Product Palette

microParticles GmbH offers monodisperse spherical research particles based on various organic and inorganic polymers. The matrix chemistry of the particles ranges from melamine resins (MF), polystyrene (PS), polydivinylbenzene (PDVB), polymethyl methacrylate (PMMA), through poly(styrene-co-divinylbenzene) and poly(styrene-co-methacrylic acid methylester) copolymers to silica (Si0₂). The product palette covers beads of mean diameters from 0.1 up to 1000 µm in more than 200 different sizes. Characterized by their outstanding quality (typical C.V. values ≤3 %), our research grade particles are the best choice at economic prices.
Due to the different polymer compositions, the physical and chemical properties of the various types of particles are distinct from each other, which makes them suited for a whole spectrum of purposes. The high quality of our research grade particles and their versatility are illustrated with numerous successful applications in research and industry. We therefore feel obliged to continuously extend our product palette.

Pack sizes:

• aqueous dispersions PS, PMMA
  0,1-0,99 µm (50 mg/ml): 10 ml, 15 ml, 50 ml
  1 µm and larger (100 mg/ml): 10 ml, 15 ml, 50 ml
• aqueous dispersion MF (100 mg/ml): 10 ml, 15 ml, 50 ml
• aqueous dispersions SiO₂
  0,1-29 µm (50 mg/ml): 10 ml, 15 ml, 50 ml
  30 µm and larger (25 mg/ml): 10 ml, 15 ml, 50 ml
• powder (MF: 1-12 µm; PS, PMMA: 5-1000 µm): 1.5 g, 5 g, 10 g
• powder (SiO₂: 1-25 µm): 0.75 g, 2.5 g, 5 g

 NIST-traceable Particle Size Standards

Particle size standards are being used in industrial, pharmaceutical, clinical, and scientific laboratories for many purposes. Among others is the calibration of various measuring instruments such as flow cytometers, laser diffraction devices, analytical disc centrifuges, or cell and particle counters. Moreover, they allow for the traceability of measurement results, the development and validation of measuring techniques, and for the assessment of measurement uncertainties. Also, they are applied in the field of quality control and for the calibration and testing of filter materials.

For these applications, microParticles GmbH offers its customers particle size standards of highest quality over a wide diameter range from 100 nm through approximately 1000 µm. They consist of polystyrene or poly(styrene-co-divinylbenzene) and are characterized by combining different methods like transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential sedimentation (high resolution disc centrifuge DC 24000), optical microscopy, and electrical sensing zone method (Coulter Multisizer™ 3 and 4).

Thereby, the certified particle size standards of microParticles GmbH are among the best characterized ones currently available in the market. Other product characteristics are:

• Traceable to primary reference materials of the National Institute of Standards and Technology (NIST/USA) and European Institute for Reference Materials and Measurements (IRMM/Belgium).
• Highly monodisperse size distribution.g
• CV < 2 % for the majority of the products.
• Absolutely spherical particle shape.

In order to guarantee high colloidal stability, the aqueous particle suspensions contain surfactants and antimicrobial agents. Every particle size comes with a certificate that documents important information like certified mean diameter, standard deviation, CV-value, size distribution graph, solids content of the suspension, particle number per ml, material density, refractive index, and other.

Pack size:

• aqueous dispersions (20 mg/ml): 10 ml, 15 ml
• powder (160 µm and larger): 1 g

Novel manufacturing techniques, developed and established at microParticles GmbH, allow the preparation of a wide variety of fluorescent nano- and microspheres ranging in size, matrix chemistry, type of fluorochrome, fluorescence intensity, and surface functional groups. The specifically chosen fluorescent dyes almost cover the complete spectral range from UV through near IR. Outstanding properties of our melamine resin (MF)-, Polystyrene-, Polymethylmethacrylate and Silica- based fluorescent particles are:

• narrow size distribution (C.V. values ≤3 %)
• available in a wide diameter range
• fluorochromes are internally incorporated with a homogeneous distribution
• intensive color and bright fluorescence
• chemical and biochemical functionalizations are possible

In comparison to PS- and PMMA-based particles, the fluorescently-labelled MF- and silica microspheres have the additional advantage that they are dispersible in common organic solvents and oils without any dye-leaching, swelling, or shrinking. The fluorescent particles of microParticles GmbH are used for flow measurements in gases and liquids like Laser Doppler Anemometry (LDA), Particle Dynamics Analysis (PDA), and Particle Image Velocimetry (PIV), filter testing, in the field of non-destructive testing of complex aircraft, railway, and automotive components, in medical research (phagocytosis testing, blood-flow measurements, imaging), or as tracers in environmental science.

Pack sizes:

• aqueous dispersions (25 mg/ml): 5 ml, 10 ml, 15 ml
• powders upon request

Functionalized Particles

In medical diagnostics, pharmaceutical industry, biotechnology, molecular biology, analytics, etc. multifunctional polymer particles with tailored surface properties are required to a growing extent. In recent years, microParticles GmbH successfully accomplished the development of functionalized polystyrene-, PMMA-, silica-, and melamine resin particles. Innovative strategies and preparation techniques, such as

• chemical derivatization of the polymer surfaces,
• sol-gel processes,
• use of functionalized monomers,
• surface polymerization in organic and aqueous media,
• modification of particle surfaces by self-assembly (SAMs),
• nanostructured surface coatings

led to the linkage of a variety of functional groups to the surface of particles, made from different materials. The adjacent figure illustrates available functionalities. Particular emphasis is placed on carboxylated polymer beads, especially on melamine resin basis. With loadings of up to 1000 µmole COOH/g, these particles show excellent monodispersity, high mechanical strength and chemical resistance, low non-specific protein adsorption, and good colloidal stability over a wide range of pH values and electrolyte concentrations. Mercapto- and amino-functionalized particles also belong to our product spectrum. Upon request, modification with sulfonic acid, maleimid, epoxy, or hydroxyl groups is possible.

