Michael A. Spaid

Controlling Data Quality and Reproducibility of a High-Sensitivity Immunoassay Using Isotachophoresis in a Microchip

This report describes a method of controlling the sensitivity and reproducibility of a microchip-based immunoassay by using isotachophoresis to preconcentrate the antigen and antibody prior to binding. Gel electrophoresis separation is coupled to the preconcentration step to separate the immunocomplex products formed. The system employs a quartz-based LabChip that automates the metering, preconcentration, reaction, separation, and detection. The system also uses a handoff mechanism that switches the immunocomplex from the stacking mode to the separation mode. We show that the handoff timing affects the data quality and repeatability of the electropherograms, and we demonstrate an automatic handoff mechanism to precisely control the signal intensity and separation of peaks of interest. In so doing, the automatic handoff mechanism also improves the reproducibility of the assay. When applied to the homogeneous liquid-phase detection of alpha-fetoprotein, a common tumor marker, the system shows a greater than 200-fold stacking of specific analytes of interest.

High-Throughput Screening on Microchips

Using a variety of uniquely designed capillary LabChip® devices; we describe several assays that we developed specifically for high-throughput screening. All of the assays use chips that have continuous flow driven by either electrokinetics or pressure. The data presented here demonstrate the use of capillary microchips for assays that can determine biochemical constants with fluorogenic and nonfluorogenic substrates, detect agonist and antagonist activity of a G-protein coupled receptor in cells, and collect dose response data automatically.

Ultraviolet Absorbance Spectroscopy in a 3-Dimensional Microfluidic Chip

The strength of absorbance by a compound is linearly dependent on the path length of the detection cell. Because of this, performing high sensitivity absorbance measurements on samples in microfluidic chips, where channel depths are roughly 10–50 µM, is extremely challenging. There have been several attempts to overcome this inherent difficulty, including 1) coupling optical fibers into the chip and directing light along a section of the channel [1], and 2) creating a multi-reflection cell [2]. We have taken another approach, which is to construct a chip containing a three-dimensional fluid path. In our chips, the section of the fluid path running perpendicular to the plane of the chip forms a detection cell with a path length equal to 720 µm, allowing for highly sensitive absorbance measurements.