Monitoring the adulteration of milk with melamine: a visualised sensor array approach

Melamine, a toxic triazine, is illegally used as an additive in milk to apparently increase the amount of protein, causing acute renal failure in thousands of Chinese infants. In this study, a rapid, simple, sensitive and selective colourimetric sensor array is reported as a potential screening tool for monitoring the adulteration of raw milk with melamine. Using chemically responsive dyes (mainly porphyrins and pH indicators) as the recognition elements, determination of melamine at different concentrations (0.1, 0.5, 1.0, 1.5 and 2.0 mg kg⁻¹) and a detection limit of 0.1 mg kg⁻¹ were achieved because of diverse and strong molecular interactions. Furthermore, the colourimetric sensor array was successfully able to discriminate between melamine and its analogues. The unique "fingerprint" of melamine was obtained with a novel signal processing method named "two-step subtraction", which made it possible for the detection results to be easily observed with the naked eye even without any statistical analysis. In addition, the process including sample pre-treatment and detection process took only 12 min at room temperature. The merits (such as simplicity, rapidity, low cost, visual colourimetry, sensitivity and selectivity) make the proposed method especially useful for on-site screening of melamine levels in milk.