$2 Saliva Test Could Help Detect Depression, Schizophrenia

Summary: Scientists have developed a wearable biosensor that can detect levels of BDNF, a protein linked to mental health conditions such as depression, schizophrenia and bipolar disorder. The flexible, low-cost device analyzes a drop of saliva in less than three minutes and offers a rapid, affordable and non-invasive diagnostic tool.

Because low levels of BDNF are associated with depression and cognitive decline, the test could help doctors detect and manage disorders earlier. At an estimated cost of just $2.19 per unit, the biosensor could transform mental health screenings, especially in low-resource settings.

Key facts

Quick Results: Saliva-based biosensor measures BDNF levels in less than three minutes. Affordable Innovation: Each unit costs around $2.19, making it affordable for widespread use. Clinical relevance: Low BDNF levels are linked to depression, while increases may follow recovery

Source: FAPESP

Brazilian researchers have developed a low-cost, wearable biosensor that can quickly identify a protein whose altered levels are associated with psychiatric disorders, such as depression, schizophrenia and bipolar disorder.

When commercially available in the future, it may contribute to early detection, which is essential to treat and monitor patients’ clinical conditions.

The biosensor is the result of a collaboration between researchers from the University of São Paulo (USP) and Embrapa Instrumentação, a decentralized unit of the Brazilian Agricultural Research Company (Embrapa). It consists of a flexible strip with electrodes that, when integrated with a portable analyzer, evaluates drops of human saliva.

In less than three minutes, the biosensor provides the concentration of BDNF (brain-derived neurotrophic factor), a protein crucial for the growth and maintenance of neurons and the development of brain functions, including learning and memory.

The research, published in ACS Polymers Au, shows that the device can reliably measure extremely low concentrations of protein in a wide range of saliva (from 10⁻²⁰ to 10⁻¹⁰ grams per milliliter), down to trace amounts that are still detectable (1.0 × 10⁻²⁰ grams per milliliter).

The biosensor has an estimated cost of $2.19 per unit (less than 12 reais at the current exchange rate) and long-term storage capacity. According to scientists, the next step is to obtain the patent.

“There are few sensors that perform this type of analysis, and ours was the one that worked 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 signal for psychiatric diseases and disorders.

“On the other hand, by being able to indicate an increase in BDNF, it contributes as a tool to monitor the patient’s evolution according to the treatment,” explains Paulo Augusto Raymundo Pereira, researcher at the São Carlos Institute of Physics (IFSC-USP) and corresponding author of the article, in an interview with Agência FAPESP.

Pereira, who has experience in chemistry and biotechnology, has been working with flexible sensors and electrochemical biosensors. Last year, he co-authored a paper in the Chemical Engineering Journal that presented results from a wearable urine self-testing sensor aimed at detecting markers for diseases such as gout and Parkinson’s.

Link to disorders

Scientific literature shows that low levels of BDNF are one of the factors involved in some neurological and psychiatric disorders associated with cognitive impairment.

Depression is one of those disorders. The effect of the protein is restored with antidepressants. Healthy people have BDNF levels above 20 nanograms per milliliter (ng/ml), while people with major depressive disorder (MDD) have levels below 10 or 12 ng/ml.

According to data from the World Health Organization (WHO), more than one billion people live with mental disorders, with anxiety and depression being the most prevalent conditions.

According to the organization’s reports, including the Mental Health Atlas 2024, these disorders have increased in prevalence in all countries, affecting people of all ages and income levels.

Between 2022 and 2024, worker absences due to mental health problems in Brazil increased by 134%. According to the Occupational Health and Safety Observatory, these absences increased from 201,000 to 472,000 and were caused by episodes of depression, anxiety and recurrent depression.

Pereira adds: “The increase in cases of mental disorders and the consequent increase in the use of medications, especially after the COVID-19 pandemic, motivated us to work on this issue and look for alternatives.” Pereira is supported by FAPESP through scholarships (16/01919-6, 23/09685-8 and 22/02164-0).

