News/Short Communications

Acid-dissolvable Melamine Resin Particles

microParticles GmbH has been sucessfully marketing acid-dissolvable melamine resin particles. As a result of recent efforts, the accessible size range could be significantly extended. Currently, monodisperse soluble melamine resin beads are available from nominal 500 nm up to 7 µm in diameter. Contrary to our stock-held highly crosslinked melamine resin research grade beads, these specialty particles are weakly crosslinked and soluble in hydrochloric acid as well as in some organic solvents. They are characterized by excellent monodispersity and highly uniform spherical shape. The particles possess a pH-dependent surface charge and are the most suitable choice for polyelectrolyte coatings or as templates for the preparation of hollow capsules.

New funktionalized melamine resin particles (MF-particles)

microParticles GmbH has successfully developed a series of novel functionalized melamine resin particles for stable, permanent attachment of biomolecules. Using innovative strategies of polymer chemistry and synthesis for surface modification, melamine resin particles with the following surface functionalities and polymer coatings are available:

• Melamine resin particles with carboxyl groups (group density controllable in a wide range up to 1000 µmole/g).
• Amino-modified melamine resin particles.
• Melamine resin particles with sulfonic acid groups, epoxy- and aldehyde functions as well as thiol und hydroxyl groups on the particle surface.
• Monodisperse melamine resin particles with maleimide-functionalization for the directed immobilization of thiol-containing compounds (e.g. HS-DNA).
• Melamine resine particles with covalently fixed polymer coatings like amino dextrane, poly(ethylene imine), poly(vinyl alcohol), etc.

These new MF particles not only combine excellent monodispersity and high mechanical and chemical stability, but also low unspecific protein adsorption, variable surface chemistry as well as high colloidal stability in a wide range of pH and electrolyte concentrations. The new products are designed for applications in medical diagnostics and in pharmaceutical and biotech industry. They can be delivered in the diameter range from 300 nm up to 12 µm.

Melamine resin nanoparticles

microParticles GmbH presents new monodisperse melamine resin (MF) nanometer particles. These research beads are currently available in the size range from 300 to 1000 nm. They are manufactured as either non-modified or fluorescently-labeled species. Other product characteristics are:

• Narrow particle size distribution.
• Spherical particles with smooth surface.
• High thermal, chemical and mechanical stability.
• Absolutely stable in all solvents, no swelling or shrinking upon contact with organic media.

Upon request, the new particles can be carboxyl-modified and are suitable that way for covalent coupling of proteins and other ligands.

New silica research beads

microParticles GmbH has expanded its product line of dense silica research beads. With optimized Sol-Gel procedures particle diameters of up to 5 microns are achieved. The particles come as 5 wt.-% aqueous dispersions or in dry powder form. The main product characteristics are:

• Particle diameters above 1 micron up to 5 microns.
• Narrow size distribution (CV 6 – 7 %).
• Spherical particles with smooth surface.
• Surface functionalities (carboxyl, amino groups) available on request.

microParticles GmbH receives DIN EN ISO 9001:2000 certification

In April 2003 microParticles GmbH has been certified under the globally approved ISO 9001:2000 Quality System. Certification validates that microParticles GmbH has implemented and maintains a quality management system (QMS) and establishes microParticles GmbH as a world-class company that continues to be customer and quality focused. For us, being a technology-oriented R&D laboratory, customer satisfaction, management responsibility, and organizational performance are major goals of our company’s philosophy. The ISO 9001:2000 standard delivers excellent means to evaluate and measure those quality metrics. Our competent partner during the process of establishing QMS was EuroNorm GmbH (www.euronorm.de).

Lichtmikroskopische Aufnahmen von Assemblies farbiger Partikel an der Phasengrenze Luft/Wasser von Schaumblasen (Blau: PS 4 µm, Rot: PS/PMMA 5,5 µm; Durchmesser der Blasen ca. 300 µm).

Monodisperse colored nano- and microparticles

microParticles GmbH introduces a new product line of intensely dyed monodisperse microspheres for use in applications like filter testing, flow tracing, medical diagnostics, and biotechnology. The particles, based on polystyrene and polystyrene copolymers, are produced with microParticles’ own technology platform and come in a wide variety of sizes, dyes, and functionalities. Using specifically designed dyeing processes, intensely colored particles with complete dye retention are obtained. The new particles come as 5 wt.-% aqueous dispersions. With larger beads also dry powders are available. The main product characteristics include:

• Size range from 500 nm to 1000 ТЕm.
• Dark blue, dark red and black colors available.
• Narrow size distribution (CV < 3 %).
• High lot-to-lot reproducibility.
• Spherical particles with smooth surface.
• Surface functionalities (carboxyl, amino, and epoxy groups) available on request.

