Brazil, November, 2025: A groundbreaking biosensor developed by Brazilian researchers may transform mental health diagnosis by detecting depression biomarkers in saliva within minutes and at a fraction of traditional testing costs.
Scientists from the University of São Paulo and Embrapa Instrumentação, a decentralized unit of the Brazilian Agricultural Research Corporation (Embrapa), have created a portable saliva-based biosensor capable of measuring brain-derived neurotrophic factor (BDNF) levels in under three minutes.
This innovation offers a fast, affordable, and noninvasive alternative to conventional diagnostic methods, including laboratory-based tests such as the dexamethasone test that have contributed to depression diagnosis for many years. 1
Current methods for measuring BDNF, a protein essential to brain health, require expensive laboratory equipment, large sample volumes, and specialized facilities. BDNF levels are typically determined by enzyme-linked immunosorbent assay (ELISA) and may be validated through Western blot analyses using a BDNF monoclonal antibody. BDNF can be reliably measured in human serum. 2
However, tests like ELISA are time-consuming and often inaccessible to patients in resource-limited settings.
The new biosensor directly addresses these challenges. Priced at approximately 2.19 dollars per unit, it provides accurate results using simple saliva samples.
The salivary BDNF immunosensor strip is constructed using a screen-printed carbon electrode functionalized with carbon spherical shells (CSSs), polyethylenimine (PEI), and glutaraldehyde. These components enhance sensitivity and allow the device to connect to a portable analyzer. Results are transmitted wirelessly to a smartphone via Bluetooth, making mental health screening easier.
Brain-derived neurotrophic factor (BDNF) is a neurotrophin involved in the survival, development, and functioning of neurons. Its levels are associated with several neurological and psychiatric conditions, including Alzheimer's disease, major depressive disorder, anxiety disorders, schizophrenia, and other neurodegenerative diseases. 3
Healthy individuals generally have BDNF concentrations above 20 nanograms per milliliter (ng/mL). People with major depressive disorder often present levels below 10 to 12 ng/mL.
The research shows Reduced BDNF levels are also linked to schizophrenia, bipolar disorder, and cognitive decline. 3
The device relies on electrochemical impedance spectroscopy, a technique that measures changes in resistance at the electrode-solution interface. The process is as follows:
The working electrode is modified with carbon nanospheres and coated with chemical components, including polyethylenimine and glutaraldehyde, which enhance sensitivity and act as a matrix to immobilize the BDNF-specific capture antibody.
The BDNF antibody (anti-BDNF) is immobilized on the electrode surface, and an ethanolamine layer is applied to prevent unwanted interactions.
When saliva containing BDNF is applied, the antibody and antigen interact to form complexes that alter electron transfer resistance.
This resistance change is detected and quantified, and results appear on a connected smartphone within three minutes.
The biosensor demonstrated exceptional sensitivity, detecting BDNF concentrations ranging from 10⁻²⁰ to 10⁻¹⁰ grams per milliliter.
According to the World Health Organization, more than one billion people worldwide live with mental disorders. Anxiety and depression are the most common and affect individuals regardless of age or income. Rates of depression have increased globally.
Lead researcher Paulo Augusto Raymundo Pereira noted that the rise in mental health conditions following the COVID-19 pandemic motivated the development of this tool.
Depression often goes undiagnosed in nearly 50 percent of cases because symptoms develop slowly or appear in unexpected forms. 4
Many individuals do not realize they are experiencing depression, delaying treatment and allowing symptoms to worsen.
Research shows that 35.5 percent to 50.3 percent of serious cases in developed countries and 76.3 percent to 85.4 percent of cases in less developed countries receive no treatment within a year of onset. 4
A major challenge is the lack of effective diagnostic classifications for identifying depressive disorders in primary care.
The biosensor provides several important advantages:
● Accessibility: At 2.19 dollars per unit, the test may be deployed widely, including in underserved communities.
● Speed: Results appear within three minutes, eliminating long laboratory wait times.
● Noninvasiveness: Saliva collection is simple and stress-free, making the test suitable for all age groups.
The research team also evaluated the biosensor's environmental impact using the Analytical Eco-Scale (AES), Analytical GREEnness Metric Approach (AGREE), and Blue Applicability Grade Index (BAGI). These tools examine environmental friendliness, sustainability, and practical applicability.
The assessments confirmed that the biosensor meets modern standards of green and practical analytical chemistry.
The Analytical Eco-Scale (AES) provides a semi-quantitative assessment of environmental friendliness in analytical procedures. AGREE is a software-based tool that quantitatively evaluates the environmental impact of an entire method. BAGI focuses on the practical utility of a procedure and complements green chemistry metrics.
The research, published in ACS Polymers Au, represents a significant scientific advancement. However, commercialization requires additional validation, and the research team is currently working toward patent protection.
The research team includes Nathalia Gomes, Marcelo Luiz Calegaro, Luiz Henrique Capparelli Mattoso, Sergio Antonio Spinola Machado, and Osvaldo de Oliveira Junior.
Key Takeaway: Brazilian researchers have developed a portable and affordable biosensor that detects depression biomarkers in saliva within three minutes. This innovation has the potential to improve mental health screening, promote early diagnosis, and support treatment monitoring.
Smith KM, Renshaw PF, Bilello J. The diagnosis of depression: current and emerging methods. Comprehensive Psychiatry. 2013;54(1):1-6. doi:10.1016/j.comppsych.2012.06.006
Naegelin Y, Dingsdale H, Säuberli K, Schädelin S, Kappos L, Barde YA. Measuring and Validating the Levels of Brain-Derived Neurotrophic Factor in Human Serum. eNeuro. 2018;5(2):ENEURO.0419-17.2018. Published 2018 Mar 22. doi:10.1523/ENEURO.0419-17.2018
Correia AS, Cardoso A, Vale N. BDNF Unveiled: Exploring Its Role in Major Depression Disorder, Serotonergic Imbalance, and Associated Stress Conditions. Pharmaceutics. 2023;15(8):2081. doi:10.3390/pharmaceutics15082081
Faisal-Cury A, Ziebold C, Rodrigues DMO, Matijasevich A. Depression underdiagnosis: Prevalence and associated factors. A population-based study. Journal of Psychiatric Research. 2022;151:157-165. doi:10.1016/j.jpsychires.2022.04.025