Nanoparticles are starting to be used in a variety of biomedical applications, including imaging, biosensing, DNA analysis and cancer treatment. Recently, scientists have started looking at the possibility of interfacing nanomaterials, such as nanotubes and nanowires, with neurons. Now, Nicholas Kotov of the University of Michigan and colleagues at the University of Texas Medical Branch at Galveston (UTMB) have succeeded in interfacing photovoltaic nanoparticle-thin films with nerve cells for the first time.

The researchers achieved their result by developing a process that builds up a sandwich of two kinds of ultrathin films layer-by-layer on top of a glass plate. The first type of film is made of semiconducting mercury-tellurium nanoparticles and the second of a positively-charged polymer called PDDA. The scientists then added a layer of clay and a biologically-compatible coating of amino acids to the structure and finished by placing a layer of cultured neurons on the very top.

When light is shone on the mercury-tellurium nanoparticle film layers, they produce electrons, which travel upwards into the PPDA film layers. When the current reaches the neuron membrane on top, it depolarizes the cell to the point where it "fires", so producing a signal in the nerve.

Researchers have previously transmitted light signals to nerve cells using silicon, but nano-engineered materials offer the possibility of being much more efficient and versatile. "It should be possible for us to tune the electrical characteristics of these nanoparticle films to get properties like colour sensitivity and differential stimulation, the sort of things you want if you're trying to make an artificial retina, which is one of the ultimate goals of this project," said Todd Pappas, lead author of the paper, which appears in Nano Letters. "You can't do that with silicon. Plus, silicon is a bulk material – silicon devices are much less size-compatible with cells."

The researchers say that although an actual, implantable artificial retina is still some way off, the results from the present work could be used in a variety of other, less complex, applications. These include new ways to connect with artificial limbs and prostheses, and in novel tools for imaging and diagnosis.

"The beauty of this achievement is that these materials can be remotely activated without having to use wires to connect them. All you have to do is deliver light to the material," said Massoud Motamedi, director of UTMB's Center for Biomedical Engineering and a co-author of the paper. "I feel that such nanotools are going to give the fields of medicine and biology brand-new capabilities that it's hard to even imagine now."