Biomedical Engineering Reference
In-Depth Information
Fig. 11 Single molecule
detection in microfluidic
devices. This scheme depicts
the optical setup used to
detect a DNA cleavage
reaction using FRET. At the
same time, the flow velocity
was measured by dual-beam
FCS. (Reprinted with
permission from [
23
] with
kind permission from
Springer Science and
Business Media)
6 Detection Methods for Diagnostics
The majority of detection within microfluidic systems uses fluorescence due to its
high sensitivity, specificity, and the availability of a wide range of different
fluorophores [
2
]. Methods such as total internal reflection microscopy, fluores-
cence lifetime imaging microscopy, fluorescence correlation spectroscopy, fluo-
rescence polarization and Förster resonance energy transfer have successfully been
used for the detection and analysis of molecular interactions within microsystems
[
22
-
24
,
42
,
54
,
88
]. Combining these detection methods in a single optical setup
can maximise the amount of information extracted from a reaction (Fig.
11
).
These techniques represent the current state-of-the-art in detection but normally
require additional labelling steps, bulky external instrumentation to achieve a high
sensitivity (laser, lamp, microscope, camera, PMT, expensive electronics) and
trained personnel, making them unsuitable for resource-limited resource settings or
home healthcare. To this end, there have been significant advances in compact
detection methods [
48
,
71
,
73
], aided by the increasing availability of low-cost
LEDs, diode-pumped solid-state lasers, photodiodes, and CCDs. This has broad-
ened the availability of excitation wavelengths without compromising sensitivity.
Technologies such as miniaturised integrated microscopes, recently developed by
Ghosh et al., could, in principle, be used with microfluidic platforms but currently
lack the required resolution [
36
].
Detection for POC devices should not only be affordable and low maintenance,
but the signal should be converted to a simple readout for easy user interpretation.
For these reasons, the future may well see increased use of simple absorbance
methods, such as those used in current lateral flow assays, that can easily be seen
