Gold Nanorods/Nanoparticles: Mechanisms, Application and Toxicity Casey Karler, George Ryan, Kirsten Sochinski

Introduction: Materials Science Background Materials science is a rapidly-growing field of science in today’s industry In the journey to find remedies for complicated diseases like cancer, materials science can offer potential solutions via nanoparticles In addition to medicine, nanoparticles are promising for applications in other areas like catalysis, energetics, and electronics As with any emerging technology, there are drawbacks, and this includes biological toxicity for some nanoparticles This presentation will cover the chemical mechanisms of gold nanoparticles, biological applications, and potential toxicity in the context of medicinal use https://xstrahl.com/xstrahl-in-action-gold-nanoparticles-as-dose-enhancement-agent-for-x-ray-therapy-of-melanomas/

Background: Materials Science Nanoparticles are small particles less than 1 micrometer in size, that are often composed of multiple layers of atoms/compounds Nanoparticle crystal structures often display altered or better optical properties than the normal material, due to better energy transfer and more consistency Nanorods, specifically, can transmit different visible light wavelengths depending on their aspect ratio (length and width) https://doi.org/10.1073/pnas.0705326104

Background: Materials Synthesis Gold nanorods can often be easily synthesized with a low cost of reactants and high precision They can be created through certain reactant ligands (CTAB) binding the sides of the growing structure with more strength This forces additional gold particles to grow on both ends instead of the sides, creating rods Rod shape/size can be tuned by changing reaction conditions (reactant concentrations, temperature, stirring, time) Surfactants (soap like molecules) such as CTAB are essential for the synthesis of uniform nanorods https://doi.org/10.1016/j.actamat.2014.12.002

Common gold nanoparticle morphologies Gold nanorods Faceted gold nanoparticles Gold nanostars Gold nanocubes https://www.sigmaaldrich.com/catalog/product/aldrich/716820?lang=en&region=US http://www.cytodiagnostics.com/store/pc/100nm-Standard-Gold-Nanoparticles-100ml-p1027.htm http://stacks.iop.org/Nano/23/465602 http://nanoseedz.com/product/au-nanocubes/

Significance: Gold nanorods Different shapes of rods transmit different specific wavelengths of visible light, which is useful for many unique applications The images to the right demonstrate how the nanorod length determines the transmitted colors This is important because some applications require specific optical properties Longer rods = more red color https://doi.org/10.1364/PRJ.1.000028 https://doi.org/10.1016/j.jare.2010.02.002

Biological Applications: Nanoparticle Shapes Nanoparticles of a specific size or shape can be used for many applications in fields of medicine, including near infrared imaging (NIR) Various gold nanoparticle shapes can be intravenously injected for cancer therapies, such as: Nanospheres: for tumour imaging (enhanced radiative property; NIR), Photothermal therapy (enhanced radiative property; NIR) and drug therapy in cancers such as: Ovarian carcinoma Nanorods: for cell imaging (visible lights), photothermal therapy and drug therapy in cancers such as: Adenocarcinoma, breast cancer and melanoma Nanoshells: for tumour imaging (enhanced radiative property; NIR), Photothermal therapy (enhanced radiative property; NIR), drug therapy and photodynamic therapy in cancers such as: Liver cancer and Glioblastoma https://doi.org/10.2147/IJN.S140772

Biological Applications: Cancer Therapy Gold nanoparticles have been shown to be effective in cancer therapies since they have theranostic properties Theranostics: When a material, such as a gold nanoparticle (AuNP) can be used for high resolution/contrast imaging for tumors while concurrently delivering therapeutic effects directly to the tumor cell Molecular imaging can be used to help visualize and characterize tumor cell types Therapeutic effects can involve direct tumor cell death through heat or actual nanoparticle-cell binding https://doi.org/10.1016/j.jconrel.2014.04.027 DOI: 10.4172/2329-9053.1000e113

Biological Applications: Cancer Therapy Types Photodynamic therapy: is a cancer treatment utilizing therapeutic agents with light and oxygen to kill cancer cells Photothermal therapy: when a therapeutic agent is excited by light to create heat that will subsequently kill the cancer cells When using thermal therapy, it is ideal to use therapeutic agent in the near-infrared (NIR) region for radiation to reduce that amount of heat that could potentially kill other normal cells Deep set tumors need very weak absorption properties to ensure that radiation therapy does not damage other vital organs (https://www.cancer.org/treatment/treatments-and-side- effects/treatment-types/photodynamic-therapy.html)

How do nanoparticles bind to the correct cells? In order for gold nanoparticles to reach the desired tumour cells, they are conjugated with antibodies that have an affinity for epidermal growth factor receptors (EGFR’s), since these are commonly found in cancer cells Utilization of antibodies helps guide researchers to tumour sites With certain wavelengths, detection of the tumour-antibody complex creates a vivid image of the tumour to use photothermal or photodynamic therapy to induce cell death Having accurate imaging with the use of antibodies ensures minimal use of photothermal therapy or photodynamic therapy https://doi.org/10.2147/IJN.S140772

Biological Applications: Gold Nanorods The cancer applications of particles such as gold nanorods are thought to extend further than their optical and energetic properties This is because of the fact that the aspect ratio (length and width) of nanorods can be tuned to very specific dimensions in the synthesis process A particle of the correct size can make its way into tumor orifices that have sizes unique to that tumor cell; this is one mechanism by which the particles can accumulate in tumors, rather than normal tissue types Particles that have accumulated in tumours can be used for tumour cell location or induced cell death via photodynamic/photothermal therapy

