Contactless pressure detection enabled by a hybrid 3D laser-printed nanophotonic sensor†

Modern wearable pressure sensors rely on converting external stimuli to electrical signals. Despite being widely developed, they still present significant disadvantages such as intrinsic heat generation due to electrical losses, which can interfere with data acquisition, limited speed of electronics, and user discomfort. Here, we propose a nanophotonic approach in which mechanical loading alters the optical behavior of photonic nanostructures. Using direct laser writing, we fabricate three-dimensional photonic structures on flexible substrates. These are coated with ZnO using atomic layer deposition enhancing their optical properties and biocompatibility. Exploiting full-wave photothermal and electromagnetic simulations, we induce a thermal conductance mismatch via a layered substrate to avoid photo-induced thermal damage of the substrate during writing and engineer the optical resonances of the sensor in the telecommunication C-band. Imitating pressure variations in the human body, we integrate our photonic device into a bulge setup to apply biaxial loading and monitor the changes of optical properties in situ. We show the potential of the technology for strain sensing applications with a sensitivity of 0.016% under cyclic loading. This study thus aims to support future investigations combining nanofabrication and coating techniques with the aim of developing biocompatible all-optical sensors for low-loss and ultrafast wearable diagnostics.