A team of researchers have developed an innovative image sensor that integrates liquid biological environments with organic electronics, mimicking core functions of the animal retina.
Both image photodetector arrays and retinas are pixelated sensors that dynamically extract various features from the visual scene – e.g., colour, brightness, and contrast – before transmitting electrical signals to either a graphical interface of a display or the brain.
Unlike conventional solid-state image sensor arrays, the device developed by the researchers, named BIOPIX, operates at the interface between electronics and biology, combining printed organic semiconductor materials with a water-based physiological medium. This integration allows the sensor to capture light through the polymer materials and convert it into electrical signals via a water-based physiological electrolyte in ways that more closely resemble the phototransduction behaviour of natural photoreceptors: the rods and cones found in the retina of animal eyes.
“We designed this device to go beyond traditional electronic sensors,” explains Prof. Thomas M. Brown, at the Electronic Engineering Department of ‘Tor Vergata’, coordinator of the research. “By letting organic electronic materials interact with a liquid biological environment, BIOPIX reacts to light in a way that is much closer to how a real retina works in nature, both in how it senses colour (spectrally) and how quickly it responds.”
The temporal response of BIOPIX, on the order of tens of milliseconds, mirrors the slower ionic dynamics of liquid-based mammalian retinas, and its sensitivity is comparable to that of established solid state polymer semiconductor photodetectors.
The array includes 12 pixels that mimic rod-like responses, responsible for low-light and contrast sensitivity, and a central 2 x 2 array that simulates cone-like di-chromatic sensitivity for colour detection in mice.
“What’s exciting about BIOPIX … is that when light strikes the liquid/solid bio-hybrid device, it is converted into electrical signals that are processed and displayed as grayscale from the rod-like pixels and colour images from the central cone-like pixels in real time on a display,” explains Ebin Joseph, PhD student and first author of the article.”
“The challenge of converting light incident on BIOPIX into direct-to-display pixelated images was addressed by developing a dedicated electronic readout system tailored to its ionic liquid retina-like temporal dynamics,” added Dr Luca Di Nunzio, expert in digital electronics and embedded signal processing both from Electronic Engineering Department of ‘Tor Vergata’.
Beyond performance, the researchers demonstrated the platform’s biocompatibility. In vitro tests using human mesenchymal stromal cells showed no adverse effects on cell viability, an important milestone for potential biomedical applications.
“Confirming biocompatibility was a key step,” said Prof. Antonella Camaioni at the Department of Biomedicine and Prevention of Tor Vergata, co-responsible for the research. “It validates the platform for fundamental research and points toward future possibilities, such as artificial retinal implants or adaptive biointerfaces.”
“Our work represents an important first step toward emulating how the retina forms images, with a long-term goal of developing better retinal prosthetic devices. With BIOPIX, we aim to mimic the spectral and temporal behaviour of the mouse retina, a widely used model for studying degenerative eye diseases, such as retinitis pigmentosa and age-related macular degeneration, that lead to photoreceptor loss and vision impairment,” explains Dr Hiroki Asari, expert in Visual Systems Neuroscience at EMBL.
The researchers emphasise that BIOPIX is more than a novel sensor: it is a scalable, versatile platform for studying how light is converted into electrical signals at the interface of biological and artificial systems. This retina emulator platform could aid in the development of artificial photoreceptors, help us better understand the biophysics of phototransduction, natural vision, and inspire new technologies in artificial vision and neural interfacing.
“The BIOPIX retina emulator platform can, for example, be used to study new photoabsorbing artificial photoreceptor materials and physiological media prior to retinal implantation or injection, as well as to evaluate their performance under varying environmental conditions. In addition, it can help understand differences in image sensing operating in fully solid-state mode versus that at the interface between biological (liquid) and semiconducting (solid) matter in a field where biology and technology are coming together to enable new possibilities,” added Brown.
Looking ahead, the team sees BIOPIX as a step toward smarter artificial vision and new kinds of technology where light, electronics, and biology work together.
The team told Electronic Specifier that: “This is the first image sensor that has created images in real time on a display that is liquid/solid in nature … the devices we designed are not only a new type of image sensor but also a retina emulator, making it hard, even for us, to decide which of the two it is (sign of a true hybrid!).”
