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Heavy metal ions, which are over-emitted from industrial production, pose a major threat to the ecological environment and human beings. Among the present detection technologies, achieving rapid and on-site detection of contaminants remains a challenge. Herein, capillaries with three-dimensional (3D) hot spot constructures are fabricated to achieve repaid and ultrasensitive mercury ion (Hg2+) detection in water based on surface-enhanced Raman scattering (SERS). The 4-mercapto pyridine (4-Mpy) serves as the Raman reporter with high selectivity, enabling the detection of Hg2+ by changes in adsorption configuration at the trace level. Under optimized conditions, the SERS response of 4-Mpy for Hg2+ exhibits good linearity, ranging from 1 pM to 0.1 μM in a few minutes, and the detection limit of 0.2 pM is much lower than the maximum Hg2+ concentration of 10 nM allowed in drinking water, as defined by the US Environmental Protection Agency (EPA). Simultaneously, combined with the theoretical simulation and experimental results, the above results indicate that the SERS substrates possess outstanding performances in specificity, recovery rate and stability, which may hold great potential for achieving rapid and on-site environmental pollutant detection using a portable Raman spectrometer. [ABSTRACT FROM AUTHOR]

Abuse of dopings is one of the serious issues affecting competitive sports globally. Traditional means of analysis for doping detection face the challenges of costly, bulky, and complicated pretreatment, as well as long detection times. Therefore, it is critical to achieve on-site and rapid detection for dopings. Herein, we proposed a strategy for ultrasensitive and quick detection of multiple dopings using a combination of liquid phase extraction and surface-enhanced Raman spectroscopy. The clenbuterol, methadone, oxycodone, and chlordiazepoxide were four dopings, which could be detected conveniently in human saliva and urine using the above approach. The limit of detection for clenbuterol, methadone, oxycodone, and chlordiazepoxide in saliva were 25, 10, 50, and 25 ng/mL, respectively, and in urine, 25, 5, 50, and 25 ng/mL. Finally, in about a minute, four dopings at concentration of 100 ng/mL in saliva and urine can be detected accurately and synchronously. This synchronous detection strategy further demonstrates the enormous advantages of SERS in on-site and rapid detection of multiple drugs. [ABSTRACT FROM AUTHOR]

The use of imaging technologies has been critical in deciphering biological phenomena, structures, and mechanisms across a wide range of spatial scales. The spatial resolution of traditional imaging modalities cannot meet the needs of high-precision research and diagnosis in biomedical fields. Plasmon resonance is the light–matter interaction that allows localizing far-field radiation in the near field with an intense electromagnetic field, enhancing the nanometric ablation, elastic/inelastic scattering of the adsorbate, and photoluminescence of the fluorophore nearby. Further, plasmon resonance scattering of nanoparticles can sensitively indicate the local environmental changes. This is accomplished by combining the spatially resolved capability with molecular spectrometry techniques such as Raman, infrared, fluorescence, etc., leading to a series of excellent imaging techniques to interrogate diverse biological processes from the tissue to subcellular level. In this tutorial review, we first provide the fundamental aspects of plasmonics. Then we give a systematic discussion of the working principle of these plasmon-based imaging techniques with an emphasis on the achievable spatial resolutions: surface-enhanced Raman spectroscopy (micrometre to nanometre), tip-enhanced ablation and ionization mass spectrometry (submicrometre), scattering-type scanning near-field optical microscopy (nanometre), tip-enhanced Raman spectroscopy (nanometre), tip-enhanced fluorescence spectroscopy (nanometre), and plasmon/molecular ruler microscopy (nanometre to angstrom). We also review the recent developments of the bioimaging applications of these techniques and expect that the plasmon-based techniques will not only pave a new way to decipher mysteries in life sciences but also hold great potential to be extended from fundamental research studies to real-life biomedical applications. [ABSTRACT FROM AUTHOR]

