Polymer-Based Lab-on-Tip Microstructures For Ultrasound Medical Diagnostics

All-optical ultrasound is an emerging minimally invasive imaging technique widely used in biomedical applications, such as intravascular diagnostics and high-resolution photoacoustic endoscopy, requiring miniaturized probes with high sensitivity. In this context, Lab-on-fiber 3D micro-structures are becoming particularly attractive thanks to their small size and easy integration in minimally invasive endoscopic tools. Considering the advancements that the Lab-on-Fiber is continuously experiencing in terms of fabrication techniques, here we propose a comparison concerning design flexibility and performances of two different polymeric ultrasound sensors integrated on the fiber tip: a polymeric multilayer configuration and a membrane-based micro-structure. The former can be realized by means of the spin coating technique, while the latter with the Two-Photon-Polymerization technique. Both configurations have been designed and studied through Finite Element Method, evaluating their performances as ultrasound detectors in terms of sensitivity and bandwidth. Furthermore, their performances have been also compared to those obtained with a third configuration based on a plano-concave Fabry-Perot, which is currently the benchmark for this kind of sensor. Interestingly, the multilayer configuration introduces additional degrees of freedom in the design allowing for improving the optical behaviour, while the membrane configuration exhibits a resonant acoustic response that strongly enhances the sensitivity at high frequencies.