Fig.1 Rayleigh(elastic) and Raman(inelastic) scattering at a molecule, and scattering intensity dependence on the wavelength of the scattered light(for ease of comparison, the scattering intensity is arbitrarily set to 1 at a wavelength of 532 nm)[7] Copyright 2013, Annual Reviews.

Fig.2 Representative electric field distribution of SERS-active Au nanoparticles Note that the SERS “hot-spot” is generated in the gap between two closely arranged nanoparticles(A)[9], and collective oscillations of electrons in a spherical nanoparticle under the action of the external electric field(B)[10]. (A) Copyright 2018, Wiley-VCH;(B) Copyright 2017, MDPI.

Fig.3 Exemplary SERS spectra of Gram-negative(a) and Gram-positive(b) bacterial cells[42] Copyright 2002, Elservier.

Fig.4 Difference in Raman spectra of sulfur bacteria(a) and sulfur-deficient bacteria(b)[45] Copyright 2015, Oxford University Press.

Fig.5 Schematic display of different approaches for SERS based detection of bacteria Whole cells can be measured on a solid substrate(A) or in a colloid suspension(B) and it is also possible to attach or deposit metallic nanoparticles directly on the bacterial cell wall(C) or to apply with SERS tags(D)[52] Copyright 2015, Elsevier.

Fig.6 Schematics of the condensation process of Au-MNPs and bacteria(left) and the biomolecular characteristics of the bacterial cell wall that can possibly be detected by SERS(right)(A)[54] and schematic illustration for bacteria detection by using nanostructured Au based biosensor(B)[55] (A) Copyright 2019, Elsevier; (B) Copyright 2014, American Chemical Society.

Fig.7 SERS spectra of the headspace(A)[64] and Raman and SERS spectra of pyocyainn(B)[65] (A) Copyright 2018, John Wiley and Sons Ltd.; (B) Copyright 2016, Springer Nature.

Fig.8 Probing and Raman imaging of N2-fixing bacteria in artfcial communities(A)[67] and flow chart of rapid Raman drug sensitivity test based on heavy water labeling(B)[68] (A) Copyright 2018, American Chemical Society; (B) Copyright 2019, American Chemical Society.

Fig.9 Time lapse of C-D component concentration map in bacteria cultivated in glucose-d7 medium C-D component concentration map in VSE(A) and VRE(B), in the presence and absence of 20 μg/mL vancomycin[70]. Copyright 2018, American Chemical Society.

Fig.10 Schematic illustration of label based and label-free based SERS method for bacteria detection[73] Copyright 2017, Elsevier.

Fig.11 Structure of the pyoverdine iron complex of P. fluorescens DSM 50090(A), scheme illustrating the proposed isolation strategy for Pseudomonas spp.(B) and Raman detection of P. fluorescens and P. aeruginosa(C)[84] (B) The (3-glycidyloxypropyl)-trimethoxysilane modified surface(Ⅰ) is functionalized with an pyoverdine iron complex(Ⅱ), subsequently the chip can be used for capturing various Pseudomonas species(Ⅲ). Copyright 2016, American Chemical Society.

Fig.12 Schematic illustration of the synthesis of Au-Van SERS tags(A), the synthesis of aptamer-modified Fe3O4@AuMNPs(B), and the operating procedure for S. aureus detection via the dual-recognition SERS biosensor(C)[85] Copyright 2019, Elsevier.

Fig.13 Phage specifically recognizes the bacteria and then immobilizes the bacteria to the surface of a nano substrate with SERS activity, able to get extremely strong Raman signals[87] Copyright 2017, American Chemical Society.