Mn2+-activated calcium fluoride nanoprobes for time-resolved photoluminescence biosensing

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  • ReceivedMar 28, 2018
  • AcceptedApr 24, 2018
  • PublishedMay 16, 2018


Time-resolved (TR) photoluminescence (PL) technique has shown great promise in ultrasensitive biodetection and high-resolution bioimaging. Hitherto, almost all the TRPL bioprobes are based on the parity-forbidden f→f transition of lanthanide ions. Herein, we report TRPL biosensing by taking advantage of the d→d transition of transition metal (TM) Mn2+ ion. We demonstrate that the Förster resonance energy transfer (FRET) signal can be distinguished from that of radiative reabsorption process through measuring the PL lifetime of Mn2+, thus establishing a reliable method for Mn2+ in homogeneous TR-FRET biodetection. We also demonstrate the biotin receptor-targeted cancer cell imaging by utilizing biotinylated CaF2:Ce,Mn nanoprobes. Furthermore, we show in a proof-of-concept experiment the application of the long-lived PL of Mn2+ for TRPL bioimaging through the burst shot with a cell phone. These findings provide a general approach for exploiting the long-lived PL of TM ions for TRPL biosensing, thereby opening up a new avenue for the exploration of novel and versatile applications of TM ions.

Funded by

This work is supported by National Program on Key Basic Research Project(973,Program,2014CB845605)

the Strategic Priority Research Program of the CAS(XDB20000000)

the National Natural Science Foundation of China(21325104,11774345,21771185,21501180,21650110462)

the CAS/SAFEA International Partnership Program for Creative Research Teams

the Youth Innovation Promotion Association(2016277)

the Chunmiao Project of Haixi Institutes of the CAS(CMZX-2016-002)

and Natural Science Foundation of Fujian Province(2017I0018,2017J05095)


This work is supported by National Program on Key Basic Research Project (973 Program, 2014CB845605), the Strategic Priority Research Program of the CAS (XDB20000000), the National Natural Science Foundation of China (21325104, 11774345, 21771185, 21501180 and 21650110462), the CAS/SAFEA International Partnership Program for Creative Re-search Teams, the Youth Innovation Promotion Association (2016277) and the Chunmiao Project of Haixi Institutes of the CAS (CMZX-2016-002), and Natural Science Foundation of Fujian Province (2017I0018 and 2017J05095).

Interest statement

The authors declare no competing interests.

Contributions statement

Wei J, Zheng W and Chen X conceived the project, wrote the paper and were primarily responsible for the experiments. Shang X and Li R carried out PL measurements. Huang P and Gong Z synthesized and characterized the NCs. Liu Y, Zhou S and Chen Z contributed to the TRPL biodetection and bioimaging. All authors contributed to the general discussion and revision of the manuscript.

Author information

Jiaojiao Wei was born in Henan province of China. She is currently a master student in the College of Chemistry and Materials, Fujian Normal University, China. She joined Prof. Xueyuan Chen’s group in Fujian Institute of Research on the Structure of Matter (FJIRSM), Chinese Academy of Sciences (CAS) in September 2016. She will graduate in June 2018. Her current research interest focuses on the controlled synthesis and optical spectroscopy of inorganic luminescent nanomaterials.

Wei Zheng earned his BSc degree (2007) in material forming and control engineering from Sichuan University and his PhD (2012) in Condensed Matter physics from FJIRSM, CAS. He joined Prof. Xueyuan Chen’s group as a research assistant professor in September 2012 and was promoted to research associate professor in 2015. He joined the Youth Innovation Promotion Association of the CAS in 2016. Currently, his research interest focuses on the chemical synthesis, optical spectroscopy and bioapplications of inorganic luminescent nanomaterials.

Xueyuan Chen earned his BSc degree from the University of Science and Technology of China (1993) and his PhD degree from FJIRSM, CAS (1998). From 2001 to 2005, he was a postdoctoral research associate at the Chemistry Division of Argonne National Laboratory, U.S. Department of Energy, where he studied the photophysics and photochemistry of heavy elements. In 2005, he joined the faculty at FJIRSM, where he is currently a professor and group leader in Materials Chemistry and Physics. His research focuses on the chemistry, optical spectroscopy and bioapplications of lanthanide-doped luminescent nanomaterials.


Supplementary information

Experimental details and supporting data are available in the online version of the paper.


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  • Figure 1

    (a) TEM and (b) HRTEM images of CaF2:5%Ce,5%Mn NPs. (c) PL photograph of the NPs dispersed in cyclohexane under 304-nm UV lamp irradiation. (d) PL emission spectrum (black) of CaF2:5%Ce,5%Mn NPs upon UV excitation at 304 nm, and their excitation spectrum (red) by monitoring the Mn2+ emission at 520 nm. (e) PL decay from 4T1g by monitoring the Mn2+ emission at 520 nm.

  • Figure 2

    (a) PL emission spectrum of CaF2:5%Ce,5%Mn NPs (black); excitation (red) and emission (blue) spectra of TRITC. (b) Steady-state and TRPL (delay time=100 μs, gate time=5 ms) emission spectra for the aqueous solution containing 50 μmol L−1 of PAA-capped NPs and 10 nmol L−1 of TRITC upon UV excitation at 304 nm. (c) PL decays of TRITC by monitoring its emission at 650 nm upon excitation with a 397-nm nanosecond pulsed laser. IR denotes the instrument response. (d) PL decay of the NPs-TRITC mixture by monitoring the TRITC emission at 650 nm under excitation at 304 nm. (e) PL decays of PAA-capped NPs (black) and NPs-TRITC mixture (red) by monitoring the Mn2+ emission at 520 nm under excitation at 304 nm.

  • Figure 3

    (a) Schematic illustration of the energy transfer processes between CaF2:Ce,Mn NPs and TRITC in cases of specific binding (left) and non-specific binding (right). TRPL spectra of (b) biotinylated and (c) PAA-capped CaF2:Ce,Mn NPs incubated with TRITC-labeled avidin as a function of the avidin concentration. PL decays from (d) biotinylated and (e) PAA-capped CaF2:Ce,Mn NPs at different avidin concentrations by monitoring the Mn2+ emission at 520 nm. (f) Effective PL lifetime of 4T1g of Mn2+ as a function of the avidin concentration, as obtained from (d, e). Each PL lifetime was measured independently for three times to yield the average value and standard deviation.

  • Figure 4

    Confocal laser scanning microscopy images of (a1−a3) HeLa cells and (b1−b3) L-02 cells after incubation with biotinylated CaF2:Ce,Mn NPs (0.5 mg mL−1) at 37°C for 2 h. Intense green PL of Mn2+ (λem=500−560 nm, λex=408 nm) was observed exclusively in HeLa cells. Panel 1 and 2 show the green PL images and bright-field images, respectively. Panel 3 is the overlay images of panels 1 and 2.

  • Figure 5

    (a) Schematic representation of the camera burst mode on a cell phone. The image in the cell phone represents the steady-state PL photo for the aqueous solution of ligand-free CaF2:Ce,Mn NPs (left) and TRITC (right) under 304-nm UV lamp irradiation. The images outside the cell phone denote the corresponding TRPL photos of the NPs and TRITC, captured by the cell phone in sequence with a time interval of 0.1 s. (b) Microscopic bright field, steady-state and TRPL images of the 5-day-old zebrafish fed with ligand-free CaF2:Ce,Mn NPs (0.5 mg mL−1).

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