Liquid marbles as biochemical reactors for the polymerase chain reaction

Dynamic behavior of floating magnetic liquid marbles under steady and pulse-width-modulated magnetic fields

Liquid marbles show promising potential for digital microfluidic devices due to their lower friction with the platform surface than non-covered droplets. In this study, the manipulation of a biocompatible magnetic liquid marble with a magnetic shell (LMMS) is experimentally studied. The movement of the floating LMMS on the water surface, which is actuated by DC and pulse width modulation (PWM) magnetic fields, is investigated under the influence of various parameters, including the LMMS volume, the initial distance of the LMMS from the magnetic coil tip, the magnetic coil current, the PWM frequency and its duty cycle. The LMMS has a shorter travel time to the magnetic coil tip under a DC magnetic field by increasing the magnetic coil current, decreasing the initial distance and its volume. In the PWM mode, these parameters show similar behavior; moreover, increasing the PWM duty cycle and decreasing the PWM frequency shorten the travel time. It is demonstrated that actuation by a PWM magnetic field with step-by-step movement provides better control over manipulation of the floating magnetic marble. The dynamic behavior of an LMMS is compared to a ferrofluid marble (FM), which is formed using a ferrofluid instead of water as its core. It is observed that the LMMS has a lower velocity than the FM.

Customizable Nichrome Wire Heaters for Molecular Diagnostic Applications

Accurate sample heating is vital for nucleic acid extraction and amplification, requiring a sophisticated thermal cycling process in nucleic acid detection. Traditional molecular detection systems with heating capability are bulky, expensive, and primarily designed for lab settings. Consequently, their use is limited where lab systems are unavailable. This study introduces a technique for performing the heating process required in molecular diagnostics applicable for point-of-care testing (POCT), by presenting a method for crafting customized heaters using freely patterned nichrome (NiCr) wire. This technique, fabricating heaters by arranging protrusions on a carbon black-polydimethylsiloxane (PDMS) cast and patterning NiCr wire, utilizes cost-effective materials and is not constrained by shape, thereby enabling customized fabrication in both two-dimensional (2D) and three-dimensional (3D). To illustrate its versatility and practicality, a 2D heater with three temperature zones was developed for a portable device capable of automatic thermocycling for polymerase chain reaction (PCR) to detect Escherichia coli (E. coli) O157:H7 pathogen DNA. Furthermore, the detection of the same pathogen was demonstrated using a customized 3D heater surrounding a microtube for loop-mediated isothermal amplification (LAMP). Successful DNA amplification using the proposed heater suggests that the heating technique introduced in this study can be effectively applied to POCT.

Liquid Marbles and Drops on Superhydrophobic Surfaces: Interfacial Aspects and Dynamics of Formation: A Review

Liquid marbles (LMs) are droplets encapsulated with powders presenting varied roughness and wettability. These LMs have garnered a lot of attention due to their dual properties of leakage-free and quick transport on both solid and liquid surfaces. These droplets are in a Cassie-Baxter wetting state sitting on both roughness and air pockets existing between particles. They are also reminiscent of the state of a drop on a superhydrophobic (SH) surface. In this review, LMs and bare droplets on SH surfaces are comparatively investigated in terms of two aspects: interfacial and dynamical. LMs present a fascinating class of soft matter due to their superior interfacial activity and their remarkable stability. Inherently hydrophobic powders form stable LMs by simple rolling; however, particles with defined morphologies and chemistries contribute to the varied stability of LMs. The factors contributing to this interesting robustness with respect to bare droplets are then identified by tests of stability such as evaporation and compression. Next, the dynamics of the impact of a drop on a hydrophobic powder bed to form LMs is studied vis-à̀-vis that of drop impact on flat surfaces. The knowledge from drop impact phenomena on flat surfaces is used to build and complement insights to that of drop impact on powder surfaces. The maximum spread of the drop is empirically understood in terms of dimensionless numbers, and their drawbacks are highlighted. Various stages of drop impact-spreading, retraction and rebound, splashing, and final outcome-are systematically explored on both solid and hard surfaces. The implications of crater formation and energy dissipations are discussed in the case of granular beds. While the drop impact on solid surfaces is extensively reviewed, deep interpretation of the drop impact on granular surfaces needs to be improved. Additionally, the applications of each step in the sequence of drop impact phenomena on both substrates are also identified. Next, the criterion for the formation of peculiar jammed LMs was examined. Finally, the challenges and possible future perspectives are envisaged.

