Biochemical sensing using Siloxane polymer waveguides

The objective of this work presented here is to extend the capabilities of siloxane waveguide technology in the field of biochemical sensing. Recent advances in the integration of polymeric optical waveguides with electronics onto standard printed circuit boards (PCBs) allow the formation of cost-effective lab-on-achip modules suitable for mass production. This technology has been primarily designed for on-board data communication. The focus of this research is to investigate the possibility of realising a Siloxane polymer based lab-on-chip sensor. Different siloxane-polymer-based optical waveguide sensor structures have been designed and analysed from the aspect of biochemical sensing. An evanescent-wave absorption sensor based on mode-selective asymmetric waveguide junctions is proposed for the first time. The device mitigates the common optical effect of spurious response in absorption sensors due to the analyte transport fluid. Head injury is the leading cause of death in the population of people under 40 years. Currently, 3 out of 5 deaths in emergency rooms are due to severe brain injuries in the developed world. Researchers at the Neurosciences Critical Care Unit (NCCU) at Addenbrooke’s Hospital have managed to correlate biochemical changes with the severeness of the injury and the likelihood of patient recovery. Considerable progress has been made to develop a lab-on-chip sensor capable of continuously monitoring glucose, lactate and pyruvate concentrations in the brain fluid, hence the contribution to the current trend in the advancement of portable lab-on-chip technologies for the deployment of point-of-care diagnostic tools. A novel recognition layer has been developed based on porphyrin in combination with glucose, lactate and pyruvate oxidase for measuring all the analytes, enabling fast and reversible chemical reactions to be monitored by optical interrogation. The operational wavelength of the developed recognition layer is 425 nm, which required the formation of polymer features that were beyond the fabrication capabilities at the time. Through considerable process development and the adoption of nanoimprinting lithography, siloxane polymer based optical waveguides were fabricated allowing the realisation of highly sensitive optical sensors. Based on the results that are presented here, it can be concluded the functionalization of siloxane polymer waveguide have a potential for realising biochemical sensors in the future. The new fabrication technique will allow the formation of more robust and complex lab-on-chip sensors based on this material.ESPR

Mode-selective optical sensing using asymmetric waveguide junctions

AbstractMeasuring a single analyte in a highly absorptive microfluidic channel has always been a challenge. Even with a highly selective sensing layer, other chemical species can affect the interrogation of the analyte. Matching the evanescent tail with the sensing layer thickness is difficult in case of evanescent field sensing. The tail typically extends beyond the sensing layer, introducing noise and spurious errors in the measurement, which scales up with analyte concentration. In this work therefore, we propose the use of a simple multimode evanescent waveguide sensor that eliminates such common spurious effects. The proposed mode-selective sensing system exploits the sensitivity differences between the different guided modes in detecting the effects of the outer medium in the sensor response. The operation of the sensor device relies on the use of an asymmetric waveguide junction, which enable efficient separation of waveguide modes and therefore detection of their differences in behaviour. The proposed device is shown through simulations to achieve very small estimation errors below 5%, even for very high absorption coefficients of the outer medium of up to 80 times larger than that of the sensing layer