Analyzing bacterial detection and transport using redox impact electrochemistry.

Understanding bacterial transport dynamics, particularly at the single-particle level, is crucial across diverse fields from environmental science to biomedical research. In recent times, the emerging impact electrochemistry method offers a transformative approach for detection of bacteria at the single-particle level. The method employs the principle of single-entity electrochemistry to scrutinize electrochemical processes during interaction with the working electrode. In this study, we utilized redox impact electrochemistry to detect bacteria and analyze their transport processes towards the working electrode. Stochastic detection using redox reactions at the ultramicroelectrode enabled the detection of individual bacteria, with collision resulting in a current spike signal due to charge transfer. Notably, the detection of bacteria was demonstrated at an exceptionally low concentration (100 CFU/mL), with recorded current spikes reaching approximately 8.1 nA. Analysis of integrated areas under these spikes unveiled a diverse distribution of charge transfer at the ultramicroelectrode during redox reactions, implying variations in bacterial sizes, collision positions on the electrode surface, and redox activity among bacteria. Remarkably, the average charge transfer per bacterium between E. coli and the electrode was found to be (244 ± 24) pC, underscoring the intrinsic redox activity of the bacteria, equivalent to (2.52 ± 0.25) × 10-15 mol. Additionally, our investigation explored the effects of cell transport mechanisms, including diffusion, migration, convection, and settlement on stochastic interactions of the bacteria at the ultramicroelectrode. Through the collision frequency calculations, we found that migration is the primary factor shaping bacterial transport, with gravitational cell settlement also exerting a significant influence.

Buoyancy-Driven Micro/-Nanomotors: From Fundamentals to Applications.

The progression of self-powered micro/-nanomotors (MNMs) has rapidly evolved over the past few decades, showing applications in various fields such as nanotechnology, biomedical engineering, microfluidics, environmental science, and energy harvesting. Miniaturized MNMs transduce chemical/biochemical energies into mechanical motion for navigating through complex fluidic environments with directional control via external forces fields such as magnetic, photonic, and electric stimuli. Among various propulsion mechanisms, buoyancy-driven MNMs have received noteworthy recognition due to their simplicity, efficiency, and versatility. Buoyancy force-driven motors harness the principles of density variation-mediated force to overcome fluidic resistance to navigate through complex environments. Restricting the propulsion in one direction helps to control directional movement, making it more efficient in isotropic solutions. The changes in pH, ionic strength, chemical concentration, solute gradients, or the presence of specific molecules can influence the motion of buoyancy-driven MNMs as evidenced by earlier reports. This review aims to provide a fundamental and detailed analysis of the current state-of-the-art in buoyancy-driven MNMs, aiming to inspire further research and innovation in this promising field.

Bacteria-derived topologies of Cu2O nanozymes exert a variable antibacterial effect.

The ability of bacteria to facilitate fabrication of nanomaterials has been adapted towards bacterial sensing applications. In this work, we fabricate spherical, cubic and truncated octahedron topologies of Cu2O nanoparticles via E. coli-facilitated redox reaction in an electrochemical setup. The Cu2O nanoparticles exhibit cytochrome c oxidase-like activity with the spherical topology displaying higher catalytic rate compared to the other geometries. The topology-dependent catalytic behavior of Cu2O nanoparticles has not been reported previously. The Cu2O nanozymes also display E. coli killing activity in a topology-correlated manner. The E. coli mediated redox reaction in an electrochemical setup is being reported for the first time for synthesis of different topologies of Cu2O which also exert a variable antibacterial effect.

pH-Responsive and Reversible A-Motif-Based DNA Hydrogel: Synthesis and Biosensing Application.

Functional DNA hydrogels with various motifs and functional groups require perfect sequence design to avoid cross-bonding interference with themselves or other structural sequences. This work reports an A-motif functional DNA hydrogel that does not require any sequence design. A-motif DNA is a noncanonical parallel DNA duplex structure containing homopolymeric deoxyadenosines (poly-dA) strands that undergo conformation changes from single strands at neutral pH to a parallel duplex DNA helix at acidic pH. Despite this and other advantages over other DNA motifs like no cross-bonding interference with other structural sequences, the A-motif has not been explored much. We successfully synthesized a DNA hydrogel by using an A-motif as a reversible handle to polymerize a DNA three-way junction. The A-motif hydrogel was initially characterized by electrophoretic mobility shift assay, and dynamic light scattering, which showed the formation of higher-order structures. Further, we used imaging techniques like atomic force microscopy and scanning electron microscope to validating its hydrogel like highly branched morphology. pH-induced conformation transformation from monomers to gel is quick and reversible, and was analysed for multiple acid-base cycles. The sol-to-gel transitions and gelation properties were further examined in rheological studies. The use of the A-motif hydrogel in the visual detection of pathogenic target nucleic acid sequence was demonstrated for the first time in a capillary assay. Moreover, pH-induced hydrogel formation was observed in situ as a layer over the mammalian cells. The proposed A-motif DNA scaffold has enormous potential in designing stimuli-responsive nanostructures that can be used for many biological applications.

Oxygen Generation Using Catalytic Nano/Micromotors.

Gaseous oxygen plays a vital role in driving the metabolism of living organisms and has multiple agricultural, medical, and technological applications. Different methods have been discovered to produce oxygen, including plants, oxygen concentrators and catalytic reactions. However, many such approaches are relatively expensive, involve challenges, complexities in post-production processes or generate undesired reaction products. Catalytic oxygen generation using hydrogen peroxide is one of the simplest and cleanest methods to produce oxygen in the required quantities. Chemically powered micro/nanomotors, capable of self-propulsion in liquid media, offer convenient and economic platforms for on-the-fly generation of gaseous oxygen on demand. Micromotors have opened up opportunities for controlled oxygen generation and transport under complex conditions, critical medical diagnostics and therapy. Mobile oxygen micro-carriers help better understand the energy transduction efficiencies of micro/nanoscopic active matter by careful selection of catalytic materials, fuel compositions and concentrations, catalyst surface curvatures and catalytic particle size, which opens avenues for controllable oxygen release on the level of a single catalytic microreactor. This review discusses various micro/nanomotor systems capable of functioning as mobile oxygen generators while highlighting their features, efficiencies and application potentials in different fields.