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Indocyanine green hot band absorption for advanced anti-Stokes fluorescence bioimaging

a, the molecular structure of ICG. b, Schematic diagram of HBA ASF energy level transition. Thermal activation (red arrow) first acts on the ground state molecule with low energy, raising the molecule to a higher ground state vibration level, and then the molecule absorbs long wavelength photons (pink arrow). It becomes excited and finally emits short-wavelength photons (orange arrow). c, Temperature dependence of the ASF spectrum (800 nm – 900 nm) of the ICG excited by the 915 nm CW laser. d, Fluorescent images of tumor mice reflecting the increase in ASF intensity of ICG in breast tumors as the temperature rises. Credits: Jing Zhou, Xiaoxiao Fan, Di Wu, Jie Liu, Yuhuang Zhang, Zikang Ye, Dingwei Xue, Mubin He, Liang Zhu, Zhe Feng, Andrey N. Kuzmin, Wen Liu, Paras N. Prasad, Jun Qian

Indocyanine green (ICG) hotband absorption-based anti-Stokes fluorescence (ASF) is much brighter than luminescence from rare earth ion-doped nanoparticles and has recently been observed and studied by Chinese and US scientists. rice field. They found that ICG’s ASF could be used for cerebrovascular tomography and blood flow velocity measurements, reflecting changes in temperature, and enabling simultaneous multi-organ imaging, including biological imaging, sensing, and even clinical translation. There is a considerable prospect of application in.


Anti-Stokes fluorescence (ASF) includes (i) direct multiphoton absorption (MPA) process, (ii) up-conversion (UC) process based on multi-step absorption by intermediate energy level, and (iii) thermal activated delayed fluorescence (iii). There are four common types of). TADF) process, and (iv) hot band absorption (HBA) process. The generation of MPA fluorescence generally requires very high excitation intensities and is usually achieved using expensive femtosecond or picosecond pulsed lasers. Rare earth ion-doped nanoparticles (UCNP) UC processes, or triplet-triplet annihilation (TTA) -based UC, can be obtained using inexpensive continuous wave (CW) diode lasers. However, the absorption cross section of UCNP is relatively small, so UC efficiency is low. TTA-based metal complex / organic compound systems are more efficient upconverters due to their higher absorption and higher quantum efficiency than UCNP. Unfortunately, the photostability of TTA-based upconverters is relatively low due to the powerful quenching process caused by molecular oxygen. The TADF and HBA processes of organic molecules excited by CW lasers are attractive anti-Stokes processes. In addition, it may provide information about the temperature of the excited volume, making its application to bioimaging more attractive.

In a new treatise published in Optical science and applicationYork, a team of scientists led by Professor Jun Qian of the National Institute of Modern Optical Instruments, Faculty of Optical Science and Engineering, Zhejiang University, China, and Professor Paras N Prasad of the State University’s Institute of Laser, Photonics, and Biophotonics , Discovered and studied HBA-based ASF at Indocyanin Green (ICG) approved by the Food and Drug Administration (FDA). Based on thermal sensitivity, they applied ICG’s ASF to assess the thermal status of subcutaneous tumors in mice during photoheat treatment. In addition, the ICG’s ASF is much stronger than the normal UC fluorescence of UCNPs excited at 980 nm, with minimal thermal damage to living tissue. Deep tomography of cerebral blood vessels and measurement of blood flow velocity in mice were performed using ASF of ICG. In addition, in combination with L1057 nanoparticles (NPs) that absorb the ICG’s ASF and emit light above 1100 nm, these two probes produce multimode images on two fluorescent channels under the excitation of a single 915 nm CW laser. Generate. One channel is used to monitor two overlapping organs, the rat urinary system and blood vessels, and the other channel displays only the urinary system.

