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LuxeSci Show Notes: S1E11: Silver

Hello again.  Welcome back to LuxeSci - a podcast to re-ignite your wonder by exploring the science behind luxury items.  I’m Dr Lex, PhD, infectious disease expert.  I’m joined by my co-host Dr. Dimos, also a PhD, electrical engineer. 

This week we’re talking about the ubiquitous metal, silver.  A vast amount of jewelry is make with silver as are other items such as coins, solar panels, water filtration, ornaments, utensils, electrical contacts and conductors, and the list goes on.  Now I have silver’s color and sheen for jewelry but I can’t wear it for too long.  It turns out that I have an allergy to silver, well, more specifically, I have an allergy to the nickel that is used to make silver jewelry.  Pure silver is too soft to make into jewelry so a small amount of nickel is mixed in to keep the shape and luster.  The nickel can seep out and cause a contact dermatitis.  The amount of nickel is highly variable, hence my range of reactions to different metals. This allergy is more common in women than in men and affects between 10-15% of the population.  Of course, my family being what it is, I just got teased for my “naturally expensive taste” since the only jewelry I can be sure I won’t react to is gold jewelry (which contains no nickel).

So here’s a microbiologists and electrical engineer’s take on silver. 

Background (Alexis)

  • Silver is a chemical element.  It’s atomic symbol is Ag (from the Latin: argentum) 

  • It’s atomic number is 47

  • Reminder - atomic number is the number of protons found in the nucleus of every atom of that element

  • Silver is a transition metal (grouping on the periodic table of elements based on how the electrons are arranged)

  • Soft, white, lustrous

  • Highest electrical conductivity, thermal conductivity and reflectivity of any metal

  • Silver is found in the earth’s crust as a pure free element and as an alloy with gold and other metals

  • Most silver is produced as a byproduct of copper, gold, lead and zinc refining

  • The word silver comes from a proto-germanic language - silubra and first appears in Old English

  • Silver is one of seven metals that were known to prehistoric humans.  It was probably used as currency but wouldn’t have been used to make tools or weapons since it’s pretty soft

  • For much of ancient history, silver was more expensive than gold since native supplies of silver were more limited than gold

  • Cupellation - ( refining process that uses very high temperatures to separate components present in ore) allowed silver to be extracted from deposits of other metals

  • Evidence of this process have been found in Asia Minor and on the islands in the Aegan Sea from as early as the 4th millennium BC

  • It’s likely that silver production in India, Japan and China is similarly as ancient but not as well documented

  • The conquistidors coming to South Amercia and discovering silver deposits made that area the number one silver producer for a time (unfortunately).  In the 19th century that moved north to MExico, US and Canada

  • As of now, the distribution of silver production around the world is pretty even

  • One fun fact = in Ovid’s Metamorphoses, that is an illustration of silver’s use of signifying second-best in a series, better than bronze but worse than gold

  • Silver was also commonly thought to have mystic powers (think killing a werewolf)

  • This is where the idiom of the silver bullet comes from

  • What’s another idiom that contains silver? (hint: it’s Biblical)

  • OK - now for the science


  • We’re going to start with the antimicrobial properties of silver, which have been known for quite some time

  • Antimicrobial = an agent that kills a microorganism or stops their growth

  • Note: this is a broad term for any microorganism as opposed to the more specific terms for antibiotic or antiviral

  • Traditionally its been incorporated into creams and dressing in the form of silver nitrate or silver sulfadiazine for anything from treating burns and ulcers to food packing to prevent contamination to home appliances and industrial applications

  • This is caused by the silver’s ability to punch holes into bacterial membranes and then bind to essential cell components like DNA, preventing the bacteria from performing essential functions

  • Interesting - research in 2015 found that the dead bacteria soak up the silver particles and then that stored silver can leach out into the environment and cause other bacteria to die.  

  • This research was summarized in a great article onthe Science website written by Emily Conover

  • Given these antimicrobial activities, researchers were interested in new silver formulations that can be used as antimicrobials

  • Scientists decided to harness emerging nanoparticle technology for their new silver formulations

  • We visited nanoparticles back in Episode 5 on gold

  • As a reminder, nanoparticles are small particles that range between 1 to 100 nanometers in size

  • As a reference for this section I used one of my beloved reference articles.  This one was authored by Tamara Bruna et al and published in the International Journal of Molecular Science in July of last year.  (The citation will be in the show notes)

  • Back to the nanoparticles: silver nanoparticles have the advantage of higher surface area compared to bulk silver

  • They also have some unique characteristics (electrical, optical and catalytic properties) that have led them to be used for targeted drug deliver, diagnosis, detection and imaging

  • So far - silver nanoparticles have been tested for antimicrobial activities against a range of pathogens, including multi-drug resistant bacteria.

