Microfluidic Capillaric Circuit for Rapid and Facile Bacteria Detection

Urinary
tract infections (UTI) are one of the most common bacterial
infections and would greatly benefit from a rapid point-of-care diagnostic
test. Although significant progress has been made in developing microfluidic
systems for nucleic acid and whole bacteria immunoassay tests, their
practical application is limited by complex protocols, bulky peripherals,
and slow operation. Here we present a microfluidic capillaric circuit
(CC) optimized for rapid and automated detection of bacteria in urine.
Molds for CCs were constructed using previously established design
rules, then 3D-printed and replicated into poly­(dimethylsiloxane).
CCs autonomously and sequentially performed all liquid delivery steps
required for the assay. For efficient bacteria capture, on-the-spot
packing of antibody-functionalized microbeads was completed in <20
s followed by autonomous sequential delivery of 100 μL of bacteria
sample, biotinylated detection antibodies, fluorescent streptavidin
conjugate, and wash buffer for a total volume ≈115 μL.
The assay was completed in <7 min. Fluorescence images of the microbead
column revealed captured bacteria as bright spots that were easily
counted manually or using an automated script for user-independent
assay readout. The limit of detection of E. coli in
synthetic urine was 1.2 × 102 colony-forming-units
per mL (CFU/mL), which is well below the clinical diagnostic criterion
(>105 CFU/mL) for UTI. The self-powered, peripheral-free
CC presented here has potential for use in rapid point-of-care UTI
screening.