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1. Acid-Triggered Switchable Near-Infrared/Shortwave Infrared Absorption and Emission of Indolizine-BODIPY Dyes

   https://doi.org/10.3390/molecules28031287  

   Saucier, Matthew A.; Smith, Cameron; Kruse, Nicholas A.; Hammer, Nathan I.; Delcamp, Jared H. (February 2023, Molecules)

   Fluorescent organic dyes that absorb and emit in the near-infrared (NIR, 700–1000 nm) and shortwave infrared (SWIR, 1000–1700 nm) regions have the potential to produce noninvasive high-contrast biological images and videos. BODIPY dyes are well known for their high quantum yields in the visible energy region. To tune these chromophores to the NIR region, fused nitrogen-based heterocyclic indolizine donors were added to a BODIPY scaffold. The indolizine BODIPY dyes were synthesized via microwave-assisted Knoevenagel condensation with indolizine aldehydes. The non-protonated dyes showed NIR absorption and emission at longer wavelengths than an aniline benchmark. Protonation of the dyes produced a dramatic 0.35 eV bathochromic shift (230 nm shift from 797 nm to 1027 nm) to give a SWIR absorption and emission (λmaxemis = 1061 nm). Deprotonation demonstrates that material emission is reversibly switchable between the NIR and SWIR. 

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2. Simultaneous enhancement of near infrared luminescence and stability of Cs ₂ AgInCl ₆ :Cr ³⁺ double perovskite single crystals enabled by a Yb ³⁺ dopant

   https://doi.org/10.1039/D2QI01104B  

   Chen, Daiwen; Zhang, Xinguo; Wei, Jianwu; Zhou, Liya; Chen, Peican; Pang, Qi; Zhang, Jin Zhong (September 2022, Inorganic Chemistry Frontiers)

   Broadband near infrared (NIR) emission materials are of interest for various applications including non-destructive biomedical imaging. In this work, ytterbium ions (Yb 3+ ) were successfully doped into Cs 2 AgInCl 6 :Cr 3+ (CAIC:Cr 3+ ) double perovskite single crystals (DPSCs) by a facile hydrothermal method. Under 365 nm excitation, the co-doped CAIC:Cr 3+ ,Yb 3+ DPSCs showed broad NIR emission ranging from 800 to 1400 nm, which spanned the NIR-I (700–900 nm) and NIR-II (1000–1700 nm) bio-windows, with an emission band at 1000 nm and a full-width at half maximum (FWHM) of 188 nm. It is found that Yb 3+ ion doping could effectively improve the photoluminescence (PL) performance of CAIC:Cr 3+ DPSCs. Compared to the photoluminescence quantum yield (PLQY) of 22.5% for the single doped CAIC:Cr 3+ , the co-doped CAIC:Cr 3+ ,Yb 3+ DPSCs show a higher PLQY of ∼45%, which is attributed to the synergistic effect of reduced non-radiative recombination due to defect passivation and increase in crystallinity, and energy transfer (ET) of self-trapped excitons (STEs) to Cr 3+ . As a demonstration of applications, NIR pc-LEDs were fabricated by combining the as-synthesized NIR-emitting phosphor CAIC:Cr 3+ ,Yb 3+ with InGaN UV chips ( λ em = 365 nm) and used to image veins in a palm and for night vision using a NIR camera. The results suggest that the synthesized CAIC:Cr 3+ ,Yb 3+ DPSCs have great potential in biological applications. 

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3. Dual Infrared 2‐Photon Microscopy Achieves Minimal Background Deep Tissue Imaging in Brain and Plant Tissues

   https://doi.org/10.1002/adfm.202404709  

   Safaee, Mohammad M; Nishitani, Shoichi; McFarlane, Ian R; Yang, Sarah J; Sun, Ethan; Medina, Sebastiana M; Squire, Henry; Landry, Markita P (October 2024, Advanced Functional Materials)