Bacteriophages in nature: recent advances in research tools and diverse environmental and biotechnological applications

Bacteriophages infect and replicate within bacteria and play a key role in the environment, particularly in microbial ecosystems and bacterial population dynamics. The increasing recognition of their significance stems from their wide array of environmental and biotechnological uses, which encompass the mounting issue of antimicrobial resistance (AMR). Beyond their therapeutic potential in combating antibiotic-resistant infections, bacteriophages also find vast applications such as water quality monitoring, bioremediation, and nutrient cycling within environmental sciences. Researchers are actively involved in isolating and characterizing bacteriophages from different natural sources to explore their applications. Gaining insights into key aspects such as the life cycle of bacteriophages, their host range, immune interactions, and physical stability is vital to enhance their application potential. The establishment of diverse phage libraries has become indispensable to facilitate their wide-ranging uses. Consequently, numerous protocols, ranging from traditional to cutting-edge techniques, have been developed for the isolation, detection, purification, and characterization of bacteriophages from diverse environmental sources. This review offers an exploration of tools, delves into the methods of isolation, characterization, and the extensive environmental applications of bacteriophages, particularly in areas like water quality assessment, the food sector, therapeutic interventions, and the phage therapy in various infections and diseases.

Experimental and Theoretical Investigation on the Dynamic Response of Ferrofluid Liquid Marbles to Steady and Pulsating Magnetic Fields

Liquid marbles are droplets enwrapped by a layer of hydrophobic micro/nanoparticles. Due to the isolation of fluid from its environment, reduction in evaporation rate, low friction with the surfaces, and capability of manipulation even on hydrophilic surfaces, liquid marbles have attracted the attention of researchers in digital microfluidics. This study investigates the manipulation of ferrofluid liquid marbles (FLMs) under DC and pulse width-modulated (PWM) magnetic fields generated by an electromagnet for the first time. At first, the threshold of the magnetic field for manipulating these FLMs is studied. Afterward, the dynamic response of the FLMs to the DC magnetic field for different FLM volumes, coil currents, and initial distances of FLM from the coil is studied, and a theoretical model is proposed. By applying the PWM magnetic field, it is possible to gain more control over the manipulation of the FLMs on the surface and adjust their position more accurately. Results indicate that with a decrease in FLM volume, coil current, and duty cycle, the FLM step length decreases; hence, FLM manipulation is more precise. Under the PWM magnetic field, it is observed that FLM movement is not synchronous with the generated pulse, and even after the coil is turned off, FLMs keep their motion. In the end, with proper adjustment of the electromagnet pulse width, launching of FLMs at a distance farther than the coil is observed.

Magnetically Driven Manipulation of Nonmagnetic Liquid Marbles: Billiards with Liquid Marbles

Liquid marbles are droplets encapsulated by a layer of hydrophobic nanoparticles and have been extensively employed in digital microfluidics and lab-on-a-chip systems in recent years. In this study, magnetic liquid marbles were used to manipulate nonmagnetic liquid marbles. To achieve this purpose, a ferrofluid liquid marble (FLM) was employed and attracted toward an electromagnet, resulting in an impulse to a water liquid marble (WLM) on its way to the electromagnet. It was observed that the manipulation of the WLM by the FLM was similar to the collision of billiard balls except that the liquid marbles exhibited an inelastic collision. Taking the FLM as the projectile ball and the WLM as the other target balls, one can adjust the displacement and direction of the WLM precisely, similar to an expert billiard player. Firstly, the WLM displacement can be adjusted by altering the liquid marble volumes, the initial distances from the electromagnet, and the coil current. Secondly, the WLM direction can be adjusted by changing the position of the WLM relative to the connecting line between the FLM center and the electromagnet. Results show that when the FLM or WLM volume increases by five times, the WLM shooting distance approximately increases by 200% and decreases by 75%, respectively.

Liquid marbles, floating droplets: preparations, properties, operations and applications

Liquid marbles (LMs) are non-wettable droplets formed with a coating of hydrophobic particles. They can move easily across either solid or liquid surfaces since the hydrophobic particles protect the internal liquid from contacting the substrate. In recent years, mainly due to their simple preparation, abundant materials, non-wetting/non-adhesive properties, elasticities and stabilities, LMs have been applied in many fields such as microfluidics, sensors and biological incubators. In this review, the recent advances in the preparation, physical properties and applications of liquid marbles, especially operations and floating abilities, are summarized. Moreover, the challenges to achieve uniformity, slow volatilization and stronger stability are pointed out. Various applications generated by LMs’ structural characteristics are also expected.

