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Fulltext Push pull microfluidics on a multi-level 3D CD

Thio TH, Ibrahim F, Al-Faqheri W, Moebius J, Khalid NS, Soin N, et al.

Lab Chip, 2013 Aug 21;13(16):3199-209.
PMID: 23774994 DOI: 10.1039/c3lc00004d

A technique known as thermo-pneumatic (TP) pumping is used to pump fluids on a microfluidic compact disc (CD) back towards the CD center against the centrifugal force that pushes liquids from the center to the perimeter of the disc. Trapped air expands in a TP air chamber during heating, and this creates positive pressure on liquids located in chambers connected to that chamber. While the TP air chamber and connecting channels are easy to fabricate in a one-level CD manufacturing technique, this approach provides only one way pumping between two chambers, is real-estate hungry and leads to unnecessary heating of liquids in close proximity to the TP chamber. In this paper, we present a novel TP push and pull pumping method which allows for pumping of liquid in any direction between two connected liquid chambers. To ensure that implementation of TP push and pull pumping also addresses the issue of space and heating challenges, a multi-level 3D CD design is developed, and localized forced convection heating, rather than infra-red (IR) is applied. On a multi-level 3D CD, the TP features are placed on a top level separate from the rest of the microfluidic processes that are implemented on a lower separate level. This approach allows for heat shielding of the microfluidic process level, and efficient usage of space on the CD for centrifugal handling of liquids. The use of localized forced convection heating, rather than infra-red (IR) or laser heating in earlier implementations allows not only for TP pumping of liquids while the CD is spinning but also makes heat insulation for TP pumping and other fluidic functions easier. To aid in future implementations of TP push and pull pumping on a multi-level 3D CD, study on CD surface heating is also presented. In this contribution, we also demonstrate an advanced application of pull pumping through the implementation of valve-less switch pumping.

Matched MeSH terms: Compact Disks*
Fulltext Sequential push-pull pumping mechanism for washing and evacuation of an immunoassay reaction chamber on a microfluidic CD platform

Thio TH, Ibrahim F, Al-Faqheri W, Soin N, Kahar Bador M, Madou M

PLoS One, 2015;10(4):e0121836.
PMID: 25853411 DOI: 10.1371/journal.pone.0121836

A centrifugal compact disc (CD) microfluidic platform with reservoirs, micro-channels, and valves can be employed for implementing a complete immunoassay. Detection or biosensor chambers are either coated for immuno-interaction or a biosensor chip is inserted in them. On microfluidic CDs featuring such multi-step chemical/biological processes, the biosensor chamber must be repeatedly filled with fluids such as enzymes solutions, buffers, and washing solutions. After each filling step, the biosensor chamber needs to be evacuated by a passive siphoning process to prepare it for the next step in the assay. However, rotational speed dependency and limited space on a CD are two big obstacles to performing such repetitive filling and siphoning steps. In this work, a unique thermo-pneumatic (TP) Push-Pull pumping method is employed to provide a superior alternative biosensor chamber filling and evacuation technique. The proposed technique is demonstrated on two CD designs. The first design features a simple two-step microfluidic process to demonstrate the evacuation technique, while the second design shows the filling and evacuation technique with an example sequence for an actual immunoassay. In addition, the performance of the filling and evacuation technique as a washing step is also evaluated quantitatively and compared to the conventional manual bench top washing method. The two designs and the performance evaluation demonstrate that the technique is simple to implement, reliable, easy to control, and allows for repeated push-pulls and thus filling and emptying of the biosensor chamber. Furthermore, by addressing the issue of rotational speed dependency and limited space concerns in implementing repetitive filling and evacuation steps, this newly introduced technique increases the flexibility of the microfluidic CD platform to perform multi-step biological and chemical processes.

Matched MeSH terms: Compact Disks*
Fulltext Theoretical development and critical analysis of burst frequency equations for passive valves on centrifugal microfluidic platforms

Thio TH, Soroori S, Ibrahim F, Al-Faqheri W, Soin N, Kulinsky L, et al.

Med Biol Eng Comput, 2013 May;51(5):525-35.
PMID: 23292292 DOI: 10.1007/s11517-012-1020-7

This paper presents a theoretical development and critical analysis of the burst frequency equations for capillary valves on a microfluidic compact disc (CD) platform. This analysis includes background on passive capillary valves and the governing models/equations that have been developed to date. The implicit assumptions and limitations of these models are discussed. The fluid meniscus dynamics before bursting is broken up into a multi-stage model and a more accurate version of the burst frequency equation for the capillary valves is proposed. The modified equations are used to evaluate the effects of various CD design parameters such as the hydraulic diameter, the height to width aspect ratio, and the opening wedge angle of the channel on the burst pressure.

Matched MeSH terms: Compact Disks
Fulltext Development of a passive liquid valve (PLV) utilizing a pressure equilibrium phenomenon on the centrifugal microfluidic platform

Al-Faqheri W, Ibrahim F, Thio TH, Bahari N, Arof H, Rothan HA, et al.

