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Figure 4: (A) RS of 0.55 mg/mL DPA in 1 N KOH in a plain glass capillary (intensity multiplied by 3.5 to match SERS intensity of 1000 cm−1 peak of (B)). Spectral conditions: 300 mW of 785 nm irradiation at the sample, 25 min acquisition time, 8 cm−1 resolution. SERS of (B) B. anthracis-Sterne, (C) B. cereus, and (D) B. subtilis all at a concentration of 109 spores/mL on the B. anthracis-Sterne peptide functionalized SERS-active substrate after a 15-min incubation period, a wash step, and the addition of acetic acid. Spectral conditions for (B)–(D) as in Figure 2.