Generation Of Single Droplets Research Articles

Automatic Single Droplet Generator with Control over Droplet Size and Detachment Frequency

This paper presents a quite simple, fully automatized single droplet generator, which can be an alternative for more expensive and complicated microfluidic devices. The simple generation nozzle connected to the pressure cells and cheap peristaltic pumps, synchronized via developed software with simple GUI (graphical user interface) implemented into the Raspberry Pi microcomputer allows precise control over the single droplet diameter and detachment frequency. The generator allows the formation of droplets of quite wide range of diameters without the need of orifice diameter replacements. Free control over time available for adsorption of surface active-substances over the surface of immobilized droplet, before its detachment from the orifice, is an advantage of the developed device.

Mobile platform for rapid sub–picogram-per-milliliter, multiplexed, digital droplet detection of proteins

Digital droplet assays-in which biological samples are compartmentalized into millions of femtoliter-volume droplets and interrogated individually-have generated enormous enthusiasm for their ability to detect biomarkers with single-molecule sensitivity. These assays have untapped potential for point-of-care diagnostics but are currently mainly confined to laboratory settings, due to the instrumentation necessary to serially generate, control, and measure tens of millions of droplets/compartments. To address this challenge, we developed an optofluidic platform that miniaturizes digital assays into a mobile format by parallelizing their operation. This technology is based on three key innovations: (i) the integration and parallel operation of a hundred droplet generators onto a single chip that operates >100× faster than a single droplet generator, (ii) the fluorescence detection of droplets at >100× faster than conventional in-flow detection using time domain-encoded mobile phone imaging, and (iii) the integration of on-chip delay lines and sample processing to allow serum-to-answer device operation. To demonstrate the power of this approach, we performed a duplex digital ELISA. We characterized the performance of this assay by first using spiked recombinant proteins in a complex media (FBS) and measured a limit of detection, 0.004 pg/mL (300 aM), a 1,000× improvement over standard ELISA and matching that of the existing laboratory-based gold standard digital ELISA system. We additionally measured endogenous GM-CSF and IL6 in human serum from n = 14 human subjects using our mobile duplex assay, and showed excellent agreement with the gold standard system ([Formula: see text]).

A Study on Critical Pulse Conditions for Single-Droplets Generation in Drop-on-Demand Technique

Generating single-droplets is significant for extensive applications of drop-on-demand (DoD) type of piezoelectric inkjet technique (PIT). Based on the mechanism of DoD technique, we theoretically analyze the effects of pulse parameters on the process of droplet generation, and the critical pulse conditions for generating single-droplets are obtained. With a single-droplet generator (SDG) fitted from an inkjet print-head based on DoD technique, we found that upper and lower limit of pulse amplitude for generating single-droplet both changes periodically with pulse width. As the critical pulse width increases, the lower limit has an exponential growth approximately, which is consistent with the theoretical consideration.

Generating high-quality single droplets for optical particle characterization with an easy setup

The high-performance and micro-sized single droplet is significant for optical particle characterization. We develop a single-droplet generator (SDG) based on a piezoelectric inkjet technique with advantages of low cost and easy setup. By optimizing the pulse parameters, we achieve various size single droplets. Further investigations reveal that SDG generates single droplets of high quality, demonstrating good sphericity, monodispersity and a stable length of several millimeters.

Coverage Area and Fading Time of Surfactant-Amended Herbicidal Droplets on Cucurbitaceous Leaves

Proper use of appropriate surfactants to control droplet behavior on leaf surfaces is critical to improving herbicide application efficacy for controlling paddy melons (). An esterified seed oil surfactant and a petroleum oil surfactant were investigated to modify spread areas and fading times of water and herbicidal droplets on watermelon leaves, which were used to simulate paddy melon leaves. A combination of two systemic herbicides (triclopyr and glyphosate) was also used to form a water-based spray solution for comparisons. The glyphosate herbicide was pre-formulated with a non-ionic surfactant. Tests were conducted with 250 and 450 I¼m sessile droplets at 30% and 60% relative humidity (RH) inside a controlled environmental chamber. The sessile droplets were produced with a single-droplet generator. Droplet fading times significantly increased with both droplet size and RH. Droplet maximal coverage areas increased only with droplet size but not RH. For the water-only solution, addition of seed oil surfactant increased the droplet coverage area by over 2.3 times, but addition of the petroleum oil surfactant did not increase the droplet coverage area. For the spray solution containing two herbicides, addition of the seed oil surfactant increased droplet coverage areas on leaves from 0.146 ±0.012 mm 2 to 0.201 ±0.014 mm 2 for 250 I¼m droplets and from 0.348 ±0.017 mm 2 to 0.537 ±0.024 mm 2 for 450 I¼m droplets. In addition, their fading times increased from 36 ±7 s to 43 ±6 s at 30% RH and from 53 ±10 s to 62 ±3 s at 60% RH for 250 I¼m droplets, and from 98 ±6 s to 107 ±5 s at 30% RH and from 145 ±5 s to 151 ±8 s at 60% RH for 450 I¼m droplets. In comparison, addition of the petroleum oil surfactant to the herbicide solution reduced the maximal coverage areas and shortened the droplet fading times but increased droplet penetration rates. Therefore, to improve spray coverage area and reduce droplet evaporation, herbicide spray solutions that already contain a surfactant could be amended with the seed oil surfactant. The petroleum oil surfactant could be used when enhancement of droplet penetration into leaf tissues is necessary.

