pH-Sensitive Cellulose Strip for Nucleic Acid Extraction
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Solution Overview
Problem
Current nucleic acid extraction methods for infectious disease detection are complex, require specialized equipment, and involve time-consuming steps, making them unsuitable for onsite rapid testing, especially in resource-limited settings.
Innovation Solution
A method using pH-sensitive cellulose fibers for isothermal amplification of nucleic acids, which eliminates the need for pH buffers and allows for visual detection of hydrogen ion release, indicating the presence of the nucleic acid of interest.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional nucleic acid extraction methods using silica gel membranes or paramagnetic beads are used, then extraction efficiency is improved, but device complexity and operation complexity increase due to requirement of centrifuges, magnet rods, and multiple washing/drying/eluting steps
Solution Approach 1:
The patent extracts the nucleic acid binding function from complex centrifugal filtration systems and paramagnetic bead systems, concentrating it into a simple pH-sensitive cellulose paper strip that can be directly immersed in sample solution. The strip selectively binds nucleic acids through its cellulose fibers while allowing other components to be washed away, eliminating the need for centrifuges and magnet rods.
Solution Approach 2:
The pH-sensitive cellulose paper strip serves multiple functions: (1) nucleic acid binding/extraction through cellulose fibers, (2) visual pH detection through pH-sensitive indicators, and (3) direct use as the reaction substrate for isothermal amplification. This multi-functionality replaces multiple separate components (extraction membrane, detection reagents, reaction vessels) with a single integrated element.
2Reliability
If traditional nucleic acid extraction methods with multiple washing and drying steps are used, then extraction purity is improved, but testing time increases making it unsuitable for rapid onsite diagnostics
Solution Approach 1:
The pH-sensitive cellulose paper strip is pre-prepared with pH-sensitive indicators bound to the cellulose fibers before use. This preliminary preparation allows the strip to immediately detect pH changes upon nucleic acid amplification without requiring separate detection steps, buffers, or additional reagents, thereby reducing testing time while maintaining detection accuracy.
Solution Approach 2:
The patent skips the traditional multiple washing and drying steps by using the pH-sensitive cellulose strip in a simplified single-step extraction where the strip is immersed in sample, briefly washed, and directly used for amplification. The pH sensitivity allows detection without extensive purification, rushing through the traditional multi-step process while maintaining sufficient purity for isothermal amplification.
3Measurement precision
If RT-qPCR gold standard method is used, then detection sensitivity and specificity are improved, but operation complexity and equipment requirement increase making it unsuitable for resource-limited settings
Solution Approach 1:
The patent replaces the complex thermal cycling mechanical system of RT-qPCR with a simpler isothermal amplification system that maintains constant temperature (e.g., 65°C) throughout the reaction. This substitution eliminates the need for programmed temperature changes while achieving comparable detection sensitivity through the pH-sensitive visual readout mechanism.
Solution Approach 2:
The patent employs pH-sensitive indicators bound to cellulose fibers that undergo color changes in response to pH variations during isothermal amplification. As amplification proceeds and pH changes occur, the visible color transition provides a simple visual readout that replaces complex fluorescence detection systems, making the assay accessible in resource-limited settings while maintaining detection precision.
4Device complexity
If FTA cards are used for nucleic acid extraction, then equipment requirement is reduced, but procedure complexity increases due to punching, washing, and drying steps
Solution Approach 1:
The patent segments the FTA card concept into a smaller, more manageable pH-sensitive cellulose strip format. Instead of using large FTA cards that require punching and multiple handling steps, the strip format allows direct immersion in sample solution and simplified washing, reducing procedural complexity while maintaining the benefit of equipment-free operation.
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 simplifies nucleic acid extraction and detection, enabling rapid, cost-effective, and instrument-free diagnostics for infectious diseases like SARS-CoV-2, with results achievable in under 46 minutes from sample to answer.
Implementation Method 1
identifying a pH detected by the pH sensitive element, wherein a pH of 7.5 or less indicates the release of hydrogen ions during the isothermal amplification and the presence of the nucleic acid of interest in the nucleic acid sample
Implementation Method 2
the isothermal amplification of the nucleic acid of interest results in the release of hydrogen ions on the pH sensitive element
Implementation Method 3
amplifying by isothermal amplification a nucleic acid of interest present in a nucleic acid sample bound in cellulose fibers of a pH sensitive element
Data Source
AI summary
Disclosed are methods, devices and kits for extracting, amplifying, detecting and visualizing nucleic acids of interest for use in onsite rapid diagnostics.