The PCR laboratory was placed on a microchip
Anna Obraztsova, N+1
A microfluidic chip has been created that checks for the presence of pathogen DNA in a blood sample. The device has a small size, works quickly and without electricity and at the same time is very cheap in production. The description of the chip is published in the journal Science Advances – Yeh et al., Self-powered integrated microfluidic point-of-care low-cost enabling (SIMPLE) chip.
Here and below are the drawings from the article in Science Advances
Polymerase chain reaction (PCR) – a method of molecular biology that allows increasing the initially low concentration of a given DNA sequence in a solution so that its presence becomes visually detectable. In medicine, this technique is widely used to check for the presence of a particular pathogen in a blood sample. However, the reaction requires equipment – a centrifuge to separate blood cells from plasma and a thermal cycler to maintain the temperature regime of the reaction. If the same is carried out Real-time PCR, which determines the amount of DNA in the sample, then the thermal cycler must also be equipped with a fluorescent detector. All this leaves the method applicable only inside the laboratory.
To solve the problem, scientists from the University of California at Berkeley have developed a microfluidic chip SIMPLE (Self-powered Integrated Microfluidic Point-of-care Low-cost Enabling) for PCR, which works autonomously. It is a die made of polydimethylsiloxane, on which there are wells connected by a channel and containing a reaction activator. A drop of blood is placed at the beginning of the channel through which it moves, gradually filling all the holes. At the same time, they are separated from the channel by a threshold that passes plasma, but not blood cells, which allowed the chip developers to get rid of the centrifugation stage.
Diagram of the chip device and demonstration that blood cells remain in the channel
The blood moves through the channel due to the vacuum system, which the authors of the chip call the "lung". It consists of a vacuum compartment that slowly sucks air out of the chip tanks through thin gas-permeable walls. The chip has two "lungs", one of which pulls blood along the channel, and the other pulls it into the wells. In order for the system not to start working ahead of time, the chips are stored in vacuum packaging.
In order for the chip to determine the amount of DNA in the blood, the authors implemented a digital PCR method in it. Its essence is that the reaction mixture is divided into many micro–samples in which the reaction goes in parallel - on the chip it happens in separate wells. After the reaction, fluorescence makes it possible to determine which micro-samples the DNA molecules got into and which did not. The proportion of luminous micro–samples (in the case of a well chip) is proportional to the concentration of the desired DNA sequence in the original sample. The only disadvantage for a portable chip is that a microscope is needed to count the holes.
In addition, the authors use a modification of PCR, which does not require temperature cycles, but is carried out at a constant temperature. Therefore, a reusable salt warmer is enough for the chip to work.
It takes only half an hour to process one sample on a chip, while the entire device fits in the palm of your hand, and the cost of materials for one piece does not exceed ten dollars. So far, it is intended only for the detection of HIV and methicillin-resistant Staphylococcus aureus (MRSA), but in the future, of course, it is planned to adapt it for other pathogens, for example, the Ebola virus or malaria plasmodium.
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24.03.2017