Incubation: A mixture of 20 μL (0.5 mg/mL) magnetic beads (MB@RB20115UD), 40 μL SERS nanotags (Au-IR808@RB20115UC), and prepared sample is incubated for 5 min.
Washing: The supernatant is removed after magnetic separation (30 s), followed by washing with PBST (pH 7.4, 0.05% Tween-20).
Detection: The separated pellet is resuspended in 10 μL ultrapure water. Then 2 μL solution is spotted onto a 2.5 mm × 2.5 mm gold substrate for air-drying. Raman spectra are acquired using a portable spectrometer (785 nm laser, 500 mW power, 5 s acquisition time, triplicate measurements). Peak areas within 540-570 cm-1 are quantified.