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A PortAbs based pathogen nucleic acid detection system using peptide nucleic acid (PNA) and a cyanine dye, DiSc2(5). The shift is measured of the absorbance induced by binding of a PNA probe to a complementary DNA strand using a portable two-color absorption system.

Step emulsification (SE), which generates droplets by a sharp change in confinement, has emerged as a potential alternative to flow-focusing technology. Water/dispersed phase is continuously pumped through a shallow inlet channel into a deep chamber pre-filled with the oil/continuous phase. The need for one or more pumps to maintain a continuous flow for droplet generation, and the consequent use of high sample volumes, limit this technique to research labs. Here, we report a pumpfree SE technique for rapid and high-throughput generation of monodisperse hydrogel (agarose) beads using µl sample volume. Instead of using syringe pumps, we sequentially pipetted oil and liquid agarose into a microfluidic SE device to generate between 20000 and 80000 agarose beads in ∼ 2 min. We also demonstrated the encapsulation of loop-mediated isothermal amplification mixture inside these beads at the time of their formation. Finally, using these beads as reaction chambers, we amplified nucleic acids fromP. falciparumand SARS-CoV-2 inside them. The pump-free operation, tiny sample volume, and high-throughput generation of droplets by SE make our technique suitable for point-of-care diagnostics.

We report a two-layer microfluidic device to study the combined effect of confinement and chemical gradient on the motility of wild typeE. coli. We track individualE. coliin 50μmand 10μmwide channels, with a channel height of 2.5μm, to generate quasi-2D conditions. We find that contrary to expectations, bacterial trajectories are super-diffusive even in absence of a chemical (glucose) gradient. The superdiffusive behaviour becomes more pronounced on introduction of a chemical gradient or on strengthening the lateral confinement. Runlength distributions for weak confinement in absence of chemical gradients follow an exponential distribution. Both confinement and chemoattraction induce deviations from this behaviour, with the runlength distributions approaching a power-law form under these conditions. Both confinement and chemoattraction suppress large angle tumbles as well. Our results suggest that wild-typeE. colimodulates both its runs and tumbles in a similar manner under physical confinement and chemical gradient.

Impact of drops on thin powder layers displaces the powder particles radially outward producing shallow craters with thick rims, for example, as observed on dust layers on the floor. Here, we report that the patterns formed on thin powder layers by drop impact are not limited to such crater-like ones. Instead, depending upon the layer properties, disc or disc-plus-ring shaped patterns are formed at the impact point. We show that air entrapment and micro-bubble formation during the drop impact result in the formation of such patterns. Based on high-speed imaging, scaling analyses, and measurements with various liquids and powder layers, we propose a mechanism for the formation of such patterns. The phenomenon that we report can open further investigations on drop impact on the granular matter.

The ability to fingerprint a few molecules via surface enhanced Raman scattering (SERS) continues to be of considerable utility in diverse fields encompassing physics, chemistry, materials sciences, nanotechnology, biomedicine, and environmental engineering. However, the development of facile and low cost approaches towards the fabrication of flexible substrates with very high SERS signal enhancement remains a challenge. Compared to conventional plasmonic-based sensors, a superhydrophobic plasmonic surface provides the combined advantage of concentration enrichment of solute molecules, the fourth power dependent localized electric field enhancement as well as the enhanced light scattering on rough surface. We demonstrate here a method to fabricate flexible SERS substrates by replicating laser-written patterns created on polymethylmethacrylate (PMMA) onto a soft-elastomer, namely polydimethylsiloxane (PDMS), followed by in situ reduction of silver nanoparticles on the surface. Laser writing of structures is fluence dependent and leads to substantial enhancement of Raman signals compared to a conventional plasmonic surface. Our fabricated surfaces provide a limit of detection of eight femtomolar for Rhodamine 6G upon 532 nm resonance excitation; an enhancement factor of ∼1010 is achieved for methyl orange. Studies of how water droplets spread on our laser-written surfaces indicate a fluence dependent enhancement in apparent contact angle with a concomitant increase in the contact angle hysteresis (CAH). Most significantly, our replicated patterns exhibit lotus effect (superhydrophobic surface with ultra-low contact angle hysteresis), that upon reduction of silver nanoparticles, exhibit superhydrophobicity with high contact angle hysteresis (rose petal effect). Our findings offer fresh opportunities for expanding the applicability of the SERS technique via superhydrophobic flexible plasmonic nanostructures.

Fabrication of hydrophobic/hydrophilic surfaces by biomimicking nature has attracted significant attention recently due to their potential usage in technologies, ranging from self-cleaning to DNA condensation. Despite the potential applications, compared to surfaces of tailored wettability, less attention has been paid towards development and understanding of air bubble adhesion and its dynamics on surfaces with varying wettability. In this manuscript, following the commonly used approach of oxygen plasma treatment, polydimethylsiloxane surfaces with tunable wettability are prepared. The role of plasma treatment conditions on the surface hydrophilicity and the consequent effect on adhesion dynamics of an underwater air bubble is explored for the first time. The ATR-FTIR spectroscopic analysis reveals that the change in hydrophilicity arises from the chemical modification of the surface, manifested as Si-OH vibrations in the spectra. The thickness of the formed thin liquid film at the surface responsible for the experimentally observed air bubble repellency is estimated from the augmented Young-Laplace equation. The concentration dependent studies using cationic as well as anionic surfactant elucidate that the reduced surface tension of the aqueous solution results in a stable thicker film and causes non-adherence of air bubble to the aerophilic surface. Furthermore, the study carried out to understand the combined effect of plasma treatment and surfactants reveals that even below critical micelle concentration, a negatively charged surface results in air bubble repellency for the anionic surfactant, whereas only enhanced air bubble contact angle is observed for the cationic surfactant.

