Microscopy is an essential tool in many fields of science. However, because of costs and fragility, the usage of microscopes is limited in classroom settings and nearly absent at home. In this article we present the construction of a microscope made of LEGO® bricks and low-cost, easily available lenses. We demonstrate that the obtained magnification and resolution are sufficient to resolve micrometer-sized objects and propose a series of experiments that explore various biophysical principles. Finally, a study with students in the age range of 9 to 13 y shows that the understanding of microscopy increases significantly after working with the LEGO microscope.
The invention of microscopy in the 17th century by Antoni van Leeuwenhoek was the start of an era of research in the micro-world (1). Although we know by now what the “little animals” are that he observed, the micro- and nano-world is an inexhaustible topic for biophysical research, for which the light microscope is the instrument of choice.
Despite the simplicity of a basic light microscope, the fundamental working principles are beyond everyday intuition for pupils, but also for most adults. Although this lack of insight into simple optics might partially be because of the perception of microscopes as complex research instruments, hands-on experience promises to drastically improve the understanding of the working principles of microscopes by any interested person, including children.
Our aim is to introduce a microscope to individual students in a classroom setting, both as a scientific tool to access the micro-world and to facilitate the understanding of fundamental principles of the optical components of a microscope in a playful and motivating, yet precise approach. By basing the design on LEGO, we aim to make the microscope modular, cheap, and inspiring. The LEGO brick system provides a low entry level for children, because it is a common toy found in most homes. The modular design, flexibility, and high level of sophistication of the different building parts make it an ideal framework to demonstrate even complex instruments with simple means. Indeed, LEGO has been used before to demonstrate the working principle of scientific instruments, such as a conceptual atomic force microscope (2) and a watt balance (3), or in actual scientific setups (4). Furthermore, this article is in line with other initiatives to create high-performance, low-cost microscopes. Although a previous version of a LEGO microscope called the Legoscope was successful in generating high-quality images, it still required an objective and custom (3D-printed) parts, hindering its capacity to be used simply to demonstrate the principles of a microscope. Another initiative used very simple but smart designs to generate a $1 foldable microscope (foldscope) (5), wherein the low adaptability of the microscope and the image quality were a trade-off for the extraordinarily low price. Finally, affordable, robust tools such as pocket microscopes and clip-ons for smartphones also allow students hands-on access to microscopy.
In this article we present the design of a fully functional microscope made entirely out of LEGO. The only non-LEGO components are the 2 optical parts, which can be purchased off the shelf at approximately 4 ($4) each. We quantify the optical performance of the microscope and find submicrometer resolution. We show how, thanks to the flexible design, the magnification of a microscope can be tuned by combining different lenses and adjusting their distance, thus providing a simple tool for teaching fundamental optics and simple biophysical concepts. Furthermore, the simple and robust design allows long-term imaging without drift in the focus of the microscope.
We design a number of experiments that can be carried out with this LEGO microscope and easily accessible materials, while exploring various biophysical themes. Finally, we demonstrate that this LEGO microscope can be used in an educational setting by letting a group of 9- to 13-y-old students build the microscope and demonstrate their progress in understanding of microscopy with a questionnaire. To ease the usage of the LEGO microscope, we designed a step-by-step workflow for a school setting or for helping parents and children discover biophysics and microscopy in an autonomous way. All materials, including parts lists, building plans, workflows and project suggestions are found in the Supplemental Material and on GitHub (6).
II. SCIENTIFIC AND PEDAGOGICAL BACKGROUND
Microscopy is a fundamental tool of modern science that is used on a daily basis to study and understand biological and biophysical questions. In sharp contrast to its importance, a layman's understanding of the fundamental principles remains superficial, and microscopes are often seen as complex instruments, exclusively usable in a science context. Although the working principles of a microscope are taught in high school settings, the usage of microscopes in the lecture setting often does not target an understanding of its principles, but simply of the use of ready-made microscopes.
Besides an understanding of optics, we suggest a series of experiments that can be conducted with the home-built microscope and readily available samples. These experiments demonstrate some fundamental biophysical concepts, such as the drastic effects of osmotic pressure on plant cells. Furthermore, the motion of easily obtainable microswimmers can be observed, where the fundamental problem faced by swimming at low Reynolds number may be integrated in the experimental description.
