In the pursuit of advancing molecular sensing through surface-enhanced Raman spectroscopy (SERS), the combination of plasmonic nanoparticles and metal–organic frameworks (MOFs) has emerged as a highly effective approach to enhance the sensitivity and selectivity of SERS substrates. However, most prior investigations have predominantly focused on MOF-coated plasmonic nanoparticles in core@shell or layer-by-layer configurations, leaving a notable knowledge gap in exploring alternative configurations. Herein we present a facile method to construct a particle-on-mirror architecture by selectively coating a MOF, zeolitic imidazolate framework-8 (ZIF-8), onto the tips of Au nanostars and subsequently depositing the resultant nanoparticles onto a Au film. This design integrates the electric field enhancement at the sharp tips and nanogaps, along with the molecular enrichment function within the porous MOF immobilized at the tips and nanogaps, leading to a substantial boost in the SERS signal intensity. Such a unique SERS platform enables consistent and outstanding SERS performance for analytes of different sizes. This work opens up a promising strategy for constructing multifunctional nanostructures for sensitive SERS detection in real-life scenarios.

We describe a route to the preparation of (metal yolk)/(porous ceria shell) nanostructures through the heterogeneous growth of ceria on porous metal nanoparticles followed by the calcination-induced shrinkage of the nanoparticles. The approach allows for the control of the ceria shell thickness, the metal yolk composition and size, which is difficult to realize through common templating approaches. The yolk/shell nanostructures with monometallic Pt and bimetallic PtAg yolks featuring plasmon-induced broadband light absorption in the visible region are rationally designed and constructed. The superior photocatalytic activities of the obtained nanostructures are demonstrated by the selective oxidation of benzyl alcohol under visible light. The excellent activities are ascribed to the synergistic effects of the metal yolk and the ceria shell on the light absorption, electron-hole separation and efficient mass transfer. Our synthesis of the (metal yolk)/(porous ceria shell) nanostructures points out a way to the creation of sophisticated heteronanostructures for high-performance photocatalysis.

Colloidal Au-core/Ag-shell nanorods with an asymmetric transverse cross-section and a strong octupolar plasmon resonance are synthesized by the controlled growth of Ag shells on one side of the Au cores. A largely enhanced second harmonic generation (SHG) from these asymmetric core–shell nanorods is demonstrated for the first time by tuning the dipolar and the octupolar plasmon modes to make them resonant with the fundamental and harmonic frequencies, respectively. The SHG intensity of the Au–Ag nanorods with dual-frequency resonances is enhanced by 21 times compared to that of the bare Au nanorods. The co-existence of the dipolar, quadrupolar, and octupolar radiations in the SHG is revealed. Additionally, the cellular uptake of the Au–Ag nanorods is monitored and the evolution of the membrane bleb is successfully observed by the SHG imaging. Our observations provide a strategy for enhancing the SHG of the colloidal metal nanoparticles and can have applications in chemical process monitoring and biological sensing.