Optofluidic devices are capable of detecting single molecules, but greater sensitivity and specificity is desired through hydrodynamic focusing (HDF). Three-dimensional (3D) hydrodynamic focusing was implemented in 10-μm scale microchannel cross-sections made with a single sacrificial layer. HDF is achieved using buffer fluid to sheath the sample fluid, requiring four fluid ports to operate by pressure driven flow. A low-pressure chamber, or pit, formed by etching into a substrate, enables volumetric flow ratio-induced focusing at a low flow velocity. The single layer design simplifies surface micromachining and improves device yield by 1.56 times over previous work. The focusing design was integrated with optical waveguides and used in order to analyze fluorescent signals from beads in fluid flow. The implementation of the focusing scheme was found to narrow the distribution of bead velocity and fluorescent signal, giving rise to 33% more consistent signal. Reservoir effects were observed at low operational vacuum pressures and a balance between optofluidic signal variance and intensity was achieved. The implementation of the design in optofluidic sensors will enable higher detection sensitivity and sample specificity.

Planar optofluidics provide a powerful tool for facilitating chip-scale light-matter interactions. Silicon-based liquid core waveguides have been shown to offer single molecule sensitivity for efficient detection of bioparticles. Recently, a PDMS based planar optofluidic platform was introduced that opens the way to rapid development and prototyping of unique structures, taking advantage of the positive attributes of silicon dioxide-based optofluidics and PDMS based microfluidics. Here, hydrodynamic focusing is integrated into a PDMS based optofluidic chip to enhance the detection of single H1N1 viruses on-chip. Chip-plane focusing is provided by a system of microfluidic channels to force the particles towards a region of high optical collection efficiency. Focusing is demonstrated and enhanced detection is quantified using fluorescent polystyrene beads where the coefficient of variation is found to decrease by a factor of 4 with the addition of hydrodynamic focusing. The mean signal amplitude of fluorescently tagged single H1N1 viruses is found to increase with the addition of focusing by a factor of 1.64.

Water absorption was studied in two types of waveguides made from unannealed plasma enhanced chemical vapor deposition (PECVD) SiO ₂ . Standard rib anti-resonant reflecting optical waveguides (ARROWs) were fabricated with thin films of different intrinsic stress and indices of refraction. Buried ARROWs (bARROWs) with low and high refractive index differences between the core and cladding regions were also fabricated from the same types of PECVD films. All waveguides were subjected to a heated, high humidity environment and their optical throughput was tested over time. Due to water absorption in the SiO ₂ films, the optical throughput of all of the ARROWs decreased with time spent in the wet environment. The ARROWs with the lowest stress SiO ₂ had the slowest rate of throughput change. High index difference bARROWs showed no decrease in optical throughput after 40 days in the wet environment and are presented as a solution for environmentally stable waveguides made from unannealed PECVD SiO ₂ .

The macro-to-micro interface method presented here meets many of the requirements for an ideal interconnect by sealing a short length of plastic tubing directly to a microfluidic chip. The adaptability and low-temperature processing make it compatible with a wide range of device materials. The method was validated on silicon, acrylic (polymethyl methacrylate), printed circuit board and glass substrates with high-pressure integrity to over 300 psi (2 MPa). Fluid interfaces created with this method were used for pressure tests on microfluidic channels constructed on silicon.

We present a 3D hydrodynamic focusing design suitable for optofluidic devices allowing planar fabrication and velocity independent particle focusing. Simulations are presented and fabrication outlined with evidence that stacked SU8 layers are suitable building blocks.