An integrated digital microfluidic lab-on-a-chip for clinical diagnostics on human physiological fluids

Gallium-based liquid metals as smart responsive materials: Morphological forms and stimuli characterization

Gallium-based liquid metals (GaLMs) have garnered monumental attention from the scientific community due to their diverse actuation characteristics. These metals possess remarkable characteristics, including high surface tension, excellent electrical and thermal conductivity, phase transformation behaviour, minimal viscosity and vapour pressure, lack of toxicity, and biocompatibility. In addition, GaLMs have melting points that are either lower or near room temperature, making them incredibly beneficial when compared to solid metals since they can be easily deformed. Thus, there has been significant progress in developing multifunctional devices using GaLMs, including bio-devices, flexible and self-healing circuits, and actuators. Despite numerous reports on these liquid metals (LMs), there is an urgent need for consolidated and coherent literature regarding their actuation principles linked to the targeted application. This will ensure that the reader gets the flavour of physics behind the actuation mechanism and how it can be utilized in diverse fields. Moreover, the actuation mechanism has been scattered in the literature, and thus, the primary motive of this review is to provide a one-stop solution for the actuation mechanism and the associated dynamics while directing the readers to specialized literature. Thus, addressing this issue, we thoroughly examine and present a detailed account of the actuation mechanisms of GaLMs while highlighting the science behind them. We also discuss the various morphologies of GaLMs and their crucial physical characteristics which decide their targeted application. Furthermore, we also delve into commonly held beliefs about GaLMs in the literature, such as their toxicity and antibacterial properties, to offer readers a more accurate understanding. Finally, we have explored several key unanswered aspects of the LM that should be explored in future research. The core strength of this review lies in its simplistic approach in offering a starting point for researchers venturing this innovative field, while we make use of existing literature to develop a comprehensive understanding.

Drop-On-Demand Microdroplet Generation under Charge Injection by Corona Discharge

In printing, microreactors, and bioassays, the precise control of micrometer-scale droplet generation is essential but challenging, often restricted by the equipment and nozzles used in traditional methods. We introduce a needle-plate electrode corona discharge technique that injects charges into an oil layer, enabling the precise manipulation of droplet polarization and splitting. This method allows for meticulous adjustment of microdroplet formation regarding location, size, and quantity by modulating the discharge voltage, discharge time, and electrode positioning. It enables the immediate initiation and cessation of droplet production, thereby facilitating on-demand droplet generation. Our study on the voltage-dependent droplet stretch coefficient shows that as the voltage increases, the droplets transition from controlled splitting to regular Taylor cone-like ejections, eventually reaching the Rayleigh limit and fully breaking apart. These advancements significantly improve microfluidic droplet manipulation, offering considerable benefits for applications in targeted drug delivery, rapid disease diagnostics, and precise environmental monitoring.

Laser-induced graphene-based digital microfluidics (gDMF): a versatile platform with sub-one-dollar cost

Digital microfluidics (DMF), is an emerging liquid-handling technology, that shows promising potential in various biological and biomedical applications. However, the fabrication of conventional DMF chips is usually complicated, time-consuming, and costly, which seriously limits their widespread applications, especially in the field of point-of-care testing (POCT). Although the paper- or film-based DMF devices can offer an inexpensive and convenient alternative, they still suffer from the planar addressing structure, and thus, limited electrode quantity. To address the above issues, we herein describe the development of a laser-induced graphene (LIG) based digital microfluidics chip (gDMF). It can be easily made (within 10 min, under ambient conditions, without the need of costly materials or cleanroom-based techniques) by a computer-controlled laser scribing process. Moreover, both the planar addressing DMF (pgDMF) and vertical addressing DMF (vgDMF) can be readily achieved, with the latter offering the potential of a higher electrode density. Also, both of them have an impressively low cost of below $1 ($0.85 for pgDMF, $0.59 for vgDMF). Experiments also show that both pgDMF and vgDMF have a comparable performance to conventional DMF devices, with a colorimetric assay performed on vgDMF as proof-of-concept to demonstrate their applicability. Given the simple fabrication, low cost, full function, and the ease of modifying the electrode pattern for various applications, it is reasonably expect that the proposed gDMF may offer an alternative choice as a versatile platform for POCT.

Electric manipulation on deformation of ionic ferrofluid sessile droplets

Active electric-driven droplet manipulation in digital microfluidics constitutes a promising domain owing to the unique and programmable wettability inherent in sessile ionic droplets. The coupling between the electric field and flow field enables precise control over wetting characteristics and droplet morphology. This study delves into the deformation phenomena of ionic sessile ferrofluid droplets in ambient air induced by uniform electric fields. Under the assumption of a pinned mode throughout the process, the deformation is characterized by variations in droplet height and contact angle in response to the applied electric field intensity. A numerical model is formulated to simulate the deformation dynamics of ferrofluid droplets, employing the phase field method for tracking droplet deformation. The fidelity of the numerical outcomes is assessed through the validation process, involving a comparison of droplet geometric deformations with corresponding experimental results. The impact of the electric field on the deformation of dielectric droplets is modulated by parameters such as electric field strength and droplet size. Through meticulously designed experiments, the substantial influence of both field strength and droplet size is empirically verified, elucidating the behavior of ionic sessile droplets. Considering the interplay of electric force, viscous force, and interfacial tension, the heightened field intensity is observed to effectively reduce the contact angle, augment droplet height, and intensify internal droplet flow. Under varying electric field conditions, droplets assume diverse shapes, presenting a versatile approach for microfluidic operations. The outcomes of this research hold significant guiding implications for microfluidic manipulation, droplet handling, and sensing applications.

Soft Epidermal Paperfluidics for Sweat Analysis by Ratiometric Raman Spectroscopy

The expanding interest in digital biomarker analysis focused on non-invasive human bodily fluids, such as sweat, highlights the pressing need for easily manufactured and highly efficient soft lab-on-skin solutions. Here, we report, for the first time, the integration of microfluidic paper-based devices (μPAD) and non-enhanced Raman-scattering-enabled optical biochemical sensing (Raman biosensing). Their integration merges the enormous benefits of μPAD, with high potential for commercialization and use in resource-limited settings, with biorecognition-element-free (but highly selective) optical Raman biosensing. The introduced thin (0.36 mm), ultra-lightweight (0.19 g), and compact footprint (3 cm2) opto-paperfluidic sweat patch is flexible, stretchable, and conforms, irritation-free, to hairless or minimally haired body regions to enable swift sweat collection. As a great advantage, this new bio-chemical sensory system excels through its absence of onboard biorecognition elements (bioreceptor-free) and omission of plasmonic nanomaterials. The proposed easy fabrication process is adaptable to mass production by following a fully sustainable and cost-effective process utilizing only basic tools by avoiding typically employed printing or laser patterning. Furthermore, efficient collection and transportation of precise sweat volumes, driven exclusively by the wicking properties of porous materials, shows high efficiency in liquid transportation and reduces biosensing latency by a factor of 5 compared to state-of-the-art epidermal microfluidics. The proposed unit enables electronic chip-free and imaging-less visual sweat loss quantification as well as optical biochemical analysis when coupled with Raman spectroscopy. We investigated the multimodal quantification of sweat urea and lactate levels ex vivo (with syntactic sweat including +30 sweat analytes on porcine skin) and achieved a linear dynamic range from 0 to 100 mmol/L during fully dynamic continuous flow characterization.

