Optical Fibre Sensing for Healthcare

PhD Supervisors:

Prof Stephen Morgan

Professor of Biomedical Engineering, Faculty of Engineering

Prof Barrie Hayes-Gill

Professor of Electronic Systems and Medical Devices, Faculty of Engineering

Dr Sergiy Korposh

Associate Professor in Electronics, Nanoscale Bioelectronics and Biophotonics, Faculty of Engineering

Dr Ricardo Goncalves Correia

Assistant Professor in Optical and Bioelectric Engineering, Faculty of Engineering

Internal Assessor:

Dr Amanda Wright

Associate Professor, Faculty of Engineering

Collaborator:

Dr Peter Worsley

Lecturer in Health Sciences, University of Southampton

Aims of the project

• Develop and fabricate optical fibre sensors to predict pressure ulcers

• Investigate biomarkers of tissue breakdown

Objectives of the project

• Fabricate an optical fibre CO2 sensor on the tip of the optical fibre and coated with 4 layers of film comprised of organically modified silica (Ormosil) doped with thymol blue and tetramethylammonium hydroxide

• Monitor CO2 emitted from human skin during loading using an optical fibre sensor

Research Achievements

A reflection mode optical fibre CO2 sensor is developed using sol-gel coating process. A single film is made by coating organically modified silica (Ormosil) doped with thymol blue and tetramethylammonium hydroxide onto the fibre tip. Light from a laser diode illuminates the fibre tip and the reflected light (proportional to CO2) is detected. This CO2 sensor is used to predict the presence of pressure ulcers (PUs) by measuring transcutaneous CO2 (TcPCO2) from human skin during loading. The step response of the CO2 sensor to different concentrations of CO2 is achieved using wavelength 590.67nm to 609.71nm. The repeatability and reverse response of CO2 sensor is monitored for CO2 concentration from 0ppm to 50000ppm (5%). The response time of the sensor is 60 seconds and the recovery time is 413 seconds. Although these results show CO2 measurement, the response is also affected by relative humidity (RH). The changes in reflection intensity for wavelength 604.06nm and wavelength shift for valley from wavelengths 580.34nm to 611.22nm are noticed for varying RH levels (60% RH - 90% RH). The sensitivity of the CO2 to humidity was calculated to be 0.0095nm/1% RH for step up response and 0.2127nm/1% RH for the step down response. An experiment was carried out to measuring TcPCO2 from human skin during loading by using an optical fibre CO2 sensor. The response of CO2 sensor rises with the increasing value of loading provided by the loading machine when the sensor is placed on skin with gas collection chamber. An increased value of PCO2 in tissue above normal values (about 5-6%) designates anaerobic metabolism and TCPCO2 becomes useful in this way as markers of tissue viability or status as a direct outcome of tissue ischemia.