Lateral Flow Tests: the silent technology that transformed diagnostics
From HIV to antibodies, from pregnancy to COVID-19. Those small white sticks you read in minutes hide decades of biochemistry and a manufacturing challenge that few people know about.
What is a Lateral Flow Test?
The Lateral Flow Immunoassay, also known as LFT, rapid test, or lateral flow assay, is one of the most widely used diagnostic devices in the world. It is the thin strip inside the plastic cassette of pregnancy tests, rapid COVID tests, blood type tests, STI tests, food allergen tests and dozens of other biological markers.
The principle is simple: a biological sample (blood, saliva, urine, nasopharyngeal swab) is applied to one end of the strip, and through capillary action, the same phenomenon that makes water rise in a paper towel, it travels through a series of functional zones that react specifically to the presence or absence of a target molecule.
The result: one or two coloured lines visible to the naked eye in some minutes, without a laboratory, without expensive equipment, without specialised operators.
Inside the strip: anatomy of a test
Inside that seemingly simple plastic cassette, there is a small masterpiece of biochemical engineering. The strip is composed of several layers laminated onto a supporting backing card:
•Sample Pad — the point of sample application. It filters impurities and conditions the pH of the liquid before it moves forward.
•Conjugate Pad — contains antibodies conjugated with colloidal gold nanoparticles (or other coloured markers). When the target molecule is present in the sample, it binds here to form a visible complex.
•Nitrocellulose Membrane — the heart of the test. Two lines of antibodies are printed here: the T Line (Test) and the C Line (Control). The T Line becomes visible only if the target is present. The C Line must always appear, confirming the test has worked correctly.
•Absorbent Pad — the final sponge that draws the liquid through, maintaining constant flow throughout the reaction time.
•Backing Card — the rigid support that holds all layers together and provides the mechanical stability of the strip during assembly into the cassette.
A red line appearing on a white membrane may look simple. Behind it lies a highly specific immunological reaction, designed to be readable without instruments by anyone, anywhere in the world.
Exploded view of a Lateral Flow cassette: sample pad, conjugate pad, membrane, backing card, absorbent pad
How the strip is produced: the industrial process
Strip production is a highly specialised process, typically carried out by dedicated membrane manufacturers who supply the pre-assembled test materials to diagnostic kit producers.
The process includes:
•Membrane preparation — nitrocellulose is cut into long sheets and treated to block non-specific binding sites.
•Antibody dispensing — a microdispensing system deposits the T and C lines with micrometric precision. Line dispensing requires high positional repeatability, because line geometry, uniformity and placement directly affect readability and test performance.
•Sheet assembly — the various pads are laminated and bonded onto the backing card, forming a wide sheet from which individual strips will be cut.
•Cutting — the sheet is cut into individual strips of the desired width (typically 3–6 mm). This step requires high mechanical precision: a slightly misaligned strip can compromise the visual reading of the result.
•Quality control — statistical sampling to verify line definition, sensitivity and specificity.
Assembly into the cassette: the manufacturing challenge
Once produced, the strip must be inserted into the plastic cassette that the end user holds and reads. This step — apparently simple — is in fact one of the most delicate in the entire production chain.
The strip must be inserted:
•in the correct orientation (sample pad alignment is critical for accurate reading),
•in the exact position (deviations of one millimetre can affect the result),
•without contaminating the sensitive surface of the membrane.
For this reason, many diagnostic kit manufacturers still work semi-manually or with expensive, inflexible machines. The market for automated Lateral Flow assembly systems is characterised by high-cost equipment designed for very large volumes — inaccessible to medium-sized producers or those managing many product variants at lower quantities.
It is precisely in this space — between fully manual and full-scale automation — that the opportunity for more agile, accessible and scalable solutions opens up.
Where Lateral Flow tests are used
Depending on the source and market definition, the global Lateral Flow Assay market is estimated in the range of several billion dollars, with recent 2025 estimates around USD 8.5–12 billion. Applications are vast:
•Food safety — allergen detection, mycotoxins, antibiotics in food products
•Environmental diagnostics — pesticide and contaminant detection in water
•Point-of-care — emergency rooms, GP clinics, pharmacies, home diagnostics
COVID-19 brought this technology into global awareness, but Lateral Flow has existed for over 40 years and is, quietly, one of the pillars of modern diagnostics.
From a shelved project to a new solution
How a 2019 project taught us to do less — and do it better
Sometimes the projects that never take off are the ones that teach you the most. This is the story of how a contract that slipped away in 2019 led us, six years later, to build something far more interesting.
2019: the complete machine that never was
In 2019 we were approached by two companies in the diagnostics sector. The goal was ambitious: build a fully automated machine for Lateral Flow test assembly. Everything in one solution — feeding both plastic components, cutting and inserting the test strip in-line, optical orientation verification, assembly, quality control and final bagging.
