Centrifugal Microfluidics Research Articles

Raman on a disc: high-quality Raman spectroscopy in an open channel on a centrifugal microfluidic disc.

The implausible combination of centrifugal disc microfluidics and un-covered channels provides a simple way in which Raman spectroscopy can be implemented in industrially-relevant lab-on-a disc technology. Here we demonstrate these advantages by detecting very low concentrations of melamine in liquid milk, without pre-processing, without surface enhancement of the Raman signal and with no evidence of spectral contamination from the polymeric chip itself. A limit of detection (LOD) of 203 ppm for melamine in milk was achieved from Raman spectra of milk after drying. The centrifugal disc rotation and microchannel geometry results in rapid and reliable filling of the channels and in meniscus shape control, enabling reproducible Raman detection with quantitative precision.

The Effect of Moment of Inertia on the Liquids in Centrifugal Microfluidics.

The flow of liquids in centrifugal microfluidics is unidirectional and dominated by centrifugal and Coriolis forces (i.e., effective only at T-junctions). Developing mechanisms and discovering efficient techniques to propel liquids in any direction other than the direction of the centrifugal force has been the subject of a large number of studies. The capillary force attained by specific surface treatments, pneumatic energy, active and passive flow reciprocation and Euler force have been previously introduced in order to manipulate the liquid flow and push it against the centrifugal force. Here, as a new method, the moment of inertia of the liquid inside a chamber in a centrifugal microfluidic platform is employed to manipulate the flow and propel the liquid passively towards the disc center. Furthermore, the effect of the moment of inertia on the liquid in a rectangular chamber is evaluated, both in theory and experiments, and the optimum geometry is defined. As an application of the introduced method, the moment of inertia of the liquid is used in order to mix two different dyed deionized (DI) waters; the mixing efficiency is evaluated and compared to similar mixing techniques. The results show the potential of the presented method for pumping liquids radially inward with relatively high flow rates (up to 23 mm3/s) and also efficient mixing in centrifugal microfluidic platforms.

Conditional siphon priming for multi-step assays on centrifugal microfluidic platforms

Centrifugal microfluidics has proven to be successful in biomedical diagnostics, biological analysis and environmental monitoring. However, the automation of multi-step sample processing, reaction and detection remains a great challenge. In this study, a conditional siphon priming technique is introduced for multi-step liquid addition or selective routing. Since the siphon channel is locally modified or venting is blocked by liquid in another chamber, siphon priming can be triggered by liquid addition or venting at low frequency. Using this technique, sequential release of liquids and selective routing in multiple manners were successfully achieved. As a proof of concept, a centrifugal microfluidic platform was designed for on-site ammonium analysis in water samples. The linear range of ammonium concentrations is extended by integration of a dilution process. This novel valving technique provides new solutions for integration of complex liquid handling processes on centrifugal platforms.

Numerical simulation of centrifugal serpentine micromixers and analyzing mixing quality parameters

Centrifugal microfluidics or the Lab on a CD (LOCD) has developed vast applications in biomedical researches and analyses. Fluid mixing is an application of the LOCD. In this paper, multiple centrifugal micromixers were simulated. Various parameters were originally presumed to have an effect on mixing performance. These parameters include inlet angle, angular velocity, cross-sectional profile, perpendicular length ratio and the number of channels in series. They were each analyzed through simulations. It was gathered that the inlet angle does not significantly affect the mixing quality. Increasing angular velocity steadily increases mixing quality for all geometries. The vertical triangular cross section gives the best mixing quality and the horizontal rectangular cross section has the worst. Also both increasing the perpendicular length ratio and adding an additional microchannel in series to the original, enhances mixing.

A numerical study of the Coriolis effect in centrifugal microfluidics with different channel arrangements

The Coriolis force has been of great interest to control the transversal flow that is critical for mixing or switching fluids in centrifugal microfluidics. Therefore, the variation in the Coriolis effect has been extensively investigated by varying the rotational speeds and the cross-sectional geometry of microchannels. However, the subject of such investigations has been limited to radially positioned microchannels even though channels can lie everywhere on the rotating platform with different arrangements. In this study, we use numerical methods to investigate the Coriolis effect resulting from the angular alignment (AA) and radial displacement (RD) of rotating microchannels. Our analysis focuses on determining the contribution that different channel arrangements have in the deviation of parabolic velocity profiles, which is generally produced by the effective Coriolis force. We found that the flow can deviate even at a low rotational speed, where the Coriolis force is negligible, with an AA of up to 33 % which is a sufficient amount for flow switching. Once the rotational speed reaches to the critical RPM, the flow deviates by an effective Coriolis force, but the deviation systematically varies with AA or RD. As the Coriolis force becomes more dominant with a high rotational speed, the deviation reaches a saturation point, while flow rate is regulated by AA or RD, enabling the flow rate to remain low even at very high RPM, without reducing the deviation. The variation in the Coriolis effect due to the different channel arrangements investigated in this study is believed to provide an essential basis to design and develop centrifugal microfluidic systems.

