If you have ever used a home pregnancy test or a rapid COVID antigen test, you already understand the basic principle behind Agdia’s ImmunoStrip technology. These are all lateral flow immunoassays – diagnostic devices that use antibodies immobilized on a membrane strip to detect specific target molecules in a sample. The difference is that instead of detecting human hormones or viral proteins, ImmunoStrips detect plant pathogens: viruses, bacteria, viroids, and genetically modified trait proteins in plant tissue.
Since their introduction, ImmunoStrips have become the standard rapid diagnostic tool in greenhouses, fields, seed testing labs, and plant quarantine stations worldwide. This article explains how they work, when to use them, and how to get the most reliable results from your testing.
How an ImmunoStrip Works: The Science in 30 Minutes
Every ImmunoStrip contains three key components arranged along a nitrocellulose membrane strip:
1. The Sample Pad: This is where you apply your plant extract. The sample wicks up into the membrane by capillary action – no pump, no power, no equipment needed.
2. The Conjugate Zone: As the sample migrates through the strip, it encounters antibodies conjugated (attached) to colored nanoparticles, typically colloidal gold. These “detector antibodies” are designed to bind specifically to the target pathogen protein. If the target is present in your sample, the detector antibodies grab onto it, forming an antibody-target complex that continues migrating up the strip – now carrying visible color with it.
3. The Test and Control Lines: Further up the strip, a second set of antibodies is immobilized in a thin line on the membrane. These “capture antibodies” also bind the target protein, but at a different site (a different epitope). When the migrating antibody-target complex reaches this line, it is captured and concentrated, producing a visible colored line – the test line. A separate control line uses anti-species antibodies to capture excess detector antibodies, confirming that the strip functioned properly regardless of the result.
Reading the result: Two lines (test + control) = positive detection. One line (control only) = negative result. No control line = invalid test (repeat with a new strip).
The entire process – from sample application to readable result – takes approximately 30 minutes. No instruments, no electricity, no trained technician required.
What Makes ImmunoStrips Different from Generic Lateral Flow Tests
Agdia ImmunoStrips are not commodity products. Several features distinguish them from basic lateral flow devices:
Monoclonal antibody specificity: Each ImmunoStrip uses highly specific monoclonal antibodies developed and validated against the target pathogen. This is what allows, for example, the ToBRFV ImmunoStrip to distinguish ToBRFV from the closely related TMV and ToMV – even though these tobamoviruses share significant protein sequence similarity.
Validated sensitivity and specificity: Every ImmunoStrip product is validated against a panel of known isolates from multiple geographic origins. Sensitivity (the lowest detectable concentration, typically 64-320 pg/mL for serological strips) and specificity (which organisms it does and does not cross-react with) are published for each product.
Optimized extraction system: Each ImmunoStrip pack includes or is compatible with Agdia’s extraction bags and buffers, designed to efficiently release target proteins from plant tissue while minimizing interference from plant pigments, phenolics, and other compounds that can cause false results in crude extracts.
Types of ImmunoStrip Formats
Single-Target ImmunoStrips
The standard format: one strip, one pathogen. Available for over 40 plant pathogens and GMO traits. Examples include ImmunoStrips for TMV, TSWV, CGMMV, Ralstonia solanacearum, Clavibacter michiganensis, and Phytophthora.
Multi-Line ImmunoStrips
Some strips contain multiple test lines on a single device, each detecting a different target. The PVY/PVY-N ImmunoStrip is a prime example: one line detects all PVY strains, while a second line specifically identifies necrotic strains – critical information for seed potato certification.
ImmunoComb Multi-Virus Panels
ImmunoComb devices contain multiple separate antibody zones on a single comb-shaped device, allowing simultaneous detection of multiple pathogens from a single sample extract. The 4-virus ImmunoComb for CMV, INSV, TMV, and TSWV is the most popular panel for greenhouse operations dealing with multiple virus threats.
Best Practices for Accurate ImmunoStrip Results
Sample selection matters. For most viruses, test newly emerging leaves rather than old lower leaves – viral titers are typically higher in actively growing tissue. For ToBRFV, recent research shows fruit and sepals also carry high viral loads. For soil-borne pathogens like Phytophthora, test root or crown tissue.
Use the right extraction method. Follow Agdia’s protocol for the specific ImmunoStrip you are using. Over-diluting or under-grinding your sample directly affects test sensitivity.
Temperature affects migration time. ImmunoStrips work best at room temperature (20-25°C). In cold greenhouses or field conditions, allow the extraction buffer to reach room temperature before testing. Very cold conditions slow capillary flow and can give weak or absent lines on genuinely positive samples.
Read results at the specified time. Most ImmunoStrips are read at 30 minutes. Reading too early may miss weak positives; reading too late may show non-specific background coloring. Set a timer.
Confirm positives with a second method. ImmunoStrips are screening tools – they are designed for rapid, field-level detection. Best practice is to confirm any positive ImmunoStrip result with ELISA or AmplifyRP XRT molecular testing before making major management decisions like crop destruction.
Browse the Complete ImmunoStrip Collection
Immunomart is Canada’s source for the full range of Agdia ImmunoStrips. Browse the complete collection at:
All Agdia ImmunoStrips for Plant Pathogens – viruses, bacteria, oomycetes, and viroids
GMO Trait Detection ImmunoStrips – Bt proteins, herbicide tolerance markers, and selectable markers
Plant ELISA Kits – for high-throughput confirmation and seed health testing
Disclaimer: Agdia diagnostic kits referenced in this article are intended for plant pathogen detection in agricultural, horticultural, and research settings. For regulatory guidance on plant health in Canada, consult the CFIA.
