1. are, in fact, superparamagnetic materials:
a core of iron oxides (maghemite and
magnetite) and a shell of polymer (PS
or PS/DVB).A classical Magnetic Beads
separation is very fast and takes less than
1 minute. Figure 1 was obtained with our
Encapsulated Magnetic Microspheres,
reference EM1-100/40 (size: 1µm and
ferrite: 45%).The use of magnetic
microspheres as the solid phase in
automated immunoassays - resulting in
automation, faster reactions, increased
sensitivity, and shorter time per assay -
has been one of the biggest technological
advances. Recently, those beads have been
used in a Development of Automated
Assays for Anticardiolipin Antibodies
Determination.
As shown in figure 1, the magnetization
of the microspheres increases with the
applied magnetic field and falls back to
zero when the field is removed. Neither
hysteresis nor residual magnetization is
observed and that provides the end use
with two very practical advantages:
●When the field is removed, the
microspheres demagnetize and redisperse
easily.This property allows efficient
washing steps, low background and good
reproducibility.
● The behaviour of the microspheres
is always the same whatever the
magnetization cycles may be. Such
behaviour is a key point for automated
instrument.
Bio-Estapor®
Microspheres
A range of Bio-Estapor®, bio-
activated microspheres, are available as
superparamagnetic. Magnetic bioseparation
or biopurification of antigens, antibodies
or nucleic acids with Estapor® coated
microspheres are both a simple and
reproducible technique which provide
an easier, faster and cheaper alternative
to column purification, centrifugation or
extraction with organic solvents. According
to the evidence that microsphere
requirements for capturing microbial cells
(such as E. Coli or Salmonella) are different
from those for isolating nucleic acids
(DNA, RNA or PCR products) or human
cells (T or B lymphocytes), we now supply
small (150-500nm), standard (750-1500nm)
and large (>2000nm) superparamagnetic
microspheres.We are proud to offer our
customers with a complete product range
of pre-activated magnetic microspheres,
coated with the most universal molecules
for diagnostic applications, Biopurification
or Bioconcentration: Streptavidin, Protein
A and anti-mouse or anti-human IgG,
anti-mouse or anti-human IgM. Used
as capture-intermediates, Bio-Estapor
Microspheres offer many advantages for
immobilising easily antibodies or antigens
onto the surface of the microspheres.
As ready-to-use reagents, Bioestapor
microspheres represent a powerful
activated solid phase dedicated to
many applications like immunoassays,
immunoprecipitation, cell sorting, cell
separation, nucleic acids technologies
and much more, making the coating
procedures and bio-reagent developments
easier and quicker.
MagPrep® Silica
Particles
The classical methods of isolating
DNA or RNA rely on density gradient
centrifugation and phenol-chloroform
extraction.These two procedures are
lengthy, laborious, difficult or impossible
to automate and they use hazardous
chemicals.Today, companies focus on
increasing the throughput of nucleic acids
purification by using safer procedures.
Our MagPrep® Silica Particles have
been developed to address these needs.
For nucleic acids purification, a number
of scientists have already replaced the
centrifugation and organic extraction
steps with our MagPrep® Silica Particles.
Their specific surface allows an easy
binding of nucleic acids DNA, RNA or
plasmid.This system enables laboratories
to automatically process tens of thousands
of samples per day.
Conclusion
In our ISO 9001 2000 and 14001 certified
facility, we offer custom development to
fit your very specific requirements.We are
continuing to develop both magnetic and
polymer beads with new surfaces in order
to allow developers to optimize and obtain
the best reagents. But we are also working
on new types of beads, such as those using
molecular print, biochips, biosensors, as well
as microfluidics.These new applications are
really interesting in several respects like
sensitivity, cost and ease of use.
 MORE INFO & references
For more information, contact the author
on fabrice.sultan@merck.fr
References available on request
(magazine@iirme.com)
Magnetic NanoSpheres
and Microspheres
FEATURE BIOTECHNOLOGY
By Fabrice Sultan,
Merck Chimie SAS
“Bio-Estapor
Microspheres offer
many advantages for
immobilising easily
antibodies or antigens
onto the surface of
the microspheres”
MedLab Issue 2 2009 31
Summary
The origins of Estapor® Microspheres go
back to 1970 when the first diagnostic
tests using the microspheres technology
were also beginning. Our original parent
company, Rhone Poulenc, manufactured
polymers used in the painting and paper
coating industries. Merck KgaA took over
the Estapor® Microspheres activities in
1993. For 35 years, Estapor® Microspheres
has been a leader in the development,
production and distribution of Polymer
Microspheres for IVD Industries and
for Academics.The use of Magnetic
NanoSpheres (<100nm) and Microspheres
in the IVD, Biotech and Life Sciences
industries is continuously increasing.The
main reason is because nanospheres and
microspheres represent a versatile tool
with many interesting properties (surface,
size, magnetization, density) and potential
applications (immunoassays, rapid tests,
IgG purification, cell sorting, nucleic acid
technologies, bacteria concentration,
biosensors, etc)
Magnetic particles represent an
efficient alternative to conventional
chromatography resins in automated
high-throughput protocols replacing
centrifugation, filtration or organic solvents
by simple magnetic separation steps.
Estapor® microspheres and MagPrep®
particles combine this advantage with
unique features like high magnetite content
and a non-porous surface, which allows
them to migrate very fast in magnetic fields
while binding target molecules with a high
signal to noise ratio.
The Estapor® Magnetic Microspheres
▶FIGURE 1 Hysteresis Loops obtained from
Estapor magnetic microspheres containing different
concentrations of magnetic pigment (13%, 48 or 60%).
■ML