Faculty Bibliography

This paper presents a continuous-flow polymerase chain reaction (PCR) microchip with a serpentine microchannel of varying width for "regional velocity control." Varying the channel width by incorporating expanding and contracting conduits made it possible to control DNA sample velocities for the optimization of the exposure times of the sample to each temperature phase while minimizing the transitional periods during temperature transitions. A finite element analysis (FEA) and semi-analytical heat transfer model was used to determine the distances between the three heating assemblies that are responsible for creating the denaturation (96 degrees C), hybridization (60 degrees C), and extension (72 degrees C) temperature zones within the microchip. Predictions from the thermal FEA and semi-analytical model were compared with temperature measurements obtained from an infrared (IR) camera. Flow-field FEAs were also performed to predict the velocity distributions in the regions of the expanding and contracting conduits to study the effects of the microchannel geometry on flow recirculation and bubble nucleation. The flow fields were empirically studied using micro particle image velocimetry (mu-PIV) to validate the flow-field FEA's and to determine experimental velocities in each of the regions of different width. Successful amplification of a 90 base pair (bp) bacillus anthracis DNA fragment was achieved.

A novel library of resin-bound receptors within a cross-reactive differential array for the identification and discrimination of tripeptides and tripeptide mixtures is reported. Pattern recognition using principal component analysis showed complete discrimination of four similar tripeptides and three tripeptide mixtures. The library is comprised of a Cu(II)-centered core with two proximally appended tripeptide arms emanating outward. One tripeptide arm was prepared using combinatorial chemistry to generate the differential nature of the library. Thirty resin-bound receptors were randomly selected from the library and placed within a silicon microchip array that included integrated microfluidics elements, and an indicator-uptake assay was used for colorimetric signaling. The indicator Orange G yielded an accurate measure of the degree of association between receptors and analytes as determined by kinetic analysis of the indicator-uptake assays. Within this paper we detail the method used for differential sensing using a novel receptor library. This work further demonstrates the power and utility of a differential array of synthetic receptors for identification and discrimination of complex bioanalytes.

Two-dimensional layered ceramics, highly anisotropic materials in terms of structure and properties, were used to produce polymer-covered metal nanorods and metal microcrystals. The procedure took advantage of the intrinsic planar, layered ordering of the metal cations suitable to be reduced and could be further used to engineer one-dimensional metal alloy nanostructures by appropriate doping of the initial layered ceramic lattice with suitable cationic species. The procedure involved the formation in an intermediate step of a polymer-intercalated ceramic nanocomposite, highly porous to the diffusion of the polymerizable reducing agent, pyrrole. Two structurally similar layered bismuthates, Bi2Sr2CaCu2O8+delta and Bi6Sr2CaO12 and a partially Rh-substituted ceramic, Bi4Rh2Sr2CaO12 were used as the precursor layered ceramics and the reducible metal cations were Cu2+, Bi3+, and Rh3+, respectively. The formation of the polymer-covered metal nanorods and metal microcrystals took place at relatively high temperatures of reaction (325 degrees C) and long reaction times (10-12 days).

This paper presents disposable protein analysis chips with single- or four-chamber-constructed from poly(dimethylsiloxane) (PDMS) and silicon. The chips are composed of a multilayer stack of PDMS layers that sandwich a silicon microchip. This inner silicon chip features an etched array of micro-cavities hosting polymeric beads. The sample is introduced into the fluid network through the top PDMS layer, where it is directed to the bead chamber. After reaction of the analyte with the probe beads, the signal generated on the beads is captured with a CCD camera, digitally processed, and analyzed. An established bead-based fluorescent assay for C-reactive protein (CRP) was used here to characterize these hybrid chips. The detection limit of the single-chamber protein chip was found to be 1 ng/ml. Additionally, using a back pressure compensation method, the signals from each chamber of the four-chamber chip were found to fall within 10% of each other.

The development of a micromachined fluidic structure for the introduction of liquid samples into a chip-based sensor array composed of individually addressable polymeric microbeads is presented. The micromachined structure consists of micromachined storage cavities combined with a covering glass layer that confines the microbeads and fluidic channels. In our sensor array transduction occurs via optical (colorimetric and fluorescence) changes to receptors and indicator molecules that are covalently attached to termination sites on the polymeric microbeads. Spectral data are acquired for each of the individual microbeads using a charged-coupled device (CCD) allowing for the near-real-time analysis of liquid sample. Hence the micromachined fluidic structure must allow for both optical access to the microbeads and fluid flow through the micromachined cavities that serve as the microreactors/analysis chambers. One of the key parts of the structure is a passive fluid introduction system driven only by capillary force. This simple means of fluid introduction realizes a compact device. The capillary flow on the inlet channel has been studied, and the responses of the microbeads (alizarin complexone) to a liquid sample have been characterized. The test results show that this system is useful in a micro-total-analysis-system (mu-TAS) and biomedical applications.