Lasers make liposomes tiny test tubes

Using laser light as tweezers and a scalpel, scientists from the National Institute of Standards and Technology in the USA have demonstrated the use of liposomes as nanovials for ultrasmall volume chemistry.

The approach may be useful for faster, cheaper identification of new pharmaceuticals and for studying cellular-level processes, said the researchers, who report their results in today's edition of the journal Langmuir​.

Liposomes measuring micrometers in diameter are currently used in cosmetics and for drug delivery applications. The NIST team has developed a method for using liposomes as tiny microreactors for mixing chemicals with volumes measured in trillionths of liters.

Their approach allows the simultaneous trapping of two liposomes without deforming or stressing their membranes, a problem with some other techniques. The researchers used pairs of infrared lasers - optical tweezers - to bring the liposomes into contact and a single ultra-violet laser pulse - the optical scalpel - to fuse the two cells together. Once fused, the contents of the two cells mix and react.

In the Langmuir experiment, one liposome in each pair contained fluorescent dye, and the other contained calcium ions. After the cells merged, fluorescence increased as a result of the reaction between the dye and the ions.

The optical scalpel achieves cleaner fusion and less leakage of contents than currently-used techniques using pulsed electric fields, according to the scientists. The liposomes fully enclose their reactant chemicals, minimising evaporation. Consequently, the technique also may be useful for quantitative studies of chemical reactions involving samples in the quadrillionths of litres, they said.