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 University, Shanghai 200072, China; lw_yan@staff.shu.edu.cn 2 School of Electronic, Electrical and Systems Engineering, Loughborough University, Ashby Road, Loughborough, Leicestershire LE11 3TU, UK; A.Alzahrani@lboro.ac.uk (A.A.); S.M.Alharbi@lboro.ac.uk (S.A.); P.Blanos@lboro.ac.uk (P.B.) 3 College of Engineering, Taif University, Airport Road, Al Hawiyah Area 888, Taif 26571, Saudi Arabia * Correspondence: S.Hu@lboro.ac.uk; Tel.: +44-150-922-7058 Received: 11 January 2017; Accepted: 16 June 2017; Published: 21 June 2017 Abstract: Different skin pigments among various ethnic group people have an impact on spectrometric illumination on skin surface. To effectively capture photoplethysmographic (PPG) signals, a multi-wavelength opto-electronic patch sensor (OEPS) together with a schematic architecture of electronics were developed to overcome the drawback of present PPG sensor. To perform a better in vivo physiological measurement against skin pigments, optimal illuminations in OEPS, whose wavelength is compatible with a specific skin type, were optimized to capture a reliable physiological sign of heart rate (HR). A protocol was designed to investigate an impact of five skin types in compliance with Von Luschan’s chromatic scale. Thirty-three healthy male subjects between the ages of 18 and 41 were involved in the protocol implemented by means of the OEPS system. The results show that there is no significant difference (p: 0.09, F = 3.0) in five group tests with the skin types across various activities throughout a series of consistent measurements. The outcome of the present study demonstrates that the OEPS, with its multi-wavelength illumination characteristics, could open a path in multiple applications of different ethnic groups with cost-effective health monitoring. Keywords: multi-wavelength; auto adaptive adjustment; opto-electronic patch sensor (OEPS); skin pigments; Von Luschan’s chromatic scale (VLCS) 1. Introduction Pigments in various human skin types could affect signal quality in photoplethysmography (PPG) and could even make physiological measurements invalid. The quality of PPG-based in vivo physiological monitoring is attributed to melanin concentration of skin and its related pigments of skin types [1]. Thereby, melanin in human skin is known to highly attenuate incident light with relevant wavelength illuminations [2]. Some researchers reported anecdotal errors (3–5%) in black skin [3]. In addition, modelling and simulations were conducted and errors due to various pigments were reported [3,4]. Ink on skin and nail polish could cause errors during measurements [5]. Four different wavelength illuminations have attempted to optimize the measurements of heart rate (HR) by using a customized PPG setup on 23 healthy subjects with various skin types on PPG system [6]. The results showed that the 520 nm wavelength (green) illumination provided a significantly greater (p < 0.001) ability to detect HR. Increasing levels of melanin, or darker skin type (Type V) showed a decreasing trend with insignificant change (p < 0.067). Moreover, it has been widely confirmed that other forms of Biosensors 2017, 7, 22; doi:10.3390/bios7020022 www.mdpi.com/journal/biosensors