Dr. Luis Ramiro Caso Vargas, researcher at the Faculty of Biological Sciences of the BUAP, generates optical biosensors to detect pathogenic bacteria (Pseudomonas aeruginosa), with application in hospital environments; as well as Brucella spp. which causes brucellosis due to the consumption of contaminated foods, mainly dairy products. Also, biosensors to identify biogenic amines that can trigger food poisoning.
Pseudomonas aeruginosa is a bacteria present in hospitals (furniture, surgical instruments, catheters and even disinfectants) capable of causing severe infections in immunosuppressed hosts. Furthermore, its resistance to antibiotics and its wide range of defenses make it an extremely difficult organism to eradicate. To identify it, Caso Vargas designed a biosensor with 1cm2 silicon dioxide wafers – used in the manufacture of computer microprocessors – whose surface he changed its molecular structure by chemical methods. Thus, he obtained a device with biological activity that immobilizes and displays the biomolecules that function as bioreceptors, in this case antibodies.
This is possible because chemical compounds are used that “stick” firmly to the surface of the silicon dioxide through a gas phase process. Thanks to this, a first layer is formed that modifies the properties of the original surface. Then a second layer is added made of special molecules called crosslinkers, which act as bridges between that base and the biomolecules that you want to immobilize. A protein called streptavidin is attached to this second layer with the ability to bind to antibodies prepared with biotin, which recognize the bacteria to be detected.
To verify the assembly of the biosensors, advanced techniques are used such as Fourier transform infrared spectroscopy (FT-IR), which provides information regarding the chemical bonds formed during the assembly between the different molecules used; in addition, Scanning Electron Microscopy (SEM) and fluorescence microscopy to observe the amount of bacteria present in the sensor. Dr. Norma Elena Rojas Ruiz, from ICUAP, collaborates in this research, who among other lines is dedicated to the isolation of microorganisms from diverse environments.
Luis Ramiro Caso Vargas, doctor in Biotechnology from the IPN, commented that another aspect for the detection of Pseudomonas aeruginosa is a biosensor built with gold nanoparticles.
“This system is much smaller, even than the bacteria. Instead of silicon, the biosensors are based on fluorescent gold nanospheres to which an antibody is also attached to trap the microorganism in question. Like guided missiles, they go directly to the bacteria.”
The nanospheres are not fixed on a surface, but in a solution that would allow other types of samples to be analyzed, for example, the inside of pipes. The presence of the bacteria is detected by the fluorescence intensity. This work is developed in collaboration with Dr. Leslie Arcila Lozano, Researcher for Mexico, commissioned to the IPN Applied Biotechnology Research Center.
For the detection of Brucella spp., the academic from the Faculty of Biological Sciences has developed biosensors based on silicon dioxide supports with an architecture similar to those used for P. aeruginosa, where only the crosslinker and the antibody change. This research is also in process and doctors Edith Chávez Bravo, from ICUAP, and Efraín Rubio Rosas, from the Directorate of Innovation and Knowledge Transfer (DITCo), participate.
Discover toxins in food
In the case of identifying harmful compounds in foods, attention was paid to the so-called biogenic amines. These substances are generated by the action of bacteria during the decomposition of food, a process that is not noticeable in the early stages. To detect them, Caso Vargas explained that in the biosensor, also based on silicon dioxide supports, instead of antibodies, the enzyme Diamine Oxidase is immobilized, which specifically recognizes these molecules.
The researcher from the Academic Body “Environmental Biotechnology” said that the detection of biogenic amines was carried out under laboratory conditions and was then tested on aged, blue and gouda cheeses, as well as salmon and tilapia. “When placing the device in an aqueous extraction from contaminated food, a change in color of the sample was observed, which indicates the recognition of biogenic amines by the biosensor. The lighter the sample, the fewer toxins; the darker the sample, the more contamination.”
Likewise, Luis Ramiro Caso Vargas, a member of the National System of Researchers, develops electrochemical sensors using a technique known as “polymers with molecular fingerprinting,” for the detection of histamine, the most powerful biogenic amine. Collaborating on this work are doctors Walter Torres Hernández, from the Universidad del Valle, in Colombia, and Harold Díaz Segura, who did a research stay in the Caso Vargas laboratory.