We got to work. We analysed the process, defined the architecture, evaluated vision systems, in-line cutting, robotic picking. The project was technically compelling and commercially promising.
Then what happens, happened. One of the two companies was acquired. Priorities shifted. Our contacts disappeared. Procurement froze. The order that was supposed to arrive by mid-2019 was postponed. Then again. Then silence.
Every engineer knows this story. Projects you have invested months of work into — gone for reasons that have nothing to do with the quality of what you proposed.
Years later: the market shows us reality
Years later, another company shows us how they work. Not an automated system. People: operators sitting at a table, assembling cassettes by hand, one by one, all day long.
The process: a machine cuts the strips. The strips are passed to operators. Operators insert the strip the in the plastic bases, position the lid, then feed the cassette through a small roller press that permanently closes it.
This is not incompetence. It is the reality of a market where fully automated machines cost a lot and are designed for massive volumes. If you produce 200.000 tests a year — not 50 million — that technology is simply out of reach. So you work by hand.
The insight: leverage the machines that already exist
Watching that manual process, we understood something important. The customer already had two machines: the cutting system and the roller press. Already paid for. Already validated. Already part of the production process.
The problem was not the entire workflow. The problem was what happens in the middle: feeding the plastic parts, placing the strip, verifying orientation, closing the cassette. That is the bottleneck. That is where the people work.
What if, instead of building a machine that does everything — cuts, assembles, verifies, bags — we built a machine that does only that middle part? A machine that slots between the existing cutter and the existing press, automating only the manual labour, at an accessible price point?
The best solution is not always the most complete one. Sometimes the best solution is the one that understands exactly where the customer's real problem begins and ends — and works precisely in that space.
The solution: the Engmotion assembly system
The result is an automatic carousel-based system with two bowl feeders for the plastic parts, a vision and inverter system for automatic component orientation, an operator belt for manual strip loading (already cut by the existing machine), and a manipulator that closes the cassette before passing it to the customer's roller press.
Strip centring and optical orientation verification on the assembly carousel
The proposed solution is not just a mechanical assembly unit.
It is a controlled automation platform designed to increase productivity while improving process consistency and quality compliance.
The target throughput of the base configuration is approximately 1.000 cassettes per hour, with a modular architecture prepared for future upgrades up to approximately 2.000 units per hour, depending on the final process configuration.
But throughput alone is not the real point.
In lateral flow cassette assembly, every detail matters: the orientation of the strip, the position inside the lower plastic part, the quality of the cassette components, the closing force, the cleanliness of the handling process, and the final readability of the result window.
For this reason, the machine concept requires carefully designed manipulators, controlled positioning systems and optical inspection stations. AI-assisted vision controls can play a key role in verifying critical conditions before, during and after assembly.
The system can be configured to check, for example:
strip presence and orientation;
correct strip positioning inside the lower cassette;
visible defects or non-conformities on the strip;
plastic component presence and orientation;
defects, deformation or contamination on the cassette parts;
correct assembly before transfer to the external roller press;
final visual conformity of the assembled cassette.
This is important because not every defect is generated by the assembly machine itself. Some issues may come from upstream processes: defective or miscut strips, non-conforming membranes, damaged plastic parts, dimensional variations, contamination or incorrect feeding. A reliable automation system must not only assemble good parts; it must also recognize when incoming components are not acceptable and automatically reject them before they become finished products.
This is where the real value of the solution is created: by combining mechanical handling, modular feeding, carousel-based assembly and intelligent inspection into a process that is productive, scalable and quality-oriented.
The system is designed to be compatible with future full integration: automatic in-line strip cutting, automatic strip collection and transfer, increased throughput, multi-variant product management and recipe-selectable cassette orientation. A customer can start with a base system today and later evolve toward a fully automated line through incremental investment, without discarding the equipment already installed.
What we learned
The 2019 project taught us the technical complexity of lateral flow cassette assembly.
This new opportunity taught us something equally important: the real industrial context in which this problem exists. Many manufacturers already have part of the process in place. They may already own a strip cutter. They may already use a final pressing unit. They may not need, or may not yet be ready for, a fully integrated high-end line.
What they need is a realistic automation step: one that reduces manual handling, increases process repeatability, improves quality control and prepares the production flow for future growth.
The most elegant solutions are not always the most complete ones.
They are the ones that understand where the customer’s real problem begins and ends — and work precisely in that space.
If you know companies producing diagnostic tests that still work manually or semi-manually for lateral flow cassette assembly, we would be glad to hear their experience. Field experience is always the best starting point for building useful automation.