Begin by preparing vertically aligned carbon nano fibers, or VACNFs. To transfer the VACNFs to a flexible substrate, first place the individual chips in acetone to separate the flexible substrate from the rigid substrate. Then, wash SU-8 films with IPA for five minutes, followed by washing with water for five minutes.
Place the chips in a commercial box with a sticky pad when transporting them. Prepare a silicone rubber PET holder by mixing the elaststomer and the crosslinker from a two-part kit. Cut out a square of PET and tape it down in a clear plastic dish.
Then, pour a very thin film of silicone rubber on top of the PET and cure it at 80 degrees Celsius for one to two hours. Transfer the SU-8 film to the PET holder using a pair of tweezers, and place the fiberless side of the SU-8 film on the silicone rubber. Press on the edges of the SU-8 square to help it stick to the silicone rubber PET and avoid breaking off fibers.
Then, place a one microliter droplet of dye onto the fiber side of the SU-8 film and let it dry for 10 minutes. After drying, place the VACNF film onto the plant surface using a pair of sharp tweezers. Then, gently roll a small makeup applicator over the VACNF film.
Mark the areas where the flexible substrates are placed with a soft tipped marker. Then remove the flexible substrates from the plant surface using tape. Repeat VACNF application for controls, such as placing dye on the fiberless side of a film, using the film without dye, and using the fiberless side of a film.
The on-chip method was used to deliver fluorescein dye to curved surfaces, such as strawberries, in which a strong fluorescein signal was observed immediately. Whereas in apples, a strong fluorescein signal was seen after two hours of delivery. Similarly, delivery of a plasmid containing yellow fluorescent protein was achieved in apples.
Also, a successful transient transformation of onions was done by delivering the plasmid containing yellow fluorescent protein using VACNF films.
