Researchers have created a flexible paper-based sensor that operates like the human brain. They fabricated a photo-electronic artificial synapse device composed of gold electrodes on top of a 10 μm transparent film consisting of zinc oxide (ZnO) nanoparticles and cellulose nanofibers (CNFs).

The transparent film serves three main purposes: 1) it allows light to pass through, enabling it to handle optical input signals representing various biological information; 2) the cellulose nanofibers impart flexibility and can be easily disposed of by incineration; and 3) the ZnO nanoparticles are photoresponsive and generate a photocurrent when exposed to pulsed UV light and a constant voltage. This photocurrent mimics the responses transmitted by synapsis in the human brain, enabling the device to interpret and process biological information received from optical sensors.

The film was able to distinguish 4-bit input optical pulses and generate distinct currents in response to time-series optical input, with a rapid response time on the order of subseconds. This quick response is crucial for detecting sudden changes or abnormalities in health-related signals. When exposed to two successive light pulses, the electrical current response was stronger for the second pulse. (Image credit: Cornell University)

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