Testing Nanosensors Based on NaYF4:Yb,Er for Measuring Temperature in Biological Media

NaYF4:Yb,Er particles are synthesized hydrothermally in the form of rods with an average size of 1.4 µm × 70 nm. Their surfaces are modified with L-cysteine, which gives them hydrophilic properties. It is shown that the modified particles exhibit upconversion luminescence in the visible spectral range upon 980-nm laser excitation. They are temperature calibrated in a physiological solution. The possibility is shown of making remote temperature measurements in the biologically relevant 293–323 K range of temperatures with an average sensitivity of 43 × 10−4 K−1 and an accuracy of ±1.0 K. A demonstration experiment is performed on the living nervous system of the grape snail Helix lucorum. Nanosensors are used for bioimaging and remote low-invasive temperature measurements with a spatial resolution of 10 µm.