A novel one-step in situ synthesis of gold nanostars (AuNSs) on a pre-cured polydimethylsiloxane (PDMS) film is proposed for the fabrication of highly sensitive surface-enhanced Raman scattering (SERS) substrates. Plasmonic activity of the substrates was investigated by collecting SERS maps of 4-mercaptobenzoic acid (4-MBA). The applicability of these flexible substrates is further demonstrated by SERS-based pesticide detection on fruit skin.