Monitoring of bacterial film formation and its breakdown with an angular-based surface plasmon resonance biosensor.

Bacterial biofilms are a leading cause of infection in health-care settings. Surface plasmon resonance (SPR) biosensors stand as valuable tools not only for the detection of biological entities and the characterisation of biomaterials but also as a suitable means to monitor bacterial film formation. This article reports on a proof-of-concept study for the use of an angular-based SPR biosensor for the monitoring of bacterial cell growth and biofilm formation and removal under the effect of different cleaning agents. The benefit of this custom-made SPR instrument is that it records simultaneously both the critical and resonant angles. This provides unique information on the growth of bacterial cells which is otherwise not obtainable with commonly used intensity-based SPR systems. The results clearly showed that a multilayer biofilm can be formed in 48 hours and the steps involved can be monitored in real-time with the SPR instrument through the measurement of the refractive index change and following the evolution in the shape of the SPR curve. The number, the depth and the sharpness of the reflection ripples varied as the film became thicker. Simulation results confirmed that the number of layers of bacteria affected the number of ripples at the critical angle. Real-time monitoring of the film breakdown with three cleaning agents indicated that bleach solution at 4.5% was the most effective in disrupting the biofilm from the gold sensor. Our overall findings suggest that the SPR biosensor with angular modulation presented in this article can perform real-time monitoring of biofilm formation and has the potential to be used as a platform to test the efficiency of disinfectants.

Surface plasmon resonance biosensor as a tool for the measurement of complex refractive indices.

Optical characterisation of liquids through the measurement of their complex refractive index is critical in environmental monitoring, food industry and medicine. While surface plasmon resonance is widely used for measurement of the real part of the refractive index there have been few studies to date on measurement of complex refractive index with this method. We present a systematic study which highlights the challenges associated with this approach. Instrument design and data analysis techniques are presented together with preliminary experimental results.

Design and analysis of a spectro-angular surface plasmon resonance biosensor operating in the visible spectrum.

Surface plasmon resonance (SPR) sensing is one of the most widely used methods to implement biosensing due to its sensitivity and capacity for label-free detection. Whilst most commercial SPR sensors operate in the angular regime, it has recently been shown that an increase in sensitivity and a greater robustness against noise can be achieved by measuring the reflectivity when varying both the angle and wavelength simultaneously, in a so-called spectro-angular SPR biosensor. A single value decomposition method is used to project the two-dimensional spectro-angular reflection signal onto a basis set and allow the image obtained from an unknown refractive index sample to be compared very accurately with a pre-calculated reference set. Herein we demonstrate that a previously reported system operated in the near infra-red has a lower detection limit when operating in the visible spectrum due to the improved spatial resolution and numerical precision of the image sensor. The SPR biosensor presented here has an experimental detection limit of 9.8 × 10(-7) refractive index unit. To validate the system as a biosensor, we also performed the detection of synthetic RNA from pathogenic Legionella pneumophila with the developed biosensing platform.

Analysis of surface plasmon spectro-angular reflectance spectrum: real-time measurement, resolution limits, and applications to biosensing.

A surface plasmon biosensing technique based on real-time measurement of the spectro-angular reflectance spectrum of a gold surface is presented. A significant improvement in refractive index resolution and drift compensation has been achieved for the spectro-angular technique to demonstrate a biosensing platform that is, in addition, applicable to plasmonic bandgap measurements. Instrumental improvements are detailed and constants for the model bovine serum albumin (BSA):oxacillin bioassay are presented.