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Upconversion nanomaterials: synthesis, mechanism, and applications in sensing.

Chen J, Zhao JX - Sensors (Basel) (2012)

Bottom Line: Over the past decade, high-quality rare earth-doped upconversion nanoparticles have been successfully synthesized with the rapid development of nanotechnology and are becoming more prominent in biological sciences.The synthesis methods are usually phase-based processes, such as thermal decomposition, hydrothermal reaction, and ionic liquids-based synthesis.In this review, the synthesis of upconversion nanoparticles and the mechanisms of upconversion process will be discussed, followed by their applications in different areas, especially in the biological field for biosensing.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of North Dakota, Grand Forks, ND 58202, USA. jiao.chen@my.und.edu

ABSTRACT
Upconversion is an optical process that involves the conversion of lower-energy photons into higher-energy photons. It has been extensively studied since mid-1960s and widely applied in optical devices. Over the past decade, high-quality rare earth-doped upconversion nanoparticles have been successfully synthesized with the rapid development of nanotechnology and are becoming more prominent in biological sciences. The synthesis methods are usually phase-based processes, such as thermal decomposition, hydrothermal reaction, and ionic liquids-based synthesis. The main difference between upconversion nanoparticles and other nanomaterials is that they can emit visible light under near infrared irradiation. The near infrared irradiation leads to low autofluorescence, less scattering and absorption, and deep penetration in biological samples. In this review, the synthesis of upconversion nanoparticles and the mechanisms of upconversion process will be discussed, followed by their applications in different areas, especially in the biological field for biosensing.

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Room temperature upconversion emission spectra of (a) NaYF4:Yb/Er (18/2 mol%), (b) NaYF4:Yb/Tm (20/0.2 mol%), (c) NaYF4:Yb/Er (25–60/2 mol%), and (d) NaYF4:Yb/Tm/Er (20/0.2/0.2–1.5 mol%) particles in ethanol solutions. The spectra in (c) and (d) were normalized to Er3+ 650 nm and Tm3+ 480 emissions, respectively. Compiled luminescent photos showing corresponding colloidal solutions of (e) NaYF4:Yb/Tm (20/0.2 mol%), (f–j) NaYF4:Yb/Tm/Er (20/0.2/0.2–1.5 mol%), and (k–n) NaYF4:Yb/Er (18–60/2 mol%). The samples were excited at 980 nm with a 600 mW diode laser [83].
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f12-sensors-12-02414: Room temperature upconversion emission spectra of (a) NaYF4:Yb/Er (18/2 mol%), (b) NaYF4:Yb/Tm (20/0.2 mol%), (c) NaYF4:Yb/Er (25–60/2 mol%), and (d) NaYF4:Yb/Tm/Er (20/0.2/0.2–1.5 mol%) particles in ethanol solutions. The spectra in (c) and (d) were normalized to Er3+ 650 nm and Tm3+ 480 emissions, respectively. Compiled luminescent photos showing corresponding colloidal solutions of (e) NaYF4:Yb/Tm (20/0.2 mol%), (f–j) NaYF4:Yb/Tm/Er (20/0.2/0.2–1.5 mol%), and (k–n) NaYF4:Yb/Er (18–60/2 mol%). The samples were excited at 980 nm with a 600 mW diode laser [83].

Mentions: The ability to manipulate color output of nanomaterials can broaden their applications, especially in the case of multiplexed biological labeling and imaging. Various approaches, based on surface plasmon resonance [91–94] or using multicolor-encoded microbeads and nanoparticles [95,96], have been applied to tune multicolor output. However, most of these methods need high energy excitation source in the UV region, which bring limitations to bioimaging studies due to the significant background (autofluorescence) and photo damage to the samples. The UCNs-based method becomes extremely promising to solve these problems, and a few current researchers have already shown the possibility to output multicolor lights. It can be obtained by adjusting the reaction temperature and time, crystal structure and phase, or changing the combinations of Ln3+ dopants and dopant concentration (Figure 12) [26,39,83,97,98]. Ehlert et al. presented that four different colors of UCNs can be spectrally separated under multiplexing conditions with a single excitation source of 980 nm [99]. Li and co-workers obtained the multicolor output signal by encapsulating organic dyes or QDs into the silica shell and the upconversion fluorescence was generated based on FRET from the UCN-cores to organic dyes or QDs [100].


