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Biophotonics|32 Article(s)
Imaging and dynamic monitoring of aging mitochondria using a two-photon nonlinear structured illumination microscope
Xinran Li, Meiting Wang, Peng Du, Xiaomin Zheng, Jiajie Chen, Yuye Wang, Junle Qu, Ning Li, and Yonghong Shao
Mitochondrial dynamics critically regulate cellular aging. Two-photon nonlinear structured illumination microscopy (TP-SIM), a low-phototoxicity live-cell imaging technique, was employed to dynamically track mitochondrial changes in senescent H9C2 cardiomyocytes. System validation in COS7 cells achieved 82-nm resolution, threefold higher than conventional microscopy, and sustained 5-min dynamic imaging. Compared to normal cells, senescent cells exhibited fragmented mitochondria. TP-SIM further captured impaired mitochondrial fusion dynamics during senescence through continuous imaging, demonstrating its dual capability for subcellular-resolution visualization and prolonged organelle tracking in live cells. Mitochondrial dynamics critically regulate cellular aging. Two-photon nonlinear structured illumination microscopy (TP-SIM), a low-phototoxicity live-cell imaging technique, was employed to dynamically track mitochondrial changes in senescent H9C2 cardiomyocytes. System validation in COS7 cells achieved 82-nm resolution, threefold higher than conventional microscopy, and sustained 5-min dynamic imaging. Compared to normal cells, senescent cells exhibited fragmented mitochondria. TP-SIM further captured impaired mitochondrial fusion dynamics during senescence through continuous imaging, demonstrating its dual capability for subcellular-resolution visualization and prolonged organelle tracking in live cells.
Chinese Optics Letters
- Publication Date: Aug. 13, 2025
- Vol. 23, Issue 9, 091701 (2025)
Structural image-assisted artifact reduction in optical coherence tomography angiography|On the Cover
Wenxin Zhang, Kangkang Wang, Hong Zhou, Jun Pan, Shiqi Tang, Ning Liu, Ping Xue, Jianfei Chen, Yuchong Lu, Zhanpeng Hong, and Mingyu Yang
Tail artifacts are a significant issue in optical coherence tomography angiography (OCTA), as they cast shadows over underlying signals and interfere with the reconstruction of 3D vessel images. While many methods have been developed to reduce these artifacts, most only shorten the tails and fail to clearly distinguish between vessels and artifacts. In this Letter, we present an image processing technique designed to reduce artifacts. By combining structural images with OCTA images, we can more effectively distinguish between vessels and artifacts, leading to shorter and less pronounced tail artifacts. This method is integrated with other tail artifact removal techniques to further enhance image quality. The vessels of the palm are used as samples to experimentally demonstrate the effectiveness of our technique. Tail artifacts are a significant issue in optical coherence tomography angiography (OCTA), as they cast shadows over underlying signals and interfere with the reconstruction of 3D vessel images. While many methods have been developed to reduce these artifacts, most only shorten the tails and fail to clearly distinguish between vessels and artifacts. In this Letter, we present an image processing technique designed to reduce artifacts. By combining structural images with OCTA images, we can more effectively distinguish between vessels and artifacts, leading to shorter and less pronounced tail artifacts. This method is integrated with other tail artifact removal techniques to further enhance image quality. The vessels of the palm are used as samples to experimentally demonstrate the effectiveness of our technique.
Chinese Optics Letters
- Publication Date: Jul. 23, 2025
- Vol. 23, Issue 8, 081701 (2025)
Vascular permeability assessment using dual-wavelength photoacoustic microscopy with spectral unmixing
Yongyan Ren, Kun Yu, Qiansong Xia, Honghui Li, and Liming Nie
Vascular permeability (VP) plays a critical role in liver and kidney fibrosis progression. Traditional VP quantification methods use single-wavelength photoacoustic microscopy (PAM) with Evans Blue (EB) dye, which have limitations including signal attenuation and decreased accuracy. To overcome these issues, we developed a dual-wavelength PAM method with a spectral unmixing algorithm for quantitative VP evaluation in liver and kidney microvasculature. This approach allows for an accurate assessment of VP dynamics by analyzing hemoglobin and EB absorption. Using murine models of fibrosis, we found that fibrosis reduces vessel density and increases vessel diameter, providing valuable insights into VP changes during fibrosis progression. Vascular permeability (VP) plays a critical role in liver and kidney fibrosis progression. Traditional VP quantification methods use single-wavelength photoacoustic microscopy (PAM) with Evans Blue (EB) dye, which have limitations including signal attenuation and decreased accuracy. To overcome these issues, we developed a dual-wavelength PAM method with a spectral unmixing algorithm for quantitative VP evaluation in liver and kidney microvasculature. This approach allows for an accurate assessment of VP dynamics by analyzing hemoglobin and EB absorption. Using murine models of fibrosis, we found that fibrosis reduces vessel density and increases vessel diameter, providing valuable insights into VP changes during fibrosis progression.
