Structures that are periodic on a microscale in three dimensions are abundant in nature, for example, in the cellular arrays that make up living tissue. Such structures can also be engineered, appearing in smart materials(1-4), photonic crystals(5), chemical reactors(6), and medical(7) and biomimetic(8) technologies. Here we report that fluid-fluid interfacial energy drives three-dimensional (3D) structure emergence in a micropillar scaffold. This finding offers a rapid and scalable way of transforming a simple pillar scaffold into an intricate 3D structure that is periodic on a microscale, comprising a solid microscaffold, a dispersed fluid and a continuous fluid. Structures generated with this technique exhibit a set of unique features, including a stationary internal liquid-liquid interface. Using this approach, we create structures with an internal liquid surface in a regime of interest for liquid-liquid catalysis. We also synthesize soft composites in solid, liquid and gas combinations that have previously not been shown, including actuator materials with temperature-tunable microscale pores. We further demonstrate the potential of this method for constructing 3D materials that mimic tissue with an unprecedented level of control, and for microencapsulating human cells at densities that address an unresolved challenge in cell therapy.

We introduce microparticle filters with temperature tuneable size cut-off and surface energy. At room temperature, the filter cut-off is 164 ±23 μm, and the filter is water-absorbing/oil-repelling (hydrophilic). At 50 °C, the filter cut-off is 695±31 μm, and the filter is oil-absorbing/water-repelling (hydrophobic).

Established digital bioassay formats, digital PCR and digital ELISA, show extreme limits of detection, absolute quantification and high multiplexing capabilities. However, they often require complex instrumentation, and extensive off-chip sample preparation. In this study, we present a dipstick-format digital biosensor (digital dipstick) that detects bacteria directly from the sample liquid with a minimal number of steps: dip, culture, and count. We demonstrate the quantitative detection of Escherichia coli (E. coli) in urine in the clinically relevant range of 10² –10⁵ CFU ml⁻¹ for urinary tract infections. Our format shows 89% sensitivity to detect E. coli in clinical urine samples (n = 28) when it is compared to plate culturing (gold standard). The significance and uniqueness of this diagnostic test format is that it allows a non-trained operator to detect urinary tract infections in the clinically relevant range in the home setting.

In this study, we demonstrate a digital bacterial detection assay in a dipstick format that can identify and quantitate Escherichia coli, Klebsiella pneumoniae, and Enterococcus faecalis, i.e., three of the most common (>90%) bacteria causing urinary tract infections (UTIs). The operation involves nothing more than dipping the stick in urine for a few seconds and let the stick incubate for 10-12 h before read-out. Each of the 180 miniaturised culture wells in the stick contain chromogenic agar and change colour if they contain a CFU. The colour of the wells identifies the presence of a specific type of bacteria; the number of coloured wells indicates the concentration. This format allows detection and quantification at a potentially low cost and without the need for complicated external equipment or technical skills. 

In sliding microfluidic platforms (“SlipChip” [1]), two plates with microfluidic wells slide in close contact to perform multiplexed reactions in a single operation. In- plane “sliding-flow” liquid transport, however, limits the potential assay operations to 1) sample compartmentalization/metering, 2) reagent addition, 3) mixing, and 4) aliquoting. Here, we introduce a three-plate sliding microfluidics platform, “Slip-X-Chip”, that additionally includes out-of-plane “cross-flow” liquid transport. Slip-X-Chip allows two additional assay operations: 5) sample concentration and 6) liquid exchange/washing, while retaining the simplicity of operation (one-step operation; no precise pipetting required; no external equipment). These additional assay operations extend the range and complexity of applications enabled by sliding microfluidics. We here demonstrate 1) splitting bead solutions in compartments with different concentrations and 2) compartmentalizing human cells from solution, followed by a viability assay. We foresee that Slip-X-Chip could be further adapted to, e.g., cell counting, cell staining, or ELISA.