Ultrasensitive detection of melamine based on a DNA-labeled immunosensor.

A DNA-labeled immunosensor for melamine (MEL) detection is presented which combined the exponential amplification and quantitative effect of Real-Time quantitative PCR (RT-qPCR) with the simplicity and specificity of competitive antigen-antibody reaction. An excellent linear relationship between cycle threshold (Ct) and MEL concentration in the range of 0.001-10 pg g⁻¹ was obtained with a limit of detection of 0.3 fg g⁻¹. Compared with other methods, the sensitivity of this DNA-labeled immunosensor showed a 1000-fold improvement, and was below the strictest safety limit of 1 ppm. Furthermore, the specificity was excellent and the recovery in liquid milk samples spiked with MEL was satisfactory. With the advantages of high sensitivity and a low limit of detection (LOD), this sensor is a powerful and promising tool for the detection of other small molecules besides MEL.