Lab on a Chip Blog

The fabrication  of 3D microstructures for microfluidic devices continues to be a challenge as traditional microfabrication techniques are not suitable for the construction of these devices.  For example, PDMS (polydimethylsiloxane) is one of the most common substrate materials for microfluidic devices, but standard packaging techniques are not able to bond multiple substrate layers with the high precision required.

Tingrui Pan (University of California, Davis) et al. have now come up with an easy and robust technique which they hope will make this problem a thing of the past.  Their new technique, CAP (capillary-driven automatic packaging) uses the interactions between a liquid capillary bridge and the top and bottom substrates to align multiple substrate layers with high precision, and has a bonding strength comparable to standard oxygen plasma processes.  The technique is also transferable to other materials, requires no thermal or mechanical treatment, nor any specialist equipment.

Illustration of the CAP-enabled microdevice fabrication process, including (a) micropatterning of a shadow mask made of dry film, (b) PDMS replica molding, (c) selective oxygen plasma treatment through the shadow mask, (d) DI water loading in the defined hydrophilic regions, and finally (e) self-alignment and self-engagement steps between two chips with identical capillary alignment patterns.

Pan et al. believe that this technique has the ability to be employed in microdevices for point-of-care diagnosis, controlled drug delivery, and combinatorial biological screening – why not take a look and see for yourself – the article’s free to access for four weeks!

Capillary-driven automatic packaging
Yuzhe Ding, Lingfei Hong, Baoqing Nie, Kit S. Lam and Tingrui Pan
Lab Chip, 2011, 11, 1464-1469
DOI: 10.1039/C0LC00710B

In recent years methicillin-resistant Staphylococcus aureus (MRSA) has become one of the most prevalent antibiotic resistant pathogens in hospitals and as such there is an urgent need for a way of rapidly detecting it to limit the spread of the infection.

Current methods of detection, involving the use of PCR, require quite bulky, power-intensive and quite expensive apparatus. Gwo-Bin Lee et al. have developed a portable hand-held system where the entire diagnostic protocol, from bio-sample pre-treatment to optical detection, can be automatically completed within an hour and with a limit of detection 1000- fold higher than conventional bench-top PCR systems.

The entire process can be accomplished automatically via magnetic bead-based hybridization of the target DNA purified from clinical samples, a loop-mediated isothermal amplification process for the amplification of the target genes, and then spectrophotometric analysis of the amplified target genes.

To find out more take a look at this HOT article which is FREE to view for 4 weeks!

A magnetic bead-based assay for the rapid detection of methicillin-resistant Staphylococcus aureus by using a microfluidic system with integrated loop-mediated isothermal amplification
Chih-Hung Wang, Kang-Yi Lien, Jiunn-Jong Wu and Gwo-Bin Lee
Lab Chip, 2011, 11, 1521-1531
DOI: 10.1039/C0LC00430H

Antiretroviral therapy (ART) increases the longevity and quality of life for HIV patients.  The lack of objective diagnostic tests to determine when to start ART and to monitor its successes hinders the effective use of treatment.  An important diagnostic procedure is to obtain a patient’s CD4+ lymphocyte count, which is traditionally carried out using optical instrumentation. However, the cost and technical requirements of such equipment make them infeasible as analytical methods in poorer countries.

William Rodriguez (Daktari Diagnostics) and Rashid Bashir (University of Illinois) present a solution to this problem with their novel microfabricated biochip to enumerate CD4+ T lymphocytes from healthy human subject blood samples.

Their biochip incorporates electrical impedance sensing coupled with immunoaffinity chromatography to electrically differentiate CD4+ cells from other leukocytes with accuracy comparable to current optical diagnostic methods.  This negates any requirement for labelling or optical detection, while its microfabricated nature suggests it may be an inexpensive, simple and portable alternative to current flow cytometric practises.

Learn more about this device by reading this HOT article, which is free to access for the next 4 weeks!

A microfabricated electrical differential counter for the selective enumeration of CD4+ T lymphocytes
Nicholas N. Watkins, Supriya Sridhar, Xuanhong Cheng, Grace D. Chen, Mehmet Toner, William Rodriguez and Rashid Bashir
Lab Chip, 2011, 11, 1437-1447
DOI: 10.1039/C0LC00556H