   Abstract Traditional deep fluorescence imaging has primarily focused on red‐shifting imaging wavelengths into the near‐infrared (NIR) windows or implementation of multi‐photon excitation approaches. Here, the advantages of NIR and multiphoton imaging are combined by developing a dual‐infrared two‐photon microscope that enables high‐resolution deep imaging in biological tissues. This study first computationally identifies that photon absorption, as opposed to scattering, is the primary contributor to signal attenuation. A NIR two‐photon microscope is constructed next with a 1640 nm femtosecond pulsed laser and a NIR PMT detector to image biological tissues labeled with fluorescent single‐walled carbon nanotubes (SWNTs). Spatial imaging resolutions are achieved close to the Abbe resolution limit and eliminate blur and background autofluorescence of biomolecules, 300 µm deep into brain slices and through the full 120 µm thickness of aNicotiana benthamianaleaf. NIR‐II two‐photon microscopy can also measure tissue heterogeneity by quantifying how much the fluorescence power law function varies across tissues, a feature this study exploits to distinguish Huntington's Disease afflicted mouse brain tissues from wildtype. These results suggest dual‐infrared two‐photon microscopy can accomplish in‐tissue structural imaging and biochemical sensing with a minimal background, and with high spatial resolution, in optically opaque or highly autofluorescent biological tissues. 

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4. Improved genetically encoded near-infrared fluorescent calcium ion indicators for in vivo imaging

   https://doi.org/10.1371/journal.pbio.3000965  

   Qian, Yong; Cosio, Danielle M.; Piatkevich, Kiryl D.; Aufmkolk, Sarah; Su, Wan-Chi; Celiker, Orhan T.; Schohl, Anne; Murdock, Mitchell H.; Aggarwal, Abhi; Chang, Yu-Fen; et al (November 2020, PLOS Biology)

   Lishko, Polina V. (Ed.)

   Near-infrared (NIR) genetically encoded calcium ion (Ca 2+ ) indicators (GECIs) can provide advantages over visible wavelength fluorescent GECIs in terms of reduced phototoxicity, minimal spectral cross talk with visible light excitable optogenetic tools and fluorescent probes, and decreased scattering and absorption in mammalian tissues. Our previously reported NIR GECI, NIR-GECO1, has these advantages but also has several disadvantages including lower brightness and limited fluorescence response compared to state-of-the-art visible wavelength GECIs, when used for imaging of neuronal activity. Here, we report 2 improved NIR GECI variants, designated NIR-GECO2 and NIR-GECO2G, derived from NIR-GECO1. We characterized the performance of the new NIR GECIs in cultured cells, acute mouse brain slices, and Caenorhabditis elegans and Xenopus laevis in vivo. Our results demonstrate that NIR-GECO2 and NIR-GECO2G provide substantial improvements over NIR-GECO1 for imaging of neuronal Ca 2+ dynamics. 

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5. Near-Infrared Imaging of Artificial Enamel Caries Lesions with a Scanning Fiber Endoscope

   https://doi.org/10.3390/s19061419  

   Lee, Robert; Zhou, Yaxuan; Finkleman, Sara; Sadr, Alireza; Seibel, Eric (March 2019, Sensors)

   Several studies have shown that near-infrared imaging has great potential for the detection of dental caries lesions. A miniature scanning fiber endoscope (SFE) operating at near-infrared (NIR) wavelengths was developed and used in this study to test whether the device could be used to discriminate demineralized enamel from sound enamel. Varying depths of artificial enamel caries lesions were prepared on 20 bovine blocks with smooth enamel surfaces. Samples were imaged with a SFE operating in the reflectance mode at 1310-nm and 1460-nm in both wet and dry conditions. The measurements acquired by the SFE operating at 1460-nm show significant difference between the sound and the demineralized enamel. There was a moderate positive correlation between the SFE measurements and micro-CT measurements, and the NIR SFE was able to detect the presence of demineralization with high sensitivity (0.96) and specificity (0.85). This study demonstrates that the NIR SFE can be used to detect early demineralization from sound enamel. In addition, the NIR SFE can differentiate varying severities of demineralization. With its very small form factor and maneuverability, the NIR SFE should allow clinicians to easily image teeth from multiple viewing angles in real-time. 

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