Tag Archive: SEM


big, fat, hairy christmas

huntsman_q003

do you see how jolly this avondale spider (molt) is?  i’m pretty sure she’s grinning from chelicera to chelicera… and i might even know why.  partly because i took this photo aaaaaaages ago and am finally posting it, but also for a more exciting reason: santa claus is bringing me tarantula molts for christmas!  long story short, one of my grad students was working with someone studying the genus Poecilotheria (arboreal tarantulas, how cool is THAT) and it came about that he had some molts he’d be interested in examining by SEM.  guess what–i can help :)  so they’re on their way, some large, empty, hairy skins of some of the most exquisitely beautiful (and sadly, at risk of extinction due to habitat loss) tarantulas i’ve ever seen.  i mean, look at this (borrowed from wikipedia here).  it’s BLUE!

File:Poecilotheria metallica.jpg

i’ll be looking at a few things on the molts including some systematic characters, which may even help understand this genus’ diversity a bit better–which could ultimately help in making a case for their, and their habitat’s protection.  i hope so!

i think 2014’s going to be a good year.  ::::)  all the best to you & yours!

Advertisements

this week we return to the fairytale kingdom of spiders under the SEM.  our subject is Badumna longinqua, the grey (or brown or black) house spider – in fact, the same one who lived in the kitchen in our old flat, featured in this older post.  we encourage them when we find them living in our house (and even took one with us when we moved house), since they cheerily reduce biting bug numbers and are also fun to feed and easy to observe.  right now we know of one nice specimen cozied up under the kitchen sink and another few around the window frames.

the hapless white-tails we come across (Lampona sp.) are usually moved outside, dispatched and/or retained for post-morterm examination.  but we value the house spiders, so the opportunity to get the images below arose from a nice molt i found in the web – no spiders were harmed in the making of this post.  :)  and since she was a pretty big girl, only select parts could be fitted into the frame at any one time.

last week, i talked a little about the (perhaps not-so-) nefarious white-tail, and mentioned that those i had found in my house hadn’t lasted long.  although most of their frozen, curled little corpses went out to the garden, two were preserved for posterity, and i’d like to show them to you today.  these two each turned up (separately) at times when i was preparing squid specimens for SEM at work, so it probably won’t surprise anyone much that i decided to have a closer look at them a much closer look.  see?

since i had two, i mounted one upside down for good look at the ventral surface.  the fangs were particularly interesting the pore you can see on the right-hand fang is where the venom comes out.


white-tails are incredibly bristly, all over, which i expected.  but what astonished me was the variety and the intricate structure of some of the setae, whose specific names i haven’t been able to track down yet.

the photos that follow are two of the best SEMs i think i’ve ever taken.

look at the claws!  the amazingly plush-looking pad of setae on the underside of the foot!  no wonder spiders can sense tiny vibrations in their webs (those that build webs Lampona doesn’t).

i love science.

Read and post comments | Send to a friend

long time no squid

it’s been a while since i posted anything squiddy. which is deceptive, because things have actually been very squiddy around here — something to do with that whole research fellow job, i guess. anyway, a couple of papers are in the works, nothing i can exactly report at the moment (mostly about squid sex — you probably wouldn’t want to know anyway), but i did prep some more specimens today for SEM next week.  so as of next wednesday (oooh, but that’s spider day — dilemma!) i’ll have some more cool shots of tiny, esoteric squid bits, like these suckers from the tentacle club of a 3mm long Onykia specimen.

squid bits for everyone!

look, three days in a row!  i remember how this goes now.

i was going to write about an excellent book i just read and how it's influencing my everyday life, but i'm going to have to put that on hold because i also went to play with the SEM again today and i have cool pictures to show for it.  i thought i had already written about the SEM process here, but i can't find any posts about it, so i'll cheat by pulling in an explanation from my old site, below.  but first – the photos.

 


for this manuscript, there's been plenty of verbal/written describing and also pen-and-ink illustrating, but by far the most fun part of it has been working with the scanning electron microscope (SEM). basically this is a machine that bounces electrons off samples and lets you take magnified photos of extremely small and detailed things, by reading the reflected electrons to form an image, kind of like using sonar.  to do that, you need to have samples coated in a very thin layer of metal that will reflect the electrons but keep the detail, and to do that, the specimens have to be completely dry or the metal coating won't stick.

so. you take your tiny specimens and use a critical-point-drying chamber (CPD) to get all the moisture out of them, making them completely dry, without deforming them in the drying process. to do this, you soak them in 100% ethyl alcohol, then load them into the inside of this chamber, and fill it up with liquid carbon dioxide (liquid because of pressure, not temperature). the carbon dioxide replaces all the the ethanol in the specimens, and then you raise the temperature and pressure in the chamber until the CO2 becomes a gas – and poof! the specimens are completely dry! so cool. i am in awe of the person who thought of this process. it takes about two hours all up.

