Brazilian biosensor warns if food is contaminated with bacteria such as salmonella Salmonella-contaminated foods: A biosensor developed in Brazil identifies contamination faster and more effectively.

Each year, 10% of the world's population contracts some form of disease transmitted by contaminated food, from gastrointestinal infections to meningitis, according to the World Health Organization.

Deaths due to these diseases reach 420 000 per year, children under five represent one-third of the victims. Most of these diseases are caused by bacteria such as Salmonella spp. ., Escherichia coli and Staphylococcus aureus .

A group of Brazilian researchers has developed a 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 Osvaldo Novais de Oliveira Junior, a physicist at the São Carlos Institute of Physics, coordinator of the team that developed the device, one of the biggest difficulties in avoiding DTAs is the detection of an early stage of the disease. contamination, that is to say when their number is still very low.

"In conventional methods, samples of food or drink are collected and then sent to a specialized laboratory for to verify the formation of colonies. "

This must be done by microscopic badysis to visualize the clusters, and can take 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 more responses. "says Oliveira, who developed the biosensor in collaboration with university researchers. Federal University of São Carlos (UFSCar) and Embrapa Instrumentação, from the same city.

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As a result, many research groups around the world have developed new methodologies for detecting food contamination by microorganisms. "Our intention was to create something fast, inexpensive and efficient at the same time," says Oliveira.

"Our methodology solves the problem of detecting initial contamination with a preconcentration strategy of the bacteria 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 silkscreen technique. The paint of the metal is spread on the polymer with the help of a machine made in Brazil with a polyester fabric.

"The peculiarity of this product is the ability to produce large quantities at low cost and in other types of materials," says Oliveira. "Not only in PET, but also in paper and cloth, as we have already tested in our labs."

The other essential element of the test is the pre-concentration of the 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 the researchers are covered with melitin, a substance extracted from the venom of the bee sting, which has an affinity for bacteria.

When these nanoparticles are introduced into a liquid sample to be badyzed, any bacteria present there are directed due to 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 crushed, homogenized and filtered sample will suffice to follow the same procedure.

For this, the sample is placed on the electrodes, and then electrical impedance measurements are made (resistance of an electrical circuit to the current flowing when a voltage is applied). "The presence of bacteria alters the value of the impedance and this modification serves as a detection mechanism," says Oliveira.

"The measurement process is fast, in 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 food or drink and monitor the growth of bacteria in order to be able to 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 R $ 0.30 each)."

Moreover, the procedures can also be simple. cost if the methodology is used on a large scale. "Another possible benefit 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 developed in three species of bacteria: Salmonella thyphi, Escherichia coli and Staphylococcus aureus .

The first can be found in foods such as eggs and birds and cause typhoid fever. The second, in turn, is quite common in the intestines of man and some animals. But there are pathogenic strains (causing diseases) related to different types of problems, including gastrointestinal, urinary and even meningitis.

Finally, Staphylococcus aureus is present in different environments and can cause diseases such as 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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