Biomedical Engineering Reference
In-Depth Information
Fig. 9 Alternative techniques for microfluidics. a Electrowetting platforms [
47
]. b Fabric-based
systems [
5
]. Both reproduced with permission of The Royal Society of Chemistry. c Thread-
based systems. Reprinted with permission from [
3
] Copyright [2011], American Institute of
Physics
the voltage of integrated electrodes, the wetting behaviour of the droplets can be
changed, which allows them to be transported, split, and merged for analysis. Such
a device, also known as 'digital microfluidics,' was recently used in tandem with
MS to quantify amino acids in dried blood samples [
47
]. This method is also
applicable to immunoassays as demonstrated by Wheeler and co-workers [
69
]. The
device was able to detect the model analyte Human IgG over a dynamic range of
one order of magnitude, faster than macroscopic approaches. Although the sample
consumption is low, the current design of these devices involves external elec-
tronic instrumentation that is not suitable for cheap mass production.
Often, advances in technologies are accelerated by necessity. The global out-
break of the pathogenic avian flu virus H5N1 in 2004 provided the drive to find a
low-cost, easy-to-use, portable diagnostic test. In 2007, Pipper et al. reported such
a device based on the manipulation of microdroplets by electromagnetic forces
[
81
]. The superparamagnetic particles contained within the droplets can be
remotely controlled by magnets located off-chip, permitting low-cost tests in
single-use disposables. Moreover, the magnetic interaction is unaffected by tem-
perature effects, making it suitable for decentralised testing. The researchers were
able to combine RNA sample preparation and real-time PCR to detect H5N1 in
28 min, considerably faster than the 4 h achieved by marketed tests.
Other low-cost microfluidic solutions include fabric-based [
5
] and thread-based
microfluidic systems [
3
,
56
,
85
,
86
](Fig.
9
). However, these methods are still in the
early stages of development. The most promising low-cost emerging technique is
