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Upconversion Modulation through Pulsed Laser Excitation for Anti-counterfeiting.

ABSTRACT: Lanthanide-doped upconversion nanomaterials are emerging as promising candidates in optoelectronics, volumetric display, anti-counterfeiting as well as biological imaging and therapy. Typical modulations of upconversion through chemical methods, such as controlling phase, composition, morphology and size enable us to rationally manipulate emission profiles and lifetimes of lanthanide ions by using continuous-wave laser excitation. Here we demonstrate that under pulsed laser excitation the emission color of NaYF₄:Er/Tm (2/0.5%)@NaYF₄ core-shell nanoparticles has an obvious transformation from green to red colors. Moreover, both pulse duration and repetition frequency are responsible for manipulating the upconversion emission color. The mechanism of the phenomena may be that the pulsed laser sequence triggers the emission levels to non-steady upconversion states first, and then cuts off the unfinished population process within the pulse duration. This pump source dependent and resultant tunable fluorescence emission enables NaYF₄:Er/Tm (2/0.5%)@NaYF₄ nanoparticles as a promising fluorophore in the transparent anti-fake printing.

SUBMITTER: Han Y

PROVIDER: S-EPMC5430986 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Fluorescence fluctuation imaging is a powerful means to investigate dynamics, interactions, and stoichiometry of proteins inside living cells. Pulsed interleaved excitation (PIE) is the method of nanosecond alternating excitation with time-resolved detection and allows accurate, independent, and quasi-simultaneous determination of fluorescence intensities and lifetimes of different fluorophores. In this work, we combine pulsed interleaved excitation with fluctuation imaging methods (PIE-FI) such as raster image correlation spectroscopy (RICS) or number and brightness analysis (N&B). More specifically, we show that quantitative measurements of diffusion and molecular brightness of Venus fluorescent protein (FP) can be performed in solution with PIE-RICS and compare PIE-RICS with single-point PIE-FCS measurements. We discuss the advantages of cross-talk free dual-color PIE-RICS and illustrate its proficiency by quantitatively comparing two commonly used FP pairs for dual-color microscopy, eGFP/mCherry and mVenus/mCherry. For N&B analysis, we implement dead-time correction to the PIE-FI data analysis to allow accurate molecular brightness determination with PIE-NB. We then use PIE-NB to investigate the effect of eGFP tandem oligomerization on the intracellular maturation efficiency of the fluorophore. Finally, we explore the possibilities of using the available fluorescence lifetime information in PIE-FI experiments. We perform lifetime-based weighting of confocal images, allowing us to quantitatively determine molecular concentrations from 100 nM down to <30 pM with PIE-raster lifetime image correlation spectroscopy (RLICS). We use the fluorescence lifetime information to perform a robust dual-color lifetime-based FRET analysis of tandem fluorescent protein dimers. Lastly, we investigate the use of dual-color RLICS to resolve codiffusing FRET species from non-FRET species in cells. The enhanced capabilities and quantitative results provided by PIE-FI make it a powerful method that is broadly applicable to a large number of interesting biophysical studies.

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Upconversion Modulation through Pulsed Laser Excitation for Anti-counterfeiting.

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