Brushed Nano‐Stirbars for Measuring Viscosity in Microscopic Systems.

Conventional methods for measuring viscosity rely on macroscopic device components, which are difficult to miniaturize. The magnetic nano‐stirbars are small enough to enter tiny spaces and can spin without precise installation, making them an ideal candidate for exploring new methods. It is shown that a dense layer of Au nanowires can be grown on the silica surface of the nano‐stirbars, as a means to modulate the viscous resistance during their spinning and to make them visible under an optical microscope. The uniform growth of Au nanowires and the slight fluctuation of the spinning rates are investigated. It is shown that the nano‐stirbars with the hairy layer of Au nanowires can be used to measure the viscosity in microscopic liquid systems, such as microfluidic chambers and capillary tubes, involving cell media and blood samples. It is believed that the success with the proof‐of‐concept tests will open a window for further miniaturization of the nano‐stirbars for measuring in ultrasmall systems. [ABSTRACT FROM AUTHOR]