Visualization of the Dynamics of Photoinduced Crawling Motion of 4-(Methylamino)Azobenzene Crystals via Diffracted X-ray Tracking

The photoinduced crawling motion of crystals is a continuous motion that azobenzene molecular crystals exhibit under light irradiation. Such motion enables object manipulation at the microscale with a simple setup of fixed LED light sources. Transportation of nano-/micromaterials using photoinduced crawling motion has recently been reported. However, the details of the motion mechanism have not been revealed so far. Herein, we report visualization of the dynamics of fine particles in 4-(methylamino)azobenzene (4-MAAB) crystals under light irradiation via diffracted X-ray tracking (DXT). Continuously repeated melting and recrystallization of 4-MAAB crystals under light irradiation results in the flow of liquid 4-MAAB. Zinc oxide (ZnO) particles were introduced inside the 4-MAAB crystals to detect diffracted X-rays. The ZnO particles rotate with the flow of liquid 4-MAAB. By using white X-rays with a wide energy width, the rotation of each zinc oxide nanoparticle was detected as the movement of a bright spot in the X-ray diffraction pattern. It was clearly shown that the ZnO particles rotated increasingly as the irradiation light intensity increased. Furthermore, we also found anisotropy in the rotational direction of ZnO particles that occurred during the crawling motion of 4-MAAB crystals. It has become clear that the flow perpendicular to the supporting film of 4-MAAB crystals is enhanced inside the crystal during the crawling motion. DXT provides a unique means to elucidate the mechanism of photoinduced crawling motion of crystals.

Saliva Analysis Based on Microfluidics: Focusing the Wide Spectrum of Target Analyte

Saliva is one of the most critical human body fluids that can reflect the state of the human body. The detection of saliva is of great significance for disease diagnosis and health monitoring. Microfluidics, characterized by microscale size and high integration, is an ideal platform for the development of rapid and low-cost disease diagnostic techniques and devices. Microfluidic-based saliva testing methods have aroused considerable interest due to the increasing need for noninvasive testing and frequent or long-term testing. This review briefly described the significance of saliva analysis and generally classified the targets in saliva detection into pathogenic microorganisms, inorganic substances, and organic substances. By using this classification as a benchmark, the state-of-the-art research results on microfluidic detection of various substances in saliva were summarized. This work also put forward the challenges and future development directions of microfluidic detection methods for saliva.

The Physics and Manipulation of Dean Vortices in Single- and Two-Phase Flow in Curved Microchannels: A Review

Microchannels with curved geometries have been employed for many applications in microfluidic devices in the past decades. The Dean vortices generated in such geometries have been manipulated using different methods to enhance the performance of devices in applications such as mixing, droplet sorting, and particle/cell separation. Understanding the effect of the manipulation method on the Dean vortices in different geometries can provide crucial information to be employed in designing high-efficiency microfluidic devices. In this review, the physics of Dean vortices and the affecting parameters are summarized. Various Dean number calculation methods are collected and represented to minimize the misinterpretation of published information due to the lack of a unified defining formula for the Dean dimensionless number. Consequently, all Dean number values reported in the references are recalculated to the most common method to facilitate comprehension of the phenomena. Based on the converted information gathered from previous numerical and experimental studies, it is concluded that the length of the channel and the channel pathline, e.g., spiral, serpentine, or helix, also affect the flow state. This review also provides a detailed summery on the effect of other geometric parameters, such as cross-section shape, aspect ratio, and radius of curvature, on the Dean vortices' number and arrangement. Finally, considering the importance of droplet microfluidics, the effect of curved geometry on the shape, trajectory, and internal flow organization of the droplets passing through a curved channel has been reviewed.

Droplet Rolling Transport on Hydrophobic Surfaces Under Rotating Electric Fields: A Molecular Dynamics Study

Driving droplets by electric fields is usually achieved by controlling their wettability, and realizing a flexible operation requires complex electrode designs. Here, we show by molecular dynamics methods the droplet transport on hydrophobic surfaces in a rolling manner under a rotating electric field, which provides a simpler and promising way to manipulate droplets. The droplet internal velocity field shows the rolling mode. When the contact angle on the solid surface is 144.4°, the droplet can be transported steadily at a high velocity under the rotating electric field (E = 0.5 V nm-1, ω = π/20 ps-1). The droplet center-of-mass velocities and trajectories, deformation degrees, dynamic contact angles, and surface energies were analyzed regarding the electric field strength and rotational angular frequency. Droplet transport with a complex trajectory on a two-dimensional surface is achieved by setting the electric field, which reflects the programmability of the driving method. Nonuniform wettability stripes can assist in controlling droplet trajectories. The droplet transport on the three-dimensional surface is studied, and the critical conditions for the droplet passing through the surface corners and the motion law on the curved surface are obtained. Droplet coalescence has been achieved by surface designs.

Light-manipulated binary droplet transport on a high-energy surface

Flexible and precise manipulation of droplet transport is of significance for scientific and engineering applications, but real-time and on-demand droplet manipulation remains a challenge. Herein, we report a strategy using light for the outstanding manipulation of binary droplet motion on a high-energy surface and reveal the underlying mechanism. Upon irradiation to a substrate by a focused light beam, the substrate can provide a localized heating source via photothermal conversion, and a binary droplet can be flexibly transported on a high-energy surface with free contact-line pinning, exhibiting light-propelled droplet transport. We theoretically showed that the surface tension gradient across the droplet interface resulting from the localized photothermal effect is responsible for actuating droplet transport. Remarkably, the high reconfigurability and flexibility of light allowed for binary droplet transport with dynamically tunable velocity and direction as well as arbitrary trajectory assisted by 2D channels on a high-energy surface. Complex droplet transportation, controllable droplet coalescence, and anti-gravity motion were realized. The promising applicability of this light-fueled droplet platform was also demonstrated by directional transport of biosample droplets containing DNA molecules and cells, as well as successional microreactions.

