Autofluorescence-free in vivo multicolor imaging using upconversion fluoride nanocrystals

Area of Science:

• Biomedical imaging
• Nanotechnology
• Optical science

Background:

• Non-invasive fluorescence imaging is crucial in biology.
• Traditional methods suffer from high background autofluorescence.
• This limits sensitivity and specificity in biological samples.

Purpose of the Study:

• To evaluate upconversion NaYF4 nanocrystals for autofluorescence-free multicolor fluorescence imaging in vivo.
• To compare NaYF4 nanocrystals with traditional imaging agents like FITC and QDs.
• To demonstrate multicolor imaging capabilities in a living animal model.

Main Methods:

• Rats were injected with various imaging agents, including NaYF4 nanocrystals (doped with Yb3+/Tm3+, Yb3+/Ho3+, or Yb3+/Ho3+/Ce3+), FITC, and CdSe/ZnS QDs.
• Tissue autofluorescence was induced using a 405 nm light source.
• Imaging was performed using a 974 nm laser for NaYF4 nanocrystals and a 405 nm light source for FITC and QDs.

Main Results:

• NaYF4 nanocrystals, when excited at 974 nm, completely eliminated tissue autofluorescence.
• This contrasts sharply with FITC and QDs, which exhibited significant background signal under 405 nm excitation.
• Multicolor imaging of multiple biological targets and organs was achieved simultaneously using NaYF4 nanocrystals under a single excitation wavelength.

Conclusions:

• NaYF4 nanocrystals provide a viable solution for autofluorescence-free multicolor fluorescence imaging in living animals.
• This technology overcomes limitations of conventional imaging techniques.
• The study demonstrates the proof-of-principle for near-infrared to visible upconversion imaging using NaYF4 nanocrystals in vivo.