A general method is described for the fabrication of polydimethylsiloxane (PDMS) lab-on-a-chip (LOC) devices with integrated optic and fluidic elements. The PDMS core layer containing the optic and fluidic components is cast and cured under pressure on a silicon master. Subsequently, outer layers of lower-index PDMS are bonded to the core layer to provide optical and fluidic confinement. The functionality of the waveguides and microchannels is demonstrated by the detection and identification of two different types of fluorescent polystyrene beads in a pressure-driven flow inside a microfluidic channel in a device fabricated by this process.

We describe the monolithic integration of microfluidic channels, optical waveguides, a collimating lens and a curved focusing transmission grating in a single PDMS-based microsystem. All optical and fluidic components of the device were simultaneously formed in a single layer of high refractive index (n~1.43) PDMS by soft lithography. Outer layers of lower-index (n~1.41) PDMS were subsequently added to provide optical and fluidic confinement. Here, we focus on the design and characterization of the microspectrometer part, which employs a novel self-focusing strategy based on cylindrical facets, and exhibits resolution <10 nm in the visible wavelength range. The dispersive behavior of the grating was analyzed both experimentally and using numerical simulations, and the results are in good agreement with simplified analytical predictions.

We propose a strategy for real time multicolour detection of light emitting particles under flow conditions, using the diffracted orders of a grating. The method relies on the fact that the spatial (angular/linear) separation between the orders of a diffraction grating is a wavelength dependent quantity. Thus, the difference in arrival times at a fixed detector for neighbouring orders produced by a moving, light-emitting particle can be used as a wavelength sensing mechanism. We demonstrate this functionality using a prototype PDMS microfluidic device that incorporates a focusing transmission grating. A key attribute of this approach is that it requires only a single sensitive detector, such as a photomultiplier tube, in contrast to many conventional approaches which require multiple sensitive detectors or a detector array.

Using a PDMS (Polydimethylsiloxane)-based chip that incorporates waveguides for delivery of excitation light and focusing optics for collection of emitted light, we demonstrate the measurement of velocity of particles in a pressure-driven flow inside a microfluidic channel. The unique geometry of the fluidic channel, particularly its orientation relative to the integrated excitation and collection optics, enables a straightforward determination of the particle velocity from the temporal signal produced at a single detector. The approach could be of interest for velocity-independent flow cytometry and particle sorting in microfluidic systems.

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