Fig. 1. The structure of FM

Fig. 2. Optimize molecular structural formula of FM (a), the blue, red, grey, white, green ball are N, O, C, H, F atom respectively; Comparison between theoretical Raman spectra and solid Raman spectra (b)

Fig. 3. Effect of gold colloid volume ratio (a), sample pH (b) and coagulant (c) on SERS signal of FM

Fig. 4. SERS spectra of flunixin meglumine inmethanol solution with different concentrations

Fig. 5. Impact of extraction environmental (a) and extractant (b)

Fig. 6. The actual sample peaks (a), Linear relationship between FM concentration and SERS intensity at 731 cm^-1 (b)