Fig. 1. (a) Schematic diagram of the optical trapping-enhanced SERS optofluidic detection system. (b) Effect of the single-beam optical trap module switch state on AgNPs aggregation. (c1) and (c2) Operational images of the single-beam optical trap-enhanced SERS optofluidic detection system, demonstrating particle trapping and Raman detection, with (c2) providing an enlarged view of the trapping area in (c1). (d) Schematic diagram of the optical trapping mechanism.

Fig. 2. (a1, a2) The simulation results of the variation in electric field intensity with distance for the 1550 nm laser emitted from the tapered optical fiber. (b1–b8) Respectively display the electric field intensity distribution at different positions. (c) Electric field distribution of 1550 nm laser emitted by a tapered fiber with a tip diameter of 25 μm in water. (d) Scattering force on 50 nm AgNPs. (e) Gradient force on 50 nm AgNPs. (f) Total force on 50 nm AgNPs. (g) AgNPs are strongly trapped near the tip of the tapered optical fiber. (h) Schematic diagram of the force analysis on AgNPs.

Fig. 3. (a) Electric field simulation model of 50 nm diameter AgNPs under 532 nm laser excitation with different gaps. (b) Electric field distribution when the gap is 1 nm. Electric field distribution when the gap is (c) 3 nm, (d) 5 nm, (e) 7 nm, (f) 9 nm and (g) 11 nm. (h) The maximal electric field as the gap between AgNPs decreased.

Fig. 4. Image observed by confocal Raman spectrometer microscope (a) when the single-beam optical trap is closed, with the detection region filled with a homogeneous and stable mixed solution. (b) When the single-beam optical trap is opened, with substances in the mixed solution captured by the optical trap emitted from the tapered fiber optical fiber. (c) Schematic diagram of AgNPs gap when the single-beam optical trap is off and on. (d) Raman spectra of 10⁻⁶ mol/L CV obtained by opening and closing the single-beam optical trap of position 7 in (b). (e) Raman characteristic peak intensity at 913, 1177 and 1621 cm⁻¹ in (d). (f) Raman line mapping obtained at different positions when the optical trap is open. (g) Raman characteristic peak intensity at 913 cm⁻¹ in (f).

Fig. 5. (a) Positions of the Raman mapping. (b) Raman characteristic peak intensity at 913 cm⁻¹ at different positions in (a). (c) Detection limit of the system for CV at a concentration of 10⁻⁹ mol/L. (d) Detection limit of the system for thiram at a concentration of 10⁻⁵ mol/L.