Surface Plasmon Resonance Shift Estimation via Fourier Transform
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Solution Overview
Problem
Surface plasmon resonance (SPR) measurements in biosensing experiments face challenges due to noise and reduced accuracy caused by the lateral distribution of light and finite bandwidth of the light source, leading to difficulties in determining the true resonance angle and index of refraction of materials.
Innovation Solution
A method and system that utilize a prism with a metal layer, a light source, and a processor to perform at least two sampled measurements, transform the data into a frequency domain, estimate the sample shift between the data sets, and determine changes in the material layer's properties, such as refractive index, using a discrete Fourier transform and weighted averaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SPR measurement methods are used, then the measurement process is simple, but the measurement precision is reduced due to noise and difficulty in determining the true resonance angle
Solution Approach 1:
The patent transforms the SPR measurement data from the spatial/angular domain to the frequency domain using Fourier transform. This dimensional transformation allows the resonance angle to be determined by identifying the peak frequency in the transformed data, which is more precise than traditional methods that rely on finding minima in reflectivity curves. The frequency domain representation separates the resonance signal from noise more effectively, improving measurement precision without significantly increasing device complexity.
Solution Approach 2:
The patent replaces traditional signal processing methods (intensity measurements, polynomial fitting, centroid calculation) with Fourier transform-based frequency domain analysis. This substitution provides a more robust mathematical framework for determining the resonance angle, as the Fourier transform inherently filters noise and provides clearer peak identification. The method maintains computational simplicity while achieving superior measurement precision through this mathematical substitution.
2Reliability
If multiple sampled measurements and Fourier transform processing are performed, then noise is reduced and sensitivity is enhanced, but the processing time and computational complexity increase
Solution Approach 1:
The patent performs multiple sampled measurements before transformation, collecting redundant data that can be processed together. By acquiring multiple measurements in advance and then applying the Fourier transform to the aggregated data set, the system enhances signal-to-noise ratio through coherent integration. This preliminary data collection strategy allows noise reduction while maintaining efficient processing, as the Fourier transform operates on the complete data set in a single computational pass.
Solution Approach 2:
The patent changes the representation parameters of the measurement data by transforming from the angular reflectivity domain to the frequency domain. This parameter transformation reveals the resonance signal more clearly and enables more accurate determination of the resonance angle. The Fourier transform efficiently handles this parameter change, and by working in the frequency domain, the system achieves better noise immunity and sensitivity without requiring excessively complex processing algorithms.
3Measurement precision
If Fourier transform and weighted averaging are used to estimate sample shift, then the determination of refractive index changes becomes more accurate, but the computational complexity increases
Solution Approach 1:
The patent introduces the Fourier transform as an intermediary processing step between raw measurement data and the final refractive index calculation. This intermediary transformation converts the data into a form where sample shifts (resonance angle changes) can be more accurately estimated through cross-correlation or peak detection in the frequency domain. The weighted averaging then refines this estimation by reducing residual noise. This two-stage approach with Fourier transform as intermediary achieves high precision while keeping the computational steps well-defined and manageable.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the sensitivity and reduces noise in SPR measurements, allowing for more accurate determination of the resonance angle shift and refractive index changes, thereby improving the quantification of biochemical interactions.
Implementation Method 1
Surface plasmon resonance (SPR) sensors have become widely employed for studying biomolecular interactions. At a specific angle of incidence, θSP ('the resonance angle'), greater than θC, the propagation constant of the light parallel to the interface surface, kX, is equal to the real part of the propagation constant of the surface plasmon, kSP. At the resonance angle there is a resonance energy transfer between the evanescent wave and surface plasmons.
Implementation Method 2
Above a certain critical angle of incidence, θC, no light is refracted across the interface, and total internal reflection is observed. While the incident light is totally reflected under these conditions, the electromagnetic field component penetrates a short distance (e.g., tens or hundreds of nanometers) into the medium of the lower refractive index (e.g., water), creating an exponentially decaying evanescent wave.
Implementation Method 3
the electromagnetic field component penetrates a short distance (e.g., tens or hundreds of nanometers) into the medium of the lower refractive index (e.g., water), creating an exponentially decaying evanescent wave
Implementation Method 4
At an interface between two transparent media of different refractive indices (e.g., glass and water), light coming from the side having the higher refractive index (e.g., glass) is partly reflected and partly refracted.
Data Source
AI summary
A surface plasmon measurement instrument measures a change in a property (e.g., refractive index) of a material layer. The method includes providing a prism with a rear surface having a metal layer disposed thereon; providing the material layer on the metal layer on the rear surface of the prism; directing a source beam through the prism toward the rear surface in a vicinity of the material layer; performing at least two sampled measurements to detect light reflected from the rear surface and to produce two corresponding data sets; transforming the data sets to a transform domain; processing the transformed data sets to estimate a sample shift between the two data sets; and determining a change in a property of the material layer using the estimated sample shift.