Low-cost saliva test could help detect depression and schizophrenia
A portable saliva biosensor costing just US$2.19 can detect protein levels linked to depression, schizophrenia and bipolar disorder in under three minutes.
The device measures brain-derived neurotrophic factor (BDNF), a protein vital for neuron health whose altered levels are associated with several psychiatric conditions.
Developed by researchers at the University of São Paulo and Embrapa Instrumentação – a unit of the Brazilian Agricultural Research Corporation – the flexible strip uses electrodes to analyse drops of saliva when connected to a portable reader.
Paulo Augusto Raymundo Pereira is a researcher at the São Carlos Institute of Physics and corresponding author of the study.
The researcher said: “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.”
BDNF supports the growth and survival of neurons – the brain’s nerve cells – and plays a key role in learning and memory.
Low levels of the protein are linked to neurological and psychiatric disorders involving cognitive decline, including depression and schizophrenia.
In healthy individuals, BDNF levels typically exceed 20 nanograms per millilitre, while those with major depressive disorder often record levels below 10–12 nanograms per millilitre. Antidepressants can help restore the protein’s function.
The biosensor can detect protein concentrations ranging from 10⁻²⁰ to 10⁻¹⁰ grams per millilitre, with sensitivity down to 1.0 × 10⁻²⁰ grams per millilitre.
Each unit costs about US$2.19 – less than R$12 at current rates – and can be stored long-term, according to the researchers.
The device is made from a flexible strip screen-printed on a polyester film containing three electrodes.
The working electrode was coated with carbon nanospheres and chemical compounds to increase sensitivity and immobilise the antibody that binds specifically to BDNF.
Detection is based on the creation of antibody-antigen complexes – when the BDNF protein binds to its antibody – which alters electron transfer resistance on the sensor surface.
This is measured using electrochemical impedance spectroscopy, a technique that analyses reactions at the electrode-solution interface.
Results can be viewed in real time on a mobile device via Bluetooth. The team’s next step is to seek a patent for the technology.
According to World Health Organization data, more than 1 billion people live with mental disorders, with anxiety and depression being the most common.
In Brazil, worker absences due to mental health problems rose by 134 per cent between 2022 and 2024, increasing from 201,000 to 472,000 cases.
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,” Pereira said.
Current techniques used to measure BDNF include enzyme-linked immunosorbent assay (ELISA), electrochemiluminescence, fluorescence, and high-performance liquid chromatography.
These methods require specialist laboratories, large sample volumes and lengthy processing times.
