The sensors are so small that you could fit several of them into a single cell, and they measure the tiny electronic signals that keep cells functioning.
When the signals become irregular, it can indicate that the cells have been damaged by inflammation, toxicity, or disease.
Experts believe their sensors could help create a test to diagnose and monitor the progress of conditions such as macular degeneration, Parkinson’s and Alzheimer’s.
They may also boost drug development by offering an insight into how cells respond to therapy.
The project, which has been in development for three years, is being led by Dr Colin Campbell of the University of Edinburgh’s school of chemistry.
He said: “Electronic activity in cells is strictly controlled and normally runs like clockwork – so when it goes wrong, it can be a sign of disease.
“Our device offers a safe, effective method to test the health of cells.” The sensor is made of molecules, known as “reporter” molecules, which are capable of responding to cell electrical activity, or “potential”.
They have been mounted on to gold particles that can be inserted harmlessly into cells.
The result is a sensor which can be scanned with a laser to give a measure of electrical activity in the cell, indicating whether it is healthy or not.
Dr Campbell said: “What you’ve got is effectively a nanosensor. The particles are about 130 nanometres in diameter. They’re absolutely tiny.
“The reporter molecule changes its structure depending on the potential inside the cell. From a single particle inside the cell, you can figure out which state those reporter molecules are in and what the potential is inside the cell.”
Researchers have so far been working on tissue cultures in the laboratory but are looking at how a test could be developed for use on patients.
They say their device improves upon existing techniques, as it has greater sensitivity, better accuracy, and does not interfere with the cell’s functioning.
Dr Campbell, who has worked closely with student Craig Auchinvole on the project, said: “We’re looking to translate it out of chemistry labs and get it more into biology labs, so that it becomes a standard tool of biology.
“We would also like to look at using it ‘in vivo’, say in a hospital situation.
“If you could use them ‘in vivo’, you could figure out which parts of a tumour are being regulated differently, in a way that makes them respond badly to therapy.
“I would also hope that we could use this to try and screen for drugs.”
The study, funded by EaStCHEM (the joint chemistry research school of Edinburgh and St Andrews) and the university, was published in the ACS Nano journal.