Biomedical Engineering Reference
In-Depth Information
Fig. 8 Dry reagent storage technique. Reproduced from [
102
] with permission of The Royal
Society of Chemistry
this work are that it can be conducted with minimum training, with no external
infrastructure or electricity, and the costs are extremely low. The price of the
reader was reported to be $74.50, the regents were $0.20 per test and each cassette
cost less than $0.10 to manufacture (in 2011).
The long-term storage of reagents within POC devices is a challenge for
diagnostics. Approaches to prolong the functionality of the immobilised proteins
include using sugars [
21
,
102
], sol-gels [
109
] and desiccants [
35
]. The mChip has a
shelf life of 6 months, if it is maintained at room temperature [
14
]. For settings
where this might not be feasible, Stevens et al. developed a microfluidic system
that solves this problem by storing the reagents in a dry form [
102
]. The labelling
reagents are dried in a preservative sugar matrix within a fibrous pad encased
within a microchannel at the time of device fabrication. To perform the assay, a
buffer is simply flowed through the pad to introduce the reagents to a porous
membrane containing the target analyte (Fig.
8
). They showed that functionality
could be preserved over a 60-day period at 4, 20 and 45 C, suitable for settings
where the temperature cannot be controlled.
5 Alternative Approaches to Microfluidic Design
Microfluidic systems typically involve fluids being transported through closed
channels, but there are alternative techniques for fluid handling that can be applied
to molecular diagnostics (Fig.
9
). Droplets containing the reagents can be
manipulated using electrowetting platforms [
8
,
47
,
69
,
82
,
99
,
116
]. By changing
