controllable by adjusting molecular weight of monomers .…”

Recent progress of microfluidics in surface‐enhanced Raman spectroscopic analysis

“…Kim's group [19][20][21] fabricated a series of SERS-active microgels through coflow-focusing microdroplet generation technique. Through agglomeration [19,20] or droplet shrinking [21], AuNPs can be concentrated in the microgel fabrication process to achieve higher SERS signal. On the other hand, AuNPs inside microgels can be protected from contamination by sample matrix in biologic application.…”