Small Volume Of Liquid Research Articles

Forming and loading giant unilamellar vesicles with acoustic jetting.

Giant unilamellar vesicles (GUVs) are a useful platform for reconstituting and studying membrane-bound biological systems, offering reduced complexity compared to living cells. Several techniques exist to form GUVs and populate them with biomolecules of interest. However, a persistent challenge is the ability to efficiently and reliably load solutions of biological macromolecules, organelle-like membranes, and/or micrometer-scale particles with controlled stoichiometry in the encapsulated volume of GUVs. Here, we demonstrate the use of acoustic streaming from high-intensity focused ultrasound to make and load GUVs from bulk solutions, without the need for nozzles that can become clogged or otherwise alter the solution composition. In this method, a compact acoustic lens is focused on a planar lipid bilayer formed between two aqueous solutions. The actuation of a planar piezoelectric material coupled to the lens accelerates a small volume of liquid, deforming the bilayer and forming a GUV containing the solution on the transducer side of the bilayer. As demonstrated here, acoustic jetting offers an alternative method for the generation of GUVs for biological and biophysical studies.

Varying the Surface Charges of Gold Nanoparticles in Span 80, AOT, and Span 80 + AOT Micellar Systems in n-Decane

Gold nanoparticles with different diameters of the metal core are obtained by reducing HAuCl4 with hydrazine in reverse emulsions stabilized by Span 80 (9.4 ± 0.4 nm), AOT (6.1 ± 0.2 nm), and an equimolar Span 80 + AOT mixture (10.0 ± 0.2 nm). After synthesis, only the nanoparticles in the AOT solutions (ζ potential 16.8 ± 0.9 mV) display electrophoretic mobility. Nanoparticles in the form of a small-volume liquid phase concentrate are also separated from excess reagents and by-products by concentration (non-aqueous electrophoresis, or centrifugation) and diluted with micellar solutions (Span 80, AOT, and Span 80 + AOT mixture) or pure solvents (n-decane and chloroform). As a result, 24 organosols are obtained, including ones with positive (11), negative (8), and uncharged (5) nanoparticles. Of particular potential interest are organosols that have the same macrostructure in terms of surfactants, but with oppositely charged gold nanoparticles (7 pairs of organosols are obtained).

An Ultrahigh Sensitivity Microwave Sensor for Microfluidic Applications

This work shows an ultrahigh sensitivity microwave sensor for microfluidic applications. The proposed sensor is made of a microstrip line loaded with a complementary splitring resonator (CSRR). The meander slot is adopted in the CSRR to achieve high field confinement and is therefore covered with a polydimethylsiloxane (PDMS) microfluidic channel to enable strong interaction between the field and the liquid sample. The complex permittivity of the liquid sample can be retrieved by the variations in the resonant frequency and peak attenuation. The proposed design requires a very small liquid volume of ~0.5 μL while offering a high sensitivity. A prototype is fabricated and tested, with a good agreement achieved between the extracted values and the reference data.

An integrated system of air sampling and simultaneous enrichment for rapid biosensing of airborne coronavirus and influenza virus

Point-of-care risk assessment (PCRA) for airborne viruses requires a system that can enrich low-concentration airborne viruses dispersed in field environments into a small volume of liquid. In this study, airborne virus particles were collected to a degree above the limit of detection (LOD) for a real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). This study employed an electrostatic air sampler to capture aerosolized test viruses (human coronavirus 229E (HCoV-229E), influenza A virus subtype H1N1 (A/H1N1), and influenza A virus subtype H3N2 (A/H3N2)) in a continuously flowing liquid (aerosol-to-hydrosol (ATH) enrichment) and a concanavalin A (ConA)-coated magnetic particles (CMPs)-installed fluidic channel for simultaneous hydrosol-to-hydrosol (HTH) enrichment. The air sampler's ATH enrichment capacity (EC) was evaluated using the aerosol counting method. In contrast, the HTH EC for the ATH-collected sample was evaluated using transmission-electron-microscopy (TEM)-based image analysis and real-time qRT-PCR assay. For example, the ATH EC for HCoV-229E was up to 67,000, resulting in a viral concentration of 0.08 PFU/mL (in a liquid sample) for a viral epidemic scenario of 1.2 PFU/m3 (in air). The real-time qRT-PCR assay result for this liquid sample was “non-detectable” however, subsequent HTH enrichment for 10 min caused the “non-detectable” sample to become “detectable” (cycle threshold (CT) value of 33.8 ± 0.06).