The recent advances in the preparation, physical properties and applications of liquid marbles, especially operations and floating abilities, are summarized.

Optically controlled coalescence and splitting of femtoliter/picoliter droplets for microreactors

Microreactor technology has attracted tremendous interest due to its features of a large specific surface area, low consumption of reagents and energy, and flexible control of the reaction process. As most of the current microreactors have volumes of microliters or even larger, effective methods to reduce the microreactors' sizes and improve their flexibility and controllability have become highly demanded. Here we propose an optical method of coalescence and splitting of femto-/pico-liter droplets for application in microreactors. Firstly, two different schemes are adopted to stably trap and directionally transport the microdroplets (oil and water) by a scanning optical tweezing system. Then, optically controlled coalescence and splitting of the microdroplets are achieved on this basis, and the mechanism and conditions are explored. Finally, the microdroplets are used as microreactors to conduct the microreactions. Such microreactors combine the advantages of miniaturization and the multi-functions of microdroplets, as well as the precision, flexibility, and non-invasiveness of optical tweezers, holding great potential for applications in materials synthesis and biosensing.

Optical trapping, transportation, coalescence and splitting of femto-/pico-liter microdroplets are realized based on a scanning optical tweezing system. On this basis, the microdroplets are used as microreactors to conduct the microreactions.

Light fueled mixing in open surface droplet microfluidics for rapid probe preparation

In this study, a contactless, flexible, and interference-free light fueled method has been developed to enhance the mixing between the ssDNA and dynabeads in a droplet, which enables rapid probe preparation for promoting the probe technology based on open surface droplet microfluidics. In this light fueled method, the use of the photothermal effect of a focused infrared laser can easily create non-uniform temperature distribution and accordingly the surface tension gradient over the interface as a result of the localized heating effect, which thereby initiates the Marangoni flow in a droplet. Experimental results confirm that the light-induced Marangoni flow greatly enhances the mixing, ensuring rapid and efficient binding between the ssDNA and dynabeads. Moreover, the mixing intensity and degree can be simply tuned by controlling the laser intensity and laser heating time. The light fueled rapid mixing method developed in the present study paves the way for rapid bio-chemical detection.

Liquid-Based Adaptive Structural Materials

Structural materials are used to provide stable mechanical architectures and transmit or support forces, and they play an important role in materials science and technology. During the long process of the exploitation of structural materials, the functionality of structural materials has gained prominence. Adaptive structures responding to external stimuli have come to the fore with significant advantages in structural materials. However, many solid adaptive structural materials still suffer from their single function and the lack of dynamic performance, such as issue around fouling and energy consumption, defects present everywhere in materials at the microscale, etc. To meet the increasing demands, more and more researchers have started turning their attention to liquid-based materials owing to their intrinsic spontaneous, dynamic, and functional properties. Liquid-based adaptive structural materials (LASMs) have been proposed and developed. Building upon both dynamic liquids and fixed solids, LASMs have been demonstrated to possess both dynamic adaptivity (from the active liquid part) and stable mechanical structure (from the fixed solid part), which are desired in many applications such as 3D printing, droplet manipulation, omniphobic surfaces, microfluidics, mass separation, etc. A unifying view of the recent progress of LASMs is presented, including liquid with particles, liquid with surfaces, as well as liquid with membranes. In addition, the discussion of the prospects and challenges are provided for promoting the development of LASMs.

A Portable Device for LAMP Based Detection of SARS-CoV-2

This paper reports the design, development, and testing of a novel, yet simple and low-cost portable device for the rapid detection of SARS-CoV-2. The device performs loop mediated isothermal amplification (LAMP) and provides visually distinguishable images of the fluorescence emitted from the samples. The device utilises an aluminium block embedded with a cartridge heater for isothermal heating of the sample and a single-board computer and camera for fluorescence detection. The device demonstrates promising results within 20 min using clinically relevant starting concentrations of the synthetic template. Time-to-signal data for this device are considerably lower compared to standard quantitative Polymerase Chain Reaction(qPCR) machine (~10–20 min vs. >38 min) for 1 × 10² starting template copy number. The device in its fully optimized and characterized state can potentially be used as simple to operate, rapid, sensitive, and inexpensive platform for population screening as well as point-of-need severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) detection and patient management.

