A novel magnetic agitating heater powered by a standard USB port was developed to enable rapid, on-site synthesis of silver colloid substrates for surface-enhanced Raman scattering (SERS). This compact device allows the preparation of Ag colloids within 15 minutes under mild conditions, eliminating the need for long-term storage and addressing the instability issues typically associated with colloidal substrates.

The freshly prepared substrates demonstrated excellent sensitivity and reproducibility, achieving SERS detection of Rhodamine 6G down to 10⁻⁹ mol L⁻¹ with a relative standard deviation of 5.52% (n = 5). Using the optimized substrate, sodium saccharin was detected with a limit of 1 mg L⁻¹. By introducing potassium thiocyanate (KSCN) as an internal standard, a strong linear correlation (R² = 0.98) was obtained between SERS intensity at 708 cm⁻¹ and sodium saccharin concentration in the range of 20–100 mg L⁻¹.

The method enabled direct extraction of sodium saccharin from cigarette tipping paper simply by immersion in water, followed by rapid SERS detection. Quantitative spike-recovery rates ranged from 95.5–116.7% with RSD values of 2.3–12.6%. The entire detection process, including substrate synthesis, was completed in just 30 minutes. This work demonstrates a practical approach for portable SERS substrate preparation and highlights its potential in real-time monitoring and food safety applications.