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A Chemo-Responsive Nanofluidic Pump That Turns Off in the Presence of Lead Ion Xiaojian Wu, Juliette Experton, Weihuang Xu, and Charles R. Martin Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b01623 • Publication Date (Web): 24 May 2018 Downloaded from http://pubs.acs.org on May 24, 2018
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Analytical Chemistry
A Chemo-Responsive Nanofluidic Pump That Turns Off in the Presence of Lead Ion Xiaojian Wu, Juliette Experton, Weihuang Xu, and Charles R. Martin* Department of Chemistry, University of Florida, Gainesville, Florida, 32611-7200, United States *
[email protected] ABSTRACT: There are many applications that require the integration of a pump and a chemical sensor so that the solution being pumped can be analyzed in real time for a specific chemical species and the flow adjusted according to the measured concentration of that species. We describe here an alternative strategy – a chemo-responsive pump where a single device acts as both the sensor and pump simultaneously. We demonstrate this concept with a nanofluidic Pb 2+-responsive pump that uses electroosmotic flow (EOF) as the pumping technology, and a Pb 2+-binding ionophore that allows the device to selectively respond to Pb 2+. The pump yields high flow rates at low Pb2+ concentrations (< 1 µM), but flow rate decreases with concentrations above this threshold, and ultimately goes to zero at concentration above 100 µM.
Using real-time data from chemical sensors to control and modulate flow in process streams is a well-known industrial technology.1, 2 The implantable glucose pump/sensor apparatus3, 4 is another example where a sensor is used in tandem with a pump to regulate flow. In all of these examples the pump and the sensor are separate devices that must be interfaced together via a computer. An alternative strategy, of increasing research interest, entails integrating the sensor and pumping functions into a single device, a chemo-responsive pump.5, 6 In the devices reported to date, a chemical reaction is used to induce fluid flow, either as convection above the surface where the reaction is occurring7 or through a porous membrane.8 We describe here an alternative chemo-responsive pumping concept where the pump is powered by an alternating current (AC) electroosmotic flow (EOF)9, 10 technology,11 and the pump is turned off by a highly selective chemical-recognition event. The AC-EOF device is a synthetic membrane with conically-shaped pores12, 13 (Figure 1) through which flow occurs. The chemical-recognition system is an ionophore, 18crown-6, that selectively binds Pb2+.14, 15 The ionophore is covalently attached to the pore walls of the conical pore membrane. If Pb2+ is present in the solution being pumped, it is captured by the ionophore, which changes the charge density on the pore wall (Figure 1c). This change in surface charge ultimately turns the AC-EOF pump off. The pump reported here yields high solution flow rates at low Pb2+ concentrations (
