Nicotine
is highly addictive and harmful. It is one of the main
active ingredients in tobacco and a major pollutant in environmental
tobacco smoke. Thus, it is important to detect the nicotine content
in tobacco and to monitor the nicotine content in environmental tobacco
smoke. However, until present, there still has been no effective device
for on-site determination of nicotine content in tobacco and environmental
tobacco smoke. In this work, a portable device is fabricated for sensitive
on-site evaluation of nicotine in tobacco and environmental tobacco
smoke based on surface-enhanced Raman scattering (SERS). The weight
of the entire device is less than 1 kg, and it uses a chargeable battery
to drive both the pump and the Raman spectrometer. The total analysis
time can be completed within 3–5 min. Thus, it has great potential
for on-site analysis of nicotine in tobacco and environmental tobacco
smoke.
Volatile organic compounds (VOCs) are detrimental to the environment and human health and must be eliminated before discharging. Oxidation by heterogeneous catalysts is one of the most promising approaches for the VOCs abatement. Precious metal catalysts are highly active for the catalytic oxidation of VOCs, but they are rare and their high price limits large‐scale application. Supported metal single‐atom catalysts (SACs) have a high atom efficiency and provide the possibility to circumvent such limitations. This Review summarizes recent advances in the use of metal SACs for the complete oxidation of VOCs, such as benzene, toluene, formaldehyde, and methanol, as well as aliphatic and Cl‐ and S‐containing hydrocarbons. The structures of the metal SACs used and the reaction mechanisms of the VOC oxidation are discussed. The most widely used SACs are noble metals supported on oxides, especially on reducible oxides, such as Mn2O3 and TiO2. The reactivity of most SACs is related to the activity of surface lattice oxygen of the oxides. Furthermore, several metal SACs show better reactivity and improved S and Cl resistance than the corresponding nanocatalysts, indicating that SACs have potential for application in the oxidation of VOCs. The deactivation and regeneration mechanisms of the metal SACs are also summarized. It is concluded that the application of metal SACs in catalytic oxidation of VOCs is still in its infancy. This Review aims to elucidate structure–performance relationships and to guide the design of highly efficient metal SACs for the catalytic oxidation of VOCs.
The application of surface-enhanced Raman scattering (SERS) in aqueous sample detection is normally limited by the low affinity between analytes and SERS-active nanoparticles. Furthermore, a tendency of uncontrollable aggregation of solute (nanoparticles or analytes) can cause poor reproducibility of the detected SERS signal. Herein, a ready-to-use plasmonic gel bead was developed for rapid and effective detection of aqueous samples with high sensitivity and reproducibility. The SERS gel bead is made of calcium alginate gel beads (CAGBs) that contain gold nanobipyramids (Au NBPs) and an aqueous sample, which can be prepared and detected within only 1 min. Au NBPs/CAGBs can generate an in-depth three-dimensional SERS-active gel network for trapping analytes and offering a uniform hotspot region, which produces a reproducible and uniform signal. Using rhodamine 6G as a model target, the proposed method exhibits excellent reproducibility with a relative standard deviation of 6.57% and a detection limit of 0.4 nM. Then, Au NBPs/CAGBs were applied to quantitatively detect serum uric acid in the range of 10−1000 μM and a limit of detection of 0.18 μM, and the results were strongly consistent with those of the commercial ELISA method. This work offers a low-cost and easy route for the fabrication of a versatile SERS substrate for monitoring disease-related biomarkers and point-of-care testing.
Surface-enhanced
Raman scattering (SERS) with the advantages of
high sensitivity, nondestructive analysis, and a unique fingerprint
effect shows great potential in point-of-care testing (POCT). However,
SERS faces challenges in rapidly constructing a substrate with high
repeatability, homogeneity, and sensitivity, which are the key factors
that restrict its practical applications. In this study, we propose
a one-step chemical printing strategy for synthesizing a three-dimensional
(3D) plasmon-coupled silver nanocoral (AgNC) substrate (only need
about 5 min) without any pretreatments and complex instruments. The
galvanic replacement between AgNO3 and Cu sheets will provide
both Ag0 for the formation of silver nanostructures and
Cu2+ for the polymerization of fish sperm DNA (FSDNA).
The protection of AgNCs is facilitated by the crosslinked FSDNA, which
can improve the stability of the substrate and promote the control
of its coral-like morphology. The obtained substrate displays excellent
capacity of signal enhancement due to the 3D plasmon coupling both
between nanocoral tentacles and between nanocorals and Cu sheets as
well. Therefore, the AgNC substrates display high activity (enhancement
factor = 1.96 × 108) and uniformity (RSD < 6%).
Food colorants have been widely used in various foods to improve their
color, but the inevitable toxicity of colorants seriously threatens
food safety. Therefore, the proposed AgNC substrates were used to
directly quantify three kinds of weak-affinity food colorant molecules
including Brilliant Blue, Allura Red, and Sunset Yellow assisted by
the capture by cysteamine hydrochloride (CA), showing the detection
limits (S/N = 3) of 0.053, 0.087,
and 0.089 ppm, respectively. The SERS method has been further applied
in the detection of the three kinds of food colorants in both complex
food samples and urine with recoveries of 91–119%. The satisfactory
detection results suggest that the facile preparation strategy of
AgNC substrates will be widely used in SERS-based POCT to promote
the development of food safety and on-site healthcare.
Surface-enhanced Raman scattering (SERS) is a supersensitive analysis technology based on the target molecular fingerprint information. The enhancement of local electromagnetic field of the SERS substrate would increase the target molecules' Raman intensity which adsorb on the surface of nanoparticles. However, the existing adhesive macromolecules in the complex mixed sample would interfere with the adsorption of small target molecules, and it weakens the Raman intensity of target molecules. Microgels are one of the potential materials to suppress the interference of adhesive macromolecules and to avoid the complex pretreatments. However, most of the current microgel synthesis methods involve complex operations with precise instrumentation or the interference of oil and organic reagents. In this work, a simple and oil-free method was proposed to synthesize the gold nanobipyramid (Au NBP) @Ag@hyaluronic acid microgel via the condensation reaction of carboxyl and amino groups. As a proof-of-concept demonstration for small-molecule detection, the rhodamine 6G (R6G) molecules were allowed to enter inside the microgel through the meshes and adsorb on the surface of Au NBP@Ag nanoparticles within 30 min, while the macromolecule (bovine serum albumin in this case) was retained outside the microgel in the meantime. In addition, under the combined action of lightning rod effect of Au NBP and surface plasmon resonance effect of silver render the microgels with high SERS activity. The synthetic Au NBP@Ag@hyaluronic acid microgels were applied to detect 6-thioguanine in the human serum without any pretreatment process, and it showed a high signal enhancement and stable SERS signal, which can satisfy the requirement of clinical diagnosis. These results show that the proposed microgels have potential applications in the field of point-of-care testing.
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