HPTLC–MS method for the determination of benzodiazepines in urine samples

Misuse and abuse of prescription drugs has become a global health problem in the last few years as the illicit drug cartels have grown exponentially. The non-medical use of prescribed medications, such as benzodiazepines, synthetic opioids, stimulants and tranquilizers, has increased rapidly due to their easy availability. Nowadays benzodiazepines are not only misused/abused, but also play a significant part in facilitating various crimes such as robbery, date rapes, sexual harassment, which has made its forensic examination important and critical. Considering the gravity of these crimes, an attempt has been made to develop and validate simultaneous quantification method for seven benzodiazepines (clonazepam, lorazepam, alprazolam, diazepam, flurazepam, oxazepam and nitrazepam) using high-performance thin-layer chromatography–mass spectrometry (HPTLC–MS) from urine. Quantitative analysis of clonazepam, lorazepam, alprazolam, diazepam, flurazepam, oxazepam and nitrazepam was carried out using HPTLC–MS. MS operating in selective ion-monitoring mode was attempted for the accurate identification of the drugs under study. Small-volume liquid extraction technique using diethyl ether–chloroform (80:20, v/v) was used for the extraction of urine. Pre-coated HPTLC (silica gel G 60 F254) plates were developed using the mobile-phase chloroform–glacial acetic acid (9:1, v/v). The screening of HPTLC plates was carried out by ultraviolet light, and the m/z ratio of drugs was obtained by extracting spots from plates using a TLC–MS interface. Method validation was carried out according to the International Council for Harmonisation guidelines. The current HPTLC–MS method is simple, sensitive, precise and accurate, and it can be used for the detection and quantitative estimation of benzodiazepines in urine.

Fluid sensing using microcantilevers: From physics-based modeling to deep learning

In-situ measurements of the viscosity and density of small volumes of liquids are required in several industrial applications. MEMS sensors deploying vibrating microstructures constitute an attractive alternative given the significant impact of the surrounding liquid on their dynamic behavior. In this work, we combine physics-based modeling approaches and deep learning techniques to simultaneously estimate the density and viscosity of liquids from the resonance frequencies and quality factors of immersed microcantilevers. The physics-based model is first validated by comparing the simulated resonance frequencies and quality factors of immersed microcantilevers to those obtained from experiments conducted on a large variety of liquids. Then, we use the simulations results to train deep neutral networks to learn the mapping from the data space to the parameter space. The deep learning method shows high prediction accuracy provided that there is enough independent input data, shows no bias in the predicted values, and provides the results instantaneously. The optimal accuracy in the estimation of the liquid viscosity and density is achieved when the first resonance frequency and corresponding quality factor are used as inputs.

EML webinar overview: Liquid metals at the extreme

Gallium-based liquid metals are often overlooked despite their remarkable properties: melting points below room temperature, water-like viscosity, low-toxicity, and effectively zero vapor pressure (they do not evaporate). They also have, by far, the largest interfacial tension of any liquid at room temperature. Normally small volumes of liquids with large tension form spherical or hemi-spherical structures to minimize surface energy. Yet, these liquid metals can be patterned and printed into non-spherical shapes (cones, wires, antennas, circuits) due to a thin, oxide skin that forms rapidly on its surface. The ability to pattern metal enables new types of ultra-stretchable wires, self-healing circuits, and soft logic devices (the latter of which perform logic in a ‘distributed’ way without conventional semiconductors). Combining liquid metals with elastomer can also lead to emergent and new material properties, such as tough fibers and composites with negative piezopermittivity (decreasing dielectric ‘constant’ with strain, which is unprecedented) and positive piezoconductivity (increasing conductivity with strain, which is highly unusual). Perhaps the most unexpected aspect of liquid metals it the ability to use interfacial electrochemistry chemistry to remove/deposit the oxide to manipulate the interfacial tension of the metal over unprecedented ranges (from the largest tension of any known liquid to near zero). The properties of liquid metals have implications for soft and stretchable devices with desirable mechanical properties for human–machineinterfaces soft robotics, and wearable electronics. EML webinar speakers and videos are updated at https://imechanica.org/node/24098.

