[RD (OP)]

Allegedly this cancer test is capable of detecting a "one single circulating tumour cell" in vivo.

I'm skeptical, here's one of the reasons why ...
a video of a normal mouse (no cancer) being given an injection of indocyanine green (ICG) whilst illuminated by Infra Red. Mickey lights-up like a Christmas-tree because ICG binds to components of normal blood.

[Bored chemist]

If this stuff was truly specific + only stuck to tumour cells then we could chemically  glue a toxic molecule to it and get it to poison those cells.
No detection needed- just kill the bastards.

[RD (OP)]

If this stuff was truly specific + only stuck to tumour cells then we could chemically  glue a toxic molecule to it and get it to poison those cells.
No detection needed- just kill the bastards.

In the video it is claimed to be a twofer: both cancer detection & treatment.

Spectroscopy is repeatedly mentioned in the video ,
but ICG will fluoresce at a known frequency, when illuminated with a specific frequency,
so no need analyse a spectrum ...


715bea9f1d7ec581a903a88a6f649213f11c.png (133.78 kB . 872x714 - viewed 716 times)

In that article, "Intraoperative Indocyanine Green Imaging Technique in Cardiovascular Surgery",
they say "penetration of fluorescence is less than 2 to 3 mm" with their superior-looking equipment. 
So if the (~2mm ø) "spectroscopy" probe attached to the skin was equally sensitive,
most of the "total blood-volume" is not going to be screened in "17 minutes".

[Bored chemist]

Spectroscopy might be needed- not so that you can see the ICG- but to screen out other fluorescence from other stuff present in the body.

It's also possible to do clever tricks like gating (so you only look for fluorescence that occurs at a specified time after the light is absorbed).
That can give you information about the environment of the fluorescent material.
https://www.ncbi.nlm.nih.gov/pubmed/28397959

But I still think it's iffy.

[RD (OP)]

... fluorescence that occurs at a specified time after the light is absorbed ...

I can see delayed-fluorescence, or phosphorescence, being included to explain why the IR optical-fiber is in the forearm but the electronic-sensor probe* is on the bicep.

Even running with the idea that CTC luminescence is delayed or persists until it reached the bicep,
if the probe* on the bicep can only see ~8mm³ then the vast majority of any CTCs illuminated by IR in the forearm will not pass under the probe*, and will go undetected.

Even one did go under the probe*, it's only 10-20µm ø, occupying >1/50,000 of the sensor's field of view.
Light emitted by it would be swamped by light from any background levels of ICG, or from autofluorescence.
Signal lost in noise.

This alleged-test is a complete non-starter IMO. 

[ * In this scenario the ICG fluorophore chemical is the called a probe.
That the good-doctor repeatedly calls the electronic-sensor a probe shows how well he understands the subject ].

[evan_au]

If they had identified a particular wavelength to which the dye was sensitive when coupled to a cancer cell, and caused it to fluoresce at a specific other wavelength, that would make it a lot more selective.

But there are many types of cancer, which display a different mix of surface proteins, so a very selective test is unlikely to detect most of them (let alone all of them).

It seems that what we have is:
- A very non-selective test
- Which is guaranteed to find a positive response in every individual
- And then pushes everyone into Phase 2, using the same equipment to treat the cancer that they have just discovered
- And then pushes them into Phase 3, which is regular follow-up treatments, just in case it comes back...

Of course, treatment of the blood will not find nor eliminate any primary cancer.
 

[RD (OP)]

It seems that what we have is:
- A very non-selective test
- Which is guaranteed to find a positive response in every individual ...

Even the cancer patient's "companion", who will be told they too have cancer and will require treatment,
( there are naive people on the premises who are not being bilked, let's scam them too ).

[Bored chemist]

I'd be a lot happier if he could pronounce phosphorescence.
There may be something in this idea, but I'm very dubious.
However, I'd love to be proven wrong.

Incidentally, delayed fluorescence typically means microseconds, rather than nanoseconds.
It's still far too fast for the cells to travel any meaningful distance.