1. Introduction
Over the years, Lateral Flow Assays
and other membrane-based Assays has
become a useful tool not only in IVD tests
(infections, cancers, fertility, and drug of
abuse) but also inVeterinary Diagnostics,
Environmental Screening and FoodTesting.
This test format is well known for its
simplicity, its utility and its low production
cost. Its simple use, which does not require
neither technical training or experienced
staff or sophisticated equipment, has
become broadly accepted at Point of Care
"POC" doctor’s offices.
Most of today's lateral-flow assays
rely on nitrocellulose membrane, a very
small pore chromatic medium, to allow
the migration of liquid specimens (urines,
plasma, blood or saliva).
For the capture lines, most assay
developers choose between gold particles
and dyed polystyrene microspheres.We
continuously develop new intensively
dyed microspheres to obtain better signal.
Sensitivity for most lateral-flow assays is
limited to the range of ng.ml-1 and above.
Specially dedicated to this application,
our microspheres (In the range of
200 to 500nm) are hydrophobic (plain
polystyrene), moderately hydrophilic
(COOH from 10 to 100 µEq/ g) or highly
hydrophilic (COOH from 200 to 500
µEq/g).Together with our COOH-modified
beads, our NH2- or CH2Cl-modified
beads are well suited for covalent coupling
using classical methods.
FEATURE LATERAL FLOW ASSAYS
By Fabrice Sultan Ph.D., Sales and Marketing
Manager. Merck Chimie S.A.S- EstaporR
Microspheres
Lateral Flowtests
and assays:The use of
Polymer Microspheres
MedLab Issue 1 2010 15
lateral flowtests
Until now, lateral flow tests are widely
used for qualitative assays of more than
250 different analytes, and our simple
recommendations are:
● Ratio of Estapor®
microspheres
diameter to membrane porosity: 0.04 to
0.2 (200 to 500nm microspheres with a 3
to 10 µm membrane)
● Small size Estapor®
microspheres (<
200 nm) are easily rehydrated by the
sample (plasma or urine) and move
quickly. But they give a weak signal.
● Large darkly dyed Estapor®
microspheres (> 300 nm) give a better
sensitivity but move slowly
● For a stronger signal use larger/darker
beads, coat more protein onto the beads
(for a higher specific activity) or do both.
For a quantitative or semi-quantitative
detection, 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 recent instrument detects the
amount of magnetic material that passes
through a detector read area.This type
of bench top instrument enables a very
good quantification but also, increases the
sensitivity by thousand fold in comparison
to existing methods of reading.
By Estapor, we recently developed small
Estapor superparamagnetic microspheres
from 150 to 350 nm and containing up to
60% of ferromagnetic material (maghemite
and magnetite).These superparamagnetic
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.
improving
existing assays
New type of monodisperse fluorescent
microspheres from 300 to 500 nm and
containing different fluorescent molecules,
have been developed and could be of
special interest for developing new lateral
flow assays or improving existing ones
with a better sensitivity.
Since the Unipath pregnancy test
(Clearblue easy) marketed in 1988 and
using blue polymer microspheres, many
diagnostics companies offer and develop
new tests using the same principle.The
development of "relatively" simple and
rapid detection by lateral flow techniques
will address the need for POC testing
in the field of Clinical andVeterinary
Diagnostics, Environmental Screening and
Food Testing. In relation with the human
genome project, diagnostics tests for
genetic diseases are on the increase but
most of the products are both complex
and expensive. Lateral-flow assays,
eliminating the need for nucleic acid
amplification and purification, simplify
the technology, and will (probably)
reduce its cost.
The latest generation of quantitative
lateral-flow assays has shown a 3 log
improvement in analytical sensitivity (pg.
ml-1 vs. ng.ml-1).Then, development
of new lateral-flow assays using these
different solid supports, dyed, fluorescent,
bio-activated or super paramagnetic
microspheres, are really promising.
 AUTHOR Info
For more information, please contact
the author on fabrice.sultan@merck.fr
or visit the website www.estapor.com
“More recent
instruments detects
the amount of
magnetic material
that passes through a
detector read area”
■ML