Fig. 1. SERS substrates with different structures. (a) Transmission electron ｍicroscope (TEM) image of freshly prepared magnetic core-gold shell popcorn-shaped nanoparticle^[19]; (b) scanned electromirror (SEM) image of escherichia coli on base of silver nanorod array^[20]; (c) two-sided TAuNP-AuNSs upper structure and AuNS high density distribution (13 nm)^[21]; (d) schematic diagram of Au nano-particles of different sizes prepared by adding 0.25, 0.50, 1.00 mL trisodium citrate, respectively^[22]

Fig. 2. Detection methods of pathogenic bacteria. (a) Non-labeling method; (b) labeling method

Fig. 3. Non-labeling detection methods. (a) TEM image of AgNPs-E.coli sample^[25]; (b) formation of NPs aggregate on surface of bacteria (left) and SERS for two species of Listeria (right)^[26]; (c) SEM image of staphylococcus aureus mixed with AgNPs+^[27]; (d) SEM images of G@AgNPs@Si from top view (left) and side view (right)^[28]

Fig. 4. Labeling detection methods.(a) Incubation time-dependent Raman spectra of single escherichia coli cells^[34]; (b) aggregation of gold nanoparticles as well as formation of microbial clusters in presence of 10⁵ CFU/mL MDRB Salmonella^[36]; (c) AuNR-DTNB@Ag core-shell plasmonic nanoparticles. Inset is high resolution transmission electron microscope (HRTEM) image of single AuNR-DTNB@Ag nanoparticle^[41]