Fully understanding the properties of plasmonic nanocavity would boost the spectral detection technologies based on plasmons. Recent efforts are mainly focused on the light-matter interactions, which greatly facilities the cognition for nano-optics in the hot spot. However, realizing the high spatial resolution of vertical plasmons in the specific plasmonic nanocavity has been elusive to date. Herein, the monolayer graphene-mediated plasmonic nanocavity has been constructed, which proves the nanoscale inhomogeneity of the enhanced electromagnetic field distribution. Via sandwiching the graphene monolayer at various positions insider fixed nanocavity, we also successfully and quantitatively elucidate the spatial-dependent resonance of the cavity plasmon mode with a resonance spectral shifts down to ca. 4.43 Ångstrom/nm. Simultaneously, the experimental results and theoretical calculation illustrate the correlation between the near field and far field in the hot spot, which also provides a novel strategy for manipulating the light-matter interactions at the nanoscale and graphene nano-devices fabrication based on plasmons. The well-defined graphene-mediated plasmonic nanocavity was fabricated, and we have successfully elucidated the spatial-dependent resonance of the cavity plasmon mode with a spatial resolution down to sub-2 nanometer and correlate near and far-field effectively. [Display omitted] • Plasmonic hot spot fabrication and controllable plasmon modes with precise gap spacer. • Monolayer graphene sandwiched in the plasmonic nanocavity serves as a probe to detect the gap-mode plasmons. • The near and far-field responses based on graphene-mediated plasmonic nanocavity are correlated effectively. [ABSTRACT FROM AUTHOR]

The overuse of pesticides results in excessive pesticide residues, posing a potential threat to human health. Herein, this work proposes a SERS substrate for the quantitative analysis of pesticide residues on food surfaces. Au cores are assembled on PS microspheres, followed by the modification of Raman internal standards (1,4-BDT) on the gold core surface and the growth of the Au shell. After incubating the analytes with PS@Au@1,4-BDT@Au particles, the mixture is dropped on the hydrophobic gold film for drying before detection. The SERS substrates exhibited high sensitivity and stability, with a detection limit of 10−12 M and an RSD of less than 7 %. Combined with a portable Raman spectrometer, the SERS detection of pesticide residues on three kinds of food surfaces is carried out, with a sensitivity of 10−11 M, meeting the US MRLs regulations. Therefore, this strategy may possess significant potential for future food safety. • PS@Core-shell particle fabricates 3D hot spots on the hydrophobic interface. • Raman Internal standard provides a reference for quantitative SERS detection. • The hydrophobic film attenuates the "coffee ring" effect of solvent evaporation. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases cause enormous morbidity and mortality worldwide. Excessive blood total homocysteine (tHcy) is an independent risk factor for cardiovascular diseases. Therefore, it is imperative to measure the content of tHcy in human blood. However, the currently available analytical methods have the disadvantages such as being time-consuming and expensive. Herein, we propose a rapid clinical quantification of tHcy in human serum using high-performance Ag Nanopolyhedra (Ag NPOLY) as surface-enhanced Raman spectroscopy (SERS) substrates. Generally, 80% of homocysteine (Hcy) in serum is oxidized, and only 20% of Hcy is free. To understand this behavior, we explored the reduction effect of tris(2-carboxyethyl) phosphine (TCEP) on serum Hcy at different pH. The results confirmed that our method can detect 2 µM of Hcy in human serum. As a proof-of-concept, the developed method was applied to the actual clinical detection of human serum tHcy, and the serum of 5 hyperhomocysteinemia (HHcy) patients was verified. Moreover, the obtained, results were consistent with high-performance liquid chromatography (HPLC) results. The linear correlation coefficient of the two methods was 0.9766. Importantly, our analysis can be completed within 15 min, while HCLP requires more than 1 h. Overall, we have successfully developed a rapid SERS-based quantitative method for human serum tHcy, which can provide a new solution for the clinical diagnosis of cardiovascular diseases in the future. [Display omitted] • Constructed a high-performance Ag NPOLY for the detection of tHcy in human serum. • The detection limit for Hcy is 1 µM. • Discussed the optimal condition of TCEP for Hcy reduction. • This method allows the clinical quantification of tHcy. [ABSTRACT FROM AUTHOR]