Indocyanine green hot band absorption for advanced anti-Stokes fluorescence bioimaging

Photothermal effect on hind limbs and liver of rats irradiated with a, 915 nm or 980 nm CW laser. b, In vivo ASF wide-field imaging of the biliary tract of two rats after receiving injection of NaYF4: Yb3 +, Tm3 + and ICG, respectively. c, In vivo ASF wide-field microscopic image of cerebral blood vessels (depth 250 μm) of mice injected with ICG. d, 3 sampled cerebrovascular flow velocity measurements. Credits: Jing Zhou, Xiaoxiao Fan, Di Wu, Jie Liu, Yuhuang Zhang, Zikang Ye, Dingwei Xue, Mubin He, Liang Zhu, Zhe Feng, Andrey N. Kuzmin, Wen Liu, Paras N. Prasad, Jun Qian

In the HBA process, the electrons in the ICG molecule absorb photons from the thermally present vibrational levels above the ground state. Excitations decay to lower vibration levels in the ground state, thus emitting photons with higher energy than those initially absorbed. These scientists summarize the main work of ICG’s HBA-based ASF.

“We found a bright ASF in the ICG under the excitation of the 915nm CW laser and compared it with the ASF of the UCNP excited by the CW laser. As a result, the ASF of the ICG was much brighter than the ASF of the UCNP and attracted attention. .. In order to elucidate the mechanism of ASF generation in ICG, we conducted a rigorous verification experiment, concluded that the mechanism of generation was HBA, and explored its potential in heat-sensing applications. Subcutaneous tumors at photoheat treatment and high temperature. Evaluation of thermal status ICG ASF was used to achieve indications, and mouse cerebrovascular tomography and blood flow velocity measurements were also performed, enabling high contrast and selective detection of adjacent organs in consideration of surgery. Prove the concept of real-time in-vivo multimode imaging (urinary tract and blood vessels) by combining ICG with fluorescent organic polymer dot L1057 under a single 915 nm CW laser excitation. This new imaging technology is intraoperative. It can help with real-time monitoring and avoiding accidental surgical injuries. “

Indocyanine green hot band absorption for advanced anti-Stokes fluorescence bioimaging

a, Optical principle of multimode imaging. 915 nm is the excitation wavelength for the ICG to generate ASF and is also the absorption peak for L1057 NP, and the ASF for channel 1 ICG is precisely located in the high absorption spectrum region of L1057 NP. On the other hand, the Stokes fluorescence (SF) signal of L1057 NP on channel 2 does not have crosstalk with the ICG signal. b, Infusion mode of multimode imaging of the urinary system and blood vessels. ICG is injected into the blood vessels and L1057NP is injected into the urinary system. c, Multimode pseudo-color imaging of rat ureters and blood vessels treated with ICG and L1057NP under excitation with a 915 nm CW laser. In channel 1, blood vessels show a bright positive visualization (shown in pseudo-color green), and the ureter that absorbs the ICG background ASF shows a clear dark negative visualization (shown in pseudo-color pink), auto 2 Achieves simultaneous visualization of organs. On channel 2, on the other hand, only the ureter has a signal (shown in pseudo-color pink), providing single-target visualization. Credits: Jing Zhou, Xiaoxiao Fan, Di Wu, Jie Liu, Yuhuang Zhang, Zikang Ye, Dingwei Xue, Mubin He, Liang Zhu, Zhe Feng, Andrey N. Kuzmin, Wen Liu, Paras N. Prasad, Jun Qian

“Interestingly, I found that ICG can generate visible ASF (

“ICG’s ASF is used deeper and more widely, with the expectation that other fluorophores with HBA-induced ASF function can be synthesized for bioimaging, sensing, seranostics, and infrared light perception in the future. “Scientists are predicting.


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For more information:
Jing Zhou et al, Indocyanine Green Hot Band Absorption for Advanced Anti-Stokes Fluorescence Bioimaging, Light: Science and application (2021). DOI: 10.1038 / s41377-021-00627-1

Quote: Indocyanine Green Hot Band Absorption for Advanced Anti-Stokes Fluorescence Bioimaging (2021, September 15) https: //phys.org/news/2021-09-hot-band-absorption-indasianine- Obtained from green- on September 15, 2021. Advanced.html

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Indocyanine green hot band absorption for advanced anti-Stokes fluorescence bioimaging

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