An in-fiber optofluidic SERS platform based on g-C3N4/Ag NPs functionalized cloverleaf hollow fiber for label-free pesticide detection

Surface-enhanced Raman scattering (SERS) technology has shown great potential for pesticide residue detection due to its high sensitivity and molecular fingerprinting capability. However, conventional SERS sensors still face challenges such as limited enhancement efficiency, insufficient environmental stability, high sample consumption, and poor portability, which restrict their practical applications. This paper first presents and demonstrates an in-fiber optofluidic SERS sensor based on the unique microstructure of a cloverleaf hollow fiber (CHF) structure, in which a graphitic carbon nitride/silver nanoparticle (g-C 3 N 4 /Ag NPs) nanocomposite is functionalized onto the inner wall as an active SERS substrate. The CHF consists of a solid core surrounded by four microchannels that naturally guide analyte solutions to efficiently interact with the evanescent field propagating along the fiber core. Through chemical bonding, the g-C 3 N 4 /Ag nanocomposite is firmly anchored to the channel surfaces, forming a stable and highly active Raman enhancement interface. Furthermore, the synergistic electromagnetic and chemical coupling between g-C 3 N 4 and Ag NPs markedly amplifies the Raman response. Benefiting from the unique structure of the cloverleaf fiber and the synergistic enhancement effect of the SERS composite substrate, the enlarged light-matter interaction area and continuous signal accumulation along the entire fiber, the sensor achieves detection limits of 5.21 × 10 −9  mol/L, 7.15 × 10 −8  mol/L and 2.88 × 10 −8  mol/L for representative pesticides, with excellent linearity and repeatability. Consequently, the compact and flexible configuration enables real-time, in situ, and trace-level detection, demonstrating great potential for portable optical sensing, environmental monitoring, and food safety applications.