Point-of-care
diagnostics based on multiplexed protein measurements
face challenges of simple, automated, low-cost, and high-throughput
operation with high sensitivity. Herein, we describe an automated,
microprocessor-controlled microfluidic immunoarray for simultaneous
multiplexed detection of small protein panels in complex samples.
A microfluidic sample/reagent delivery cassette was coupled to a 30-microwell
detection array to achieve sensitive detection of four prostate cancer
biomarker proteins in serum. The proteins are prostate specific antigen
(PSA), prostate specific membrane antigen (PSMA), platelet factor-4
(PF-4), and interlukin-6 (IL-6). The six channel system is driven
by integrated micropumps controlled by an inexpensive programmable
microprocessor. The reagent delivery cassette and detection array
feature channels made by precision-cut 0.8 mm silicone gaskets. Single-wall
carbon nanotube forests were grown in printed microwells on a pyrolytic
graphite detection chip and decorated with capture antibodies. The
detection chip is housed in a machined microfluidic chamber with a
steel metal shim counter electrode and Ag/AgCl reference electrode
for electrochemiluminescent (ECL) measurements. The preloaded sample/reagent
cassette automatically delivers samples, wash buffers, and ECL RuBPY-silica–antibody
detection nanoparticles sequentially. An onboard microcontroller controls
micropumps and reagent flow to the detection chamber according to
a preset program. Detection employs tripropylamine, a sacrificial
reductant, while applying 0.95 V vs Ag/AgCl. Resulting ECL light was
measured by a CCD camera. Ultralow detection limits of 10–100
fg mL<sup>–1</sup> were achieved in simultaneous detection
of the four protein in 36 min assays. Results for the four proteins
in prostate cancer patient serum gave excellent correlation with those
from single-protein ELISA