  • So how are these nanoparticles made?

  • There are two different categories of metal nanoparticle synthesis, bottom-up or top-down

  • Top-down synthesis is where metallic silver or a solid or aerosolized state is whittle down to the nanoscale with physical techniques such as ball milling, laser ablation or sputtering

  • These can yield large amounts of highly pure nanoparticles and usually required large amounts of energy, expensive instrumentation and high pressure and temperature conditions

  • Bottom-up synthesis is where nanostructuring and stabilization is used on silver atoms to form the nanoparticles.  These include chemical and biological techniques

  • Chemical methodsare considered low cost and simple to perform as well as scalable but can lead to the generation of polluting or hazardous waste

  • Biological methodssynthesizes the nanoparticles using fungal or bacterial mediated synthesis.  They are high solubility, yield and stability.  This is considered the most processing synthesis method

  • Mechanism of action, aka, how do these little things work

  • The exact mechanism or mechanisms of action is not fully known

  • One hypothesis is that the particles can penetrate the out membrane of bacteria, accumulate in the inner membrane and then the particles adhere to the cell generating destabilization and damage, leading to increased membrane permeability, leakage and cell death

  • The second hypothesis is that the particles can not only penetrate the cell wall but can enter the cell and interact with sulfur and phosphorous groups present in cell components such as DNA and proteins.

  • The third hypothesis is that once the particles are inside the cell, they can interfere with the cell respiratory chain, generating damage to the intracellular machinery and activating the apoptosis pathway.  (apoptosis = programmed cell death, sort of like a self-destruct switch)

  • Despite their promise as antimicrobials, silver nanoparticles may come with some caveats

  • One is the potential for resistance.  Several in vitro studies with Pseudomonas aeruginosa, E. coli and Staphylococcus aureus have shown some tolerance to the nanoparticles over time.  

  • An additional study conducted by Kaweeteerawat et al showed that pre-exposure of bacteria to silver nanoparticles decreased the efficiency of antibiotics for those bacteria.

  • However, at the same time, other studies have shown an additive or synergistic effect of silver nanoparticles and different compounds such as plant extracts, polymers or antibiotics

  • This is definitely an area of active research so stay tuned!

  • One other area of active research is in the potential for cytotoxicity from nanoparticles. It appears that smaller nanoparticles have the ability to induce greater damage so further studies on size and dose are crucial for this technology to move forward

  • One recent study in Finland found that colloidal silver products found on websites found the products to be very detrimental “the use of quackery products such as colloidal silver can be dangerous, and their use and marketing should be controlled and restricted”

  • Applications in health care

  • One of the main applications of silver nanoparticles is in face masks.  Face masks coated with the particles exhibited an ability to reduce up to 100% of E. coli and S.aureus within 24h.  In hospitals where patient-to-patient transmission of bacteria is a big concern, this could be a huge improvement

  • So overall - silver nanoparticles may represent the future of antibiotics either for goods such as masks, catherers, wound dressing or as an ingested product, or both

  • A note about colloidal silver

  • Since it was mentioned in the study from Finland

  • Colloidal silver consists of silver particles and silver ions in aqueous suspension.  The particle size of the silver varies between nanoparticles and microparticles

  • The silver ions mediate toxic effects on the human body

  • It is often marketed as an “essential” mineral supplement

  • While silver can be found in the human body it is most definitely not an essential mineral and it has no physiologic function

  • Interesting fact - when taken orally, the silver from this suspension builts up in your body.  Over months to years, it can result in a bluish-gray skin discoloration.  This is called argyria.  And it’s usually permanent


  • Atomic number

  • Transition metal

  • Cupellation

  • Antimicrobial

  • Apoptosis - the process of programmed cell death

Fun cocktail party facts quiz

  • What is mixed with silver to make jewelry?

  • Where did the concept of silver being second-best show up in early literature

  • What is argyria

I hope you’ve enjoyed exploring silver with me and Dimos and I hope you remember a little fact from this episode the next time you see silver.  Thanks for listening to this episode of LuxeSci.  A very special thank you to my audio engineer and co-host, Dimos.  Our theme music is Harlequin Moon by Burdy. We’re on Twitter and Instagram at luxescipod.  Please subscribe and review where ever you listen. This time we’re asking that you share one of our tweets.  We’ll make sure to comment on it. 



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