ac010423z_si_001.pdf (39.4 kB)
An Integrated Fluorescence Detection System in Poly(dimethylsiloxane) for Microfluidic Applications
journal contribution
posted on 2001-08-15, 00:00 authored by Michael L. Chabinyc, Daniel T. Chiu, J. Cooper McDonald, Abraham D. Stroock, James F. Christian, Arieh M. Karger, George M. WhitesidesThis paper describes a prototype of an integrated fluorescence detection system that uses a microavalanche photodiode (μAPD) as the photodetector for microfluidic
devices fabricated in poly(dimethylsiloxane) (PDMS). The
prototype device consisted of a reusable detection system
and a disposable microfluidic system that was fabricated
using rapid prototyping. The first step of the procedure
was the fabrication of microfluidic channels in PDMS and
the encapsulation of a multimode optical fiber (100-μm
core diameter) in the PDMS; the tip of the fiber was placed
next to the side wall of one of the channels. The optical
fiber was used to couple light into the microchannel for
the excitation of fluorescent analytes. The photodetector,
a prototype solid-state μAPD array, was embedded in a
thick slab (1 cm) of PDMS. A thin (80 μm) colored
polycarbonate filter was placed on the top of the embedded μAPD to absorb scattered excitation light before it
reached the detector. The μAPD was placed below the
microchannel and orthogonal to the axis of the optical
fiber. The close proximity (∼200 μm) of the μAPD to the
microchannel made it unnecessary to incorporate transfer
optics; the pixel size of the μAPD (30 μm) matched the
dimensions of the channels (50 μm). A blue light-emitting
diode was used for fluorescence excitation. The μAPD was
operated in Geiger mode to detect the fluorescence. The
detection limit of the prototype (∼25 nM) was determined
by finding the minimum detectable concentration of a
solution of fluorescein. The device was used to detect the
separation of a mixture of proteins and small molecules
by capillary electrophoresis; the separation illustrated the
suitability of this integrated fluorescence detection system
for bioanalytical applications.