Experimental Set-Up and Data Analysis Methods
Experimental Set-Up
We used the standard Kretschmann configuration for SPR [1]. This included:
A 625 nm p-polarized laser. The laser was p-polarized to remove components of the light that did not contribute to SPR [2].
A 50.0 mm convex lens to focus the light on a triangular prism where it reflected off of a thin (33 - 100 nm) sample of silver.
A MoticCAM camera to record the resonance in the reflected light
A 45° reference angle was marked on the ruler and used for angle calibration
Our setup is pictured here for reference:
Data Analysis Methods
In order to measure the angles where surface plasmon resonance occurred we made several calibration measurements and several measurements for each sample
(see figure below). Our calibration measurements correspond to light incoming at 45 degrees, and we measured where the light exited the crystal (point d) and where the
light was on our ruler (point b). Then to find the angle of incoming light for an unknown angle we measured where the light exited the crystal (point c) and the position of
our camera on the ruler (point a). Then we measured the distance from where the light exited the crystal to the camera shutter.
From those measurements we were able to determine the angle of the camera. And then converting the pixels of the camera to distance enabled us to determine the
external angle of resonance. We then used Snell's law to determine the interior angle at which resonance occurred.
We took two photos for each sample, with the laser s-polarized and p-polarized. In MATLAB the images were converted to arrays, with each array element corresponding the intensity at that pixel. The images were then subtracted to remove noise.
We rotated the image to assure the resonance was vertical, and averaged down the columns so that we could graph the intensity profile.
Using the geometry of our set-up, Snell’s law, and the angle calibrated images of SPR, we calculated the angle at which the resonance bands occurred
References:
[1] Erik J. Sánchez, Prof.: Portland State University, Surface Plasmon Resonance (SPR) Lab, 2010.
[2] Nagata, Kazuhiro., et al. Real-Time Analysis of Biomolecular Interactions: Applications of BIACORE. Springer, 2000.