Microfluidic Impedance Cytometry with Hydrodynamic Focusing
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Solution Overview
Problem
Current microfluidic impedance cytometry systems face challenges in accurately counting and identifying particles, particularly anisotropic cells, due to variations in particle position and alignment within the microfluidic channel, leading to spread in data points and reduced identification and separation efficiency.
Innovation Solution
A system utilizing AC impedance spectroscopy with hydrodynamic focusing and multiple frequency measurements to consistently position and align particles within the microfluidic channel, allowing for precise detection and identification of anisotropic cells by analyzing amplitude and phase characteristics at integer multiple frequencies, and using higher frequency harmonics to correct for alignment inaccuracies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If particles are allowed to flow freely through the microfluidic channel, then the system is simpler to operate, but the spread in data points increases due to variations in particle position and alignment
Solution Approach 1:
The patent employs hydrodynamic focusing using a sheath fluid to constrain particle positions and alignments in the microfluidic channel. The sheath fluid flows around the sample particles, creating a focused flow that positions particles at a consistent location and orientation relative to the detection electrodes, thereby reducing data spread while maintaining operational simplicity
2Measurement precision
If multiple frequency measurements are implemented, then identification accuracy improves, but device complexity increases
Solution Approach 1:
The patent uses a single impedance detection system that measures electrical impedance across multiple frequency ranges (low frequency for cell size, mid frequency for membrane properties, high frequency for internal structure). This multi-functional approach allows one detection system to extract multiple types of cellular information simultaneously, improving identification accuracy without proportionally increasing device complexity
Solution Approach 2:
The patent varies the frequency parameter of the applied electrical signal to probe different cellular characteristics. By measuring impedance at multiple frequencies, the system extracts complementary information about cell size, membrane capacitance, and internal conductivity, thereby improving identification accuracy through parameter variation rather than adding multiple physical sensors
3Reliability
If hydrodynamic focusing is applied to align anisotropic particles, then identification reliability improves, but the system complexity increases
Solution Approach 1:
The patent uses hydrodynamic focusing with a sheath fluid to align anisotropic particles (such as sperm cells or elongated cells) in a consistent orientation as they flow through the detection region. The sheath flow creates a laminar flow pattern that orients particles parallel to the flow direction, ensuring reliable and repeatable impedance measurements for identification
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 significantly reduces the spread of data points from a population of cells, enabling more robust and accurate identification and separation of anisotropic particles, such as mammalian cells and sperm cells, by accounting for orientation and alignment variations, thereby improving the resolution and reliability of particle analysis.
Implementation Method 1
measure a complex signal in response to the energising of the detection electrodes, the measure of the complex signal comprising a measure of an amplitude of the complex signal and a measure of a phase of the complex signal
Implementation Method 2
When referring to laminar flow regime, we shall imply the flow conditions that fall under the Stokes regime (∼1 Re=ρUH/μ, where p, U and μ, are the fluid density, the average velocity and dynamic viscosity respectively and H is the characteristic channel dimension)
Implementation Method 3
Homodyne detector is a device that detects frequency-modulated signal by non-linear mixing it with a signal having the same frequency as the modulation signal
Implementation Method 4
Multi-frequency impedance measurements can be used to determine the electrical properties of single cells in a microchip
Data Source
Figure 1a~1b
Figure 1c~2
Figure 3a~3b
AI summary
This invention relates to the field of microfluidic flow cytometry and more generally microfluidic techniques for analysis of particulate-containing fluids. It deals with the improvements to such technologies in order to identify subsets of particles or sub-populations of cells that differ in their properties, and, if necessary, separate the said identified sub-populations of cells, e.g. sex of semen cells, alive cells from the dead ones, cancerous cells from the healthy ones, subsets of viruses, bacteria or subsets of particles. In particular, the invention deals with a microfluidic chip, whereby the stream of particles or cells is positioned within a cross-section of the common microfluidic channel in a controlled way to reduce a variation of detected signal and thus make distinction between subsets of cells or particles, more robust.