Carl K. Fredrickson

Macro-to-micro interfaces for microfluidic devices

Since the concept of miniaturized total analysis systems (microTAS) was invented, a great number of microfluidic devices have been demonstrated for a variety of applications. However, an important hurdle that still needs to be cleared is the connection of a microfluidic device with the rest of the world, which is often referred to as the macro-to-micro interface, interconnect, or world-to-chip interface. In this review, we will examine the methods used by pioneers in the field and other investigators, review the approaches for capillary electrophoresis-based devices and those using pneumatic pumping, and present additional discussion on interface standardization and choosing and designing interconnects for your applications.

Cell-Free Protein Synthesis in Microfluidic Array Devices

We report the development of a microfluidic array device for continuous‐exchange, cell‐free protein synthesis. The advantages of protein expression in the microfluidic array include (1) the potential to achieve high‐throughput protein expression, matching the throughput of gene discovery; (2) more than 2 orders of magnitude reduction in reagent consumption, decreasing the cost of protein synthesis; and (3) the possibility to integrate with detection for rapid protein analysis, eliminating the need to harvest proteins. The device consists of an array of units, and each unit can be used for production of an individual protein. The unit comprises a tray chamber for in vitro protein expression and a well chamber as a nutrient reservoir. The tray is nested in the well, and they are separated by a dialysis membrane and connected through a microfluidic connection that provides a means to supply nutrients and remove the reaction byproducts. The device is demonstrated by synthesis of green fluorescent protein, chloramphenicol acetyl‐transferase, and luciferase. Protein expression in the device lasts 5–10 times longer and the production yield is 13–22 times higher than in a microcentrifuge tube. In addition, we studied the effects of the operation temperature and hydrostatic flow on the protein production yield.

Laser-Induced Fluorescence Imaging System for Protein Separations in Microfluidic Devices

This paper describes a laser-induced fluorescence (LIF) detection system for imaging proteins separated in a microfluidic device. The diameter of a laser beam is first increased through a beam expander, and subsequently focused into a line using a cylindrical lens. The resultant laser line is used to image an entire capillary or channel in which protein separation took place. The fluorescence emission is collected with a cooled, scientific grade charge-coupled device (CCD) camera. The detection limit was determined using a series of concentrations of fluorescein solutions. The temporal and spatial effects of photobleaching from laser irradiation were analyzed and the parameters to reduce the effect of photobleaching are discussed. We used the imaging system to demonstrate rapid analysis of proteins using isoelectric focusing.

Rapid Protein Separations in Microfluidic Devices

Abstract : This paper describes fabrication of glass and plastic microfluidic devices for protein separations. Although the long-term goal is to develop a microfluidic device for two-dimensional gel electrophoresis, this paper focuses on the first dimension-isoelectric focusing (IEF). A laser-induced fluorescence (LIF) imaging system has been built for imaging an entire channel in an IEF device. The whole-channel imaging eliminates the need to migrate focused protein bands, which is required if a single-point detector is used. Using the devices and the imaging system, we are able to perform IEF separations of proteins within minutes rather than hours in traditional bench-top instruments.

Fabricating a Plastic Microfluidic Device for Protein Synthesis

We developed an array device consisting of miniaturized wells and a mechanism of fluid manipulation for cell-free protein synthesis. The array offers high-throughput protein production, matching the format of gene discovery. Each unit in the array is for synthesis of one individual protein and it consists of a tray chamber and a well chamber. The tray chamber is for in vitro protein synthesis reaction, while the well functions as a nutrient reservoir. The tray and well are separated by a dialysis membrane, which is glued to the bottom of the tray. The connection between the tray and the well provides a means to supply nutrients and remove the reaction byproducts. The device was demonstrated by synthesis of green fluorescent protein (GFP). The effectiveness of the device design on the protein production yield has been studied. The resultant advantages due to miniaturization include rapid analysis, less consumption of samples and reagents, and the decrease in the cost of protein synthesis.Copyright

Fabricating Plastic Microfluidic Devices With Photodefinable Microvalves for Protein Separations

This paper describes the results of fabricating plastic microfluidic devices and creating a microvalve array for protein separation. Plastic devices are selected due to low cost of raw materials, bio-compatibility, and disposability. Although the methods for fabricating plastic devices have appeared in literature, reports typically indicate one set of conditions that yield functional devices. We report a systematic study of fabrication process parameters including compression rate, molding temperature, and the compression force used by a hydraulic press. Their effects on the device thickness, channel dimension, and pattern transfer fidelity will be discussed. In addition, we investigated creating an array of pseudo-microvalves using photodefinable, in situ gel polymerization. The valves were developed for introducing two types of separation media for performing two-dimensional protein separation in a microfluidic device. We also demonstrated rapid protein separation using the mechanism for the first dimension, isoelectric focusing.Copyright