Several companies offer microscopes specifically designed for microfluidic applications and cell imaging, but a limited budget requires building a customized microfluidics microscope that is affordable.

In addition to being price prohibitive, in most cases, the microscopes do not readily fit the specific requirements for a particular microfluidic application.

If a commercially available microscope meets all the requirements of the application, it is often advisable to use such a microscope.

However, for applications that require specific tweaks and customization, this blog outlines ideas for building an affordable customized microscope for monitoring droplet generation in a microfluidic format.

A standard microscope is not ideal or appropriate due to the space required to position the microfluidic device along with all its required interfaces and connectors. There are application-specific microscopes available commercially, however, adapting them to microfluidic purposes may require customization and additional fixtures.

Such microscope may require a different light source or fluidic fixtures, and the lenses may need to be replaced with large working distance objective lens to provide space for the microfluidic device and its accessories on top of, or under the lens.

Listing the requirements

As the first step in the design process, it is important to identify your requirements. These will serve as a guide to designing and building a microscope that will be appropriate for your application.

Our goal for this blog is to design and build a microscope to monitor droplet generation. Monitoring the droplets as they flow through the microfluidic channels is important for quality control purposes. Viewing the droplets will enable the operator to adjust parameters such as the flow rate, throughput, and size of the droplets.

The microfluidic cartridge requires a channel depth of 50 um and width of 100 um and requires 20 um orifices. The viewing area must be approximately 1 cm x 1.5 cm with a working distance from the lens to the cartridge of at least 50 mm. A bright field lighting using an LED is a good solution.

The system must have an easy-focusing feature and the ability to digitally zoom “in” and “out”. There must be a monitor that can be attached to the camera via HDMI. The microscope must incorporate an actuation system for fluidic flow and must be portable for desktop use.

Lastly, the overall cost must be less than US $2500 including the enclosure and optical sub-system.

Identifying critical components

A sketch of system architecture includes the following:

(1) an enclosure with a top cover to protect the cartridge from contamination and to mount the light to illuminate the cartridge from the top, and a bottom enclosure to house the other major components,

(2) a camera that is able to capture and save high-resolution images and video that can be displayed on the monitor,

(3) an optical sub-system that includes an objective lens, filter, and a vertical translation stage for focusing the cartridge channel,

(4) peristaltic pumps with a controller to flow the fluids from an external reservoir to the channel,

(5) a light source for illuminating the droplets inside the channel as they are being generated,

(6) an HDMI or USB connector for image display,

(7) a clamping device to position and align the cartridge to the viewing area,  and lastly,

(8) a 12 V DC source to power the entire system.

The critical components for this build are (a) the camera and optical paths, (b) fluidic actuation, and (c) the enclosure to house the components with a user interface.

Maintaining the build cost to target

The goal is to make the cost as low as possible while attaining the maximum functionality for our intended use.

Overall cost is the limiting factor. For the build, only parts necessary to run the functions of the microscope were used. Another important consideration was availability of the selected parts in terms of lead time, as well as shipping, duties, and taxes, which could significantly increase the cost.

Below is a list of the parts and components, their specifications, and their costs.

Parts	Specifications	Cost (USD)
1.        Enclosure	Acrylic ½ Inch and 6mm thick Laser cut per CAD design	155
2.        Camera	4K camera @60fps, 12MP  1” Sony CMOS IMX sensor, Pixel size: 1.55 x 1.55um	900
3.        Optical path and lenses	A compact lens, 145 mm with an objective lens Attachment, manual focus WD=86mm	650
4.        Fluid pumps	0-50 mL/min Low flow peristaltic pump, 12 Vdc Low noise: 55 dB	105
5.        Light source	RGB LED multicolored 2500-9000K dimmable with diffuser	30
6.        Vertical stage	Small X translation stage for focusing	220
7.        HDMI or USB connectors	Connector for monitor and LED lights.	25
8.        Clamping device	Screw clamp for microfluidic cartridge	10
9.        Power supply	12 Vdc 3A, 90-240 Vac	70
10.     Monitor	15.6-inch LCD IPS monitor High Resolution1080p FHD	160
11.     Other parts	PWM controller, plugs, outlets and tubing	110
	Total Cost	US $2,435

Evaluating image quality

The completed microscope was evaluated based on output image quality and performance. The first test conducted was to evaluate the optical system’s ability to focus on the cartridge channel and produce an acceptable image of the droplets as they are being generated. Light settings were adjusted to optimize the image quality.

The second test is the integration of a fluidic flow to the channel to generate droplets. Using different flow rates, the captured video of the droplets flowing inside the channel were of good quality.

Lastly, a simple test for reliability was done. The custom-built microfluidic microscope was allowed to run for 48 hours continuously while regularly checking the image quality over time. There are some imperfections and limitations on the output quality, but as per the intended application and budget, the build worked perfectly!