Measurement of red blood cell deformability during morphological changes using rotating-glass-plate-based scanning optical tweezers

It is important to measure the deformability of red blood cells (RBCs) before transfusion, which is a key factor in the gas transport ability of RBCs and changes during storage of RBCs in vitro. Moreover, the morphology of RBCs also changes during storage. It is proposed that the change in morphology is related to the change in deformability. However, the efficiency of typical methods that use particles as handles is low, especially in the deformability measurement of echinocyte and spherocytes. Therefore, the deformability of RBCs with different morphologies is hard to be measured and compared in the same experiment. In this study, we developed a cost-effective and efficient rotating-glass-plate-based scanning optical tweezers device for the measurement of deformability of RBCs. The performance of this device was evaluated, and the deformability of three types of RBCs was measured using this device. Our results clearly show that the change of erythrocyte morphology from discocyte to echinocyte and spherocyte during storage in vitro is accompanied by a decrease in deformability.

Flexible Stacked Perovskite Photodetectors for High-Efficiency Multicolor Fluorescence Detection

A flexible, multicolor detector based on stacked perovskite layers with graded band gaps was presented. Different perovskite layers generate a series of photocurrents corresponding to light intensities at different wavelengths. Experimentally, the flexible detector demonstrated acceptable long-term stability and temperature stability in the bending state. To demonstrate the advantages of the flexible multicolor detector in biological applications, a tubular-shaped multicolor fluorescence detector that embraces the sample cell was constructed. As a result, the detection limits of three kinds of CdTe quantum dots (QDs) with central wavelengths of 545, 625, and 730 nm were 0.52, 0.85, and 0.43 nM, respectively, which was significantly improved by more than 10 times compared to those of planar detectors. Additionally, the detector was able to detect three kinds of QDs simultaneously in a mixed solution, and the relative deviation was smaller than 10% compared to the preset concentration. These results demonstrate that the flexible stacked perovskite detector and the tubular-shaped detection configuration hold promise for the simultaneous fluorescent detection of multiple biomolecules.

Development and Evaluation of a Low-Cost Triglyceride Quantification Enzymatic Biosensor Using an Arduino-Based Microfluidic System

Overweight and obesity promote diabetes and heart disease onset. Triglycerides are key biomarkers for cardiovascular disease, strokes, and other health issues. Scientists have devised methods and instruments for the detection of these molecules in liquid samples. In this study, an enzymatic biosensor was developed using an Arduino-based microfluidic platform, wherein a lipolytic enzyme was immobilized on an ethylene-vinyl acetate polymer through physical adsorption. This low-cost optical biosensor employed a spectrophotometric transducer and was assessed in liquid samples to indirectly detect triglycerides and fatty acids using p-nitrophenol as an indicator. The average triglyceride level detected in the conducted experiments was 47.727 mg/dL. The biosensor exhibited a percentage of recovery of 81.12% and a variation coefficient of 0.791%. Furthermore, the biosensor demonstrated the ability to detect triglyceride levels without the need for sample dilution, ranging from 7.6741 mg/dL to 58.835 mg/dL. This study successfully developed an efficient and affordable enzymatic biosensor prototype for triglyceride and fatty acid detection. The lipolytic enzyme immobilization on the polymer substrate provided a stable and reproducible detection system, rendering this biosensor an exciting option for the detection of these molecules.

Microfluidic platform using focused ultrasound passing through hydrophobic meshes with jump availability

Applications in chemistry, biology, medicine, and engineering require the large-scale manipulation of a wide range of chemicals, samples, and specimens. To achieve maximum efficiency, parallel control of microlitre droplets using automated techniques is essential. Electrowetting-on-dielectric (EWOD), which manipulates droplets using the imbalance of wetting on a substrate, is the most widely employed method. However, EWOD is limited in its capability to make droplets detach from the substrate (jumping), which hinders throughput and device integration. Here, we propose a novel microfluidic system based on focused ultrasound passing through a hydrophobic mesh with droplets resting on top. A phased array dynamically creates foci to manipulate droplets of up to 300 μL. This platform offers a jump height of up to 10 cm, a 27-fold improvement over conventional EWOD systems. In addition, droplets can be merged or split by pushing them against a hydrophobic knife. We demonstrate Suzuki-Miyaura cross-coupling using our platform, showing its potential for a wide range of chemical experiments. Biofouling in our system was lower than in conventional EWOD, demonstrating its high suitability for biological experiments. Focused ultrasound allows the manipulation of both solid and liquid targets. Our platform provides a foundation for the advancement of micro-robotics, additive manufacturing, and laboratory automation.

Research progress of electrode shapes in EWOD-based digital microfluidics

Digital microfluidics (DMF) is an innovative technology used for precise manipulation of liquid droplets. This technology has garnered significant attention in both industrial applications and scientific research due to its unique advantages. Among the key components of DMF, the driving electrode plays a role in facilitating droplet generation, transportation, splitting, merging, and mixing. This comprehensive review aims to present an in-depth understanding of the working principle of DMF particularly focusing on the Electrowetting On Dielectric (EWOD) method. Furthermore, it examines the impact of driving electrodes with varying geometries on droplet manipulation. By analyzing and comparing their characteristics, this review offers valuable insights and a fresh perspective on the design and application of driving electrodes in DMF based on the EWOD approach. Lastly, an assessment of the development trend and potential applications of DMF concludes the review, providing an outlook for future prospects in the field.

Integrated Digital Microfluidics NMR Spectroscopy: A Key Step toward Automated In Vivo Metabolomics

Toxicity testing is currently undergoing a paradigm shift from examining apical end points such as death, to monitoring sub-lethal toxicity in vivo. In vivo nuclear magnetic resonance (NMR) spectroscopy is a key platform in this endeavor. A proof-of-principle study is presented which directly interfaces NMR with digital microfluidics (DMF). DMF is a "lab on a chip" method allowing for the movement, mixing, splitting, and dispensing of μL-sized droplets. The goal is for DMF to supply oxygenated water to keep the organisms alive while NMR detects metabolomic changes. Here, both vertical and horizontal NMR coil configurations are compared. While a horizontal configuration is ideal for DMF, NMR performance was found to be sub-par and instead, a vertical-optimized single-sided stripline showed most promise. In this configuration, three organisms were monitored in vivo using ¹H-¹³C 2D NMR. Without support from DMF droplet exchange, the organisms quickly showed signs of anoxic stress; however, with droplet exchange, this was completely suppressed. The results demonstrate that DMF can be used to maintain living organisms and holds potential for automated exposures in future. However, due to numerous limitations of vertically orientated DMF, along with space limitations in standard bore NMR spectrometers, we recommend future development be performed using a horizontal (MRI style) magnet which would eliminate practically all the drawbacks identified here.

