You are more transparent than you think – Sajan Saini

It’s an increasingly common sight
in hospitals around the world: a nurse measures our height,
weight, blood pressure, and attaches a glowing plastic
clip to our finger. Suddenly, a digital screen reads out
the oxygen level in our bloodstream. How did that happen? How can a plastic clip learn something
about our blood… without a blood sample? Here’s the trick: our bodies are translucent, meaning they don’t completely
block and reflect light. Rather, they allow some light to actually
pass through our skin, muscles, and blood vessels. Don’t believe it? Hold a flashlight to your thumb. Light, it turns out, can help probe the
insides of our bodies. Consider that medical fingerclip— it’s called a pulse oximeter. When you inhale, your lungs transfer
oxygen into hemoglobin molecules, and the pulse oximeter measures the ratio
of oxygenated to oxygen-free hemoglobin. It does this by using a tiny red LED light
on one side of the fingerclip, and a small light detector on the other. When the LED shines into your finger, oxygen-free hemoglobin in your blood
vessels absorbs the red light more strongly than its oxygenated
counterpart. So the amount of light that makes
it out the other side depends on the concentration ratio
of the two types of hemoglobin. But any two patients will have different-sized
blood vessels in their fingers. For one patient, a saturation reading of
ninety-five percent corresponds to a healthy oxygen level, but for another with smaller arteries, the same reading could dangerously
misrepresent the actual oxygen level. This can be accounted for with a second
infrared wavelength LED. Light comes in a vast spectrum
of wavelengths, and infrared light lies just beyond
the visible colors. All molecules, including hemoglobin, absorb light at different efficiencies
across this spectrum. So contrasting the absorbance of red
to infrared light provides a chemical fingerprint to
eliminate the blood vessel size effect. Today, an emerging medical sensor industry
is exploring all-new degrees of precision chemical fingerprinting, using tiny light-manipulating devices
no larger than a tenth of a millimeter. This microscopic technology, called integrated photonics, is made from wires of silicon
that guide light— like water in a pipe— to redirect, reshape, even
temporarily trap it. A ring resonator device,
which is a circular wire of silicon, is a light trapper that enhances chemical
fingerprinting. When placed close to a silicon wire, a ring siphons off and temporarily stores
only certain waves of light— those whose periodic wavelength
fits a whole number of times along the ring’s circumference. It’s the same effect at work when
we pluck guitar strings. Only certain vibrating patterns dominate
a string of a particular length, to give a fundamental
note and its overtones. Ring resonators were originally
designed to efficiently route different
wavelengths of light— each a channel of digital data— in fiber optics communication networks. But some day this kind of data
traffic routing may be adapted for miniature chemical
fingerprinting labs, on chips the size of a penny. These future labs-on-a-chip may easily,
rapidly, and non-invasively detect a host
of illnesses, by analyzing human saliva or sweat
in a doctor’s office or the convenience of our homes. Human saliva in particular mirrors the composition of our bodies’
proteins and hormones, and can give early-warning signals for
certain cancers and infectious and autoimmune diseases. To accurately identify an illness, labs-on-a-chip may rely on
several methods, including chemical fingerprinting, to sift through the large mix of trace
substances in a sample of spit. Various biomolecules in saliva absorb
light at the same wavelength— but each has a distinct chemical
fingerprint. In a lab-on-a-chip, after the light passes
through a saliva sample, a host of fine-tuned rings may each siphon off a slightly different
wavelength of light and send it to a partner light detector. Together, this bank of detectors will
resolve the cumulative chemical fingerprint
of the sample. From this information,
a tiny on-chip computer, containing a library of chemical
fingerprints for different molecules, may figure out their relative
concentrations, and help diagnose a specific illness. From globe-trotting communications
to labs-on-a-chip, humankind has repurposed light to both
carry and extract information. Its ability to illuminate continues
to astonish us with new discoveries.


  1. When he said put a flashlight to your thumb, I actually paused the video on my phone, turned on flashlight, and tested it.