To make the work with the microscope an efficient experience, we provide a detailed work plan that can be followed at the individual or the class level. As we provide all information as freely accessible and extensible GitHub repositories (6), we hope that the instructions might be translated into other languages by the community. We have already provided versions in English, German, Dutch, Spanish, and French.
III. MATERIALS AND METHODS
A. Microscope assembly
We designed the microscope by taking advantage of the modular and flexible characteristics of the LEGO brick system. The design of the microscope is shown in Figure 1a,b. The building plans, including a list of components, can be found in Supplemental Files S1 and S2. The main components are the illumination part, the objective holder, including the objectives, and the ocular part.
Illumination is one of the simplest parts of the microscope (Fig 1c). In case of a group work to construct the full microscope, this part can also be built by young children that are less used to complex building instructions. The illumination itself is a special LEGO brick integrating an orange LED. It is straightforward to replace the orange LED with a different color. A short video demonstrating the opening and replacement of the LED is given in Supplemental Movie S1. Because the light source is positioned close to the sample, no special condenser is included, which helps reduce the optical parts to a minimum. The absence of a condenser means the illumination with the lower magnification objective can become slightly nonuniform. To avoid this, a diffuser can be made from a thin sheet of paper placed between the LED and the sample.
2. Objective holder
To allow precise focus adjustment even with a high-magnification objective, an accurate and smooth positioning with submillimeter precision is required (Fig 1d). Because LEGO is not designed to generate such precise motion, we had to push the limits of the brick system by combining a gear rack with a gear worm screw that results in approximately 3 mm of travel for every full rotation. This movement is sufficient for the final adjustment of the focus, even when looking at samples of only several micrometers in size. Although the objective holder is the smallest of all the individual parts of the microscope, it is the most demanding with respect to building skills. Hence, building this part should either be done by older and more experienced children, or the building should be supervised by an adult to prevent frustration in an early phase of constructing the microscope. Once built, the gear system will move the objective in the vertical direction when rotating the control wheel (black wheel in Fig 1d). The precision and repeatability of this threaded system suffices for both objectives presented below.
The ocular is a key element of the microscope, which is first built in the proposed classroom or exploration setting and then used as a classical magnifying glass. Although the overall construction of the ocular remains quite simplistic, the positioning of the lenses is still demanding. Although the lenses used here are cheap yet powerful, mishandling plastic lenses will rapidly lead to scratches on the surface. Users need to be careful when handling the lenses, because scratches on the surface disturb the image quality.
The only non-LEGO components in the building plans are the lenses in the objectives and the ocular. The designs for 2 different objectives are included (Fig 1d), with a higher and a lower magnification. However, other lenses or even lens systems can be easily integrated. However, it is important that such adapted objectives position the optical elements in the same position, to keep the alignment of the microscope. For the high-magnification objective (Fig 1d, left), the lens of a replacement iPhone 5 camera module is used. Such highly specialized plastic lenses of nonspherical shape have outstanding optical performance compared with glass or polymer beads and are suitable for high-resolution microscopy that approaches the diffraction limit (7), while also being available at a low price. The lens used here has a reported focal length of 3.85 mm, leading to a numerical aperture of 0.54 as discussed in the Results section. After carefully peeling the lens off the chip, it is attached to a LEGO brick with transparent tape and a glass cover slip. Detailed photographs of this procedure are shown in Supplemental File S1.
For the low-magnification objective (Fig 1e, right), a glass lens with a focal length of 26.5 mm and a numerical aperture of 0.29 was used, which was built into a holder that shares the attachment brick and also has the same optical center as the high-magnification objective.
The ocular consists of 2 acrylic lenses with a focal length of 106 mm each, with 1 flat and 1 convex side. Placing the 2 lenses with their flat sides on top of each other, the focal length is reduced to 53 mm (see Fig 1f).
5. Sample holder
The sample holder is a surface of flat LEGO bricks that can be covered with rough tape to reduce the risk of accidentally moving the microscope slide. Furthermore, advanced students are encouraged to design a stage to position the microscope slide accurately. Either the gear rack and worm screws of the objective holder or a translation stage [e.g., as in Tsung-Han et al. (2)], can be used as a starting point.
Table 1 summarizes the list of non-LEGO components used in the assembly of this microscope, including their costs in euro at the time of writing. A smartphone is not included but recommended for image acquisition. In case no LEGO parts are already available, the typical cost of the full set of parts is also listed.