How particle-particle and liquid-particle interactions govern the fate of evaporating liquid marbles

Liquid marbles refer to droplets that are covered with a layer of non-wetting particles. They are observed in nature and have practical significance. These squishy objects bounce, coalesce, break, inflate, and deflate while the liquid does not touch the substrate underneath. Despite the considerable cross-disciplinary interest and value of the research on liquid marbles, a unified framework for describing the mechanics of deflating liquid marbles-as the liquid evaporates-is unavailable. For instance, analytical approaches for modeling the evaporation of liquid marbles exploit empirical parameters that are not based on liquid-particle and particle-particle interactions. Here, we have combined complementary experiments and theory to fill this gap. To unentangle the contributions of particle size, roughness, friction, and chemical make-up, we investigated the evaporation of liquid marbles formed with particles of sizes varying over 7 nm-300 μm and chemical compositions ranging from hydrophilic to superhydrophobic. We demonstrate that the potential final states of evaporating liquid marbles are characterized by one of the following: (I) constant surface area, (II) particle ejection, or (III) multilayering. Based on these insights, we developed an evaporation model for liquid marbles that takes into account their time-dependent shape evolution. The model fits are in excellent agreement with our experimental results. Furthermore, this model and the general framework can provide mechanistic insights into extant literature on the evaporation of liquid marbles. Altogether, these findings advance our fundamental understanding of liquid marbles and should contribute to the rational development of technologies.

Functional liquid droplets for analyte sensing and energy harvesting

Over the past century, rapid miniaturization of technologies has helped in the development of efficient, flexible, portable, robust, and compact applications with minimal wastage of materials. In this direction, of late, the usage of mesoscale liquid droplets has emerged as an alternative platform because of the following advantages: (i) a droplet is incompressible and at the same time deformable, (ii) interfacial area of a spherical droplet is minimum for a given amount of mass; and (iii) a droplet interface allows facile mass, momentum, and energy transfer. Subsequently, such attributes have aided towards the design of diverse droplet-based microfluidic technologies. For example, the microdroplets have been utilized as micro-reactors, colorimetric or electrochemical (EC) sensors, drug-delivery vehicles, and energy harvesters. Further, a number of recently reported lab-on-a-chip technologies exploit the motility, storage, and mixing capacities of the microdroplets. In view of this background, the review initiates discussion by highlighting the different attributes of the microdroplets such as size, shape, surface to volume ratio, wettability, and contact line. Thereafter, the effects of the surface or body forces on the properties of the droplets have been elaborated. Finally, the different aspects of such liquid droplet systems towards technological adaptations in health care, sensing, and energy harvesting have been presented. The review concludes with a tight summary on the potential avenues for further developments.

Loop-Mediated Isothermal Amplification in a Core-Shell Bead Assay for the Detection of Tyrosine Kinase AXL Overexpression

The upregulated expression of tyrosine kinase AXL has been reported in several hematologic and solid human tumors, including gastric, breast, colorectal, prostate and ovarian cancers. Thus, AXL can potentially serve as a diagnostic and prognostic biomarker for various cancers. This paper reports the first ever loop-mediated isothermal amplification (LAMP) in a core-shell bead assay for the detection of AXL gene overexpression. We demonstrated simple instrumentation toward a point-of-care device to perform LAMP. This paper also reports the first ever use of core-shell beads as a microreactor to perform LAMP as an attempt to promote environmentally-friendly laboratory practices.

Liquid marble-based digital microfluidics - fundamentals and applications

Liquid marbles are droplets with volume typically on the order of microliters coated with hydrophobic powder. Their versatility, ease of use and low cost make liquid marbles an attractive platform for digital microfluidics. This paper provides the state of the art of discoveries in the physics of liquid marbles and their practical applications. The paper first discusses the fundamental properties of liquid marbles, followed by the summary of different techniques for the synthesis of liquid marbles. Next, manipulation techniques for handling liquid marbles are discussed. Applications of liquid marbles are categorised according to their use as chemical and biological reactors. The paper concludes with perspectives on the future development of liquid marble-based digital microfluidics.