Chinese Optics Letters
- Publication Date: Jun. 19, 2025
- Vol. 23, Issue 7, 071701 (2025)
An all-in-one optical fiber probe leveraging black phosphorus/gold nanostar for optimized sensing and photothermal efficiency
Fangzhou Jin, Haopeng Wang, Qingyue Ye, Zhuoran Li, Yongkang Zhang, Bai-Ou Guan, and Yang Ran
An interventional fiber optic strategy, as a representative optical medical technology, is flexible, highly sensitive, minimally invasive, anti-electromagnetic, and has good biosafety. Fiber optics can approach deep cancer lesions and provide direct theranostics, which other optical technologies cannot achieve. However, the realization of cancer sensing and therapy relies on the functionalization of optical fibers, which requires the strict selection and optimization of functional materials used to modify the optical fibers, ensuring high photothermal conversion efficiency without affecting fluorescence detection efficiency. Herein, we propose the use of black phosphorus, which does not interfere with fluorescence and provides a safer and more efficient photothermal effect compared to other nanomaterials, such as graphene, graphene oxide, carbon nanotubes, and MXene. We propose a fiber-optic theranostic probe that combines nitroreductase (NTR) fluorescent molecules and a black phosphorus/gold nanostar (BP/AuNS) nanomaterial hydrogel to develop an integrated strategy for cancer sensing and photothermal therapy (PTT). The sensor has high sensitivity, and the limit of detection (LOD) is 1.61 ng mL-1. The BP/AuNS fibers have excellent photothermal effects, and the probe temperature reaches 212°C in air as 150 mW of pump power is delivered. In the phantom test, the simulation and test results showed that the fiber probe conferred hyperthermia (>45°C) to an area with a radius of 2.5 mm. These results indicate that the minimally invasive BP/AuNS fiber exhibits excellent sensing performance and high photothermal efficiency, making it promising for tumor diagnosis and treatment and potentially advancing the development of optical fiber medicine. An interventional fiber optic strategy, as a representative optical medical technology, is flexible, highly sensitive, minimally invasive, anti-electromagnetic, and has good biosafety. Fiber optics can approach deep cancer lesions and provide direct theranostics, which other optical technologies cannot achieve. However, the realization of cancer sensing and therapy relies on the functionalization of optical fibers, which requires the strict selection and optimization of functional materials used to modify the optical fibers, ensuring high photothermal conversion efficiency without affecting fluorescence detection efficiency. Herein, we propose the use of black phosphorus, which does not interfere with fluorescence and provides a safer and more efficient photothermal effect compared to other nanomaterials, such as graphene, graphene oxide, carbon nanotubes, and MXene. We propose a fiber-optic theranostic probe that combines nitroreductase (NTR) fluorescent molecules and a black phosphorus/gold nanostar (BP/AuNS) nanomaterial hydrogel to develop an integrated strategy for cancer sensing and photothermal therapy (PTT). The sensor has high sensitivity, and the limit of detection (LOD) is 1.61 ng mL-1. The BP/AuNS fibers have excellent photothermal effects, and the probe temperature reaches 212°C in air as 150 mW of pump power is delivered. In the phantom test, the simulation and test results showed that the fiber probe conferred hyperthermia (>45°C) to an area with a radius of 2.5 mm. These results indicate that the minimally invasive BP/AuNS fiber exhibits excellent sensing performance and high photothermal efficiency, making it promising for tumor diagnosis and treatment and potentially advancing the development of optical fiber medicine.
