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An acoustic microfluidic system for miniaturized fluorescence-activated cell sorting ([micro]FACS) is presented. By excitation of a miniaturized piezoelectric transducer at 10 MHz in the microfluidic channel bottom, an acoustic standing wave is formed in the channel. The acoustic radiation force acting on a density interface causes fluidic movement, and the particles or cells on either side of the fluid interface are displaced in a direction perpendicular to the standing wave direction. The small size of the transducer enables individual manipulation of cells passing the transducer surface. At constant transducer activation the system was shown to accomplish up to 700 [micro]m sideways displacement of 10 [micro]m beads in a 1 mm wide channel. This is much larger than if utilizing the acoustic radiation force acting directly on particles, where the limitation in maximum displacement is between a node and an antinode which at 10 MHz is 35 [micro]m. In the automatic sorting setup, the system was demonstrated to successfully sort single cells of E-GFP expressing [beta]-cells.

An external electric field driven in-channel detection technique for on-chip electrochemical detection in micro fabricated devices is described based on a microfluidic system containing an array of 20 microband electrodes. It is shown that an external electric field induces a potential difference between two gold microband electrodes in a poly(dimethylsiloxane) (PDMS) microchannel, and that this enables the electrochemical detection of electroactive species such as ascorbic acid and Fe[(CN).sub.6.sup.4-]. The results, which are supported by simulations of the behavior of the microband electrodes in the microfluidic system, show that the induced potential difference between the electrodes can be controlled by altering the external electric field or by using different microbands in the microband array. As the obtained currents depend on the concentrations of electroactive species in the flowing solution and the detection can be carded out anywhere within the channel without interference of the external electric field, the present approach significantly facilitates electrochemical detection in capillary electrophoresis. This approach consequently holds great promise for application in inexpensive portable chip-based capillary electrophoresis (CE) devices.

A novel scheme for the integration of diffractive optical elements onto silicon is presented. The processing is made in reverse order, meaning that the process of structuring the optical elements on the wafer precedes the silicon microstructuring. The first processing step on the wafer is the hot embossing of the optical microstructures into an amorphous fluorocarbon polymer spin coated on the wafer. The cured polymer forms a highly stable material with excellent optical properties. The remaining silicon processing is thus performed with the diffractive optical elements already in place. Two different diffractive structures were used in the development of the method--a (Fresnel) lens with a rather low f-number and a diffractive element producing a fan-out of a large number of paraxial beams. OCIS codes: 220.4000, 130.5990.

We have developed a multipurpose microfluidic platform that allows for sensitive fluorescence detection on inexpensive disposable chips. The fabrication scheme involves rapid injection molding of thermoplastics, followed by silica deposition and covalent attachment of an unstructured flexible lid. This combines the virtues of elastomer technology with high-throughput compact disk injection molding. Using this technique, the time to produce 100 chips using a single master can be lowered from more than 1 week by standard PDMS technologies to only a couple hours. The optical properties of the fabricated chips were evaluated by studying individual fluorescence-labeled DNA molecules in a microchannel. Concatemeric DNA molecules were generated through rolling circle replication of circular DNA molecules, which were labeled by hybridization of fluorescence-tagged oligonucleotides. Rolling circle products (RCPs) were detected after as little as 5 min of DNA polymerization, and the RCPs in solution showed no tendency for aggregation. To illustrate the versatility of the platform, we demonstrate two additional applications: The flexible property of the lid was used to create a peristaltic pump generating a flow rate of 9 nL/ s. Biocompatibility of the platform was illustrated by culturing Chinese hamster ovary cells for 7 days in the microfluidic channels.

In this study, sheathless electrospray from polymer microchips with conducting layer on the emitter tip is described for the first time. The electrospray emitter tips were fabricated directly from the end of the microchips that were made of polycarbonate or poly(methyl methacrylate) with injection molding. A variety of tip shapes and conducting coatings were evaluated using an electrospray time-of-flight mass spectrometer run in the sheathless mode. Stable electrospray was obtained both from hand-polished and machine-milled three-dimensional tips coated with either polymer-embedded gold particles or graphite particles as the conducting layer. Sputtered gold, on the other hand, suffered from poor stability mainly due to bad adhesion to the polymer tip. The durability of the different coatings was confirmed with electrochemical experiments under simulated electrospray conditions. The relative standard deviations of the response received from the ion current of the MS analysis were in the range of 3.5-12%. The detection limit for a standard mixture containing five neuropeptides was lower than 0.5 fmol. The low detection limit makes the emitter tips highly attractive for the analysis of low-abundance biological species.

The transfer of continuous-relief micro-optical structures from resist into GaAs by the use of direct-write electron-beam (e-beam) lithography followed by dry etching in an inductively coupled plasma is demonstrated. B[Cl.sub.3]-Ar chemistry was found to give satisfactory results; [N.sub.2] and [Cl.sub.2] were added to change the selectivity between GaAs and e-beam resist. The transfer process generates smooth etched structures. Distortion of the diffractive structures in the transfer process was examined. Blazed gratings with a period of 10 [micro]m were optically evaluated with a 940-nm VCSEL. This grating was a five-step approximation of a blazed profile. The diffraction efficiency was 67% in the first order, with a theoretical value of 87%. Also, simulations of the optical performance of the transferred diffractive elements were made by use of a Fourier transform of the grating profile. Our goal is to integrate micro-optical structures with VCSELs. OCIS codes: 350.3950, 160.6000, 220.4000, 140.3300, 050.1970.

Micromirrors were fabricated in gallium phosphide by mass transport to provide spatial-mode control of vertical-cavity surface-emitting lasers (VCSEL's). The concave mirrors were used in an external-cavity configuration to provide spatial filtering in the far field. Single-mode cw lasing was demonstrated in 15-[[micro]meter]-diameter VCSEL's with currents as high as 6 times threshold. The fabrication process was extended to micromirrors in gallium arsenide by use of a replication and dry-etch transfer process.

A diffractive beam homogenizer, based on an array of square, off-axis, continuous-relief diffractive microlenses, for use with an excimer laser has been studied. We originally fabricated the homogenizer by direct-write electron-beam lithography, from which we made replicas in UV-grade fused silica by hot embossing and reactive ion etching. Atomic force microscopy measurements of original and replicated elements showed the accuracy of the replication fidelity. One of the replicated homogenizers was evaluated together with a KrF excimer laser. The homogenized beam had a flat-top profile with 31% of the beam energy contained within an area where the beam intensity was above a threshold level of 90% of the maximum intensity. Key words: Diffractive optical element, homogenizer, excimer laser, replication, hot embossing, reactive ion etching.

Continuous-relief diffractive optical elements have been replicated by use of conventional compact disc injection-molding techniques. Two continuous-relief microstructures, a blazed grating and a fan-out element, were chosen to evaluate the replication process. Original elements were fabricated by direct-write electron-beam lithography. Optical measurements and atomic force microscopy were used for investigating the replication fidelity. Key words: Diffractive optics, injection molding, replication, electron-beam lithography, compact disc.

It is shown that multilevel SAL 110 resist kinoforms can be developed stepwise. Measurements of the kinoform diffraction pattern, performed between the development steps, permitted correct final developments to be made. No significant relief shape degradation was observed for development times as high as 25 min. The results imply that the electron-beam exposure doses, and hence the exposure time, can be reduced by a factor of 3 compared with doses used currently.