Electronic drop sensing in microfluidic devices: automated operation of a nanoliter viscometer (original) (raw)
Related papers
Nanoliter droplet viscometer with additive-free operation
Lab on a Chip, 2013
Measurement of a solution's viscosity is an important analytic technique for a variety of applications including medical diagnosis, pharmaceutical development, and industrial processing. The use of dropletbased (eg, water-in-oil) microfluidics for viscosity measurements allows nanoliter-scale sample volumes to be used, much smaller than those either in standard macro-scale rheometers or in single-phase microfluidic viscometers.
Microfluidic droplet content detection using integrated capacitive sensors
Microfluidic capacitive sensors have been used for detection of droplets, however they have been lacking the sensitivity required for detecting the content of droplets. In this study, we developed a scalable, portable, robust and high sensitivity capacitive microdroplet content detection system using coplanar electrodes with nanometer thick silicon dioxide (SiO 2) passivation layer and off-the-shelf capacitive sensors. The microfluidic chip we have designed provides easy and rapid modification of droplet content by mixing two aqueous liquids at any given ratio. The change in dielectric constant of the droplet content leads to the change in capacitive signal. The dielectric content of droplets was modified continuously while corresponding capacitance signal was measured. The resolution of the system was measured as 3 dielectric permittivity units. The results were verified using a semiconductor parameter analyzer. The application specific integrated circuit used in this work enables a portable, low-cost detection system and matches the performance of bench-top analyzers. Automated and precise measurement of dielectric content in droplets for biochemical assay monitoring is a major application of the presented system.
Detection of microdroplet size and speed using capacitive sensors
Detection of the presence, size and speed of microdroplets in microfluidic devices is presented using commercially available capacitive sensors which make the droplet based microfluidic systems scalable and inexpensive. Cross-contamination between the droplets is eliminated by introducing a passivation layer between the sensing electrodes and droplets. A simple T-junction generator is used to generate droplets in microchannels. Coplanar electrodes are used to form a capacitance through the microfluidic channel. The change in capacitance due to the presence of a droplet in the sensing area is detected and used to determine the size and speed of the droplet. The design of a single pair of electrodes is used to detect the presence of a droplet and the interdigital finger design is used to detect the size and speed of the droplet. An analytical model is developed to predict the detection signal and guide the experimental optimization of the sensor geometry. The measured droplet information is displayed through a Labview interface in real-time. The use of capacitance sensors to monitor droplet sorting at a T-junction is also presented. The discussions in this paper can be generalized to any droplet detection application and can serve as a guideline in sensor selection.
A capacitive sensor for non-contact nanoliter droplet detection
Sensors and Actuators A: Physical, 2009
This paper reports on a sensor for the detection of microdroplets in flight. The presented sensor is based on a capacitive principle, which allows for non-contact monitoring of a complete droplet dispensing process. In the presented experiments the change in capacity caused by liquid droplets in the range of a few nanoliters passing through the electric field of the sensor is studied. From the capacitive change the droplet presence can be deduced with a reliability of 100%, which means that every single droplet dispensed within the experiments caused a significant signal change. In addition, the sensor signal is sensitive to the droplet's volume V, dielectric constant ε r (epsilon) and velocity v. It turns out that every specific droplet exhibits a characteristic "fingerprint" signal depending on these parameters. Especially the droplet volume correlates very well with the peak value of the extracted signal. Therefore, the calibrated sensor is able to determine the volume of dispensed droplets in the range from 20 to 65 nl with a resolution of less than 2 nl. Furthermore, the printed circuit board (PCB) technology applied for fabrication of the sensor enables a very cost efficient and flexible realisation of the whole sensor unit. The non-contact capacitive principle prevents contamination and loss of media. Therefore, the proposed approach is well suited for high precision droplet presence detection and low cost online monitoring of liquid volumes in microdispensing processes for various applications.
Electroanalysis, 2019
Microfluidic devices were designed to electrochemically detect in a two-phase flow the velocity, size and content of aqueous droplets containing redox species. The principle of these determinations is based on the analysis of a unique chronoamperometric response recorded during the passage of a droplet over channel microelectrodes. Two configurations of electrochemical cell with different geometries were investigated both theoretically and experimentally. Velocity and size of droplets, as well as internal recirculating convection within droplets, were evaluated from chronoamperometric curves by specific transition times depending on the cell configuration. In addition, the droplet content was probed from the Faradaic current controlled by mass transport and by internal hydrodynamic regime. For droplet velocity and size, experimental data were systematically compared to optical measurements. All the results demonstrated the high performance of the electrochemical detection reached under these conditions. They successfully validate the concept of self-consistent electrochemical detections of aqueous droplets within microchannels for the simultaneous determination of their velocity, size and content.
