In this work, the core-satellite optoplasmonic particle comprised of the central dielectric silica sphere and the surrounding gold nanorods (AuNRs) with varied aspect ratio (AR) were fabricated through electrostatic-assisted self-assembly. The manipulation over the optoplasmonic resonance of the hybrid material was accomplished through tuning the AR of AuNRs at the perimeter of the silica microsphere, which enables the optimization of local plasmonic-photonic electric field enhancement in accordance with the incident wavelength. The monolayer structure assembled by the hybrid particles, termed as optoplasmonic surface, serves as a robust surface-enhanced Raman spectroscopy (SERS) sensing substrate because the building block is surprisingly agglomeration-resistive under severe conditions including the dryness and salination. The optimal SERS excitation plane of the optoplasmonic surface was found to be the equatorial one due to the geometrical factor holding the higher density of AuNRs, the plasmonic-photonic interaction between adjacent optoplasmonic particles and the light guiding effect. The fabricated optoplasmonic surface (silica sphere diameter = 4 µm, AR of AuNR = 3.2) was implemented for the SERS sensing of 3,4-methylenedioxymethamphetamine (MDMA) and the corresponding precursors including safrole and piperonal, achieving a limit of detection (LOD) down to the magnitude of 5 nM with the excitation wavelength at 785 nm. Practical SERS tests on the glassware surface and mimic drug demonstrate the compatibility of the optoplasmonic sensing platform in cooperation with the portable Raman spectrometers. This hybrid probe with engineerable resonance and elevated stability is a promising candidate for the application of SERS inspection in forensic activities. 

Engineered Optoplasmonic Core-Satellite Microspheres for SERS Determination of Methamphetamine Derivative and its Precursors

Fabrication of optoplasmonic particles through electroless deposition and the application in SERS-based screening of nodule-involved lung cancer.

Benefiting from the electromagnetic enhancement of noble metal nanoparticles (NPs) and the capture ability of organic frameworks, plasmonic metal-organic framework (MOF) structures have greatly promoted the development of gas detection by surface-enhanced Raman spectroscopy (SERS). In those detections, the kinetic process of gaseous molecules in plasmonic-MOF structures has a great influence on SERS spectra, which is still lacking intensive investigation in previous reports. In this work, the kinetic processes of gaseous thiophenol compounds (TPC) in the plasmonic Zeolitic Imidazolate Framework (Ag@ZIF) core-shell NPs are studied by SERS spectra. The experimental data demonstrate that the SERS intensities of gaseous TPC could be enhanced once more in an H2 mixed gas environment with different functional groups of TPC. Further results reveal that the two-step enhancement of SERS intensities is not only related to the thicknesses of the MOF shell but also affected by the ambient mixed gas. To understand this novel phenomenon, the binding energy between the gaseous molecule and ZIF is calculated based on first-principles computation. In combination with the plasmonic properties of the Ag core, a molecular collision model is introduced here to show the distribution of gaseous TPC molecules in ZIF, which could be responsible for this interesting two-step enhancement of SERS intensities. Furthermore, the H2 assisted kinetic process of gaseous p-aminothiophenol (PATP) is also analyzed by the classical pseudo-first-order kinetic model, which is consistent with our experimental SERS data. Our work not only reveals the novel phenomenon of plasmonic-MOF structures to improve the gas detection by SERS spectra but also enriches the understanding of the microcosmic process of gaseous molecules in the mixed gas environment to optimize MOF structures for gas capture and storage.

SERS Monitored Kinetic Process of Gaseous Thiophenol Compound in Plasmonic MOF Nanoparticles.

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Mxenes–Au NP Hybrid Plasmonic 2D Microplates in Microfluidics for SERS Detection

For its ultrahigh sensitivity, the microfluidic system combined with surface-enhanced Raman spectroscopy (SERS) becomes one of the most interesting topics in integrated online monitoring related fields. In previous reports, the commonest surface plasmon-enhanced substrates in microfluidics consist of immobilized metal nanostructures on the channel surface to overcome the disturbance of Brownian motion. In this work, a hybrid optoplasmonic microfluidic conveyer is developed, in which the movable, highly ordered optoplasmonic particles are delivered to the detection spot for SERS detection. Here, the optoplasmonic particle is the SiO2 microsphere with in situ photochemical reduced Ag nanoparticles on the surface. Because of the converged light at the SiO2 microsphere surface, the SERS spectra collected at this optoplasmonic particle in the channel exhibit excellent performance, which is confirmed by the simulated electric field distribution. In addition, the experimental data also demonstrate that the quantitative analysis is achieved at 1 nM in this optoplasmonic microfluidic conveyer. Furthermore, the used optoplasmonic particle can be ejected from the microfluidic channel by modulating the velocity of injected fluid such that the new optoplasmonic particle will be delivered to the detection spot for repeatable SERS detection in the same channel. The dynamic process of optoplasmonic particle transport is investigated in this microconveyer, and the built theoretical model to predict the particle release is highly identical with the experimental data. These data point out that our hybrid optoplasmonic microfluidic conveyer has repeatable enhanced substrates with the high SERS sensitivity to overcome the cross-contamination of different target molecules in repeatable detection.

Chuanyu Liu

Papers

Microfluidic Transport of Hybrid Optoplasmonic Particles for Repeatable SERS Detection