Toxicity concerns with gold nanorods used for cancer therapy Medicinal nanorods have significant potential for guidance and diagnoses of human diseases. However, the potential for adverse effects is a risk that still warrants further investigation While most gold nanorods have shown no adverse effects on their own, the CTAB (cetyltrimethylammonium bromide) needed to synthesize them has been investigated for its potentially toxic effects In efforts to reduce toxicity, researchers are looking to purify or reduce the toxicity of the free CTAB by coating the particles in polyelectrolyte shells, or by using free radicals. However, these methods are still being under development

How are gold nanorod toxicity levels measured? In vitro, there are various factors that need to be accounted for when it comes to cellular health; this process is similar to processes used for drug development screening criteria. LDH assay: looks at cellular damage by release of lactic acid MTT assay: looks for disruption of metabolic processes ROS assay: Looks for oxidative stress

The nano debate…. Although progress has been made in the area of biological nanoparticle research over the last couple decades, questions remain concerning the fundamental characteristics of nanorods and their interactions with biological environments Various experimental techniques have been implemented to determine if gold nanorods and their components are heavily toxic An MTT assay was used to determine that nanorods had no pertinent metabolic effects on the cell, nor did they cause any phenotypic changes Another study found that excess administration of nanorods at precisely 2nm in length will covalently interact with cell membranes which will then lead to apoptosis (similar to the interaction of PLA2 proteins from snake venom that we discussed in class) Researchers are currently working on

CTAB toxicity in cells Research pertaining to CTAB toxicity to cells is ongoing There are two theories that suggest why CTAB can induce cell death CTAB interacts with and destabilizes the phospholipid bilayer, resulting in apoptosis CTAB dissociates into a CTA+ ion, which will bind to ATP synthase. This results in energy depletion for the cell https://en.wikipedia.org/wiki/ATP_synthase

Gold nanorods in vivo Currently, tests to determine toxicity are being conducted pertaining to nanorods, and these tests are looking for toxicity to specific tissues The studied effects include nephrotoxicity, hepatotoxicity, immunogenic toxicity, oxidative stress, and hematological toxicity Another in vivo experiment looked into nanorod distribution throughout the body, as well as nanorod removal once they are no longer needed https://news.usc.edu/148242/nanoparticle-targets-kidney-disease-for-drug-delivery/

Conclusions Materials science and nanotechnology are rapidly emerging fields of science, and new synthesis methods are constantly being developed that yield uniform nanoparticles with very specific dimensions and properties Gold nanorods/nanoparticles are desired for their unique optical and energetic properties Particles like gold nanorods offer very real and promising solutions to a wide array of biological applications, in addition to their known other inorganic catalytic applications Gold nanorods appear to be ideal for applications in biological imaging, photodynamic therapy, and photothermal therapy Although gold nanorods are promising, potential toxicity of the rods themselves or reactants needed to synthesize them require further investigation

Works Cited Primary sources Guo, J., et. al. (2017). Gold nanoparticles enlighten the future of cancer theranostics. International Journal of Nanomedicine. (12) 6131- 6152. doi:10.2147/ijn.s140772 Perez-Juste, J., et. al. (2005). Gold nanorods: Synthesis, characterization and applications. Coordination Chemistry Reviews, 249(17- 18), 1870-1901. doi:10.1016/j.ccr.2005.01.030 Alkilany, A. M., & Murphy, C. J. (2010). Toxicity and cellular uptake of gold nanoparticles: What we have learned so far? Journal of Nanoparticle Research, 12(7), 2313-2333. doi:10.1007/s11051-010-9911-8 Au, L., et. al. (2009). Quantifying the Cellular Uptake of Antibody-Conjugated Au Nanocages by Two-Photon Microscopy and Inductively Coupled Plasma Mass Spectrometry. ACS Nano, 4(1), 35-42. doi:10.1021/nn901392m Huang, X., et. al. (2006). Cancer Cell Imaging and Photothermal Therapy in the Near-Infrared Region by Using Gold Nanorods. Journal of The American Chemical Society. 128 (6) 2115-2120. DOI: 10.1021/ja057254a Ryu, J., et. al. (2014). Theranostic nanoparticles for future personalized medicine. Science Direct. (190) 477-484. https://doi.org/10.1016/j.jconrel.2014.04.027

Works Cited Digital images, retrieved from: https://en.wikipedia.org/wiki/ATP_synthase https://xstrahl.com/xstrahl-in-action-gold-nanoparticles-as-dose-enhancement-agent-for-x-ray-therapy-of-melanomas/ https://doi.org/10.1073/pnas.0705326104 https://doi.org/10.1016/j.actamat.2014.12.002 https://www.sigmaaldrich.com/catalog/product/aldrich/716820?lang=en&region=US http://www.cytodiagnostics.com/store/pc/100nm-Standard-Gold-Nanoparticles-100ml-p1027.htm http://stacks.iop.org/Nano/23/465602 http://nanoseedz.com/product/au-nanocubes/ https://doi.org/10.1364/PRJ.1.000028 https://doi.org/10.1016/j.jare.2010.02.002 https://news.usc.edu/148242/nanoparticle-targets-kidney-disease-for-drug-delivery/