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Abstract: Microfluidic systems enable rapid diagnosis of diseases, biological analysis, drug screening, and high‐precision materials synthesis. In spite of these remarkable abilities, conventional microfluidic systems are microfabricated monolithically on a single platform and their operations rely on bulky expensive external equipment. This restricts their applications outside of research laboratories and prevents development and assembly of truly versatile and complex systems. Here, novel magnetorheological elastomer (MRE) microactuators are presented including pumps and mixers using an innovative actuation mechanism without the need of delicate elements such as thin membranes. Modularized elements are realized using such actuators, which can be easily integrated and actuated using a single self‐contained driving unit to create a modular, miniaturized, and robust platform. The performance of the microactuators is investigated via a series of experiments and a proof‐of‐concept modular system is developed to demonstrate the viability of the platform for self‐contained applications. The presented MRE microactuators are small size, simple, and efficient, offering a great potential to significantly advance the current research on complex microfluidic systems. [ABSTRACT FROM AUTHOR]

Liquid metal marbles that are droplets of liquid metal encapsulated by micro- or nanoparticles are introduced. Droplets of galinstan liquid metal are coated with insulators (including Teflon and silica) and semiconductors (including WO3, TiO2, MoO3, In2O3 and carbon nanotubes) by rolling over a powder bed and also by submerging in colloidal suspensions. It is shown that these marbles can be split and merged, can be suspended on water, and are even stable when moving under the force of gravity and impacting a flat solid surface. Furthermore, the marble coating can operate as an active electronic junction and the nanomaterial coated liquid metal marble can act as a highly sensitive electrochemical based heavy metal ion sensor. This new element thus represents a significant platform for the advancement of research into soft electronics. [ABSTRACT FROM AUTHOR]

Exploring and controlling surface tension‐driven phenomena in liquid metals may lead to unprecedented possibilities for next‐generation microfluidics, electronics, catalysis, and materials synthesis. In pursuit of these goals, the impact of minor constituents within liquid alloys is largely overlooked. Herein, it is showed that the presence of a fraction of solute metals such as tin, bismuth, and zinc in liquid gallium can significantly influence their electrocapillarity and electrochemistry. The instability‐driven fractal formation of liquid alloy droplets is investigated with different solutes and reveals the formation of distinctive non‐branched droplets, unstable fractals, and stable fractal modes under controlled voltage and alkaline solution conditions. In their individually unique fractal morphology diagrams, different liquid alloys demonstrate significantly shifted voltage thresholds in transition between the three fractal modes, depending on the choice of the solute metal. Surface tension measurements, cycle voltammetry and surface compositional characterizations provide strong evidence that the minor alloy components drastically alter the surface tension, surface electrochemical oxidation, and oxide dissolution processes that govern the droplet deformation and instability dynamics. The findings that minor components are able to regulate liquid alloys' surface tensions, surface element distributions and electrochemical activities offer great promises for harnessing the tunability and functionality of liquid metals. [ABSTRACT FROM AUTHOR]

Correction for 'Modular off-chip emulsion generator enabled by a revolving needle' by Yuxin Zhang et al., Lab Chip, 2020, 20, 4592–4599, DOI: 10.1039/D0LC00939C. [ABSTRACT FROM AUTHOR]

Conductive elastic composites have been used widely in soft electronics and soft robotics. These composites are typically a mixture of conductive fillers within elastomeric substrates. They can sense strain via changes in resistance resulting from separation of the fillers during elongation. Thus, most elastic composites exhibit a negative piezoconductive effect, i.e. the conductivity decreases under tensile strain. This property is undesirable for stretchable conductors since such composites may become less conductive during deformation. Here, we report a liquid metal-filled magnetorheological elastomer comprising a hybrid of fillers of liquid metal microdroplets and metallic magnetic microparticles. The composite's resistivity reaches a maximum value in the relaxed state and drops drastically under any deformation, indicating that the composite exhibits an unconventional positive piezoconductive effect. We further investigate the magnetic field-responsive thermal properties of the composite and demonstrate several proof-of-concept applications. This composite has prospective applications in sensors, stretchable conductors, and responsive thermal interfaces. Liquid metal-filled elastic composites for strain sensing devices exhibit reduced conductivity under strain, which limits their usefulness. Here, the authors report a positive piezoconductive effect in liquid metal-filled magnetorheological elastomers and illustrate proof-of concept applications. [ABSTRACT FROM AUTHOR]

