biosensors Article A Multi-Wavelength Opto-Electronic Patch Sensor to Effectively Detect Physiological Changes against Human Skin Types Liangwen Yan 1, Sijung Hu 2,*, Abdullah Alzahrani 2,3, Samah Alharbi 2 and Panagiotis Blanos 2 1 School of Mechatronic Engineering and Automation, Shanghai ...