Mesoporous Silica‐Coated Plasmonic Nanostructures for Surface‐Enhanced Raman Scattering Detection and Photothermal Therapy

Abstract

The design and fabrication of core-shell and yolk-shell nanostructures with surface plasmon resonance (SPR)-active center protected by permeable mesoporous channels can raise the new vitality into the catalysis and biological applications. Hybrid plasmonic-mesoporous silica nanocarriers consisting of Ag and Au-Ag alloy nanoparticles are fabricated through spatially confined galvanic replacement approach. The plasmonic absorption peaks can be finely controlled to the near-infrared (NIR) region (500-790 nm) that is beneficial for tissue transmittance. The mesoporous silica shell facilitates also protection of Au-Ag cores and affords the channels between the exterior and interior capsule environments, thereby endowing the multiple applications. In the present work, it is successfully demonstrated that mesoporous silica-coated Au-Ag alloy core-shell and yolk-shell nanocarriers can serve as good substrates for surface-enhanced Raman scattering (SERS) detection. The SERS signal intensities of nanocarriers are highly dependent on the SPR peaks and the contents of gold. Simultaneously, the synthesized Au-Ag@mSiO2 nanocarriers with SPR peak at ≈790 nm can be applied in NIR-sensitive SERS detection and photothermal therapy.

Synthesis of Mesoporous Silica/Reduced Graphene Oxide Sandwich-Like Sheets with Enlarged and “Funneling” Mesochannels

“…First, TEOS in the upper organic solvent gradually diffused to the biphase interface, slowly hydrolyzed and polymerized into negatively charged silicate oligomers, which would drive into the bottom aqueous solution owing to the gravity and hydrophilic/hydrophobic interactions. 15,[62][63][64][65][66][67] Simultaneously, hemiemulsion micelles were supposed to generate at the biphase interface as a result of the lowest interface energy. 15,64-66 Some of negatively charged silicate oligomers could then gather around CTA + head groups of the hemiemulsion micelles, forming oligomers/surfactant /organic solvent hemiemulsion micelles (Scheme 1b), which would drive into the bottom aqueous solution and serve as new building blocks for subsequent mesostructure growth.…”

“…15,64-66 Some of negatively charged silicate oligomers could then gather around CTA + head groups of the hemiemulsion micelles, forming oligomers/surfactant /organic solvent hemiemulsion micelles (Scheme 1b), which would drive into the bottom aqueous solution and serve as new building blocks for subsequent mesostructure growth. 15,[64][65][66] In the bottom aqueous solution, silicate oligomers and CTAC molecules could co-assemble into micelles, then nucleating on the surface of GO nanosheets (Scheme 1b, c). 17,[55][56][57][58][59] Remaining silicate oligomers in aqueous solution would be further bound to the micelles and polymerized in the gap between neighboring micelles and GO sheets to form pore walls (Scheme 1c, d).…”

“…17,[55][56][57][58][59]61 As the reaction continues, the GO/surfactant/inorganic species could get in touch with the hemiemulsion micelles repeatedly, resulting in the formation of "funneling" mesochannels owing to the pore-expanding effect of organic solvent (Scheme 1d, e). 15,[64][65][66][67] Free silicate oligomers also continuously polymerized in the gap between neighboring micelles to form self-adaptive pore walls (Scheme 1e). After solvent extraction and reduction, the rGO@mSiO 2 sheets with enlarged mesochannels oriented perpendicularly to the rGO substrate were obtained (Scheme 1f).…”

“…Hence it makes the overall heterogeneous nucleation and growth of mesostructures on GO sheets controllable in the bottom aqueous solution. 15,61,[64][65][66][67] In addition, the formation of hemimicelles (oligomers/surfactant/organic solvent molecules) is a critical step, which can act as the enlarged building blocks for the final "funneling" mesochannels. Because both the lower silica resource concentration and smallermolecule-weight organic solvent would make the interfacial curvature of micelles to be larger.…”

Mesoporous titania based yolk–shell nanoparticles as multifunctional theranostic platforms for SERS imaging and chemo-photothermal treatment

“…However, for the production of SERS labeled multifunctional nanomedicine, this sequence would induce problems because the pre-generated SERS disappeared because several severe synthesis conditions (high concentration of CTAB at the mSiO 2 coating process and NaOH etching stage) could detach Raman reporters from the metal substrates. Herein, we proposed a versatile "up-down" strategy, in which SERS nanosubstrates were pre-stabilized by polymers 32 or mesoporous materials, 33,34 followed by Raman reporters' subsequent mixing and infiltration step. In our case, it was crucial to load the Raman reporter DTDC and the therapeutic drug DOX at appropriate positions of the nanoplatform (on AuNR and in mTiO 2 , respectively), which determined the optical and therapeutic properties.…”