Characterization of nanoparticle size distributions using a microfluidic device with integrated optical microcavities

Novel cobalt-based aerogels for uric acid detection in fluids at physiological pH

A sensor for uric acid (UA) based on the urate oxidase enzyme (UOx) immobilized in novel Co-based aerogels with transition metals synthesized by the sol-gel method was developed and evaluated. The Co-based aerogels: Co, Ni-Co and Pd-Co were physicochemically characterized by XRD and HR-TEM. The surface area values of 53, 57 and 66 m2 g-1 were determined for Co, Ni-Co and Pd-Co, respectively by N2 adsorption-desorption technique. Co-based aerogels were mixed by cross-linking with UOx enzymes and electrochemically characterized in buffers at pH 7.4 and 5.6 (pH values reported for biological fluids such as blood and sweat) in the presence of different uric acid concentrations. Co-based aerogels with UOx showed improved performance as a uric acid biosensor compared to using the enzyme alone. At a pH of 7.4, a higher sensitivity of 11 μA μM-1 was obtained with Pd-Co/UOx, 1.6 times higher than with UOx. At a pH value of 5.6, the highest sensitivity is achieved with Ni-Co/UOx. Stability and selectivity tests were performed in the presence of biological interferents without significant changes in the sensor. These results indicate a pleasing synergistic activity between Co-based aerogels and the enzyme.

Fully autonomous water monitoring by plant-inspired robots

Developing countries struggle with water quality management owing to poor infrastructure, limited expertise, and financial constraints. Traditional water testing, relying on periodic site visits and manual sampling, is impractical for continuous wide-area monitoring and fails to detect sudden heavy metal contamination. To address this, plant-inspired robots capable of fully autonomous water quality monitoring are proposed. Constructed from paper, the robot absorbs surrounding water through its roots. This paper robot is controlled by paper-based microfluidic logic that sends absorbed water to petal-shaped actuators only when the water is polluted by heavy metals. This triggers the actuators to swell and bend like a blooming flower, visually signaling contamination to local residents. In tests with copper-contaminated water, the robotic flower's diameter increased from 4.69 cm to 14.89 cm, a more than threefold expansion (217.25 %). This significant blooming movement serves as a highly visible and easily recognizable indicator of water pollution, even for the public. Furthermore, the paper robot can be mass-produced at a low cost (∼$0.2 per unit) and deployed over large areas. Once installed, the paper robot operates autonomously using surrounding water as a power source, eliminating the need for external electrical infrastructure and expert intervention. Therefore, this autonomous robot offers a new approach to water quality monitoring suitable for resource-limited environments, such as Sub-Saharan Africa.

Bioelectrochemical biosensors for water quality assessment and wastewater monitoring

Bioelectrochemical biosensors offer a promising approach for real-time monitoring of industrial bioprocesses. Many bioelectrochemical biosensors do not require additional labelling reagents for target molecules. This simplifies the monitoring process, reduces costs, and minimizes potential contamination risks. Advancements in materials science and microfabrication technologies are paving the way for smaller, more portable bioelectrochemical biosensors. This opens doors for integration into existing bioprocessing equipment and facilitates on-site, real-time monitoring capabilities. Biosensors can be designed to detect specific heavy metals such as lead, mercury, or chromium in wastewater. Early detection allows for the implementation of appropriate removal techniques before they reach the environment. Despite these challenges, bioelectrochemical biosensors offer a significant leap forward in wastewater monitoring. As research continues to improve their robustness, selectivity, and cost-effectiveness, they have the potential to become a cornerstone of efficient and sustainable wastewater treatment practices.

Mass measurement under medium vacuum in optically levitated nanoparticles based on Maxwell speed distribution law

As one of the directions of optical levitation technology, the mass measurement of micro-nano particles has always been a research hotspot in extremely weak mechanical measurements. When nanoscale particles are trapped in an optical trap, parameters such as density, diameter, and shape are unknown. Here we propose what we believe to be a new method to measure mass by fitting particle motion information to the Maxwell speed distribution law, with an accuracy better than 7% at 10 mbar. This method has the characteristics of requiring no external driving force, no precise natural frequency, no prior information such as density, and non-destructive testing within the medium vacuum range. With the increasing iterations, the uncertainty of mass measurement is reduced, and the accuracy of mass measurement of levitated particles is verified under multiple air pressures. It provides what we believe is a new method for the future non-destructive testing of nanoscale particles, and provides an apparently new way for the sensing measurement and metrology application fields of levitation dynamics systems.

Mode mixing and losses in misaligned microcavities

We present a study on the optical losses of Fabry-Pérot cavities subject to realistic transverse mirror misalignment. We consider mirrors of the two most prevalent surface forms: idealised spherical depressions, and Gaussian profiles generated by laser ablation. We first describe the mode mixing phenomena seen in the spherical mirror case and compare to the frequently-used clipping model, observing close agreement in the predicted diffraction loss, but with the addition of protective mode mixing at transverse degeneracies. We then discuss the Gaussian mirror case, detailing how the varying surface curvature across the mirror leads to complex variations in round trip loss and mode profile. In light of the severe mode distortion and strongly elevated loss predicted for many cavity lengths and transverse alignments when using Gaussian mirrors, we suggest that the consequences of mirror surface profile are carefully considered when designing cavity experiments.

Microfluidic systems for particle capture and release: A review

Microfluidic technology has emerged as a promising tool in various applications, including biosensing, disease diagnosis, and environmental monitoring. One of the notable features of microfluidic devices is their ability to selectively capture and release specific cells, biomolecules, bacteria, and particles. Compared to traditional bulk analysis instruments, microfluidic capture-and-release platforms offer several advantages, such as contactless operation, label-free detection, high accuracy, good sensitivity, and minimal reagent requirements. However, despite significant efforts dedicated to developing innovative capture mechanisms in the past, the release and recovery efficiency of trapped particles have often been overlooked. Many previous studies have focused primarily on particle capture techniques and their efficiency, disregarding the crucial role of successful particle release for subsequent analysis. In reality, the ability to effectively release trapped particles is particularly essential to ensure ongoing, high-throughput analysis. To address this gap, this review aims to highlight the importance of both capture and release mechanisms in microfluidic systems and assess their effectiveness. The methods are classified into two categories: those based on physical principles and those using biochemical approaches. Furthermore, the review offers a comprehensive summary of recent applications of microfluidic platforms specifically designed for particle capture and release. It outlines the designs and performance of these devices, highlighting their advantages and limitations in various target applications and purposes. Finally, the review concludes with discussions on the current challenges faced in the field and presents potential future directions.