Programmable UV-Curable Resin by Dielectric Force

In this study, UV-curable resin was formed into different patterns through the programmable control of dielectric force. The dielectric force is mainly generated by the dielectric chip formed by the interdigitated electrodes. This study observed that of the control factors affecting the size of the UV resin driving area, current played an important role. We maintained the same voltage-controlled condition, changing the current from 0.1 A to 0.5 A as 0.1 A intervals. The area of droplets was significantly different at each current condition. On the other hand, we maintained the same current condition, and changed the voltage from 100 V to 300 V at 50 V intervals. The area of droplets for each voltage condition was not obviously different. The applied frequency of the AC (Alternating Current) electric field increased from 10 kHz to 50 kHz. After driving the UV resin, the pattern line width of the UV resin could be finely controlled from 224 um to 137 um. In order to form a specific pattern, controlling the current and frequency could achieved a more accurate shape. In this article, UV resin with different patterns was formed through the action of this dielectric force, and after UV curing, tiny structural parts could be successfully demonstrated.

Integration of Impedimetric Sensors for In Situ Electrochemical Impedance Spectroscopy in Free-Flow Electrophoresis Applications in Lab-on-Chip Systems

Miniaturization and integration of chemical reactions into fluidic systems in combination with product purification or buffer exchange can reduce the amount of solvents and reactants required while increasing synthesis efficiency. A critical step is the regulation of flow rates to realize optimal synthesis conditions and high purification rates, so real-time, label-free monitoring is required in methods such as free-flow electrophoresis. Optical detection methods are widely used, but they often have complex excitation and detection setups that are disadvantageous for point-of-care applications. The method we have chosen is electrochemical impedance spectroscopy for detecting charged compounds in aqueous buffers with low ionic strength. Propranolol was selected for proof of concept and was separated from the organic solvent and the precursor oxirane by free-flow electrophoresis. For this purpose, electrode structures were fabricated in microfluidic channels by photolithographic lift-off technique and optimized in terms of positioning, electrode size and distance for sensitive detection, and quantification of propranolol in the nanomolar range. It is also noteworthy that the organic solvent dimethyl sulfoxide (DMSO) could be detected and quantified by an increased impedance magnitude. Subsequently, the optimized interdigital electrode structures were integrated into the outlet channels of the electrophoretic separation chamber to monitor the various outgoing fluidic streams and provide in-line control of the fluidic flows for the purification step. In conclusion, we can provide a microfluidic chip to monitor the separation efficiency of a substance mixture during free-flow electrophoresis without the need of complex analytical techniques using electrochemical impedance spectroscopy.

Water-in-water droplet microfluidics: A design manual

Droplet microfluidics is utilized in a wide range of applications in biomedicine and biology. Applications include rapid biochemical analysis, materials generation, biochemical assays, and point-of-care medicine. The integration of aqueous two-phase systems (ATPSs) into droplet microfluidic platforms has potential utility in oil-free biological and biomedical applications, namely, reducing cytotoxicity and preserving the native form and function of costly biomolecular reagents. In this review, we present a design manual for the chemist, biologist, and engineer to design experiments in the context of their biological applications using all-in-water droplet microfluidic systems. We describe the studies achievable using these systems and the corresponding fabrication and stabilization methods. With this information, readers may apply the fundamental principles and recent advancements in ATPS droplet microfluidics to their research. Finally, we propose a development roadmap of opportunities to utilize ATPS droplet microfluidics in applications that remain underexplored.

Recent Advances in Biosensor Technologies for Point-of-Care Urinalysis

Human urine samples are non-invasive, readily available, and contain several components that can provide useful indicators of the health status of patients. Hence, urine is a desirable and important template to aid in the diagnosis of common clinical conditions. Conventional methods such as dipstick tests, urine culture, and urine microscopy are commonly used for urinalysis. Among them, the dipstick test is undoubtedly the most popular owing to its ease of use, low cost, and quick response. Despite these advantages, the dipstick test has limitations in terms of sensitivity, selectivity, reusability, and quantitative evaluation of diseases. Various biosensor technologies give it the potential for being developed into point-of-care (POC) applications by overcoming these limitations of the dipstick test. Here, we present a review of the biosensor technologies available to identify urine-based biomarkers that are typically detected by the dipstick test and discuss the present limitations and challenges that future development for their translation into POC applications for urinalysis.

Numerical Analysis of Mixing Performance in an Electroosmotic Micromixer with Cosine Channel Walls

Micromixers have significant potential in the field of chemical synthesis and biological pharmaceuticals, etc. In this study, the design and numerical simulations of a passive micromixer and a novel active electroosmotic micromixer by assembling electrode pairs were both presented with a cosine channel wall. The finite element method (FEM) coupled with Multiphysics modeling was used. To propose an efficient micromixer structure, firstly, different geometrical parameters such as amplitude-to-wavelength ratio (a/c) and mixing units (N) in the steady state without an electric field were investigated. This paper aims to seek a high-quality mixing solution. Therefore, based on the optimization of the above parameters of the passive micromixer, a new type of electroosmotic micromixer with an AC electric field was proposed. The results show that the vortices generated by electroosmosis can effectively induce fluid mixing. The effects of key parameters such as the Reynolds number, the number of electrode pairs, phase shift, voltage, and electrode frequency on the mixing performance were specifically discussed through numerical analysis. The mixing efficiency of the electroosmotic micromixer is quantitatively analyzed, which can be achieved at 96%. The proposed micromixer has a simple structure that can obtain a fast response and high mixing index.

A Novel Step-T-Junction Microchannel for the Cell Encapsulation in Monodisperse Alginate-Gelatin Microspheres of Varying Mechanical Properties at High Throughput

Cell encapsulation has been widely employed in cell therapy, characterization, and analysis, as well as many other biomedical applications. While droplet-based microfluidic technology is advantageous in cell microencapsulation because of its modularity, controllability, mild conditions, and easy operation when compared to other state-of-art methods, it faces the dilemma between high throughput and monodispersity of generated cell-laden microdroplets. In addition, the lack of a biocompatible method of de-emulsification transferring cell-laden hydrogel from cytotoxic oil phase into cell culture medium also hurtles the practical application of microfluidic technology. Here, a novel step-T-junction microchannel was employed to encapsulate cells into monodisperse microspheres at the high-throughput jetting regime. An alginate–gelatin co-polymer system was employed to enable the microfluidic-based fabrication of cell-laden microgels with mild cross-linking conditions and great biocompatibility, notably for the process of de-emulsification. The mechanical properties of alginate-gelatin hydrogel, e.g., stiffness, stress–relaxation, and viscoelasticity, are fully adjustable in offering a 3D biomechanical microenvironment that is optimal for the specific encapsulated cell type. Finally, the encapsulation of HepG2 cells into monodisperse alginate–gelatin microgels with the novel microfluidic system and the subsequent cultivation proved the maintenance of the long-term viability, proliferation, and functionalities of encapsulated cells, indicating the promising potential of the as-designed system in tissue engineering and regenerative medicine.