Compressed Air-Driven Continuous-Flow Thermocycled Digital PCR for HBV Diagnosis in Clinical-Level Serum Sample Based on Single Hot Plate

We report a novel compressed air-driven continuous-flow digital PCR (dPCR) system based on a 3D microfluidic chip and self-developed software system to realize real-time monitoring. The system can ensure the steady transmission of droplets in long tubing without an external power source and generate stable droplets of suitable size for dPCR by two needles and a narrowed Teflon tube. The stable thermal cycle required by dPCR can be achieved by using only one constant temperature heater. In addition, our system has realized the real-time detection of droplet fluorescence in each thermal cycle, which makes up for the drawbacks of the end-point detection method used in traditional continuous-flow dPCR. This continuous-flow digital PCR by the compressed air-driven method can meet the requirements of droplet thermal cycle and diagnosis in a clinical-level serum sample. Comparing the detection results of clinical samples (hepatitis B virus serum) with commercial instruments (CFX Connect; Bio Rad, Hercules, CA, USA), the linear correlation reached 0.9995. Because the system greatly simplified the traditional dPCR process, this system is stable and user-friendly.

Interfacial Crystallization within Liquid Marbles

We report interfacial crystallization in the droplets of saline solutions placed on superhydrophobic surfaces and liquid marbles filled with the saline. Evaporation of saline droplets deposited on superhydrophobic surface resulted in the formation of cup-shaped millimeter-scaled residues. The formation of the cup-like deposit is reasonably explained within the framework of the theory of the coffee-stain effect, namely, the rate of heterogeneous crystallization along the contact line of the droplet is significantly higher than in the droplet bulk. Crystallization within evaporated saline marbles coated with lycopodium particles depends strongly on the evaporation rate. Rapidly evaporated saline marbles yielded dented shells built of a mixture of colloidal particles and NaCl crystals. We relate the formation of these shells to the interfacial crystallization promoted by hydrophobic particles coating the marbles, accompanied with the upward convection flows supplying the saline to the particles, serving as the centers of interfacial crystallization. Convective flows prevail over the diffusion mass transport for the saline marbles heated from below.

Elemental Sulfur-Stabilized Liquid Marbles: Properties and Applications

Sulfur-stabilized liquid marbles were readily prepared by rolling water droplets on a sulfur (S₈) powder bed. Because of the construction of a gel layer on the surface of liquid marbles, the resulting liquid marbles have shape-designable characteristics. The effects of rolling time and volume of droplets on the deformability of sulfur-stabilized liquid marbles were investigated along with their mechanical stability and lifetime. The capability of sulfur-stabilized liquid marbles to be deformed at different pH values enables these liquid marbles to act as microreservoirs with desired shapes for aqueous solutions. Immersing the sulfur-stabilized liquid marbles into organic liquids leads to an increase in the liquid marbles' lifetime, and thereby they can survive at the interface of aqueous-organic two-phased systems for a long time. Finally, the applications of sulfur-stabilized liquid marbles as photocatalytic microreactors, electrochemical microcells, and monodisperse Pickering-like emulsions were demonstrated.

Liquid marble technology to create cost-effective 3D cardiospheres as a platform for in vitro drug testing and disease modelling

Three-dimensional (3D) cell culturing has several advantages over 2D cultures. 3D cell cultures more accurately mimic the in vivo environment, which is vital to obtain reliable results in disease modelling and toxicity testing. With the introduction of the Yamanaka factors, reprogramming of somatic cells to induced pluripotent stem cells (iPSCs) became available. This iPSC technology provides a scalable source of differentiated cells. iPSCs can be programmed to differentiate into any cell type of the body, including cardiomyocytes. These heart-specific muscle cells, can then serve as a model for therapeutic drug screening or assay development. Current methods to achieve multicellular spheroids by 3D cell cultures, such as hanging drop and spinner flasks are expensive, time-consuming and require specialized materials and training. Hydrophobic powders can be used to create a micro environment for cell cultures, which are termed liquid marbles (LM). In this procedure we describe the first use of the LM technology for 3D culturing in vitro derived human cardiomyocytes which results in the formation of cardiospheres within 24h. The cardiospheres could be used for several in depth and high-throughput analyses.

