Photon excitation and emission at the NIR‐II spectral window enable high‐contrast deep‐tissue bioimaging. However, multiplexed imaging with NIR‐II excitation and emission has been hampered by the limited chemical strategies to develop bright fluorophores with tunable absorption in this spectral regime. Herein, we developed a series of heptamethine cyanines (HCs) with varied absorption/emission maxima spanning from 1100 to 1600 nm through a physical organic approach. A bulky counterion paired to HCs was found to elicit substantial improvements in absorptivity (7‐fold), brightness (14‐fold), and spectral profiles in water, addressing a notorious quenching problem of NIR‐II cyanines due to aggregation and polarization. We demonstrated the utilities of HC1222 and HC1342 for high‐contrast dual‐color imaging of circulatory system, lymphatic structures, tumor, and organ function in living mice under 1120 nm and 1319 nm excitation, showing HCs as a promising platform for non‐invasive bioimaging.

Visualizing biomolecules such as enzymes in the deep tissue of living organisms via molecular ratiometric fluorescent probes in the second near-infrared window (NIR-II) with a built-in self-calibration function can provide reliable information about relevant pathophysiological processes directly but so far is not feasible due to the lack of a fluorescence modulation strategy in the NIR-II window. Here we present a molecular platform Py-2 by integrating the rhodamine 6G scaffold and polymethine. The maximal emission wavelength of Py-2 was 1010 nm and blue-shifted to 945 nm when its secondary amine was acylated. Based on Py-2, two molecular ratiometric NIR-II fluorescent probes, nitroreductase-responsive Rap-N and ROS-responsive Rap-R, were constructed and successfully demonstrated in vitro and in vivo. Overall, this report presents a unique approach to developing ratiometric NIR-II molecular probes for in vivo biosensing.

Fluorescence probes have great potential to empower bioimaging, precision clinical diagnostics and surgery. However, current probes have been limited for in vivo high-contrast diagnostics, due to substantial background interference from...

Ratiometric fluorescence nanosensors provide quantitative biological information. However, spectral shift and distortion of ratiometric nanosensors in biological media often compromise sensing accuracy, limiting in vivo applications. Here, we develop a fluorescent dyad (aBOP-IR1110) in the second near-infrared (NIR-II) window by covalently linking an asymmetric aza-BODIPY with a ONOO–-responsive meso-thiocyanine. The dyad encapsulated in the PEGylated nanomicelle largely improves spectral fidelity in serum culture by >9.4 times compared to that of its noncovalent counterpart. The increased molecular weights (>1480 Da) and hydrophobicity (LogP of 7.87–12.36) lock dyads inside the micelles, which act as the shield against the external environment. ONOO–-altered intramolecular Förster resonance energy transfer (FRET) generates linear ratiometric response with better serum tolerance, enabling us to monitor the dynamics of oxidative stress in traumatic brain injury and evaluate therapeutic efficiency. The results show high correlation with in vitro triphenyltetrazolium chloride staining, suggesting the potential of NIR-II dyad-doped nanosensor for in vivo high-fidelity sensing applications.

Photon excitation and emission at the NIR‐II spectral window enable high‐contrast deep‐tissue bioimaging. However, multiplexed imaging with NIR‐II excitation and emission has been hampered by the limited chemical strategies to develop bright fluorophores with tunable absorption in this spectral regime. Herein, we developed a series of heptamethine cyanines (HCs) with varied absorption/emission maxima spanning from 1100 to 1600 nm through a physical organic approach. A bulky counterion paired to HCs was found to elicit substantial improvements in absorptivity (7‐fold), brightness (14‐fold), and spectral profiles in water, addressing a notorious quenching problem of NIR‐II cyanines due to aggregation and polarization. We demonstrated the utilities of HC1222 and HC1342 for high‐contrast dual‐color imaging of circulatory system, lymphatic structures, tumor, and organ function in living mice under 1120 nm and 1319 nm excitation, showing HCs as a promising platform for non‐invasive bioimaging.