Assay Device Wicking Zone Projections Flow Control
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Solution Overview
Problem
Miniaturized lateral flow assay devices face challenges with reduced signal detection and sensitivity due to smaller sample sizes, leading to inadequate conjugate in the detection zone and inefficient use of samples, resulting in lower signal read by instruments and reduced flow time.
Innovation Solution
The assay device incorporates a wicking zone with specific projection configurations, such as rectangular or circular shapes and varying pillar densities, to control the flow rate and increase total flow time, enhancing analyte capture and signal detection by maintaining a wider reagent plume and increasing contact time between reagents and analytes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the assay device is miniaturized to reduce sample size requirements, then patient comfort and ease of use is improved, but signal detection sensitivity deteriorates due to reduced conjugate in the detection zone
Solution Approach 1:
The wicking zone is divided into multiple segments with different projection densities - a first portion with higher projection density and a second portion with lower projection density. This segmentation allows different regions to perform different functions: the higher density region slows flow to enhance analyte capture, while the lower density region maintains adequate flow rate, thereby resolving the contradiction between sensitivity and signal detection in miniaturized devices.
Solution Approach 2:
Different regions of the wicking zone are assigned different local properties - specifically, varying projection densities. The first portion has a higher density of projections to increase flow resistance and contact time for analyte capture, while the second portion has lower density to prevent excessive flow restriction. This local differentiation enables the device to maintain both sensitivity and adequate signal generation despite miniaturization.
2Measurement precision
If the wicking zone projection density is increased to increase flow time and enhance analyte capture, then assay sensitivity is improved, but flow rate decreases which may delay results
Solution Approach 1:
The wicking zone is segmented into two portions with different projection densities. The first portion (closer to sample application zone) has higher projection density to maximize analyte capture and flow time extension where it is most needed. The second portion (closer to detection zone) has lower projection density to maintain adequate flow rate and prevent excessive delays, thus balancing sensitivity improvement with productivity maintenance.
Solution Approach 2:
The higher projection density is positioned in the first portion of the wicking zone where the sample first enters, allowing analyte capture to be enhanced at the point of maximum analyte concentration. This preliminary enhancement of capture efficiency in the initial flow region reduces the need for uniformly high flow resistance throughout, thereby maintaining better overall flow rates.
3Quantity of substance
If the device dimensions are reduced to accommodate smaller sample volumes, then sample size requirement is decreased, but conjugate material contact time is reduced leading to lower signal
Solution Approach 1:
The wicking zone is segmented with varying projection densities to create different flow resistance regions. The first portion with higher density acts as a flow control region that extends contact time between the sample/conjugate mixture and the detection surface. This segmented approach allows the device to maintain adequate contact time despite reduced overall dimensions, thereby preserving signal generation capability while using smaller sample volumes.
Solution Approach 2:
The projection density parameter is varied spatially within the wicking zone rather than being uniform. By changing this physical parameter (projection density) across different regions, the device optimizes flow characteristics and contact time within the constraints of miniaturized dimensions, enabling effective analyte capture and signal generation with reduced sample volumes.
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 configuration increases the sensitivity and signal detection in miniaturized devices by optimizing the flow path and pressure gradient, allowing for effective detection of analytes in smaller sample volumes, improving assay sensitivity and comfort for patients.
Implementation Method 1
the projections have a height, cross-section and a distance between one another that defines a capillary space between the projections capable of generating capillary flow parallel to the substrate surface
Data Source
AI summary
An assay device includes: a detection zone which includes a first set of projections which are capable of generating capillary flow. A wicking zone (WZ) has a capacity to receive liquid sample flowing from the detection zone and includes a second set of projections which are capable of generating capillary flow. The WZ is rectangular in shape and the longer side of the rectangle extends in the direction of flow to thereby reduce the pressure gradient in the assay device which increases the total flow time of liquid sample compared to a WZ having equal length sides and same volume. At least a portion of the second set of projections have at least one dimension selected from a diameter, a center-to-center spacing, or a gap between projections that is different from the first set of projections, and is selected to increase the total flow time of the sample.