Rational design of MnO nanoparticles assemblies for sensitive magnetic relaxation detection of melamine

A versatile protocol has been developed for highly sensitive magnetic relaxation detection of the analyte based on the fabrication of MnO nanoparticles (NPs) assemblies. Based on the strategy that positively charged analyte could induce the assembly of negatively charged MnO NPs through electrostatic interaction, which will generate the change of magnetic relaxation rate of MnO NPs, we achieved highly sensitive and convenient detection of the analytes. By applying the detection of melamine as an example, we found that the detection limit can be as low as 0.733 ppb. Furthermore, this strategy has been applied for the initially detection of commercially available milk spiked with melamine as proof of its potential applicability of detection in complicated food samples.