Temperature sensing and bio-imaging applications based on polyethylenimine/CaF2 nanoparticles with upconversion fluorescence

Abstract

Rare earth ion-doped upconversion nanoparticles (UCNPs) have become a research hotspot for their applications such as nano-thermometry and bio-imaging. Here we report one pot solvothermal synthesis of polyethylenimine (PEI) coated CaF: 1%Er, 2%Yb UCNPs with good water-solubility and biocompatibility. The nanoparticles show a spherical shape with an average size of 40nm and display intense green light (Yb and Er) under the 980nm irradiation. The maximum sensitivity of temperature sensing in the biological temperature range is obtained to be 0.00215K using the fluorescence intensity ratio (FIR) technique. Furthermore, after the UCNPs are incubated with Hela cancer cells for 6h, the obvious green sign from Er can be observed under the excitation at 980nm. All the experimental results imply that the PEI/CaF: 1%Er, 2%Yb nanoparticles are excellent candidates for nano-thermometry and have good potential for biological applications.

Transparent Aluminosilicate Oxyfluoride Glass Ceramics Containing Upconversion Luminescent CaF2 Nanocrystals: Glass-to-Crystal Structural Evolution Studied by the Advanced Solid-State NMR Spectroscopy

“…CaF 2 is a nontoxic optical material with high solubility of REIs, low phonon energy, high chemical stability, and wide transmittance range, thus exhibiting great potential applications involving upconversion, optical waveguides, solar cells, biological windows, etc. − Therefore, it is expected that CaF 2 can be used as a good alternative material for Pb x Cd (1– x ) F 2 and PbF 2 . Fu et al first reported Eu 2+ -doped transparent oxyfluoride glass ceramics containing CaF 2 nanocrystals where the Eu 2+ has higher luminescence than in the precursor glasses .…”

Effect of Mn2+ on Upconversion Emission, Thermal Sensing and Optical Heater Behavior of Yb3+ - Er3+ Codoped NaGdF4 Nanophosphors

“…Among temperature dependent optical performance, such as peak position (Jiang et al, 2014), luminescent lifetime (Peng et al, 2010), emission intensity (Zhou et al, 2016), and bandwidth (Walsh and Di Bartolo, 2015), fluorescence intensity ratio (FIR) technique (Liu et al, 2017; Xu et al, 2017) can achieve accurate temperature measurement, which is independent of external interferences, spectral losses, as well as fluctuations in the excitation density (Wade et al, 2003; Wawrzynczyk et al, 2012; Zhou et al, 2014; Pandey et al, 2015; Wang et al, 2015). Using this ratiometric technique, the sensitivity of sensor is strongly dependent on the energy gap of thermally coupled levels (TCL), which is confined in the range of 200–2,000 cm −1 (Zheng et al, 2016; Du et al, 2017; Tong et al, 2017; Wang et al, 2017).…”

Multipath optical thermometry realized in CaSc2O4: Yb3+/Er3+ with high sensitivity and superior resolution

“…In particular, the fluorescence intensity ratio ( FIR ) between two thermally coupled energy levels of trivalent rare earth ions is considered to be a promising technology to provide fast and accurate optical thermometry, due to its rapid response capability, high spatial resolution, strong anti‐jamming ability, etc 12‐17 . Up to date, numerous trivalent rare earth ions are used for ratiometric thermometry, such as Er 3+ , Ho 3+ , Tm 3+ , Nd 3+ , and Eu 3+ 18‐25 . Among these ions, Er 3+ is the most widely used activator for temperature sensing which has been realized in an enormous variety of materials, due to the excellent thermal coupling between the green emitting levels 2 H 11/2 and 4 S 3/2 of Er 3+ as well as their strong UC intensity under the excitation of 980 nm excitation with the sensitization of Yb 3+ 26,27 .…”

“…[12][13][14][15][16][17] Up to date, numerous trivalent rare earth ions are used for ratiometric thermometry, such as Er 3+ , Ho 3+ , Tm 3+ , Nd 3+ , and Eu 3+ . [18][19][20][21][22][23][24][25] Among these ions, Er 3+ is the most widely used activator for temperature sensing which has been realized in an enormous variety of materials, due to the excellent thermal coupling between the green emitting levels 2 H 11/2 and 4 S 3/2 of Er 3+ as well as their strong UC intensity under the excitation of 980 nm excitation with the sensitization of Yb 3+ . 26,27 Nevertheless, the thermometric sensitivity and resolution as well as the signal to noise ratio (SNR) of Er 3+typed optical thermometer are still need to be improved.…”