then you need to coat the specimens, so you put them inside a different chamber, beneath a foil made of gold-palladium. you fill up the chamber with argon gas, and then you run an electrical charge through the chamber. at this point the argon atoms get charged (and they glow purple), and go shooting around inside the chamber, running into the gold-palladium foil and knocking off some atoms, which then drift down onto your specimens and stick to them, coating them in a very thin (less than 10 nanometer thick) layer of metal. this takes about 20 minutes. i am also in awe of the person who thought of this. and the glowing purple part really is cool. and then your specimens are dry and coated, so you store them in a desiccating (dry) chamber to keep them from re-absorbing any moisture, and then you're ready to take them to the SEM, where you put them in, pressurize the chamber, start shooting the electrons and then take all the pictures you want, using the computer to control the camera.

of course, there are also a lot of non-microscopic aspects to my thesis…

Read and post comments | Send to a friend

the right tool for the job

i like science.

it ‘blows my frock up,’ as a former colleague used to say.  i was going to be more specific and say ‘i like biology’ but the occasional physics or geological phenomenon has also been known to elicit the ‘oooooh, cool’ response in me.  and today, unlikely as this seems, it’s chemistry.

chemistry and i are not generally good friends.  i took the required three semesters for my undergrad environmental science major, with limited success – i survived, and passed, but with a few mental scars.  one residual effect is that  certain chemistry-related words are indelibly etched into my brain in the voices / accents of certain professors.  for example, i still hear the word antibondin’ in the jamaican accent of my inorganic chem prof, a person in whose presence many unhappy and frustrating hours were spent.  thus do chemistry and i keep happily parted company under normal circumstances.

but today, i bring you the marvels of a particular chemical process, and of the ingenuity of the scientific minds who figured out how to make it occur in a controlled environment, and – even more impressive – do something useful with it.  i speak of the process called critical-point drying, or CPD.

to give some background, CPD is one step in preparing specimens (in my case, squid bits) for scanning electron microscopy, or SEM, which is a way of photographing very small things.  by bombarding a metal-coated piece of squid, or crustacean, or anything else you can think of, with electrons and then reading the pattern as the electrons bounce back, you get amazing, extremely detailed pictures of your specimen at, say, 20,000x magnification.  beauty, eh?  it is used by systematists (and probably specialists in a number of other fields i haven’t thought of) to observe and compare tiny physical features on our beasties, and then to differentiate them from one another.  in the case of the Onychoteuthidae, the squid family i’m revising for my PhD, the important parts are the radula, palatine teeth, surfaces of the arm and tentacular suckers at all life stages, and the growing and mature tentacular hooks.  (if you really want to know more about these parts, bless you (but you need a head check) – you can find them defined on the tree of life’s cephalopoda glossary.  all except the palatine teeth, which are kind of an unknown quantity – working on it!)

in order to get the electons to bounce right, the specimen must be coated in a very thin layer of metal (more on this in a minute), and for the metal to stick, the specimen must first be completely dry.

enter the CPD chamber.

a surprisingly compact, squat little doo-hickey, the CPD chamber looks a little like mickey mouse head-on (an unfortunate resemblance – i hate mickey mouse), with pressure and temperature gauges forming the ears.  it allows the specimen (stored in 100% ethanol prior to drying) to be flooded with liquid carbon dioxide initially and then to sit in this bath for an hour (long enough to make sure there’s no other liquid remaining in the chamber); then it increases the temperature and pressure inside the chamber to the critical point of CO2 – the point at which the liquid becomes gas.  when that happens (temperature is controlled by a recirculating bath of water, pressure by simply heating the chamber without allowing it to expand), *poof* – all the liquid in the specimen turns to gas, leaving it bone-dry.  brilliant.   (it takes about  2.5 hours for one drying run, so fortunately a decent number of specimens can be done at once.)

the dry specimen is then ready to be coated.  i don’t know whether the coating machine has a particular name other than ‘sputter-coater’ but it deserves something awe-inspiring like The Purple Zowza Machine of Glory because, well, it inspires science-geeky excitement at its finest.  the specimen to be coated sits on a little aluminum stub inside a vacuum chamber, beneath a disc of gold-palladium foil.  the chamber gets pumped full of argon gas, and then a current is passed through the gas, causing the argon atoms to get excited.  look out!  no, really.  argon atoms are surprisingly impressive when excited – they glow bright purple!  so you see this electric violet cloud surrounding the specimen, and although you can’t actually see this happening, the big, excited argon atoms are bouncing around and knocking into everything – including the foil above the specimen.  some of the gold-palladium atoms are dislodged by the careening argon, and they fall onto the specimen, and coat it in a metal layer several atoms thick.  voila – after just 4 minutes, you have a specimen ready for electron bombardment.

pretty neat, huh?

…. hello?

… ?

philistines.

Read and post comments | Send to a friend