We present the design, fabrication, and characterisation of an array of optical slot-waveguide ring resonator sensors, integrated with microfluidic sample handling in a compact cartridge, for multiplexed real-time label-free biosensing. Multiplexing not only enables high throughput, but also provides reference channels for drift compensation and control experiments. Our use of alignment tolerant surface gratings to couple light into the optical chip enables quick replacement of cartridges in the read-out instrument. Furthermore, our novel use of a dual surface-energy adhesive film to bond a hard plastic shell directly to the PDMS microfluidic network allows for fast and leak-tight assembly of compact cartridges with tightly spaced fluidic interconnects. The high sensitivity of the slot-waveguide resonators, combined with on-chip referencing and physical modelling, yields a volume refractive index detection limit of 5 x 10(-6) refractive index units (RIUs) and a surface mass density detection limit of 0.9 pg mm(-2), to our knowledge the best reported values for integrated planar ring resonators.

QC 20100715

No abstract

We present an experimental study of an integrated slot-waveguide refractive index sensor array fabricated in silicon nitride on silica. We study the temperature dependence of the slot-waveguide ring resonator sensors and find that they show a low temperature dependence of -16.6 pm/K, while at the same time a large refractive index sensitivity of 240 nm per refractive index unit. Furthermore, by using on-chip temperature referencing, a differential temperature sensitivity of only 0.3 pm/K is obtained, without individual sensor calibration. This low value indicates good sensor-to-sensor repeatability, thus enabling use in highly parallel chemical assays. We demonstrate refractive index measurements during temperature drift and show a detection limit of 8.8 x 10-6 refractive index units in a 7 K temperature operating window, without external temperature control. Finally, we suggest the possibility of athermal slot-waveguide sensor design.

High efficiency surface grating couplers for silicon nitride waveguides have been designed, fabricated, and characterized. Coupling efficiencies exceeding 60 % are reported at a wavelength of 1.31 mum, as well as angular and wavelength -3 dB tolerances of 4 degrees and 50 nm, respectively. When the wavelength is increased from 1310 nm to 1450 nm the coupling efficiency progressively decreases but remains above 20 % at 1450 nm. The influence of the duty ratio of the grating has also been investigated: maximum coupling efficiency was obtained at 50 % duty ratio.