A low cost, low temperature process for sealing microfluidic devices composed of at least one organic polymeric substrate is presented. The process is based on the surface modification of the organic substrate by means of a silane solution, resulting in irreversible bonding. It is a generic method of bonding polymeric/plastic substrates, bare or structured ones, such as poly(methylmethacrylate) (PMMA), polystyrene (PS) or epoxy-type polymers, to Si-containing substrates, such as poly(dimethylsiloxane) (PDMS), Si and glass. In the case that bonding between organic polymer (PMMA, PS, etc) substrates is desired, an intermediate thin PDMS layer is required.

An optical real-time affinity biosensor, which is based on a monolithic silicon optoelectronic transducer and a microfluidic module, is described. The transducer monolithically integrates silicon avalanche diodes as light sources, silicon nitride optical fibers, and p/n junction detectors and efficiently intercouples these elements through a self-alignment technique. The transducer surface is hydrophilized by oxygen plasma treatment, silanized with (3-aminopropyl)triethoxysilane and bioactivated through adsorption of the biomolecular probes. The use of a microfluidic module allows real-time monitoring of the binding reaction of the gold nanoparticle-labeled analytes with the immobilized probes. Their binding within the evanescent field at the surface of the optical fiber causes attenuated total reflection of the waveguided modes and reduction of the detector photocurrent. The biotin-streptavidin model assay was used for the evaluation of the analytical potentials of the device developed. Detection limits of 3.8 and 13 pM in terms of gold nanoparticle-labeled streptavidin were achieved for continuous- and stopped-flow assay modes, respectively. The detection sensitivity was improved by silver plating of the immobilized gold nanoparticles, and a detection limit of 20 fM was obtained after 20-min of silver plating. In addition, two different analytes, streptavidin and anti-mouse IgG, were simultaneously assayed on the same chip demonstrating the multianalyte potential of the sensor developed.

Broad-band Mach-Zehnder interferometry is analytically described and experimentally demonstrated as an analytical tool capable of high accuracy refractive index measurements over a wide spectral range. Suitable photonic engineering of the interferometer sensing and reference waveguides result in sinusoidal TE and TM spectra with substantially different eigen-frequencies. This allows for the instantaneous deconvolution of multiplexed polarizations and enables large spectral shifts and noise reduction through filtering in the Fourier Transform domain. Due to enhanced sensitivity, optical systems can be designed that employ portable spectrum analyzers with nm range resolution without compromising the sensor analytical capability. Practical detection limits in the 10(-6)-10(-7) RIU range are achievable, including temperature effects. Finally, a proof of concept device is realized on a silicon microphotonic chip that monolithically integrates broad-band light sources and single mode silicon nitride waveguides. Refractive index detection limits rivaling that of ring resonators with externally coupled laser sources are demonstrated. Sensitivities of 20 μm/RIU and spectral shifts in the tens of a pm are obtained.

The intrinsic carrier density in silicon has been measured by a novel technique based on low-frequency capacitance measurements of a p+-i-n+ diode biased in high injection. The major advantage of the method is its insensitivity to uncertainties regarding the exact values of the carrier mobilities, the recombination parameters, and the doping density. The intrinsic carrier density was measured in the temperature range from 78 to 340 K. At 300 K the value of ni was found to be (9.7±0.1)×109 cm−3.