DNA hydrogels combined with microfluidic chips for melamine detection

The illegal addition of melamine (MEL) into pet foods and infant milk powder has caused great concern among people. In this study, a point-of-care testing (POCT) method was developed by combining stimuli-responsive deoxyribonucleic acid (DNA) hydrogels with microfluidic chips to achieve portable and sensitive detection of MEL. With the MEL aptamer (MA) acting as a cross-linker, DNA hydrogel-coated gold nanoparticles (AuNPs) served as a basis for colorimetric detection and quantitative analysis. In the presence of MEL, it competitively binds to the aptamer, causing disintegration of the DNA hydrogels and a release of the coated AuNPs, making it possible to visually detect and quantitatively measure the MEL. Under optimal conditions, the detection range of MEL using DNA hydrogels was 0.1–100 μM and the limit of detection (LOD) was 42 nM. This portable, sensitive, and user-friendly field test equipment was developed to avoid the use of non-portable laboratory instruments. Furthermore, we combined microfluidic chips with the properties of DNA hydrogels, making it possible to quantitatively detect MEL by taking photos and analyzing the gray value using software in accordance with the different colors of copolymerization solutions after the reaction. The detection range of MEL using the microfluidic chip-based method was 0.2–50 μM, and the LOD was 37 nM. Neither trained operators nor large-scale instruments are needed for using this method to conduct portable and sensitive field detection of the targets, which highlights the methods excellent potential in food security, clinical tests, environmental monitoring, and other aspects.