The study of organelles’ dynamics and their interactions have been limited by optical diffraction. Recently, teams from the Chair Prof. Dayong Jin at SUSTech and Prof. Xi Peng (Peking University) successfully created a super-resolution “street view” of intracellular organelles’ interactions and has this published in Nature Communications.

This is the first time that researchers get the dynamics of lipid heterogeneity inside subcellular organelles with optical imaging technology. They have developed a Spectrum and Polarization Optical Tomography (SPOT) technique, which can resolve the membrane morphology, polarity, and phase from the intensity, spectrum, and polarization, respectively. Combined with lipophilic probes, the team successfully revealed more than ten types of organelles simultaneously and analyzed their sophisticated lipid dynamics.

A cell is a self-efficient “micro-world” with various organelles responsible for nutrition import, metabolism, endocrine modulation, protein manufacturing, waste transportations, and all the efficient communications. The study of organelles’ dynamics and their interactions will help us understand the cell functions and diagnose the cause of diseases, as well as develop potential drug treatments. As widely-used fluorescence microscopy has limits in the color and type of fluorescent dyes and in temporal and spatial resolutions, it is extremely difficult to get simultaneous imaging of multiple organelle species.

Lipid membranes in subcellular compartments synergistically regulate biophysical membrane properties, membrane protein function, and lipid-protein interactions. Despite its significant role in biochemical function and interaction of subcellular organelles, due to their similar chemical composition, it is challenging to study the classification and interaction of different types of lipid membranes and observe their dynamics for a long time.

Compared with the other existing fluorescence microscopy techniques, SPOT is superior in optical throughput that correlatively obtains the high-dimensional information from six raw images within tens of milliseconds. SPOT’s optical section ability improves the measurement accuracy of polarity and phase. This is the first time that researchers quantitatively study the lipid heterogeneity inside subcellular organelles.

Figure 1 Heterogeneity of subcellular lipid membranes revealed by SPOT.

With SPOT, the lipid heterogeneity on the outer membrane and the cristae of mitochondria, as well as lipid dynamics through endosome maturation, can be clearly imaged in real-time. With the new imaging platform established at SUSTech, researchers observed the multi-organelle interactive activities of cell division, lipid dynamics during the plasma membrane separation, tunneling nanotubules formation, and mitochondrial cristae dissociation.

Figure 2 Time-lapse high-dimensional super-resolution imaging of the late-stage division of two U2-OS cells

Figure 3 Dynamic changes of lipid membrane during mitochondrial cristae dissociation

Most microscopes can only image four or fewer color channels, far less than the types of intracellular organelles. The synergistic use of membrane morphology, lipid polarity, and the lipid phase can classify more than ten types of organelles.

SUSTech Research Assistant Professor Karl Zhanghao is the co-first author and the co-corresponding author of the work. His contribution includes: (1) Super-resolution Dipole Orientation Mapping (SDOM) technique, (Light: Sci. Appl. 2016, https://doi.org/10.1038/s41467-019-12681-w, highlighted by Nat. Methods, https://doi.org/10.1038/nmeth.4061); (2) polarized Structured Illumination Microscopy (pSIM) technique, (https://10.1038/s41467-019-12681-w, highlighted by Nat. Methods, https://doi.org/10.1038/s41592-019-0682-6); (3) pSIM with improved imaging resolution (Opt. Express, https://doi.org/10.1364/OE.395092), and low-cost SIM with laser interference and digital micro-mirror device (Appl. Phys. Lett. 2020, https://doi.org/10.1063/5.0008264).

Doctoral students Wenhui Liu from Tsinghua University, and Meiqi Li from Peking University are the co-first authors of this work.

This work has been supported by the National Natural Science Foundation of China, National Key Research and Development Program of China, Beijing Natural Science Foundation, and Shenzhen Science and Technology Program.

Article Link：https://doi.org/10.1038/s41467-020-19747-0

Chris Edwards | 10/03/2020 40

Optical imaging has emerged as one of the promising imaging techniques in both research and clinical practice. Photoacoustic imaging and fluorescent imaging are the two leading representatives of optical-related imaging approaches. Their imaging qualities highly rely on contrast agents. The ideal photoacoustic and fluorescent agent is still to be found. The theoretical system that guides the construction of efficient contrast agents has not been widely established.

Associate Professor Kai Li (Biomedical Engineering – BME) teamed up with several research teams. They have made significant progress in designing near-infrared two-zone imaging materials and biomedical diagnosis. Their research outcomes have been published in Angewandte Chemie International Edition (Angew Chem Int Ed), Biomaterials, and Research.

The teams verified their design concepts and strategies through theoretical calculations. They obtained various high-performance photoacoustic and fluorescent imaging materials with optical activity in the second near-infrared window (NIR-II, 1000-1700 nm). They have applied them in different research fields, such as vascular imaging and tumor detection.

The first paper at Angew Chem Int Ed. was titled “An Ester‐substituted Semiconducting Polymer with Efficient Nonradiative Decay Enhances NIR‐II Photoacoustic Performance for Monitoring of Tumor Growth.”