Chinese Optics Letters
- Publication Date: Apr. 28, 2025
- Vol. 23, Issue 5, 051701 (2025)
Method for measuring retinal capillary blood flow velocity by encoded OCTA
Shujiang Chen, Kaixuan Hu, Wei Yi, Fuwang Wu, Yi Wan, Lei Zhang, Jianmei Li, Aiqun Wang, and Weiye Song
The quantification of microvascular blood flow velocity is pivotal in elucidating the characteristics of retinal microcirculation, and it plays a vital role in the early detection of numerous ophthalmic pathologies. However, non-invasive technology with a large field of view for directly measuring retinal capillary blood flow velocity is lacking. In this study, a novel imaging modality called encoding optical coherence tomography angiography (En-OCTA) is presented, utilizing retinal optical coherence tomography angiography (OCTA) encoding to accurately measure the absolute blood flow velocity in retinal capillaries. En-OCTA employs a scanning speed of 250 kHz to capture multiple OCTA images at two different locations on the same unbranched capillary. As red blood cells (RBCs) slowly flow through capillaries in a single file, intermittent light and dark changes can be observed on OCTA images. Analyzing the correlation of light and dark patterns in chronologically coded images of the capillary region allows for the determination of the lag time in RBC movement between two points. Combining this lag time with the distance between scan points allows the absolute blood flow velocity in the capillaries to be accurately calculated. Animal experiments demonstrate that the method can accurately measure capillary blood flow velocity and detect changes in velocity over the duration of anesthesia. The quantification of microvascular blood flow velocity is pivotal in elucidating the characteristics of retinal microcirculation, and it plays a vital role in the early detection of numerous ophthalmic pathologies. However, non-invasive technology with a large field of view for directly measuring retinal capillary blood flow velocity is lacking. In this study, a novel imaging modality called encoding optical coherence tomography angiography (En-OCTA) is presented, utilizing retinal optical coherence tomography angiography (OCTA) encoding to accurately measure the absolute blood flow velocity in retinal capillaries. En-OCTA employs a scanning speed of 250 kHz to capture multiple OCTA images at two different locations on the same unbranched capillary. As red blood cells (RBCs) slowly flow through capillaries in a single file, intermittent light and dark changes can be observed on OCTA images. Analyzing the correlation of light and dark patterns in chronologically coded images of the capillary region allows for the determination of the lag time in RBC movement between two points. Combining this lag time with the distance between scan points allows the absolute blood flow velocity in the capillaries to be accurately calculated. Animal experiments demonstrate that the method can accurately measure capillary blood flow velocity and detect changes in velocity over the duration of anesthesia.
Chinese Optics Letters
- Publication Date: Apr. 23, 2025
- Vol. 23, Issue 4, 041701 (2025)
Label-free cellular imaging of mouse retina with dual-mode full-field optical coherence tomography
Keyi Fei, Bingying Lin, Zhongzhou Luo, Yupei Chen, Jin Yuan, and Peng Xiao
High-resolution label-free dual-mode full-field optical coherence tomography (FFOCT) is developed for simultaneous structural and functional imaging of mouse retinas, achieving both static contrasts gained from structural refractive index gradients and dynamic contrasts induced by endogenous cell motility. Imaging experiments on normal mouse retinas show that static FFOCT images better reveal the relative stationary structures like nerve fibers, vascular walls, and collagens, and dynamic FFOCT images show enhanced contrasts of cells with active intracellular metabolic motions, offering complementary information about major retinal layers. Specifically, dual-mode FFOCT imaging on early ischaemia/reperfusion (I/R) injured mouse retinas highlights the transparent ganglion cells at the cellular level without contrast agent labeling, visualizing their structural and dynamic alterations in early I/R injured retina. High-resolution label-free dual-mode full-field optical coherence tomography (FFOCT) is developed for simultaneous structural and functional imaging of mouse retinas, achieving both static contrasts gained from structural refractive index gradients and dynamic contrasts induced by endogenous cell motility. Imaging experiments on normal mouse retinas show that static FFOCT images better reveal the relative stationary structures like nerve fibers, vascular walls, and collagens, and dynamic FFOCT images show enhanced contrasts of cells with active intracellular metabolic motions, offering complementary information about major retinal layers. Specifically, dual-mode FFOCT imaging on early ischaemia/reperfusion (I/R) injured mouse retinas highlights the transparent ganglion cells at the cellular level without contrast agent labeling, visualizing their structural and dynamic alterations in early I/R injured retina.