Layer-by-layer self-assembly of MoS2/PDDA hybrid film in microfluidic chips for ultrasensitive electrochemical immunosensing of alpha-fetoprotein

Ultrasensitive detection of cancer biomarkers holds great promise for early stage detection and diagnosis of cancer. Microfluidic electrochemical immunochips have been assessed as powerful detection platforms due to their high sensitivity, low cost, portability, and ease of miniaturization. In this work, an ultrasensitive electrochemical immunochip based on MoS2/PDDA hybrid film is designed via layer-by-layer self-assembly method. An electrochemical impedance detection platform is developed for the detection of alpha-fetoprotein (AFP) by integrating a three-electrode system in the micro-channel, which introduces MoS2/PDDA film modified with antibodies as the working electrode, Ag/AgCl wire as the reference electrode and indium tin oxide (ITO) as the counter electrode. After MoS2/PDDA film is modified with AFP antibodies, the immobilization of various concentrations of AFP antigens is carried on which can cause changes in the electrochemical impedance value. This proposed approach exhibits a linear range from 0.1 ng/mL to 10 ng/mL and a low detection limit of 0.033 ng/mL (S/N = 3). The applicability of the MoS2/PDDA immunochip is further investigated by detecting human serum samples. This ultrasensitive microfluidic immunochip is proved to be highly selective with small input liquid volume, which could realize trace detection of AFP and be potentially applied in clinical diagnosis of other biomolecules.

Characterization of Fluid-Phase Behavior Using an Advanced Microwave Re-Entrant Cavity

To advance the thermodynamic models needed for many industrial processes, accurate measurements of fluid-phase behavior are essential. Therefore, we present a newly designed microwave re-entrant cavity apparatus to deliver improved phase-behavior measurements of pure and multicomponent fluids. The re-entrant geometry has spatially distinct resonant modes, which are used to determine the dielectric permittivity of the liquid and vapor phase and the liquid volume fraction (Λ). The first mode (fvac ≈ 320 MHz) is sensitive to small liquid volumes, the second (1.86 GHz) is sensitive to small vapor volumes, and the third (6.57 GHz) is sensitive to the interface location. At equilibrium, a system of three equations, one for each mode, allows for the dielectric permittivity of each phase and Λ to be determined from the measured resonant frequencies. The cavity’s suitability for solving this inverse problem was explored using finite element analysis and experiments with pure propane and pentane. A primary limitation of the method was the dependence of the mode-shape functions (Gn) on phase permittivities, which become measurable for high-frequency modes. We propose a solution to account for this dependence using finite element simulations that map the Gn surface as a function of Λ and the ratio of phase dielectric permittivities.

Aerosol-to-Hydrosol Sampling and Simultaneous Enrichment of Airborne Bacteria For Rapid Biosensing.

Rapid monitoring of biological particulate matter (Bio-PM, bioaerosols) requires an enrichment technique for concentrating the Bio-PM dispersed in the air into a small volume of liquid. In this study, an electrostatic air sampler is employed to capture aerosolized test bacteria in a carrier liquid (aerosol-to-hydrosol (ATH) enrichment). Simultaneously, the captured bacteria are carried into a fluid channel for hydrosol-to-hydrosol (HTH) enrichment with Concanavalin A coated magnetic particles (CMPs). The ATH enrichment capacity of the air sampler was evaluated with an aerosol particle counter for the following test bacteria: Staphylococcus aureus, Bacillus cereus, Escherichia coli, and Acinetobacter baumannii. Then, the HTH enrichment capacity for the ATH-collected sample was evaluated using the colony-counting method, scanning electron microscopy based image analysis, fluorescence microscopy, electrical current measurements, and real-time quantitative polymerase chain reaction (qPCR). The ATH and HTH enrichment capacities for the given operation conditions were up to 80 000 and 14.9, respectively, resulting in a total enrichment capacity of up to 1.192 × 106. Given that air-to-liquid enrichment required to prepare detectable bacterial samples for real-time qPCR in field environments is of the order of at least 106, our method can be used to prepare a detectable sample from low-concentration airborne bacteria in the field and significantly reduce the time required for Bio-PM monitoring because of its enrichment capacity.