MEDA Based Biochips: Detection, Prevention and Rectification Techniques for Cyberphysical Attacks

Recent advances of microelectrode-dot-array (MEDA) based Biochips have revolutionized the application of Lab-on-chip devices. New techniques for MEDA based biochips confide on the concepts on computer-aided design automation and cyberphysical integration to provide ease of use, higher throughput and reliability. One of the major security concerns in MEDA based biochips is actuation tempering attacks targeted to change control sequence daisy chain input resulting in incorrect bioassays. In this paper, we attempted to identify different types of actuation tampering attacks specific to MEDA based biochips. We proposed one technique to detect errors in order to secure the biochips against actuation tempering attacks. This proposed technique is able to monitor such malicious operations and can stall it under any abnormality in operation. Our analysis proves that the proposed method is able to detect errors accurately and proves that this technique is naturally implemented in MEDA.

Application of Micro/Nanoporous Fluoropolymers with Reduced Bioadhesion in Digital Microfluidics

Digital microfluidics (DMF) is a versatile platform for conducting a variety of biological and chemical assays. The most commonly used set-up for the actuation of microliter droplets is electrowetting on dielectric (EWOD), where the liquid is moved by an electrostatic force on a dielectric layer. Superhydrophobic materials are promising materials for dielectric layers, especially since the minimum contact between droplet and surface is key for low adhesion of biomolecules, as it causes droplet pinning and cross contamination. However, superhydrophobic surfaces show limitations, such as full wetting transition between Cassie and Wenzel under applied voltage, expensive and complex fabrication and difficult integration into already existing devices. Here we present Fluoropor, a superhydrophobic fluorinated polymer foam with pores on the micro/nanoscale as a dielectric layer in DMF. Fluoropor shows stable wetting properties with no significant changes in the wetting behavior, or full wetting transition, until potentials of 400 V. Furthermore, Fluoropor shows low attachment of biomolecules to the surface upon droplet movement. Due to its simple fabrication process, its resistance to adhesion of biomolecules and the fact it is capable of being integrated and exchanged as thin films into commercial DMF devices, Fluoropor is a promising material for wide application in DMF.

Technique Evolutions for Microorganism Detection in Complex Samples: A Review

Rapid detection of microorganisms is a major challenge in the medical and industrial sectors. In a pharmaceutical laboratory, contamination of medical products may lead to severe health risks for patients, such as sepsis. In the specific case of advanced therapy medicinal products, contamination must be detected as early as possible to avoid late production stop and unnecessary costs. Unfortunately, the conventional methods used to detect microorganisms are based on time-consuming and labor-intensive approaches. Therefore, it is important to find new tools to detect microorganisms in a shorter time frame. This review sums up the current methods and represents the evolution in techniques for microorganism detection. First, there is a focus on promising ligands, such as aptamers and antimicrobial peptides, cheaper to produce and with a broader spectrum of detection. Then, we describe methods achieving low limits of detection, thanks to Raman spectroscopy or precise handling of samples through microfluids devices. The last part is dedicated to techniques in real-time, such as surface plasmon resonance, preventing the risk of contamination. Detection of pathogens in complex biological fluids remains a scientific challenge, and this review points toward important areas for future research.

Microfluidics for 3D Cell and Tissue Cultures: Microfabricative and Ethical Aspects Updates

The necessity to improve in vitro cell screening assays is becoming ever more important. Pharmaceutical companies, research laboratories and hospitals require technologies that help to speed up conventional screening and therapeutic procedures to produce more data in a short time in a realistic and reliable manner. The design of new solutions for test biomaterials and active molecules is one of the urgent problems of preclinical screening and the limited correlation between in vitro and in vivo data remains one of the major issues. The establishment of the most suitable in vitro model provides reduction in times, costs and, last but not least, in the number of animal experiments as recommended by the 3Rs (replace, reduce, refine) ethical guiding principles for testing involving animals. Although two-dimensional (2D) traditional cell screening assays are generally cheap and practical to manage, they have strong limitations, as cells, within the transition from the three-dimensional (3D) in vivo to the 2D in vitro growth conditions, do not properly mimic the real morphologies and physiology of their native tissues. In the study of human pathologies, especially, animal experiments provide data closer to what happens in the target organ or apparatus, but they imply slow and costly procedures and they generally do not fully accomplish the 3Rs recommendations, i.e., the amount of laboratory animals and the stress that they undergo must be minimized. Microfluidic devices seem to offer different advantages in relation to the mentioned issues. This review aims to describe the critical issues connected with the conventional cells culture and screening procedures, showing what happens in the in vivo physiological micro and nano environment also from a physical point of view. During the discussion, some microfluidic tools and their components are described to explain how these devices can circumvent the actual limitations described in the introduction.

Microfluidic manipulation by spiral hollow-fibre actuators

A microfluidic manipulation system that can sense a liquid and control its flow is highly desirable. However, conventional sensors and motors have difficulty fitting the limited space in microfluidic devices; moreover, fast sensing and actuation are required because of the fast liquid flow in the hollow fibre. In this study, fast torsional and tensile actuators were developed using hollow fibres employing spiral nonlinear stress, which can sense the fluid temperature and sort the fluid into the desired vessels. The fluid-driven actuation exhibited a highly increased response speed (27 times as fast as that of air-driven actuation) and increased power density (90 times that of an air-driven solid fibre actuator). A 0.5 K fluid temperature fluctuation produced a 20° rotation of the hollow fibre. These high performances originated from increments in both heat transfer and the average bias angle, which was understood through theoretical analysis. This work provides a new design strategy for intelligent microfluidics and inspiration for soft robots and smart devices for biological, optical, or magnetic applications.

Design of a microfluidic manipulation system that can sense a liquid and control its flow is challenging. Here, the authors demonstrate fast torsional and tensile actuators using hollow fibres employing spiral nonlinear stress which can sense the fluid temperature and sort the fluid into the desired vessels.