Droplet ejection from an interface between two immiscible liquids under pulsed ultrasound

The emphasis of this study is on the ejection of single droplets of a certain size under pulsed ultrasound. Droplet ejection from an interface of two immiscible liquids in this mode, which differs from the well-known ultrasonic fountain (where liquid droplets arise spontaneously), has been experimentally implemented and investigated. The spatial and time evolution of the interface deformation and violation of interface integrity, caused by pulsed acoustic radiation pressure, has been recorded with a high-speed video camera. It is shown that, depending on the ultrasound intensity, three characteristic modes of interface response can be distinguished. In the first (low-intensity)mode, the interface undergoes forced oscillations, without violation of its integrity. In the second (intermediate-intensity) mode, which is in the focus of our study, the interface integrity is violated due to the ejection of a single droplet of a certain size; the latter continuously changes its shape when moving in the second liquid. In the third (high-intensity) mode, the predictable ejection of droplets of a predictable size turns into stochastic ejection of multiple droplets with unpredictable sizes. The dependence of the sizes of single droplets on the parameters of focused ultrasound beam have been measured in the second (stable) mode of ultrasound ejection. Based on these measurements, the range of ultrasound parameters providing controlled generation of single droplets of a specified size is estimated. Differences in the dynamics of interface motion and specific features of droplet generation for the liquid/liquid interface in comparison with the liquid/gas interface are indicated. Possible applications of the observed effects are discussed.

Determination of Foliar Uptake of Water Droplets on Waxy Leaves in a Controlled Environmental System

<abstract> <b>.</b> More definitive techniques for determination of plant cuticle permeability are required to select proper doses of active ingredients and spray additives to improve pesticide application efficacy. A controlled environmental system with 100% relative humidity was developed for direct measurements of foliar uptake rates of sessile water droplets at various locations on waxy leaf surfaces during two diurnal periods between 10:30 and 13:00 (noon) and between 16:00 and 19:00 (evening) at ambient temperatures of 15°C and 20°C. Sessile droplets of 340 and 540 μm diameter were produced with a single-droplet generator. Stomatal densities and osmotic pressures on leaves were also measured with a cold field emission scanning electronic microscope (CFESEM) and a vapor pressure osmometer, respectively. At 100% relative humidity inside the environmental chamber, droplets remained unchanged after they were deposited on a non-permeable glass, but they penetrated leaf tissues after they were deposited on leaves. Foliar uptake time varied with droplet size, droplet deposition location on leaves, and diurnal period, but varied little with <ext-link ext-link-type=uri xlink:href=app:ds:osmotic%20pressure>osmotic pressure</ext-link> and stomatal density. An average uptake rate of 540 μm diameter droplets on a leaf surface at 20°C and 100% relative humidity was 0.401 × 10^-3 ±0.063 × 10^-3 μL s^-1, which was 2.1 times the average uptake rate of 340 μm diameter droplets. The incorporation of the controlled environmental system with 100% relative humidity and the sessile droplet generator to measure foliar uptake rates of water droplets would provide a unique approach to elucidate the foliar uptake mechanism of spray droplets for efficient and effective control of target pests on specific plants.