Influencia del diseño de una cámara de niebla en la deposición de nano-películas delgadas líquidas – prueba de concepto

Diferentes diseños de cámaras de niebla, cuyo propósito es la generación de un fino aerosol, fueron evaluados en términos de su aplicación para la deposición de capas delgadas homogéneas sobre superficies sólidas. El abordaje desarrollado comprende un generador de aerosol que se adapta a las diferentes cámaras estudiadas, lo que se denomina en adelante como cámara de niebla (mist chamber). Particularmente, el foco de interés fue la utilización de pequeños volúmenes de líquidos para la generación de una niebla fina, debido a su importancia en aplicaciones donde la concentración de aerosol y la distribución del tamaño de las gotas deben ser ajustadas a necesidades específicas. Cuatro cámaras de niebla fueron evaluadas y sometidas a pruebas experimentales, con el fin de caracterizar el rendimiento de cada propuesta. Como prueba de concepto para las cámaras de niebla diseñadas, una mezcla líquida de monómeros de base acrílica fue depositada en obleas de silicio y posteriormente polimerizadas mediante un plasma jet a presión atmosférica. Finalmente, un riguroso análisis de la superficie de las capas obtenidas reveló que estas tienen un grosor en el rango nanométrico y presentan un patrón de deposición homogéneo.

Detection of Electrooxidation Products in Microfluidic Devices Using Raman Spectroscopy

Microfluidic devices combined with Raman Spectroscopy have great promise for in-situ and online detection of reaction processes with only a small volume of liquid required. This advanced method allows for flexible manipulation of fluids, micro/nano-particles, and biological samples1. Lab-on-a-chip applications are often used for chemical analysis, but Raman microscopy has also been used to monitor reactions within microreactors. The combination of the controlled mass transport in microfluidics with detection of soluble intermediate and product species by Raman offers the possibility of mechanistic kinetic studies of electrocatalytic reactions. We here show the feasibility of this method for studying electrocatalysis of oxidation of alcohols.Two types of microfluidic flow devices were fabricated, which used glass slides and printed circuit boards (PCBs) as substrates, respectively. For glass-slide-based microfluidic devices, Raman spectra were used to monitor methanol oxidation catalyzed by a Pt mesh electrode, and calibration with known solutions enabled quantification of methanol and formate concentrations. A comparative study of catalytic oxidations of glycerol, ethanol, ethylene glycol and 1-propanol using electrodeposited Ni on carbon paper showed that under strong alkaline conditions, glycerol and ethylene glycol principally gave formate and carbonate products, while ethanol and 1-propanol did not give formate. Acetate was found to be the major oxidation product of ethanol, with only a small amount of carbonate. For PCB-based microfluidic substrates, electroplated Ni on Cu pads gave planar working electrodes, which were used to catalyze the oxidation of glycerol. On-board PdH reference electrodes were incorporated2.1. A.F. Chrimes, K. Khoshmanesh, P.R. Stoddart, A. Mitchell, K. Kalantar-zadeh, Microfluidics and Raman microscopy: current applications and future challenges, Chem. Soc. Rev., 42, 5880 (2013).2. E.V. Fanavoll, D.A. Harrington, S. Sunde, G. Singh and F. Seland, A Microfluidic Electrochemical Cell with Integrated PdH Reference Electrode for High Current Experiments, Electrochim. Acta., 225 , 69 (2017).Acknowledgement: This research was conducted as part of the Engineered Nickel Catalysts for Electrochemical Clean Energy project administered from Queen’s University and supported by Grant No. RGPNM 477963-2015 under the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Frontiers Program. Figure 1