Dioxin is a highly toxic and carcinogenic pollutant created during industrial production and waste incineration. Pollutant monitoring has made extensive use of surface-enhanced Raman spectroscopy (SERS) as a quick, non-destructive, sensitive, and affordable analytical method. However, the fabrication of a SERS substrate with ultrahigh sensitivity is a challenging task, the detection cost is expensive. Currently, these are the challenges faced by SERS technique for the detection of dioxin pollutants. In this paper, we present Au nanocakes (Au NCs) as an easy-to-build SERS substrate for sensitive SERS detection of dioxins in real samples. Based on three-dimensional finite-difference time-domain (3D-FDTD) calculations, the enhancement factor of the substrate following aggregation is approximately 1010. Using a portable Raman spectrometer, the limit of detection for dioxins such as 1-chloro-dibenzo-p-dioxin (1-CDD), 2,8-dichloro-dibenzo-p-dioxin (2,8-DCDD), and 2,3,7-trichloro-dibenzo-p-dioxin (2,3,7-TrCDD) in clean water reached as low as 5, 5, and 10 ng/mL, respectively. As a real-world application, the same toxic pollutants were detected in sewage water samples. Our findings could lead to the development of novel SERS-based sensors for the rapid detection of dioxins in real-world scenarios. Moreover, a portable Raman spectrometer is used to detect the pollutants, which is easy to use and inexpensive. [Display omitted] • Ultra-sensitive Au nanocake was constructed for detection of dioxins in water. • This facile approach provides a stable platform for field-based analysis. • All experimental data were measured by a portable Raman spectrometer with a detection limit of 5 ppb. [ABSTRACT FROM AUTHOR]

Identification of waste oils is challenging in the field of food safety due to the lack of common markers and straightforward analytical methods. Herein, we developed a novel label-free surface-enhanced Raman spectroscopy (SERS) strategy to identify waste oils using Ag nanoparticles solution (Ag NPs sol.) as a SERS substrate to significantly enhance the Raman signal of capsaicin marker molecule usually contained in the waste oils. The enhanced signal was directly detected by a portable Raman spectrometer with the limit of detection (LOD) of 2.9 μg L−1 within 10 min. Concentration-dependent SERS investigation showed the linear relationship between the SERS signal intensity of the characteristic peaks and the concentrations of capsaicin in the range of 10–2500 μg L−1 and the correlation coefficient was 0.9895. Our findings show the sensitivity, accessibility, and reliability of this method for the rapid identification of waste oils and furthermore for the practical applications in the field of food safety. [Display omitted] • Capsaicin is used as the gold standard for the identification of waste oils. • The procedure was completed within 10 min, showing the great performance waste oils identification. • The concentration-dependent SERS research shows reliable quantitative analysis of capsaicin. • The detection limits of capsaicin in waste oil is down to 2.9 μg/L, 104 lower than reported results. • The method uses portable Raman to achieve rapid identification of waste oil, which has great potential for on-site detection. [ABSTRACT FROM AUTHOR]

• A flexible SERS substrate was developed for rapid detection of pesticide residues. • The substrate was highly sensitive due to the enhanced electromagnetic fields. • The substrate can identify thiram as low as 5 × 10-7 M. • The substrate was successfully used for detection of pesticide residues. Pesticide residues will be a huge threat to food security and ecological environment; therefore, there is an urgent need to achieve rapid and on-site detection of pesticide residues. Herein, a plasmonic substrate with multiple "hot spots" was fabricated by transferring three-dimensional (3D) Au nanoparticles (NPs) onto the polydimethylsiloxane (PDMS) membrane for highly sensitive surface-enhanced Raman scattering (SERS) detection of pesticide residues. In combination with 3D-FDTD simulations, high SERS enhancement (EF = 1.2 × 108) and high detection sensitivity (LOD = 6.3 × 10-10 M) were achieved, mainly due to the enhanced electromagnetic fields around the "hot spots". Additionally, the PDMS-based SERS substrate held good transparency and flexibility, enabling conformal contact with non-planar surfaces and allowing the laser to penetrate the back of the analytes. Combined with a portable Raman spectrometer, the substrates holds great potential for rapid, high-sensitive, and on-site detection of contaminants in food, especially for the analyte on the nonplanar surfaces. [ABSTRACT FROM AUTHOR]