Amorphous‐Crystalline Synergy in CoSe₂/CoS₂ Heterostructures: High‐Performance SERS Substrates for Esophageal Tumor Cell Discrimination

Abstract Although surface‐enhanced Raman scattering (SERS) spectroscopy is applied in biomedicine deeply, the design of new substrates for wider detection is still in demand. Crystalline‐amorphous CoSe₂/CoS₂ heterojunction is synthesized, with high SERS performance and stability, composed of orthorhombic (o‐CoSe₂) and amorphous CoS₂ (a‐CoS₂). By adjusting feed ratio, the proportion of a‐CoS₂ to o‐CoSe₂ is regulated, where CoSe₂/CoS₂‐S50 with a 1:1 ratio demonstrates the best SERS performance due to the balance of two components. It is confirmed through experimental and simulation methods that o‐CoSe₂ and a‐CoS₂ have unique contribution, respectively: a‐CoS₂ has rich vacancies and a higher density of active sites, while o‐CoSe₂ further enriches vacancies, enhances electron delocalization and charge transfer (CT) capabilities, and reduces bandgap. Besides, CoSe₂/CoS₂‐S50 achieves not only SERS detection of two common esophageal tumor cells (KYSE and TE) and healthy oral epithelial cells (het‐1A), but also the discrimination with high sensitivity, specificity, and accuracy via machine learning (ML) analysis.