B. Sample preparation
1. Salt crystals
To create sodium chloride crystals, a 1 M sodium chloride solution is prepared by dissolving 5.8 g of kitchen salt in 100 mL of lukewarm water. A drop of the solution is placed on a microscope slide and left at room temperature for approximately an hour, during which the water evaporates and salt crystals are formed.
2. Onion cell monolayer
A monolayer of red onion cells is obtained by cutting a red onion with a sharp knife and carefully peeling off a thin slice with a pair of tweezers. This layer is then spread out on a microscope slide and covered with a drop of water and a coverslip. The coverslip is sealed off on 2 opposing sides with nail polish and left open on the 2 other opposing sides for the influx and efflux of liquid. Supplemental Movies S2, S3, and S4 show the preparation procedure.
A selection of water-based microorganisms such as amoeba, paramecia, and water fleas are obtained by collecting water from a local pond in a plastic bottle. Because water fleas feed on bacteria and algae, some grass was added as a source of nutrients for bacterial growth. The mixture was then left for 1 wk at room temperature, so that the water fleas could multiply. Afterward, a few drops were placed on a microscope slide, which was covered with a coverslip and sealed off with nail polish. Because harmful bacteria can also grow in the bottle, strict hygiene must be followed, and careful hand washing after contact with the water is important. Alternatively, paramecia and water fleas can be bought from pet shops.
Eggs are obtained in powder form from a pet shop and put in water to revitalize them. After 2–3 d the organisms have hatched, and a drop of water with the Artemia is placed on a microscope slide, which is covered with a glass coverslip.
C. Workflow for classroom and individual exploration
To support the usage of the LEGO microscope and to optimize the learning experience, we designed a workflow plan. Such workflows can be included either in a classroom environment by separating a class into several groups, where 2 or 3 pupils work on a single LEGO microscope set and the project is split into different sets. Alternatively, the workflow can also be followed in an individual setting. Because the help of an experienced adult is not guaranteed, the workflow includes help sections to ensure that certain steps are successful before the next steps are initialized. This step is important to avoid frustration, in case some questions or tasks turn out to be difficult. The full workflow, translated in several languages, is found in Supplemental File S3 and on GitHub (6).
IV. RESULTS AND DISCUSSION
The microscope can be used both for direct observation by eye, or images can be recorded with a smartphone camera. For the images in this article, a Sony Xperia XZ2 Compact smartphone was used. Its rear camera has a chip of 5057 × 3796 pixels with a pixel size of approximately 1.2 μm. To record images or movies, the Android camera app was used. In all experiments, the autofocus setting was used.
The following subsections quantify the specifications of the microscope. Although this is important to assess the capabilities of the microscope, it might be beyond the interest of middle school students.
A. Measuring magnification
B. Calculating the magnification
Total magnification with the low-magnification objective and the glass lens is determined in a similar way, substituting f = 26.5 mm in Eq. 5 for the focal length. In this case, dobject = 32 mm and dintermediate = 155 mm, leading to a total magnification of M = 23×, again in good agreement with the value that was determined experimentally.
C. Quantifying the resolution
For the high-magnification objective, we found a numerical aperture of 0.54, which, combined with an average wavelength of light of approximately λ = 550 nm, leads to a resolution of d = 0.51 μm, which is only slightly smaller than the measured 0.78 μm that was estimated from the intensity profile in Figure 4e. For the low-magnification objective, the radius of the aperture of the LEGO brick that holds the lens needs to be used, rather than the radius of the actual lens. We found a numerical aperture of 0.29, which led to a resolution limit of d = 0.95 μm, a factor of 4.5 smaller than what was experimentally estimated from the intensity profile in Figure 4f. The poorer performance of the low-magnification objective compared with the high-magnification objective is likely because a single lens is used in the low-magnification objective rather than the composite lens system of the smartphone camera lens used in the high-magnification objective. Indeed, a smartphone camera lens is designed to provide good image quality for low and high angles of incidence; here, we show that this lens functions close to the theoretically possible limit.
As an alternative to calculating the numerical aperture from the lens radius and its focal length, the numerical aperture is experimentally determined in Supplemental Figure S1. The measured value of the NA was comparable with the calculated value.
