Fig. 1. Micro?uidic SERS microsystem with integrated competitive displacement for DNA sequence detection, where silica microspheres functionalized with DNA probe?-?reporter pairs (inset) are packed against a frit. (Reprinted with permission from Yazdi et al. [23] Copyright 2012 American Chemical Society.).

Fig. 2. (a) Schematic design of a gradient droplet microfluidic chip for SERS-based high throughput gradient analysis. Diluting the gold nanoflowers (AuNFs), injecting target analyte, buffer solution, and carrier oil into the channel inlets to form various concentrations of a target reagent trapped by the tiny droplets, and the SERS signals were measured using a He-Ne laser. (b) The system consists of two parallel layers: (i) The top layer is for target loading and serial dilution (ii) The middle layer is for sample reaction and SERS detection (c) Specific middle layer image: The droplet generation and SERS detection process is shown in image (left) and photo (right). (Jinhyeok Jeon et al. [25] Copyright The Royal Society of Chemistry 2019).

Fig. 3. Scheme for laser fabrication of SMAs inside a microfluidic channel. (Bin-Bin Xu et al. [26] Copyright The Royal Society of Chemistry 2012).

Fig. 4. (a) Schematic of microfluidic chip, (b) The process of photoinduced growth of silver nanoaggregates and SERS measurements for CV in situ. (Adapted from Yan et al. [27] Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2017).

Fig. 5. Procedure used to fabricate a 3D microfluidic SERS chip by all-femtosecond-laser-processing (Adapted from Shi Bai et al. [30] Copyright 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

Fig. 6. Illustration of a single-cell encapsulation event within the microfluidic device. (A) The inset displays the PDMS Raman spectrum through a droplet without functionalized nanoprobes and the SERS spectra from wheat germ agglutinin (WGA)-functionalized nanoprobes. (B) Zoom-in of the cell membrane shows the expression of sialic acid. And the individual components of the nanoprobes are shown and named (Sialic acid expressed by cancerous prostate cells can be targeted using the lectin WGA [35].) (Adapted from Marjorie R. Willner et al. [32] Copyright 2018 American Chemical Society).

Fig. 7. Schematic illustration of the battery-controlled composite SERS-based fluidic system. An electrical heating constantan wire covered with the ZnO nanotapers and Ag-nanoparticles is inserted into a glass capillary. The mixture in the capillary is heated up when SERS detection. (Reproduced from Zhou et al. [37] with permission from Nature Publishing Group).

Fig. 8. Optofluidic SERS microsystem with packed microspheres for passive concentration, an integrated micromixer to promote adsorption of the target analyte, and integrated fiber optic cables for optical excitation and collection. (Adapted from Soroush et al. [39] Copyright 2012 American Chemical Society).

Fig. 9. Melamine sensing in milk products by using SERS sensor chips and a portable Raman spectrometer. (Adapted from A. Kim et al. [40] Copyright 2012 American Chemical Society).

Fig. 10. (a) Schematic of the portable silicon-based SERS analytical platform for on-site detection of Pb2+ and Hg2+ from industrial wastewater. (b) SERS spectra and (c) corresponding SERS relative intensities for Pb2+ and Hg2+ (Adapted from Yu Shi et al. [41] Copyright The Royal Society of Chemistry 2018).