Assay Device Interrupting Wash Controls Sample Volume
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Solution Overview
Problem
Existing lateral flow assay devices face challenges in reducing sample size while maintaining sensitivity and specificity, particularly when using smaller sample volumes such as those from a fingerstick blood draw, as this leads to inadequate conjugate in the detection zone and reduced signal availability due to inefficient sample use and shorter flow times.
Innovation Solution
The introduction of an 'interrupting wash' fluid in the assay device, added at a predetermined fill volume, controls sample volume and washes the detection channel, ensuring sufficient reagent contact time and conjugate material interaction, thereby enhancing sensitivity and signal detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If smaller sample volumes are used in lateral flow assay devices, then patient comfort and ease of sample collection are improved, but sensitivity and signal detection are worsened due to inadequate conjugate in the detection zone
Solution Approach 1:
The flow path is segmented into distinct zones (sample addition zone, reagent zone, detection zone, wicking zone) with specific functions. The reagent zone contains conjugate material that is dissolved by the sample, creating a conjugate plume that flows to the detection zone. This segmentation ensures that even small sample volumes can effectively dissolve and transport sufficient conjugate to the detection zone for sensitive detection.
Solution Approach 2:
The conjugate material is pre-deposited in the reagent zone in a concentrated form before sample addition. When the sample is added, it automatically dissolves the conjugate material and forms a conjugate plume that flows downstream. This preliminary positioning of conjugate ensures adequate signal availability even when using small sample volumes from fingerstick blood draws.
2Ease of operation
If smaller sample volumes are used, then sample collection is simplified, but flow time is reduced leading to insufficient reagent contact time and decreased assay performance
Solution Approach 1:
The assay device utilizes dynamic capillary flow through the porous matrix to control fluid movement. The porous material properties and flow path design create optimal flow dynamics that maintain sufficient contact time between sample/reagents and detection zones, even with smaller sample volumes. The wicking zone at the end provides continuous flow drive to ensure complete reagent interaction.
3Device complexity
If conventional lateral flow devices are used with small sample volumes, then device simplicity is maintained, but sample utilization efficiency is reduced leading to inadequate signal
Solution Approach 1:
The assay device employs a porous matrix (nitrocellulose or similar material) as the flow path support. This porous structure provides large surface area for reagent deposition and efficient capillary flow, maximizing sample utilization. The porous material allows small sample volumes to effectively dissolve and transport conjugate material through the flow path to the detection zone, improving sample efficiency without increasing device complexity.
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 allows for accurate detection of analytes in smaller sample volumes, improving sensitivity and specificity by controlling sample size and flow within the assay device, enabling reliable results with reduced sample sizes like 25 μl or less from fingerstick blood draws.
Implementation Method 1
a porous material, e.g., nitrocellulose, defining a path for fluid flow capable of supporting capillary flow
Implementation Method 2
The sample-addition zone frequently consists of a more porous material, capable of absorbing the sample, and, when separation of blood cells is desired, also effective to trap the red blood cells
Data Source
AI summary
Disclosed is an assay device which comprises a liquid sample addition zone, a reagent zone, a detection zone, and a wicking zone, all defining a fluid flow path. The device further comprises a reagent addition zone along and in fluid communication with the fluid flow path downstream of the sample addition zone and upstream of the detection zone. An interrupting wash is added at this reagent addition zone in accordance with the method of the subject invention to control sample volume. The interrupting wash fluid is added at a predetermined fill volume on the chip device and also serves to wash the detection channel and fill the remaining chip volume.