We
fabricated a plasmon–nanocavity coupling structure composed
of Au nanoparticles (Au-NPs), titanium dioxide, and Au-film (ATA)
as a highly sensitive and spatially homogeneous surface-enhanced Raman
scattering (SERS) substrate. The SERS intensity of the ATA was ∼11
times higher than that of the Au-NPs/TiO2 substrates without
cavity enhancement. This SERS enhancement was attributed to the remarkable
near-field enhancement of Au-NPs under coupling with cavity resonance.
Under the present experimental conditions, crystal violet (CV) molecule
decorated ATA prepared from a concentration as low as 10–7 mol/L could be detected, which is 1 order of magnitude higher sensitivity
than the samples without cavities. More importantly, a spatially homogeneous
SERS signal distribution of Raman mapping on the ATA was demonstrated
over a 20 × 20 μm2 area on the sample, attributed
to the homogeneous near-field distribution over the Au-NPs under coherent
coupling between plasmon resonance and cavity resonance. We envision
that this plasmon–nanocavity coupling SERS structure with high
sensitivity, repeatability, and spatial homogeneity can be practically
used in chemical and biomolecule detection devices.
Capacitively coupled contactless conductivity detection (C4D) is an improved approach to avoid the problems of labor-intensive, time-consuming and insufficient accuracy of plate count as well as the high-cost apparatus of flow cytometry (FCM) in bacterial counting. This article describes a novel electrode-integrated printed-circuit-board (PCB)-based C4D device, which supports the simple and safe exchange of capillaries and improves the sensitivity and repeatability of the contactless detection. Furthermore, no syringe pump is needed in the detection, it reduces the system size, and, more importantly, avoids the effect on the bacteria due to high pressure. The recovered bacteria after C4D detection at excitation of 25 Vpp and 60–120 kHz were analyzed by flow cytometry, and a survival rate higher than 96% was given. It was verified that C4D detection did not influence the bacterial viability. Moreover, bacteria concentrations from 106 cells/mL to 108 cells/mL were measured in a linear range, and relative standard deviation (RSD) is below 0.2%. In addition, the effects on bacteria and C4D from background solutions were discussed. In contrast to common methods used in most laboratories, this method may provide a simple solution to in situ detection of bacterial cultures.
Strong coupling between a localized surface plasmon resonance
(LSPR)
at the surface of metal nanoparticles (NPs) and a Fabry–Pérot
(FP) nanocavity can facilitate photochemical reactions. It is very
interesting and critical to study the enhancement mechanism of plasmon-induced
chemical reactions under plasmon–nanocavity strong coupling
to further improve the photochemical reaction efficiency. In this
study, we fabricated a LSPR–FP nanocavity strong coupling photoelectrode
composed of Au–Ag alloy NPs, titanium dioxide (TiO2), and a Au film as a working electrode to investigate the mechanism
of water oxidation enhancement under plasmon–nanocavity strong
coupling conditions. In situ electrochemical surface-enhanced Raman
spectroscopy measurements were performed to detect the intermediate
species of water oxidation under a series of electrochemical potentials.
The Au–O and Au–OH stretching vibrations related to
the intermediates of water oxidation were investigated. Compared with
the Au–Ag alloy NPs/TiO2 structure without strong
coupling, the surface-enhanced Raman spectroscopy signal of the Au–O
stretching vibration on the strong coupling electrode exhibited a
more negative onset potential, indicating that more efficient water
oxidation occurred on it. This efficient water oxidation in the strong
coupling photoelectrode was considered a result of the quantum coherence
between the Au–Ag alloy NPs through the nanocavity.
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