The presented plasma source was developed for biomedical applications. It has been optimized for the best bactericidal effect and has been tested on a wide range of microorganisms, including microfungi, yeasts, gram-positive and gram-negative bacteria. The bactericidal and physical characteristics of the NTP source are presented in our article [Sci. Rep. 14, 15930 (2024)]. The plasma source can be also used in other applications, but optimizing it can be useful to achieve the best effect in a particular application.
The use of the NTP source is allowed for research and individual purposes. However, using the information provided here for commercial purposes without obtaining written permission from the authors is prohibited. Please note that the NTP source has parts that are under high voltage, which poses a danger to life. Do not attempt to make a NTP source without experience in working with high voltage. We are not responsible for your actions, your health and the safety of your equipment. When using the NTP source or any information provided here for scientific research, please don't forget to cite our article: M. Klenivskyi, J. Khun, L. Thonová, E. Vaňková, and V. Scholtz. Portable and affordable cold air plasma source with optimized bactericidal effect. Sci. Rep. 14, 15930 (2024).
List of required parts for the NTP source:
- High-voltage power supply. Can be purchased here: link1, link2, link3.
- 12 V (1 A) power supply with a 2.1×5.5 mm coaxial power connector (barrel connector).
- 3D-printed case of the NTP source (*.stl files to generate G-code for loading into a 3D printer can be downloaded from here: link).
- Self-locking button with LED backlight. Can be purchased here: link.
- 2.1×5.5 mm male coaxial power connector (barrel connector). Can be purchased here: link.
- Resistor from 2 to 5 kΩ (0.125 W).
- Rifle cartridge case (7.62×51 mm NATO or .308 Winchester).
- Intramuscular injection needle (0.6×25 mm).
- Metal mesh made of thin wire with a diameter of approximately 0.2 mm. One can take a protective mesh, which is used as covers on frying pans to prevent grease splashes.
After printing, you should end up with five parts, as shown in the following picture.
The circuit diagram of the NTP source is shown schematically in the picture below. Do not turn on a HV power supply without a load, i.e. without a properly configured electrode system, as the HV power supply can be easily damaged.
Take a button and remove the nut. Take a resistor, bend one of its leads 180°, trim the longer lead to have them the same, and solder the cut lead to the button pin marked “+”. Leave the other lead of the resistor unsoldered, but ready to be soldered to the pin 1 of the button. Take two insulated thin pieces of wire: black and red. Solder the black wire to the button pin marked “–” and the red wire to the pin 2 of the button, as shown in the following picture.
Take a HV power supply and cut out the side of its case right down to the compound. Do not leave sharp edges after cutting. For details, including a description of the high voltage power supply, see the picture below.
Put the HV power supply inside the part 3 and the low-voltage (thin) red wire from the HV power supply through the hole for a button in the part 3 and solder the red wire to the pin 1 of the button along with the other unsoldered lead of the resistor.
Using tweezers, pass the low-voltage (thin) black wire from the HV power supply and the free two wires from the button through the connector hole on the side of the part 3. Take a 2.1×5.5 mm male coaxial power connector (barrel connector) and remove its plastic housing. Solder the black wires to the negative (outer) terminal of the power connector and the red wire to the positive (inner) terminal of the connector.
Position properly the HV power supply inside the part 3 and glue the accessible leg. Insert a piece of foam between the HV power supply and the part 3 to secure the HV power supply. Apply some glue to the button and power connector and push them into their places. Let the glue dry.
Take the part4 and pass the free ends of the HV wires of the HV power supply through the holes in the part 4. Insert the part 4 into the part 3, gradually pulling out the HV wires. Glue the part 4.
Take the part 1 and carefully remove the support material. Drill a hole with a diameter of 0.6 mm for the needle electrode (there is a small mark at the top of the part 1 for the correct placement of the needle).
Making a needle electrode. Take an intramuscular injection needle and trim it so that its length is ~25 mm. Make a small hook at the blunt end of the needle. Make sure the hook you make is small and the length of the needle from the hook is at least 18 mm.
Trim approximately 7 cm of the HV (thick) black wire from the HV power supply. At one end of this piece of wire, remove 1-1.5 cm of insulation, wrap the stripped wire tightly around the needle hook and solder.
To make a cone electrode, take a rifle cartridge case and cut off 2 mm from the top by using for example a lathe. Then cut the cartridge case just (~1 mm) above the fold as shown in the picture. Remove all burrs and sharp edges on the cone electrode using a fine round file.
Solder the red HV wire from the HV power supply to the cone electrode.
Connect the part 2 with the part 3 and glue them.
Insert the cone electrode into the hole in the part 1 and glue it, for example, with hot-melt adhesive.
By a twisting motion, carefully insert the needle into the hole at the top of the part 1 so as not to bend the needle. Check if there is plastic on the tip of the needle. Remove plastic from the tip of the needle, if any. Place a small, flat piece of paper on the cone electrode and insert the needle deeper until it touches the paper. Carefully remove the paper. Make sure that the needle is not bent and its tip is on the axis of the cone electrode. Cover the hook of the needle sticking out of the part 1 with hot-melt adhesive. Make sure that the needle, contact and stripped end of the black HV wire are covered by a thick layer of adhesive.
Position and fix the NTP source so that the trimmer of the HV power supply is accessible. Connect a microammeter in series to the HV circuit. The common terminal of the microammeter should be connected to the black HV wire coming from the power supply and the positive terminal of the microammeter should be connected to the wire coming from the needle electrode. Be extremely careful as there will be high voltage on the electrodes after the next step. Plug the 12 V power supply to the mains and power connector on the NTP source. Press the button on the NTP source. If everything is done correctly, the button should light up and the HV power supply should “squeak”. Note that the discharge is not visible under room lighting. Using a screwdriver, turn the trimmer on the HV power supply until the current in the HV circuit is (200±5) μA. Note that it may take several full turns of the trimmer, during which the current will increase and decrease several times.
For the next step, you need the room to be dark. In complete darkness, make sure that the discharge is uniform. If not, turn off the NTP source and carefully bend the needle to the desired direction. Do not touch the tip of the needle as it is easily deformed. After adjusting the needle, the current in the HV circuit may change. Set it to (200±5) μA.
Disconnect the microammeter. Place two heat-shrink tubes onto the black HV wire coming from the power supply and solder it with the wire coming from the needle electrode. Slide one heat-shrink tube over the soldered contact and let it shrink by heating it. After that, do the same with the other heat-shrink tube.
Carefully place the HV wires inside the part 2 (rotating the part 1 relative to the part 2 can help with wire placement). Connect and glue the part 1 with the part 2.
Close the hole on the part 3 by gluing the part 5.
Take the metal mesh. Cut out a circle with a diameter of 27 mm. Glue the mesh to the output of the NTP source. Once dry, the NTP source is ready for use.
Feel free to contact us if you have questions or experience difficulties with making the NTP source. We are open to proposals for cooperation and, as part of cooperation, we can provide you with an NTP source. Questions and proposals can be directed to Dr. Khun (e-mail) or Dr. Klenivskyi (e-mail).