The device

The researchers developed a flexible strip screen-printed on a polyester film substrate with three electrodes: a functionalized working electrode, a pure carbon auxiliary electrode, and a silver reference electrode.

The working electrode was modified with carbon nanospheres. It was coated with two chemicals (polyethyleneimine and glutaraldehyde) to increase sensitivity and act as a matrix to immobilize the BDNF-specific capture antibody (anti-BDNF). To avoid other types of interaction, a reactive ethanolamine layer was added.

The detection of BDNF is based on the formation of antibody-antigen immune complexes, which increase the resistance to electron transfer on the sensor surface. This growth is captured using electrochemical impedance spectroscopy, a technique used to study processes that occur at the interface between an electrode and a solution.

The results can be viewed in real time on a mobile device (smartphone) via wireless communication (Bluetooth).

Current techniques used to analyze BDNF levels include enzyme-linked immunosorbent assay (ELISA), electrochemiluminescence, fluorescence, and high-performance liquid chromatography (HPLC). These techniques require time, large volumes of samples and specialized laboratories.

“We are moving towards personalized medicine, in which treatments will be increasingly adapted to each individual. In the case of the biosensor, it can be optimized to adapt to different profiles,” says the researcher.

Funding: FAPESP also supported the study through the thematic project “Towards the convergence of technologies: from sensors and biosensors to information visualization and machine learning for data analysis in clinical diagnosis”, in addition to two other projects (23/07686-7 and 20/09587-8).

The team is made up of the following researchers: Nathalia Gomes, Marcelo Luiz Calegaro, Luiz Henrique Capparelli Mattoso, Sergio Antonio Spinola Machado and Osvaldo de Oliveira Junior.

Key questions answered:

About this mental health and neurotechnology research news

Author: Heloisa Reinert
Source: FAPESP
Contact: Heloisa Reinert – FAPESP
Image: Image is credited to Neuroscience News.

Original research: Open access.
“Low-cost disposable biosensor for the detection of brain-derived neurotrophic factor biomarker in non-invasively collected saliva for the diagnosis of mental disorders” by Paulo Augusto Raymundo Pereira. ACS Au Polymers

Abstract

Low-cost disposable biosensor for the detection of brain-derived neurotrophic factor biomarker in non-invasively collected saliva for the diagnosis of mental disorders

The importance of early detection of biomarkers of neurodegenerative disorders has increased, as these biomarkers are essential for timely applications in diagnosis, treatment, healthcare, and wellness.

We present a disposable, cost-effective electrochemical immunodetection strip for the rapid and decentralized detection of brain-derived neurotrophic factor (BDNF), one of the major neurotrophins (NTs) associated with neurological and psychiatric disorders, in human saliva.

The salivary BDNF immunosensor strip is fabricated on a screen-printed carbon electrode functionalized with carbon spherical shells (CSS), polyethyleneimine (PEI), and glutaraldehyde to improve sensitivity.

Through systematic optimization, the sensor achieved excellent analytical performance, with a wide dynamic detection range of 1.0 × 10–20 to 1.0 × 10–10 g mL–1, a fast response time of less than 3 minutes, and an ultra-low detection limit of 1.0 × 10–20 g mL–1 for BDNF in human saliva.

The BDNF immunosensor demonstrated high selectivity, reproducibility, robustness, stability, and long-term storage capacity.

At a cost of less than $2.19 per unit, this disposable sensor also enabled rapid detection of BDNF in saliva samples collected from healthy volunteers without interference from other saliva components.

Environmental impact was assessed using the Analytical Ecological Scale (AES), the Analytical GREEN (AGREE) metric approach, and the Blue Applicability Degree Index (BAGI), which assesses the practicality (“blue”) of the device. These evaluations confirmed the sustainability of the disposable BDNF immunosensor strip.

This device provides a rapid, efficient, cost-effective, and reliable method for decentralized, non-invasive salivary analysis of BDNF, enabling broader applications in healthcare, wellness monitoring, and medical diagnostics related to the neurotrophin family of biomarkers.