Sensors (Basel), 2015 Feb 25;15(3):4658-76.
PMID: 25723143 DOI: 10.3390/s150304658

In this paper, we propose an easy-to-implement passive liquid valve (PLV) for the microfluidic compact-disc (CD). This valve can be implemented by introducing venting chambers to control the air flow of the source and destination chambers. The PLV mechanism is based on equalizing the main forces acting on the microfluidic CD (i.e., the centrifugal and capillary forces) to control the burst frequency of the source chamber liquid. For a better understanding of the physics behind the proposed PLV, an analytical model is described. Moreover, three parameters that control the effectiveness of the proposed valve, i.e., the liquid height, liquid density, and venting chamber position with respect to the CD center, are tested experimentally. To demonstrate the ability of the proposed PLV valve, microfluidic liquid switching and liquid metering are performed. In addition, a Bradford assay is performed to measure the protein concentration and evaluated in comparison to the benchtop procedure. The result shows that the proposed valve can be implemented in any microfluidic process that requires simplicity and accuracy. Moreover, the developed valve increases the flexibility of the centrifugal CD platform for passive control of the liquid flow without the need for an external force or trigger.

Matched MeSH terms: Compact Disks
Fulltext A Colorimetric Enzyme-Linked Immunosorbent Assay (ELISA) Detection Platform for a Point-of-Care Dengue Detection System on a Lab-on-Compact-Disc

Thiha A, Ibrahim F

Sensors (Basel), 2015;15(5):11431-41.
PMID: 25993517 DOI: 10.3390/s150511431

The enzyme-linked Immunosorbent Assay (ELISA) is the gold standard clinical diagnostic tool for the detection and quantification of protein biomarkers. However, conventional ELISA tests have drawbacks in their requirement of time, expensive equipment and expertise for operation. Hence, for the purpose of rapid, high throughput screening and point-of-care diagnosis, researchers are miniaturizing sandwich ELISA procedures on Lab-on-a-Chip and Lab-on-Compact Disc (LOCD) platforms. This paper presents a novel integrated device to detect and interpret the ELISA test results on a LOCD platform. The system applies absorption spectrophotometry to measure the absorbance (optical density) of the sample using a monochromatic light source and optical sensor. The device performs automated analysis of the results and presents absorbance values and diagnostic test results via a graphical display or via Bluetooth to a smartphone platform which also acts as controller of the device. The efficacy of the device was evaluated by performing dengue antibody IgG ELISA on 64 hospitalized patients suspected of dengue. The results demonstrate high accuracy of the device, with 95% sensitivity and 100% specificity in detection when compared with gold standard commercial ELISA microplate readers. This sensor platform represents a significant step towards establishing ELISA as a rapid, inexpensive and automatic testing method for the purpose of point-of-care-testing (POCT) in resource-limited settings.

Matched MeSH terms: Compact Disks*
Fulltext A portable automatic endpoint detection system for amplicons of loop mediated isothermal amplification on microfluidic compact disk platform

Uddin SM, Ibrahim F, Sayad AA, Thiha A, Pei KX, Mohktar MS, et al.

Sensors (Basel), 2015 Mar 05;15(3):5376-89.
PMID: 25751077 DOI: 10.3390/s150305376

In recent years, many improvements have been made in foodborne pathogen detection methods to reduce the impact of food contamination. Several rapid methods have been developed with biosensor devices to improve the way of performing pathogen detection. This paper presents an automated endpoint detection system for amplicons generated by loop mediated isothermal amplification (LAMP) on a microfluidic compact disk platform. The developed detection system utilizes a monochromatic ultraviolet (UV) emitter for excitation of fluorescent labeled LAMP amplicons and a color sensor to detect the emitted florescence from target. Then it processes the sensor output and displays the detection results on liquid crystal display (LCD). The sensitivity test has been performed with detection limit up to 2.5 × 10(-3) ng/µL with different DNA concentrations of Salmonella bacteria. This system allows a rapid and automatic endpoint detection which could lead to the development of a point-of-care diagnosis device for foodborne pathogens detection in a resource-limited environment.

Matched MeSH terms: Compact Disks
Fulltext Effect of Multimedia Education on Nutritional Behaviour for Colorectal Cancer Prevention: An Application of Health Belief Model

Hatami T, Noroozi A, Tahmasebi R, Rahbar A

Malays J Med Sci, 2018 Nov;25(6):110-120.
PMID: 30914884 DOI: 10.21315/mjms2018.25.6.11

Background: Colorectal cancer is a major public health problem. A way to decrease this cancer is through dietary behavioural changes. The aim of this study was to determine the effects of education on dietary behaviour based on the health belief model (HBM) using multimedia.
Methods: In this clinical trial study, 98 participants were randomly allocated to an HBM group (n = 48) and a control group (n = 50). The HBM group received an audiovisual compact disc (CD) that contained information about nutritional behaviour of colorectal cancer (CRC) prevention based on HBM that lasted 45 min. Both groups completed questionnaires regarding demographic factors, knowledge and HBM constructs, and a three-day dietary recall at the beginning of the study, 1 week after, and 3 months after the education. The outcome of this study was measured by the amount of food servings consumed and dietary micronutrient intake.
Results: At the baseline, there were no significant differences between groups regarding demographic factors. Findings showed that self-efficacy (P < 0.001), severity (P < 0.001), and benefits (P < 0.001) were perceived to be higher, and knowledge (P < 0.001) was increased in the HBM group compared to control group 3 months after education. There was a significant increase in fruit and vegetable (P < 0.001) and dairy (P = 0.001) intake and a significant decrease in red meat servings (P = 0.016) in the HBM group compared to the control group. Also, intake of vitamin D (P < 0.001), folate (P < 0.001), calcium (P = 0.008), and dietary fibre (P < 0.001) was increased in the HBM group compared to the control group 3 months after education.
Conclusion: Education plans based on HBM and implemented through multimedia can change nutritional beliefs and behaviours for the prevention of colorectal cancer.

Matched MeSH terms: Compact Disks