Nanothermometry: Quantum dots for high resolution temperature sensing

Bridging the realms of physics and materials science with the life sciences, nanoparticles have spent many years at the forefront of biological and medical research. Quantum dots can be fabricated to have particular emission properties and can be labelled to target specific binding sites in biological samples to act as biomarkers. A class of QDs made from cadmium telluride show a peak emission wavelength which increases linearly with temperature and have potential to become useful biological nanothermometers.
We use optical traps to generate localised heat in samples and measure this heating using cadmium telluride (CdTe) QDs. A conventional optical tweezer system was modified to incorporate a number of different sources to controllably heat our sample, an excitation source and spectrometer. Using samples which contained CdTe QDs in solution, we optically trapped particles using laser sources of different wavelengths and trapping powers whilst recording the emission spectrum of the CdTe QDs. Shift in emission spectra indicated temperature shift within and nearby the optical trap. Commercially available 2.3nm diameter CdTe QDs, em λ=540nm at 25°C, which exhibit an emission shift of 0.6nm/°C were used to quantify localised heating by focused laser beams in a variety of samples. We discuss the limitations of the technique including quenching by surrounding liquid and cytotoxicity.
We have demonstrated the use of CdTe QDs as nanothermometers to measure heating in samples due to a focused laser beam with sensitivities of 0.6˚C. These particles hold promise for performing temperature measurements with high spatial resolution in biological environments.