The research groups headed by professors Yongqiang Wen and Xueji Zhang from our School of Chemical and Biological Engineering recently published an article titled, “Control of Capillary Behavior through Target-Responsive Hydrogel Permeability Alteration for Sensitive Visual Quantitative Detection,” in Nature Communications (DOI: 10.1038/s41467-019-08952-1). The study was supported by the National Key Research and Development Program and the National Natural Science Foundation of China.

DNA is an editable biological macromolecular functional material that can usually be obtained through synthesis or natural extraction. DNA hydrogels can be prepared using a three-dimensional cross-linking to form a space network. Owing to the good editability of DNA and the rapid development of SELEX in recent years, DNA hydrogels have drawn wide attention from analytical chemists owing to their excellent specific recognition and response characteristics. However, the large cost of a DNA synthesis, the high consumption rate of DNA hydrogels, and the current reliance on large devices for a quantitative reading from DNA hydrogel-based sensors all hinder the further development of DNA hydrogel-based sensors to a certain extent.

Figure 1. Scheme of a target-responsive hydrogel film in a capillary tube for visual quantitative detection.

Through collaboration between the research groups of professors Yongqiang Wen and Xueji Zhang from the University of Science and Technology Beijing and professor Chaoyong Yang from Shanghai Jiaotong University, a novel DNA hydrogel-based sensor has been developed, which is capable of solving all issues mentioned above. Based on the thermal reversible principle of a DNA hydrogel, contact between hot capillary tubes and a DNA hydrogel results in an increased mobility of the hydrogel. Through capillary action, the hydrogel is driven into the capillary tubes, where a hydrogel film forms as the temperature decreases. The capillary tube containing a hydrogel film is fixed on a scale substrate to form a simple sensor.

Figure 2. Working principle of the CSDR-sensor

In the current investigation, the addition of specific targets was shown to increase the permeability of the hydrogel film within the capillary tubes. Varying the permeability of the hydrogel films results in visually detectable changes in the self-driven motion within the capillary tubes. The duration of the capillary action is used to visually quantify the targets. Only 0.01 μL of a DNA hydrogel is required. Using the detection of cocaine as the test target, this study has realized the highly sensitive and specific visual quantification of cocaine without relying on other types of measurement equipment.