Self-driven micropumps propelled by salts show high efficiency in water decontamination

by Virginia Greco

A study recently published in “Nature Communications” and led by ICN2 researcher Dr María José Esplandiu introduces micropatterned pumps that use salts as fuel and that can selectively remove cadmium ions from water samples. Reusable, operable in high salt concentrations and able to drive unidirectional fluid flows, these devices look promising for various environmental and biomedicine applications.

Chemically propelled micropumps –i.e., small devices capable of driving the flow of a surrounding fluid by generating a chemical gradient and, hence, causing diffusion-osmotic or electroosmotic movements— have attracted great interest for their possible application in water decontamination and environmental remediation, as well as in biomedicine (for drug delivery and biosensing). Different material compositions and working principles are being investigated, with remarkable results. Nevertheless, most of these devices are triggered by toxic chemicals –which prevents their applicability in various contexts—, do not work at high salt concentrations, or cannot pump the fluid in a precise direction.

A team of researchers from the ICN2, the University of Barcelona and the University of Extremadura has developed a self-driven micropump made of a polymer (Nafion), which is fueled by innocuous chemicals, is reusable, can operate in a wide range of salt concentrations, and can trigger both radial and unidirectional fluid flows. This work, coordinated by Dr María José Esplandiu (first author), from the ICN2 Magnetic Nanostructures Group, and Dr Jordi Fraxedas (last author), from the ICN2 Thermal Properties of Nanoscale Materials Group, has been recently published in Nature Communications and included in the Editors’ Highlights on inorganic and physical chemistry.

Nafion is a polymer exhibiting high ion-exchange capabilities. When immersed in an aqueous salt solution, the Nafion-based microdevice exchanges protons by other ions that diffuse at different speeds. This generates a chemical gradient and thus an electric field, which can drive the fluid flow by electroosmosis. By means of nanofabrication techniques, an array of Nafion microstrips can be designed to obtain long-range unidirectional fluid pumping.

These Nafion micropumps were tested experimentally for the removal of cadmium (which is a dangerous contaminant) from water samples. They showed high selectivity towards cadmium ions, with a remarkable removal efficiency (superior to 95%) in very short times of operation. They were also proved to work at high salt concentrations and to be reusable. Remarkably, the own cadmium contaminant acts as fuel to drive the fluid pumping. All these properties make Nafion micropumps promising candidates for water decontamination, as well as for other environmental and biomedical applications.

This study provides an important proof of concept, which opens the way to the use of ion-exchange polymers and nanofabrication techniques to generate self-propelled micropumps. Further developments will allow adapting these devices to operate by removing other contaminants with different chemical fuels and to meet the requirements of each specific application.

Reference article:

Esplandiu, M.J., Reguera, D., Romero-Guzmán, D. et al. From radial to unidirectional water pumping in zeta-potential modulated Nafion nanostructures. Nature Communications 13, 2812 (2022). DOI: 10.1038/s41467-022-30554-7