Lab on a Chip Blog

Cilia are microscale ‘eyelash-like’ extensions of eukaryotic cells found in epithelial linings throughout the body. In the fallopian tubes, windpipe, and lungs, motile cilia beat rhythmically to move objects within the viscous liquid above. Non-motile cilia in the inner ear transduce mechanical vibrations to electrical signals to ultimately excite auditory nerves.

Previously, these appendages have been built using advanced microfabrication techniques. Now, for the first time, researchers at Eindhoven University of Technology in the Netherlands present a simple bench-top fabrication method for self-assembly of artificial cilia using magnetic beads and latex particles. 

Jaap den Toonder and his team created the artificial cilia sans cleanroom by coating magnetic beads with latex particles in a fluid cell using a magnetic field to control bead orientation. Latex particles were attracted to the beads by electrostatic forces and the whole structure was bonded together using a heating cycle. The completed artificial cilia were 3 μm in diameter and could be made into lengths of up to 33 μm by optimizing the magnetic field strength and protocol duration. The cilia were actuated by oscillating magnetic fields after fabrication to produce flow velocities of 3 μm/s.

Microfluidic devices operate under low Reynolds numbers where inertia is negligible, presenting a significant challenge to efficient mixing and moving of objects. Cilia and flagella evolved in organisms living in low Reynolds numbers to enable swimming by generating fluid flow using nonreciprocal (nonreversible) motions of beating and twisting.^{1, 2} The fabrication method presented in this work powerfully enables artificial cilia to be fabricated in situ in assembled platforms and “ship-in-a-bottle” constructed devices, thus facilitating practical applications for these structures in existing microfluidic platforms for bio-inspired fluid manipulation at the microscale.

Out of the cleanroom, self-assembled magnetic artificial cilia, Ye Wang, Yang Gao, Hans Wyss, Patrick Anderson, and Japp den Toonder, Lab Chip, 2013, 13, 3360-3366. DOI: 10.1039/C3LC50458A

References:
1. E. M. Purcell, AIP Conference Proceedings, 1976, 28, 49.
2. S. Khaderi, J. den Toonder and P. Onck, Biomicrofluidics, 2012, 6, 014106.

Researchers at Virginia Tech have designed a microfluidic system that integrates optimized fluid handling, liquid chromatography, and a mass spectrometry sample platform – all in one small device.

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) is a powerful analytical tool which enables the identification and quantification of thousands of proteins and peptides within a single complex sample. Liquid chromatography (LC) can be used to pre-sort sample contents by mass, increasing the sensitivity and selectivity of the MS measurements. A novel system designed by Iulia Lazar and Jarod Kabulski (view the full paper here) allows the entire process of LC-MS to be carried out on a microfluidic chip.

Lazar and Kabulski’s chip has several features that set it apart from previous microfluidic devices incorporating LC and MS.¹ It comprises a unique microfluidic system² driven by electro-osmotic pumps, an LC channel packed with microparticles, and a novel system of transverse microchannels to draw LC fractions from the main separation channel and into a series of reservoirs. The chip can then be directly loaded into the MALDI-MS instrument for analysis. Flow control in the LC channel was carefully optimized so that the solution components would be perfectly distributed along the channel length.

Figure: The LC-MS microfluidic chip. (Figure 2 from the original paper.)

Using the microfluidic LC-MS chip, the researchers were able to obtain results comparable to conventional LC-MS, for both peptide mixtures and cytoplasmic cell extract. Thus, the chips are very promising for practical high-throughput applications such as biomarker screening. The chip format will also enable samples to be collected and prepped by an MS non-expert at a remote location, then transported to a MS lab for analysis.

Learn more from this HOT article from Lab on a Chip!

Microfluidic LC device with orthogonal sample extraction for on-chip MALDI-MS detection
Iulia M. Lazar and Jarod L. Kabulski
DOI: 10.1039/c3lc50190f

1. D. Gao et al., Lab on a Chip 13, 3309-3322, 2013.
2. I. Lazar et al., Analytical Chemistry 78 (15), 5513-5524, 2006.

Many diseases, especially cancers (and recurrences), are not detected until it is too late for effective treatment. Often, this is because available tests lack the sensitivity to find the appropriate protein biomarker in the body.¹ Consequently, ultrasensitive tools for measuring proteins are vital for early diagnosis of diseases, and monitoring the effectiveness of surgery or therapy.

For 40 years, scientists and clinicians have been using immunoassays for protein detection. This technique relies on the precise recognition of a target molecule (antigen) by a unique Y-shaped protein (antibody) among thousands of interfering species. However, to achieve ultrasensitive detection, the antigen must be effectively transported to the antibody on the detection surface.²

To tackle this problem, a research team led by Prof. Martin Gijs drew inspiration from the human immune system. In the body, white blood cells are transported to the site of injury with the help of adhesion molecules. In the presence of blood flow, weak adhesion molecules cause the cells to slow down and roll along the vessel wall. This “rolling adhesion” allows the cells to search the wall meticulously for a stop signal. If they come across this signal, the cells will adhere firmly to the wall and squeeze into the site of injury.

Taking cue from this phenomenon, the research team designed a microfluidic immunoassay using two sizes of magnetic beads coated with antibodies. First, ‘large’ (2.8 micrometer) beads are loaded with antigen (from the serum sample) in an on-chip mixing chamber. After unbound components are washed away, the large beads are flown over a surface decorated with a pattern of ‘small’ antibody-coated (1.0 micrometer) beads. In the presence of a magnet, the large beads will roll on the surface and interact closely with the small beads (via magnetic dipolar forces). Beads that are loaded with antigen will adhere firmly to the surface through antibody-antigen complexes, while beads with no antigen are washed away (via flow-induced drag forces).

The antigen concentration in the serum sample can be detected by simply counting the number of large beads in the detection area. This method can rapidly (<20 min) detect down to 200 proteins (Tumor necrosis factor-α) in a 5 microliter of sample (i.e. 60 attomolar), making it one of the fastest and most sensitive immunoassays ever reported. Such salient technique has the potential to improve treatment and outcome for cancer patients worldwide.

The above paper is part of our Lab on a Chip Top 10%, a collection of articles selected by the Editors at Lab on a Chip, from all our high quality papers, to be of exceptional significance for the miniaturisation community. Papers in this category will have received excellent reports during peer review, and demonstrate a breakthrough in device technology, methodology or demonstrate important new results for chemistry, physics, biology or bioengineering enabled by miniaturisation.

The full paper details are here: Attomolar protein detection using a magnetic bead surface coverage assay, H. Cumhur Tekin, Matteo Cornaglia and Martin A. M. Gijs*, Lab Chip, 2013, 13, 1053-1059. DOI: 10.1039/C3LC41285G

1. C. S. Thaxton, R. Elghanian, A. D. Thomas, S. I. Stoeva, J.-S. Lee, N. D. Smith, A. J. Schaeffer, H. Klocker, W. Horninger, G. Bartsch and C. A. Mirkin, Proceedings of the National Academy of Sciences, 2009, 106, 18437-18442.

2. T. M. Squires, R. J. Messinger and S. R. Manalis, Nature Biotechnology, 2008, 26, 417-426.