Lab on a Chip Blog

US researchers have used ferrofluids as liquid pistons that could be used to make adjustable liquid lenses with nearly perfect spherical interfaces for applications such as an optometrist’s phoropter. A phoropter measures the way light is focused in the eye and is used to determine prescriptions for glasses and contact lenses.

Ferrofluids are colloidal solutions of ferromagnetic nanoparticles suspended in a dispersing liquid. Ferrofluid droplets can be manipulated by a magnetic field, so they could be used in systems that need precise control, such as optics, drug delivery, and electronic devices.

Amir Hirsa and colleagues from Rensselaer Polytechnic Institute in Troy, New York, have made such a device by filling three of four holes in a substrate with ferrofluid; the ferrofluid’s surface tension allows droplets to protrude from either side of the substrate. They filled the fourth hole with 1-methylnaphthalene, a compound used as a liquid lens. They sealed the system and filled it with water, producing two chambers, with the substrate as the separator and the ferrofluid and 1-methylnaphthalene being the only connections between them.

As a magnetic field was applied to the device, the ferrofluid moved further into one chamber, pushing the 1-methylnaphthalene liquid lens and changing its curvature

Read the full story here

Link to journal article
Electromagnetic liquid pistons for capillarity-based pumping 
Bernard A. Malouin Jr, Michael J. Vogel, Joseph D. Olles, Lili Cheng and Amir H. Hirsa,
Lab Chip, 2011, DOI: 10.1039/c0lc00397b

Artificial lung technology could reduce the death rate for patients awaiting a lung transplant, say US scientists.

Advanced lung disease is characterised by an inability to remove carbon dioxide from the blood and reduced oxygen uptake efficiency. A shortage of donors can mean long delays and high mortality rates for those awaiting a transplant. The only technology available to aid sufferers during this time is based in intensive care units, hindering quality of life.

Now, Joseph Vacanti and coworkers at Massachusetts General Hospital, Boston, have developed a device that achieves the CO2/O2 gas exchange that, when implanted in the body, could allow patients more freedom when awaiting a transplant. Their design is a microfluidic branched vascular network through which blood flows, separated from a gas-filled chamber by a silicone membrane less than 10um thick. The network is formed by casting polydimethylsiloxane, a biocompatible polymer, on a micro machined mould.

A device that achieves carbon dioxide/oxygen gas exchange could allow patients more freedom when awaiting a lung transplant

Read the full story here

Link to journal article
Lung assist device technology with physiologic blood flow developed on a tissue engineered scaffold platform
David M. Hoganson, Howard I. Pryor II, Erik K. Bassett, Ira D. Spool and Joseph P. Vacanti, Lab Chip, 2011
DOI: 10.1039/c0lc00158a

Korean scientists have developed a fast and simple mobile phone-based device to test urine samples for common diseases in developing countries. This could provide a cheap, painless solution for detecting disease in remote areas.

Dae-Sik Lee at the Electronics and Telecommunications Research Institute and colleagues developed a pocket-sized urinalysis colorimetric reader capable of sending data wirelessly via a smart phone. To take urine samples, the team used a commercially available 10-parameter urinalysis paper strip that detects glucose, protein, bilirubin, urobilinogen, ketones, nitrite, pH, specific gravity, erythrocytes and leukocytes.

Lee’s team tested the device on 1000 human urine samples and the results were comparable with those given by hospital equipment, demonstrating reliable glucose and protein analysis. It uses a colorimetric multidetection diode comprising LEDs, photodiodes and an optical splitter, which reads the colour intensity changes on the paper strips.

In remote areas of the developing world early detection and prevention of disease is rare. Portable lab on a chip devices have been developed to help combat this but many are not up to the standards required for use in such environments, as they are often expensive with high power consumption and take a long time to produce results, whereas Lee’s device can produce readings within six seconds.

The simple and easy to use handheld device could prove vital for patients in remote areas of the developing world

Read the full story here

Link to journal article
A simple and smart telemedicine device for developing regions: a pocket-sized colorimetric reader
Dae-Sik Lee, Byoung Goo Jeon, Chunhwa Ihm, Je-Kyun Park and Mun Yeon Jung, Lab Chip, 2011
DOI: 10.1039/c0lc00209g

Microfluidics can be used to trap a single DNA-enzyme complex in its native state for real-time analysis without having to immobilise the DNA or the enzyme, claim US researchers.

Enzymes called restriction enzymes are used to chop up DNA at specific points called recogition sites, making them useful tools in biochemistry. To anayse how they recognise and cleave DNA, the enzyme or DNA needs to be immobilised on a glass slide, but this can modify their properties, and make it difficult to analyse the products. To combat this, Susan Muller and Weilin Xu at the University of California, Berkeley, pre-bound a restriction enzyme to DNA, and fed it through a microfluidic system. This trapped the complex, and then stretched it out. Adding Mg2+ then activated the enzyme, cleaving the DNA, and permitting analysis of the products.

Ron Larson, a chemical engineering expert at the University of Michigan, Ann Arbor, US, says: ‘this work represents a novel and elegant use of fluidics to trap and stretch single DNA molecules without interference by surfaces.’ He adds that ‘the “look Ma, no hands” approach pursued by Xu and Muller has a number of advantages, not least of which is the ability to recover cleavage products for further study.’

Molecular configuration image showing the trapping, stretching and subsequent cleavage of DNA

Read the full story here

Link to journal article
Exploring both sequence detection and restriction endonuclease cleavage kinetics by recognition site via single-molecule microfluidic trapping
Weilin Xu and Susan J. Muller, Lab Chip, 2011
DOI: 10.1039/c0lc00176g