Gold Nanorod-assisted Optical Stimulation of Neuronal Cells

This protocol outlines how to use the transient heating associated with the optical absorption of gold nanorods to stimulate differentiation and intracellular calcium activity in neuronal cells. These results potentially open up new applications in neural prostheses and fundamental studies in neuroscience.

The overall goal of this procedure is to stimulate neuronal cells cultured with gold nano rods using a near infrared laser diode. This is accomplished by first preparing the gold nanoparticles at the right optical density. The second step is to culture the neuronal cells and add the nanoparticles to them.

Next step is the laser irradiation. The final step is to verify cell differentiation through beta three to tubulin expression. Ultimately, confocal microscopy is used to show the intracellular calcium transience.

We first had the idea for this method when we are looking for a way to stimulate action potential in single neurons amongst a cell population. Demonstrating the procedure will be Jamie May and undergraduate students from our laboratory. To begin this procedure, place a vet of gold nano rod solution in the UV visible spectrophotometer.

Measure the initial optical density by recording the absorption values from 300 nanometers to 1000 nanometers with a resolution between 0.5 to two nanometers. Prepare a one milliliter stock solution by diluting the initial gold anoro sample to an optical density of one centrifuge. One milliliter of the gold nano rod solution twice to remove any chemical excess.

Then remove the supernatants and resuspend the gold nano rods in deionized water. To prepare for use in cell culture, sonicate the gold Anoro solution for five minutes, and then sterilize it with UV light for 30 minutes. In this procedure, prepare 500 milliliters of sterile dmem for the cell culture medium.

Next, grow the NG 1 0 8 15 neuronal cells in 10 milliliters of cell culture medium in a T 75 flask, subsequently incubated at 37 degrees Celsius and humidified atmosphere. When the cells are 70 to 80%confluent, change the medium with warm fresh medium. After that, mechanically detach the cells by gently knocking the bottom of the confluent flask.

Centrifuge a cell suspension for five minutes at 600 G and resuspend the cell palette in two milliliters of warm cell differentiation medium. Then see the cells in a 96 well plate with 200 microliters of cell differentiation medium. Incubate the sample for one day at 37 degrees Celsius.

The next day, add the gold nano rod solution and incubate it for an additional 24 hours. In this procedure, couple the laser with a single mode optical fiber and terminate it with an FC connector. Measure the output laser power with a standard power meter on day three of nano rod incubation.

Fix the FC connector to the well irradiate the sample and the control at room temperature for one minute in a continuous wave at different laser powers on day five, remove the cell differentiation medium from the sample and fix it with 3.7%volume per volume formaldehyde solution for 10 minutes. Then permeable the cells with 0.1%volume per volume Triton X 100 for 20 minutes. Afterward, add 3%weight per volume BSA to the sample for 60 minutes.

To block the unreactive protein binding sites, label the sample with anti beta three tubulin overnight at four degrees Celsius. The next day, incubate the cells for 90 minutes in the dark with an appropriate secondary antibody. Subsequently label the cell nuclei with DAP E for 10 minutes.

Then image the sample with epi fluorescence or confocal microscopy using at least a 20 x objective. Choose the microscope filters according to the secondary antibody and select a DAPI filter to visualize a cell nuclei. In this step, prepare a 20%weight per volume stock solution of onic F1 27 by dissolving two grams of solute in 10 milliliters of DMSO.

Heat the solution of onic F1 27 at 40 degrees Celsius for 20 minutes to increase the solubility. On day three of anaro incubation, prepare a balanced salt solution. Next, remove the cell differentiation medium and replace it with the BSS solution.

Supplemented with five micromolar of flu, 4:00 AM in DMSO and 0.1%weight per volume of onic F1 27 stock solution. Afterward, couple the laser with a single mode optical fiber and cleave the tip. Using standard technique.

Observe the resulting tip under an optical microscope to ensure that the tip is flat and perpendicular to the fiber axis. Then measure the output laser power with the standard power meter. Next, insert the light delivery fiber into an optical fiber holder and affix it to the micro positioner.

After that, connect an oscilloscope to the signal generator. To monitor the optical modulation. Use a binary signal with variable frequencies and pulse lengths.

Then connect the laser and use the modulation signal as TTL input for the microscope. Use an argon ion laser to excite the internalized flu oh 4:00 AM dye and the synchronized laser dde. For the excitation of the endocytose nano rods, place the cells under an inverted confocal microscope and position the light delivery fiber away from the target cell in transmission illumination mode.

Then calculate the beam radius at the target. Perform the imaging of the sample and control at room temperature using 40 x objective and collect the time series scans at 256 by 256 pixels per frame resolution in roundtrip mode. Then perform recording without any laser DIO excitation in order to identify any baseline argon ion laser interference shown here is an epi fluorescence image of the differentiated NG 1 0 8 15 roal cells cultured alone and irradiated with the laser power of 7.5 watts squared centimeter.

And this is an image of the cells cultured with gold nano rods irradiated with the laser power of 1.25 watts squared centimeters. Here is an example of the differentiated NG 1 0 8 15 neuronal cells loaded with flu oh 4:00 AM calcium indicator. The image was taken using an inverted confocal microscope with a 40 x oil immersion objective.

This figure shows the representative samples of laser induced calcium variations as a function of time. In NG 1 0 8 15, neuronal cells cultured in serum free conditions for three days with polystyrene sulfonate gold nano rods, gold nano rods, and without nano rods. F max over F zero indicates the increase of maximum fluorescence detected in NG 1 0 8 15 neuronal cells After its development.

This technique paved the way for future application in optica simulation of neuronal cells.