Tunable superamphiphobic surfaces: a platform for naked-eye ATP detection

Visual Biosensing with Specific Liquid-Based Interface Behaviors

Liquid-based interface behaviors at micro/nano or even smaller scales induced by biomolecules take us into a fascinating realm, fostering a deeper understanding and innovation in visual biosensing. This biosensing technology, grounded in specific liquid-based interface behaviors, redefines how diseases can be detected, monitored, and diagnosed in resource-limited settings, providing rapid, cost-effective, and self-testing solutions to the current healthcare landscape. To date, the technology has witnessed significant advancements in visual sensing, driven by diverse liquid-based materials, advanced nanomanufacturing techniques, and a profound understanding of interface-material interactions. In this Perspective, we discuss and elucidate the interface biosensing mechanisms arising from three types, including liquid-solid, liquid-liquid, and liquid-gas interfaces, and we provide insights into the challenges and future development of visual biosensing applications.

Molecular Visual Sensing, Boolean Logic Computing, and Data Security Using a Droplet-Based Superwetting Paradigm

Inspired by information processing and logic operations of life, many artificial biochemical systems have been designed for applications in molecular information processing. However, encoding the binary synergism between matter, energy, and information in a superwetting system remains challenging. Herein, a superwetting paradigm was proposed for multifunctional applications including molecular visual sensing and data security on a superhydrophobic surface. A Triton X-100-encapsulated gelatin (TeG) hydrogel was prepared and selectively decomposed by trypsin, releasing the surfactant to decrease the surface tension of a droplet. Integrating the droplet with the superhydrophobic surface, the superwetting behavior was utilized for visual detection and information encoding. Interestingly, the proposed TeG hydrogel can function as an artificial gelneuron for molecular-level logic computing, where the combination of matters (superhydrophobic surface, trypsin, and leupeptin) acts as inputs to interact with energy (liquid surface tension and solid surface energy) and information (binary character), resulting in superwettability transitions (droplet surface tension, contact angle, rolling angle, and bounce) as outputs. Impressively, the TeG gelneuron can be further developed as molecular-level double cryptographic steganography to encode, encrypt, and hide specific information (including the maze escape route and content of the classical literature) due to its programmability, stimuli responsive ability, and droplet concealment. This study will encourage the development of advanced molecular paradigms and their applications, such as superwetting visual sensing, molecular computing, interaction, and data security.

Robust Super-Amphiphobic Titanium Surface for Liquid/Liquid Mini Separations

Super-amphiphobic surface with low robustness is not suitable for practical application due to its weak mechanical strength. In this work, an in-site growth of micro-/nanoscale flower-like TiO2 on the surface of a titanium mesh was successfully fabricated through hydrothermal synthesis, followed by chemical modification with low-surface-energy heptadecafluoro-1,1,2,2-tetrahydrodecyl trichlorosilane. The resultant super-amphiphobic coating was highly repellent to all of the ethanol–water mixtures with surface tensions ranging over 26.0–72.8 mN/m, as well as excellent chemical and mechanical durability. After it was irradiated for 8 h with ultraviolet light, it was used for oil/water and oil/oil mini-separation with the help of its Janus characteristic. This was attributed to its unidirectional penetration for liquid droplets with different surface tension values. This kind of smart super-amphiphobic mesh with photochemical activity could potentially gate and sort liquids via surface tensions.

Sorting Liquid Droplets by Surface Tension Using Devices with Quasi-Superamphiphobic Coatings

Any solid surface with homogenous or varying surface energy can spontaneously show variable wettability to liquid droplets with different or identical surface tensions. Here, we studied a glass slide sprayed with a quasi-superamphiphobic coating consisting of a hexane suspension of perfluorosilane-coated nanoparticles. Four areas on the glass slide with a total length of 7.5 cm were precisely tuned via ultraviolet (UV) irradiation, and droplets with surface tensions of 72.1–33.9 mN m⁻¹ were categorized at a tilting angle of 3°. Then, we fabricated a U-shaped device sprayed with the same coating and used it to sort the droplets more finely by rolling them in the guide groove of the device to measure their total rolling time and distance. We found a correlation between ethanol content/surface tension and rolling time/distance, so we used the same device to estimate the alcoholic strength of Chinese liquors and to predict the surface tension of ethanol aqueous solutions.

Temperature-Driven Precise Control of Biological Droplet's Adhesion on a Slippery Surface

Precise control of a biological droplet's adhesive force on a liquid-repellent surface for smart antifouling systems is critical and fundamental to scientific research and industrial applications. Although slippery surfaces with stimuli-responsive wetting behaviors have been reported, challenge still remains in designing responsive biological droplets to achieve controllable adhesion and antifouling property. Here, we developed a thermoresponsive biological droplet adhesion system to precisely control its adhesion on the lubricant-infused slippery surface. Single-stranded DNA (ssDNA) in the biological droplet displays molecular configuration reversible deformation under external thermal stimuli. This property ascribes to the changing amount of exposed hydrophobic moieties of ssDNA, which strongly affects the interfacial hydrophobic interaction with the lubricant. This work may improve the understanding of the principles underlying liquid-lubricant interfacial adhesion, open up opportunities for a new class of antifouling systems, and provide a promising system for controllable manipulation of liquids' motion in biochips and microreactor devices.