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Abstract Förster resonance energy transfer (FRET)‐based devices have been extensively researched as potential biosensors due to their highly localized responsivity. In particular, dye‐conjugated upconverting nanoparticles (UCNPs) are among the most promising FRET‐based sensor candidates. UCNPs have a multi‐modal emission profile that allows for ratiometric sensing, and by conjugating a biosensitive dye to their surface, this profile can be used to measure localized variations in biological parameters. However, the complex nature of the UCNP energy profile as well as reabsorption of emitted photons must be taken into account in order to properly sense the target parameters. To the authors’ knowledge, no proposed UCNP‐based sensor has accurately taken care of these intricacies. In this article, the authors account for these complexities by creating a FRET‐based sensor that measures pH. This sensor utilizes Thulium (Tm3+)‐doped UCNPs and the fluorescent dye fluorescein isothiocyanate (FITC). It is first demonstrated that photon reabsorption is a serious issue for the 475 nm Tm3+emission, thereby limiting its use in FRET‐based sensing. It is then shown that by taking the ratio of the 646 and 800 nm emissions rather than the more popular 475 nm one, it is possible to measure pH exclusively through FRET.
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Unlocking Multimodal Nonlinear Microscopy for Deep‐Tissue Imaging under Continuous‐Wave Excitation with Tunable Upconverting Nanoparticles
Abstract Nonlinear microscopy provides excellent depth penetration and axial sectioning for 3D imaging, yet widespread adoption is limited by reliance on expensive ultrafast pulsed lasers. This work circumvents such limitations by employing rare‐earth doped upconverting nanoparticles (UCNPs), specifically Yb3+/Tm3+co‐doped NaYF4nanocrystals, which exhibit strong multimodal nonlinear optical responses under continuous‐wave (CW) excitation. These UCNPs emit multiple wavelengths at UV (λ ≈ 450 nm), blue (λ ≈ 450 nm), and NIR (λ ≈ 800 nm), whose intensities are nonlinearly governed by excitation power. Exploiting these properties, multi‐colored nonlinear emissions enable functional imaging of cerebral blood vessels in deep brain. Using a simple optical setup, high resolution in vivo 3D imaging of mouse cerebrovascular networks at depths up to 800 µmm is achieved, surpassing performance of conventional imaging methods using CW lasers. In vivo cerebrovascular flow dynamics is also visualized with wide‐field video‐rate imaging under low‐powered CW excitation. Furthermore, UCNPs enable depth‐selective, 3D‐localized photo‐modulation through turbid media, presenting spatiotemporally targeted light beacons. This innovative approach, leveraging UCNPs' intrinsic nonlinear optical characteristics, significantly advances multimodal nonlinear microscopy with CW lasers, opening new opportunities in bio‐imaging, remote optogenetics, and photodynamic therapy.
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- Award ID(s):
- 2011924
- PAR ID:
- 10640792
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 37
- Issue:
- 19
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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