Upconversion nanomaterials: synthesis, mechanism, and applications in sensing.

Chen J, Zhao JX - Sensors (Basel) (2012)

Room temperature upconversion emission spectra of (a) NaYF4:Yb/Er (18/2 mol%), (b) NaYF4:Yb/Tm (20/0.2 mol%), (c) NaYF4:Yb/Er (25–60/2 mol%), and (d) NaYF4:Yb/Tm/Er (20/0.2/0.2–1.5 mol%) particles in ethanol solutions. The spectra in (c) and (d) were normalized to Er3+ 650 nm and Tm3+ 480 emissions, respectively. Compiled luminescent photos showing corresponding colloidal solutions of (e) NaYF4:Yb/Tm (20/0.2 mol%), (f–j) NaYF4:Yb/Tm/Er (20/0.2/0.2–1.5 mol%), and (k–n) NaYF4:Yb/Er (18–60/2 mol%). The samples were excited at 980 nm with a 600 mW diode laser [83].
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3376553&req=5

f12-sensors-12-02414: Room temperature upconversion emission spectra of (a) NaYF4:Yb/Er (18/2 mol%), (b) NaYF4:Yb/Tm (20/0.2 mol%), (c) NaYF4:Yb/Er (25–60/2 mol%), and (d) NaYF4:Yb/Tm/Er (20/0.2/0.2–1.5 mol%) particles in ethanol solutions. The spectra in (c) and (d) were normalized to Er3+ 650 nm and Tm3+ 480 emissions, respectively. Compiled luminescent photos showing corresponding colloidal solutions of (e) NaYF4:Yb/Tm (20/0.2 mol%), (f–j) NaYF4:Yb/Tm/Er (20/0.2/0.2–1.5 mol%), and (k–n) NaYF4:Yb/Er (18–60/2 mol%). The samples were excited at 980 nm with a 600 mW diode laser [83].
Mentions: The ability to manipulate color output of nanomaterials can broaden their applications, especially in the case of multiplexed biological labeling and imaging. Various approaches, based on surface plasmon resonance [91–94] or using multicolor-encoded microbeads and nanoparticles [95,96], have been applied to tune multicolor output. However, most of these methods need high energy excitation source in the UV region, which bring limitations to bioimaging studies due to the significant background (autofluorescence) and photo damage to the samples. The UCNs-based method becomes extremely promising to solve these problems, and a few current researchers have already shown the possibility to output multicolor lights. It can be obtained by adjusting the reaction temperature and time, crystal structure and phase, or changing the combinations of Ln3+ dopants and dopant concentration (Figure 12) [26,39,83,97,98]. Ehlert et al. presented that four different colors of UCNs can be spectrally separated under multiplexing conditions with a single excitation source of 980 nm [99]. Li and co-workers obtained the multicolor output signal by encapsulating organic dyes or QDs into the silica shell and the upconversion fluorescence was generated based on FRET from the UCN-cores to organic dyes or QDs [100].

Bottom Line: Over the past decade, high-quality rare earth-doped upconversion nanoparticles have been successfully synthesized with the rapid development of nanotechnology and are becoming more prominent in biological sciences.The synthesis methods are usually phase-based processes, such as thermal decomposition, hydrothermal reaction, and ionic liquids-based synthesis.In this review, the synthesis of upconversion nanoparticles and the mechanisms of upconversion process will be discussed, followed by their applications in different areas, especially in the biological field for biosensing.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of North Dakota, Grand Forks, ND 58202, USA. jiao.chen@my.und.edu

ABSTRACT
Upconversion is an optical process that involves the conversion of lower-energy photons into higher-energy photons. It has been extensively studied since mid-1960s and widely applied in optical devices. Over the past decade, high-quality rare earth-doped upconversion nanoparticles have been successfully synthesized with the rapid development of nanotechnology and are becoming more prominent in biological sciences. The synthesis methods are usually phase-based processes, such as thermal decomposition, hydrothermal reaction, and ionic liquids-based synthesis. The main difference between upconversion nanoparticles and other nanomaterials is that they can emit visible light under near infrared irradiation. The near infrared irradiation leads to low autofluorescence, less scattering and absorption, and deep penetration in biological samples. In this review, the synthesis of upconversion nanoparticles and the mechanisms of upconversion process will be discussed, followed by their applications in different areas, especially in the biological field for biosensing.

Show MeSH