  2. 0:05
    Saw the quote and loved the video instantly. It is my new mantra now by the way. Love your hard work and BEAUTIFUL animations. My god they are some serious business.

  3. My Samsung s7e has this Oxygen saturation sensor, yeah a red light shines through…and yeah it's roughly accurate as I tried it before and after holding my breath for a while and my O2 saturation level decreased. But the thing is, my phone's sensor doesn't have a detector on the other side so how does it receive the reading?

  4. After a surgery, they taped a pulse oximeter to my finger, but it was too tight, so the damn machine kept beeping due to lack of blood-flow to the finger. However, they kept thinking I want breathing enough, even though I kept complaining about the thing being too tight. They didn't about their mistake until they finally removed it and let my finger breathe.

  5. Alright , but how does my Samsung S7 Pulse Oximetre work without a counterpart to the infra-red-LED?
    Please explain !

  6. We are still far from the tech used by Dr. Leonard McCoy…but it seems we're heading towards the right direction

  7. a place in my town wants to change all the underground Electrical Connections into Light Connections ones to make the energy travel faster….. Could you explain it plz??

  8. Oh nice video as always! That's why I see red things on my finger when I put light close to it! Now we know. (lol?)

  9. Light may also help manage and cure illnesses someday. I read an article not too long ago about how light and sound were used to counteract the effects of dementia in mice. Imagine if, in a few decades, that was a viable treatment for humans.

  10. Why do I feel this could be easily hacked to lure people? "Oh, you're ill, come to this clinic"

  11. It amazes me how we are inventing these things. Who knows what the future will be like? Things like these sometime terrify me of what humans can do

  12. I really thought this refers to the deeper meaning of being "transparent" actually. Turns out it's completely literal and scientific and I'm here for it. It's TED-Ed!

  13. My makeup shade is called “translucent” and I can see all my veins through my skin, so yeah makes sense.

  14. I am studying biochemistry so this video is very informative for me thank you ted- ed for this … from INDIA…🤗😊

  15. 👌👌👌 licks coins in the future
    🤔🤔 What if you lick your 10 cent then use it to buy chips

  16. If the school system taught like this I think we would find that people would be more motivated and happy to walk into their classrooms.

  17. Yess! I learn so much from these videos. If TED-Ed wasn't around I wouldn't have as much knowledge as I have now, haha!

  18. If you’ve never shined a light on any part of yourself then you don’t have a life honestly.

  19. When we do finally combine all of those amazing little sensors into a single multi-use sensor device, I hope we call it a tricorder. 🖖🏻

  20. "humankind"? I am pretty sure thid was the work of hard working engineers. Maybe we should spend less time appluading the work of fake superheroes on the big screen and celebrating the real superheroes who invented these!

  21. I hated the brown one that they wrap on your finger. After surgery, mine was always in my way when I wanted to do something. Not to mention it was setting off the monitor. And it was so loud in the ICU.

  22. Ted ed always amazes us by it's amazing animations. It's really appreciable 👍👍.love the way you teach us Ted ed. 💓

  23. Had the pleasure of interviewing a researcher working on something a lot like that coin-sized blood tester earlier this year. We’ll be buying them from the local chemist before long.

  24. How did I end up here? I started from cyanide and happiness. Btw , this is really great educational content.

  25. My dad told me that when he was a kid his brothers would put a powerful light behind him, like the ones they use for construction at night, they could see his organs and stuff like if he was transparent. 🙃

  26. Atoms are mostly empty space,
    We are made of atoms,
    Thus light mostly passes our body rather than being reflected by it

  27. I was expecting a video on behavioral psychology and unconscious visual cues that can expose your mood and emotions, but this works too.

  28. This can be potentially dangerous since this lab chips can collect your data and be used in unknowingly and creepily motives.

    Don't ask me what motives are those, but if there are, please do tell me, and I might expand my opinion on how dangerous this device might be.

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