scientists at the king abdullah university of science and technology (kaust) in thuwal, saudi arabia have developed sensors from gallium nitride nanomembranes just 40 nanometers thick that provide detailed measurements of heat transfer across the surface of living cells, according to a report on the university website.

by monitoring the emitted photoluminescent light (blue arrows), the researchers can calculate the thermal transport properties of the cell. (rami elafandy/ kaust)

as the article noted, there has been extensive research done on the optical, mechanical and electrical properties of cells but the challenges of tiny cell volumes and irregular shapes has limited the knowledge of cells’ thermal properties.

the article explained, “after attaching the sensor to the cell surface, the researchers applied a pulsed ultraviolet laser beam, heating the nanomembrane and causing a photoluminescent emission of light at a frequency dependent on the temperature of the nanomembrane. this temperature, in turn, depended on how well the heat was transferred into the cell.”

to avoid damaging cells with the laser, a thin, gold disc was added between the nanomembrane and the cell to absorb the laser radiation while allowing the heat to diffuse into the cell. researchers measured the frequency of the photoluminescent light to calculate the thermal conductivity and thermal diffusivity of the cells.

this could be used to detect cancer cells and other medical applications.

the research was published in small. the abstract stated:

“knowledge of materials' thermal-transport properties, conductivity and diffusivity, is crucial for several applications within areas of biology, material science and engineering. specifically, a microsized, flexible, biologically integrated thermal transport sensor is beneficial to a plethora of applications, ranging across plants physiological ecology and thermal imaging and treatment of cancerous cells, to thermal dissipation in flexible semiconductors and thermoelectrics.

“living cells pose extra challenges, due to their small volumes and irregular curvilinear shapes. here a novel approach of simultaneously measuring thermal conductivity and diffusivity of different materials and its applicability to single cells is demonstrated. this technique is based on increasing phonon-boundary-scattering rate in nanomembranes, having extremely low flexural rigidities, to induce a considerable spectral dependence of the bandgap-emission over excitation-laser intensity.

“it is demonstrated that once in contact with organic or inorganic materials, the nanomembranes' emission spectrally shift based on the material's thermal diffusivity and conductivity. this nm-based technique is further applied to differentiate between different types and subtypes of cancer cells, based on their thermal-transport properties.

“it is anticipated that this novel technique to enable an efficient single-cell thermal targeting, allow better modeling of cellular thermal distribution and enable novel diagnostic techniques based on variations of single-cell thermal-transport properties.”