Chemistry World podcast - May 2012

1:08- A temporary tattoo measures athletic performance

3:46- A graphene tooth tattoo detects bacteria

6:42- Graham Turnbull is sensing explosives with his electronic nose

13:49- Solving the source of static

17:32- What does it mean if your bacon is green?

20:20- Bringing chemistry to life with Lee Cronin

28:19- Nanoparticles: a concern for children

31:37- The world's first germanone

34:09- Trivia - 50 years since the invention of which ubiquitous device?

(Promo)

Brought to you by the Royal Society of Chemistry, this is the Chemistry World Podcast.

(End Promo)

Interviewer - Chris Smith

This month a new technology that's said to give sniffer dogs a run for their money.

Interviewee - Graham Turnbull

So, we routinely are detecting vapours at a few parts per billion concentration.   I think that this sort of approach is probably the closest thing that anyone has got yet to the sensitivity of a dog's nose.  

Interviewer - Chris Smith

That's E-nose pioneer Graham Turnbull, who joins us shortly to introduce his plastic semiconductor sensors. Plus bug detecting tooth tattoos and why bacon goes that beautiful iridescent green colour in the fridge.   Hello I'm Chris Smith and with me for this May 2012 episode of Chemistry World, are Laura Howes, Bibiana Campos-Seijo, and Patrick Walter.

(Promo)

The Chemistry World podcast is brought to you by the Royal Society of Chemistry; look us up online at chemistry world dot org.

(End Promo)

(1:08 - A temporary tattoo measures athletic performance)

Interviewer - Chris Smith

And up first, the latest fashion must have a biometric temporary tattoo.   Laura.

Interviewee - Laura Howes

John Rogers at the University of Illinois Urbana  Champaign, last year he published a science paper, where he was demonstrating this work for the first time.   This is a temporary tattoo that can measure various things like your skin hydration.

Interviewer - Chris Smith

How do they actually work these tattoos, what do they do, what are they made of?

Interviewee - Laura Howes

They're actually made of silicon components, but they're very very thin.   Once you get down to being very thin, the material properties change, the silicon becomes much more flexible, which is obviously a bonus if you were to be wearing it on your skin.   So, you have these flexible components wired together with bits of gold and the way they're connected means that they can bend and flex with your skin and they can also stretch a bit.

Interviewer - Chris Smith

Sure. So, they're microprocessors quite literally in contact with the skin. You can do things at a stretch and as you say hydration measure things like that.   How do you get the energy in there?

Interviewee - Laura Howes

So, obviously there's not a battery there at the moment, that's one of the things that I think perhaps they'll be looking at in the future.   But at the moment there's what they call a RF tag or a radiofrequency tag so that's just a coil that will pick up radio waves and use that as an induction to power it and that's also how you can then get the information back off in a wireless fashion.

Interviewer - Chris Smith

And what they have done with it so far?   Because there was a science paper that was the proof of concept, you mentioned that.

Interviewee - Laura Howes

Yeah.

Interviewer - Chris Smith

What's the latest development, if you can?

Interviewee - Laura Howes

So, the reason why we are talking about this now is I am recently back from the American Chemical Society's meeting which is in Santiago and that's where I met John and actually saw these things, he was actually wearing them on his skin showing how they were working.   They are now sort of teaming up with people and they actually put it on a Nascar driver, so there's this driver called,  Paulie Harraka, so they're putting it on him to measure yeah his hydration, his temperature, and how his body is sort of moving and responding while he is actually going around the race.

Interviewer - Chris Smith

And beyond Nascar, what other applications might there be, because I mean, not everyone can be a Nascar driver?

Interviewee - Laura Howes

Nascar is a bit niche perhaps, yeah.   John Rogers was also saying that he is teaming up with a certain sportswear brand, to look at the hydration levels of athletes.   He wants to look at using it for measuring your skin hydration if you're looking at cosmetics, it's a much easier way of, you know, poking skin, when you're trying out different face creams and slightly further on in the future, he was saying that he has actually put on his neck and used the muscles in his neck to control a computer game.

Interviewer - Chris Smith

So, there are sort of accessibility hoping disabled people type spin-offs from this too.

Interviewee - Laura Howes

Precisely.   So, you're looking at maybe controlling prosthetic limbs and things like that.  

(3:46 - A graphene tooth tattoo detects bacteria)

Interviewer - Chris Smith

Well, from one kind of tattoo to another.   There's one actually you can really get your teeth into.   This is a tattoo from graphene that goes onto teeth Bibi.

