Fiber surface enhanced Raman scattering sensor based on patterned biphasic gold-silver nanoalloys

► A photochemical method is used to deposit Au-Ag nanoalloys for fiber SERS sensor. ► The nanoalloys are separated into two phases patterned in a concentric circle. ► One phase presents flower-like morphology and shows more on dispersibility of Au. ► One phase owns spike-like morphology and focuses more on high SERS enhancement of Ag. ► The fiber SERS sensor has good reproducibility and high sensitivity.