Motivation
During last few decades, Surface Plasmon Resonance (SPR) and its
advancement with imagining (SPRi) has demonstrated a great benefits in
microfluidic sensors. SPR-based sensors are suitable and dependable
systems for monitoring biological and chemical reactions. Currently, such
platforms show a rapid growth in use in medical diagnosis, biological
studies, food safety etc. (1). However, besides of high sensitivity,
performing measurements in real-time and multi purpose use, this
method has still a high limitations of sensitivity and selectivity of
components. Most of the commercial and home-made setups were
verified with the use of simple compounds, often previously treated or
enhanced. The aim of this project is to develop a optofluidic plasmonic
system that will result in direct detection of viruses and/or bacterias
(E-coli) from biological media (e.g. Urine) which will be provided by
Sønderborg Hospital.
First step of the project is to measure influences of most important
components of the sample to the angular shift in SPR. Combination of
all data about the composition of urine, will give the range of changes
which are related to the normal state of the patient's health. Next step
of the project will focus on different chemical reagents and physical
properties of the surface to enhanced the sensitivity and selectivity of
the surface. The idea is to bond to the surface only those bacteria or
viruses which are crucial for the project and decrease the affect of
other components to the signal.
Figure 2. A schematic drawings
of examples of surface
functionalization for SPR
systems. ”A. Sandwich
immunoassay for large
molecules, B, Protein conjugate
immobilized indirect inhibition
immunoassay with optional
secondary antibody-gold
nanoparticle labeling in a
second step. C. Protein-labeled
inhibition immunoassay,
D. Direct small molecule
immunoassay . ”(2)
The SPRi technique is a basic premise for this project. This method is based
on the utilization of surface plasmon resonance phenomenon and its
dependence on intensity, angle of incidence, polarization and wavelength of
the incident light. The operation principles are shown on Fig 1 with usage of
Kretschmann configuration. The idea is to use the monochromatic light as
the excitation source. Then the incident angle is adjusted to the resonance
angle, which depends on the type of metal, dielectric and wavelength of
the light. The drop of the intensity of the light in the reflected beam
correspond to the SPR absorption maximum. Any changes in the refractive
index of the dielectric above the metal surface result in different resonance
angle, which can be easily seen as different position of the dark line (Fig 1.).
Figure 1. Principles of the Surface Plasmon Resonance imagining technique applied to
the Kretschmann configuration (2).
The second important part of the project is to observe and work with the
degradation of the metal surface in microfluidic systems. Since, the flow
of the liquid as well as the harsh environment of the urine have a
significant impact on the stability, durability and quality of the metal
surface. This situation greatly reduces the possibility of using the system in
medical diagnostics. This part of the project will be dedicated to finding
material and method, which could be used on top of metal surface to
protect it against degradation process and simultaneously with no
significant influence on the phenomenon of surface plasmon resonance.
The effect of all experiments should result in an optofluidic system with
practical medical usage to detect e.g. E-coli in a urine sample.
(1) Mariani S, Minunni M., Surface plasmon resonance applications in clinical analysis. Anal Bioanal Chem 2014, 406, 2303–2323
(2) Mitchell, J. Small Molecule Immunosensing Using Surface Plasmon Resonance. Sensors 2010, 10, 7323-7346.