Interviewee - Bibiana Campos-Seijo 

Yes, basically these tattoos have got three components, one is graphene, the other one is bifunctional peptide and then also we have an RFID device as well.   So basically what happens is that these chemical based sensors are able to tell the researchers when bacteria are in contact with the teeth.  

Interviewer - Chris Smith

How does the graphene actually work, is that the bit that is doing the processing, are these sort of graphene transistors or is the graphene the thing that's actually doing the detection of the substrata, whatever it is they're measuring?

Interviewee - Bibiana Campos-Seijo 

The first step in this process is printing the graphene grid onto a thin layer of silk, then the silk is used as a transfer onto the tooth and actually because of the properties of graphene, the van der Waals forces may mean that it adheres very strongly to the surface, then on top of that they add the bifunctional peptides and basically here one of the ends is very rich in antibiotic residues and therefore it sticks to the graphene.   The other one contains antimicrobial protein, which actually has a strong affinity for the bacterial strains that they are trying to detect.   So what happens then is that when the bacteria bind the antimicrobial protein, there are very small changes in charge on the cell membranes of the bacteria, which the graphene picks up as a change in conductivity and then this is wirelessly transferred onto an external detector. 

Interviewer - Chris Smith

So, this would literally be stuck onto all your teeth, one of your teeth, some of your teeth? How is this being used?

Interviewee - Bibiana Campos-Seijo 

Probably just one tooth, but it can also be deployed onto soft tissues as well, and it is the first time that a device like this has been interfaced with biological tissue.   At the moment, he said proof of concept as well because they haven't really looked into the selectivity of the antimicrobial proteins. So it's not ideal at the moment but also they haven't looked at how well these devices will stand up to abrasions 

Interviewer - Chris Smith

When you're cleaning your teeth for example, 

Interviewee - Bibiana Campos-Seijo 

Yeah, exactly,   Yeah, it's quite likely that once you know you've brushed your teeth, your device will be gone.

Interviewer - Chris Smith

But, how do they say this is being used though, is the idea that you have sort of Salmonella sensor, so that you take it by from a dodgy kebab or a   dodgy hamburger and you sort of know not to swallow or something.

Interviewee - Bibiana Campos-Seijo 

Yeah yeah, spit it out.

Interviewer - Chris Smith

What's the point, yeah is that the idea?

Interviewee - Bibiana Campos-Seijo 

Yeah, yeah, yeah when the alarm bells go off somewhere.   I don't know but I think that could be potentially one of the uses in the future, but at the moment the selectivity is not there, but it is a good proof of concept.

Interviewer - Chris Smith

And Bibi was describing the work of Princeton scientist,  Michael McAlpine, if you want to look him up, order your own tooth tattoo.   Now sticking with sensors.

(6:42 - Graham Turnbull is sensing explosives with his electronic nose)

Interviewee - Graham Turnbull

My name is Graham Turnbull. I'm a senior lecturer in the School of Physics and Astronomy at the University of St. Andrews.   So the aim of these sensors is to try to detect very, very low concentration vapours of explosive molecules.   Essentially what we want to do is to try to make an electronic version of a dog's nose. 

Interviewer - Chris Smith

How sensitive is a sniffer dog.   What sort of concentrations are their nasal passages able to pick up? 

Interviewee - Graham Turnbull

A sniffer dog's nose is incredibly sensitive.   The saturated vapour pressure for TNT is of the order of a few tens of parts per billion in the air, the levels of concentrations that sniffer dogs can detect are orders of magnitude lower than that.

Interviewer - Chris Smith

You're doing it via a chemical and physical route.   So, what's your approach?

Interviewee - Graham Turnbull

Our approach is to use   novel class of plastic material called conjugated polymers.   They're essentially organic semiconductors.   They have semiconducting properties like silicon or gallium arsenide, but they also have very simple processing properties of plastics.   These sorts of materials are in use in light-emitting diodes in displays in Samsung mobile phones, they are being widely developed to make flexible printed solar cells on plastic sheets, but we're using the same sorts of materials as a sensor to try to detect these very low concentration levels of nitroaromatic molecules like TNT.

Interviewer - Chris Smith

So, how are you registering, when the molecule, say TNT interacts with the plastic semiconductor material, what chemical changes are taking place that you can detect in an objective and quantitative way?

