Liquid crystal surfaces enable manipulation of liquid mobility and cargo release via temperature, electrolytes, and light.

Rapid, robust virus detection techniques with ultrahigh sensitivity and selectivity are required for the outbreak of the pandemic coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2). Here, we report that the femtomolar concentrations of single-stranded ribonucleic acid (ssRNA) of SARS-CoV-2 trigger ordering transitions in liquid crystal (LC) films decorated with cationic surfactant and complementary 15-mer single-stranded deoxyribonucleic acid (ssDNA) probe. More importantly, the sensitivity of the LC to the severe acute respiratory syndrome (SARS) ssRNA, with a 3 base pair-mismatch compared to the SARS-CoV-2 ssRNA, is measured to decrease by seven orders of magnitude, suggesting that the LC ordering transitions depend strongly on the targeted oligonucleotide sequence. Finally, we design a LC-based diagnostic kit and a smartphone-based application (App) to enable automatic detection of SARS-CoV-2 ssRNA, which could be used for reliable self-test of SARS-CoV-2 at home without the need for complex equipment or procedures.

Stretchable and durable superhydrophobic materials are of potential interest for developing ultra-flexible electronics, flexible microfluidics, gas sensors, functional textiles, wearable devices etc. In general, the physical deformation of a material compromises the embedded antifouling property through perturbation of appropriate surface topography, and appears as a potential ‘Achilles' heel’ of the application of this prospective antifouling property in practical settings. Here we report a highly stretchable and durable superhydrophobic membrane that strongly repels aqueous phase both in air and under oil, by strategically exploiting a facile and robust 1,4-conjugated addition reaction between amine and acrylate groups from branched poly(ethyleneimine) (BPEI) and dipentaerythritol pentaacrylate (5Acl), respectively, where amine ‘reactive’ (due to the presence of residual acrylate groups) nanocomplexes—which were formed on just mixing of BPEI and 5Acl in ethanol—were directly immobilized on a modified polyurethane fibrous substrate to adopt appropriate topography, and further covalent modification of these immobilized ‘reactive’ nanocomplexes with strategically selected small molecules (i.e. octadecylamine) ensured the essential surface chemistry in the synthesized material. In the current design, scalable and facile dip coating (through covalent chemistry) followed by appropriate post-chemical modifications of the material yielded a highly durable superhydrophobicity—which is capable of being sustained, even at 150% physical deformation of the material for 1000 times without compromising the embedded antifouling property. Moreover, the synthesized material can survive exposure to various other physical and chemical insults—which are common in practical settings. The synthesized material is further exploited in energy efficient and rapid separation of both heavy and light oils from complex (sea, river, extremes of pH etc.) aqueous phases, where oil can be separated with a rate of 115 mL min⁻¹ and with efficiency above 99% for multiple times.

Oil contamination in aqueous phases by regular industrial discharges and accidental oil spillages during the production and transportation of oil is emerging as a global challenge due to its catastrophic effect on the aquatic ecosystem. Here, a naturally abundant fibrous substrate (i.e., a cotton ball) is strategically exploited in the energy-efficient and environmentally-friendly cleaning of different forms of oil-contamination, including floating light-oil, and sedimentary heavy-oil and emulsions, after the appropriate optimization of both the topography and the essential chemistry of the fibrous substrate through a catalyst-free, simple and scalable 1,4-conjugate addition reaction between amine and acrylate groups under ambient conditions. The synthesized superhydrophobic cotton (SHC), that is capable of extreme repellence of water both in air and under oil, has provided a single avenue for both highly selective (1) absorption (with an efficiency above 2000 wt% for both heavy and light oils) and (2) gravity-driven active filtration of oil. The synthesized material is highly efficient in the separation of oil from aqueous phases that are chemically harsh, including extremes of pH (1 & 12), artificial seawater, etc. The embedded superhydrophobicity in the synthesized material remained unperturbed, even after prolonged (10 days) exposure to UV irradiation (both at 254 nm and 365 nm) and after incurring various physical deformations. Although this synthesized material was repeatedly (100 times) used in removing oil contamination, the antifouling property remained intact with an advancing water contact angle of 157° and the oil/water separation efficiency remained around 95%. Further, the current approach provided a simple basis to separate oil from a complex three-phase oil/water mixture that was composed of a heavy-oil phase (the bottom layer), an aqueous phase (the middle layer), and a light-oil phase (the top layer), where the strategic application of SHC allowed the successful clean-up of oils through the complementary use of absorption and filtration processes.

The controlled modulation of both oil (under water) and water (in air) wettability is an emerging approach to develop several functional materials for various prospective applications including oil/water separation, anti-corrosive coatings, underwater robotics, protein crystallization, drug delivery, open microfluidics, water harvesting etc. Here, we report a ‘reactive’ and covalently cross-linked coating through a facile and robust Michael addition reaction, which is suitable for the controlled and extreme regulation of both water and oil wettability in air and under water respectively. Along with extremes (super-philicity and super-phobicity) of water (in air) and oil (under water) wettability, this single multilayer construction was also able to display special liquid wettability (i.e.; extremely liquid repellent—but with controlled adhesive properties) both in air and under water, after strategic post chemical modifications, again through 1,4-conjugate addition reaction. The super-wetting properties in the materials were able to withstand various physical and chemical insults including adhesive tape test, sand drop test, and exposure to extremes of pH, salt, and surfactant contaminated aqueous media. Moreover, this approach also allowed the decoration of various flexible and rigid substrates (i.e.; wood, Al-foil, synthetic fabric etc.) with various bio-inspired wettability properties including (1) non-adhesive superhydrophobicity (lotus leaf), (2) adhesive superhydrophobicity (rose petal), (3) underwater superoleophobicity (fish scale) etc. This single polymeric coating—which is capable of displaying several bio-inspired interfaces both in air and under water, even after harsh physical/chemical insults—would be useful in various prospective and relevant applications for practical scenarios.