Fabrication and Testing of Miniature Automatic Photophoretic Trapping Rigs

This protocol allows almost anyone to take part in the research process. This method democratizes cutting-edge research in a way that hasn't been done before. The photophoretic trapping test rig is inexpensive and can be easily fabricated unlike many other rigs used for photophoretic trapping.

The instructions are written so that anyone can be involved with this technology. Our protocol is focused on the creation of our test rigs. Some previous knowledge of optics or fabrication tools may help, but is not necessary.

Begin the setup of wooden rigs by placing the base piece down with the Y emblem facing up, then hold the two long side pieces on either side of the base while the first laser holder is slid into place on one end and the first test tube holder on the other end. Put two electromagnet holders onto the camera holder ensuring that the magnet holders are separated by one centimeter on each side, then insert the magnet holders and the camera holder as a unit next to the first test tube holder spaced at one centimeter. Next, place the second test tube holder after the electromagnet holders, so that there is one centimeter space between the second test tube holder and the second electromagnet holder.

If using the optional light shield or blocker, slide the light shield onto the opposite side from the camera holder. Slide the second laser holder into place at the desired distance depending on the length of the laser. An optical rail can be placed under all the holders to align other elements of the trapping system.

The placement will help align the lens with the laser and test tube. Then place the electromagnet into the electromagnet holders. Build the electromagnet controlling circuit using a voltage regulator, a breadboard, and a few wires.

To do so, place the voltage regulator in the breadboard so that each pin is in a different row and wire the input pin of the voltage regulator to one of the five volt power pins on the microcontroller board. Wire the adjusted pin of the voltage regulator to the general purpose input and output or GPIO23 on the microcontroller board. Next, connect the input wire of the electromagnet to the output pin of the voltage regulator and the output wire of the electromagnet to a ground pin on the microcontroller.

For the test preparations, place the lens inside the lens holder with the help of hot glue. Once done, place the lens holder on the optical rail and the laser in the laser holder. Next, use the lens and the laser to find the focal point of the laser and slide the lens holder along the optical rail until the focal point is centered over the electromagnet.

Mark the focal point on the wooden base with a pencil. To prepare the trapping site, ensure that the laser is properly turned off, then use a hot glue gun to glue a small button magnet of the same polarity as the electromagnet onto the flat surface of the platform so that the electromagnet will repel the platform. Coat a 3D printed cantilever-like platform in black aluminum foil to protect the platform from melting.

After coating, place the selected particle type on the slanted side of the platform for testing, then insert the cantilever arms into the circular holder with the magnet side facing out and insert the test tube into the same circular holder. When done correctly, the magnet will almost be touching the glass. Place the test tube onto the tube holder to center the platform over the electromagnet.

The cantilever should appear to be in an upward position repelled by the electromagnet. Complete the setup by placing the camera in the camera holder to capture and observe any traps above or around the platform. After double checking all the positionings, begin the test by pressing Start in the developing environment or start the file normally from the terminal.

If using the alternative code option, start the test with the terminal command from the proper directory. When running from the terminal, the command should include the number of tests and the parameter that the test is focused on. A test of 10 different particles was conducted to find the particle with the best trapping rate.

It was found the diamond nanoparticles and printer toner were the two best particle types. A second particle type test was conducted with a camera detection system and the best four of the original 10 particles were tested. The diamond nanoparticles were still the best, but did have a slightly lower trapping rate than before.

The rate of trapping for different laser power levels was measured during the laser power test. It was observed that a high optical power output corresponded with a higher rate of trapping. The laser at full power had the highest recorded trapping rate for this test.

The most important thing to remember throughout the protocol is safety, particularly laser safety. Proper laser safety guidelines must be followed. This procedure makes it easy to change small variables.

We tested laser power and particle type, but any other variables like lens type could easily be changed. The researchers can implement their version of the technique for academic and educational purposes. It enables people to do rapid meaningful research.