Challenges in the Use of Compact Disc-Based Centrifugal Microfluidics for Healthcare Diagnostics at the Extreme Point of Care.

Since its inception, Compact Disc (CD)-based centrifugal microfluidic technology has drawn a great deal of interest within research communities due to its potential use in biomedical applications. The technology has been referred to by different names, including compact-disc microfluidics, lab-on-a-disk, lab-on-a-CD and bio-disk. This paper critically reviews the state-of-the-art in CD-based centrifugal microfluidics devices and attempts to identify the challenges that, if solved, would enable their use in the extreme point of care. Sample actuation, manufacturing, reagent storage and implementation, target multiplexing, bio-particle detection, required hardware and system disposal, and sustainability are the topics of focus.

Analysis and experiment of transient filling flow into a rectangular microchannel on a rotating disk

In order to predict the time-dependent behaviors of the moving front in lab-on-a-CD systems or centrifugal pumping, an analytical expression and experimental methods of centrifugal-force-driven transient filling flow into a rectangular microchannel in centrifugal microfluidics are presented in this paper. Considering the effect of surface tension, and neglecting the effect of Coriolis force, the velocity profile, flow rate, the moving front displacement and the pressure distribution along the microchannel are characterized. Experiments are carried out using the image-capturing unit to measure the shift of the flow in rectangular microchannels. The flow characteristics in rectangular microchannels with different cross-sectional dimensions (200, 300 and 400 μm in width and 140, 240 and 300 μm in depth) and length (18 and 25 mm) under different rotational speed are investigated. According to the experimental data, the model can be more reasonable to predict the flow displacement with time, and the errors between theoretical and the experimental will decrease with increasing the cross-section size of the microchannel.

Photochemical Synthesis and Versatile Functionalization Method of a Robust Porous Poly(ethylene glycol methacrylate-co-allyl methacrylate) Monolith Dedicated to Radiochemical Separation in a Centrifugal Microfluidic Platform.

The use of a centrifugal microfluidic platform is an alternative to classical chromatographic procedures for radiochemistry. An ion-exchange support with respect to the in situ light-addressable process of elaboration is specifically designed to be incorporated as a radiochemical sample preparation module in centrifugal microsystem devices. This paper presents a systematic study of the synthesis of the polymeric porous monolith poly(ethylene glycol methacrylate-co-allyl methacrylate) used as a solid-phase support and the versatile and robust photografting process of the monolith based on thiol-ene click chemistry. The polymerization reaction is investigated, varying the formulation of the polymerisable mixture. The robustness of the stationary phase was tested in concentrated nitric acid. Thanks to their unique “easy-to-use” features, centrifugal microfluidic platforms are potential successful candidates for the downscaling of chromatographic separation of radioactive samples (automation, multiplexing, easy integration in glove-boxes environment, and low cost of maintenance).

Challenges and Opportunities of Centrifugal Microfluidics for Extreme Point-of-Care Testing.

The advantages offered by centrifugal microfluidic systems have encouraged its rapid adaptation in the fields of in vitro diagnostics, clinical chemistry, immunoassays, and nucleic acid tests. Centrifugal microfluidic devices are currently used in both clinical and point-of-care settings. Recent studies have shown that this new diagnostic platform could be potentially used in extreme point-of-care settings like remote villages in the Indian subcontinent and in Africa. Several technological inventions have decentralized diagnostics in developing countries; however, very few microfluidic technologies have been successful in meeting the demand. By identifying the finest difference between the point-of-care testing and extreme point-of-care infrastructure, this review captures the evolving diagnostic needs of developing countries paired with infrastructural challenges with technological hurdles to healthcare delivery in extreme point-of-care settings. In particular, the requirements for making centrifugal diagnostic devices viable in developing countries are discussed based on a detailed analysis of the demands in different clinical settings including the distinctive needs of extreme point-of-care settings.

A Review of Biomedical Centrifugal Microfluidic Platforms.

