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Optical microcavities are useful as probes in cells due to their narrow emission spectra and high sensitivity to environment. Here, the authors use the unique spectral features of microcavities, which are unaffected by tissue scattering, and show 3D localisation and tracking of cells deep in tissues.

Abstract Temperature is a critical parameter in biology, affecting the speed of reactions that occur in living systems. Nevertheless, measuring temperature with subcellular resolution (micrometric scale) and reliability remains a challenge to overcome. In this perspective, luminescence nanothermometry is a non‐contact technique which aims to measure temperature with a sub‐micrometric spatial resolution through the use of nanomaterials whose luminescence is affected solely by changes in temperature. Here, TiO2 nanoparticles doped with Eu+3 ions (Eu+3‐TiO2) are used for sensing temperature differences within single living cells. XRD, XPS, SEM, TEM and NEXAFS analysis allow the determination of the physicochemical characteristics of the Eu+3‐TiO2 nanoparticles and, the variation of the luminescence intensity of the Eu+3‐TiO2 nanoparticles with their temperature is investigated. The successful internalization of Eu+3‐TiO2 nanoparticles in different types of cells is observed. The luminescence of nanoparticles internalized in L929 fibroblast cells is measured when the system is heated in a biological relevant temperature range. Making use of an appropriate calibration curve the temperature variation inside the cells is determined with sensitivity of 0.5 K per 1% of luminosity change when heated.

Biological functions of cell membranes and their correlation to the heterogeneity of the latter’s lipid composition are still poorly understood. Fluorescence provides one of the most versatile tools for studying biological membranes. However, few bright and photostable fluorescent probes for labeling plasma membranes are available. We have designed and synthesized two such probes, 8 and 9, that are based on the thiazole-coumarin scaffold. Both are environment sensitive and exhibit similar shifts of emission spectra in a variety of solvents as probes based on 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD). In particular, the second, positively charged probe 9 labels the plasma membrane selectively with limited redistribution to other membranes of the cell. Unfortunately, compared to the other two probes tested, 8 and 6-NBD-PC, it exhibits the highest rate of photobleaching. Nevertheless, these new thiazole-coumarin based membrane probes provide a viable approach to the design of novel membrane probes.

Background & aimTiO2 nanoparticles have generally low toxicity in the in vitro systems although some toxicity is expected to originate in the TiO2-associated photo-generated radical production, which can however be modulated by the radical trapping ability of the serum proteins. To explore the role of serum proteins in the phototoxicity of the TiO2 nanoparticles we measure viability of the exposed cells depending on the nanoparticle and serum protein concentrations.Methods & resultsFluorescence and spin trapping EPR spectroscopy reveal that the ratio between the nanoparticle and protein concentrations determines the amount of the nanoparticles' surface which is not covered by the serum proteins and is proportional to the amount of photo-induced radicals. Phototoxicity thus becomes substantial only at the protein concentration being too low to completely coat the nanotubes' surface.ConclusionThese results imply that TiO2 nanoparticles should be applied with ligands such as proteins when phototoxic effects are not desired - for example in cosmetics industry. On the other hand, the nanoparticles should be used in serum free medium or any other ligand free medium, when phototoxic effects are desired - as for efficient photodynamic cancer therapy.