A novel on-orbit monitoring method - handheld two-photon microscopy

Zhang Rong, Wang Hongjiang, Jia Haiying, Yang Yuan, Sun Bo, Yang Kai, Gao Junfeng, Gao Chuan, Strategic Support Force Characteristic Medical Center, Research Department, Special Service Health Center, Aerospace Clinical Medicine Department, Shenzhou Medical Team

The emergence of new on-orbit monitoring methods has brought a major breakthrough to the monitoring research of on-orbit astronauts. In this method, the three-dimensional image of the in-vivo skin cells of astronauts in orbit was acquired by using the Portabl Handheld Two-Photon Microscope.

Portable handheld two-photon microscope is a high-tech product that combines elite optical microscope technology, advanced photoelectric conversion technology and liquid crystal screen technology perfectly. It has the characteristics of small size and easy to carry, and can convert the physical image seen by the microscope into digital and analog images, so that it can be imaged on the screen or computer that comes with the microscope.

Two-photon microscopy is a new type of microscope that combines laser scanning confocal microscopy and two-photon excitation techniques. Its main feature is the ability to perform two-photon excitation with a high-energy mode-locked pulsed laser, resulting in non-destructive imaging of deep tissues.

The basic principle of two-photon excitation is that at high photon density, a fluorescent molecule can simultaneously absorb two photons of a longer wavelength and then emit a photon of a shorter wavelength after a short excited state lifetime. This process has the same effect as using a photon with a wavelength half the long wavelength to excite a fluorescent molecule.

Since two-photon excitation requires a high photon density, two-photon microscopy uses a high-energy mode-locked pulsed laser in order not to damage the cells. The lasers emit high peak energies and very low average energies, with pulse widths of only 100 femtoseconds and frequencies of 80 to 100 MHz. This laser ensures that only fluorescent molecules in the focal plane are excited, and fluorescent molecules outside the focal plane are not, allowing more excitation light to penetrate deeper specimens.

In addition, the new two-photon microscope is equipped with an ultra-sensitive direct detector that is capable of recording the most subtle internal structures deep in tissues. Up to 7 external channels and spectral resolution software fully support multicolor multiphoton experiments. Combined with a high-speed 12kHz scanning head and maximum scanning field of view, the axial shift is minimized, effectively collecting faint photons from deep tissues, making the image brighter and minimizing the phototoxicity of the specimen.

In February 2023, the Shenzhou-15 astronaut crew successfully carried out an on-orbit verification experiment using a space station two-photon microscope independently developed by China, which further demonstrated the application potential of two-photon microscopy in life science research and medical diagnosis.

In general, two-photon microscopy is a microscope technology with high application value, which can achieve non-destructive imaging of deep tissues with extremely high sensitivity and resolution, which is of great significance for the development of life science research and medical diagnosis.

Portable handheld two-photon microscopy can be used to observe multi-scale and multi-level dynamic changes in peripheral skin and central nervous synapses, neurons, neural networks, and remote connections over a long period of time under the natural behavior of animals. In the field of space medicine, it can monitor the three-dimensional image of in-vivo skin cells of astronauts in orbit, and carry out on-orbit monitoring research at the cellular and molecular level.

The significance of this monitoring method lies in the fact that it conducts on-orbit monitoring studies at the cellular and molecular level. Cells are the basic unit of life, and monitoring at the cellular molecular level can provide deeper and more granular information.

Specifically, this approach has the following important features and advantages:

1. Non-invasive: There is no need for invasive manipulation of astronauts, reducing the harm and risk to the body.
2. Real-time: It can obtain three-dimensional images of skin cells in real time and understand the changes in the physical condition of astronauts in time.
3. High Resolution: Provides high-resolution images that make the observation of cells and molecules clearer and more accurate.
4. Portable: Handheld design for easy use in on-orbit environments.
5. Comprehensiveness: Monitoring at the cellular and molecular level provides a comprehensive understanding of the physiological and pathological changes in the body.

With this new on-orbit monitoring method, researchers can:

1. Monitor the health status of astronauts: detect potential health problems in time and provide a basis for ensuring the health of astronauts.
2. Studying the effects of the space environment on the human body: Understanding the effects of the space environment on skin cells and molecules provides a scientific basis for addressing the challenges of the space environment on the human body.
3. Promote the development of aerospace medicine: promote technological innovation and theoretical research in the field of aerospace medicine.
4. Improve the safety of space missions: ensure the safety of astronauts in space missions and ensure the smooth progress of space missions.

However, this new on-orbit monitoring method also faces some challenges and problems:

1. High technical difficulty: Advanced microscopy techniques and data analysis methods are required.
2. Complex operation: The skills and experience of the operators are required.
3. High volume of data processing: Efficient data processing and analysis methods are required.
4. Equipment reliability: In the space environment, the reliability and stability of equipment is critical.

In order to better apply this new on-orbit monitoring method, the following measures are required:

1. Strengthen technology research and development: continuously improve the technical level and reduce the technical difficulty.
2. Training professionals: Ensure that operators have sufficient skills and experience.
3. Optimize data processing methods: Improve the efficiency and accuracy of data processing.
4. Ensure the reliability of the equipment: Take effective measures to ensure the normal operation of the equipment in the space environment.

In short, the application of the new on-orbit monitoring method provides new means and methods for the monitoring and research of on-orbit astronauts, which has important scientific and practical significance. Although there are some challenges, it is believed that this approach will play an increasingly important role in the space field through continuous technological innovation and improvement of measures.