Functional liquid metal nanoparticles (NPs), produced from eutectic alloys of gallium, promise new horizons in the fields of sensors, microfluidics, flexible electronics, catalysis, and biomedicine. Here, the development of a vapor cavity generating ultrasonic platform for nebulizing liquid metal within aqueous media for the one‐step production of stable and functional liquid metal NPs is shown. The size distribution of the NPs is fully characterized and it is demonstrated that various macro and small molecules can also be grafted onto these liquid metal NPs during the liquid‐based nebulization process. The cytotoxicity of the NPs grafted with different molecules is further explored. Moreover, it is shown that it is possible to control the thickness of the oxide layer on the produced NPs using electrochemistry that can be embedded within the platform. It is envisaged that this platform can be adapted as a cost‐effective and versatile device for the rapid production of functional liquid metal NPs for future liquid metal‐based optical, electronic, catalytic, and biomedical applications. An ultrasonic platform for nebulizing liquid metal within aqueous media is developed to achieve one‐step production of stable and functional liquid metal nanoparticles grafted with different molecules. This platform is able to control the thickness of the oxide layer on the produced nanoparticles using embedded electrochemical components. The demonstrated technique may enable future liquid metal‐based electronic, catalytic, and biomedical applications. [ABSTRACT FROM AUTHOR]

In the regime of inertial microfluidics, the secondary flow is widely adopted to reduce the number of the equilibrium position and improve the focusing performance of particles. At the same time, secondary flow can also enhance the mixing effect and may deteriorate particle focusing due to the induced rotating streams, especially for the particle with a small size. In a double-layered microchannel with slanted groove structures, it has been demonstrated that the generated secondary flow at a high flow rate could focus the particle with a large size (> 8 µm). However, the manipulation of small-size particles (< 8 µm) was unsuccessful as the effects of secondary flow on the small-size particles were not strong enough. In this work, to manipulate the small-size particle, we proposed a scheme to utilize a top sheath flow to enhance the focusing efficiency of the structure-induced secondary flow. The effects of the total flow rate and the flow rate ratio between the sheath and sample flow were investigated comprehensively in a large range. The 4.8 µm particle could be manipulated effectively at different flow rates with the assistance of appropriate sheath flows. Besides, the effects of other factors, such as the quantity of the expansion groove structure, and particle concentration and size, on particle focusing performance were also investigated. We found that the particles with the diameter of 2.9 µm can also be effectively focused within the double-layered microchannel. Furthermore, we demonstrated the continuous plasma extraction from the undiluted whole blood using this proposed technique to validate its potential biological applications. The results show that the purity of plasma extracted could reach up to ~ 99% after a single process. As such, this demonstrated that sheath flow-assisted particle manipulating method can overcome the limitations of conventional design and offer much better performance for controlling smaller particles. Such a platform may enable great potential in the applications of biological and diagnostic assays, for bioparticles smaller than the normal cell size. [ABSTRACT FROM AUTHOR]