The research teams synthesized several thiadiazoloquinoxaline (TQ)-based semiconducting polymers (SPs) with a broad absorption covering the NIR-I to NIR-II regions. The excited s-BDT-TQE shows a large dihedral angle, narrow adiabatic energy, and low radiative decay. It is attributed to the strongly electron-deficient ester-substituted TQ-segment.

The more vigorous molecular motions trigger higher reorganization energy. They yield an efficient photo-induced nonradiative decay. BDT-TQE SP-cored nanoparticles with twisted intramolecular charge transfer (TICT) exhibit a high NIR-II photothermal conversion efficiency (61.6%). They also exhibit the preferable PA tracking in-situ hepatic tumor growth for more than 20 days.

The research teams proposed a new approach that adjusted the TICT effect in polymer chains for augmented PNRD property. It enhanced the photothermal conversion & photoacoustic performance for monitoring in-situ tumor growth in mice.

BME masters student Menglei Zha is the co-first author, along with City University of Hong Kong (CityU) Dr. Xiangwei Lin and National Kaoshiung University of Science and Technology (NKUST), Professor Jen-Shyang Ni. Dr. Kai Li is a co-corresponding author of this paper, with CityU Professor Lidai Wang and NKUST Dr. Jen-Shyang Ni.

The authors are grateful to the National Natural Science Foundation of China, Guangdong Innovative and Entrepreneurial Research Team Program, the Shenzhen Science and Technology Program, Research Grants Council of the Hong Kong Special Administrative Region, and Fundamental Research Funds for the Central Universities for financial support. The authors also acknowledge the Center for Computational Science and Engineering at SUSTech for theoretical calculation support and SUSTech Core Research Facilities for their technical support.

Figure 1. Improve the nonradiative transition efficiency of semiconductor polymers to achieve long-term real-time monitoring of tumor growth via NIR-II photoacoustic imaging

The paper published in Biomaterials was titled, “Self-assembled AIEgen nanoparticles for multi-scale NIR-II vascular imaging.” It looked at how fluorogens with aggregation-induced emission (AIEgens) have been intensively explored in biomedical applications.

One primary strategy to bring these hydrophobic AIEgens into the aqueous biological environment is to encapsulate them in nanoparticles with functionalized polymeric matrices. Most fluorophores are insoluble in water, requiring post-modification like amphiphilic polymer encapsulation. The traditional preparation of AIEgen nanoparticles is convenient. These methods are hard to fulfill the required uniform size and stable loading efficiency. The exploration of reliable strategies that can afford AIE nanoparticles with the above requirements with minimized batch-to-batch variation remains challenging.

The research team designed amphiphilic AIEgens, built with a hydrophobic donor-acceptor-donor (D-A-D) core and hydrophilic polyethylene glycol (PEG) chain. These AIEgens can self-assemble into uniform nanoparticles with average sizes of ~35 nm, showing an emission maximum beyond 1000 nm and quantum yields (QYs) above 10%. The team used the bright AIE nanoparticles for multi-scale intravital vascular fluorescence imaging in the second near-infrared window (NIR-II, 1,000-1,700 nm) in mouse and rabbit models.

Advanced AIE nanoparticles with efficient self-assembly strategies were constructed for angiography. The early stages of demonstration for the AIEgen nanoprobes for NIR-II imaging in large animal models (rabbits with an average weight of 3 kg) will inspire more research opportunities in designing advanced NIR-II probes and promoting the translational studies of this emerging imaging technique.

BME doctoral student Yaxi Li and Shenzhen Institute of Advanced Technology (SIAT) Dr. Dehong Hu are the co-first authors. Dr. Kai Li and SIAT Dr. Hairong Zhang are the co-corresponding authors of this paper.

This work was supported by the National Natural Science Foundation of China, Guangdong Innovative and Entrepreneurial Research Team Program, the Science and Technology Innovation Committee of Shenzhen Municipality, the Shenzhen key laboratory of ultrasound imaging and therapy, and CAS key laboratory of health informatics. The authors also acknowledge the Center for Computational Science and Engineering at SUSTech for theoretical calculation support and SUSTech Core Research Facilities for technical support.

Figure 2. Self-assembly strategy to prepare aggregation-induced luminescence nanoprobes to achieve multi-scale NIR-II vascular imaging

The paper published in Research was titled, “Centimeter-Deep NIR-II Fluorescence Imaging with Nontoxic AIE Probes in Non-Human Primates.” In biomedical fluorescence imaging, AIEgens plays an increasingly important role. However, there is still a lack of in-depth toxicological research and deep imaging evaluation in primate models.

The research team studied the high intravenous injection dose of AIE probes, 30 times the standard clinical dosage in primate blood and histological analysis report. The results showed that the AIE probes were in the normal range after 35 days of metabolism in primates, which proved that the AIE probes were not biologically toxic. The research team also utilized the biological safety and high-brightness optical performance of the AIE probe. They successfully achieved a depth of 1.5cm blood vessel imaging in primates, breaking the current limit of near-infrared two-zone fluorescence imaging at the millimeter level.