Pack sizes:

• aqueous dispersions PS-, PMMA-COOH
  0,1-0,99 µm: 50 mg/ml; 5 ml, 10 ml, 15 ml
  1 µm and larger: 100 mg/ml; 5 ml, 10 ml, 15 ml
• aqueous dispersions MF-COOH (100 mg/ml): 5 ml, 10 ml, 15 ml
• aqueous dispersions MF-Fluo-COOH (25 mg/ml): 5 ml, 10 ml, 15 ml
• aqueous dispersions SiO₂-COOH, -NH₂ (50 mg/ml): 5 ml, 10 ml, 15 ml

Metal-coated Polymer Particles

Monodisperse metal-coated microspheres have found wide applications in the fields of catalysis, anisotropically conductive adhesives (ACAs), microelectronics, Surface Enhanced Raman Scattering (SERS), Particle Image Velocimetry (PIV), and bioassays. During recent years, scientists at microParticles GmbH have successfully developed strategies to metallize chemically different microspheres like melamine resins, polystyrene, polystyrene-divinylbenzene copolymers, poly(methyl methacrylate) copolymers, or silica. The composite microspheres consist of a monodisperse polymer core whereas the shell either consists of metal nanoparticles or a thin metal film of e.g. gold, silver, copper, or others.

The use of the monodisperse melamine resin particles (MF) has a number of advantages:

• the surface of the MF particles is well-defined, having a large number of reactive amino and imino groups for immobilization of different metal ions or metal nanoparticles
• under acidic environments, the unmodified surface of MF particles is positively charged and shows a high binding capacity to complex anions like AuCl₄^-, PdCl₄^2-, PtCl₆^2-
• in particular, the AuCl₄^- adsorbance on MF microparticles of about 500 nm diameter reaches a very high value of about 0,5 g/g.

Generally, for the preparation of our metal-coated microspheres three approaches have been used:

Self-assembly approach:
In the self-assembly approach, preformed colloidal nanoparticles are adsorbed on the specifically modified particle surface by electrostatic interactions, for instance. The extent of nanoparticle surface coverage can be controlled by varying the pH value of the solution, the immersion time, the metal colloid concentration in suspension, nanoparticle dimensions, and the chemical surface properties of the polymer particles. In this way, monodisperse microspheres with individually dispersed nanoparticles of gold, silver, platinum, or palladium can be prepared.

In-situ synthesis approach:                                                                                                                                                          In the in-situ approach AuCl₄^-, PdCl₄^2-, PtCl₆^2- precursor ions are bound on the surface of chemically modified monodisperse particles by complexation and/or electrostatic interactions, followed by their in situ reduction to nanosized metal particles. TEM images show the in situ synthesized metal nanoparticles being homogeneously distributed on the particle surface without aggregation. The average diameter is around 2-3 nm with a narrow size distribution.

Electroless deposition approach:                                                                                                                                                In the electroless deposition approach, the specifically surface-modified microspheres are immersed in an electroless plating bath, which consists of the metal ions and a reducing agent. Gold, silver, palladium, or platinum nanoparticles immobilized on the particle surface can be used as seeds for the auto-catalytic deposition of the metal. The result is a metal nanoshell with variable thickness of gold, silver, or copper on the particle surface. High-quality metal coatings can be achieved with particles in the size region above 1 µm. Research is underway to develop particles with gold nanoshells in the submicron range, too

Superparamagnetic Polymer Particles

MicroParticles GmbH offers its customers a series of newly developed magnetic spheres in the diameter range from 300 nm through 50 microns. The particle matrix consists of either polystyrene or silica with homogeneously incorporated nanometer-sized iron oxide. Special surface coatings encapsulate the particles towards surrounding media thus preventing the leaching of iron species. Outstanding properties of the new magnetic microspheres of microParticles GmbH are:

• Narrow size distribution (CV <5%) and absolutely spherical shape.
• Superparamagnetic.
• The iron oxide content can be adjusted in a wide range up to 50 wt.-%.
• The special surface coating minimizes aggregation in aqueous suspension and non-specific binding of proteins and nucleic acids.

In addition to plain magnetic particles (PS-MAG and SiO₂-MAG) and magnetic particles with COOH-modification (PS-MAG-COOH and SiO₂-MAG-COOH), we also supply magnetic beads with streptavidin coatings (PS-MAG-SA and SiO₂-MAG-SA). Moreover, microParticles GmbH offers the custom made covalent coupling of other proteins (protein A, hIgG, trypsin, BSA, ...) to carboxylated superparamagnetic particles. Upon request, we also manufacture superparamagnetic particles with reduced autofluorescence which are suitable for flow-cytometry.

The currently available spectrum of monodisperse superparamagnetic particles is listed in the product tables as given below:

Pack sizes:

• Aqueous dispersions
  (25 mg/ml): 5 ml, 10 ml, 15 ml (MAG, 0,3 - 0,99 µm)
  (50 mg/ml): 5 ml, 10 ml, 15 ml (MAG, 1 - 10 µm)
• Aqueous dispersions
  (25 mg/ml): 5 ml, 10 ml, 15 ml (MAG-COOH, 0,3 - 0,99 µm)
  (50 mg/ml): 5 ml, 10 ml, 15 ml (MAG-COOH, 1 - 10 µm)
• Aqueous dispersions
  (10 mg/ml): 1 ml, 5 ml, 10 ml (MAG-SA, 0,3 - 10 µm)