Versatile sensing matrixes are essential for the development of enzyme-immobilized optical biosensors. A novel three-dimensional titanium dioxide nanotubes/alginate hydrogel scaffold is proposed for the detection of sweat biomarkers, lactate, and glucose in artificial sweat. Hydrothermally synthesized titanium dioxide nanotubes were introduced to the alginate polymeric matrix, followed by cross-linking nanocomposite with dicationic calcium ions to fabricate the scaffold platform. Rapid colorimetric detection (blue color optical signal) was carried out for both lactate and glucose biomarkers in artificial sweat at 4 and 6 min, respectively. The superhydrophilicity and the capillarity of the synthesized titanium dioxide nanotubes, when incorporated into the alginate matrix, facilitate the rapid transfer of the artificial sweat components throughout the sensor scaffold, decreasing the detection times. Moreover, the scaffold was integrated on a cellulose paper to demonstrate the adaptability of the material to other matrixes, obtaining fast and homogeneous colorimetric detection of lactate and glucose in the paper substrate when image analysis was performed. The properties of this new composite provide new avenues in the development of paper-based sensor devices. The biocompatibility, the efficient immobilization of biological enzymes/colorimetric assays, and the quick optical signal readout behavior of the titanium dioxide nanotubes/alginate hydrogel scaffolds provide a prospective opportunity for integration into wearable devices.

Lactate is present in sweat at high concentrations, being a metabolite of high interest in sport science and medicine. Therefore, the potential to determine lactate concentrations in physiological fluids, at the point of need with minimal invasiveness, is very valuable. In this work, the synthesis and performance of an alginate bead biosystem was investigated. Artificial sweat with different lactate concentrations was used as a proof of concept. The lactate detection was based on a colorimetric assay and an image analysis method using lactate oxidase, horseradish peroxidase and tetramethyl benzidine as the reaction mix. Lactate in artificial sweat was detected with a R² = 0.9907 in a linear range from 10 mM to 100 mM, with a limit of detection of 6.4 mM and a limit of quantification of 21.2 mM. Real sweat samples were used as a proof of concept to test the performance of the biosystem, obtaining a lactate concentration of 48 ± 3 mM. This novel sensing configuration, using alginate beads, gives a fast and reliable method for lactate sensing, which could be integrated into more complex analytical systems.

In this report, we investigated the TiO nanofibers coated stainless steel mesh as a novel underwater superoleophobic membrane for the effective separation of contaminated oil-water mixtures. The membrane was fabricated by spray deposition of hydrothermally synthesized TiO nanofibers on stainless steel mesh. The fabricated membrane exhibits superhydrophilicity and supereleophobicity properties in air and underwater respectively allowing the separation of oil-water efficiently. Randomly deposited TiO nanofibers on mesh exhibit rough surface property and hence superhydrophilic nature. Water oil separation efficiencies of ∼90 and ∼99% were achieved with this filter for less viscous and highly viscous oil respectively. Additionally, the TiO nanofibers coated mesh can degrade immiscible organic molecules due to photocatalytic activity of TiO nanofibers under UV light. As a result of self-cleaning property of TiO nanofibers coated mesh, the durability of the filter membrane is enhanced.

The accumulation and deposition of undesired air bubbles on the surface of microfluidic channels and on underwater functional systems is a major drawback, which worsen their performance. Present de-bubbling strategies...

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Remote manipulation of superhydrophobic surfaces provides fascinating features in water interface-related applications. A superhydrophobic magnetic nanoparticle colloid layer is able to float on the water–air interface and form a stable water–solid–air interface due to its inherent water repulsion, buoyancy, and lateral capillarity properties. Moreover, it easily bends downward under an externally applied gradient magnetic field. Thanks to that, the layer creates a stable twister-like structure with a flipped conical shape, under controlled water levels, behaving as a soft and elastic material that proportionally deforms with the applied magnetic field and then goes back to its initial state in the absence of an external force. When the tip of the twister structure touches the bottom of the water container, it provides a stable magneto movable system, which has many applications in the microfluidic field. We introduce, as a proof-of-principle, three possible implementations of this structure in real scenarios, the cargo and transport of water droplets in aqueous media, the generation of magneto controllable plugs in open surface channels, and the removal of floating microplastics from the air–water interface.

For the effective oil/water separation, a novel superhydrophilic (underwater superoleophobic) filter is fabricated with the naturally and hydrothermally treated mica particles. To fabricate a double layered filter, hydrothermally treated mica particles were initially electrodeposited on a stainless steel mesh and a natural mica particles were sprayed on the first hydrothermally deposited mica layer. The double layered mica coated membrane showed superamphiphilic and superhydrophilic/superoleophobic (contact angle >159°) characteristics in air and underwater respectively. The membrane can separate range of oil-water mixtures with oil/water separation efficiency over ∼99%. Properties of double layered mica membrane were investigated and noted that the surface adhesion properties of mica is enhanced by the hydrothermal treatment of mica and the higher roughness of the mica layer is maintained by the natural mica.

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