Centrifugal microfluidic or lab-on-a-disc platforms have many advantages over other microfluidic systems. These advantages include a minimal amount of instrumentation, the efficient removal of any disturbing bubbles or residual volumes, and inherently available density-based sample transportation and separation. Centrifugal microfluidic devices applied to biomedical analysis and point-of-care diagnostics have been extensively promoted recently. This paper presents an up-to-date overview of these devices. The development of biomedical centrifugal microfluidic platforms essentially covers two categories: (i) unit operations that perform specific functionalities, and (ii) systems that aim to address certain biomedical applications. With the aim to provide a comprehensive representation of current development in this field, this review summarizes progress in both categories. The advanced unit operations implemented for biological processing include mixing, valving, switching, metering and sequential loading. Depending on the type of sample to be used in the system, biomedical applications are classified into four groups: nucleic acid analysis, blood analysis, immunoassays, and other biomedical applications. Our overview of advanced unit operations also includes the basic concepts and mechanisms involved in centrifugal microfluidics, while on the other hand an outline on reported applications clarifies how an assembly of unit operations enables efficient implementation of various types of complex assays. Lastly, challenges and potential for future development of biomedical centrifugal microfluidic devices are discussed.

CD-Based Microfluidics for Primary Care in Extreme Point-of-Care Settings.

We review the utility of centrifugal microfluidic technologies applied to point-of-care diagnosis in extremely under-resourced environments. The various challenges faced in these settings are showcased, using areas in India and Africa as examples. Measures for the ability of integrated devices to effectively address point-of-care challenges are highlighted, and centrifugal, often termed CD-based microfluidic technologies, technologies are presented as a promising platform to address these challenges. We describe the advantages of centrifugal liquid handling, as well as the ability of a standard CD player to perform a number of common laboratory tests, fulfilling the role of an integrated lab-on-a-CD. Innovative centrifugal approaches for point-of-care in extremely resource-poor settings are highlighted, including sensing and detection strategies, smart power sources and biomimetic inspiration for environmental control. The evolution of centrifugal microfluidics, along with examples of commercial and advanced prototype centrifugal microfluidic systems, is presented, illustrating the success of deployment at the point-of-care. A close fit of emerging centrifugal systems to address a critical panel of tests for under-resourced clinic settings, formulated by medical experts, is demonstrated. This emphasizes the potential of centrifugal microfluidic technologies to be applied effectively to extremely challenging point-of-care scenarios and in playing a role in improving primary care in resource-limited settings across the developing world.

An in-line spectrophotometer on a centrifugal microfluidic platform for real-time protein determination and calibration.

In this paper, an in-line, low-cost, miniature and portable spectrophotometric detection system is presented and used for fast protein determination and calibration in centrifugal microfluidics. Our portable detection system is configured with paired emitter and detector diodes (PEDD), where the light beam between both LEDs is collimated with enhanced system tolerance. It is the first time that a physical model of PEDD is clearly presented, which could be modelled as a photosensitive RC oscillator. A portable centrifugal microfluidic system that contains a wireless port in real-time communication with a smartphone has been built to show that PEDD is an effective strategy for conducting rapid protein bioassays with detection performance comparable to that of a UV-vis spectrophotometer. The choice of centrifugal microfluidics offers the unique benefits of highly parallel fluidic actuation at high accuracy while there is no need for a pump, as inertial forces are present within the entire spinning disc and accurately controlled by varying the spinning speed. As a demonstration experiment, we have conducted the Bradford assay for bovine serum albumin (BSA) concentration calibration from 0 to 2 mg mL(-1). Moreover, a novel centrifugal disc with a spiral microchannel is proposed for automatic distribution and metering of the sample to all the parallel reactions at one time. The reported lab-on-a-disc scheme with PEDD detection may offer a solution for high-throughput assays, such as protein density calibration, drug screening and drug solubility measurement that require the handling of a large number of reactions in parallel.

The use of polybutene for controlling the flow of liquids in centrifugal microfluidic systems

The field of centrifugal microfluidics has evolved over the last several decades to allow implementation of complex biological and chemical assays on Lab-on-Disc (LOD) platforms. Present study describes the use of polymer polybutene for tuning hydrophobic siphons and for liquid volume definition on a centrifugal microfluidic platform. Both the siphon tuning and the volume definition steps are carried out by generating negative pressure that results from the volume expansion caused by the transfer of polybutene from a dedicated chamber into a secondary reservoir via a connecting siphon. The hydrophobic valve of the chamber that holds polybutene bursts open at specific angular velocities that depend on the height and density of the liquid column. Thus, the parameters of siphon activation can be adjusted by tuning the burst angular velocity of the valve that is driven by filling the tuning reservoir with a specific volume of polybutene. The same disc construction can be utilized to provide volume definition functionality to transfer liquids from one reservoir to another reservoir in as many fractions as there are immiscible liquids of different densities in the tuning chamber. The presented work also demonstrates the use of polybutene in sealing fluidic chambers to improve heating efficiency and to minimize evaporation during thermal cycling required for applications such as PCR amplification. Finally, the use of polybutene as a stationary liquid phase in droplet production on a spinning disc is demonstrated.

