Microfluidic Capillaric Circuit for Rapid and Facile Bacteria Detection

Abstract

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 × 10 colony-forming-units per mL (CFU/mL), which is well below the clinical diagnostic criterion (>10 CFU/mL) for UTI. The self-powered, peripheral-free CC presented here has potential for use in rapid point-of-care UTI screening.

Capillary microfluidics in microchannels: from microfluidic networks to capillaric circuits

“…3D stereolithographic printing was used to fabricate an array of capillaric elements and circuits with a turnaround time of tens of minutes and at material costs of a few dollars 44 and have already shown the potential for clinically-relevant applications. 45 CCs made by rapid …”

“…Inlets can be designed to avoid corner flow by literally removing them, and using virtual inlets without any features and applying liquids directly to a narrow conduit protruding laterally beyond the edge of the cover. 45 Rounded inlets can also be milled as vertical holes in the microchip cover (or from the back of the chip) to provide large and easy to manufacture rounded features. Inlets are a simple, yet essential part of CCs and attention to detail is required to ensure that their design is user-friendly without interfering with subsequent fluidic operations.…”

“…Depending on the intended application, reservoirs can be very small with volumes in the picoliter range 5 or very large with volumes up to 100 μL. 45 Reservoirs typically have low flow resistance and low capillary pressure so that they are quickly and easily drained. Reservoirs can also be connected to air vents in a CC, so that flow is not triggered in a desired region of the CC until a particular reservoir is emptied as described in section 6.3.…”

“…76 More recently, functionalized microbeads have been used to increase surface area and improve the efficiency of mass transport within CCs. 45,[77][78][79] Beads can be readily functionalized in batch mode while reducing issues related to surface anisotropy, depletion, and edge effects that can afflict surface-coated conduits and confound assay results. Conversely, bead barriers must be included in the CC, and the CCs pre-filled with bead solution beforehand, without compromising surface chemistry following drying of the delivery solution 78,79 or then delivered on-the-fly during the assay.…”

“…Conversely, bead barriers must be included in the CC, and the CCs pre-filled with bead solution beforehand, without compromising surface chemistry following drying of the delivery solution 78,79 or then delivered on-the-fly during the assay. 45 Reaction chambers must be designed keeping in mind the analyte concentration that needs to be detected, liquid delivery within the CC, and the user-friendliness of the CC.…”