Mesoporous Silica-Capped Silver Nanoparticles for Sieving and Surface-Enhanced Raman Scattering-Based Sensing

Abstract

Surface-enhanced Raman scattering (SERS) is observed solitarily for analytes that are placed in the vicinity of plasmonic nanoparticles since the amplitude of the electric field on their surface decays with distance. Taking this idea forward, we have designed core−shell plasmonic systems for SERS sensing, consisting of silver nanoparticles coated with mesoporous silica (Ag@m-SiO 2 ) having an average pore size of 2.4 nm. Studies presented herein show that a Ag nanoparticle core of ∼55 nm and an m-SiO 2 shell of ∼40 nm represent a preferred combination for sieving and sensing, established by following the SERS of a standard marker, namely, rhodamine 6G. However, under identical conditions, Ag nanoparticles capped with microporous silica (Ag@SiO 2 ) inhibit the passage of analyte molecules into the plasmonic field. Yet another level of selectivity is provided by the negative surface charge of Ag@m-SiO 2 (ζ = −33 mV), eliminating negatively charged molecules from SERS sensing due to strong electrostatic repulsion. These aspects are confirmed using pyrene molecules, which are neutral, and pyrene derivatives carrying positive and negative charges. Thus, the SERS signal arises only from the neutral and positively charged molecules, which can penetrate into the pores, and not from the negatively charged analytes. The practical application of Ag@m-SiO 2 having a shell thickness of ∼40 nm for SERS sensing has been established using two commonly used organophosphorus pesticides (quinalphos and triazophos) directly from various vegetable matrices after the removal of plant pigments. The mesoporous silica shell of Ag@m-SiO 2 having a thickness of ∼40 nm sieves large molecules such as proteins and keeps them away from the electric field generated by the Ag nanoparticle, thus enabling the sensing of small molecules such as pesticides that penetrate into the shell.

Core–Shell Plasmonic Nanostructures on Au Films as SERS Substrates: Thickness of Film and Quality Factor of Nanoparticle Matter

“…Silver nanoparticles with a size of ∼50 ± 3 nm are prepared using the Turkevich method and coated with poly­(vinylpyrrolidone) (PVP) to make the surface vitreophilic and to facilitate silica coating. The Stöber method of coating is adopted to achieve silica coating around the silver nanoparticles, and the advantages of using silica as a capping agent for plasmonic nanoparticles are as follows: (i) high stability, (ii) chemical inertness, (iii) optical transparency, (iv) tunability in thickness, (v) controllable porosity, and (vi) the possibility of surface modification. , Similarly, gold nanoparticles are synthesized by seed-mediated synthesis and are coated with PVP for stabilization. These particles are then coated with SiO 2 having a thickness t ∼ 3 nm.…”

Silver Mesoporous Silica Nanoparticles: Fabrication to Combination Therapies for Cancer and Infection

“…[39] It has been reported that a comprehensive method for silver nanoparticles coated with mesoporous silica with core-shell plasmonic systems for SERS detecting (Figure 2). [40] Ag-MSNs with core-shell structure had an obvious SERS phenomenon. So far, more studies have been carried out drug delivery for tumor therapy, SERS imaging and tumor photothermal therapy.…”

“…(D)The fabrication procedure for the Ag-MSNs@CHX and application for SERS imaging and pH-sensitive drug delivery in cancer therapy. Reconstructed with permission from [29,40,42].…”

Recent advances in silver nanoparticle-based electrochemical sensors for determining organic pollutants in water: a review

“…They could be generally divided into metal-based, metal oxides-based, and carbon-based NPs. Metal-based NPs (MNPs), especially the noble metals, have drawn more attention because of their optical, electrical, and sensing characteristics [18][19][20][21] . MNPs could be synthesized via several pathways such as electrochemical techniques, laser ablation, γ-radiation, photochemical techniques, and chemical reduction 22 .…”