Scientists have developed the first liquid nanoscale laser technology that could lead to a new way of doing 'lab on a chip' medical diagnostics.

The laser is tunable in real time, meaning you can quickly and simply produce different colours, a unique and useful feature, researchers said.

The laser technology could lead to practical applications, such as a new form of a "lab on a chip" for medical diagnostics, they said.

To understand the concept, imagine a laser pointer whose colour can be changed simply by changing the liquid inside it, instead of needing a different laser pointer for every desired colour.

In addition to changing colour in real time, the liquid nanolaser has additional advantages over other nanolasers: it is simple to make, inexpensive to produce and operates at room temperature.

Nanoscopic lasers - first demonstrated in 2009 - are only found in research labs today. They are, however, of great interest for advances in technology and for military applications.

"Our study allows us to think about new laser designs and what could be possible if they could actually be made," said Teri W Odom, from the Northwestern University, who led the research.

"We believe this work represents a conceptual and practical engineering advance for on-demand, reversible control of light from nanoscopic sources," said Odom.

The liquid nanolaser in this study is not a laser pointer but a laser device on a chip, Odom explained. The laser's colour can be changed in real time when the liquid dye in the microfluidic channel above the laser's cavity is changed.

The laser's cavity is made up of an array of reflective gold nanoparticles, where the light is concentrated around each nanoparticle and then amplified.

In contrast to conventional laser cavities, no mirrors are required for the light to bounce back and forth.

Notably, as the laser colour is tuned, the nanoparticle cavity stays fixed and does not change; only the liquid gain around the nanoparticles changes.

The small lasers can be used as on-chip light sources for optoelectronic integrated circuits; they can be used in optical data storage and lithography, researchers said.

They can operate reliably at one wavelength and should be able to operate much faster than conventional lasers because they are made from metals, they said.

The findings were published in the journal Nature Communications.