Rigorous buoyancy driven bubble mixing for centrifugal microfluidics.

We present batch-mode mixing for centrifugal microfluidics operated at fixed rotational frequency. Gas is generated by the disk integrated decomposition of hydrogen peroxide (H2O2) to liquid water (H2O) and gaseous oxygen (O2) and inserted into a mixing chamber. There, bubbles are formed that ascent through the liquid in the artificial gravity field and lead to drag flow. Additionaly, strong buoyancy causes deformation and rupture of the gas bubbles and induces strong mixing flows in the liquids. Buoyancy driven bubble mixing is quantitatively compared to shake mode mixing, mixing by reciprocation and vortex mixing. To determine mixing efficiencies in a meaningful way, the different mixers are employed for mixing of a lysis reagent and human whole blood. Subsequently, DNA is extracted from the lysate and the amount of DNA recovered is taken as a measure for mixing efficiency. Relative to standard vortex mixing, DNA extraction based on buoyancy driven bubble mixing resulted in yields of 92 ± 8% (100 s mixing time) and 100 ± 8% (600 s) at 130g centrifugal acceleration. Shake mode mixing yields 96 ± 11% and is thus equal to buoyancy driven bubble mixing. An advantage of buoyancy driven bubble mixing is that it can be operated at fixed rotational frequency, however. The additional costs of implementing buoyancy driven bubble mixing are low since both the activation liquid and the catalyst are very low cost and no external means are required in the processing device. Furthermore, buoyancy driven bubble mixing can easily be integrated in a monolithic manner and is compatible to scalable manufacturing technologies such as injection moulding or thermoforming. We consider buoyancy driven bubble mixing an excellent alternative to shake mode mixing, in particular if the processing device is not capable of providing fast changes of rotational frequency or if the low average rotational frequency is challenging for the other integrated fluidic operations.

System-level network simulation for robust centrifugal-microfluidic lab-on-a-chip systems.

Centrifugal microfluidics shows a clear trend towards a higher degree of integration and parallelization. This trend leads to an increase in the number and density of integrated microfluidic unit operations. The fact that all unit operations are processed by the same common spin protocol turns higher integration into higher complexity. To allow for efficient development anyhow, we introduce advanced lumped models for network simulations in centrifugal microfluidics. These models consider the interplay of centrifugal and Euler pressures, viscous dissipation, capillary pressures and pneumatic pressures. The simulations are fast and simple to set up and allow for the precise prediction of flow rates as well as switching and valving events. During development, channel and chamber geometry variations due to manufacturing tolerances can be taken into account as well as pipetting errors, variations of contact angles, compliant chamber walls and temperature variations in the processing device. As an example of considering these parameters during development, we demonstrate simulation based robustness analysis for pneumatic siphon valving in centrifugal microfluidics. Subsequently, the influence of liquid properties on pumping and valving is studied for four liquids relevant for biochemical analysis, namely, water (large surface tension), blood plasma (large contact angle hysteresis), ethanol/water (highly wetting) and glycerine/water (highly viscous). In a second example, we derive a spin protocol to attain a constant flow rate under varying pressure conditions. Both examples show excellent agreement with experimental validations.

Fully automated chemiluminescence detection using an electrified-Lab-on-a-Disc (eLoaD) platform

Typical Lab-on-a-Disc (LoaD) platforms cannot make a continuous measurement while the disc is spinning; this drawback means that the disc usually must be stopped and aligned with a sensor. This can result in measurement errors in time-dependent assays along with inaccuracies due to liquid displacement and bubble formation in the absence of a stabilising centrifugal field. This paper presents a novel concept for a wirelessly electrified-Lab-on-a-Disc (eLoaD) platform that allows continuous measurement of experimental parameters while the disc is spinning. This platform incorporates all the components needed for measurement within the rotating frame of reference, and bidirectional transmission of data outside this reference frame, thus allowing for online measurement independent of the rotation of the disc. The eLoaD platform is conceived in a modular manner whereby an interchangeable and non-disposable 'Application Disc' can be fitted to the eLoaD platform and so the system can be adapted for a range of optical, electrochemical and other measurement types. As an application example, optical readout, using the Application Disc fitted with a silicon photomultiplier, is demonstrated using a tagged chemiluminescent antibody, which is commonly used, for instance, in ELISA assays. The precision of the eLoaD platform is >94%, while its accuracy, when compared to a commercial benchtop luminometer, is higher than 96%. The modular design of this platform will permit extension of this technology to many other LoaD applications.

