In vivo optical resolution photoacoustic microscopy using glancing angle-deposited nanostructured Fabry–Perot etalons

In this Letter, reflection-mode optical resolution photoacoustic microscopy (OR-PAM) using glancing angle-deposited (GLAD) nanostructured Fabry-Perot interferometers (FPI) for in vivo applications is reported. GLAD is a single-step physical vapor deposition (PVD) technique used to fabricate porous nanostructured thin films. Using titanium dioxide, a transparent semiconductor with a high refractive index (n=2.4), the GLAD technique can be employed to fabricate samples with tailored nano-porosity, refractive index periodicities, and high Q-factor reflectance spectra. The OR-PAM in vivo images of chorioallantoic membrane (CAM) of 5-day chicken embryo model are demonstrated. The phantom study shows lateral resolution and signal-to-noise ratio better than 7 μm and 35 dB, respectively. The sensitive GLAD FPI allows photoacoustic imaging down to a few-nJ pulse energy. To the best of our knowledge, this is the first time that a FPI-based reflection mode optical resolution photoacoustic imaging technique is demonstrated for in vivo applications.