Research on Microfluidic Chip Design and Droplet Related Technology

Microfluidic Chips, also known as chip labs, integrate basic operating units in the fields of chemistry and biology on a chip. The droplet is a technique for controlling a small volume of liquid on a microfluidic chip. One of the two incompatible liquids is used as one continuous phase and the other as a dispersed phase, and the dispersed phase is dispersed in a continuous phase in a micro volume unit. Droplet fusion is the basic tool for controlling droplets in microfluidic devices and their use as microreactors, allowing precise mixing of reagents and fusion of samples at well-defined points in space and time.This topic is based on microfluidic technology, designed and processed PDMS chip, research on droplet generation and droplet fusion technology in microfluidic chip. Using a constant pressure pump designed by the laboratory to drive the sample injection, study the effects of continuous phase, discrete phase convergence angle, flow path width, liquid flow rate, etc. on the droplet formation of the cross-shaped structure. Based on the droplet generation technology, The subject then studied the droplet fusion technology, completed the droplet fusion chip design and processing, and achieved 1:1 1:2 fusion of two sample droplets.

Minipotentiostat controlled by smartphone on a micropipette: A versatile, portable, agile and accurate tool for electroanalysis

In this paper, we show an unprecedented device obtained by coupling a small potentiostat to an electronic micropipette. The minipotentiostat is powered by the micropipette battery and controlled by a smartphone via a Bluetooth wireless connection. A set of 3 electrodes is inserted into the tip of the micropipette with the aid of an adapter that allows electrochemical measurements to be carried out without affecting the precision and trueness of handling of small volumes of liquid. Studies with the device show significant gains in portability, versatility, agility and for analytical procedures. This approach requires small volume of samples and reagents with the possibility of recovery after analysis. Determination of hydrogen peroxide with the aim for future development of enzymatic biosensors for clinical analysis was shown as an example of application. We consider that the device shown here contributes to a new way to performing electrochemical analysis on site.

Adjusting the dose in paediatric care by dispersing fragments of four different aspirin tablets.

AimTablets can be manipulated in several ways to obtain a fraction as the dose—a practice frequently seen in paediatric care due to lack of suitable formulations. Splitting tablets prior to fragment dispersion in a small volume of liquid is one such method. The objective of this study was to investigate the accuracy and precision of this method.MethodsFour different types of aspirin tablets (two dispersible, one conventional and one chewing) were split with a tablet splitter into half and quarter fragments. The fragments were dispersed in a medicine measure or an oral syringe. The amount recovered was determined by UHPLC analysis.ResultsThe largest quarter fragments ranged from 26.7% to 31.5% of the full tablet weight. Dispersing the fragment in an oral syringe, the amount recovered was greater than 90.8% of the fragment manipulated for all four tablet types, when rinsing was performed. Dispersing the fragment in a medicine measure, the amounts recovered spanned from 32.9% for the conventional tablets to 98.7% for one of the dispersible tablets.ConclusionDispersion of half or quarter tablets directly in an oral syringe, but not a medicine measure, could give satisfactory recovery from fragments of all the investigated aspirin tablets.

Cryopreservation of primary cultures of mammalian somatic cells in 96-well plates benefits from control of ice nucleation

Cryopreservation of mammalian cells has to date typically been conducted in cryovials, but there are applications where cryopreservation of primary cells in multiwell plates would be advantageous. However excessive supercooling in the small volumes of liquid in each well of the multiwell plates is inevitable without intervention and tends to result in high and variable cell mortality. Here, we describe a technique for cryopreservation of adhered primary bovine granulosa cells in 96-well plates by controlled rate freezing using controlled ice nucleation. Inducing ice nucleation at warm supercooled temperatures (less than 5 °C below the melting point) during cryopreservation using a manual seeding technique significantly improved post-thaw recovery from 29.6% (SD = 8.3%) where nucleation was left uncontrolled to 57.7% (9.3%) when averaged over 8 replicate cultures (p < 0.001). Detachment of thawed cells was qualitatively observed to be more prevalent in wells which did not have ice nucleation control which suggests cryopreserved cell monolayer detachment may be a consequence of deep supercooling. Using an infra-red thermography technique we showed that many aliquots of cryoprotectant solution in 96-well plates can supercool to temperatures below −20 °C when nucleation is not controlled, and also that the freezing temperatures observed are highly variable despite stringent attempts to remove contaminants acting as nucleation sites. We conclude that successful cryopreservation of cells in 96-well plates, or any small volume format, requires control of ice nucleation.

