2 propanol

Silver nitrate (AgNO₃, 99.9%) was purchased from Kojima Chemical (Japan). Sodium borohydride (NaBH₄, 98%) and melamine (99%) were obtained from Sigma-Aldrich (Republic of Korea). Hydrofluoric acid (48–51%), sulfuric acid (98%), nitric acid (65–70%), rhodamine B (pure), mineral oil (light molecular biology grade), sorbitan monooleate (SPAN 80), and trisodium citrate dehydrate (TCD) (99%) were purchased from Alfa Aesar (Republic of Korea). Sylgard 184 A&B was obtained from Sewang Hitech (Republic of Korea), and the XL-1500 UV cross-linker used for UV curing was purchased from Krackeler Scientific (USA). Methyl alcohol, hydrogen peroxide (35%), sodium hydroxide (<97%), ammonia water (25–29%), acetone (99.5%), ethyl alcohol (95%), and 2-propanol (99.5%) were bought from Daejung (Republic of Korea). The Formlabs 3D printer and clear V4 resin were purchased from Formlabs (USA). Deionized water with a resistivity of 18 MΩ·cm⁻¹, provided by a Milli-Q water purification system (Millipore Corp., MA, USA), was used throughout all the experiments.
The morphologies of Ag NPs and SERS substrates were examined using a field-emission scanning electron microscope (FE-SEM, Mira II, TESCAN). A UV–vis spectrometer (Agilent 8453, Agilent, USA) and a micro-Raman spectrometer (NS200, Nanoscope System, Republic of Korea) were used to record the absorption spectra and Raman spectra, respectively.

Benzopyrrole (C₈H₇N, >99%), dodecylbenzenesulfonic acid (DBSA, >95%), ammonium persulfate (APS, >98%), acetone (99%), and chloroform (>99.8%) were purchased from Sigma Aldrich (St. Louis, MI, USA). Toluene and sulfuric acid (H₂SO₄, 98%) were obtained from Scharlau (Barcelona, CAT, Spain). 2-Propanol and dimethyl sulfoxide (DMSO) were purchased from Daejung (Seoul, Korea). All the chemicals were of analytical grade and were used as received. Millipore deionized water (>18 MΩ) was used throughout the experimental work.