V. USE IN EDUCATIONAL SETTING
The goal of this project is to provide an accessible, hands-on microscope that can be used in an educational setting. In a preliminary attempt to quantify the effectiveness of the LEGO microscope as a learning tool, 8 students in the age range of 9–13 y were tested before and after following the provided workflow instructions. The tests were identical and contained 5 questions on the subject of microscopy as well as 5 general questions related to natural sciences that served as a benchmark (see Supplemental File S4). Although the subject of the microscopy questions was discussed in the workflow instructions, the answers were not included and had to be obtained by working through the different steps.
The workflow instructions were organized in a 13-step procedure during which the students built the microscope step by step. The manual explores various aspects of the microscope. The workflow consists of the following basic steps:
1. Building of the 3 main parts of the microscope
The relevant parts should be built individually. At this point, the students are not necessarily aware that the final outcome will be a microscope. Objectives are not yet added in this stage. However, the lens of the ocular is already mounted.
2. Exploration of the different parts
The students are asked to play with the different parts and to guess what they can be used for.
3. Focus on the ocular
The students are asked to inspect the ocular closely. They should find out that it can be used as a magnifying glass. They should realize that because of the closed construction, typically not enough light is delivered to the sample.
4. Combination of light source and ocular
To overcome the problem of low light, the students should realize that using a light source, built in a previous step, produces a better view of the magnified sample.
5. Exploration of individual samples
The students are asked to inspect arbitrary samples with the magnifying property of the ocular.
6. Interruption to recapitulate experiences
The students are asked to collect the main experiences gathered so far. This ensures that the important lessons to work on the following steps have been learned. In a classroom setting this should be done together with all groups.
7. Identifying possible ways to increase magnification
Besides using stronger lenses, the students should figure out that 2 magnifying glasses might improve the total magnification. If this step was not suggested by the students, it will be introduced either by the teacher or by the help in the manual.
8. Introduction of the objectives
To begin, the students are exposed to the low-magnification objective. They should try to use both the ocular and the second lens to have an improved magnification. Because this step requires very precise alignment, students will mostly fail, thus introducing the requirement of stable mounting. Several helping strategies are included for this step.
9. Interruption to collect experiences
The idea of fixing the lens position is discussed or introduced in the help section of the manual.
10. Combination of all parts
In this step, the students combine all parts to get a working microscope. Now they are also told that they have successfully constructed a LEGO microscope.
11. Exploration of samples with the microscope
Samples are explored, as suggested in the sample part of this paper or provided by the teacher.
12. High-magnification objective
To improve the magnification, the second objective is introduced at this stage. Because of the appearance of the lens, the similarity with a magnifying glass is lost. However, after integration in the microscope, micrometer-sized objects can be visualized.
13. Inspection of micrometer-sized samples
In the final step, the students are asked to inspect samples from the micro-world. Biophysical effects, such as osmotic pressure and the motion of microswimmers, are introduced here.
After having finished this workflow, the second test was taken, asking the same questions as the initial test. The general questions serve as a control benchmark, and, as shown in Figure 5, the fraction of correct answers of this control changes only marginally after the students have worked with the microscope. The fraction of correct answers on the microscopy questions however, almost doubles. Although the group size was relatively small, the effect is significant.
B. Example experiments
One aim of the LEGO microscope is to provide children and teenagers an easy and playful access to optics and biophysics. After building the microscope, simple objects of everyday use can be imaged, such as hairs from humans and animals or natural and artificial fibers from clothing. To improve the learning effect, we furthermore propose a series of simple experiments that can be performed at home that allow discovering some of the main biophysical principles. Specifically, we suggest discovering the process of crystallization, to observe the effect of osmosis on plant cells and to discover the motion of microswimmers.
Among the simplest, yet impressive samples is a salt crystal (Figure 6a). The shape of a sodium chloride (NaCl) crystal reflects the face-centered cubic lattice formed by the larger chloride ions that are surrounded by the smaller sodium ions. As described in the material section, these crystals can be prepared and observed.
Alternatively, when a thin film of the salt solution is placed on a microscope slide, the concentration of salt will slowly increase from evaporation of water so that the crystallization process itself can be recorded.
