Ascorbic acid–driven formation of defect-rich Cu2O Nanocubes toward durable and versatile Raman detection

Abstract

Preparing semiconductor-based surface-enhanced Raman scattering (SERS) substrates remains challenging, as it requires simultaneous control over morphology, defect chemistry and stability. Here, L-ascorbic acid (AA) served a dual function as both a shape-directing and mild reducing agent in the hydrothermal synthesis of Cu-based nanostructures (denoted as Cu2O_AAn, where n represents the volume of AA added). The addition of AA initially induces a phase transition from bulk-type CuO to Cu2O nanocubes. Subsequent increases in AA further facilitate morphological evolution, leading to smaller and well-faceted Cu2O structures. The optimized Cu2O_AA30 nanocubes exhibited abundant copper vacancies, as confirmed by EPR analysis, which introduce charge-carrying holes. Zeta potential analysis further revealed that SERS enhancement could not be explained by simple electrostatic adsorption, as even negatively charged probes such as methyl orange displayed strong amplification. Instead, the dominant enhancement pathway was attributed to defect-mediated charge transfer, consistent with the facet-dependent electronic structure of Cu2O. As a result, Cu2O_AA30 substrates consistently delivered strong SERS responses for both cationic and anionic analytes and maintained stable performance for more than two months under ambient conditions, highlighting the long-term stability and practical applicability. © 2026 Elsevier Inc.