Chinese Optics Letters
- Publication Date: Mar. 25, 2025
- Vol. 23, Issue 3, 031701 (2025)
CNPRN: Chebyshev non-explicit prior regularizer network for fluorescence molecular tomography
Heng Zhang, Xiaowei He, Beilei Wang, Jingjing Yu, Xuelei He, Huangjian Yi, Hongbo Guo, and Yuqing Hou
Fluorescence molecular tomography (FMT) can non-invasively monitor glioblastomas in small animals. Both handcrafted prior regularization and deep learning algorithms have made remarkable achievements in this field. But handcrafted priors often cannot deal well with different kinds of tumors. Also, some deep learning methods still rely on handcrafted priors. In this paper, we introduce a Chebyshev non-explicit prior regularizer network (CNPRN). It replaces the handcrafted prior with a non-explicit prior and combines it with an optimization-inspired network. The CNPRN has two main parts: First, because of the long-range spatial correlation of light transmission in the finite element mesh, we create a non-explicit prior regularizer using high-order Chebyshev graph convolution. We also add inter-stage information pathways to combine useful data from the reconstructed outputs of each phase’s regularizer; Second, to solve the problem of heavy computation in iterative optimization and make the network more flexible, we introduce a dynamic gradient descent module. This module allows parameters to be adjusted adaptively. As a deep unrolling method, CNPRN naturally obtains the solution constraints of the half-quadratic splitting method. This improves the network’s generalizability and stability. Both simulations and in vivo experiments indicate that CNPRN has superior reconstruction performance. Fluorescence molecular tomography (FMT) can non-invasively monitor glioblastomas in small animals. Both handcrafted prior regularization and deep learning algorithms have made remarkable achievements in this field. But handcrafted priors often cannot deal well with different kinds of tumors. Also, some deep learning methods still rely on handcrafted priors. In this paper, we introduce a Chebyshev non-explicit prior regularizer network (CNPRN). It replaces the handcrafted prior with a non-explicit prior and combines it with an optimization-inspired network. The CNPRN has two main parts: First, because of the long-range spatial correlation of light transmission in the finite element mesh, we create a non-explicit prior regularizer using high-order Chebyshev graph convolution. We also add inter-stage information pathways to combine useful data from the reconstructed outputs of each phase’s regularizer; Second, to solve the problem of heavy computation in iterative optimization and make the network more flexible, we introduce a dynamic gradient descent module. This module allows parameters to be adjusted adaptively. As a deep unrolling method, CNPRN naturally obtains the solution constraints of the half-quadratic splitting method. This improves the network’s generalizability and stability. Both simulations and in vivo experiments indicate that CNPRN has superior reconstruction performance.
Chinese Optics Letters
- Publication Date: Nov. 06, 2025
- Vol. 23, Issue 12, 121701 (2025)
Modified Kelvin-Voigt fractional derivative model for viscoelasticity measurement in optical coherence elastography
Chenming Yang, Zhongliang Li, Nan Nan, Teng Liu, Yaoli Luo, and Xiangzhao Wang
Optical coherence elastography (OCE) can quantitatively obtain the viscoelasticity of tissues using rheological models and is widely applied to the clinical diagnosis of diseases. However, commonly used rheological models in OCE do not account for the distinctive dependence of high-frequency storage and loss moduli on frequency in tissues, which results in the rheological models failing to accurately measure the viscoelastic properties of tissues. In this paper, a modified Kelvin-Voigt fractional derivative model is presented based on the power-law behavior of soft tissues and the dependence of high-frequency complex shear modulus on frequency in living cells. In the rheometer and OCE tests, the modified model can provide the prediction of the power-law relationship between the low-frequency shear viscosity and frequency; compared with the Kelvin-Voigt and Kelvin-Voigt fractional derivative models, the modified model has a higher goodness-of-fit (accuracy >96%) for the high-frequency storage moduli of gelatin phantoms. Furthermore, the proposed model can reduce the root mean square error of fit by approximately 83% for the high-frequency (1–128 kHz) storage modulus of the polydimethylsiloxane phantoms obtained from publicly available data. Overall, the modified model accurately predicts the mechanical properties of biomimetic materials over a wide frequency range, with the potential to more accurately reflect pathological changes in tissues. Optical coherence elastography (OCE) can quantitatively obtain the viscoelasticity of tissues using rheological models and is widely applied to the clinical diagnosis of diseases. However, commonly used rheological models in OCE do not account for the distinctive dependence of high-frequency storage and loss moduli on frequency in tissues, which results in the rheological models failing to accurately measure the viscoelastic properties of tissues. In this paper, a modified Kelvin-Voigt fractional derivative model is presented based on the power-law behavior of soft tissues and the dependence of high-frequency complex shear modulus on frequency in living cells. In the rheometer and OCE tests, the modified model can provide the prediction of the power-law relationship between the low-frequency shear viscosity and frequency; compared with the Kelvin-Voigt and Kelvin-Voigt fractional derivative models, the modified model has a higher goodness-of-fit (accuracy >96%) for the high-frequency storage moduli of gelatin phantoms. Furthermore, the proposed model can reduce the root mean square error of fit by approximately 83% for the high-frequency (1–128 kHz) storage modulus of the polydimethylsiloxane phantoms obtained from publicly available data. Overall, the modified model accurately predicts the mechanical properties of biomimetic materials over a wide frequency range, with the potential to more accurately reflect pathological changes in tissues.