CARBOXYL-FUNCTIONALIZED MELAMINE RESIN BEADS (white or fluorescent) Recently, microParticles has developed a new generation of carboxyl-functionalized monodisperse melamine resin (MF) microspheres. Using innovative surface polymerization techniques, functionalized beads with low, medium, or high density of carboxyl groups with up to 1000 ТЕmole/g can be obtained. The new product line can be supplied with diameters from 1 to 12 ТЕm. Combining advantageous material properties of MF with the newly achieved functionalization, these particles enter completely new applications, e.g. in Life Sciences. Main features of these carboxyl-modified microspheres are:

• Excellent chemical resistance and thermal stability.
• High density (1.5 g/cm3).
• Good solvent stability.
• High mechanical strength.
• Narrow particle size distribution.
• High colloidal stability.
• Covalent coupling of biologands, e.g. streptavidin, possible.
• Can be handled in dry powder form.

MONODISPERSE NANO- and MICROSPHERES with POLYELECTROLYTE MULTILAYERS

a new product line of microParticles GmbH, are especially designed for applications in Life Sciences. Using proprietary Layer-by-Layer technology monodisperse particles of different core materials, e.g. polystyrene, melamine resin, or silica in the size range between 300 nm and 50µm, are coated by layers of alternately charged polyelectrolytes. This technology has the advantage over known particle modifications that due to the layering technique several functionalities can be combined without cross-reactions. The following functions are offered

• positive or negative surface charge,
• high concentration of reactive binding sites e.g. amino or carboxyl groups,
• photo-reactive surface groups,
• covalently coupled fluorescent dyes,
• superparamagnetic properties.

For example, various combinations of fluorescent colour labels can be deposited on particle surfaces. Due to the LbL technology the dyes are located in spatially separated layers which avoids undesired interactions between them. Using 4 dyes with selected fluorescence wavelengths, a library of 15 differently tagged particles is available. The particles can be delivered as aqueous suspensions in 2 or 10 ml packages. The concentration varies in dependence on the particle size from 5 x 108 particles/ml for 0.5 -2 µm, 2 x 107 particles/ml for 2-10 µm to 5 x 105 particles/ml for 10 – 50 µm. MONODISPERSE, HOLLOW LBL-CAPSULES® with CONTROLLED PERMEABILITY are designed by means of the patented Layer-by-Layer technology. Their preparation is based on the coating of monodisperse soluble colloidal core particles with polyelectrolytes. After the layering procedure the core particles are removed from the interior. The surface and wall properties of the remaining capsules can be taylor-made as outlined above. The permeability can be varied from low permeability for molecules above 500 g/mol to high permeability for macromolecules with a molecular weight up to 50 kD. Capsule diameters between 500 nm and 10 µm are available. Our new capsules have some outstanding advantages:

• their interior can be used as container for uptake, transport, and release of different materials,
• they are stable in most inorganic and organic solvents,
• the thin wall (15-30 nm) results in very low weight avoiding fast precipitation,
• capsule walls cause only small light refraction or turbidity of the suspension,
• our broad label program offers the opportunity to use the capsules in combinatorial libraries, as sensors in different environments, or as photochemically reactive species.

The capsules can be delivered as aqueous suspensions in 1-10 ml packages. The concentration varies in dependence on the capsule size from 5 x 108 particles/ml for 0.5 -2 µm, 2 x 107 particles/ml for 2-10 µm to 5 x 105 particles/ml for 10 – 50 µm.

New NIST-traceable particle size standards

of 3 µm, 20 µm, 40 µm, 60 µm, 200 µm, and 250 µm nominal diameter are now available from microParticles GmbH. The new size standards may be used in industrial, pharmaceutical, clinical, and scientific laboratories for quality control and calibration of particle sizing instruments. The particle size standards are monodisperse polystyrene microspheres produced by microParticles’ innovative polymerization technologies. Product characteristics are:

• Most accurate size standards available, traceable to primary reference materials from the National Institute of Standards and Technology (NIST) and the Community Bureau of Reference (BCR).
• Extremely narrow size distribution.
• CV (Coefficient of Variation) <1,5 %.
• Absolutely spherical shape and smooth particle surface.

Particle sizes and size distributions are determined by Optical Microscopy and Electrical Sensing Zone method (COULTER® Multisizer III). Particle size standards are supplied as aqueous suspensions at 2 wt.-% solids in dropper tipped bottles. The rather high solids concentration facilitates dilution of the standards for use in calibration of many different particle analyzers. Diameters larger than 160 microns are packaged as dry powders in screw-capped bottles. All particles come with Certificate of Analysis and MSDS.