Stimuli-responsive microgels with fluorescent and SERS activities for water and temperature sensing

Design and application of stimulus-responsive microgels is still in its infancy but is an exhilarating topic in controllable sensing device. Here, we have fabricated a dual-responsive platform capable of both sensitive on-spot fluorescence analysis and reliable surface-enhanced Raman scattering (SERS) quantification of water and temperature by in-situ encapsulating 4,4'-dimercaptoazobenzene (DMAB), meso-formyl-1,3,5,7-tetramethyl pyrromethene fluoroborate (FPF) probe and Ag nanoparticles (AgNPs) into polyvinyl alcohol (PVA) microgels. The smart microgels exhibit ultra-sensitive (detection limit 10^-4% v/v) and reversible response towards water due to the liner relationship between network volume and SERS performance of the microgels. Furthermore, the presence of water triggers the conversion of FPF to aldehyde hydrate, facilitating visual assay of trace water in matrix samples through the enhanced fluorescence signals. Interestingly, the SERS signals can be precisely tuned by the thermo-sensitive microgels substrate, thus achieving the temperature monitoring from 32 to 50 °C. The microgels-based sensor has fast-response (2 min), excellent stability, and enables accurate and reliable response of water in organic solvent and pharmaceutical products. As a smart and flexible sensor, the hybrid microgels will facilitate the field of POC analysis, as well as molecular recognition in the future.

Controlled release of monodisperse silver nanoparticles via in situ cross-linked polyvinyl alcohol as benign and antibacterial electrospun nanofibers

A facile methodology was explored by using glutaraldehyde as a cross-linking reagent for in situ modification of polyvinyl alcohol (PVA) electrospun nanofibers doped with monodisperse silver nanoparticles (AgNPs) via the one-pot reactions. The hydroxyl groups along the PVA molecule chains can serve as both the reactive sites and stabilizers for AgNPs. Meanwhile, the cross-linking degree can be easily tuned by controlling the charged amounts of glutaraldehyde to obtain either partial or cured cross-linked PVA nanofibrous mats doped with AgNPs. It was revealed that such different cross-linking degrees could effectively control the release contents and rates of the embedded Ag to the surrounding aqueous solution. Furthermore, such release behavior was also found to be pH-responsive and acid-labile due to the formation of acetal groups during the cross-linking reactions. Besides both the partial and cured cross-linked PVA doped with Ag nanoparticles can still bear good antibacterial efficacy against S. aureus while have low cytotoxicity against mouse embryo fibroblasts (NIH3T3), human embryonic kidney cells (293T) and human histiocytic lymphoma cells (U937).

Plasmonic nanostructures for surface enhanced spectroscopic methods

The development within the last five years in the field of surface enhanced spectroscopy methods was comprehensively reviewed.

One-pot preparation of pomegranate-like polydopamine stabilized small gold nanoparticles with superior stability for recyclable nanocatalysts

A pre-mixing and post-polymerization strategy has been developed to fabricate polydopamine (PDA) stabilized small gold nanoparticles (size of AuNPs < 5 nm) with high stability for recyclable catalysis of 50 mM 4-nitrophenol with a TOF of 1006 h⁻¹.

pH-Triggered Molecular Alignment for Reproducible SERS Detection via an AuNP/Nanocellulose Platform

The low affinity of neutral and hydrophobic molecules towards noble metal surfaces hinders their detection by surface-enhanced Raman spectroscopy (SERS). Herein, we present a method to enhance gold nanoparticle (AuNP) surface affinity by lowering the suspension pH below the analyte pK_a. We developed an AuNP/bacterial cellulose (BC) nanocomposite platform and applied it to two common pollutants, carbamazepine (CBZ) and atrazine (ATZ) with pK_a values of 2.3 and 1.7, respectively. Simple mixing of the analytes with AuNP/BC at pH < pK_a resulted in consistent electrostatic alignment of the CBZ and ATZ molecules across the nanocomposite and highly reproducible SERS spectra. Limits of detection of 3 nM and 11 nM for CBZ and ATZ, respectively, were attained. Tests with additional analytes (melamine, 2,4-dichloroaniline, 4-chloroaniline, 3-bromoaniline, and 3-nitroaniline) further illustrate that the AuNP/BC platform provides reproducible analyte detection and quantification while avoiding the uncontrolled aggregation and flocculation of AuNPs that often hinder low pH detection.

Tweaking anisotropic gold nanostars: covariant control of a polymer–solvent mixture complex

A versatile polymer–binary solvent mixture based tweaking of gold stars enables them as excellent candidates for tunable SERS substrates.

Mesoporous poly(ethylene-co-vinyl alcohol) monolith captured with silver nanoparticles as a SERS substrate: facile fabrication and ultra-high sensitivity

A facile method to fabricate a mesoporous poly(ethylene-co-vinyl alcohol) (EVOH) monolith captured with silver nanoparticles (AgNPs) was developed.

Three-dimensional plasmonic hydrogel architecture: facile synthesis and its macroscale effective space

A facile strategy was developed to fabricate a 3D hydrogel decorated with Ag nanoparticles as a SERS substrate. The macro effective depth in this 3D network was confirmed. The substrate produced satisfactory results in the analysis of trace environmental molecules.

Coffee-ring effect-based simultaneous SERS substrate fabrication and analyte enrichment for trace analysis

Based on the "coffee-ring effect", we developed a highly efficient SERS platform which integrates the fabrication of SERS-active substrates and the preconcentration of analytes into one step. The high sensitivity, robustness, reproducibility and simplicity make this platform ideal for on-site analysis of small volume samples at low concentrations in complex matrices.

High performance surface-enhanced Raman scattering via dummy molecular imprinting onto silver microspheres

A new strategy for achieving high performance SERS was proposed by using the dummy molecular imprinting technique.