Laboratory testing showed that the device was able to identify the low dopamine levels associated with Parkinson's disease.
Traditionally, dopamine levels are measured through blood tests, urine samples or implanted monitoring devices — methods that can be invasive, time-consuming or uncomfortable. A tear-based test could provide doctors with a simpler way to detect the earliest biochemical signs of Parkinson's disease, potentially long before symptoms such as tremors and stiffness become apparent.
Why Dopamine Matters
Dopamine acts as a messenger between nerve cells and is essential for smooth, controlled movement.
As the brain cells responsible for producing dopamine gradually die off, dopamine levels decline, leading to the characteristic symptoms of Parkinson's disease.
Beyond movement, dopamine also influences mood, motivation and learning. Abnormal dopamine levels have been linked to a range of psychiatric conditions, including schizophrenia.
A New Window into Brain Health
The sensor was developed by a team led by Neftalí Lênin Villarreal Carreño, a materials scientist at the Federal University of Pelotas (UFPel) in southern Brazil.
The researchers wanted to find a way to assess brain chemistry without the need for needles or surgical procedures. Existing dopamine-monitoring methods are either invasive or poorly suited to regular testing.
Tears, by contrast, are easy and painless to collect. Previous research has also shown that tears contain biomarkers linked to neurological processes, including changes associated with Parkinson's disease.
How the Sensor Was Built
To create the device, the researchers used a laser to trace patterns onto a thin plastic film.
The heat generated by the laser transformed the material into graphene, a highly conductive form of carbon. The resulting electrode is roughly the size of a postage stamp.
Graphene alone can function as a sensor, but the team enhanced its performance by coating it with nickel and a nitrogen-rich compound. This created additional active sites where chemical reactions could occur.
Designed Specifically for Tears
Under an electron microscope, the modified surface appeared porous and sponge-like, providing more opportunities for dopamine molecules to bind.
When dopamine comes into contact with the electrode, it releases electrons. The sensor detects this tiny electrical signal and converts it into a measurable reading.
Laser-produced graphene has become an increasingly popular material for low-cost biosensors. Similar dopamine-detection systems have been described in a recent study, but the Brazilian researchers tailored their version specifically for use in tear fluid rather than blood or sweat.
What the Tests Revealed
To evaluate the sensor, the team added known concentrations of dopamine to artificial tears and monitored the device's response.
The results showed a clear relationship: as dopamine concentrations increased, the electrical signal rose accordingly across a broad range of levels.
Artificial tears allowed the researchers to control dopamine concentrations precisely, making it easier to map the sensor's full response before moving on to real-world testing.
One of the most notable findings was the sensor's sensitivity.
It was capable of detecting dopamine concentrations below 20 nanomoles per litre, significantly lower than those typically found in healthy human tears.
Importantly, this detection range also covered dopamine levels previously reported in the tears of people with Parkinson's disease.
Accurate Even in Complex Tear Fluid
The researchers also tested whether other compounds normally present in tears would interfere with the readings.
The sensor maintained its accuracy even when mixed with other tear components, demonstrating that everyday eye chemistry did not significantly affect performance.
It was sensitive enough to detect dopamine levels ranging from well below normal healthy values to concentrations several times higher.
"Our sensor can detect dopamine from levels well below the healthy baseline and up to three times higher," said Lucas Minghini Gonçalves, a co-author of the study.
Potential for Earlier Diagnosis
Because dopamine levels begin to decline before the visible symptoms of Parkinson's disease emerge, a test capable of detecting these subtle early changes could help identify the disease sooner.
Earlier diagnosis could give doctors a greater opportunity to intervene while more dopamine-producing brain cells remain intact.
"We aim to facilitate the ultra-early detection of neurological disorders, creating opportunities for clinical interventions before major symptoms manifest," said Carreño.
The researchers envision a portable handheld device that could analyze a tear sample on the spot in a clinic. The low-cost materials and laser-manufacturing process could make widespread screening practical and affordable.
From Laboratory Research to Clinical Use
At present, the sensor has only been tested using artificial tears, meaning studies involving real human tear samples will be the next critical step.
Researchers worldwide are increasingly investigating tears as a source of Parkinson's biomarkers. One earlier study identified a misfolded protein associated with the disease in tear samples.
What the Brazilian team has demonstrated is a low-cost, laser-fabricated sensor capable of detecting dopamine at concentrations linked to Parkinson's disease in tear-like fluid.
If future testing confirms similar performance in real tears, the technology could provide a simple, painless and accessible method for monitoring brain chemistry and detecting Parkinson's disease at an earlier stage.
The findings were published in the journal ACS Omega.
Source: earth.com
