“I want to ingest nanogold as an experiment to see if it really does turn your brain into a hyper processor.”
– question submitted by a Sustainable Nano reader

As a chemist, I cringe at the thought of drinking nanoparticles (or anything) out of a beaker in lab. In fact, my knee-jerk response to your question was “DON’T DO IT!” However, a lot of nanoparticles are FDA approved and used for medical purposes, most of which are injected; some are also approved for ingestion as food additives.¹ There are also many more hopeful candidates for medical diagnostics and therapeutics in development, awaiting further testing and approval. It is important to recognize that drug development, with small molecules or nanoparticles, requires a lot of lengthy and costly benchmarks before any clinical trials with humans are attempted.^2,3

Using gold nanoparticles to create a microprocessor without specialized equipment seems like a large research project on its own, but what if we assumed that technical problem was solved? In this science fiction scenario, you would still run into the same challenges as many other scientists working with nanoparticles for medicinal applications. Creating a nanoparticle with certain desired properties may be easy at the benchtop where you control your nanoparticle’s environment, but within the complex milieu of the body everything gets more complicated. You need to make new considerations to keep your nanoparticle stable, get it to the right location in the body, and avoid unwanted side effects, all while maintaining its original function.

For now, let’s just consider getting nanoparticles to the brain. If they are ingested by eating or drinking, they will then need to get out of the digestive track and into the blood stream, and then somehow enter and stay in the brain. Gold nanoparticles are actually a good choice for ingesting, because they are hardy enough not to get degraded by stomach acid or the enzymes in your saliva. And they can potentially get into the bloodstream: studies with gold nanoparticles have indicated that they are primarily absorbed through the intestines and that smaller nanoparticles (4 nm) are more easily absorbed into the blood stream.⁴

Once the nanoparticles are in the blood, things might get trickier: the particles still have to get into the brain, but unlike other organs, the brain has a protective barrier called the blood-brain barrier. The blood-brain barrier is a membrane that only allows specific proteins and small molecules, such as oxygen and nutrients, to travel from blood vessels into the brain.⁵ This barrier is intended to prevent bacteria (and therefore infections) from entering the brain. Ordinarily, nanoparticles wouldn’t be allowed through the blood-brain barrier, but researchers have discovered several coatings that can be applied to the outside of nanoparticles and drugs which greatly increase uptake into the brain.⁶

But wait! Before you can celebrate getting your sci-fi microprocessor nanoparticles into the brain, you still need to consider unintended exposure of the nanoparticles to other organs. While the nanoparticles in the blood stream are being transported to the brain, they are also being exposed to every other organ in the body. Medical researchers are currently exploring a variety of methods to get around this problem so that  nanoparticles will only interact with the specific target tissue.⁷ However, targeting methods are not perfect and some untargeted organs will still take up nanoparticles. This is especially true for organs which are part of the body’s natural defense system, the immune system.

Even if your nanoparticles go exactly where they are supposed to go, eventually they will be removed by your body’s waste disposal system. If the nanoparticles are small enough (< 5nm) they will leave through the kidneys and urinary tract.⁸ This process is pretty quick – probably within days. If the nanoparticles are larger, they are typically removed through the liver and spleen, via bile (i.e. poop). Finally, it is likely that a small amount of the nanoparticles would get left behind by the waste disposal system and would linger in the body. Although gold nanoparticles are generally considered non-toxic, they do not easily break down in the body and there is concern that prolonged exposure (months) could cause damage to the liver or spleen.⁹

In conclusion, I do not recommend ingesting gold nanoparticles, even if you could make microprocessors out of them! Gold nanoparticles do have characteristics that make them a good choice for clinical studies, though. In fact, there are many ongoing studies of their medicinal applications, mostly focused on targeting cancer tissues. For example Aurimmune, a potential therapy for head and neck cancer. The potential side effects to organs with unintended nanoparticle uptake, such as the liver, kidneys, and spleen, still need to be understood before this new technology can be applied in the clinic.³

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EDUCATIONAL RESOURCES:

• Neuroscience for Kids: The Blood-Brain Barrier: “Keep Out”
• “Battling Cancer with Nanotechnology” Video from NISE Network. (Intended for ages 11-adult.)

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REFERENCES

1. U.S. Food & Drug Administration. Nanotechnology Fact Sheet, 2015.
2. Tufts Center for the Study of Drug Development. Cost to Develop and Win Marketing Approval for a New Drug is $2.6 Billion. 2014.
3. Pillai, G. Nanomedicines for Cancer Therapy: An update of FDA Approved and Those under Various Stages of Development. SOJ Pharmacy & Pharmaceutical Sciences, 2014. 1(2) 1-13.
4. Hillyer, J.F. and R.M. Albrecht. Gastrointestinal persorption and tissue distribution of differently sized colloidal gold nanoparticles. Journal of Pharmaceutical Sciences, 2001. 90(12) 1927-1936. doi: 10.1002/jps.1143
5. Jain, K.K. Nanobiotechnology-Based Strategies for Crossing the Blood-Brain Barrier. Nanomedicine, 2012. 7(8)1225-1233. doi: 10.2217/nnm.12.86
6. Silva, G.A. Nanotechnology approaches to crossing the blood-brain barrier and drug delivery to the CNS. BMC Neuroscience, 2008. 9, S4. doi: 10.1186/1471-2202-9-S3-S4
7. Friedman, A.D., S.E. Claypool, & R. Liu. The Smart Targeting of Nanoparticles. Current Pharmaceutical Design, 2013. 19(35) 6315-6329. PMCID: PMC4016770
8. Longmire, M.R., Ogawa, M., Choyke, P., & Kobayashi, H. Biologically Optimized Nanosized Molecules and Particles: More than Just Size. Bioconjugate Chemistry, 2011. 22(6) 993-1000. doi: 10.1021/bc200111p
9. Khlebtsov, N. & Dykman, L. Biodistribution and toxicity of engineered gold nanoparticles: a review of in vitro and in vivo studies. Chemical Society Reviews, 2011. 40(3): p. 1647-1671. doi: 10.1039/C0CS00018C