Biomedical subjects

H M Hertz

Publications and source records attributed to H M Hertz.

7 recordsLinked to original sources

PubMed2007

Proliferation and viability of adherent cells manipulated by standing-wave ultrasound in a microfluidic chip.

Ultrasonic-standing-wave (USW) technology has potential to become a standard method for gentle and contactless cell handling in microfluidic chips. We investigate the viability of adherent cells exposed to USWs by studying the proliferation rate of recultured cells following ultrasonic trapping and aggregation of low cell numbers in a microfluidic chip. The cells form 2-D aggregates inside the chip and the aggregates are held against a continuous flow of cell culture medium perpendicular to the propagation direction of the standing wave. No deviations in the doubling time from expected values (24 to 48 h) were observed for COS-7 cells held in the trap at acoustic pressure amplitudes up to 0.85 MPa and for times ranging between 30 and 75 min. Thus, the results demonstrate the potential of ultrasonic standing waves as a tool for gentle manipulation of low cell numbers in microfluidic systems.

Animals↗

PubMed2006

Ultrasonic standing wave manipulation technology integrated into a dielectrophoretic chip.

Several cell-based biological applications in microfluidic systems require simultaneous high-throughput and individual handling of cells or other bioparticles. Available chip-based tools for contactless manipulation are designed for either high-precision handling of individual particles, or high-throughput handling of ensembles of particles. In order to simultaneously perform both, we have combined two manipulation technologies based on ultrasonic standing waves (USWs) and dielectrophoresis (DEP) in a microfluidic chip. The principle is based on the competition between long-range ultrasonic forces, short-range dielectrophoretic forces and viscous drag forces from the fluid flow. The ultrasound is coupled into the microchannel resonator by an external transducer with a refractive element placed on top of the chip, thereby allowing transmission light microscopy to continuously monitor the biological process. The DEP manipulation is generated by an electric field between co-planar microelectrodes placed on the bottom surface of the fluid channel. We demonstrate flexible and gentle elementary manipulation functions by the use of USWs and linear or curved DEP deflector elements that can be used in high-throughput biotechnology applications of individual cells.

Electrophoresis, Microchip↗

PubMed2006

Ultrasonic enhancement of bead-based bioaffinity assays.

Ultrasonic radiation forces can be used for non-intrusive manipulation and concentration of suspended micrometer-sized particles. For bioanalytical purposes, standing-wave ultrasound has long been used for rapid immuno-agglutination of functionalized latex beads. More recently, detection methods based on laser-scanning fluorometry and single-step homogeneous bead-based assays show promise for fast, easy and sensitive biochemical analysis. If such methods are combined with ultrasonic enhancement, detection limits in the femtomolar region are feasible. In this paper, we review the development of standing-wave ultrasonic manipulation for bioanalysis, with special emphasis on miniaturization and ultrasensitive bead-based immunoassays.

Immunoassay↗

PubMed2003

Ultrasonic-trap-enhanced selectivity in capillary electrophoresis.

We combine ultrasonic trapping and capillary electrophoresis (CE) with the goal to detect ultra-low concentrations of proteins via size-selective separation and enrichment of antibody-coated latex spheres. An 8.5 MHz standing ultrasonic wave is longitudinally coupled into the sub-100- micro m diam capillary of the CE system. Competition between acoustic and viscous forces result in in-flow separation of micro m-diam spheres according to their size. Experiments separating 2.8- and 2.1- micro m-diam fluorescent latex particles, which model a protein-specific immunocomplex/free particle mixture, indicate a potential improvement of the concentration limit of detection of 10(4) compared to current CE systems. Theoretical calculations show room for further improvement.

Electrophoresis, Capillary↗

PubMed2003

Wavelet-based image restoration for compact X-ray microscopy.

Compact water-window X-ray microscopy with short exposure times will always be limited on photons owing to sources of limited power in combination with low-efficency X-ray optics. Thus, it is important to investigate methods for improving the signal-to-noise ratio in the images. We show that a wavelet-based denoising procedure significantly improves the quality and contrast in compact X-ray microscopy images. A non-decimated, discrete wavelet transform (DWT) is applied to original, noisy images. After applying a thresholding procedure to the finest scales of the DWT, by setting to zero all wavelet coefficients of magnitude below a prescribed value, the inverse DWT to the thresholded DWT produces denoised images. It is concluded that the denoising procedure has potential to reduce the exposure time by a factor of 2 without loss of relevant image information.

Algorithms↗

PubMed2001

Microparticles for selective protein determination in capillary electrophoresis.

A system for detection of trace amounts of protein was developed. Two different monoclonal antibodies against human chorionic gonadotropin (hCG) were covalently bound to latex particles. When the latex particles were mixed with a sample containing hCG, a latex-protein-latex complex (immunocomplex) was formed. The complex was separated from the single latex particles using capillary electrophoresis and detected using UV-Vis detection. Limit of detection was 8 amol hCG. The separation was also monitored in real time using laser induced fluorescence - charge coupled device (LIF-CCD) imaging detection. However, a limitation of the method is the restriction to detection of proteins for which monoclonal antibodies are available.

Antibodies, Monoclonal↗

PubMed2000

Compact water-window transmission X-ray microscopy.

We demonstrate sub-100 nm resolution water-window soft X-ray full-field transmission microscopy with a compact system. The microscope operates at lambda = 3.37 nm and is based on a 100 Hz table-top regenerative debris-free droplet-target laser-plasma X-ray source in combination with normal-incidence multilayer condenser optics for sample illumination. High-spatial-resolution imaging is performed with a 7.3% efficiency nickel zone plate and a 1024 x 1024 pixel CCD detector. Images of dry test samples are recorded with exposure times of a few minutes and show features smaller than 60 nm.

Diatoms↗