12 February 2015

Laboratory on a smartphone: premature delight?

mChip v.3 – Smartphone-based medical laboratory

Andrey Vasilkov, Computerra

Columbia University of New York has developed a diagnostic console for a smartphone that quickly detects HIV antibodies and syphilis markers in a blood sample. The mChip test system costs $34, uses disposable cartridges with a cost of less than a ruble and is being tested in Rwanda.

To perform the analysis, the medical worker places a blood sample into one of the cartridges, which is automatically mixed with reagents and passes through many channels inside the cartridge. They form a long system of microtubules of different diameters, acting simultaneously as a filter, dispenser and setting the required time delay for the complete reaction.

This is not the first version of such a device. In recent years, the authors have reduced the size of the installation and power consumption by several times, having mastered the form factor of the console and bringing it to the size of the smartphone itself.

The system of microtubules and sensors of the 2011 version of mChip
(photo: nature.com ).

A prototype of a "laboratory on a chip" for the diagnosis of HIV and syphilis, created in 2013.
(photo: Columbia Engineering)

Diagnostic console mChip – modern version
(photo: gadgets2use.de )

The power is connected via a 3.5" headphone jack, and the control is carried out via a mobile application.

The development gives hope that an economical and portable diagnostic laboratory can be implemented on a handheld device and demonstrate results in the field that are close in accuracy to the indicators of complex and cumbersome laboratory installations of previous years.

Already, an extremely small volume of blood is required for the simultaneous determination of antibodies to HIV and pale treponema – literally a microdrop. First, gold nanoparticles selected in shape and size selectively bind to certain antibodies in the blood sample under study. Then the smallest silver particles form an opaque layer. This silver film blocks the propagation of the light of the translucent sample, and against its background, the sensor registers the passage of detectable antibodies surrounded by gold particles.

Schematic diagram of the mChip diagnostic console
(image: Samuel K Sia et al.).

It takes about fifteen minutes from taking a blood sample to receiving the test result. The received data is automatically loaded into the smartphone's memory. In fact, the prototype reproduces in miniature enzyme immunoassay (ELISA) using the ELISA method, which requires expensive laboratory equipment. According to Samuel Sia, associate professor of biomedical engineering at Columbia University, the accuracy of the portable system is almost as high as that of the reference ELISA.

However, such statements should be taken with a fair amount of skepticism. Any developer praises his brainchild, so let's figure out the details. The ELISA method itself was once the "gold standard" in express diagnostics, but now it has been replaced by more accurate ones. They no longer determine antibodies to the causative agent of the disease (which may not exist for various reasons), but directly the presence of DNA of pathogenic microorganisms in the blood.

Practitioners know that from the moment of infection to the appearance of a registered immune response, sometimes a considerable time passes. In the case of HIV, this is about three weeks, during which the patient will unnecessarily consider himself healthy, rejoicing at the false negative result of the ELISA tests. If he had immediately donated blood to determine the DNA of the pathogen (by PCR), he would have had a much better chance to start a set of preventive measures in a timely manner. The real opportunity to get rid of the immunodeficiency virus is only at an early stage.

"This work is proof that technology can improve diagnosis, making it faster, easier and cheaper without compromising quality," says Sabine Nsanzimana, head of the department for combating STDs of the Ministry of Health of Rwanda. "However, the implementation may take some time, or require additional research."

MIT Technology Review literally extols the new portable laboratory, but let's look at the figures of the original article in Science. The cartridge really costs "just pennies" – it's just a plastic container with a microtubule system (although even it would be expensive here – just by tradition). Here are reagents and colloidal (nano)gold/silver particles of a certain shape are already worth a lot, which is modestly silent in the article.

96 pregnant women took part in the study voluntarily (as far as this term is generally known in Rwanda). Ninety-three of them found the new method more convenient. Only three participants expressed cautious doubts... and they were right. The specificity of the experimental technique was 79%. Some nanoparticles still bind to the wrong proteins, somewhere the sensor gives false positives or other errors occur. Simply put, every fifth result was erroneous. This is already better than fortune-telling, but it is still very far from the requirements of medical standards.

To be implemented into clinical practice as a reference, it is required to achieve an accuracy level of 95% or higher. In some cases, lower indicators are allowed, but they are accepted only temporarily (from no alternative) and until the appearance of accurate methods. Fifty percent accuracy with a large number of patients is provided by a simple coin toss. Every percentage above fifty in screening diagnostics comes at the cost of increasing optimizations.

Many promising techniques have not become a breakthrough precisely because of insurmountable difficulties at the stage of refinement. They have not passed the tests of the FDA and other regulatory authorities, as well as the portable test system created at Columbia University has not yet passed it. Therefore, yes, this is another interesting idea from the "laboratory on a chip" series, but for an indefinite time it will not be able to become a replacement for proven methods.

The authors plan to increase the scale of field trials and see smartphones as the basis of portable diagnostics in developing countries. "So far we are identifying HIV and syphilis, but it is obvious that this technology is more universal," says Samuel Sia. "The healthcare system can be radically transformed if patients can receive accurate measurements in a decentralized manner."

Portal "Eternal youth" http://vechnayamolodost.ru12.02.2015

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