A Single Wavelength Mid-Infrared Photoacoustic Spectroscopy for Noninvasive Glucose Detection Using Machine Learning

According to the International Diabetes Federation, 530 million people worldwide have diabetes, with more than 6.7 million reported deaths in 2021. Monitoring blood glucose levels is essential for individuals with diabetes, and developing noninvasive monitors has been a long-standing aspiration in diabetes management. The ideal method for monitoring diabetes is to obtain the glucose concentration level with a fast, accurate, and pain-free measurement that does not require blood drawing or a surgical operation. Multiple noninvasive glucose detection techniques have been developed, including bio-impedance spectroscopy, electromagnetic sensing, and metabolic heat conformation. Nevertheless, reliability and consistency challenges were reported for these methods due to ambient temperature and environmental condition sensitivity. Among all the noninvasive glucose detection techniques, optical spectroscopy has rapidly advanced. A photoacoustic system has been developed using a single wavelength quantum cascade laser, lasing at a glucose fingerprint of 1080 cm-1 for noninvasive glucose monitoring. The system has been examined using artificial skin phantoms, covering the normal and hyperglycemia blood glucose ranges. The detection sensitivity of the system has been improved to ±25 mg/dL using a single wavelength for the entire range of blood glucose. Machine learning has been employed to detect glucose levels using photoacoustic spectroscopy in skin samples. Ensemble machine learning models have been developed to measure glucose concentration using classification techniques. The model has achieved a 90.4% prediction accuracy with 100% of the predicted data located in zones A and B of Clarke's error grid analysis. This finding fulfills the US Food and Drug Administration requirements for glucose monitors.

Microfluidics based point-of-care for disease diagnostics

Microfluidics platform is widely used for several basic biological to advanced biotechnological applications. It reduces the expenditure of reagent consumption by readily reducing the volume of the reaction system. It is being used for early diagnosis of diseases, detection of pathogens, cancer markers, high-throughput screening and many such applications. Currently, microfluidics and lab-on-chip is integrated together with sample preparation, extraction, analysis and detection of biomarkers for disease diagnosis. This technology offers low-cost, rapid, sensitive and paper-based lateral flow mode of detection which is user-friendly and scalable. In this chapter, we highlight recent developments in microfluidics platform for disease diagnosis.

A Monolithic 3D Printed Axisymmetric Co-Flow Single and Compound Emulsion Generator

We report a microfluidic droplet generator which can produce single and compound droplets using a 3D axisymmetric co-flow structure. The design considered for the fabrication of the device integrated a user-friendly and cost-effective 3D printing process. To verify the performance of the device, single and compound emulsions of deionized water and mineral oil were generated and their features such as size, generation frequency, and emulsion structures were successfully characterized. In addition, the generation of bio emulsions such as alginate and collagen aqueous droplets in mineral oil was demonstrated in this study. Overall, the monolithic 3D printed axisymmetric droplet generator could offer any user an accessible and easy-to-utilize device for the generation of single and compound emulsions.

Structural order of water molecules around polyrotaxane including PEG, α-cyclodextrin, and α-lipoic acid linker on gold surface by molecular dynamics simulations

In materials science, water plays an important part, especially at the molecular level. It shows various properties when sorbed onto surfaces of polymers. The structure of the molecular water ensemble in the vicinity of the polymers is under discussion. In this study, we used molecular dynamics methods to analyze the structure of water in the vicinity of the polymer polyrotaxane (PR), composed of α-cyclodextrins (α-CDs), a poly(ethylene glycol) (PEG) axial chain, and α-lipoic acid linkers, at various temperatures. The distribution of water around the functional groups, hydrogen bond network, and tetrahedral order were analyzed to classify the various types of water around the polymer. We found that the tetrahedral order of water had a strained relationship from the XES experiment. Four water regions were separated from each other in the vicinity of 1 to 5 Å around PR. The intermediate and non-freezing water were formed due to the interaction between water molecules and the functional groups, such as hydroxyl, ether, and ester.

Visible-light and near-infrared fluorescence and surface-enhanced Raman scattering point-of-care sensing and bio-imaging: a review

This review article deals with the concepts, principles and applications of visible-light and near-infrared (NIR) fluorescence and surface-enhanced Raman scattering (SERS) in in vitro point-of-care testing (POCT) and in vivo bio-imaging. It has discussed how to utilize the biological transparency windows to improve the penetration depth and signal-to-noise ratio, and how to use surface plasmon resonance (SPR) to amplify fluorescence and SERS signals. This article has highlighted some plasmonic fluorescence and SERS probes. It has also reviewed the design strategies of fluorescent and SERS sensors in the detection of metal ions, small molecules, proteins and nucleic acids. Particularly, it has provided perspectives on the integration of fluorescent and SERS sensors into microfluidic chips as lab-on-chips to realize point-of-care testing. It has also discussed the design of active microfluidic devices and non-paper- or paper-based lateral flow assays for in vitro diagnostics. In addition, this article has discussed the strategies to design in vivo NIR fluorescence and SERS bio-imaging platforms for monitoring physiological processes and disease progression in live cells and tissues. Moreover, it has highlighted the applications of POCT and bio-imaging in testing toxins, heavy metals, illicit drugs, cancers, traumatic brain injuries, and infectious diseases such as COVID-19, influenza, HIV and sepsis.

A Perfusion Model to Evaluate Response to Photodynamic Therapy in 3D Tumors

Numerous cancer models have been developed to investigate the effects of mechanical stress on the biology of cells. Here we describe a protocol to fabricate a perfusion model to culture 3-dimensional (3D) ovarian cancer nodules under constant flow. The modular design of this model allows for a wide range of treatment regimens and combinations, including PDT and chemotherapy. Finally, methods for a number of readouts are detailed, allowing researchers to investigate a variety of biological and cytotoxic parameters related to mechanical stress and therapeutic modalities.

Human Organs-on-Chips: A Review of the State-of-the-Art, Current Prospects, and Future Challenges

New emerging technologies, remarkably miniaturized 3D organ models and microfluidics, enable simulation of the real in vitro microenvironment ex vivo more closely. There are many fascinating features of innovative organ-on-a-chip (OOC) technology, including the possibility of integrating semipermeable and/or stretchable membranes, creating continuous perfusion of fluids into microchannels and chambers (while maintaining laminar flow regime), embedding microdevices like microsensors, microstimulators, micro heaters, or different cell lines, along with other 3D cell culture technologies. OOC systems are designed to imitate the structure and function of human organs, ranging from breathing lungs to beating hearts. This technology is expected to be able to revolutionize cell biology studies, personalized precision medicine, drug development process, and cancer diagnosis/treatment. OOC systems can significantly reduce the cost associated with tedious drug development processes and the risk of adverse drug reactions in the body, which makes drug screening more effective. The review mainly focus on presenting an overview of the several previously developed OOC systems accompanied by subjects relevant to pharmacy-, cancer-, and placenta-on-a-chip. The challenging issues and opportunities related to these systems are discussed, along with a future perspective for this technology.

