This was inspired by the designs by Pacific Northwest Laboratories, using a glass bead to magnify samples that are then imaged on a smartphone. However, after using it for several short lessons and demonstrations, I wanted to improve some areas of their design.
This design has several improvements:
- Multiple magnifications that can be easily switched
- Ability to move samples easily
- Use of the higher resolution rear camera
- Optional USB LED lighting and optics system
This design uses a 0.5 mm, 1.0 mm, and 3.5 mm beads, which have a magnification of about 500X, 350X, and 100X respectively. Using digital zoom on the camera will allow even higher magnification.
It works great with prepared slides, where some slides look best at high magnification and some look best at low magnification, but can also be used to look at fresh samples.
Depending on the nozzle size, temperature, feed rate, and other printing parameters, the size of the holes on the microscope may need to be adjusted to properly fit the beads.
Print as many height extensions and crosslinkers as needed for the particular setup.
To print a clean slot for the microscope slide, it is best not to use supports, but they may need to be added and later cleaned up.
Thank you to Dr. Paul Paukstelis and the Department of Chemistry and Biochemistry at the University of Maryland for access to 3D printers.
- Glass beads of sizes 0.5 mm, 1.0 mm, and 3.5 mm. A sample pack is sold by BioSpec at a reasonable price. Cat. No. 11079SMS
USB LED Lighting System:
- 5W USB Lightbulb
- USB switch
- USB power bank, wall adapter, or free USB port on a computer
- Aspheric condenser lens to focus the light from the LED (optional), I used a Thor Labs aspheric condenser lens Ø1/2", f=8 mm, NA=0.78. Cat. No. ACL12708U-A
Assembly - Bead Addition
- If there is no hole on the 0.5 mm bead slot, use a needle or a safety pin to carefully poke a small hole
- Using a tweezer, add each bead into the slot
- Press the bead into place
The size of the hole will depend on the printer resolution and printer parameters. If needed, a safety pin may be used to slightly widen the holes.
Assembly - LED Lighting System
- Remove the top diffuser of the USB lightbulb, it should easily twist off
- If desired, pop the LED PCB out of the plastic shell and remove the plastic housing sides with pliers
- If the LED was removed from the plastic housing, tape or glue the PCB onto the holder
- Connect the USB switch to the lightbulb and a USB power source
- If using a condenser lens, place the lens on top of the lens holder, and place it over the LED
Assembly - Height Adjustment
- Pop the 5 cm height adjustment into the grooves on the microscope
- Use the crosslinkers to attach adjustments to each other and give structural support
Using the Microscope
- Turn on the LED using the USB switch and make sure it is passing through the beads. The best way to know if the bead is properly slotted and has light passing through is to look for a small bright point of light coming from the bead.
- Place the microscope slide into the table, keeping it flat during insertion
- Use the rear camera, and place the camera on the bead hole to image. The closer the phone is to the bead, the larger the FOV.
If the microscope slide is out of focus, adjust the slot height on the microscope slide. The main cause of fuzzy images is due to the bead being too far from the slide itself. Try another bead if possible, or clean the bead using rubbing alcohol.
The parts were designed in TinkerCAD, which can be tinkered at the links below. The size of the bead holes will vary depending on printing conditions, so it may take some trial and error to get the right sized holes. It is best to print a smaller hole and widen it slightly afterwards. Currently, there is 0.25 mm extra clearance for each of the bead slots,
If only pre-prepared slides are used, the slot for the slide on the microscope does not need to be as tall, and will improve focus of the image. The current design is for a 2.5 mm height, which is enough clearance for a microscope slide (25.4x76.2x1mm) + coverslip (22x22x0.13mm). A height of 1.5 mm can be used if using only pre-prepared slides.
Overview and Background
Microscopy is a powerful technique to visualize what is otherwise invisible. When learning about cells, cell types, and cellular organelles, animated graphics or photos are used to illustrate them. However, it is better if students are able to directly look at and take pictures of cells in order to study them.
