The Fabrication of Photonic Crystal Microchip with Controllable Wettability and SERS Activity based on Surface Roughness for Trace Organic Compounds Determination

Inspired by the fog collection structure on the back of the desert beetle, the hydrophobic photonic crystal microchip (HPCM) with dual functions of hydrophobic enrichment and surface-enhanced Raman spectroscopy (SERS) activity is fabricated by depositing thin Ag film on the photonic crystals (PC) surface, and this is the first time that the wettability and SERS activity are controlled simultaneously by adjusting surface roughness. A 5 nm thin silver film is deposited on the PC surface of hydrophilic SiO₂ to increase surface roughness so that the wettability is transformed from hydrophilicity to hydrophobicity. The hydrophobic surface not only reduces the influence of the “coffee ring” effect but also enriches the samples during analysis. Moreover, due to the sputtering of Ag film, the “hot spots” on the PC surface are increased while the periodic structure of PC remains unchanged. By coupling the photonic bandgap (PBG) of HPCM with Raman laser wavelength, the enhancement factor (EF) reaches 2.3 × 10⁶. The outstanding performance of HPCM is attributed to the synergy between the rough surface and the PBG of PC. The designed HPCM can not only quickly, efficiently, and sensitively detect organic compounds determination, but also has potential application in environmental monitoring.