On–Chip Droplets Sensing using Capacitive Technique
Jurnal …, 2013
Significant attention has been given on the development of droplets-based microfluidic system because of its potential and apparent advantages. Beside the advantages of reducing the sample volume, it's also offer less time consuming for the analysis. Optical and fluorescence among the famous method that was used in detection of droplets but they are normally bulky, expensive and not easily accessed. This paper proposed a simple, low cost and high sensitivity for droplets sensing in microfluidic devices by using capacitive sensor. Coplanar electrodes are used to form a capacitance through the microfluidic channel. The design of eight pair of electrodes was used to detect the presence of a droplet. Changes in capacitance due to the presence of a droplet in the sensing area is detected and used to trigger the microscope to capture the image of detected droplets in microchannel. The measurement of droplets detected and counting are displayed through a LABVIEW interface in the real time.
In-line characterization and identification of micro-droplets on-chip
Optofluidics, Microfluidics and Nanofluidics, 2014
We present an integrated optofluidic sensor system for in-line characterization of micro-droplets. The device provides information about the droplet generation frequency, the droplet volume, and the content of the droplet. Due to its simplicity this principle can easily be implemented with other microfluidic components on one and the same device. The sensor is based on total internal reflection phenomena. Droplets are pushed through a microfluidic channel which is hit by slightly diverging monochromatic light. At the solid-liquid interface parts of the rays experience total internal reflection while another part is transmitted. The ratio of reflected to transmitted light depends on the refractive index of the solution. Both signals are recorded simultaneously and provide a very stable output signal for the droplet characterization. With the proposed system passing droplets were counted up to 320 droplets per second and droplets with different volumes could be discriminated. In a final experiment droplets with different amounts of dissolved CaCl 2 were distinguished based on their reflected and transmitted light pattern. This principle can be applied for the detection of any molecules in microdroplets which significantly influence the refractive index of the buffer solution.
Micro/Nanodroplets in Microfluidic Devices
Springer Handbook of Nanotechnology, 2007
Fluid is often transported in the form of droplets in nature. From the formation of clouds to the condensation of dew on leaves, droplets are formed spontaneously in air, on solids and in immiscible fluids. In biological systems, droplets with lipid bilayer membranes are used to transport subnanoliter amounts of reagents between organelles, between cells, and between organs, in processes that control our day-today metabolic activities. The precision of such systems is self-evident and proves that dropletbased systems provide intrinsically efficient ways to perform controlled transport, reactions and signaling. This precision and efficiency can be utilized in many lab-on-a-chip applications by manipulating individual droplets using microfabricated force gradients. Complex segmented flow processes involving generating, fusing, splitting and sorting droplets have been developed to digitally control fluid volumes and concentrations to nanoliter levels. In this chapter, microfluidic techniques for manipulating droplets are reviewed and analyzed.
Optical detection for droplet size control in microfluidic droplet-based analysis systems
Sensors and Actuators B: Chemical, 2006
This paper reports on a hybrid polymeric microfluidic device with optical detection for droplet-based systems. The optical part of the device is integrated by a hybrid concept. The microfluidic structures were fabricated using CO 2 laser on poly methylmethacrylate (PMMA) substrate. The microfluidic network consists of two microchannels for forming droplets of an aqueous liquid in an immiscible carrier liquid. The optical component consists of two optical fibers for guiding laser light from the source, through the detection point, to a photo diode. The formed droplets pass the detection point and diffract the incoming laser light. The detected signal at the photo diode can be used for evaluating droplet size, droplet shape, and droplet formation frequency. The device can detect very high formation frequencies, which are not detectable using a conventional CCD camera/microscope setup.
Label-Free Sensing in Microdroplet-Based Microfluidic Systems
Chemosensors, 2018
Droplet microfluidic systems have evolved as fluidic platforms that use much less sample volume and provide high throughput for biochemical analysis compared to conventional microfluidic devices. The variety of droplet fluidic applications triggered several detection techniques to be applied for analysis of droplets. In this review, we focus on label-free droplet detection techniques that were adapted to various droplet microfluidic platforms. We provide a classification of most commonly used droplet platform technologies. Then we discuss the examples of various label-free droplet detection schemes implemented for these platforms. While providing the research landscape for label-free droplet detection methods, we aim to highlight the strengths and shortcomings of each droplet platform so that a more targeted approach can be taken by researchers when selecting a droplet platform and a detection scheme for any given application.