Biomedical Engineering Reference
In-Depth Information
Fig. 7 The mChip. Reprinted by permission from Macmillan Publishers Ltd: Nature Medicine
[ 14 ] copyright (2011)
kept separate from each other by allowing air to space out the fluids (Fig. 7 d).
The tubing is then attached to the inlet of the chip and flowed through the channels
using a syringe attached to the outlet. This can easily be performed by local
workers in remote settings with minimal training. The capture proteins on the
surface of the chip (Fig. 7 e) can be spotted manually by pipetting or in an auto-
mated fashion using robots. An envelope antigen (gp41-gp36) was used for
capturing HIV-specific antibodies and an outer membrane antigen (TpN17) was
used for capturing treponemal-specific antibodies (the causative agent of syphilis).
One region was coated with BSA to serve as a negative control and another with
antibodies to goat IgG to provide a positive control. Signal amplification was
realised by the reduction of silver ions onto gold nanoparticles. Gold-labelled
antibodies were introduced after the sample, followed by silver reagents. The
resulting silver formation over a 5-min. time period could then be monitored by
eye or quantified by measuring the optical absorbance using a simple low-cost
device made from LEDs and photodetectors. To evaluate its performance in the
field, the device was taken to Rwanda and 70 patients with known statuses were
tested for HIV using less than 1 ll of whole blood. The results showed 100%
sensitivity and 96% specificity, rivalling current lab-based techniques. Similar
accuracy for HIV was also obtained for patients who were positive for hepatitis B
and C. The combined HIV-syphilis test was performed using the serum and plasma
samples of Rwandan patients and achieved a sensitivity of 100 and 94% and a
specificity of 95 and 76% for HIV and syphilis, respectively. The advantages of
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