Microalgae not only play a vital role in the ecosystem but also hold promising commercial applications. Conventional methods of detecting and monitoring microalgae rely on field sampling followed by transportation to the laboratory for manual analysis, which is both time-consuming and laborious. Although machine learning (ML) algorithms have been introduced for microalgae detection in the laboratory, no integrated platform approach has yet emerged to enable real-time, on-site sampling and analysing. To solve this problem, here, we develop an automated and intelligent microfluidic platform (AIMP) that can offer automated system control, intelligent data analysis, and user interaction, providing an economical and portable solution to alleviate the drawbacks of conventional methods for microalgae detection and monitoring. We demonstrate the feasibility of the AIMP by detecting and classifying four microalgal species (Cosmarium, Closterium, Micrasterias, and Haematococcus Pluvialis) that exhibit varying sizes (from a few to hundreds of microns) and morphologies. The trained microalgae species detection network (MSDN, based on YOLOv5 architecture) achieves a high overall mean average precision at 0.5 intersection-over-union (mAP@0.5) of 92.8%. Furthermore, the versatility of the AIMP is demonstrated by long-term monitoring of astaxanthin production from Haematococcus Pluvialis over a period of 30 days. The AIMP achieved 97.5% accuracy in the detection of Haematococcus Pluvialis and 96.3% in further classification based on astaxanthin accumulation. This study opens up a new path towards microalgae detection and monitoring using portable intelligent devices, providing new ideas to accelerate progress in the ecological studies and commercial exploitation of microalgae. [ABSTRACT FROM AUTHOR]

Rapid and accurate detection of nucleic acids plays a critical role in public health, food safety and environmental management. Clustered regularly interspaced short palindromic repeats powered electrochemical sensor (E-CRISPR) is attractive as a point-of-care (POC) testing platform to fulfil this purpose. Yet, bulk noble metals (e.g., gold and platinum) based electrodes that have been widely adopted in E-CRISPR suffer from limited analytical performance and high manufacturing costs. Here, to address this limitation, we present a carbon-based E-CRISPR modified with gold nanoparticles and MXene Ti 3 C 2 (a class of two-dimensional transition metal carbide nanomaterials) that provides highly stable and sensitive transduction of CRISPR-Cas12a trans-cleavage activity. Through systematic evaluation and optimization, our AuNPs/MXene Ti 3 C 2 based E-CRISPR achieve the quantification of human papillomavirus 18 (HPV-18) DNA with a wide range of concentrations from 10 pM to 500 nM with a detection limit of 1.95 pM. We further evaluate the selectivity, degradation resistance and detection capability of the developed sensor during long-term storage. Notably, AuNPs/MXene based E-CRISPR retain more than 70% of initial current after 2 months and deliver reliable analytical results that are unaffected over 42-day storage. Owing to its excellent biofouling-resistant and analytical performance and robust shelf life, our E-CRISPR sensor offers a universal, scalable and low-cost strategy for POC nucleic acid testing. • Integrating MXene Ti 3 C 2 and AuNPs with CRISPR-Cas12a enables sensitive, selective and rubost detection of HPV-related DNA. • Nanocomposites of MXene Ti 3 C 2 and AuNPs significantly enhance the electrochemical signal output for target DNA detection. • Without amplification, picomolar limit of detection and 5 orders of magnitude detection range for HPV18 DNA is achieved. • MXene Ti 3 C 2 /AuNPs based E-CRISPR retains 70% of initial signals and delivers reproducible results after 2-month storage. [ABSTRACT FROM AUTHOR]

Pairing droplet microfluidics and CRISPR/Cas12a techniques creates a powerful solution for the detection and quantification of nucleic acids at the single-molecule level, due to its specificity, sensitivity, and simplicity. However, traditional water-in-oil (W/O) single emulsion (SE) droplets often present stability issues, affecting the accuracy and reproducibility of assay results. As an alternative, water-in-oil-in-water (W/O/W) double emulsion (DE) droplets offer superior stability and uniformity for droplet digital assays. Moreover, unlike SE droplets, DE droplets are compatible with commercially available flow cytometry instruments for high-throughput analysis. Despite these advantages, no study has demonstrated the use of DE droplets for CRISPR-based nucleic acid detection. In our study, we conducted a comparative analysis to assess the performance of SE and DE droplets in quantitative detection of human papillomavirus type 18 (HPV18) DNA based on CRISPR/Cas12a. We evaluated the stability of SEs and DEs by examining size variation, merging extent, and content interaction before and after incubation at different temperatures and time points. By integrating DE droplets with flow cytometry, we achieved high-throughput and high-accuracy CRISPR/Cas12a-based quantification of target HPV18 DNA. The DE platform, when paired with CRISPR/Cas12a and flow cytometry techniques, emerges as a reliable tool for absolute quantification of nucleic acid biomarkers. • Double emulsion (DE) droplets show enhanced stability in CRISPR/Cas12a-based DNA detection than single emulsion droplets. • The remarkable stability of DE droplets prevents content mixing, reducing contamination risks during incubation. • DE droplets significantly minimize sample loss during encapsulation and incubation, outperforming SE droplets. • DE droplets, compatible with flow cytometry, enable precise and high-throughput CRISPR/Cas12a-based DNA quantification. [ABSTRACT FROM AUTHOR]

