The effects of silica nanoparticles on the properties of a commonly used Sylgard 184 polydimethylsiloxane (PDMS) in microfluidics were systemically studied. Two kinds of silica nanoparticles, A380 fumed silica nanoparticles and MCM-41 mesoporous silica nanoparticles, were individually doped into PDMS, and the properties of PDMS with these two different silica nanoparticles were separately tested and compared. The thermal and mechanical stabilities of PDMS were significantly enhanced, and the swelling characteristics were also improved by doping these two kinds of nanoparticles. However, the transparency of PDMS was decreased due to the light scattering by nanoparticles. By contrast, PDMS/MCM-41 nanocomposites showed a lower coefficient of thermal expansion (CTE) owing to the mesoporous structure of MCM-41 nanoparticles, while PDMS/A380 nanocomposites showed a larger elastic modulus and better transparency due to the smaller size of A380 nanoparticles. In addition, A380 and MCM-41 nanoparticles had the similar effects on the swelling characteristics of PDMS. The swelling ratio of PDMS in toluene was decreased to 0.68 when the concentration of nanoparticles was 10 wt %.

Cardiovascular disease is one of the most common causes of mortality in the world. Most of the diagnostic processes usually require bulky instruments and trained professionals, which cannot meet the demand for fast, early and regular bedside diagnosis. In this paper, a bespoke app on a smartphone and an autonomous capillary microfluidic chip (ACMC) are combined to realize the point-of-care testing of cardiac troponin I (cTnI). The smartphone-app-ACMC platform was based on the sandwich immunofluorescence principle and featured self-aligned on-chip focusing (SOF) lenses which can avoid the complex optical coupling process. The operator only needs to introduce 100 μl sample into the ACMC, where the priming, time-delaying, mixing and washing steps for the assay can be accomplished automatically. With the help of the bespoke app and a palm-sized optical attachment, the smartphone can capture fluorescence images, process fluorescence intensity information, output detection results and save the results for long-term monitoring. Our results showed that within 12 min, the detection limit of 78 pg ml⁻¹ and 94 pg ml⁻¹ for cTnI was attained in buffer and spiked human serum, respectively. Our proposed platform has the potential to be applied in the POCT field especially for some resource-limited settings.

Stomatal transpiration, which is an efficient way to carry water from the roots up to the leaves, can be described by “diameter-law”. According to the law, the flow rate induced by micropore transpiration far exceeded that induced by macroscale evaporation, and it can be controlled by opening (or closing) some micropores. In this research, a bio-inspired micropump based on stomatal transpiration is presented. The micropump is composed of three layers: the top layer is a 93 μm-thick PVC (polyvinylchloride) film with a group of slit-like micropores; the second layer is a PMMA sheet with adhesives to join the other two layers together; the third layer is a microporous membrane. Using this pump, controllable flow rates of 0.13–3.74 μl min⁻¹ can be obtained. This micropump features high and adjustable flow-rates, simple structure and low fabrication cost. It can be used as a “plug and play” fluid-driven unit without any external power sources and equipment.

In plants, transpiration draws the water upward from the roots to the leaves. However, this flow can be blocked by air bubbles in the xylem conduits, which is called xylem embolism. In this research, we present the design of a biomimetic microfluidic pump/valve based on water transpiration and xylem embolism. This micropump/valve is mainly composed of three parts: the first is a silicon sheet with an array of slit-like micropores to mimic the stomata in a plant leaf; the second is a piece of agarose gel to mimic the mesophyll cells in the sub-cavities of a stoma; the third is a micro-heater which is used to mimic the xylem embolism and its self-repairing. The solution in the microchannels of a microfluidic chip can be driven by the biomimetic “leaf” composed of the silicon sheet and the agarose gel. The halting and flowing of the solution is controlled by the micro-heater. Results have shown that a steady flow rate of 1.12 µl/min can be obtained by using this micropump/valve. The time interval between the turning on/off of the micro-heater and the halt (or flow) of the fluid is only 2∼3 s. This micropump/valve can be used as a “plug and play” fluid-driven unit. It has the potential to be used in many application fields.