Live laser for cancer diagnosis
A laser made of human blood
Laser illumination of the tumor. Illustration: Alfred Pasieka / SPL
When using the word "laser", many imagine a kind of electronic device using doped crystals, semiconductors, synthetic dyes and purified gases. In fact, this is not necessary. Lasers can be made from ordinary biological material. In principle, working lasers can be assembled right inside the human body.
Actually, what is a laser? A certain design that converts the pumping energy into the energy of a coherent, monochromatic, polarized and narrowly directed radiation flux. Roughly speaking, three things are needed: 1) energy source; 2) active medium (signal amplification material); 3) resonator (reflecting cavity).
The first laser from human cells (more precisely, from one kidney cell) it was designed in 2011 by scientists from South Korea and the USA. Green fluorescent protein (ZFB) was used as a medium for optical signal amplification in it. When pumped with nanosecond nanojoule pulses, individual cells generate bright directed laser radiation in a narrow band.
Live laser from a human kidney cell with ZFB expression
Illustration: Nature Photonics, doi:10.1038/nphoton.2011.99
The ZFB protein isolated from the jellyfish Aequorea victoria fluoresces in the green range when illuminated with blue light. It is still widely used in cellular and molecular biology to study the expression of cellular proteins. This is a completely safe protein that is injected into the patient's blood. Thus, it can be safely used to generate laser radiation inside the human body.
Candidate of Physical Sciences Xudun (Sherman) Fan and colleagues from the University of Michigan continued the work of their predecessors. They found out that the optical signal is significantly enhanced not only by ZFB, but also by another common diagnostic dye, indocyanine green (ICG), if mixed with human blood cells, namely, with blood plasma. In this case, ICG binds to plasma proteins and together with them generates a magnificent narrowly directed radiation stream. "Without blood, just in ICG solution, the laser does not work at all," he explained Xudun Fan.
A mixture of blood with ICG is placed in a small reflecting cylinder and illuminated with a conventional laser, after which the blood begins to generate bright directional laser radiation. It glows much brighter than the usual fluorescence of indocyanine, and this is important. The fact is that ICG accumulates in blood vessels, so that vessels with a large amount of blood – for example, tumors – will glow much brighter. Thus, it is an excellent tool for the diagnosis of malignant or benign tumors.
For diagnosis, the patient should be given an injection of harmless indocyanine green. Then highlight the skin area with a conventional laser (laser pointer?) – and look at this area in the infrared range. By the way, conventional digital cameras and smartphones register IR quite well – if you point the camera lens at the remote control from the TV, then you can see the signal from the remote.
As a result, a fairly accurate diagnosis of cancerous tumors is carried out using the usual household items – a laser pointer and a smartphone (and ICG).
To make this possible, it is still necessary to bring the technology to mind and develop safety techniques. Scientists believe that gold nanoparticles can be used as a reflecting cavity in living tissue. But a number of experiments should be carried out to determine the exact concentration of gold nanoparticles and the necessary laser power. Experiments on laser optical tomography will first be conducted on animals.
"Eventually, we will try to do this in the human body," says the author of the scientific paper. He assures that the laser power will be less than the recommended safety standards. "You don't want to fry the fabric."
Professor Fan's scientific work was published on July 21, 2016 in the Optica magazine (by the way, it was even put on the cover of the issue).
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06.09.2016