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Every year, 10% of the world's population contract a type of disease transmitted by contaminated food – from gastrointestinal infections to meningitis, reports the World Health Organization.
The number of deaths due to these diseases reaches 420 one year, children under five years representing one third of fatal victims. Most of these diseases are caused by bacteria such as Salmonella spp . .
Escherichia coli and Staphylococcus aureus. biosensor using magnetic nanoparticles and a substance extracted from bee venom to detect contamination of food and beverages much faster and more efficiently than traditional methods.
According to physicist Osvaldo Novais Oliveira Junior of the USP Institute of Physics São Carlos, coordinator of the team that has developed the device, one of the biggest difficulties to avoid DTA is to detect bacteria in the initial stage of contamination, ie when their number is still very low. "
" In conventional methods, samples of food or drink are collected and sent to a specialized laboratory.
This must be done by microscopic badysis to visualize the clusters, and can last a long time (up to 72 hours), especially if the contamination is at the beginning. "
]" There are other methods, such as ELISA (enzyme-linked immunosorbent baday) and PCR (polymerase chain reaction), which can provide faster responses, " explains Oliveira, who developed the biosensor in collaboration with researchers at the Federal University of (19659002) "The problem is that they require sophisticated and expensive equipment, as well as specialized staff for badysis."
That is why it is necessary to develop new methodologies for detecting contamination.Research on foods by microorganisms has been the goal of many research groups around the world. "Our intention was to create something fast, inexpensive and efficient at the same time ", explains Oliveira.
" Our methodology solves the problem of the detection of the initial contamination by a strategy of preconcentration of bacterium ies. in the sample. "
According to him, the sensor itself is quite simple.It contains silver electrodes, deposited on plastic films, polyethylene terephthalate – or PET-, with a screen printing technique.The painting of the metal is spread on the polymer with the help of a machine made in Brazil with a polyester mesh.
"The peculiarity of this product is the ability to produce large quantities at low cost, as well as in d & # 39; 39; other types of materials, "says Oliveira." Not only in PET, but also in paper and cloth, as we have already tested in our laboratories. "
The other essential ingredient of test is the preconcentration of samples This is done to solve the difficulty of detecting small concentrations of microorganisms.In the technology developed in São Carlos, the magnetic nanoparticles produced in the laboratory by researchers are covered with m litine, substance extracted from the venom of & # 39; bee that has an affinity with the bacteria.
When these nanoparticles are introduced into a liquid sample to be badyzed. any bacteria present is directed to them because of the presence of melittin. After a while – about 20 minutes – the magnetic nanoparticles, with adhered microorganisms, are attracted to a magnet. It is this material with pre-concentrated bacteria that is used for detection. In the case of solid foods, a small, ground, homogenized and filtered sample will suffice to perform the same procedure.
For this, the sample is placed on the electrodes, and then electrical impedance measurements are made (resistance of a current electrical circuit when a voltage is applied). "The presence of bacteria changes the impedance value, and this modification serves as a detection mechanism," says Oliveira.
"The measurement process is fast, on the order of a few minutes, which is advantageous compared to traditional methods."
According to the USP researcher, it is necessary to badyze the entire volume or mbad of the food or drink and monitor the growth of bacteria so as to be able to count it in the colony . This procedure can take between 24 and 72 hours for cases of early stage contamination, that is, with a small number of microorganisms.
Oliveira cites a number of advantages of the technology developed by his group. "The first is the shortest time required for badysis because the steps of growing and growing bacteria are eliminated," he says. "This allows real-time monitoring, the other being the low possible cost of each scan because the electrodes are very inexpensive (about .30 dollar each)."
In addition, the procedures can also be simple. cost if the methodology is used on a large scale. "Another possible advantage is the simplicity in performing detection measurements, even for small concentrations of bacteria, which can be done by non-specialists in badysis, with very little training," adds Oliveira
. The researchers tested the biosensor that they developed. in three species of bacteria:
.
The first is found in foods such as eggs and birds and causes typhoid fever. Salmonella thyphi, Escherichia coli and Staphylococcus aureus. The second, in turn, is quite common in the intestines of man and some animals. Staphylococcus aureus occurs in different environments and can cause diseases such as bacterial, fungal and fungal infections. conjunctivitis, meningitis and pneumonia. "These bacteria can be present in any type of environment where sterilization conditions are not strict," Oliveira said. "This is the case of mishandled foods, such as in the industry or in supermarkets."
In addition, the biosensor created in São Carlos may have other applications. With some adaptations, it will be possible to use it to detect different types of contamination in hospital environments, such as operating theaters and operating theaters, as well as in the instruments and equipment used in these environments, as well as in patients with wounds, burns and bedsores
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