Wireless magnetoelectrically powered organic light-emitting diodes

Abstract

Biomedical implants, such as brain stimulators, have significantly enhanced the quality of life for many individuals. Recently, the emergence of photonic implants has opened new avenues for innovative treatment methods and high-resolution neuronal stimulation through a technique known as optogenetics. However, classical photonic implants, such as optical fibres tether the subject to an external light source. Wireless light sources, which combine an energy receiver for wireless power transfer with an integrated light source in a compact volume, are revolutionizing treatment methods and propel optogenetic research forward. Nevertheless, current electromagnetic field based wireless stimulators are still bulky or require high frequency fields to operate, which are strongly absorbed by opaque watery environments such as tissue. The composite magnetoelectric (ME) effect, which enables the conversion of magnetic fields to electric fields via mechanical oscillations, has the potential to overcome limitations related to miniaturization, power supply, and low-frequency device operation. In this work, we explore the combination of composite ME materials and organic light-emitting diodes (OLEDs) to create a compact light source that operates at frequencies below one megahertz. We present the first sub-cubic millimetre, low frequency wireless light source by directly manufacturing a specifically tailored OLED stack onto an ME transducer. The device demonstrates robust performance with no signs of degradation over hours of continuous operation and can be operated deep inside a tissue phantom. We show that the light output is sufficient to trigger an optogenetic response in Drosophila melanogaster fruit fly larvae and outline efforts towards mammalian animal models. To provide enough power for the OLED, ME transducers must be operated at their mechanical resonance frequency. We exploit this property to demonstrate the clustered activation of multiple devices located in the same magnetic field. A computational optimization strategy allows guided resonance frequency tuning by changing the shape of the device. Our work lays the foundations for a novel type of tiny, wireless light source operable centimetres deep inside tissue.