Fig. 1. Specific preparation of AuNPs-cysteamine composite SERS substrate

Fig. 2. SEM characterization of cysteamine and AuNPs-cysteamine composite SERS substrate. (a) Cysteamine without soaking in deionized water; (b) cysteamine after soaking in deionized water; (c) AuNPs-cysteamine composite SERS substrate without soaking in deionized water; (d) AuNPs-cysteamine composite SERS substrate after soaking in deionized water

Fig. 3. SEM images of AuNPs with different densities after binding to cysteamine. (a) 15 mL gold sol; (b) 20 mL gold sol; (c) 25 mL gold sol

Fig. 4. Effect of cysteamine and gold nanoparticle contents on enhancement performance of SERS substrate. (a) Performance comparison of SERS substrate with different contents of cysteamine combined with AuNPs; (b) performance comparison of SERS substrate with different densities of AuNPs combined with cysteamine

Fig. 5. Raman spectra of different concentrations of potassium nitrate on AuNPs-cysteamine composite SERS substrate

Fig. 6. Raman spectra of potassium nitrate in AuNPs-cysteamine composite SERS substrates and SERS substrate without enhancement

Fig. 7. Raman spectra of potassium nitrate on 8 different AuNPs-cysteamine composite SERS substrates