Multiple Gold Nanoparticle Cores within a Single SiO2 Shell for Preservable Solid-State Surface-Enhanced Raman Scattering and Catalytic Sensing

Metal@dielectriccore@shell nanoparticles (NPs) have attractedsignificant attention due to their multifunctional properties andvast applications in different fields of catalysis, photonics, sensing,nanomedicine, etc. However, there is a dearth of reports about thesynthesis of controlled aggregation of gold cores without using anycross-linkers and the effects of the presence of multiple metalliccores in one shell, particularly for surface-enhanced Raman scattering(SERS) and electrochemical sensing. Nanoaggregates, N & GE; 2 (where N is the number of nanoparticlesin aggregation), can effectively be used for fine-tuning plasmon wavelength,whereas collective encapsulation of number-selected nanoaggregatesby functionalized SiO2 generates multiple capacitors whichin turn enhance the field at the nanojunctions and nanogaps for improvedSERS and catalytic sensing activity. We successfully prepared controlledAuNP aggregation, passivated them by the SiO2 outer layerto make them suitable for preservation in the solid state and functionalizationby 3-aminopropyl trimethoxysilane (APTMS), and separated the nanoaggregatesbased on the aggregation size (individual nanoaggregates having 2to 100 nanoparticles in each). The thickness of the silica shell wasengineered in such a way that shell thickness does not make any hindrancein optical measurements, and the effect of multiple nanoparticle coreson the surface plasmon resonance and SERS can be understood properlyand also allows external molecules to reach active gold nanoparticlesurface for electrocatalytic activity. Functionalization allows individualencapsulations to further form multi-junction capacitors by bridgingthem through a positively charged dye molecule, here Rhodamine 6G(Rh6G). By using these multiple gold nanoparticle cores within a singlesilica shell (multi-Au@SiO2 core@shell nanoparticles) withimproved SERS and electrocatalytic activity, we have also successfullyultrasensed (0.003 & mu;A & BULL;& mu;M-1 & BULL;cm(-2)) glucose in a nonenzymatic electrochemical pathway.