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

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

In drug discovery it is important to know as early as possible whether a potential drug candidate forms toxic metabolites or not.  Normally, each drug candidate must be evaluated by extensive in vitro metabolism experiments however these are generally time-consuming and expensive.

Scientists in Finland, however, have developed a microchip to mimic phase I metabolic reactions of low-molecular weight compounds.  Raimo Ketola and colleagues at the University of Helsinki have designed an integrated TiO₂ nanoreactor/ionisation chip with UV radiation and direct MS analysis to produce and identify photocatalysed reaction products of selected drug molecules.

This enables rapid on-line analyses which have shown remarkable consistency with metabolites obtained from other in vivo and in vitro methods.  It is hoped that this technique, with its rapid prediction of phase I metabolites, will speed up the discovery of new potential drug candidates.

This HOT article is available to download, free of charge, for the next 4 weeks – careful, don’t burn your fingers!

Integrated photocatalytic micropillar nanoreactor electrospray ionization chip for mimicking phase I metabolic reactions
Teemu Nissilä, Lauri Sainiemi, Mika-Matti Karikko, Marianna Kemell, Mikko Ritala, Sami Franssila, Risto Kostiainen and Raimo A. Ketola
Lab Chip, 2011, Advance Article
DOI: 10.1039/C0LC00689K

Isolating biological or biochemical content in aqueous droplets within an immiscible oil medium on a microfluidic device allows samples to be transported without cross-contamination or dispersion.  But generating droplets at a suitably high speed with precise volume control has been a challenge.

Now Pei-Yu Chiou and Sung-Yong Park from UCLA have developed a pulse laser-driven droplet mechanism that allows droplet formation of up to 10000 droplets per second with controllable volumes between 1-150 pL and >1% volume variation.

Their device (shown below) consists of two microfluidic channels connected by a nozzle-like opening. A highly focused intense laser pulse induces a rapidly expanding cavitation bubble to push the nearby water into the oil channel for droplet formation.

This HOT article is free to access until the end of March – so download it today and see how they did it!

High-speed droplet generation on demand driven by pulse laser-induced cavitation
Sung-Yong Park, Ting-Hsiang Wu, Yue Chen, Michael A. Teitell and Pei-Yu Chiou
Lab Chip, 2011, 11, 1010-1012
DOI: 10.1039/C0LC00555J