Using a 3D printed microscope have several advantages over traditional microscopes:
- Significantly less expensive, with each microscope costing less than $20 when not using a condenser lens, allowing each student to be able to use the microscope
- Rugged, not having to worry about students accidentally cracking the slide or scratching the lens. Beads, LEDs, and 3D printed parts can easily be replaced.
- Low power, using only a USB port, it can even be used for field work to visualize samples collected from ponds, dirt, etc.
- Interactive, students will be able to assemble the microscopes themselves, seeing how each part works and fit together
- Customizable and extensible, potentially including darkfield microscopy, imaging using webcams, and more
Onion cells are large plant cells that can be easily visualized at all magnifications, with a clear cell wall. Using household iodine, the nucleus can be selectively stained and identified. Using fresh onions, students will be able to prepare their own microscope slides and visualize them using the 3D printed microscopes. Afterwards, different samples (yeast, skin cells, cheek cells, etc.) can be used to highlight the differences between plant and animal cells as well as different cell types.
- Students will be able to prepare and stain cells for microscopy.
- Students will be able to identify major cellular structures including the cell wall and the nucleus.
- Students will be able to explain how a microscope works and list uses of microscopes.
- Middle School Biology
- Science demonstrations or outreach events
- All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). (MS-LS1-1)
- Within cells, special structures are responsible for particular functions, and the cell membrane forms the boundary that controls what enters and leaves the cell. (MS-LS1-2)
- Complex and microscopic structures and systems can be visualized, modeled, and used to describe how their function depends on the relationships among its parts, therefore complex natural structures/systems can be analyzed to determine how they function. (MS-LS1-2)
- Engineering advances have led to important discoveries in virtually every field of science, and scientific discoveries have led to the development of entire industries and engineered systems. (MS-LS1-1)
Lesson Plan and Activity
Before starting the lesson, ask students what is a cell? What are the types of cells? What
organelles are inside cells?
Onion Slide Preparation:
- Using a tweezer, peel off a thin layer of onion cells from diced onions and place on the microscope slide
- Dab household tincture of iodine on top of the onion sheet
- Let sit for 3 minutes for the stain to hold
- Place a coverslip on top of the onion sheet
- Using a paper towel, dab the edges to remove excess water and iodine
- Carefully insert the microscope slide into the slot.
- Connect the USB switch to a USB port on a computer, power bank, or wall adapter, and turn on the LED light
- Line up the biggest bead with the onion sample
- Using a smartphone or tablet, line up the rear camera with the largest bead and slowly place the camera on top of the bead.
- Take a picture of the sample, moving around the slide if necessary to get a better view
- Repeat with different beads
Have students draw what they see at each magnification, labeling the cell wall and nucleus. Ask them how did they know what the nucleus was? What color was it?
Repeat the process with different cell types. Some ideas include:
- Sets of pre-prepared slides, including animal tissue sections, blood smears, and plant samples which can be bought for low cost on Amazon
- A culture of yeast, which can be stained with methylene blue. Add a drop of 1% methylene blue and wait for at least 5 minutes for all cells to be stained.
- Cheek cell can be swabbed using a cotton swab soaked in salt water and streaked on the microscope slide.
- Skin cells can be lifted using clear tape. The skin cells can be stained by dotting the skin with a washable marker before lifting with tape. Press the clear tape onto the arm, peel, and place directly on the microscope slide.
- Pond or puddle water samples can be used to visualize protozoa and small organisms
Have students visualize, draw, and compare between the onion cell and other cell types. Ask them how do the shape and size differ?
Live onion cell sample seen under the microscope. The nucleus is stained in brown circles using iodine.
Preprepared onion cell sample seen under the microscope
- One assembled 3D printed microscope per 1-2 students
- Fresh onion, diced, in water, washed several times
- Tweezers to replace beads that have fallen out and to peel the sheet of onion cells
- Tincture of iodine, with transfer pipettes or droppers to stain
- Microscope slide (25.4x76.2x1mm) and coverslip (22x22x0.13mm)
- cell staining
- slide preparation
If working with younger students, it is best to have the microscopes assembled before the start of the lesson.