The Ultimate Guide to Purchase Coverslip

Coverslip is one of the essential consumables in microscopic imaging experiments. Whether it is routine cell staining or high-resolution confocal imaging, the quality and parameters of the coverslips directly affect the clarity and repeatability of the experimental results. This guide will help you quickly understand the key parameters, common types, application scenarios of cover glass, and how to choose the right product according to your experimental needs.

What is a coverslip?

Coverslip, also known as coverglass, is an extremely thin piece of glass, which is mainly used to cover samples during microscopic observation to protect the samples, fix the sample position, and form an optical path of uniform thickness, so as to obtain clear and stable microscopic images.

What is the purpose of the coverslip?

• Covering samples during microscopic observation: The most basic use of a cover glass is to cover the sample on the slide to form a stable and flat observation layer. This ensures a constant distance between the objective lens and the sample, which helps with focusing and imaging.
• Prevent samples from drying or evaporating: During microscopic observation, especially for liquid samples, blood smears, cell suspensions, etc., the microscope glass coverslips can prevent the sample from drying out quickly or evaporating when exposed to the air, thus keeping the sample in its original state.
• Maintaining imaging quality: The uniform thickness of the cover glass forms a standard optical path. Especially in high-resolution microscopy (such as fluorescence microscopy, confocal microscopy), using a cover glass with a thickness of #1.5 or #1.5H can accurately match the optical design of the objective lens to obtain the clearest image.
• Prevent contamination and cross infection: The microscope slide coverslips seal the sample to prevent dust, impurities, bacteria or DNA in the air from contaminating the sample. It is especially suitable for research with high requirements for cleanliness, such as RNA experiments and immunostaining.
• Cell adhesion and live cell imaging: In cell experiments, coverslips with hydrophilic or treated surfaces can allow cells to adhere and grow. They can be used for live cell imaging, cell migration experiments, etc., and are often used in conjunction with chamber slides or confocal culture dishes.
• Sealing and preservation: In pathology and histology, coverslips are used to seal samples and are fixed with sealing agents to prevent stained samples from fading or peeling over time, facilitating long-term storage and archiving.
• Assisting experimental standardization: In experiments such as quantitative microscopy analysis, image comparison, and automatic recognition, coverslips can provide a consistent imaging background and refractive index environment, which is conducive to data standardization and machine recognition.

Why coverslip is used in microscope?

•  Ensure clear imaging

Microscope objective lenses, especially high-power objective lenses, are designed with the assumption that light will pass through a certain thickness of glass (usually 0.17 mm, that is, #1.5 cover glass). If a cover glass is not used, the refraction environment of light will be broken, which can easily lead to blurred and deformed images, or even inability to focus correctly. Using a cover glass of appropriate thickness can help light propagate along a predetermined trajectory, thereby obtaining a clear and sharp microscopic image.

• Prevent samples from drying and evaporating

Many experimental samples are liquid or water-containing samples, such as blood, culture medium, cell suspension, etc. If exposed to the air, they will quickly dry or evaporate, affecting the observation effect. The cover glass can form a closed environment on the sample surface, effectively locking in moisture, extending the observation time, and reducing human errors.

• Improve sample stability

Under a microscope, even a tiny sample movement can cause field of view jumps and make observation difficult. After the cover glass covers the sample, it can flatten and fix it, preventing liquid flow or sample drift, making the image more stable, especially suitable for scanning observation or image recording.

•  Avoid contamination

During the experiment, samples are easily contaminated by dust, bacteria, pollen and other particles in the air. Covering with a cover glass can effectively protect the sample, reduce external interference, and ensure the accuracy of the observation results. This is especially important for sensitive experiments (such as RNA experiments and immunofluorescence staining).

• Conducive to sealing and preservation

Some experiments, such as pathological sections and tissue staining samples, need to be preserved for a long time. The cover glass is used together with the sealing agent to stably seal the sample to prevent fading, cracking, and contamination, which is convenient for archiving, subsequent observation or remote consultation.

How to choose coverslip?

1. Coverslip thickness. Common thickness of coverslip include #1 (about 130–160μm), #1.5 (about 160–190μm), #2 (about 190–220μm), and the more precise #1.5H (170±5μm). If you are engaged in high-resolution imaging experiments such as fluorescence microscopy, confocal microscopy, or spatial omics, it is recommended to choose #1.5 or #1.5H specifications. This type of coverslipping can achieve the best match between the focal length of the objective lens and the image quality. Relatively speaking, in ordinary teaching or basic microscopic observation, the use of #1 thickness can also meet basic needs.
2. Glass material. Ordinary optical glass is suitable for daily experiments or teaching due to its low cost. However, for scientific research work with high precision requirements, such as live cell imaging or time series photography, it is recommended to use high borosilicate glass or imported ultra-clear glass with better optical properties. These materials have higher light transmittance, lower optical distortion, and stronger thermal stability.
3. Appearance and edge treatment. The shape of the coverslips for cell culture is generally square or round, and the common sizes include coverslip 22×22, 24×24mm, and 18mm coverslips in diameter. In terms of edges, some coverslips with polished edges can effectively prevent operators from scratching their hands and are more suitable for automated cover application systems. Polished coverslips for microscope is not easy to stick, and it is easier to pick up with tweezers and position accurately, which is particularly suitable for batch sealing, microscopic image acquisition and other tasks.If there is no special requirement for edge safety, unpolished coverslips are more economical.
4. Surface treatment process. High-quality cover slips should have high cleanliness to avoid dust or grease contamination that interferes with imaging. If your experiment has high requirements for cleanliness (such as RNA experiments or fluorescence detection), it is recommended to choose dust-free clean packaging cover slips that have been plasma treated or electron beam sterilized. In addition, you can also choose hydrophobic or hydrophilic surface treatment according to the purpose of the experiment: the former is suitable for droplet imaging, while the latter helps cells adhere to the wall.
5. Experimental purpose and budget. If you are engaged in scientific research projects or journal publications, you should give priority to high-end cover glasses with stable performance and excellent optical performance. Although the price is slightly higher, it can significantly improve the data quality. For daily teaching or low-magnification observation, you can choose conventional products to control costs.