The two features of NIR-II AIE probes enable them to become promising fluorophore candidates for angiography and lymphadenopathy. They could pave the way to promote clinical translation of NIR-II AIE probes in human clinical trials.

Dr. Kai Li is a co-corresponding author of this paper, with the Hong Kong University of Science and Technology (HKUST) Professor Ben Zhong Tang and SIAT Dr. Hairong Zheng. Additional contributions came from the National Cancer Center, National Clinical Research Center for Cancer, Cancer Hospital & Shenzhen Hospital.

Figure 3. The NIR-II AIE probe achieves high signal-to-noise ratio blood vessel imaging in primates with a depth of 1.5 cm

The second paper published in Angew Chem Int Ed. was titled “Sub‐10 nm Aggregation‐Induced Emission Quantum Dots Assembled by Microfluidics for Enhanced Tumor‐Targeting and Reduced Retention in the Liver.” AIE dots (AIE dots) obtained by hybridization with phospholipids have been widely used in biomedical imaging. However, the particle size of the AIE dots prepared in this traditional method is usually larger than 25 nm. Due to the interception of the liver, spleen, and other organs, the ideal imaging effect is often difficult to obtain with such large AIE dots.

The research team developed a microfluidic chip with a double spiral mixing pipe (pipe width 300 microns, height 60 microns) to prepare AIE nanoparticles. These are known as AIE quantum dots (QDs), separate from the larger AIE dots. AIE QDs allow more efficient cellular uptake and imaging without surface modification of any membrane-penetrating peptides or other targeting molecules.

NIR-II AIEgens were used to demonstrate that AIE QDs can achieve high contrast at the tumor as small as 80 mm3 and evade the liver more efficiently than AIE dots.

The sub-10 nm organic AIE QDs were successfully synthesized in a microfluidic chip, showing better in-vitro and in-vivo solid-tumor imaging than AIE dots. These AIE QDs promises a pathway for efficient cell labeling and sensitive & precise detection of the tumor. The microfluidic method may help make a broad range of multi-function AIE molecules into sub-10 nm AIE QDs. They could have immense potential in diverse biological applications.

Doctor Xuanyu Li from the University of the Chinese Academy of Sciences (UCAS) is the first author, and Menglei Zha is the co-first author. Dr. Kai Li is a co-corresponding author. Additional contributions came from the BME Microfluidic Research laboratory.

The research teams thank the National Key R&D Program of China, the National Natural Science Foundation of China, the Chinese Academy of Sciences, the Guangdong Innovative and Entrepreneurial Research Team Program, the Science and Technology Innovation Committee of Shenzhen Municipality, and the Tencent Foundation through the XPLORER PRIZE for financial support. The authors also acknowledge the Center for Computational Science and Engineering at SUSTech for theoretical calculation support and SUSTech Core Research Facilities for technical support.

Figure 4. The new microfluidic synthesis strategy prepares sub-10 nm AIE QDs to reduce liver retention and enhance tumor targeting in tumor-bearing mice.

 

Related links:

https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202010228

https://www.sciencedirect.com/science/article/pii/S0142961220306116

https://doi.org/10.34133/2020/4074593

https://onlinelibrary.wiley.com/doi/10.1002/anie.202008564

Chris Edwards | 09/09/2020

 

In recent days, Shenzhen Municipal Science, Technology, and Innovation Commission (STIC) Deputy Director Xuan QIU led a delegation to the Department of Biomedical Engineering (BME) at Southern University of Science and Technology (SUSTech). SUSTech University Council Chairperson Yurong GUO met with the STIC delegation, along with long-term distinguished visiting BME professor Daping WANG.

At the meeting, SUSTech University Council Chairperson Yurong GUO said that SUSTech’s rapid and high-quality development is inseparable from the support of the city, the province, and the state. The ongoing support from STIC for SUSTech’s development highlights its continuing commitment to “research, innovation, and entrepreneurship.” It will focus on the development of its talent pipeline, the transformation of its technology, and global cooperation to continue to contribute to the progress of Shenzhen.

STIC Deputy Director Xuan QIU affirmed the developments SUSTech and BME has made in recent years. She spoke about the policies to promote the development of the bioengineering and pharmaceutical industry in Shenzhen. She pointed out that the biological and life health industry is one of the most dynamic emerging industries in the world. Numerous advantages are available to SUSTech, so the ongoing scientific and technological work conducted at SUSTech would encourage the implementation of the strategic goals for regional development.

SUSTech Acting Vice President Yusheng ZHAO and Office of Research Deputy Director Yi GONG introduced the major scientific progress of SUSTech and related research projects. BME head Xingyu JIANG spoke about the teaching and research achievements of the department. He said that it would continue to integrate world-class technologies with more robust cooperation with Shenzhen enterprises.

Long-term distinguished visiting BME professor Daping WANG said that BME would continue to build several international exchanges and cooperation platforms. It will improve the level of international cooperation and exchange. They will conduct extensive scientific research exchanges and technology transformations for the city’s sustainable development.