Provided herein are medical devices, systems and platforms to monitor tissue properties such as oxygen saturation, temperature and degree of tissue edema for diagnosis and post-operative patient monitoring. The medical devices may be handheld or portable or may be removable patches. The medical devices utilize light of various visible and near-infrared wavelengths to interrogate a tissue where the intensities of reflected light correlate to one or more tissue property. Also provided are methods for measuring tissue properties, for detecting pressure ulcers and for remotely monitoring in real time a surgical flap on a post-operative subject via the medical devices.