Quantitative detection methods used for identification, quantification, property evaluation of biochemical molecules provide key guidance in the fields of environmental assessment, homeland security, clinical drug testing and health care systems, especially during the current epidemic period, developing new technologies to achieve portable and rapid target molecules. The principles of current analytical methods rely mainly on molecular recognition events, to convert information about the analytes into electrically detectable spectroscopic signals¹. If analytical signal transduction method that do not require expensive optical detectors or electrochemical components are available, it will facilitate t the development of sensors for applications in resource-limited environments such as fieldwork or underdeveloped areas.

In our recent paper published in Nature Communications, we put forward a host-guest liquid gating mechanism to translate biochemical molecular interface recognition behaviors into visually quantifiable detection signals without optical/electrical equipment to open avenues for analytical chemistry, biochemistry, biomedical engineering and beyond (Fig. 1). The idea of using liquids as a structural material to build responsive gates has attracted increasing attention because it provides a special combination of dynamic and interface physicochemical behaviors², and it has been selected as one of the 2020 Top Ten Emerging Technologies by the International Union of Pure and Applied Chemistry (IUPAC)^{3, 4}. The behavior of a liquid gating technology is based on reversible reconfigurable gates, which can use a capillary-driven functional gating liquid to seal microscale pores that can be opened at a certain pressure^{5, 6}. The liquid gating technology is emerging as a promising approach to address these needs as an easily deployable detection platform because of its very sensitive response to target stimuli such as chemical, physical or biological targets^{7, 8}. In this host-guest liquid gating system, surfactant molecules in solution usually reside preferentially at the interface with the interfacial structure of the hydrophobic end facing the air phase, allowing surface activity to reduce the system's surface tension. The surface activity is shielded when the hydrophobic chain of the surfactant molecule enters the hydrophobic cavity of a macrocyclic molecule, which provides a potential framework for the analyst-response mechanism. When a specific and competitive target molecule is present in the gating liquid, the surfactant indicator is displaced into the solution, where it occupies the surface, leading to a low P_Critical and the system releases gas. The concentration of target molecule can be visually quantified by reading the movement distance of the marker or observing the color change of indicator solution. In contrast, nonspecific molecules (weak competitors) cannot displace the surfactant indicator, and the system still maintains a high P_Critical.

In summary, we have demonstrated a specific recognition interface behavior mechanism that converts molecular interface recognition behavior to visually quantifiable detection signals. This work will be a milestone for liquid gating technology, because it is the first time to realize chemical quantitative detection instead of qualitative detection (such as dipole-induced reconfiguration)⁸ by this technology , which will open avenues for more in-depth exploration of chemical detection and spur advances in environmental monitoring, point-of-care test, public health security, and biomedical applications.

To read more about our work at Nature Communications: https://www.nature.com/articles/s41467-022-29549-1.

For more information of the Xu Hou research group, please visit: https://xuhougroup.xmu.edu.cn

References

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