Parallel Phase Analysis Light Scattering for Nanoparticle Mobility
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for measuring electrophoretic mobility, particularly for small particles below 5nm, are limited by the need for expensive and sensitive detectors, restricted dynamic ranges, and lengthy measurement times, which can damage fragile samples and limit the detection of low-mobility species.
Innovation Solution
The implementation of a massively parallel phase analysis light scattering (MP-PALS) technique using a coherent laser beam split into sample and reference beams, combined in free space with a detector array to measure phase modulation, allowing simultaneous independent measurements across multiple elements, reducing measurement time and eliminating the need for high-intensity ratio adjustments and expensive detectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional heterodyne light scattering methods are used with single-mode fiber to combine beams, then high contrast fringes are generated, but a large fraction of energy is lost to modes not supported by the fiber
Solution Approach 1:
The patent replaces the mechanical/optical fiber-based beam combination system with a free-space optical interference system. Instead of using single-mode fiber to combine the local oscillator beam and scattered light beam, the invention uses free-space propagation and direct optical interference to achieve beam combination, eliminating fiber-related energy losses while maintaining high fringe contrast through precise optical alignment.
2Measurement precision
If expensive and sensitive detectors are used to measure electrophoretic mobility of small particles, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces expensive, sensitive detectors (such as photomultiplier tubes or avalanche photodiodes) with inexpensive silicon photodiode arrays. The invention demonstrates that by using free-space optical interference and proper signal processing, conventional photodiodes can achieve sufficient measurement precision for electrophoretic mobility of small particles, eliminating the need for costly specialized detectors.
3Measurement precision
If lengthy measurement times are used to achieve accurate mobility measurements, then measurement precision is improved, but sample damage increases and productivity decreases
Solution Approach 1:
The patent implements a continuous measurement approach using parallel detection across multiple photodiode elements. Instead of requiring lengthy integration times to achieve sufficient signal-to-noise ratio, the invention uses simultaneous independent measurements from multiple detectors to rapidly accumulate statistical data, enabling accurate mobility measurements in much shorter time periods and reducing sample exposure to potentially damaging conditions.
4Measurement precision
If beam intensity ratios are strictly controlled to be less than 30:1, then measurement accuracy is maintained, but the dynamic range is restricted and coherent amplification cannot be fully utilized
Solution Approach 1:
The patent changes the operational parameters of the detection system by allowing flexible beam intensity ratios exceeding the traditional 30:1 limit. The invention uses free-space optical interference combined with phase modulation and digital signal processing to maintain measurement accuracy across a wide dynamic range of intensity ratios, enabling full utilization of coherent amplification effects even when the local oscillator beam is much stronger than the scattered light beam.
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 enables precise measurement of electrophoretic mobility for particles smaller than 5nm with reduced sample damage and measurement time, improving sensitivity and extending the linear range to lower concentrations and sizes, while using cost-effective silicon photodiode arrays.
Implementation Method 1
A beam of coherent monochromatic light, usually from a laser source, illuminates a sample of liquid borne particles
Implementation Method 2
Electrophoresis is the migration of macro-ions under the influence of an electric field
Implementation Method 3
the scattered signal is combined coherently with the incident light to produce a heterodyned signal. Such combination of the two beams generates fringes with high contrast
Implementation Method 4
one of the combining beams is directed to reflect first from an oscillating mirror. This causes the detected fringes to acquire an intensity modulation
Data Source
Figure 1
Figure 2(a)
Figure 2(b)
AI summary
A method and apparatus is disclosed for measurement of the Electrophoretic mobility of particles and molecules in solution. A sample of particles is placed in a cell containing two electrodes that apply an alternating electric field. A monochromatic light beam passes through the sample. Light scattered by the particles, along with the unscattered beam, is collected and collimated as it exits the cell. This beam is combined in free space with a phase modulated reference beam. The interference forms a frequency modulated speckle pattern, which is detected by a photodetector array. Each array element collects a narrow range of well-defined scattering angles. The signal from each is demodulated to extract the optical phase information providing a first-principle measurement of the Electrophoretic mobility of the scattering particles. Each detector element provides a simultaneous independent measurement. This inherent parallelism drastically increases the amount of information available in a given time. The resulting increased sensitivity extends the mobility measurement to particles below one nanometer, reduces the required concentration and electric field compared to previous methods. This minimizes damage to fragile samples, increases the electrode useful life, and reduces joule heating. Electrophoretic mobility is a critically important parameter for predicting the stability of nanoparticle suspensions and pharmaceutical formulations such as protein therapeutics. This invention enables reliable free-solution phase measurement of these samples.