Biosensor Using a One-Port Interdigital Capacitor: A Resonance-Based Investigation of the Permittivity Sensitivity for Microfluidic Broadband Bioelectronics Applications

Electronics is a field of study ubiquitous in our daily lives, since this discipline is undoubtedly the driving force behind developments in many other disciplines, such as telecommunications, automation, and computer science. Nowadays, electronics is becoming more and more widely applied in life science, thus leading to an increasing interest in bioelectronics that is a major segment of bioengineering. A bioelectronics application that has gained much attention in recent years is the use of sensors for biological samples, with emphasis given to biosensors performing broadband sensing of small-volume liquid samples. Within this context, this work aims at investigating a microfluidic sensor based on a broadband one-port coplanar interdigital capacitor (IDC). The microwave performance of the sensor loaded with lossless materials under test (MUTs) is achieved by using finite-element method (FEM) simulations carried out with Ansoft’s high frequency structure simulator (HFSS). The microfluidic channel for the MUT has a volume capacity of 0.054 μL. The FEM simulations show a resonance in the admittance that is reproduced with a five-lumped-element equivalent-circuit model. By changing the real part of the relative permittivity of the MUT up to 70, the corresponding variations in both the resonant frequency of the FEM simulations and the capacitance of the equivalent-circuit model are analyzed, thereby enabling assessment of the permittivity sensitivity of the studied IDC. Furthermore, it is shown that, although the proposed local equivalent-circuit model is able to mimic faithfully the FEM simulations locally around the resonance in the admittance, a higher number of circuit elements can achieve a better agreement between FEM and equivalent-circuit simulation over the entire broad frequency going range from 0.3 MHz to 35 GHz.

A Fiber-Optic pH Sensor for Microbioreactors

A fiber-optic sensor for microbioreactors has been developed and manufactured that records pH changes in the range from 6.5 to 9 with an accuracy of ±0.2 for small volumes of liquid. The principle of detection is based on measuring the degree of absorption of LED radiation as it passes through a controlled environment with an indicator. Phenol red is used as a biocompatible indicator.

WATER DROPLET EVAPORATION IN A CHAMBER ISOLATED FROM THE EXTERNAL ENVIRONMENT

With an increase in the productivity of power equipment and the miniaturization of its components, the use of traditional thermal management systems becomes insufficient. There is a need to develop drip heat removal systems, based on phase transition effects. Cooling with small volumes of liquids is a promising technology for microfluidic devices or evaporation chambers, which are self-regulating systems isolated from the external environment. However, the heat removal during evaporation of droplets into a limited volume is a difficult task due to the temperature difference in the cooling device and the concentration of water vapor that is unsteady in time depending on the mass of the evaporated liquid. This paper presents the results of an experimental study of the distilled water microdrops’ (5-25 μl) evaporation on an aluminum alloy AMg6 with the temperatures of 298-353 K in an isolated chamber (70 × 70 × 30 mm3) in the presence of heat supply to its lower part. Based on the analysis of shadow images, the changes in the geometric dimensions of evaporating drops were established. They included the increase in the contact diameter, engagement of the contact line due to nano roughening and chemical composition inhomogeneous on the surface (90-95% of the total evaporation time) of the alloy and a decrease in the contact diameter. The surface temperature and droplet volume did not affect the sequence of changes in the geometric dimensions of the droplets. It was found that the droplet volume has a significant effect on the evaporation time at relatively low substrate temperatures. The results of the analysis of droplet evaporation rates and hygrometer readings have shown that reservoirs with salt solutions can be used in isolated chambers to control the concentration of water vapor. The water droplets evaporation time was determined. The analysis of the time dependences of the evaporation rate has revealed that upon the evaporation of droplets in an isolated chamber under the conditions of the present experiment, the air was not saturated with water vapor. The latter did not affect the evaporation rate.

Оптоволоконный датчик pH для микробиореакторов

A fiber-optic sensor for microbioreactors was designed and manufactured. It measures pH in the range from 6.5 to 9 with an accuracy of ± 0.2 for small volumes of liquid. The principle of detection is the measurement of blue and green LEDs light absorption in liquid with an indicator. Phenol red is used as a biocompatible indicator.