Crystals Made to Sprout Tiny Tubes

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The researchers can change the tubes' diameters and the rate at which they grow by changing the concentration of the fluorescent molecules. The tubes range from 1 to 120 micrometers wide. By applying a voltage, they can make the tubes grow in specific directions. They can make branched tubes in two different ways. One is to let two tubes collide, which makes a single tube emerge at the collision point. The other is to puncture a tube with a micromanipulator needle so that the material flows out and grows another branch. To show that the tubes are hollow and can carry liquids, the researchers inject fluorescent dye through them.

Kogerler says that the work is promising because the tubes maintain their structure and do not decompose. Also, they have a relatively high surface-to-volume ratio, which is beneficial for catalysis and sensing applications. But it is not yet evident that they will be ideal for these applications. That is because the surface of the tubes is not just made of interlinked polyoxometalate molecules: it also contains positively charged fluorescent molecules. "The question is, would you gain any kind of reactivity from that?" Kogerler asks.

Kogerler says that it would be really interesting if the researchers could find a way to grow similar tubes in the nanometer range. Metal-oxide compounds are known to form structures on this scale, and the approach would yield even larger surfaces.