A portable visual capillary sensor based on functional DNA crosslinked hydrogel for point-of-care detection of lead ion

We proposed a facile DNA-based hydrogel capillary sensor (DHCS) for sensitive detection of Pb 2+ . This proposed biosensor took advantage of the capillary action of the capillary tube controlled by the hydrogel film and the mesh size of the hydrogel based on target-responsive DNA. In the presence of Pb 2+ , the crosslinker substrate strand was cleaved leading the hydrogel fractured partly, and the mesh size of the hydrogel film plugging the end of the capillary tube changed. Owing to this, the behavior of the solution flowing through the capillary controlled by the hydrogel film was affected by the concentration of Pb 2+ . Therefore, through reading the distance and duration time by the naked eye, quantitative detection of Pb 2+ was achieved without any equipment. Additionally, and importantly, the tiny Pb 2+ responsive DNA hydrogel (0.02 μL) can be directly applied to analysis without encapsulation operations of nanoparticles or enzymes. Benefiting from the DNAzyme merits of high sensitivity and selectivity, in the range of 0.01 –50 μM, the developed method was able to detect as low as 10 nM Pb 2+ in less 1 h with the distance under 20 mm, meanwhile, the signals of blank and other high concentration metal ions were negligible. This sensor could be utilized to detect Pb 2+ in tap water with good reliability. Therefore, this proposed strategy provided a miniature, portable, sensitive and highly selective, visual platform for the detection of Pb 2+ in situ measurement.