Multifunctional Hybrid Fe₂O₃-Au Nanoparticles for Efficient Plasmonic Heating

The overall goal of this research study is to investigate the properties of a new class of multifunctional iron oxide gold nanoparticles produced by a wet chemical approach, and show how they can efficiently transduce light to heat through plasmonic effects. One way to reduce the costs associated with noble metal nanoparticles for industrial applications is to create cheaper alternatives that have the same properties at a fraction of the cost. For example, the iron oxide gold nanoparticles can photothermally heat aqueous solutions as efficiently as pure gold nanoparticles, while retaining the original properties of the latter.

Due to their low cost and unique properties, our nanoparticles can be used for such applications as AnaLight photothermal manipulation, biomedical imaging and sensing, analytic processing, and magnetic sensing. To begin this procedure, prepare a 25 milliMolar stock solution of iron oxide in deionized water. Add 10 milliliters of deionized water and a stir bar to a 25 milliliter conical flask.

After placing the flask on a heating block, add 100 microliters of the iron oxide stock solution, and heat the mixture while stirring for approximately five minutes. Next, prepare 10 milliliters of a 1%sodium citrate solution by dissolving 0.1 grams of sodium citrate in 10 milliliters of water. Add 1 milliliter of the 1%sodium citrate solution to the flask containing the iron oxide solution.

After heating the solution to 100 degrees Celsius, add 250 microliters of 0.01 Molar chloroauric acid to the flask. Continue heating the solution at 100 degrees for 10 minutes. Then, remove the solution from the heating block and allow it to cool to room temperature for one to two hours.

Following this, purify the samples by centrifugation for seven minutes at 4, 700 x g. When finished, remove the supernatant from the samples. Then, redisburse the nanoparticles in up to one milliliter of deionized water.

To characterize the nanoparticles, place three milliliters of the reddish-brown aqueous solution in a methacrylate cuvette. Place a commercially purchased magnet in close proximity to the cuvette. At this point, turn on the laser power supply and balance.

Position the balance windows so they do not obstruct the laser path or block the IR thermocouples. After removing the protective covers from the IR thermocouples, open the data collection software program, click on Run, and name the measurement, Warm Up.While the system is warming up, in a hood, prepare the sample by pipetting the appropriate amount of the desired solution into a methacrylate cuvette. Adjust the laser power to the lowest setting that produces a barely visible beam.

Check to make sure that the laser beam spot is unobstructed, and remains at the focal point of the IR thermocouple. Following this, place the sample on the balance arm, such that the side of the cuvette is perpendicular to the IR measurement beam of the thermocouple, and the laser beam spot strikes the center of the solution. Reduce the laser power until the beam is no longer visible.

Once the warm up is complete, stop the measurement program and exit out of the software. After rezeroing the balance and opening the data collection software program, click, Run, and create a name for the data file. Start the data collection by clicking, Save.

After 120 seconds of data collection, turn up the laser power to the desired setting. Following data collection for another 1000 seconds, adjust the laser power to the minimum setting and turn off the laser power supply. Once the experiment is complete, exit out of the program.

After turning everything off and recovering all of the equipment, save the experimental data in an ascii format for further processing. SEM analysis reveals the morphology of the iron oxide gold nanoparticles, showing aggregates of rounded irregular iron oxide particles that appear functionalized with smaller, bright, and rounded gold nanoparticles. A distinct absorbance peak in the UV-Vis-NIR spectrum of the hybrid nanoparticles is observed at 520 nanometers, and is attributed to the LSPR mode of the gold nanoparticles, functionalizing the iron oxide.

The UV-Vis absorbance spectra of the reaction solution shows some initial slight visible light absorbance, attributed to the iron oxide nanoparticles dispersed in the solution. As the reaction proceeds, a peak forms at 1.5 minutes, which corresponds with the gold nanoparticle formation and deposition on the iron oxide surface. Photothermal heating measurements of the iron oxide gold and gold nanoparticles exhibit an almost identical temperature profile, with temperatures increasing by more than 40 degrees Celsius.

The deionized water experiment shows no change, which demonstrates that the temperature rise in the nanoparticles solutions is solely due to the dissipation of absorbed electromagnetic energy in the nanoparticles. The change in the mass for the nanoparticles solution is much greater than the background evaporation rate, indicating sufficiently high surface temperatures to generate steam at a significant rate. Once mastered, this technique can be done in two hours if it is performed properly.

While attempting this procedure, it is important to use clean laboratory glassware in order to ensure reproducible results. Following this procedure, other methods like electron microscopy, UV-Vis, and DLS can be performed in order to determine if any laser induced damages occurred. Take appropriate precautions when working with open laser beams, such as aligning the system with minimum laser powers, checking foreign blocking stray reflections, and closing the laser whenever possible, and wearing appropriate laser safety glasses when necessary.

After watching this video, you should have a good understanding of how to produce cheap nanoparticles in large quantities, and how to generate targeted heat wirelessly and on-demand for real world applications.