All-Serotype Dengue Virus Detection through Multilayered Origami-Based Paper/Polymer Microfluidics.

The dengue virus (DENV) infection commonly triggers threatening seasonal outbreaks all around the globe (estimated yearly infections are in the order of 100 million, combining all the viral serotypes), testifying the need for early detection to facilitate disease management and patient recovery. The laboratory-based testing procedures for detecting DENV infection early enough are challenged by the need of resourced settings that result in inevitable cost penalty and unwarranted delay in obtaining the test results due to distance-related factors with respect to the patient's location. Recognizing that the introduction of alternative extreme point-of-care technologies for early detection may potentially mitigate this challenge largely, we develop here a multiplex paper/polymer-based detection strip that interfaces with an all-in-one simple portable device, synchronizing the pipeline of nucleic acid isolation, isothermal amplification, and colorimetric analytics as well as readout for detecting all the four serotypes of dengue viruses in around 30 min from about 50 µL of human blood serum with high specificity and sensitivity. Aligned with the mandatory guidelines of the World Health Organization, the ultralow-cost test is ideal for dissemination at different community centers via a user-friendly device interface, not only as a critical surveillance measure in recognizing the potential cocirculation of the infection across regions that are hyperendemic for all four DENV serotypes but also for facilitating effective monitoring of patients infected by any one of the particular viral serotypes as well as timely administration of life-saving measures on need.

Thermally Programmable Dynamic Capillarity in Nanofluidic Channels Grafted with Smart Elastomeric Layers.

This work demonstrates thermally programmable dynamic capillarity in exclusively engineered nanochannels functionalized by grafted smart elastomeric layers onto their inner surfaces. Tunable control of the capillarity is observed over the temperature window of 25-31 °C, deciphering the possibility of a sevenfold alteration in the rate of capillary flow. A simple theory explains the confluence of viscous and capillary interactions as mediated by the non-trivial interplay of the substrate wettability, confinement-induced surface layering of molecules, and thermally activated modulation of surface tension, to bring out this intriguing effect. The technology is demonstrated to be completely reconfigurable over the intended spatial and temporal regimes, via selective grafting of the channel surface and preferential choice of the activation temperature. Such favorable features as opposed to more complex yet non-reconfigurable flow manipulation strategies previously reported are likely to open up new possibilities of highly precise controlled nanofluidic manipulation of temperature-sensitive biological samples and chemical species on-demand, for applications ranging from biomedical technologies to energy harvesting and water purification.

Fabricating Antipathogenic Interfaces via Nanoscale Topographies Inspired from Snake Skin.

Advancements in developing antipathogenic interfaces are critical in mitigating the risk of infection spread amid the practical limitations of hygienic control in crowded and resource-limited settings. Such requirements are also extremely compelling in busy patient care centers including intensive care units where the statutory maintenance of environmental standards often appears to be impractical because of the overflooded patient loads. While advances in surface engineering have emerged with great promises to cater these needs, the underlying technological complexities appear to be prohibitive against practicable applications amid constrained technological resources. Here, we harnessed the role of unique topographical features of the skin of Ptyas mucosa (oriental rat snake), a commonly found snake species in south and southeast Asia, in terms of exhibiting supreme antifouling properties via natural inheritance, leading to pathogenic resistance. Our characterization studies unveiled that unlike the previously reported vertical pillars, hairs, and needles, arrays of horizontal denticulation, offering favorable topographical characteristics of structured roughness and hierarchical features, emerged to be responsible for exhibiting the desired functionalities. We subsequently adapted these structures with certain simplifications by biomimicking artificially engineered topologies on a polydimethylsiloxane (PDMS) surface. The resulting surfaces were proven to offer dual antimicrobial mechanisms such as resistances to adhesion or colonization of different bacteria (Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus mutans) and facilitation for cell wall deformation and programmed cell death as evidenced by an abundance of oxidative stresses. These results opened up strategies of producing biomimetic surface textures and their effective implementation against pathogenic invasion in a plethora of applications ranging from medical implants to marine propulsion.

Fast Transport of Water Droplets over a Thermo-Switchable Surface Using Rewritable Wettability Gradient.

In spite of the reported temperature dependent tunability in wettability of poly(N-isopropylacrylamide) (PNIPAAm) surfaces for below and above lower critical solution temperature (32 °C), the transport of water droplets is inhibited by the large contact angle hysteresis. Herein, for the first time, we report on-demand, fast, and reconfigurable droplet manipulation over a PNIPAAm grafted structured polymer surface using temperature-induced wettability gradient. Our study reveals that the PNIPAAm grafted on intrinsically superhydrophobic surfaces exhibit hydrophilic nature with high contact angle hysteresis below 30 °C and superhydrophobic nature with ultralow contact angle hysteresis above 36 °C. The transition region between 30 and 36 °C is characterized by a large change in water contact angle (∼100°) with a concomitant change in contact angle hysteresis. By utilizing this "transport zone" wherein driving forces overcome the frictional forces, we demonstrate macroscopic transport of water drops with a maximum transport velocity of approximately 40 cm/s. The theoretical calculations on the force measurements concur with dominating behavior of driving forces across the transport zone. The tunability in transport velocity by varying the temperature gradient along the surface or the inclination angle of the surface (maximum angle of 15° with a reduced velocity 0.4 mm/s) is also elucidated. In addition, as a practical application, coalescence of water droplets is demonstrated by using the temperature controlled wettability gradient. The presented results are expected to provide new insights on the design and fabrication of smart multifunctional surfaces for applications such as biochemical analysis, self-cleaning, and microfluidics.