Core-Shell Beads as Microreactors for Phylogrouping of E. coli Strains

Multiplex polymerase chain reaction (PCR) is an effective tool for simultaneous detection of target genes. Nevertheless, their use has been restricted due to the intrinsic interference between primer pairs. Performing several single PCRs in an array format instead of a multiplex PCR is a simple way to overcome this obstacle. However, there are still major technical challenges in designing a new generation of single PCR microreactors with a small sample volume, rapid thermal cycling, and no evaporation during amplification. We report a simple and robust core-shell bead array for a series of single amplifications. Four core-shell beads with a polymer coating and PCR mixture were synthesized using liquid marble formation and subsequent photo polymerization. Each bead can detect one target gene. We constructed a customised system for thermal cycling of these core-shell beads. Phylogrouping of the E. coli strains was carried out based on the fluorescent signal of the core-shell beads. This platform can be a promising alternative for multiplex nucleic acid analyses due to its simplicity and high throughput. The platform reported here also reduces the cycling time and avoids evaporation as well as contamination of the sample during the amplification process.

Elevating Chemistry Research with a Modern Electronics Toolkit

With the rapid development of high technology, chemical science is not as it used to be a century ago. Many chemists acquire and utilize skills that are well beyond the traditional definition of chemistry. The digital age has transformed chemistry laboratories. One aspect of this transformation is the progressing implementation of electronics and computer science in chemistry research. In the past decade, numerous chemistry-oriented studies have benefited from the implementation of electronic modules, including microcontroller boards (MCBs), single-board computers (SBCs), professional grade control and data acquisition systems, as well as field-programmable gate arrays (FPGAs). In particular, MCBs and SBCs provide good value for money. The application areas for electronic modules in chemistry research include construction of simple detection systems based on spectrophotometry and spectrofluorometry principles, customizing laboratory devices for automation of common laboratory practices, control of reaction systems (batch- and flow-based), extraction systems, chromatographic and electrophoretic systems, microfluidic systems (classical and nonclassical), custom-built polymerase chain reaction devices, gas-phase analyte detection systems, chemical robots and drones, construction of FPGA-based imaging systems, and the Internet-of-Chemical-Things. The technology is easy to handle, and many chemists have managed to train themselves in its implementation. The only major obstacle in its implementation is probably one's imagination.

Liquid Marbles as Miniature Reactors for Chemical and Biological Applications

The need for miniaturised reaction systems has led to the development of various microreactor platforms, such as droplet-based microreactors. However, these microreactors possess inherent drawbacks, such as rapid evaporation and difficult handling, that limit their use in practical applications. Liquid marbles are droplets covered with hydrophobic particles and are a potential platform that can overcome the weaknesses of bare droplets. The coating particles completely isolate the interior liquids from the surrounding environment, thus conveniently encapsulating the reactions. Great efforts have been made over the past decade to demonstrate the feasibility of liquid marble-based microreactors for chemical and biological applications. This review systemically summarises state-of-the-art implementations of liquid marbles as microreactors. This paper also discusses the various aspects of liquid marble-based microreactors, such as the formation, manipulation, and future perspectives.

Rapid In Situ Photoimmobilization of a Planar Droplet Array for Digital PCR

Digital PCR (dPCR) is a powerful technique capable of absolute quantification of nucleic acids with good accuracy. Droplet-based dPCR (ddPCR), among others, is one of the most important dPCR techniques. However, the surface tension-controlled droplets may suffer from fusion/fission due to the vigorous temperature change in PCR thermal cycling. Besides, the free movement of droplets makes them unsuitable for real-time fluorescence monitoring. In this paper, we first developed a photoimmobilized planar droplet array (PIPDA) by using a photocurable polyurethane as the continuous oil phase. It is found that uniform water-in-oil droplets of various sizes can be readily generated, and more importantly, the oil phase can be rapidly solidified in just a few seconds upon exposure to UV irradiation. This process will leave the droplets immobilized in the accommodation chamber as a stable planar array and, thus, effectively prevent the movement, coalescence, and breakup of droplets. In addition, a novel multilayered chip design has been proposed, which can thoroughly overcome the evaporation issue that commonly exists in polydimethylsiloxane (PDMS)-based dPCR chips. With these two innovations, the ddPCR experiment could be performed in a robust manner, and shows a promising potential in the development of real-time ddPCR technique. These features may therefore enable the wide application of PIPDA-based ddPCR in various fields.

