The smartphone heats the chip in which biochemical reactions occur to 37 degrees Celsius
Huan Xu et al. / Science Advances, 2020
–
Scientists have created a portable device for DNA analysis. It weighs about 60 grams, its cost is less than $ 7. The device uses a smartphone to heat the reagents and automatically recognize the result. The device is highly sensitive and versatile; it recognizes various types of mutations and DNA of pathogens in blood, urine and saliva samples, as well as in products and plants. The article is published in the journal. Science advances.
One of the most common ways to determine the DNA sequence is through polymerase chain reaction (PCR). For PCR, special equipment, a source of electricity and a trained specialist are needed. Scientists are trying to create portable devices for DNA analysis, which will allow analyzes in any conditions.
Determining the DNA sequence requires a number of procedures: sample preparation, amplification (multiple copying of DNA molecules in samples) and detection itself. Each of these steps must be fitted into a portable device. One of the problems along this path is to make the process independent of electricity, because most DNA analysis methods require heating the samples.
They are trying to make the device not only compact, but also universal: it should be able to work with analyzes of saliva, blood and urine and recognize various forms of DNA, for example, pathogen and mutation genes.
Scientists from China and the United States, led by Ming Chen from the Third Military Medical University, have created an ultra-portable device for DNA analysis weighing less than 100 grams. The device consists of two main parts: a four-gram chip, which is printed on a 3D printer, and a folding box. Together with the smartphone, which is necessary for the device to work, all the details are placed in a package or envelope in B5 format (25 by 17 centimeters). The cost of production of the device is about $ 2.5, and consumables for the analysis of one sample – about four dollars.
–Device complete set: cardboard box, smartphone, lens and chip
Huan Xu et al. / Science Advances, 2020
–
–
–
–
The chip consists of two parts: a sample preparation unit and a signal amplification unit. The sample is placed on a disk that binds DNA, and washed from the cellular components with a buffer solution. Then add reagents for recombinase polymerase amplification – a method that allows you to propagate DNA molecules at a constant temperature.
Solutions are injected into the chip using a syringe onto which a Teflon tube is inserted. It already has all the necessary reagents in the right order and quantity. Different solutions separate the air bubbles, and the device operator only needs to press the syringe plunger until the desired fluid comes out of it.
–Five stages of the device. 1: samples are placed on a chip; 2: buffer washes away cell debris; 3: recombinase polymerase amplification; 4: DNA binds to samples; gold nanoparticles sit on them; 5: samples cover silver ions
Huan Xu et al. / Science Advances, 2020
–
–
–
–
To heat the samples to the required 37 degrees Celsius, use a smartphone. Scientists have developed an application that launches operations that require intensive work of the processor. The program automatically controls the number of operations to maintain the temperature at the desired level. The kit also provides disposable packages that will protect your smartphone from biological fluids.
Recombinase polymerase amplification is carried out for 20 minutes, after which the samples enter the signal amplification unit through the microfluidic channel. The sample fluid passes through a glass chip on which DNA samples are fixed. DNA molecules from samples that are complementary to samples bind to those and are fixed on a glass surface, and the rest are washed off. DNA on a glass chip is coated with gold nanoparticles, on which many silver ions are deposited as a result of a catalytic cascade.
–Signal amplification unit. Pink – microfluidic channel, color – various DNA samples
Huan Xu et al. / Science Advances, 2020
–
–Sectional gain of the signal. Pink – microfluidic channel, color – various DNA samples
Huan Xu et al. / Science Advances, 2020
–
–
–
–
Thanks to silver ions, the points at which the DNA of the samples binds to the samples are visible to the naked eye. To automatically read the result, you need the second part of the device. It includes a cardboard folding box (stand for smartphone) and an optical unit with a macrolens and LED. The phone’s camera captures the glow of the samples, and the application digitizes the result.
–The second part of the device: a folding cardboard box and signal detection using a smartphone
Huan Xu et al. / Science Advances, 2020
–
–
–
–
Using the device, it was possible to recognize different types of mutations (deletions of DNA fragments of different lengths, single nucleotide inserts and substitutions), allelic genes and pathogen specific DNA sequences. It was only necessary to choose the right primers. The sensitivity limit of the device is 113 copies of DNA per milliliter of sample.
The device has demonstrated its versatility for various types of biological samples: blood, saliva, urine, food and plants. The device can be used for medical tests to determine food safety and detect pathogens of cultivated plants.
The fashion for portable devices penetrates into various fields of medicine: there are “chiometers” that determine asthma by exhaled air; sweat sensors mounted on the wrist; and even portable bioreactors for drug synthesis.
Alice Bakhareva
–
