Figure 3: Our device from top.

As seen in figure 3, the basic setup is fairly simple. Light from an LED enters a lens to obtain a parallel light beam. To achieve this, the distance from the LED to the lens should be close to one focal length. Next, the light hits the iRIf slide where it is reflected (under the same angle as it hits the slide) and enters a second lens that projects an image of the slide onto the CCD chip of the camera.

To rebuild our iRIf device, we used the following parts:

Part	Description	Manufacturer / Part name	Price[USD]
A fairly strong LED	In our case a 3W green 520 nm LED	Cree XP-E on star circuit board	10
A cooling element	Used to prevent the LED from overheating	Fischer Elektronik ICK S	9
A constant-current-source	To ensure static LED light (no flickering)	Roschwege GmbH KSQ-3W	15
An AC/DC rectifier	Used to grant direct current to the LED	Goobay 67951	16
Two optical lenses	Here we used two identical 60 mm lenses	Thorlabs AC254-060-A	160
A camera	We used a SLR camera	Canon 550D	200-400
A microfluidics chamber	Our chamber consists of an iRIf slide attached to a PDMS flow cell	Made ourselves
Magnets	Used to attach the flow cell to the device	5 mm Neodymium magnets	3
A small syringe	We used a regular 10 ml syringe	BRAUN INJEKT 10 ml	< 1
A microfluidic tube	Used to connect the flow chamber with the syringe	-	< 1
A case for the device	5 mm thick acrylic glass cutouts to hold the parts in place	Ordered at http://formulor.com	100

Figure 3: (A) The LED glued to the cooling element with thermal adhesive; (B) The 10 magnets, each 5x5x5 mm as well as a PDMS flow chamber (depth of the flow chamber: 30 µm); (C) One of the lenses used in the setup

A major problem that we encountered when building the device from scratch was to ensure that all components are at the proper distance and angle to each other. Correct alignment is crucial as a slight misplacement of a component may lead to lower signal strength, blurred images or, in the worst case, no signal at all. This can be difficult since our device does not rely on straight angles. We overcame this challenge by designing a case for the device that ensures the right placement of the components inside the device. We calculated all distances between the LED, lenses, camera and slide using the laws of geometrical optics and drew a vector graphic blueprint for our device. Next, we constructed a digital 3D model of the casing based on the vector blueprint to avoid an expensive and time-consuming trial and error process (figure 4).

Figure 4: 3D model of our device, built from the vector files used to order the parts.

Figure 5: The 3D model of our device without walls and top part. Parts have been colorized for clarification - Green: The wall where light exits the device and enters the camera; Pink: a platform holding the cooling element and LED in place; Blue: platforms for holding the lenses in place; Gray: rear end wall where the flow chamber is attached to. The slits in the top and bottom part where the magnets need to be attached.

The casing is designed to keep all the necessary parts (lenses, LED) safely in place during a measurement, but allows them to be removed to facilitate transportation of the device (i.e. to the Giant Jamboree). Figure 5 illustrates the parts that hold the lenses and LED in place.

Subsequently to the setup of the 3D model of our device, we created a vector graphic of all required parts in a 2D plane. Using this vector graphic, we ordered the parts at Formulor, a service which uses laser cutting to cut out parts from acrylic glass and other materials. The cutting laser is guided by the paths defined in the vector graphic template. The template is shown in figure 6, and may be downloaded and used by everyone for building their own device. To allow easy mounting of the casing, we also provide an easy to understand manual. One advantage of acrylic glass is that the parts can be glued together easily using a few drops of acetone. The vector graphic also contains a template for the parts which are necessary to attach the glass and PDMS slide to the device. They should be cut from 1 mm thick acrylic glass. The microfluidic tubes can be glued to these parts (figure 7) and attached to the device with the magnets (figure 8)

Figure 6: An image of the vector file used to order the parts. The vector file is used to excise parts of a 5 mm acrylic glass board with a laser. Black lines are cut out by the laser, gray lines/areas are engravings. Refer to the download section to downloaded the vector graphic files.

The most difficult part to build is the PDMS flow chamber since it requires a microstructured silicon wafer, which can only be produced in a cleanroom environment. The template used for our PDMS flow cell is shown in figure 9. If your facility has an engineering department, there is a high chance that a cleanroom is present. Ask the personnel in charge if they can help you out with producing your flow cell. If you already use another type of microfluidic flow chamber, our device should still be compatible with it, though some adaptions might be necessary. If you have no possibility of creating a flow chamber, you might want to consider building a very simplified DIY flow chambers from two glass slides, separated by thin tape. Note that our device was not primarily build to support such a chamber and would need appropriate modifications.

Figure 7 - left: a flow chamber consisting of an iRIf slide attached to a PDMS (red) flow cell - center: a syringe attached to a pipette tip, used to inject antibody solutions into the flow chamber - right: the part of our device which connects the flow chamber, the syringe and the iRIf device.

Figure 8: The device with and without the mounted flow chamber.

Figure 9: Layout used to produce the wafer of our PDMS flow cell.

Download section

Click on the image to download a manual which will show you how to mount the casing of the device.

• Blueprint of the casing for cutting out your own parts - SVG
• Blueprint of the casing for cutting out your own parts - Adobe Illustrator
• PDF manual showing how to build your own device

Legal notice

The iRIf detection method is patented. Biametrics and associated persons own patents concerning the detection principle. These patents are:

• Method for examining physical, chemical and biochemical interactions (DE102004051098.9, DE102005015030.6, EP05797776.1)


• Study of molecular interactions on and / or in thin layers (DE102007038797.2)


• Method and apparatus for determining reflection coefficients to filter arrangement with thin layers (DE102009019711.7)


• Again Detectable support for optical measuring methods (DE102009019476.2)