Gallium (Ga) and Ga-based liquid metal (LM) alloys offer low toxicity, excellent electrical and thermal conductivities, and fluidity at or near room temperature. Ga-based LM particles (LMPs) synthesized from these LMs exhibit both fluidic and metallic properties and are suitable for versatile functionalization in therapeutics. Functionalized Ga-based LMPs can be actuated using physical or chemical stimuli for drug delivery, cancer treatment, bioimaging, and biosensing. However, many of the fundamentals of their unique characteristics for therapeutics remain underexplored. We present the most recent advances in Ga-based LMPs in therapeutics based on the underlying mechanisms of their design and implementation. We also highlight some future biotechnological opportunities for Ga-based LMPs based on their extraordinary advantages. The surface tension of gallium (Ga)-based liquid metals (LMs) can be broken using mechanical and chemical means, and smaller Ga-based LM particles (LMPs) can be constructed. Ga-based LMPs offer both fluidic and metallic cores and peculiar interfacial properties, which differ fundamentally from the properties of solid metal particles. Ga-based LMPs hold great potential for therapeutics. Functionalized Ga-based LMPs can be designed and activated for drug delivery, cancer treatment, bioimaging, and biosensing on stimulation by light, electromagnetic fields, mechanical means, or chemical reactions. Fundamental understanding of the effects of Ga-based LMPs' surface oxides, their interactions with cells and their organelles, and their specific alloy composition with other elements should be further explored to expand the horizons of therapeutics using LMPs. [ABSTRACT FROM AUTHOR]

Biopotential signals, like electrocardiography (ECG), electromyography (EMG), and electroencephalography (EEG), can help diagnose cardiological, musculoskeletal and neurological disorders. Dry silver/silver chloride (Ag/AgCl) electrodes are commonly used to obtain these signals. While a conductive hydrogel can be added to Ag/AgCl electrodes to improve the contact and adhesion between the electrode and the skin, dry electrodes are prone to movement. Considering that the conductive hydrogel dries over time, the use of these electrodes often creates an imbalanced skin-electrode impedance and a number of sensing issues in the front-end analogue circuit. This issue can be extended to several other electrode types that are commonly in use, in particular, for applications with a need for long-term wearable monitoring such as ambulatory epilepsy monitoring. Liquid metal alloys, such as eutectic gallium indium (EGaIn), can address key critical requirements around consistency and reliability but present challenges on low viscosity and the risk of leakage. To solve these problems, here, we demonstrate the use of a non-eutectic Ga–In alloy as a shear-thinning non-Newtonian fluid to offer superior performance to commercial hydrogel electrodes, dry electrodes, and conventional liquid metals for electrography measurements. This material has high viscosity when still and can flow like a liquid metal when sheared, preventing leakage while allowing the effective fabrication of electrodes. Moreover, the Ga–In alloy not only has good biocompatibility but also offers an outstanding skin-electrode interface, allowing for the long-term acquisition of high-quality biosignals. The presented Ga–In alloy is a superior alternative to conventional electrode materials for real-world electrography or bioimpedance measurement. [ABSTRACT FROM AUTHOR]