Plasmon-Free Zn-BTC Microflower SERS Colloids for Enantiomeric Discrimination

Porous metal–organic frameworks (MOFs) facilitating molecular enrichment and chemical enhancement hold promise as enhancers for surface-enhanced Raman spectroscopy (SERS). The nanochannels in MOFs provide abundant binding sites for modification with chiral amino acids for enantiomeric discrimination. Here we develop a solvent-regulated method to synthesize plasmon-free Zn-BTC microflower (Zn-BTC MF) with a high surface area of 346 ± 14 m2/g as SERS colloids. The morphology and surface area of Zn-BTC are effectively controlled by an ethanol/DMF solvent combination strategy, significantly promoting the molecular adsorption for detection. Combining with the charge-transfer-resonance chemical enhancement, the Zn-BTC SERS colloids provide an enhancement factor of 1.1 × 104 with the limit of detection down to 10–8 M for rhodamine 6G. The l-lysine@Zn-BTC MF is further synthesized by postmodification via an EDC/NHS coupling reaction for quantitative chiral recognition of d-histidine, a typical biomarker for clinical diagnosis of diseases, with the g-factor up to 1.16 ± 0.06 at the concentrations down to 10–5 M. This present work paves a new way to design and synthesize plasmon-free MOFs-based SERS colloids for trace enantiomeric discrimination.