Lauren Alvarenga on cleaning and troubleshooting microscopes
Microscopes are precision medical devices where the data and results are translated through a system of optics that produces an image of a sample. This means that they require routine care and maintenance to ensure that they are producing the best images they possibly can. This improves data integrity, patient care, quantitative imaging and more. Here we discuss a variety of topics on microscope care ranging from proper cleaning procedures to troubleshooting your digital images for a practical approach to microscope maintenance.
Similar to the image acquisition process, microscope maintenance follows a ‘macro-to-micro’ approach. Before you begin performing maintenance, start with a clean and tidy work environment and a microscope frame that is free of immersion oil or tissue media spills. To clean the microscope frame of dirt or stains, first, wipe the dirt away with a cloth moistened with a little bit of water and neutral detergent. You want to avoid harsh organic solvents as they can damage plastic components and optical cements. After your detergent, wipe the external components of the frame with a cloth that is wet – but isn’t dripping – with lukewarm water. This removes any residual detergent, and the combination with water is strategic; water is needed to remove any soluble substances, such as salt, from tissue media, and the detergent helps remove things that are not soluble in water. When cleaning the frame, take care to avoid touching the optical surfaces, such as the eyepieces and objectives, to avoid watermarks.
Especially now that viral transmission is on the minds of every person working in the labs, it’s good to know how to disinfect your microscope frame. There are a few high-touch areas on microscopes, so for shared environments, we recommend a solution of 70% ethanol to 30% water sprayed onto a cloth to wipe down the microscope components, such as focus knobs. This ensures sufficient contact time to disinfect the components. Be sure to follow proper hand hygiene as well so you don’t contaminate a microscope immediately following its disinfection. Wear gloves during the cleaning process and discard them after you are finished. Wash your hands with soap and hot water for at least 20 seconds, or use an alcohol-based hand sanitiser with at least 60% alcohol if soap and water isn’t immediately available to you.
Optical components require a bit more specialised care. To help prevent scratches on coatings and optical glass, remove dirt and dust that sticks to their surface with an air gun or blower brush. This way, you aren’t pressing them into the optical surface when you make contact with the glass. Cotton tipped swabs are great from a precision standpoint, but they can be a little abrasive on special surfaces. Speciality swabs designed for use in clean rooms are an ideal solution, but they tend to be costly.
You can make your own cleaning swab using a bamboo stick and a piece of lens paper. First, lay out a piece of lens paper on a clean, dry surface. Place your bamboo stick on top of the lens paper and then fold the paper in half so that the tip of the bamboo stick is covered.
Next, fold the left edge of the lens paper and begin rolling the bamboo stick until the paper is rolled entirely around the stick. That’s it! If you choose to use a solvent during your cleaning process, don’t immerse the swab into the solution as this will compromise the integrity of your lens paper. Instead, use a dropper or a transfer pipet to apply a small drop of solution to the swab.
You can use lens cleaner or 100% ethanol on your cleaning swab. We recommend you store your ethanol in a container of dri-rite or other anhydrous environments so that it doesn’t absorb water, as this will cause streaking on your optic. The intention here is to remove oils, not disinfect, so the higher ethanol content is preferred for its quicker evaporation times. Gently wipe the front surface of the lens in a circular motion from the centre to the edge. Repeat as needed with a fresh cleaning swab—you don’t want to reuse them.
To get a clearer view of your optical surface, you can remove one of the microscope objectives and a single eyepiece. Turn the eyepiece around and look in the ‘wrong-end’ so that it can be used as a loupe. Hold them both up to your eye near a room light and move the objective until you catch a reflection.
Oil immersion objectives will likely require more frequent cleaning than air objectives. It’s important to clean immersion oil from your objective if the lens won’t be in use for a period of time so the oil doesn’t dry out and collect dust. This will degrade your image quality even with fresh immersion oil applied on top and could potentially be damaging to your expensive optics!
At the same time, you also want to avoid over-cleaning your objectives. This can damage the optical cement that holds the top lens element in place, resulting in oil seepage under the top lens. This will distort the images created by the objective and they’ll need to go back to the manufacturer for repair.
If you can’t see an image when you turn on your microscope, there are a few things you want to check first. Start at the light source and trace the light as it travels to the objective. Are there any mechanical barriers in place, like shutters, sliders, or switches, that could be completely or partially in place in the light path blocking the light? Partial obstructions like this are very common and usually present as dark, crescent-shaped artifacts. If you can see the light coming out of the objective lens, then that’s not where the problem is coming from, and we can look at a few more things.
If you’re using fluorescence, check to make sure that the right filters and dichroics are in position, especially if using a manual microscope where these components are not automated. Also check to be sure that the emission light path is directing the light to the right component. It should be sending light to the eyepieces if viewing by eye or to the camera if viewing your image on a screen.
If you can see the light coming out of the objective, but you don’t see an image at the detector itself or through the eyepieces, then the problem is likely between these two components. You can check the emission path by using a known sample. Plastic fluorescent slides are a popular choice.
If you’re imaging on a detector, check the exposure or gain to make sure that you would expect to see a signal at the settings you are using.
With these few tips, you can trust that your microscope is producing quality images. Routine care is an essential part of a microscopy workflow, and we recommend routine cleaning procedures be performed as needed and that preventative maintenance visits be scheduled on an annual basis. A small investment in time caring for your microscope will keep it functional for years to come.
Lauren Alvarenga is with Evident Scientific