We demonstrate an extremely simple and practical surface-enhanced Raman spectroscopy (SERS) technique for trace melamine detection in milk with PVDF membranes as supports. Through trisodium citrate reduction method, gold nanoparticles with average diameter of 30 nm were obtained. Upon addition to trace-level melamine, gold nanoparticle solution exhibits a highly sensitive colour change from red to blue and rapid aggregation behavior within several minutes. The SERS detection platform was constructed after trapping the mixture of aggregates and melamine on PVDF membrane through a simple filter-based approach, and the lowest detectable concentration was 0.05 mg/L in aqueous solution. Moreover, for the melamine-spiked milk samples, the lowest detectable concentration was 1 mg/L, which could meet the requirement accepted by most countries that the threshold in infant formula was 1ppm. Thus, due to the simple procedure, the low-cost of the substrates and the short total analysis time, our technique enables SERS to be practical for a broad range of analytical applications, including field-based detection of toxins in large volume samples.