As the main head of signal recorder, 2D plasmonic nano structure has been fabricated by nano imprint lithography onto the Kapton substrate as follows. First, a CCD was extracted and separated from a camera. Then, a layer of the Kapton tape was placed onto the CCD by applying pressure. In the next stage, the sample was placed on the heater at 750C for 30 minutes. The sample was maintained under pressure at the room temperature for one week to stabilize the two-dimensional pattern onto the Kapton tape. Then, the Kapton tape was carefully removed from the CCD after one week, and a 2D flexible structure with very low thickness was achieved. Finally, a thin layer of gold with a thickness of 35 nm was deposited on the 2D Kapton substrate. Accordingly, a 2D flexible and very thin plasmonic crystal consisting of Kapton-Au was produced.
After characterizing surface by scanning electron microscopy (SEM) and recording surface lattice resonance (SLR) of the sample in the visible region, microchip pickup head of conventional DVD-ROM was used (Fig. 1a). The head consisted of a semiconductor laser diode, 680 nm, with 5 mW power, a lens for focusing the laser beam, and photodiodes for detecting the light reflected from the 2D plasmonic surfacewhich put onto the fixed toad, and three immature Eurasian green toads (weight 50–70 grams) on the optical set-up (Fig. 1b). Finally, the reflected signals from toads were collected by digital oscilloscope.
As shown, the sample at SLR wavelength has more sensitivity and can distinguish and follow the input signal more in PQR region of the hart signal instead of other areas. There is the dependency of the reflections under p- and s-polarized incident light on the frequency and current from two-dimensional plasmonic sample, which comes from the charge redistribution at the interface influencing the plasmonic resonance, especially SLR of the main head sample.
During the second step, continuous 532 nm laser irradiation fixed at the distance of 5 cm from the top of the toad onto main head was used to trace thermoplsmonic effect onto heart signals. First, the toad heart area was illuminated just by laser, and then plasmonic substrate was added to the heart area to determine the different effects of Au nano-rods heating and laser radiation. Regarding the required time for increasing the temperature, the heart area was irradiated for more than 5 minutes (Fig. 1b).
As shown, the microchip was placed on the top of the toad heart after fixing the green laser. The arrangement should be in such a way that the green laser can hit only the two-dimensional sample on the toad heart without damaging the microchip. In this experiment, the temperature was measured by a thermocouple (TM-916, LUTRON electronic enterprise co, Taiwan). All of the tests were performed under the same conditions at a laboratory temperature of about 23°C. After time and local heating, the microchip was turned on and the toad heart signal was measured after heating. Thus, the use of anesthetics such as ether or chloroform interferes with the normal heart rhythm and heart rate of the toad . Thus, no anesthetic was used in this experiment.
When we shine a 532 nm pump laser at three different powers (10, 60, and 100 MW) over time, a layer of gold particles heats up on the sample, and transfers heat to the toad skin and the underlying tissue. To confirm the assumption, the sample was simulated in a commercial finite element method (FEM) solver, COMSOL Multiphysics 5.2 to approve the warming of the toad skin, which transfers to the tissue.
To simulate surface lattice resonance (SLR) of the sample, Wave Optics Module and the Electromagnetic Waves, and Frequency Domain interface were used. In addition, a plane TE-polarized electromagnetic wave propagation was modeled in a single unit cell of a gold layer on a Kapton substrate. Based on the electron microscope images, the thickness of the Kapton and gold layer were considered as 6 micrometers and 35 nm, respectively.
All methods were carried out in accordance with relevant guidelines.
All experimental procedures were performed in accordance with guidelines and regulations approved by a regional Institutional Animal Care and Use Ethics Committee of the "Ethical committee of Vice president of research of Shahid Beheshti university/IR.SBU.REC.1405".