We recently developed capillaric circuits (CCs) – advanced capillary microfluidic devices assembled from capillary fluidic elements in a modular manner similar to the design of electric circuits (Safavieh & Juncker, Lab Chip, 2013, 13, 4180–4189).

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.

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Capillaric circuits (CCs) are advanced capillary microfluidic devices that move liquids in complex pre-programmed sequences without external pumps and valves -relying instead on microfluidic control elements powered by capillary forces. CCs were thought to require high-precision micro-scale features manufactured by photolithography in a cleanroom, which is slow and expensive. Here we present rapidly and inexpensively 3D-printed autonomous CCs. Molds for CCs were fabricated with a benchtop 3D-printer, Poly(dimethylsiloxane) replicas were made, and fluidic functionality was verified with aqueous solutions. We established design rules for 3D-printed CCs by a combination of modelling and experimentation. The functionality and reliability of 3D-printed trigger valves -an essential fluidic element that stops one liquid until flow is triggered by a second liquid -was tested for different geometries and different solutions. Trigger valves with geometries up to 80-fold larger than cleanroom-fabricated ones were found to function reliably. We designed 3D-printed retention burst valves that encode sequential liquid drainage and delivery using capillary pressure differences encoded by varying valve height and width. Using an electrical circuit analogue of the CC, we established circuit design rules for ensuring strictly sequential liquid delivery. We realized a 3D-printed CC with reservoir volumes 60 times larger than cleanroom-fabricated circuits and autonomously delivered eight liquids in a pre-determined sequence in < 7 min, exceeding the number of sequentially-encoded, self-regulated fluidic delivery events previously reported. Taken together, our results demonstrate that 3D-printing enables rapid prototyping of reliable CCs with improved functionality and potential applications in diagnostics, research and education.