Interviewee - Graham Turnbull

The process that we use is one of light emission looking at the fluorescence from the polymer, the semiconducting polymer or looking at laser machine from the material.   When we absorb photon of light in the polymer then the excited state on the polymer chain will normally re-emit a photon of light at a longer wavelength.   If you have a TNT molecule sitting on the chain, then what can happen is this excited state instead of the electron falling back down to ground state and emitting a photon of light, the electron will transfer on to the TNT molecule and thereby relax by going to the ground state without the emission of light.

Interviewer - Chris Smith

It effectively quenches out the fluorescence then, doesn't it?

Interviewee - Graham Turnbull

Yeah, so if we have fluorescence present then it means there is no explosive vapours, if explosive vapours are present then the fluorescence which is off.

Interviewer - Chris Smith

And how do you make it specific for TNT so that you don't go around detecting potential bombers and people with ordinance amongst a whole bunch of individuals who are completely innocent?

Interviewee - Graham Turnbull

Our mechanism is not a very specific one. It essentially can detect any strongly electronegative material, so materials have energy levels relative to the polymer that we'll tend to allow this electron transfer to be favoured.   So, essentially what it will do is it will detect any nitroaromatic molecule like TNT, but that's fine in the correct circumstance.   If you're standing on a mine field and if you find any strongly electronegative molecule then you have a reason to feel concerned. 

Interviewer - Chris Smith

We started this conservation discussing the sensitivity of a dog's nose for example, so compared with a dog, how good are you with your plastic semiconductors.   What sorts of concentrations can you detect?

Interviewee - Graham Turnbull

So, we routinely are detecting vapours at a few parts per billion concentrations. We and other people have shown that you can go to much lower concentrations.   I think that this sort of approach is probably the closest thing that anyone has got yet to the sensitivity of a dog's nose, so that's still is the most sensitive approach.   But the thing about dogs is that if you're going to use a sniffer dog to sniff an explosive, you have to keep them interested.   They're playing a game where they sniff for the explosives and when they find something they get a reward, but if you want to do a long and highly repetitive survey like for example sniffing every suitcase down a conveyer belt at Heathrow Airport, then the dog gets bored and there will be an advantage in having hi-tech approach to detecting the explosives that can deal with these long repetitive surveys.

Interviewer - Chris Smith

I guess part of my question is well was probing or intent to probe, the idea of practicality, dogs are good because they're mobile and yes you do have to keep rewarding them but they're relatively easy to train and you can deploy them where the bags are. How easy is it to deploy your system and how likely is it to be able to pick up with the explosives as a bag goes under an array of say your sensors.

Interviewee - Graham Turnbull

At the moment our research is very much at a stage of a laboratory based proof of concept but we're aiming to develop this into a more practical system within a European funded project and focused on the area of humanitarian demining, essentially looking for mine fields, the presence of mine fields and looking for individual land mines.   And so within that we aim to develop a small box that's portable, can be mounted on a robot vehicle to essentially make the dog's nose for a robot dog that can travel around a suspected mine field.

Interviewer - Chris Smith

And I think probably the most important thing with any sort of new emerging technology, what about the cost?   Is this going to be cost-effective and scalable on the sort of level of the anticipated demand and there is over a 100 billion land mines out there across the world, can you meet that challenge in a cost effective way?

Interviewee - Graham Turnbull

One of the advantages of organic semiconductors is that they're very amenable to low cost processing and so people are looking at various printing techniques for making organic LEDs, organic solar cells, organic transistors and electronic circuits.   And so in principle you can mass manufacture at relatively low cost.   And so we would hope that this sort of sensor would be amenable to that as well.

Interviewer - Chris Smith

St Andrew's scientist Graham Turnbull.   When you stick a balloon or wipe it by rubbing it on your hair, the dogma goes that you're moving charges on to it, not true a new study says, Patrick.

(13:49 - Solving the source of static)

Interviewee - Patrick Walter

Things always are a bit more complex than the way they're often told at school, so static charges has been something that's been confusing chemists for some time.   So chemists have been trying to build up a triboelectric series, so you can place the materials in different places according to how positive and negative they are when they're rubbed.

Interviewer - Chris Smith

So, balloon on hair would be somehow on series and burrowed with silk, handkerchief, somewhere else on the series and so on, all these different things that you can rub together and you get a charge differential happening.

