Low-Cost Microdevices for Point-of-Care Testing - Point-of-Care Diagnostics on a Chip - page 8

Fig. 1.3 Microfluidic platform for miniaturized immunoassays at ELISA-level performance [ 31 ].
( a ) Picture of injection-molded cassette. ( b ) Picture of reader

1.4.1.1 Signal Detection

Our group has demonstrated signal amplification using reduction of silver ions
on gold nanoparticles [ 30 ] in cassettes made of injection-molded plastic (from
Claros Diagnostics) for the simultaneous detection of HIV and syphilis antibod-
ies (Fig. 1.3 ). Gold-catalyzed silver reduction is an attractive method of signal
amplification and detection because the signals can be developed under continuous
flow and can be read using low-cost optics. In a preclinical evaluation at several
clinical sites in Rwanda, the technology showed sensitivity and specificity rivaling
those of reference benchtop assays on hundreds of patient samples, with a time-to-
result of no more than 20 min [ 31 ]. We also demonstrated excellent performance of
HIV diagnosis using only 1L of unprocessed whole blood. The potential social
impact of this test is high when used in remote settings (e.g., clinics providing
antenatal care), since treatments for HIV and syphilis are affordable and effective
for minimizing disease transmission from mother to child.
Surface plasmon resonance is another suitable detection method, given appropri-
ate signal amplification schemes. Sensata Technologies has previously developed
a low-cost, disposable device which can detect heterogeneous antigen/antibody
binding with changes in refractive index measured at the gold surface.

1.4.1.2 Fluid Control

Valves are an essential component of fluid control on microdevices. Pneumatic
deflection of elastomers, such as PDMS, in multilayer systems has been demon-
strated to be robust, leak-free, and capable of facilitating highly multiplexed systems