Tips

If you are doing fluorescent labeling experiments, it is recommended to choose #1.5 thickness, clean glass material.

If you are doing live cell imaging, you can consider using confocal dishes or chamber slides to improve image stability.

For routine cell observation or teaching, economical cover glass (#1 thickness) can meet the needs.

If it involves long-term sealing or specimen preservation, it is recommended to use it with sealing media and store it in a special coverslip box to prevent dust and moisture.

What is the difference between microscope slides and coverslips?

1. Different basic definitions

Slide for Microscope is a glass slide used to hold samples, and experimental samples (such as cells, tissue slices, liquid samples) are placed directly on it.

Coverslips for microscope slides is a thin glass slide used to cover the sample, which is placed on the sample to protect the sample and form an optical channel.

2. Different sizes and thicknesses

The size of the slide is generally 25 × 75 mm or 26 × 76 mm, and the thickness is about 1.0–1.2 mm.

The microscope slide coverslips are usually square (such as coverslip 22×22) or round (such as 18 mm diameter), and the thickness is only 0.13–0.22 mm.

3. Different functions

The slide is responsible for providing a stable and flat sample-carrying surface and is the “basic platform” for the entire experiment.

The coverslip glass is responsible for fixing the sample, flattening the liquid, preventing evaporation and contamination, and forming a suitable optical refraction environment under the microscope, which is helpful for imaging.

4. Different materials and surface treatments

Glass slides need to have high strength. Some special types also have frosted label areas, hydrophilic treatments, positive charge treatments, etc., which are suitable for different staining or adhesion experiments.

Microscope coverslips focus on optical transparency and thickness consistency. Ultra-white glass and high borosilicate glass are often used, and they can be cleaned, antistatic or plasma modified.

5. Experiments are used together and cannot be replaced

In standard microscope experiments, slides are used for loading and coverslips are used for covering. Glass slide and coverslip must be used together. Once mixed or replaced, it will lead to problems such as blurred images, unstable focus, and cracked samples.

What is the difference between a hemocytometer coverslip and an ordinary coverslip?

•  Different uses

Coverslip for hemocytometer is designed for hemocytometers (such as Neubauer counting chambers) and is used for manual counting of red blood cells, white blood cells, platelets, yeast, sperm, etc. It is used in conjunction with the hemocytometer to ensure the formation of a liquid layer of fixed thickness (usually 0.1 mm), which is the prerequisite for cell volume counting.

Ordinary coverslip lab is used for general microscopic observation, such as tissue sections, cell smears, bacterial staining specimens, etc. Its main function is to cover and protect samples, keep samples moist, and assist in focusing, and does not involve volume control.

• Different thicknesses

Coverslips for hemocytometer are usually 0.4 mm or 0.5 mm thick, much thicker than ordinary cover glasses, in order to form a strictly standardized counting chamber height (0.1 mm) between the hemocytometer and the counting chamber.

Ordinary cover glasses are generally 0.13–0.17 mm thick, which is ultra-thin and suitable for the standard working distance of microscope objectives without interfering with optical imaging.

• Different dimensional accuracy and edge treatment

The size of the hemocytometer cover glass is very precise (such as 20 × 20 mm, 22 × 22 mm), the edge is polished, and the thickness is uniform, which is convenient for stable and flat suspension on the support platform on both sides of the hemocytometer.

Although ordinary cover glass also has dimensional consistency requirements, the accuracy standard is not as strict as the counter cover glass, and some products have unpolished edges, which is lower in cost.

• Different requirements for optical performance

The cover glass of the hemocytometer has high requirements for optical uniformity, transparency and flatness to ensure clear observation of cell boundaries under high-power microscopes and facilitate accurate counting.

The optical requirements of ordinary cover glass are relatively low, and only basic light transmittance and flatness are required, which is mainly used to observe sample morphology.

Summary

 Every detail of scientific research deserves serious attention. Although the cover glass is small, it “magnifies” the success or failure of the entire experiment under the microscope. Choosing the right cover glass is the beginning of being responsible for the experimental results and a key step to improve scientific research efficiency.

If you are hesitant about choosing a cover glass, please visit our website to view the detailed parameters and usage recommendations of different types of cover glasses and slides, or contact us for professional configuration solutions.