Development of High-Speed Image Acquisition Systems for Spray Characterization Based on Single-Droplet Experiments

Abstract. Accurate spray and droplet characterization is important for increased understanding of the pesticide spray application process. The goal of this study was to develop two image acquisition systems based on single-droplet experiments using a piezoelectric single-droplet generator and a high-speed imaging technique, which will be used in a later stage of this study to evaluate micro and macro spray characteristics and droplet impact behavior. Experiments with different camera settings, lenses, diffusers, and light sources and the resulting image quality parameters showed the necessity of having a good image acquisition and processing system. The image analysis results contributed to selecting the optimal setup for measuring droplet size and velocity, which consisted of a high-speed camera with 6 I¼s exposure time, a microscope lens at a working distance of 430 mm resulting in a field of view of 10.5 mm A— 8.4 mm, and a xenon backlight without a diffuser. The high-speed camera with a macro video zoom lens at a working distance of 143 mm with a larger field of view (88 mm A— 110 mm) in combination with a halogen spotlight with a diffuser was found to have the best potential for measuring macro spray characteristics, such as the droplet trajectory, spray angle, and spray shape.

Microfluidic methods for non-viral gene delivery.

Microfluidics is a compelling technology that shows considerable promise in applications ranging from gene expression profiling to cell-based assays. Owing to its capacity to enable generation of single droplets and multiple droplet arrays with precisely controlled composition and a narrow size distribution, recently microfluidics has been exploited for delivery of genes. This article provides an overview of recent advances in microfluidic gene delivery, and speculates the prospects for further research. The objectives of this article are to illustrate the potential roles played by microfluidics in gene delivery research, and to shed new light on strategies to enhance the efficiency of gene therapy.

Droplet generation and characterization using a piezoelectric droplet generator and high speed imaging techniques

Accurate spray (droplet) characterization helps in the better understanding of the pesticide spray application process. The goal of this research was to evaluate the characteristics of a single droplet generated using a piezoelectric single droplet generator in 2 modes: Droplet-On-Demand (DOD) and continuous with 4 different orifice sizes. The droplet generator can produce a single droplet, or a continuous stream of uniformly sized droplets. Using a high speed imaging system and image processing algorithms, the effects of pulse width and pulse amplitude in DOD mode and of frequency and pulse amplitude in continuous mode on droplet characteristics (droplet size, droplet velocity and inter droplet spacing) were investigated for different orifice sizes. The system was able to produce droplet diameters within the range from 134.1 to 461.5 μm in DOD, and from 167.2 to 458.6 μm in continuous mode. In addition, droplet velocities ranged from 0.08 to 1.8 m/s in DOD mode and from 1.8 to 4.7 m/s in continuous mode. Validation using a droplet weighing method showed good agreement with the droplet image analysis results.

Detection of Ni, Pb and Zn in water using electrodynamic single-particle levitation and laser-induced breakdown spectroscopy

We report the development of a unique laser-induced breakdown spectroscopy (LIBS) based method for the trace metal analysis of water. The method is further applied to the analysis of aqueous samples containing known concentrations of nickel, lead and zinc. Effects that reduce the sensitivity of the LIBS analysis of aqueous samples were avoided in the presented technology by performing the LIBS analysis from a single dried salt particle which was levitated in an electric field. The salt is added to the water sample prior to analysis. A single-droplet generator injects a droplet of the solution to the measurement chamber. The droplet is trapped using electrodynamic balance technology and metals are highly concentrated as the water from the droplet rapidly evaporates without a need for additional heating. The resultant solid 7μm particle is levitated with a high spatial stability in the LIBS focal volume. The constant mass and position of the particle enable the high reproducibility of the LIBS signal. The limits of detection in the original solution were recorded low 60ppb, 60ppb, and 50ppb for nickel, lead, and zinc, respectively using low, 14mJ excitation pulse energy. The methodology is applicable to the online monitoring of industrial waters due to the achieved sensitivity and robust instrumentation.

Dispersion and evaporation of droplets amended with adjuvants on soybeans

Quantification of the effects of adjuvants on droplet behaviour on plant surfaces is needed to improve pesticide spray application efficiency for soybeans. Dispersion and evaporation of single 300-μm diameter droplets amended with each of four spray adjuvants at five concentrations were investigated for four soybean plant surfaces (abaxial and adaxial leaflet surfaces, petiole, basal stem). The four adjuvants were a crop oil concentrate (COC), a modified seed oil (MSO), a non-ionic surfactant (NIS) and an oil surfactant blend (OSB). A single-droplet generator was used to produce and deposit 300-μm diameter droplets on target surfaces under controlled environmental conditions. Adjuvants significantly increased the dispersion (or wetted area) of droplets on plant surfaces. Droplet-wetted areas increased with increased adjuvant concentrations but not in direct proportion. The average increases of wetted areas across the four soybean plant surfaces were 443, 462, 416, or 343% when the spray mixture was amended with COC, MSO, NIS or OSB at the manufacturer-recommended concentrations, respectively. Among the four surfaces, the largest wetted area was on the abaxial surface, followed by the adaxial surface, the petiole and then the basal stem. Droplet evaporation times were inversely proportional to the wetted areas. The evaporation time of 300-μm diameter droplets ranged from 36 to 142s on the four surfaces when the spray mixture was amended with an adjuvant, whereas the water-only droplets ranged from 161 to 190s. The results demonstrated that use of adjuvants offers great potential to improve the homogeneity of sprayed pesticides, to increase spray coverage and to reduce pesticide application rates on soybean plants. These effects could benefit farmers economically and reduce environmental contamination by pesticides.

