Integrated microfluidic biochips for immunoassay and DNA bioassays.

Bioassays involve multi-stage sample processing and fluidic handling, which are generally labor-intensive and time-consuming. Using microfluidic technology to integrate and automate all these steps in a single chip device is highly desirable in many practical applications such as clinical diagnostic and in-field environmental testing. We have developed self-contained and fully integrated biochip systems for immunoassay and DNA analysis. These microfluidic biochip devices can perform detection of multiple bioagents (including antigens and DNA) using electrochemical detection methods. Microfluidic mixer, valves, pumps, channels, chambers, and Combimatrix microelectrode array are integrated to perform parallel immunoassays to detect infectious particles (viruses and bacteria) from complex biological samples in a single, fully automated biochip device. All microfluidic components use very simple and inexpensive approaches in order to reduce chip complexity. Back-end detection is accomplished using an enzyme-based electrochemical detection method that has many advantages including high sensitivity ( approximately fM) and simple apparatus. The sensor is a miniaturized array of individually addressable microelectrodes controlled by active CMOS circuitry. Pathogenic bacteria and DNA detections are both demonstrated. The devices with capabilities of on-chip sample processing and detection provide a cost-effective solution to direct sample-to-answer biological analysis for point-of-care genetic analysis, disease diagnosis, and in-field bio-threat detection.

Plastic biochannel hybridization devices: a new concept for microfluidic DNA arrays.

Conventional DNA hybridization assay kinetics depends solely on the diffusion of target to surface-bound probes, causing long hybridization times. In this study, we examined the possibilities of accelerating the hybridization process by using microfluidic channels ("biochannels") made of polycarbonate, optionally with an integrated pump. We produced two different devices to study these effects: first, hybridization kinetics was investigated by using an eSensor electrochemical DNA detection platform allowing kinetic measurements in homogenous solution. We fabricated an integrated cartridge for the chip comprising the channel network and a micropump for the oscillation of the hybridization mixture to further overcome diffusion limitations. As a model assay, we used an assay for the detection of single-nucleotide polymorphisms in the HFE-H gene. Second, based on the biochannel approach, we constructed a plastic microfluidic chip with a network of channels for optical detection of fluorescent-labeled targets. An assay for the simultaneous detection of four pathogenic bacteria surrogate strains from multiple samples was developed for this device. We observed high initial hybridization velocities and a fast attainment of equilibrium for the biochannel with integrated pump. Experimental results were compared with predictions generated by computer simulations.

Bubble-induced acoustic micromixing.

A mixing technique based on the principle of bubble-induced acoustic microstreaming was developed. The mixer consists of a piezoelectric disk that is attached to a reaction chamber, which is designed in such a way that a set of air bubbles with desirable size is trapped in the solution. Fluidic experiments showed that air bubbles resting on a solid surface and set into vibration by the sound field generated steady circulatory flows, resulting in global convection flows and thus rapid mixing. The time to fully mix a 22 microL chamber is significantly reduced from hours (for a pure diffusion-based mixing) to tens of seconds. Numerical simulations showed that the induced flowfield and thus degree of mixing strongly depend on bubble positions. Optimal simulated mixing results were obtained for staggered bubble distribution that minimizes the number of internal flow stagnation regions. Immunomagnetic cell capture experiments showed that acoustic microstreaming provided efficient mixing of bacterial cell (Esherichia coli K12) matrix suspended in blood with magnetic capture beads, resulting in highly effective immunomagnetic cell capture. Bacterial viability assay experiments showed that acoustic microstreaming has a relatively low shear strain field since the blood cells and bacteria remained intact after mixing. Acoustic microstreaming has many advantages over most existing chamber micromixing techniques, including simple apparatus, ease of implementation, low power consumption (2 mW), and low cost.