Definition
An inverted microscope is a type of optical microscope with an illumination system located above the sample and an objective lens below the sample. This structural design allows for the observation of samples in containers (e.g., petri dishes, flasks) without the need for sample removal or special preparation, and is especially suitable for observing suspended matter in living cells, tissue sections, or liquids.
Principle
Inverted microscopes are based on the principles of geometric optical imaging. The light from the light source is focused through a condenser that illuminates the sample from above. The light passing through the sample or the fluorescence emitted by the sample itself enters the objective lens downwards, and is magnified by the objective lens to form an intermediate real image. This real image is further magnified by the eyepiece or camera system to form a virtual or digital image that can be observed. Its core optical formula is the total magnification of the microscope: M = M_objective × M_ocular, where M_objective is the objective magnification and M_ocular is the eyepiece magnification. In digital imaging systems, the total magnification also considers the relationship between sensor size and display size.
Measurement method
When observing with an inverted microscope, a standardized operating procedure is usually followed. First, the container containing the sample is placed smoothly on the stage. The coarse and fine-tuning knobs adjust the objective to a working distance close to the sample, while adjusting the condenser's aperture diaphragm and field of view diaphragm to the appropriate state for uniform illumination and proper contrast. For transparent samples, brightfield observation is mostly used. To enhance contrast, optical techniques such as phase contrast or differential interference phase contrast are available. When performing morphological measurements or counts, the target size, quantity, or area in the image is quantitatively analyzed, usually in combination with eyepiece micrometers or image analysis software.
Influencing factors
The imaging quality and measurement results of an inverted microscope are influenced by a variety of factors. The effects of the optical part include the numerical aperture and correction level of the objective lens, the matching adjustment of the condenser, and the stability and color temperature of the light source. The state of the sample itself, such as the thickness and optical uniformity of the culture vessel, the transparency of the culture medium, and the density and viability of the cells, can also directly affect the observation effect. Operating environmental factors, such as the stability of the mechanical platform, environmental vibrations, and temperature fluctuations, can interfere with long-term live cell observation. In addition, whether the observer uses the diaphragm correctly and chooses the appropriate observation method is also the key to obtaining reliable results.
Application:
Inverted microscopes are widely used in a variety of industrial and research fields. In the field of cell biology and biotechnology, it is a fundamental tool for cell culture, long-term imaging of live cells, and cell-cell interaction research. In materials science, it can be used to observe the corrosion or dissolution process of metals, polymer materials, etc. in solution. In the food industry, it is used to monitor microbial fermentation processes or to detect suspended particles in beverages. In environmental monitoring, it helps analyze plankton or particulate matter in water samples. Its characteristics of not preparing samples and observing dynamic processes in vivo make it suitable for scenarios that require non-destructive, in-situ observation.
Selection
When choosing an inverted microscope, several parameters need to be considered based on the specific application needs. In terms of core optical components, attention should be paid to the numerical aperture of the objective lens, working distance, and whether it has special functions such as phase difference and fluorescence. The mechanical system needs to examine the range, accuracy and stability of the stage, and whether it supports specialized containers such as perforated plates. For imaging systems, depending on the recording and analysis needs, choose the appropriate eyepiece or digital camera interface. For live cell research, models with environmental control features may be required. In addition, the scalability of the system, the ergonomic design and the ease of subsequent maintenance support should also be included in the evaluation. Users should weigh the functional configurations of different models based on their own sample characteristics, observation goals, and budget.