The biosensor is the result of a collaboration between researchers from the University of São Paulo (USP) and Embrapa Instrumentação. The study was published in ACS Polymers Au.
The platform is equipped with a flexible strip embedded with electrodes that, when used in conjunction with a portable analyzer, assesses samples of human saliva. In under three minutes, the biosensor can measure the concentration of BDNF (brain-derived neurotrophic factor), a protein essential for the growth and maintenance of neurons, as well as the development of brain functions such as learning and memory.
The study indicates that the device possesses long-term storage capabilities and is capable of accurately measuring extremely low levels of the protein across a broad spectrum of saliva concentrations (ranging from 10-20 to 10-10 grams per milliliter). The next step for the researchers is securing a patent.
There are few sensors that perform this type of analysis, and ours was the one that performed best. It detected a wide range of concentrations, which is a very good result from a clinical point of view. When protein levels are very low, it can serve as a warning sign for diseases and psychiatric disorders. On the other hand, by being able to signal an increase in BDNF, it contributes as a tool to monitor the patient's progress according to the treatment.
Paulo Augusto Raymundo Pereira, Researcher, São Carlos Institute of Physics
Pereira, possessing expertise in chemistry and biotechnology, has spent years in the development of flexible sensors and electrochemical biosensors. In a recent paper in the Chemical Engineering Journal, he helped showcase the findings of a portable sensor designed for urine self-testing, intended to identify markers of diseases, including gout and Parkinson's.
Link to Disorders
Scientific research indicates that diminished levels of BDNF are among the factors contributing to various neurological and psychiatric disorders, such as depression, linked to cognitive decline. Antidepressants can help restore the effects of this protein.
Healthy individuals typically exhibit BDNF levels exceeding 20 ng/mL, while those suffering from major depressive disorder (MDD) present levels below 10 or 12 ng/mL.
Data from the World Health Organization (WHO) reveals that over one billion individuals are affected by mental disorders, with anxiety and depression being the most common conditions. The organization's reports, including the Mental Health Atlas 2024, indicate that the prevalence of these disorders has risen across all nations, impacting individuals of varying ages and income levels.
From 2022 to 2024, the rate of worker absences attributed to mental health concerns in Brazil surged by 134 %. The Occupational Safety and Health Observatory reports that these absences escalated from 201,000 to 472,000, primarily due to instances of depression, anxiety, and recurring depression.
The increase in cases of mental disorders and the consequent rise in the use of medication, especially after the COVID-19 pandemic, motivated us to work on this issue and seek alternatives.
Paulo Augusto Raymundo Pereira, Researcher, São Carlos Institute of Physics
Pereira has the support of FAPESP through scholarships.
The Device
The flexible strip is screen-printed on a polyester film substrate which holds three electrodes: a functionalized working electrode, a pure carbon auxiliary electrode, and a silver reference electrode.
The working electrode was modified with carbon nanospheres and treated with a layer of two chemical compounds, polyethyleneimine and glutaraldehyde, to enhance sensitivity and serve as a matrix for immobilizing the BDNF-specific capture antibody (anti-BDNF). A reactive layer of ethanolamine was also incorporated to inhibit other forms of interaction.
The detection of BDNF relies on the creation of antibody-antigen immunocomplexes, which increase resistance to electron transfer on the sensor's surface. This increase is monitored through electrochemical impedance spectroscopy, a method employed to investigate phenomena occurring at the interface of an electrode and a solution.
Results can be presented in real time on a mobile device through wireless communication, such as a smartphone using Bluetooth.
Current methods for analyzing BDNF levels include the enzyme-linked immunosorbent assay (ELISA), electrochemiluminescence, fluorescence, and high-performance liquid chromatography (HPLC). These methods necessitate considerable time, large sample volumes, and specialized laboratory settings.
“We're moving toward personalized medicine, in which treatments will be increasingly tailored to each individual. In the case of the biosensor, it can be optimized to suit different profiles,” says one of the researchers.
Journal Reference:
Gomes, O. N., et al. (2025) Low-Cost, Disposable Biosensor for Detection of the Brain-Derived Neurotrophic Factor Biomarker in Noninvasively Collected Saliva toward Diagnosis of Mental Disorders. ACS Polymers Au. doi.org/10.1021/acspolymersau.5c00038.