Optofluidics has emerged in the past few years as one of the most rapidly developing areas in the optics fields. We are concentrating on optofluidic waveguides in our research, which are defined as structures capable of optical confinement and transmission through fluid filled cores. Optofluidic waveguides are an important photonic technology because they allow for light guiding in very low refractive index materials, especially water – making them relevant to biosensing. In the past five years we have introduced and advanced a new class of hollow waveguides built on silicon for picoliter volumes and based on the anti-resonant reflecting optical waveguide (ARROW) principle. We have concentrated on combining optofluidic waveguides with solid-core waveguides to form lab-on-a-chip sensors, especially for single molecule optical analysis. This work was conducted in close collaboration with Professor Holger Schmidt’s research group at UC Santa Cruz with funding provided by NSF, NIH, and the David Huber Foundation.


Figure 1 - Planar optofluidic chip. (a) Schematic of integrated optofluidic chip showing hollow- and solid-core waveguides; (b) Photograph of finished chip.

Figure 1 shows a typical ARROW based platform in which solutions containing biomolecules are introduced into a hollow waveguide. Fluorescence is excited in the biomolecules at waveguide intersections and then directed to off-chip detectors. Liposomes in particular were analyzed using Fluorescence Correlation Spectroscopy (FCS) and demonstrated that the chips were capable of single molecule detection sensitivities. Surface Enhanced Raman Scattering (SERS) were also performed on ARROW based chips as shown in Figure 3.



Figure 2 – FCS of single liposomes on a chip. (a) Top: background detector signal from buffer solution; bottom: fluorescence trace showing bursts from fluorescing liposomes in ARROW waveguide intersection. Inset: Liposome containing Alexa dye molecules. (b) Corresponding FCS trace (circles) and theoretical fit (line). G(0) > 1 indicates sub-single particle sensitivity.


Figure 3 – (a) Detected SERS signals at different active concentrations corrected to a nominal input excitation irradiance level of 15.2 kW/cm2 for differing alignments between measurements. The lowest three concentrations are multiplied by factors of 2, 40, and 50 as denoted. (b) detected SERS power vs concentration.

Supported By:

David Huber Foundation