摘要： The copper (Cu)-based nanoalloys loaded on graphene-like nanoplates have a great promise for boosting surface-enhanced Raman scattering spectroscopy (SERS), due to low-cost Cu species in comparison with noble metals and unique additional Raman enhancement originated from two-dimensional (2D) supports. Herein, we report an ingenious strategy to load highly dense and monodisperse CuAg nanoalloys (NAs) on hexagonal boron nitride (h-BN) by blue laser (405 nm) -induced photochemical reaction. Without the aid of any complex auxiliary reagents, the co-reduction of Cu and Ag ions is driven by photon-excited electron on semiconductor h-BN, resulting in the coalescence and overgrowth of “clean” CuAg NAs. As expected, the proposed h-BN/CuAg NAs provide ultrahigh SERS activity with the limit of detections (LODs) of crystal violet (CV) at femtomole level (~10?16 M), thiram and tricyclazole at pico-molar (10?12 M) and nanomolar levels (10?9 M), respectively. Most importantly, the as-prepared h-BN/CuAg NAs were also directly combined with polyethylene terephthalate (PET) by simple dripping and drying processes to form uniform flexible substrates. The low-cost Cu-based flexible substrates can be used to realize the ultrasensitive SERS detection of residual tricyclazole on tomato surfaces, thus facilitating the widespread precise assessment of pesticide residues in various practical applications.