We introduce an automated digital microfluidic (DMF) platform capable of performing immunoassays from sample to analysis with minimal manual intervention. This platform features (a) a 90 Pogo pin interface for digital microfluidic control, (b) an integrated (and motorized) photomultiplier tube for chemiluminescent detection, and (c) a magnetic lens assembly which focuses magnetic fields into a narrow region on the surface of the DMF device, facilitating up to eight simultaneous digital microfluidic magnetic separations. The new platform was used to implement a three-level full factorial design of experiments (DOE) optimization for thyroid-stimulating hormone immunoassays, varying (1) the analyte concentration, (2) the sample incubation time, and (3) the sample volume, resulting in an optimized protocol that reduced the detection limit and sample incubation time by up to 5-fold and 2-fold, respectively, relative to those from previous work. To our knowledge, this is the first report of a DOE optimization for immunoassays in a microfluidic system of any format. We propose that this new platform paves the way for a benchtop tool that is useful for implementing immunoassays in near-patient settings, including community hospitals, physicians' offices, and small clinical laboratories.

Abstract-A monolithic waveguide system using poly(dimethyl siloxane) (PDMS) was designed, fabricated, and characterized. The waveguide demonstrated good confinement of light and relatively low attenuation at 0.40 dB/cm. The robustness and handling properties of the completed waveguides were excellent, and the process yield exceeded 96%. The waveguide did exhibit moderate temperature and humidity sensitivity but no temporal variation, and insertion loss remained stable over extended periods of time. Applications of this waveguide system in microscale sensing are immense, judging by the frequency of use of PDMS as the substrate for microfluidic and biomedical systems. The monolithic nature of the waveguides also reduces their cost and allows integration of optical pathways into existing PDMS-based microsystems.Index Terms-Micro-total-analysis systems, poly(dimethyl siloxane), soft lithography, waveguide.

This paper reports the characterization of a microfluidic packaging technique involving the use of press-fit interconnects to microfluidic channels molded in PDMS. This packaging technique is implemented by, first, coring a small hole in the PDMS to access molded or buried microchannels using a modified 20 gauge needle; and second, inserting an unmodified needle into the hole to create a direct connection to the microchannel that requires no bonding or molding. The needles can then easily be removed and reinserted multiple times since the seal is created purely by the compression of the PDMS around the needle. The luer fitting on the needles can easily be connected to standard fluid fittings. The quality of the interconnects is correlated with observations of the PDMS after coring. Methods of coring examined include pushing straight through and twisting the coring tool by hand or by machine. These comparisons demonstrated that all methods can produce viable interconnects; however, machine coring was the most consistent. The interconnects were characterized mechanically primarily by measuring their leak resistance under pressure. Leak tests were performed on interconnects (1) fabricated using different methods, (2) experiencing rotation or bending and (3) fabricated at various linear densities. Static pressure testing revealed that interconnect pressure limits varied from 100 kPa to over 700 kPa depending on the fabrication method. Suggestions are presented on how the technique could be modified to reach much higher pressures. Interconnect flexibility testing demonstrated a minimum of 30° of bending and a maximum of 60° before failure depending on the direction rotated. Density testing showed that PDMS was strong enough to allow at least six interconnects on a 1 cm linear channel.

This paper details the design and fabrication of an integrated optical biochemical sensor using a select oxygen-sensitive fluorescent dye, tris(2,2'-bipyridyl) dichlororuthenium(ii) hexahydrate, combined with polymeric waveguides that are fabricated on a glass substrate. The sensor uses evanescent interaction of light confined within the waveguide with the dye that is immobilized on an SU-8 waveguide surface. Adhesion of the dye to the integrated waveguide surface is accomplished using a unique process of spin-coating/electrostatic layer-by-layer formation. The SU-8 waveguide was chemically modified to allow the deposition process. Exposure of the dye molecules to the analyte and subsequent chemical interaction is achieved by directly coupling the fluid channel to the integrated waveguide. The completed sensor was linear in the dissolved oxygen across a wide range of interest and had a sensitivity of 0.6 ppm. A unique fabrication aspect of this sensor is the inherent simplicity of the design, and the resulting rapidity of fabrication, while maintaining a high degree of functionality and flexibility.