Interviewee - Patrick Walter

Exactly, I mean, there's a lot of work in the literature that's gone towards trying to solve some of these problems about where things should come in the series but there's been completely conflicting results where one group said it's over more towards the positive side, one group said this material actually charges a bit more negative,. It's opening a whole can of worms here perhaps, Bartosz Grzybowski at Northwestern University in the US thinks he has come up with part of the solution to actually creating a triboelectric series where you can actually place these materials.

Interviewer - Chris Smith

What have they done, how they've done it?

Interviewee - Patrick Walter

So, what Grzybowski did was he was thinking back over some previous work that he did with George Whitesides, I think is about a decade ago and they found that there was some kind of material transfer between surfaces when you rub them together.

Interviewer - Chris Smith

So, physically bits of one thing are going on one surface to the other.

Interviewee - Patrick Walter

Yeah

Interviewer - Chris Smith

So when you rub the balloon on your hair, there's bits of hair or bits of balloon going one direction or the other between the two surfaces and that's carrying the charge.

Interviewee - Patrick Walter

That's it, exactly, yeah.  

Interviewer - Chris Smith

How did they prove that?

Interviewee - Patrick Walter

Right, what they did was they took some Teflon beads and some polystyrene beads and when you rub them to start the Teflon normally charges as negative and the polystyrene charges as positive, They are keeping   rubbing them for a while what actually happens is the polarity reverses, so the Teflon now instead of being negative is positive and it's the same for the polystyrene, it's changed.

Interviewer - Chris Smith

So, this whole idea of electrons falling off of one and accumulating preference on the other can't be right then, something else must have been going on.

Interviewee - Patrick Walter

Exactly. So, by using atomic force microscopy they were able to create a topological map of the particles and they could actually watch them start and then watch them after a bit of rubbing and then after a bit more and as they did that they could actually see the bits of material rubbing off, I mean it's not a lot.   After about half an hour of the Teflon and the polystyrene beads rubbing only as much as 5 micrograms per square centimetre transferred from one bead to the other.

Interviewer - Chris Smith

But in terms of matter that's still a lot, that's a lot of electrons.

Interviewee - Patrick Walter

Yeah the thing about static charge is when people have looked into it, it's not about the properties of the bulk material, it's about the surface, so the surface is where it's all going on and that's what's happening here, the surface is being transferred from one particle to the other and vice versa.

Interviewer - Chris Smith

Does this mean we now do generally have this series, where you can say we know when you rub this with this much stuff and therefore this much charge is going to transit between the two surfaces and this should be the ultimate charge?

Interviewee - Patrick Walter

So yes, it certainly looks like they could start building a triboelectric series by looking at the hardness and softness of the particle, so the harder your particle is the less likely there is something will fall off that particle and this is how it can begin to build up a series.

Interviewer - Chris Smith

Why would a series like that be useful?

Interviewee - Patrick Walter

So, static charges are actually very important for a lot of things delicate electronics for instance, static charge can be very damaging.   So, knowing quite what's going to happen when you combine certain materials would be very important.

(17:32 - What does it mean if your bacon is green?)

Interviewer - Chris Smith

Over to something totally different but it does accumulate I suppose, in one sense Bibi and that's bacon accumulates a green colour, I've got some in my fridge which is labelled definitely for the dog, here it is.   So what is this green colour and what have scientists learnt about it recently.

Interviewee - Bibiana Campos-Seijo

Yeah, this is not a very glamorous story at all, but yeah there has been some work done on green bacon or the iridescence that you can see on the surface of bacon and the team that did it are based at the University of Oklahoma in the US and the lead researcher is George Richter-Addo. So basically well we all have seen green bacon, a chemical that has been used for centuries to preserve meat is nitrite.   So what these guys have discovered is that it actually reacts with myoglobin on the surface of the bacon to produce the green pigment that you see.

Interviewer - Chris Smith

The myoglobin being the iron-containing pigment which is a bit like haemoglobin but in muscle when it gets oxygen off of haemoglobin in blood and puts it into the muscle cells.

Interviewee - Bibiana Campos-Seijo

Absolutely that very same one. What happens here is that people are a little bit concerned that they even know what the effect of nitrite, the preservative that we are talking about or nitrite burn which is the term that has been used to describe this iridescence, in the body; does it have any health implications?   So this group of researchers have decided to actually fully characterize the structure of nitrite burn using x-ray diffraction and this is the very first step towards discovering how or whether it would react with myoglobin or haemoglobin in the body.

Interviewer - Chris Smith

So you take basically the molecule that you get this green colour   , do x-ray investigations on it, what did they find?

