Christoph Haiden

Sizing of metallic nanoparticles confined to a microfluidic film applying dark-field particle tracking.

We present Brownian motion-based sizing of individual submicron and nanoparticles in liquid samples. The advantage of our approach is that particles can freely diffuse in a 10 μm thin liquid film and are therefore always within the focal depth of a low numerical aperture objective. Particles are visualized with dark-field microscopy, and the resulting diffraction-limited spots are tracked over a wide field of view of several hundred micrometers. Consequently, it is ascertained that long 2D trajectories are acquired, which leads to significantly increased particle sizing precision. The hydrodynamic diameters of metal particles with nominal sizes ranging from 70 to 200 nm in aqueous solution were determined by tracking for up to 2 min, and it was investigated if the diffusion characteristics were influenced by the proximity of substrates. This was not the case, and the estimated diameters were in good agreement with the values obtained by electron microscopy, thus validating the particle sizing principle. Furthermore, we measured a sample mixture to demonstrate the distinction of close particle sizes and performed the conjugation of a model protein (BSA) on the nanoparticle surface. An average increase in the radius of 9 nm was determined, which corresponds to the size of the BSA protein.

A Microfluidic Chip and Dark-Field Imaging System for Size Measurement of Metal Wear Particles in Oil

We present a dark-field video microscopy setup and microfluidic sample cell to detect suspended particles and measure their size. The microfluidic chip was fabricated by etching of shallow chambers in silicon and bonding with glass, thus achieving robust devices with low background signal for dark-field microscopy. The system is suitable for measuring particles in liquid media, such as metallic wear particles originating from lubricated tribocontacts in oil. Here, sample wear particles were generated in the laboratory by sliding a piston ring section against a cylinder liner section with a reciprocating tribometer using base oil (PAO8) as lubricant. Individual microparticles and nanoparticles are visualized by means of their scattered light, and sizes are determined by tracking of the diffusive Brownian motion in liquid. By heating the oil sample, the viscosity is reduced, which increases the extent of Brownian motion and facilitates tracking-based size calculations. The height of the microfluidic chamber was matched with the focal depth of the optical system, so that particles stay in focus during the whole measurement time. The resulting particle size distributions were monomodal and displayed a peak diameter of 230 nm, as confirmed by reference measurements with dynamic light scattering. Our approach represents a straightforward way to determine the size of microparticles and nanoparticles and has the potential for a continuous online operation. Compared with the state-of-the-art particle counters used in condition monitoring of industrial machinery, it is possible to detect much smaller particles and, therefore, allow early detection of wear before severe failure events take place.

Concurrent particle diffusion and sedimentation measurements using two-dimensional tracking in a vertical sample arrangement

This letter reports a method for simultaneous tracking of Brownian motion and superimposed sedimentation movement of multiple micro- and nanoparticles in liquid. Simple two-dimensional particle tracking can be employed because the thin liquid sample film is arranged vertically and viewed from the side with a dark field video microscopy setup. Therefore, both diffusion and sedimentation can be used for particle size calculation, allowing analyses over a wide range of sizes and mass densities. To validate the method, size distributions of reference particles with known density and diameters ranging from 100 nm to 6 μm were determined. Brownian motion for size calculation is useful for sufficiently small particles, whereas sedimentation can only be applied if there is significant settling motion superimposed on Brownian motion (which requires large diameters and/or densities). Within a certain range, both principles are suitable for size measurements. As a consequence, this method can be used to determine th...

Dark field imaging system for size characterization of magnetic micromarkers

In this paper we demonstrate a dark field video imaging system for the detection and size characterization of individual magnetic micromarkers suspended in liquid and the detection of pathogens utilizing magnetically labelled E.coli. The system follows dynamic processes and interactions of moving micro/nano objects close to or below the optical resolution limit, and is especially suitable for small sample volumes (~ 10 μl). The developed detection method can be used to obtain clinical information about liquid contents when an additional biological protocol is provided, i.e., binding of microorganisms (e.g. E.coli) to specific magnetic markers. Some of the major advantages of our method are the increased sizing precision in the micro- and nano-range as well as the setup’s simplicity making it a perfect candidate for miniaturized devices. Measurements can thus be carried out in a quick, inexpensive, and compact manner. A minor limitation is that the concentration range of micromarkers in a liquid sample needs to be adjusted in such a manner that the number of individual particles in the microscope’s field of view is sufficient.

Mid-infrared CH2-stretch ratio sensor for suspended mammalian cells

In this contribution we present a sensor system to measure the CH2-stretch ratio of suspended mammalian cells. To overcome the strong infrared absorbance of water our sensor system comprises a sample chip with three equal chambers with an inner height of only 20 μm.