Pneumatic siphon valving and switching in centrifugal microfluidics controlled by rotational frequency or rotational acceleration

Air-pressure-mediated, pneumatic siphon valves employ temporary storage and subsequent release of pneumatic energy, exclusively controlled by rotation of the disk. Implementation is easy, and robust valves can be integrated in a monolithic way at minimum additional costs. However, so far, pneumatic siphon valving requires deceleration from high to low rotational frequencies. Valve opening is performed always when the rotation of the disk drops below a critical rotational frequency. To overcome this limitation, we introduce new concepts for pneumatic siphon valving which enable operation of the disk at any rotational frequency without unwanted bursts of the siphon valves. Thus, the design space for pneumatic siphon valves in centrifugal microfluidics is significantly extended. Three types of pneumatic siphon valves are presented with release control at (1) rotational frequencies between 25 and 48 Hz, (2) positive rotational accelerations between 1 and 22 Hz s−1, and (3) negative rotational accelerations between 5 and 20 Hz s−1. Finally, we combine two valve types to realize robust switching into two fluidic paths with flow rate ratios of 94/6 and 0/100.

Microfluidic size separation of cells and particles using a swinging bucket centrifuge.

Biomolecular separation is crucial for downstream analysis. Separation technique mainly relies on centrifugal sedimentation. However, minuscule sample volume separation and extraction is difficult with conventional centrifuge. Furthermore, conventional centrifuge requires density gradient centrifugation which is laborious and time-consuming. To overcome this challenge, we present a novel size-selective bioparticles separation microfluidic chip on a swinging bucket minifuge. Size separation is achieved using passive pressure driven centrifugal fluid flows coupled with centrifugal force acting on the particles within the microfluidic chip. By adopting centrifugal microfluidics on a swinging bucket rotor, we achieved over 95% efficiency in separating mixed 20 μm and 2 μm colloidal dispersions from its liquid medium. Furthermore, by manipulating the hydrodynamic resistance, we performed size separation of mixed microbeads, achieving size efficiency of up to 90%. To further validate our device utility, we loaded spiked whole blood with MCF-7 cells into our microfluidic device and subjected it to centrifugal force for a mere duration of 10 s, thereby achieving a separation efficiency of over 75%. Overall, our centrifugal microfluidic device enables extremely rapid and label-free enrichment of different sized cells and particles with high efficiency.

Automated Forensic Animal Family Identification by Nested PCR and Melt Curve Analysis on an Off-the-Shelf Thermocycler Augmented with a Centrifugal Microfluidic Disk Segment.

Nested PCR remains a labor-intensive and error-prone biomolecular analysis. Laboratory workflow automation by precise control of minute liquid volumes in centrifugal microfluidic Lab-on-a-Chip systems holds great potential for such applications. However, the majority of these systems require costly custom-made processing devices. Our idea is to augment a standard laboratory device, here a centrifugal real-time PCR thermocycler, with inbuilt liquid handling capabilities for automation. We have developed a microfluidic disk segment enabling an automated nested real-time PCR assay for identification of common European animal groups adapted to forensic standards. For the first time we utilize a novel combination of fluidic elements, including pre-storage of reagents, to automate the assay at constant rotational frequency of an off-the-shelf thermocycler. It provides a universal duplex pre-amplification of short fragments of the mitochondrial 12S rRNA and cytochrome b genes, animal-group-specific main-amplifications, and melting curve analysis for differentiation. The system was characterized with respect to assay sensitivity, specificity, risk of cross-contamination, and detection of minor components in mixtures. 92.2% of the performed tests were recognized as fluidically failure-free sample handling and used for evaluation. Altogether, augmentation of the standard real-time thermocycler with a self-contained centrifugal microfluidic disk segment resulted in an accelerated and automated analysis reducing hands-on time, and circumventing the risk of contamination associated with regular nested PCR protocols.

Detection methods for centrifugal microfluidic platforms.

Centrifugal microfluidics has attracted much interest from academia as well as industry, since it potentially offers solutions for affordable, user-friendly and portable biosensing. A wide range of so-called fluidic unit operations, e.g. mixing, metering, liquid routing, and particle separation, have been developed and allow automation and integration of complex assay protocols in lab-on-a-disc systems. Besides liquid handling, the detection strategy for reading out the assay is crucial for developing a fully integrated system. In this review, we focus on biosensors and readout methods for the centrifugal microfluidics platform and cover optical as well as mechanical and electrical detection principles.