Droplet Transportation through an Orifice on Electrode for Digital Microfluidics Modulations

A digital microfluidic modular interface (chip-to-chip interface) which possesses an electrode with an orifice to vertically transport core-shell droplets is presented. The electrodes were geometrically designed to promote droplet deformation and suspension. The droplets were then applied with an electrical potential for insertion into and passage through the orifice. The concepts were tested with three types of droplets at the volume of 0.75~1.5 μL, which is usually difficult to transfer through an orifice. The integration of electrowetting on dielectric (EWOD) with paper-based microfluidics was demonstrated: the droplet could be transported within 10 s. More importantly, most of the core droplet (~97%) was extracted and passed through with only minimal shell droplets accompanying it.

Colloidal Self-Assembly Approaches to Smart Nanostructured Materials

Colloidal self-assembly refers to a solution-processed assembly of nanometer-/micrometer-sized, well-dispersed particles into secondary structures, whose collective properties are controlled by not only nanoparticle property but also the superstructure symmetry, orientation, phase, and dimension. This combination of characteristics makes colloidal superstructures highly susceptible to remote stimuli or local environmental changes, representing a prominent platform for developing stimuli-responsive materials and smart devices. Chemists are achieving even more delicate control over their active responses to various practical stimuli, setting the stage ready for fully exploiting the potential of this unique set of materials. This review addresses the assembly of colloids into stimuli-responsive or smart nanostructured materials. We first delineate the colloidal self-assembly driven by forces of different length scales. A set of concepts and equations are outlined for controlling the colloidal crystal growth, appreciating the importance of particle connectivity in creating responsive superstructures. We then present working mechanisms and practical strategies for engineering smart colloidal assemblies. The concepts underpinning separation and connectivity control are systematically introduced, allowing active tuning and precise prediction of the colloidal crystal properties in response to external stimuli. Various exciting applications of these unique materials are summarized with a specific focus on the structure-property correlation in smart materials and functional devices. We conclude this review with a summary of existing challenges in colloidal self-assembly of smart materials and provide a perspective on their further advances to the next generation.

Beyond liquid biopsy: Toward non-invasive assays for distanced cancer diagnostics in pandemics

Liquid biopsy technologies have seen a significant improvement in the last decade, offering the possibility of reliable analysis and diagnosis from several biological fluids. The use of these technologies can overcome the limits of standard clinical methods, related to invasiveness and poor patient compliance. Along with this there are now mature examples of lab-on-chips (LOC) which are available and could be an emerging and breakthrough technology for the present and near-future clinical demands that provide sample treatment, reagent addition and analysis in a sample-in/answer-out approach. The possibility of combining non-invasive liquid biopsy and LOC technologies could greatly assist in the current need for minimizing exposure and transmission risks. The recent and ongoing pandemic outbreak of SARS-CoV-2, indeed, has heavily influenced all aspects of life worldwide. Ordinary tasks have been forced to switch from “in presence” to “distanced”, limiting the possibilities for a large number of activities in all fields of life outside of the home. Unfortunately, one of the settings in which physical distancing has assumed noteworthy consequences is the screening, diagnosis and follow-up of diseases.

In this review, we analyse biological fluids that are easily collected without the intervention of specialized personnel and the possibility that they may be used -or not-for innovative diagnostic assays. We consider their advantages and limitations, mainly due to stability and storage and their integration into Point-of-Care diagnostics, demonstrating that technologies in some cases are mature enough to meet current clinical needs.

Solution for Mass Production of High-Throughput Digital Microfluidic Chip Based on a-Si TFT with In-Pixel Boost Circuit

As one of the most popular research hotspot of lab-on-chip, digital microfluidic (DMF) technology based on the principle of electrowetting has unique advantages of high-precision, low cost and programmable control. However, due to the limitation of electrodes number, the throughput is hard to further upgrade. Therefore, active matrix electrowetting-on-dielectric (AM-EWOD) technology is a solution to acquire larger scale of driving electrodes. However, the process of manufacturing of AM-EWOD based on thin-film-transistor (TFT) is complex and expensive. Besides, the driving voltage of DMF chip is usually much higher than that of common display products.In this paper, a solution for mass production of AM-EWOD based on amorphous silicon (a-Si) is provided. Samples of 32 × 32 matrix AM-EWOD chips was designed and manufactured. A boost circuit was integrated into the pixel, which can raise the pixel voltage up by about 50%. Customized designed Printed Circuit Board (PCB) was used to supply the timing signals and driving voltage to make the motion of droplets programmable. The process of moving, mixing and generation of droplets was demonstrated.The minimum voltage in need was about 20 V and a velocity of up to 96 mm/s was achieved. Such an DMF device with large-scale matrix and low driving voltage will be very suitable for POCT applications.

Precise Microfluidic Luminescent Sensor Platform with Controlled Injection System

Efforts have been devoted to screening various prevalent diseases, such as severe acute respiratory syndrome (SARS) and coronavirus disease 2019 (COVID-19). Real-time polymerase chain reaction (RT-PCR), which is currently the most widely used, has high accuracy, but it requires several facilities and takes a relatively long time to check; so, new testing technology is necessary for a higher test efficiency. A chemiluminescence (CL) sensor is a relatively simple device and suitable as an alternative because it can detect very precise specimens. However, in measurements via CL, the quantitative formulation of reagents that cause color development is important. In the case of mixing using micropipettes, precise analysis is possible, but this technique is limited by uncontrollable errors or deviations in detection amounts. In addition, in using a microfluidic chip to increase field applicability, a syringe pump or other quantification injection tools are required, so problems must be overcome for practical use. Therefore, in this study, a microchip was designed and manufactured to supply a sample of a certain volume by simply blowing air and injecting a sample into the chamber. By utilizing the luminescence reaction of luminol, CuSO4 and H2O2 the performance of the prepared chip was confirmed, and the desired amount of the sample could be injected with a simple device with an error rate of 2% or less. For feasible applications, an experiment was performed to quantitatively analyze thrombin, a biomarker of heart disease. Results demonstrated that biomarkers could be more precisely detected using the proposed microchips than using micropipettes.

