Prints of precision

Ultra-precise, high-resolution microstructures could be created pixel by pixel using a tiny pipette and a novel two-tone molecular printing process, claimed a UK research team.

Dr David Klenerman and his joint team from Cambridge University and Imperial College, London, hope their nanopipette-based system will help enable advances in bio-molecular research.

The process could be used to make miniature biosensors that detect changes in fluorescence in a target molecule. It could also create arrays of molecules such as DNA, or protein nanoarrays, where the small size would mean less sample is required and analysis could be performed much faster than with current microarrays.

A spin-off company called Ionscope Ltd has been set up to commercialise the technology, said Klenerman. ‘We see this as a great tool for prototyping, such as making novel structures or determining the best combination of components.’

The team has already produced a colourful, fluorescing microscale portrait of Isaac Newton to demonstrate the system’s potential for molecular printing.

The technique is based on the same principle as scanning probe microscopy, where an extremely fine tip travels over a surface at a very short distance from it.

The device features a glass nanopipette whose interior is divided into two chambers by a membrane. Each chamber can be filled with a different solution and each contains an electrode to which a voltage is applied. This voltage adjusts the distance between the pipette tip and the surface to be printed on. When the pipette is very close to the surface, a drop of liquid leaves the tip, causing a current to flow between the two electrodes.

Unlike other voltage-based methods, which can only operate in a liquid, the pipette can operate in air. As only the meniscus of the drop touches the surface of the support the ink cannot run. The choice of ink to be dispensed is controlled by the voltage between the electrodes in the two chambers. One is negatively charged, the other is positive. A substance that is attracted to the positive electrode can be retained in the chamber, allowing only the ink in the chamber with the negative electrode to flow out. If the other ink is needed, the polarity is simply reversed.

Substances can be applied on top of each other, and as each is dispensed from a single pipette tip, positioning is much more accurate than with multi-pipette systems, according to the developers.