Interviewee - Bibiana Campos-Seijo

They basically found that the nitration occurs at the 2-vinyl group of the macrocycle rather than the 4-vinyl group and this is attributed to steric factors.   So I wouldn't say that it's a huge discovery, but it actually helps them understand how nitrite burn is formed potentially would help understand how it is going to behave once it enters the body.

Interviewer - Chris Smith

So, going   back to my point, can I eat green bacon?

Interviewee - Bibiana Campos-Seijo

Yes.

Interviewer - Chris Smith

Safely, so that safely   and then what would be the implication then of the back of this piece of work.

Interviewee - Bibiana Campos-Seijo

Well, the next study that they have to do is around whether this nitrite burn affects the physiological function of myoglobin, we know that there is a very little change to the overall configuration of the macrocycle but they need to look at the physiological function and then we should be able to know whether we are okay with the green bacon or not.

Interviewer - Chris Smith

In the mean time I do what I do, and give it to the dog.

Interviewer - Chris Smith

You're listening to Chemistry World with me Chris Smith.   Still to come, why nanoparticles are worse for young lungs and 50 years of the LCD screen, but first to artificial life.   Biology has had a crack   in   creating life, now it's the turn of chemistry,   Lee Cronin

(20:20 - Bringing chemistry to life with Lee Cronin)

Interviewee - Lee Cronin

Right now biology is abuzz with the term synthetic biology where people are playing around with the current infrastructure biology, there are nuts and bolts, proteins and DNA and regulatory mechanism, but I want to get below that and ask a question where did that biology come from and what was the chemistry set that we used to start that biology off.

Interviewer - Chris Smith

Because there was enormous fanfare when Craig Venter a couple of years ago created what he called synthetic life, but the reality was although they re-edited a genome from scratch they still had to bunk into another cell a   bacterial cell so then kick start life in that bacterial cell and that left that outstanding question , where did the cell come from in the first place.

Interviewee - Lee Cronin

Exactly, now what Craig did was amazing but all he did do was basically take, I do not know,   BMW and a mini and take the engine from one and the bits and bunked it in the other, he didn't make a new engine.   Well he did make the engine but he already had the blue prints and I think that we are asking something fundamentally much more important which is how do we actually re-write those blue prints and what is the feature for.   What features do the living systems have to find in this blue prints. 

Interviewer - Chris Smith

Indeed well, first of all let's take a look at what it is you're trying to do.   Because there is a number of problems which frustrates scientists who are trying to recreate life, not at least actually how you get something which is this miniature reacting vessel, a cell, so how are you tackling that?

Interviewee - Lee Cronin

One of the things that people are trying to do right now is devide out the properties of the cell. So the cell is a container, it contains some information, it contains a database and it contains a synthetic machinery that makes protein, this may contain some metabolism.   So, what people are trying to do right now is de-engineer that in such a way that they come up with chemical analogies on biology, they try to use more basic methods and more basic database and a more basic metabolism and that the problem is that they are trying to put them together that is rather like when Frankenstein was assembling he was trying to get a spark of life back into the dead pox, they look like they should talk to each other but despite our current efforts it is very difficult to do that system.

Interviewer - Chris Smith

Are we slightly thinking inside the box or inside the constraints of the existing cell if you will, in the sense that we're all looking for a way to make something which biology already has.   Should we not think differently and do we have to be constrained by the present chemical and structural architecture of a cell.   Is there an alternative we could use instead?

Interviewee - Lee Cronin

Oh yeah, well there is no such an alternative for cellular architecture, there's probably a whole alternative environmental architecture but to do that first of all one needs to think about what properties are you trying to give your chemical system.   And so my thesis here, my coming into this is to say right now on planet earth what is the minimal chemical building block or chemical unit that can exhibit Darwinian evolution.   And when you think about that question in that way you come up with an obvious but yet profound answer and that's a very simple cell or bacterial cell or amoeba or something of that ilk.

Interviewer - Chris Smith

So, biology has got about 3.9 billion year head start over you, do you think though that you'll end up at the same position biology is to just to reinvent the whale or is there a genuinely better way of doing this or a way which is distinct which has advantages for chemistry and will be unconstrained by the requirements of biology.

Interviewee - Lee Cronin

It will be fair to say that biology on planet earth is really a product of the available chemistry and so if we're to use a different chemistry set then we're going to get some common features hopefully you know we are aiming for Darwinian e