Published RT-LAMP studies increasingly use lyophilized reagents to reduce cold-chain dependence and simplify point-of-care preparation. The literature supports the feasibility of freeze-drying complete or partial RT-LAMP systems, but it does not support a universal excipient recipe, cycle, or ambient shelf-life claim. Results depend on enzyme source, primer set, indicator, fill volume, container, residual moisture, package, storage condition, and performance criterion.
This literature review organizes the evidence by formulation mechanism and study design. It distinguishes early accelerated screening from real-time shelf-life evidence and emphasizes that preserved endpoint color alone may conceal slower kinetics, rising background, or reduced low-copy detection.
Freezing concentrates salts and solutes into the unfrozen fraction, which can expose enzymes and RNA components to local pH and ionic changes. Ice formation can perturb proteins and interfaces. Primary drying removes ice by sublimation, while secondary drying reduces more tightly associated water. Excess residual moisture can accelerate degradation; over-drying can also damage some formulations or slow rehydration.
RT-LAMP contains at least a strand-displacing polymerase, reverse-transcription function, primers, dNTPs, magnesium or a separated activation system, salts, detection reagent, and often contamination-control components. These materials do not share identical stability needs.
| Excipient family | Proposed role | RT-LAMP-specific concern |
|---|---|---|
| Disaccharides such as trehalose or sucrose | Water replacement and glass formation around biomolecules | High concentration can change viscosity, rehydration, and enzyme kinetics |
| Sugar alcohols and polyols | Protein stabilization and bulking | Crystallization can exclude enzymes and change cake structure |
| Polymers such as dextran or PVP | Glass formation, bulking, and surface protection | May slow dissolution or alter crowding and amplification |
| Proteins or carrier macromolecules | Reduce adsorption and stabilize interfaces | May introduce nucleic-acid contaminants, background, or lot variability |
| Surfactants | Reduce surface and freeze-concentration stress | Can affect polymerase, RT, indicators, and downstream membranes |
| Antioxidants or chelators | Limit oxidation or trace-metal damage | May reduce free magnesium or interfere with Cas coupling |
The literature frequently reports sugars, especially trehalose, as useful stabilizers, but direct comparison is difficult because formulations and performance endpoints differ. Excipient concentration should be optimized in the final reaction, not only for cake appearance.
A complete pellet can minimize user steps but forces all components to share freezing and drying. Separating magnesium, pH indicator, guide RNA, or another sensitive component can improve stability and control activation, at the cost of additional manufacturing or user operations.
Partial drying may place enzymes and primers in one compartment while liquid sample buffer supplies remaining salts. Paper, bead, pellet, cake, and dried-film formats have different mass transfer and package needs. Literature conclusions should not be transferred across formats without comparability evidence.
Formulation screening and cycle development are linked. Collapse temperature, glass transition, eutectic behavior, fill depth, vial heat transfer, and chamber conditions affect cake structure and residual moisture. A conservative laboratory cycle may protect a small batch but transfer poorly to different vials, trays, or load sizes.
A development record should include:
Studies of lyophilized LAMP reagents have shown that dried systems can retain diagnostic function and tolerate selected elevated-temperature exposures. More recent colorimetric RT-LAMP work demonstrates protocol-specific preservation after lyophilization and storage. An open-source RT-LAMP study published in 2025 provides additional evidence for low-resource-oriented dry formulation.
These studies are valuable proof points, but their targets, enzymes, excipients, packages, timepoints, and acceptance rules differ. A result such as “positive after storage” does not establish unchanged detection probability at the low end of the measuring range. Literature-supported feasibility should lead to product-specific development, not a copied shelf-life claim.
| Endpoint | What it can reveal | What it may miss |
|---|---|---|
| High-positive endpoint color | Gross retention of complete reaction function | Early sensitivity loss, slower kinetics, weak color separation |
| Time to positive | Rate changes and partial activity loss | Product identity and some endpoint artifacts |
| Low-copy detection rate | Function near the intended detection boundary | Mechanistic source of failure |
| NTC and non-target time course | Rising background and loss of specific-result window | Sample-matrix inhibition |
| Residual enzyme activity | Biochemical loss in polymerase or RT | Primer, indicator, salt, rehydration, and system-level failure |
| Residual moisture and reconstitution | Physical state and package-related trends | Clinical or analytical performance alone |
pH-based color systems require limited buffer capacity so proton generation changes color. Lyophilization can alter volatile components, carbon dioxide exposure, starting pH, and local salt distribution. Sample buffers may overwhelm the intended color transition even when amplification remains active.
Stability panels should therefore measure initial color, pH where meaningful, parallel fluorescence or product confirmation, and matrix-specific endpoint interpretation. A dry reagent that looks visually acceptable may have an altered chemical blank.
When dUTP and a compatible UDG system are used, the enzyme must remain active after drying and storage while avoiding harmful activity during amplification. Thermolabile UDG strategies depend on the setup and heating profile. The dry format can change rehydration timing and exposure before inactivation.
Carryover protection should be challenged with a defined uracil-containing contaminant after storage. No-template background must also be monitored because UDG does not prevent fresh primer-driven nonspecific amplification.
Elevated temperature and humidity are useful for ranking formulations and identifying failure modes. Extrapolation assumes that degradation mechanisms remain comparable. In dry molecular reagents, glass transition, crystallization, moisture ingress, seal failure, and indicator chemistry may change nonlinearly. A short high-temperature study cannot by itself prove a long ambient shelf life.
CLSI EP25 and ISO 23640 provide general frameworks for establishing and evaluating IVD reagent stability. The product-specific plan should include baseline, intermediate, claim-point, and beyond-claim observations, representative lots, final packaging, predefined acceptance criteria, and real-time evidence.
Foil barrier, vial or tube polymer, stopper, headspace, desiccant, seal, and opening frequency determine the actual moisture and oxygen exposure. A reagent stable in a sealed vial may fail in a multidose format or after repeated pouch opening. Shipping stress and uncontrolled field storage should be modeled separately from labeled storage.
A responsible use of the literature follows these steps:
Reported storage statements should be translated into a common evidence table before comparison. Record whether time was real-time or accelerated, whether humidity was controlled, whether the package was final, how many lots and replicates were used, and which target levels were tested. Note whether performance was assessed immediately after rehydration or after an in-use hold.
| Literature detail | Why it changes interpretation |
|---|---|
| High-copy positive only | May mask substantial activity loss near the detection boundary |
| No extended NTC monitoring | Cannot show whether drying increased late background |
| Unpackaged laboratory vial | Does not represent moisture ingress in the proposed product |
| Single formulation and lot | Shows feasibility but limited manufacturing generalizability |
| Elevated-temperature exposure only | Supports screening but may not establish ambient shelf life |
A rigorous review separates the authors' measured observations from extrapolations. Product developers should cite the exact conditions rather than reducing diverse studies to “RT-LAMP is stable at room temperature.”
