Atto-Molar Raman detection on patterned superhydrophilic-superhydrophobic platform via localizable evaporation enrichment

The detection of molecules in ultra-low concentration solution is essential in numerous fields including pollutant monitoring, explosive detection and disease early diagnosis. Recently, studies indicated that surface-enhanced Raman scattering (SERS) combining with superhydrophobic surfaces were capable of breaking diffusion limit, realizing detection in femto/atto-molar range. However, the complicated and costly fabrication methods limited larger-scale practical application. In this regard, patterned superhydrophilic-superhydrophobic platform fabricated by ultrafast laser, which could simplify the preparation process and fix the droplet, attracted attention. Nevertheless, the related works reported cannot realize atto-molar detection. Therefore, the SERS platform with abilities of simplified fabrication processes, on-demand locating analyte and ultra-high sensitivity (1 aM) is needed. In this paper, we processed a new patterned SERS platform via femtosecond laser, achieving atto-molar detection with an enhancement factor of 1.09 × 1014. After evaporation enrichment, the target molecules were deposited on the superhydrophilic area of ∼0.01 mm2. We further optimized the SERS substrates by comparing three types of colloids: Ag nano-particles, Au nano-particles and Au nano-stars, finding Au nano-stars exhibited the best. Meanwhile, this platform showed good uniformity: the relative standard deviation (RSD) was 11.7 % at 10−14mol/L. The results offer valuable information and potentials on the ultra-low concentration molecular detection in biosensors.