Over the past decade, membrane based-lateral flow assays have become an important tool not only in medical diagnostics but also in veterinary diagnostics and in environment and agricultural fields. This test format is well known for its simplicity, its utility and its production cost. Together, researchers and physicians have demonstrated the clinical interest of more than 150 different analytes. Many of these have been introduced as products and are designed for the use in hospital, doctor’s offices or pharmacies.

 

Now, most assay developers choose between gold particles (from 20 to 45 nm) and dyed polystyrene microspheres (from 150 to 400 nm). Several rapid-tests, using our Estapor® dyed microspheres, are already marketed.

 

Today, Estapor® dyed microspheres offer several advantages over the gold particles such as good lot to lot reproducibility, batch size of 1kg and more, uniform size distribution, easy to use for passive adsorption or covalent coupling, and above all, more than 100 different colours.

 

The last advantage is significant, in particular when several tests are run together, we can easily used different colours of dyed microspheres. In fact the reading is faster, easier and of course more secure. Using the gold particles, the colour lines are always the same and this could induce mistake or, at least, false interpretation. With the dyed microspheres, the different analytes are perfectly and easily identified.

 

Finally, dyed microspheres offer several advantages over the classical gold particles which should be of interest, not only for R&D people, but also for Marketing and Sales Managers. The competition is always stronger; it is one way to be different!

 

By Estapor, we recently developed new Estapor® dyed microspheres in the range of 200 nm and highly carboxylated (500 µEq/g)! These new products, very well suited for lateral flow assays, are available in red and blue and, very soon, will be available in green and yellow. Ask for our complete inventory.

 

Due to their specific light emission properties, our Estapor® dyed microspheres in the range of 150 to 400 nm could be of special interest for developing new lateral flow assays or improving existing ones with a better sensitivity.

 

Our simple recommendations for using Estapor® dyed microspheres in lateral flow assays are available on simple request.

 

It is sometime difficult to coat directly antibodies or proteins onto the microspheres. This is the reason why, we developed our own bio-activated dyed microspheres called BioEstapor®. Used as capture-intermediates, BioEstapor® dyed microspheres are coated and bio-activated with streptavidin or secondary antibody (anti-IgG or IgM) and offer many advantages for immobilising easily antibodies or antigens onto their surface.

 

Until now, lateral flow assays are widely used for the qualitative detection of several analytes : pregnancy test (b-hCG); fertility and ovulation tests (LH and FSH); Infectious diseases (HIV, Strep A, Helicobacter Pylori, HbsAg, Chlamydia, Infectious mononucleosis); cancer detection (PSA, aFP, human haemoglobin faecal); cardiac markers (troponin I); drug abuse (amphetamine, cocaine, BZO).

 

The quantitative determination of individual human proteins in biological fluids such blood, plasma, serum, urine or cerebrospinal fluid serves as an important tool not only in diagnosing diseases but also in monitoring the course of a disease and, of course the effect of the treatment. During the last ten years, visual techniques are increasingly being replaced by fast and automated optical detection systems.

 

It is now evident that optimal programming of the instrument is a very important factor for obtaining reliable and reproducible results.

 

Several analysers are designed to read strip-tests, based on colloidal gold or polystyrene microspheres labelled with different analytes, by remission or retransmission photometry.

 

More recently, new analysers can detect the amount of magnetic material that passes through a detector. This instrument enables a very good quantification but also, increases the sensitivity by thousand folds in comparison to existing methods of reading.

 

By Estapor, we recently developed small Estapor® superparamagnetic microspheres of 300nm and containing 30 to 40% of ferrite (M1-030/40) . These new and unique magnetic beads are well suited for developing new lateral flow assays. Then, it is now quite simple to use Estapor® superparamagnetic microspheres as labels in lateral flow assays.

 

Development of lateral flow assays using these different new solid supports, dyed, fluorescent, bio-activated or superparamagnetic microspheres are really promising.