Nature-inspired engineering of roughness of the surfaces at micro and nano-length scales offers possibilities of tailoring materials for diverse applications including self-cleaning surfaces, droplet transportation, cell adhesion and oil-water separation. Recent efforts have begun to focus on employing femtosecond-long laser pulses to create such dual length scale roughness at the surface of different kinds of materials including metals, semiconductors and polymers. Herein, we report the fabrication of polymer surfaces that exhibit simultaneous superhydrophobicity and underwater superaerophobicity by replicating femtosecond laser fabricated patterns via soft lithography. Further, by tailoring a single parameter-the laser fluence-we demonstrate tunability of material parameters like anisotropy in wetting, contact angle hysteresis, work of adhesion, and droplet (air bubble) splitting (transport) of the replicated structures. We confirm, using micro-Raman spectroscopy and atomic force microscopy, that our laser patterning does not induce any chemical modification on the polymer but only induces physical modifications-changes in surface roughness-are responsible for the observed tailoring capability. We believe that the replication route provides a cost-effective and green approach to fabricate surfaces with superhydrophobicity and underwater superaerophobicity. Such surfaces can have enormous potential applications in microfluidic devices, droplet manipulation, and energy conversion and storage. Keywords: Wetting, Femtosecond laser patterning, Superhydrophobicity, Superaerophobicity

Introduction: To evaluate the effect of different chelating agents on the wettability of AH Plus and BioRoot RCS sealers on intraradicular dentin. Materials and Methods: Fifty single-rooted premolars were split longitudinally and divided into five groups according to irrigant regimen. Group 1: 2.5% sodium hypochlorite (NaOCl) – 17% ethylenediaminetetraacetic acid (EDTA); Group 2: 2.5% NaOCl – 7% maleic acid (MA); Group 3: 2.5% NaOCl – SmearOFF™ (containing chlorhexidine and EDTA); Group 4: 2.5% NaOCl – Dual Rinse® hydroxyethylidene diphosphonic acid (HEDP); Group 5: 2.5% NaOCl – distilled water. Specimens were treated with controlled volume of experimental sealers and subjected to contact angle measurement. Results: Wettability of both sealers on intraradicular dentin was found to be best with MA. For AH Plus sealer, wettability was better with SmearOFF™, followed by EDTA, Dual Rinse® HEDP, and distilled water. However, there was no statistical difference between SmearOFF™ and EDTA (P > 0.05). For BioRoot RCS, wettability was better with SmearOFF™ and EDTA, with the former showing better results (P Conclusion: Within the limitations of the study, it can be concluded that MA when used as a final irrigant showed better wettability of both AH Plus and BioRoot RCS sealers compared to the other tested solutions.

A femtosecond oscillator is employed to create periodic grid patterns in a commonly used polymer, poly (methyl methacrylate), PMMA. The wettability measured in terms of static water contact angle shows that the laser patterning causes an enhancement in water contact angle and the magnitude of change depends on the irradiation fluence during writing.A water droplet placed on a laser-patterned surface spreads anisotropically and exhibits different static water contact angle along different directions. Micro-Raman and Scanning Electron Microscope studies carried out on laser patterned and nonpatterned regions clearly confirm that the observed wettability change is due to physical (morphological) changes rather than chemical changes. More interestingly, the replica of the periodic laser patterned structures created on a soft polymer,polydimethylsiloxane (PDMS), via soft lithography technique exhibits superhydrophobic behaviour with a rolling-off nature for the water droplet. This is likely to find variety of applications in diverse fields ranging from passive defogging of windscreen to waterproof clothing to non-stick cookware.

In spite of large amount of research in fabricating surfaces of varying wettability by biomimicking the naturally occurring surfaces, the work on fundamentally and industrially important air bubble adhesion on solid surfaces and its applications are still in the burgeoning stage. The present progress report provides a discussion and a critical evaluation of the recent literature available on the fabrication of superaerophilic/superaerophobic surfaces via synergic modification of surface topography and surface chemistry. An abridge on the physics behind bubble wetting on a solid in a liquid medium is deciphered here, considering the interfacial surface tension balance at the three-phase contact line, Laplace pressure, hydrostatic pressure, and surface forces, respectively. Emphasis is made on the advancement in micro/nanofabrication technologies to fabricate surfaces that break the conventional wisdom of complementary behavior of water and air bubble contact angles. The progress report presented here also shines light on the mechanism of air bubble dynamics on solid surfaces and the latest developments in achieving surfaces of varied air bubble adhesion and its applications. Finally, the prospects of the superaerophobic and superaerophilic surfaces in the near future together with the challenges faced in accomplishing them are also insinuated.