Chinese Optics Letters
- Publication Date: Feb. 11, 2025
- Vol. 23, Issue 1, 011701 (2025)
Flat-top beam illumination for polarization-sensitive second-harmonic generation microscopy
Bing Wang, Xiang Li, Wenhui Yu, Binglin Shen, Rui Hu, Junle Qu, and Liwei Liu
Wide-field second-harmonic generation (SHG) was used to obtain the second-harmonic signal from the entire image area for rapid imaging, despite the fact that conventional Gaussian beam illumination has low energy utilization efficiency, which makes it easy to overexpose the intensity of the image center area. However, flat-top beam illumination has uniform spatial distribution, thereby improving the photon excitation efficiency in the entire image region and reducing laser damage and thermal effect. By combining flat-top beam illumination and wide-field SHG polarization measurement, we can calculate more myosin fibril symmetrical axis orientations through polarization analysis of 16 images at a fast imaging speed while expanding the field of view. More importantly, the application of a flat-top beam can further improve the capability of polarization measurement in SHG microscopy. Wide-field second-harmonic generation (SHG) was used to obtain the second-harmonic signal from the entire image area for rapid imaging, despite the fact that conventional Gaussian beam illumination has low energy utilization efficiency, which makes it easy to overexpose the intensity of the image center area. However, flat-top beam illumination has uniform spatial distribution, thereby improving the photon excitation efficiency in the entire image region and reducing laser damage and thermal effect. By combining flat-top beam illumination and wide-field SHG polarization measurement, we can calculate more myosin fibril symmetrical axis orientations through polarization analysis of 16 images at a fast imaging speed while expanding the field of view. More importantly, the application of a flat-top beam can further improve the capability of polarization measurement in SHG microscopy.
Chinese Optics Letters
- Publication Date: Jun. 07, 2024
- Vol. 22, Issue 6, 061701 (2024)
Multi-focus non-periodic scanning method for femtosecond lasers based on DMD and galvanometer scanners [Invited]|Editors' Pick
Huaming Li, Yu Wang, Qinglei Hu, Zhuoyu Zhang, Xiaohua Lü, and Shaoqun Zeng
Multi-focus parallel scanning can effectively increase laser fabrication throughput. However, the conventional approach of using a spatial light modulator (SLM) to generate multi-foci and scan this fixed number of foci with galvanometer scanners can only achieve a periodic scanning trajectory due to the low switching speed of the SLM. Here we demonstrate a multi-focus non-periodic scanning method for femtosecond lasers by using, instead, a fast-switching digital micromirror device (DMD) to generate a dynamic number of foci. The number of effective foci is quickly switched by introducing aberration to the undesired focus. In this way, the intensity allocated to each focus will not be affected by the number of foci, and a uniformity of 98% with different numbers of foci is achieved without adjusting the total laser energy. Finally, we validate the effectiveness of this scanning method by demonstrating corneal flap fabrication of porcine cornea in vitro. Multi-focus parallel scanning can effectively increase laser fabrication throughput. However, the conventional approach of using a spatial light modulator (SLM) to generate multi-foci and scan this fixed number of foci with galvanometer scanners can only achieve a periodic scanning trajectory due to the low switching speed of the SLM. Here we demonstrate a multi-focus non-periodic scanning method for femtosecond lasers by using, instead, a fast-switching digital micromirror device (DMD) to generate a dynamic number of foci. The number of effective foci is quickly switched by introducing aberration to the undesired focus. In this way, the intensity allocated to each focus will not be affected by the number of foci, and a uniformity of 98% with different numbers of foci is achieved without adjusting the total laser energy. Finally, we validate the effectiveness of this scanning method by demonstrating corneal flap fabrication of porcine cornea in vitro.
Chinese Optics Letters
- Publication Date: May. 17, 2024
- Vol. 22, Issue 5, 051701 (2024)
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