Eric Altendorf

Differential blood cell counts obtained using a microchannel based flow cytometer

This paper reports results demonstrating the ability to use single microfabricated silicon flow channels for the differential counting of granulocytes, lymphocytes, monocytes, red blood cells (RBCs), and platelets, in a sample of blood by means of laser light scattering. The microfabrication-based flow cytometer described does not rely on sheath flow in order to align the blood cells.

Results Obtained using A Prototype Microfluidics-Based Hematology Analyzer

Microfluidic laminate-based structures incorporating hydrodynamic focusing and flow channels with dimensions much less than 1 mm were fabricated and used to transport and analyze blood samples. Optically transparent windows integral to the flow channels were used to intercept the sample streams with a tightly focused diode laser probe beam. The size and structure of the blood cells passing through the laser beam determined the intensity and directional distribution of the scattered light generated. Forward and small angle light scattering channels were used to count and differentiate platelets, red blood cells, and various populations of white blood cells. All the blood samples used were characterized using a commercial hematology analyzer for comparison and validation purposes.

Implementation of novel optical detection methods for clinically important blood analytes using microfabricated flow structures (T-Sensors)

T-Sensors enable the optical detection of clinically significant analytes directly in whole blood. In microfluidic channels, fluids usually show laminar behavior. This allows the movement of different fluidic layers in a channel without mixing other than by diffusion. A sample solution, a detection solution, and a reference solution are introduce din a common channel. Smaller particles such as ions or small proteins diffuse rapidly across the fluid boundaries, whereas larger molecules diffuse more slowly. Large particles show no significant diffusion within the time the flow streams are in contact. Two interface zones are formed between the fluidic layers. The ratio of a property of the two interface zones is a function of the concentration of the analyte. In this paper, we introduce a novel optical geometry to determine absorbance or fluorescence at a number of distinct wavelength ranges, and to perform spectroscopic measurements with 1D or 2D spatial. Resolution in a flow channel. A flow channel is coupled to an optical filter with variable transmission in one or two dimensions, a light source, and a CCD detector. Such a device allows, for example, the absorption- or fluorescence- based detection of a variety of analytes in a T-sensor using a non-color-sensitive spatial detector, while retaining diffusion and reference information provided by the T-sensor principle.

Optical flow cytometry utilizing microfabricated silicon flow channels

A benchtop optical flow cytometer utilizing microfabricated silicon V-groove flow channels (25 micron diameter) has been constructed and tested using diluted whole blood. A 1.2 mw diode laser probe beam focused onto the flow stream is used to generate scattered light from passing blood cells. Photodiode detectors are used to collect both small and large angle signals which are counted and analyzed for pulse peak intensities. Count rates as high as 1000/second have been obtained using pressure heads of about 0.5 psi. Optical modeling has also been carried out in order to determine the light scattering signature of blood cells passing down various channel flow lines. Results suggest that a significant amount of experimental signal variability may be due to variations in the positions of cells passing through the sampling region, but that this degree of signal variation should not prohibit the discrimination of different cell populations. Experimental and computational results are presented and discussed, as well as the possibility of developing a miniature portable flow cytometer based on microfabricated flow channels.

Microfabrication-based ektacytometer for blood cell deformability measurements

A unique ektacytometer for monitoring blood cell deformability constructed using a silicon and glass microfabricated flow cell, a diode laser source and CCD detector, is presented. The device described in this paper relies on the reflection of the incident laser beam from the silicon surface, and hence does not act as a transmission cell. In this sense the device is compatible with other microfabricated devices which also utilize a reflection based optical geometry. Flow induced changes in the diffraction pattern generated by blood samples flowing through the microfabricated cell, and passing through the laser beam, are analyzed and compared with expected results based on shear induced changes in erythrocyte (red blood cell) shape within the flow cell. Finally, optimization of the flow cell design, and possible applications toward biomedical instrumentation are also discussed.

Microfabricated interlock system for precision alignment

A mechanical interlock system is reported that achieves the manual alignment of two components accurate to within plus or minus 10 micrometers in three spatial coordinates. In addition, the system allows rapid component interchange. The system is based on a novel two stage application of the principles of the kinematic location of instrument components. A macro scale kinematic mount allows manual handling while a micro scale mount delivers the accuracy required. Silicon microfabrication methods are used to create features in the micron size range accurately and repeatable for the micro scale mount. Such a system could be used for fluidic, pneumatic, electrical, optical, or mechanical interconnects. We use it for the alignment of optics to flow channel in an optical flow cytometer which is part of a microfluidic total chemical analysis system we are developing.