Communication—Evaporation Driven Micro/Nanofluidic Pumping Device

Abstract

A compact portable nanofluidic pump that enables precise manipulation of ultra-small amount of liquid is highly desirable for the trend in miniaturization. Here we develop an integrated micro/nanofluidic pumping device utilizing nanopillar structures with diminishing intervals and locally controlled evaporation. A continuous and steady flow rate of 2.7 pL/s was achieved for more than 12 h without external mechanical power source. The liquid transports in the nanofluidic channels were controllable by adjusting the temperature of evaporation surface. The picoliter-scale flow rates meet the demands for performing nanofluidic immunoassays and other interdisciplinary applications. Microfluidics have recently emerged as powerful platforms for mechanical, physical, chemical, and biomedical applications.1-3 A compact portable microfluidic system requires an integrated micropump that drives a continuous liquid flow along functional elements. Among many micro-pumping methods, open capillary pumps based on the combination of evaporation and capillarity are simpler to realize a continuous flow at reduced production cost. Several evaporation driven pumping devices have been described to manipulate liquids for various microfluidic lab-on-chips. [4][5][6] Recent advances in nanofabrication have enabled a significant growth of research in nanofluidics.7 New physical phenomena and mechanisms start to emerge in fluidic geometries with characteristic dimensions in a range of 10-1000 nm (known as "extended nanospace"), e.g., higher viscosity, lower dielectric constant, and higher proton mobility of liquid water than in the bulk. 8 These unique properties can be applied to the analysis of ultra-small volume samples, such as nanofluidic immunoassays at picoliters (pL = 10 −12 L) or smaller scales. 9 Although there have been a number of studies on the evaporation driven pumping in microfluidic devices, 10-12 little attention has been dedicated to nanofluidic channels. Those narrow spaces possess a significant flow resistance and thus require evaporation driven pumps having small flow resistance and high capillary pressure (i.e., Laplace pressure). More importantly, the pump should minimize the risk of entrapping air, which is occasionally present in hydrophilic nanochannels, 13 to provide continuous and steady flow rates for long-term periods.The concept of the evaporation-driven pump is inspired by the water transports in plants.14 Liquid water is pulled out of the soil at the root, transported via the xylem to leaves with capillary pressures, and evaporated through stomas at the leaf surface, as shown in Fig. 1a. To further advance this field, we developed a capillary pump that combines nanopillar structures with diminishing intervals and locally controlled evaporation to mimic the continuous pumping in leaf-like biosystem, as shown in Fig. 1b. Our designed pump has a comparatively lower flow resistance and high Laplace pressure differential, which showed the ability to create steady flows lasting longterm periods in nanochannels. F...

Nanofluidic Devices and Applications for Biological Analyses

“…Pumps to control fluid in a nanochannel are also rarely found. For 2D nanochannels, passive and electrokinetic pumps have been reported. Meanwhile, due to technical difficulties in nanofabrication, only one mechanical pump has been reported that fits a 1D nanochannel .…”

“…60 Pumps to control fluid in a nanochannel are also rarely found. For 2D nanochannels, passive 61 and electrokinetic 62…”

Manipulating nanoliter fluid circuits on an all-glass chip by the magnetic field

“…For example, many nanoflow studies have focused on using carbon nanotubes to transport water flows 1. 16 Scientists use evaporation, 17 , 18 electroosmotic flow, 19 high voltage, 20 ions, 21 nanowires, 22 surface charge, 23 and even large HPLC pumps 24 to control the nanometer flow. Nanofluidic technology also needs microfluidic technology, such as temperature-controlled peristaltic pumps, 25 air-controlled valves, 26 microfluidics combined with membranes, 27 170 V silicon dioxide thin film deformable pumps, 28 and 4W ultrasonic drives.…”

Nanofluidic peristaltic pumps made from silica thin films

“…Other nano-scale pumps have been demonstrated that use evaporation [11] and external pressure [12]. Driving flow with evaporation can be convenient because no external power is needed to drive flow.…”

“…Driving flow with evaporation can be convenient because no external power is needed to drive flow. However, it is a loosely controlled fluid transport mechanism that varies with the temperature, relative humidity, and even airflow over the exit reservoir [11]. Similarly, devices that generate flow based on external pressure mandate additional supporting equipment, which hinders miniaturization.…”