Preparation of Biocompatible Liquid Marbles Stabilized by Food-Grade Stearate Microparticle for Aerobic Bacteria Cultivation

Liquid marble (LM), a non-stick drop coated with micro- or nano-scale particles, has great potential in a wide range of applications. LMs have an advantageous feature in which gas or vapor can freely transport through their particle shell; therefore, it makes them an ideal candidate to be utilized as microbioreactor containing aerobic microorganisms. In this study, safer and more biocompatible LMs were successfully prepared using a food-grade calcium stearate microparticle as a stabilizer. As the volume of core liquid increased, the height of LM increased and reached a constant value, as a similar trend has been reported in conventional LMs. The drying rate curve of the LMs confirmed that the LMs have a similar pattern with the drying of typical wet powders. The drying rate depended on the salt species in the core solution and the environmental humidity. For instance, in the case of MgCl₂, by changing humidity from 40 to 80% RH, the lifetime of LMs (time in which the LM dried completely) was increased to about 900 min. This is nearly three times longer than those have no salt and at 40% RH. Model aerobic bacteria Bacillus subtilis has actively proliferated inside the LM during 24-h incubation. Comparing with the test tube cultivations under O₂-rich stationary or O₂ rich-shaken conditions, the cultivation in the LM system showed a higher proliferation than the test tube systems. As a conclusion, we demonstrated that the calcium stearate LM system would be an ideal candidate for safer and easily available microbioreactor containing aerobic bacteria.

Core-Shell Beads Made by Composite Liquid Marble Technology as A Versatile Microreactor for Polymerase Chain Reaction

Over the last three decades, the protocols and procedures of the DNA amplification technique, polymerase chain reaction (PCR), have been optimized and well developed. However, there have been no significant innovations in processes for sample dispersion for PCR that have reduced the amount of single-use or unrecyclable plastic waste produced. To address the issue of plastic waste, this paper reports the synthesis and successful use of a core-shell bead microreactor using photopolymerization of a composite liquid marble as a dispersion process. This platform uses the core-shell bead as a simple and effective sample dispersion medium that significantly reduces plastic waste generated compared to conventional PCR processes. Other improvements over conventional PCR processes of the novel dispersion platform include increasing the throughput capability, enhancing the performance and portability of the thermal cycler, and allowing for the contamination-free storage of samples after thermal cycling.

Contactless sensing of liquid marbles for detection, characterisation & computing

Liquid marbles (LMs) are of growing interest in many fields, including microfluidics, microreactors, sensors, and signal carriers. The generation of LMs is generally performed manually, although there has recently been a burst of publications involving 'automatic marble makers'. The characteristics of a LM is dependent on many things, including how it is generated, it is therefore important to be able to characterise LMs once made. Here is presented a novel contactless LM sensor, constructed on a PCB board with a comb-like structure of 36 interlacing electrical traces, 100 μm wide and 100 μm apart. This cheap, scalable, and easy to use sensor exploits the inherent impedance (comprised of the electrical resistance, capacitive reactance and inductive reactance) of different LMs. With it, parameters of a LM can be easily determined, without interfering with the LM. These parameters are (1) particle size of the LM coating, (2) the concentration of a NaCl solution used as the LM core, and (3) the volume of the LM. Additionally, due to the comb-like nature of the sensor, the accurate positioning (down to the inter-trace spacing) of the LM can be ascertained. The new sensor has been shown to work under both static and dynamic (mobile) conditions. The capacitance of a LM was recorded to be 0.10 pF, which compares well with the calculated value of 0.12 pF.

Microfluidic Array Chip for Parallel Detection of Waterborne Bacteria

The polymerase chain reaction (PCR) is a robust technique used to make multiple copies of a segment of DNA. However, the available PCR platforms require elaborate and time-consuming operations or costly instruments, hindering their application. Herein, we introduce a sandwiched glass-polydimethylsiloxane (PDMS)-glass microchip containing an array of reactors for the real-time PCR-based detection of multiple waterborne bacteria. The PCR solution was loaded into the array of reactors in a single step utilising capillary filling, eliminating the need for pumps, valves, and liquid handling instruments. Issues of generating and trapping bubbles during the loading chip step were addressed by creating smooth internal reactor surfaces. Triton X-100 was used to enhance PCR compatibility in the chip by minimising the nonspecific adsorption of enzymes. A custom-made real-time PCR instrument was also fabricated to provide thermal cycling to the array chip. The microfluidic device was successfully demonstrated for microbial faecal source tracking (MST) in water.