This method provides an original solution for cellular analysis, a field that is currently lacking suitable recording systems that are multiparametric, biocompatible, mechanically compliant, and finally low cost. With this method, it is possible to obtain sensing systems with different sensing capabilities, such as the ability to monitor both the electrical and the metabolic activity of cells using a single type of electronic organic device. Besides helping to reduce in vivo animal experimentation, in vitro multiparametric systems are an extremely promising tool in a variety of biomedical fields, such as personalized medicine, and studies on neurodegenerative diseases.
All in the high versatility of the organic charge, modulator field effect transistor, it is also possible to integrate other sensors, such as for example, sensors for the detection of volumes of different biomarkers. Cut 6 by 6 square centimeter pieces from a new 250 micrometer PET sheet, then, rinse the PET substrates with acetone, isopropyl alcohol, and deionized water. Dry them using streams and nitrogen, and store them in clean, plastic petri dishes.
For titanium deposition, pre-cleaned the substrates with plasma oxygen and place them on the substrate holder inside the backroom chamber of the thermal evaporator. Next, place 60 milligrams of titanium in the crucible, close the shutter, and pump down the evaporation chamber until it reaches 10 to the 6 tour. Increase the power of the evaporator until the crucible glows red and wait for 30 seconds.
Then, open the shutter, increase the power to 60%and wait for 60 seconds. After 60 seconds, close the shutter and turn down the power. For patterning, place one substrate at a time on the Spin Coater placed inside a fume hood.
Using a disposable plastic pipette, deposit four milliliters of photoresist on the substrate to obtain a two micrometer thick photoresist layer using the spin coating parameters mentioned in the text manuscript. Soft bake the photoresist by placing the substrate on a hot plate and then store the substrate inside an aluminum foil wrapped petri dish or a plastic container. Next, place the substrate in a brahma graph and position the plastic photolithographic mask, but the desired floating gate layout onto the substrate, expose the mask to UV light from the top for one minute.
Then carefully remove the mask, taking care to minimize the lateral movements of the mask over the substrate, plunge the substrate for 10 seconds in a glass container filled with the developing solution. Then quickly rinse it in deionized water, etched the exposed titanium by submerging it in the titanium etching solution for 15 seconds, then rinse with deionized water and dry using nitrogen. Optically, inspect the substrate and remove the photo resist using acetone.
Then rinse the substrate with isopropyl alcohol and deionized water and dry it with nitrogen. For gate dielectric deposition, place 300 milligrams of Parylene C dimer onto the parylene coater and set the pressure values. After the deposition, clean the substrates with acetone, isopropyl alcohol and deionized water and dry them with nitrogen as demonstrated previously.
After depositing the photo resist on the substrate as demonstrated previously, place the substrate in a Bromograph and position the plastic photolithographic mask onto the substrate for the bias under a stereoscopic microscope. After a one minute UV exposure from the top, carefully, remove the mask as demonstrated earlier. Develop the photo resist as demonstrated earlier, then expose the substrate with the patterned photo resist to oxygen plasma to remove the Parylene C from the sensing areas.
Place the substrates into a glass container filled with acetone inside the ultrasonic bath for 10 seconds to remove the photo resist completely, then rinse the substrates with acetone, isopropyl alcohol and water and dry them with nitrogen as demonstrated previously. After depositing the photo resist on the substrate, as demonstrated previously, place the substrate in a Burmograph and position onto the substrate a plastic photolithographic mask with simple black rectangles, that entirely covered the transistors areas. After a one minute exposure to UV light from the top and bottom carefully, remove the mask and develop the photo resist, as demonstrated earlier.
Clean the substrates with the gentle plasma treatment to promote the adhesion of the metal on the Parylene C then place them on the substrate holder inside the vacuum chamber of the thermal evaporator. Place 30 milligrams of gold in the crucible, close the shutter and pump down the evaporation chamber until it reaches 10 to the minus five Tor. Increase the power of the evaporator until the crucible glows red and wait for 30 seconds.
Open the shutter, increase the power to 40%and wait 60 seconds. Then close the shutter and turn down the power. Place the substrates into an acetone container inside the ultrasonic bath for 10 seconds to lift off the photo resist thus removing the gold from the transistors channel.
Rinse, dry and deposit the photo resist on the substrates as demonstrated earlier. After placing the substrate in a Bromograph, position onto the substrate a plastic photolithographic mask with the desired sources, drains and control gate layout. After a one minute UV exposure from the top, carefully remove the mask and develop the photo resist as demonstrated previously.
Etch the exposed gold by submerging it in the gold etching solution for 10 seconds, then rinse with deionized water and dry using nitrogen as demonstrated. After optically inspecting the substrate, remove the photo resist using acetone, rinse with isopropyl alcohol and deionized water and dry with nitrogen. After depositing the photo resist on the substrate, place, the substrate and a Bromograph in position onto the substrate a plastic photolithographic mask with openings corresponding to the pH sensing areas of the OCMFET.
After a one minute UV exposure from the top carefully remove the mask as demonstrated before. Develop the photo resist as demonstrated previously, then protect the whole device except for the pH sensing areas with polyimide insulation tape and deposit 500 nanometer layer of Parylene C on the substrate using the parameters mentioned in the text manuscript. After carefully removing the polyamide insulation tape, expose the substrate to oxygen plasma to activate the Parylene C on the pH sensing areas of the OCMFET's.
Then, place the substrates into an acetone container inside the ultrasonic bath for 10 seconds to completely remove the photo resist. Rinse the substrates with acetone and isopropyl alcohol and dry them with nitrogen. Place the substrates onto a hot plate at 50 degrees Celsius before casting a one microliter droplet of semiconductor solution onto each channel area.
Cover the whole substrate with the lid and dry it out under a chemical hood for 30 minutes. Cut out the device from the PET, either manually or using a laser cutter. A confluent culture of rat cardiomyocytes adhering to the surface of an MOA was immunostate for the sarcomeric protein tropomyosin.
An example of a single cardiomyocyte signal measured with an OCMFET is shown here. The device could detect both spontaneous cellular electrical activity and the activity induced upon the administration of different chemicals or drugs. Thanks to the array configuration of the MOA, it was to estimate the propagation velocity of the cardiac signal within the cellular culture.
The OCMFET was also able to amplify neuronal field potentials with remarkable stability and good signal to noise ratios. The different responses of a pH sensitive and pH insensitive channel of an MOA to chemical stimulation with bicuculline and tetrodotoxin demonstrated the ability of the device to discriminate between different cellular metabolic states. Carefully inspect the substrate before every step of the fabrication protocol.
This will increase dramatically the yield of the process. By using different functionalization methods, it is possible to obtain chemical and physical sensors that can be used in application like lab on a chip and robotic skin.