Design of a Hand-Held and Battery-Operated Digital Microfluidic Device Using EWOD for Lab-on-a-Chip Applications

Microfluidics offer many advantages to Point of Care (POC) devices through lower reagent use and smaller size. Additionally, POC devices offer the unique potential to conduct tests outside of the laboratory. In particular, Electro-wetting on Dielectric (EWOD) microfluidics has been shown to be an effective way to move and mix liquids enabling many PoC devices. However, much of the research surrounding these microfluidic systems are focused on a single aspect of the system capability, such as droplet control or a specific new application at the device level using the EWOD technology. Often in these experiments the supporting systems required for operation are bench top equipment such as function generators, power supplies, and personal computers. Although various aspects of how an EWOD device is capable of moving and mixing droplets have been demonstrated at various levels, a complete self-contained and portable lab-on-a-chip system based on the EWOD technology has not been well demonstrated. For instance, EWOD systems tend to use high voltage alternating current (AC) signals to actuate electrodes, but little consideration is given to circuitry size or power consumption of such components to make the entire system portable. This paper demonstrates the feasibility of integrating all supporting hardware and software to correctly operate an EWOD device in a completely self-contained and battery-powered handheld unit. We present results that demonstrate a complete sample preparation flow for deoxyribonucleic acid (DNA) extraction and isolation. The device was designed to be a field deployable, hand-held platform capable of performing many other sample preparation tasks automatically. Liquids are transported using EWOD and controlled via a programmable microprocessor. The programmable nature of the device allows it to be configured for a variety of tests for different applications. Many considerations were given towards power consumption, size, and system complexity which make it ideal for use in a mobile environment. The results presented in this paper show a promising step forward to the portable capability of microfluidic devices based on the EWOD technology.

DNA Aptamer Functionalized Hydrogels for Interferometric Fiber-Optic Based Continuous Monitoring of Potassium Ions

In the present paper, we describe a potassium sensor based on DNA-aptamer functionalized hydrogel, that is capable of continuous label-free potassium ion (K+) monitoring with potential for in situ application. A hydrogel attached to the end of an optical fiber is designed with di-oligonucleotides grafted to the polymer network that may serve as network junctions in addition to the covalent crosslinks. Specific affinity toward K+ is based on exploiting a particular aptamer that exhibits conformational transition from single-stranded DNA to G-quadruplex formed by the di-oligonucleotide in the presence of K+. Integration of this aptamer into the hydrogel transforms the K+ specific conformational transition to a K+ concentration dependent deswelling of the hydrogel. High-resolution interferometry monitors changes in extent of swelling at 1 Hz and 2 nm resolution for the hydrogel matrix of 50 µm. The developed hydrogel-based biosensor displayed high selectivity for K+ ions in the concentration range up to 10 mM, in the presence of physiological concentrations of Na+. Additionally, the concentration dependent and selective K+ detection demonstrated in the artificial blood buffer environment, both at room and physiological temperatures, suggests substantial potential for practical applications such as monitoring of potassium ion concentration in blood levels in intensive care medicine.

Application of Microfluidics in Immunoassay: Recent Advancements

In recent years, point-of-care testing has played an important role in immunoassay, biochemical analysis, and molecular diagnosis, especially in low-resource settings. Among various point-of-care-testing platforms, microfluidic chips have many outstanding advantages. Microfluidic chip applies the technology of miniaturizing conventional laboratory which enables the whole biochemical process including reagent loading, reaction, separation, and detection on the microchip. As a result, microfluidic platform has become a hotspot of research in the fields of food safety, health care, and environmental monitoring in the past few decades. Here, the state-of-the-art application of microfluidics in immunoassay in the past decade will be reviewed. According to different driving forces of fluid, microfluidic platform is divided into two parts: passive manipulation and active manipulation. In passive manipulation, we focus on the capillary-driven microfluidics, while in active manipulation, we introduce pressure microfluidics, centrifugal microfluidics, electric microfluidics, optofluidics, magnetic microfluidics, and digital microfluidics. Additionally, within the introduction of each platform, innovation of the methods used and their corresponding performance improvement will be discussed. Ultimately, the shortcomings of different platforms and approaches for improvement will be proposed.

Recent advances in magnetic digital microfluidic platforms

Magnetic Digital microfluidics (DMF), which enables the manipulation of droplets containing different types of samples and reagents by permanent magnets or electromagnet arrays, has been used as a promising platform technology for bioanalytical and preparative assays. This is due to its unique advantages such as simple and "power free" operation, easy assembly, great compatibility with auto control systems, and dual functionality of magnetic particles (actuation and target attachment). Over the past decades, magnetic DMF technique has gained a widespread attention in many fields such as sample-to-answer molecular diagnostics, immunoassays, cell assays, on-demand chemical synthesis, and single-cell manipulation. In the first part of this review, we summarised features of magnetic DMF. Then, we introduced the actuation mechanisms and fabrication of magnetic DMF. Furthermore, we discussed five main applications of magnetic DMF, namely drug screening, protein assays, polymerase chain reaction (PCR), cell manipulation, and chemical analysis and synthesis. In the last part of the review, current challenges and limitations with magnetic DMF technique were discussed, such as biocompatibility, automation of microdroplet control systems, and microdroplet evaporation, with an eye on towards future development.

Designing an Ultrathin Film Spectrometer Based on III-Nitride Light-Absorbing Nanostructures

In this paper, a spectrometer design enabling an ultrathin form factor is proposed. Local strain engineering in group III-nitride semiconductor nanostructured light-absorbing elements enables the integration of a large number of photodetectors on the chip exhibiting different absorption cut-off wavelengths. The introduction of a simple cone-shaped back-reflector at the bottom side of the substrate enables a high light-harvesting efficiency design, which also improves the accuracy of spectral reconstruction. The cone-shaped back-reflector can be readily fabricated using mature patterned sapphire substrate processes. Our design was validated via numerical simulations with experimentally measured photodetector responsivities as the input. A light-harvesting efficiency as high as 60% was achieved with five InGaN/GaN multiple quantum wells for the visible wavelengths.

Application and research progress of in vitro liver cancer cell culture models

Liver cancer is gradually becoming an important burden on public health around the world, and many drugs are currently available for the treatment of liver cancer, so the correct choice of drugs will significantly improve the prognosis of patients. In vitro liver cancer cell culture model is an important way to study the pathogenesis of liver cancer and drug screening. Long-term practice has proved that the traditional two-dimensional (2D) drug screening method cannot truly reproduce the complex drug resistance mechanism of tumor. The emergence of in vitro three-dimensional (3D) hepatocellular carcinoma cell model enriches the selection of methods for hepatoma experiments in vitro. The experimental sensitivity of hepatoma drugs in vitro and the study of pathology and physiology of hepatoma cells in vitro have also been greatly improved. In this paper, we review the main types of liver cancer cells cultured in vitro and discuss their advantages and disadvantages, in order to clarify the development and research direction of in vitro liver cancer culture models.