Adjuvant Effects on Evaporation Time and Wetted Area of Droplets on Waxy Leaves

The use of an appropriate adjuvant for pesticide applications is a critical process to improve spray deposit characteristics on waxy leaves and to reduce off-target losses. After deposition and evaporation, residue patterns of 500 ° m sessile droplets that incorporated four classes of adjuvants on five different waxy plants were investigated. Droplets were generated with a single-droplet generator and deposited on target leaves placed in an environmentally controlled chamber at 60% relative humidity and 25°C ambient temperature. Adjuvants tested were two oil-based types (crop oil concentrate, or COC; and modified seed oil, or MSO), a nonionic surfactant (NIS), and a mixture (oil surfactant blend, or OSB). Water-only droplets were also tested for comparative purposes. The five waxy plants were difficult to wet and had a water contact angle greater than 90°. The water-only droplets did not spread at all and formed extremely small wetted areas on the leaf surface. The addition of an adjuvant to the spray solution significantly reduced the contact angle and increased the wetted area, but the change or improvements varied with the plant species and adjuvant class. In general, MSO and NIS enhanced the droplet spread and maintained the droplet evaporation time on the waxy leaf surfaces. After evaporation, the residues formed patterns of coffee rings. Droplets with oil-based adjuvants had more uniform residual distribution in the deposition patterns than droplets with the surfactant adjuvant. Results of this study demonstrated that selection of the appropriate class of adjuvants significantly improved deposit formation on waxy leaves, leading to more effectiveness of pesticides.

On-line single droplet deposition for MALDI mass spectrometry

A single droplet generator was coupled with a rotating ball inlet matrix-assisted laser desorption/ionization (MALDI) time of flight (TOF) mass spectrometer. Single droplets with 100 picoliter volume were ejected by a piezoelectric-actuated droplet generator and deposited onto a matrix-coated rotating stainless steel ball at atmospheric pressure. The single droplet deposit was transported to the vacuum side of the instrument where ionization was accomplished using a UV pulsed laser. Using this on-line interface, it was possible to obtain protonated molecule signal from as little as 10 fmol analyte.

Thermo-optical investigation of burning biomass pyrolysis oil droplets

An extensive investigation has been carried out on the thermal behavior of biomass pyrolysis oil derived from different feedstocks (mixed hardwood, pine, and poplar). Experiments were performed on streams of monodispersed droplets (50–100 μm) and on large suspended droplets (300–600 μm). The small droplets were generated by a single-droplet generator and injected in a drop-tube furnace, the temperature of which ranged from 300 to 850°C. Light-scattering methods have been used to follow the process undergone by the pyrolysis oil droplets. The solid material, residual of the droplet heating and vaporization processes, has been examined by means of optical and scanning electron microscopy. Two different morphologies of residual particles have been observed at the exit of the furnace: (a) more compact, mechanically resistant spheres, with typical diameter of 10–40 μm, and (b) fragile, glasslike cenospheres with thin walls and menisci, with diameter of 100–200 μm. The large droplets were suspended at the exit of the furnace, using both a quartz fiber and an exposed junction thermocouple. The furnace temperature was varied between 400 and 1200°C. The phenomena, occurring during the vaporization and burning of each droplet, were followed by coupling the thermocouple measurement to high-speed visualization. The imaging was performed by means of fast digital video recording (50–250 frames/s) and high-speed cinematography (400–1000 frames/s). Temperature-time curves of the burning droplets show a stepped behavior, with two zones at constant temperature, at ∼100 and ∼450°C. The first step is due to the vaporization of water. The second plateau corresponds to the heating of heavy compounds due to selective vaporization and liquid-phase pyrolysis. Swelling, shrinking, and microexplosions with ejection of matter characterize this phase. The combustion of the droplets starts with an enveloping blue flame. The flame then develops a yellow tail of increasing size. After the flame extinction, the remaining char particle burns without residual.