Osmosis is an important biophysical effect that regulates shape and pressure in many biological systems, such as the turgor pressure in plant cells that presses the plasma membrane against the cell wall and gives plant tissue its rigidity. In Figure 6b, a time-lapse is shown of red onion epidermal cells exposed to an osmotic shock. The full movie is shown in Supplemental Movie S5. At approximately t = 30 s, a drop of 1 M NaCl solution is placed on one open side of the coverslip, which, because of capillary forces and a piece of absorbing paper on the other side of the coverslip, ensured that the cells were rapidly surrounded by the NaCl solution, creating a large difference in osmotic pressure between the inside and outside of the cells and resulting in a loss of water. As a consequence of the volume reduction, the plasma membrane detaches from the cell walls starting around t = 3 min, and the pigment becomes more concentrated. At approximately t = 5 min, the NaCl solution is replaced with distilled water, which enters the cells and returns them to their original volume. During the recording, care was taken not to touch the microscope to avoid movement of the microscope slide. No drift in focus was observed during our measurements, avoiding the need to adjust the height of the objective, which in turn would lead to motion of the microscope.
To discover and image systems that are currently the research focus of many biophysics groups, a series of different microswimmers can be imaged with the LEGO microscope. The propulsion of microswimmers is fundamentally different from macroscopic swimmers because it occurs in a low Reynolds number regime, where friction is the dominating force (10). Relatively large microswimmers are Artemia shrimps. Their movement is imaged with the low-magnification objective and is shown in Figure 6c and Supplemental Movie S6. Artemia shrimps can swim relatively fast by using their antennae for regular strokes. In contrast, unicellular organisms apply different strategies for propulsion. These organisms can be grouped in two categories: flagellates that use a small number of long flagella for movement and ciliates that have a large number of small, hair-like flagella (called cilia) covering the entire organism (11). Flagellates are typically smaller than ciliates, and they are hard to resolve with the LEGO microscope. On the other hand, the movement of ciliates can be imaged well. An example is the propulsion of paramecia, unicellular organisms that are covered with cilia and are commonly found in ponds. Their movement is imaged with the high-magnification objective and is shown in Figure 6d and Supplemental Movie S7.
With LEGO and low-cost, easily available lenses, it is possible to construct a microscope that can resolve micrometer-sized objects with a resolution that is close to the diffraction limit of light. A series of experiments is suggested covering different fields of natural sciences that can be conducted with household ingredients. The modular design of the microscope itself also lets it be incorporated easily into a curriculum on optics. A preliminary study with 8 students in the age range of 9–13 y shows that the understanding of microscopy increases after working with the LEGO microscope.
Because the design of the microscope presented here is only one of many possible configurations, customization is highly encouraged.
Supplemental materials are available at: https://doi.org/10.35459/tbp.2021.000191/. Supplemental File S1 has step-by-step building instructions for the LEGO microscope. File S2 is a list of parts for the LEGO microscope. File S3 is a manual to explore the LEGO microscope step by step. File S4 has a series of questions that were used to test knowledge on microscopy before and after using the LEGO microscope.
Supplemental Movie S1 has instructions for replacing the LED in the LEGO brick to change the color of illumination. Movie S2 has instructions for the preparation of red onion epidermal cells for microscopy. Movie S3 has instructions for closing the sides of a sample slide for flow experiments. Movie S4 has instructions for performing an osmotic shock experiment. Movie S5 shows red onion epidermal cells exposed to an osmotic shock by the addition of a 1 M sodium chloride solution. Movie S6 shows the movement of Artemia shrimps observed with the low-magnification objective. Movie S7 shows the movement of paramecia observed with the high-magnification objective.
Supplemental Fig S1. Experimental determination of the numerical aperture of the high-magnification objective. A green laser is refracted by the smartphone camera lens and illuminates the back side of a paper box. By measuring the distance from the lens to the box and the diameter of the refracted circle, the maximum angle θ under which light left the lens is estimated. The average of multiple measurements results in a numerical aperture of 0.53, close to what was calculated from the lens diameter and its focal length.
BEV, EBB, and TB designed the microscope. BEV and TB carried out experiments, analyzed data, and wrote the manuscript.
This project was supported by the European Research Council (Consolidator Grant 771201). We also acknowledge teachers from the Pascal Gymnasium in Münster for useful discussions and their students for testing the building instructions of the microscope and the workflow and for providing helpful feedback.