Optical fiber sensors for monitoring in critical care.

Monitoring of key physiological and pharmacological parameters is an important part of a closed loop control system in critical care. Optical fiber sensors provide a versatile platform technology that can be easily incorporated into existing in-dwelling catheters or face masks. With appropriate functional coatings they can be used to monitor a range of relevant parameters and two different examples are presented: (i) respiration monitoring; (ii) drug level monitoring. Respiration monitoring involves monitoring of temperature and humidity in inhaled and exhaled breath. The optical fiber sensor consists of a fiber Bragg grating to measure temperature and a tip coating whose refractive index changes with humidity. The sensor is demonstrated to be able to track breath to breath changes when incorporated into a mask. Drug level monitoring is demonstrated in vitro using a long period grating coated with molecularly imprinted polymer nanoparticles that are sensitive to fentanyl. The sensor has a limit of detection of 50ng/ml.

Highly sensitive optical fibre long period grating biosensor anchored with silica core gold shell nanoparticles.

An optical fibre long period grating (LPG), modified with a coating of silica core gold shell (SiO2:Au) nanoparticles (NPs) deposited using the layer-by-layer method, was employed for the development of a biosensor. The SiO2:Au NPs were electrostatically assembled onto the LPG with the aid of a poly(allylamine hydrochloride) (PAH) polycation layer. The LPG sensor operates at the phase matching turning point to provide the highest sensitivity. The SiO2:Au NPs were modified with biotin, which was used as a ligand for streptavidin (SV) detection. The sensing mechanism is based on the measurement of the refractive index change induced by the binding of the SV to the biotin. The effect on sensitivity of increasing the surface area by virtue of the SiO2:Au nanoparticles' diameter and film thickness was studied. The lowest measured concentration of SV was 2.5nM, achieved using an LPG modified with a 3 layer (PAH/SiO2:Au) thin film composed of SiO2 NPs of 300nm diameter with a binding constant of k=1.7(pM)(-1), sensitivity of 6.9nm/ng/mm(2) and limit of detection of 19pg/mm(2).