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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 10 10. 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.

We report a novel approach for surface-enhanced Raman spectroscopy (SERS) detection in digital microfluidics (DMF). This is made possible by a microspray hole (?SH) that uses an electrostatic spray (ESTAS) for sample transfer from inside the chip to an external SERS substrate. To realize this, a new ESTAS-compatible stationary SERS substrate was developed and characterized for sensitive and reproducible SERS measurements. In a proof-of-concept study, we successfully applied the approach to detect various analyte molecules using the DMF chip and achieved micro-molar detection limits. Moreover, this technique was exemplarily employed to study an organic reaction occurring in the DMF device, providing vibrational spectroscopic data.

Raman and infrared (IR) spectroscopy are powerful analytical techniques, but have intrinsically low detection sensitivity. There have been three major steps (i) to advance the optical system of the light excitation, collection, and detection since 1920s, (ii) to utilize nanostructure-based surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA) since 1990s, and (iii) to rationally couple (i) and (ii) for maximizing the total detection sensitivity since 2010s. After surveying the history of SERS and SEIRA, we outline the principle of plasmonics and the different mechanisms of SERS and SEIRA. We describe various interactions of light with nano/microstructures, localized surface plasmon, surface plasmon polariton, and lightning-rod effect. Their coupling effects can significantly increase the surface sensitivity by designing nanoparticle–nanoparticle and nanoparticle–substrate configuration. As the nano/microstructures have specific optical near-field and far-field behaviors, we focus on how to systematically design the macro-optical systems to maximize the excitation efficiency and detection sensitivity. We enumerate the key optical designs in particular ATR-based operation modes of directional excitation and emission from visible to IR spectral region. We also present some latest advancements on scanning-probe microscopy-based nanoscale spectroscopy. Finally, prospects and further developments of this field are given with emphasis on emerging techniques and methodologies.