Design and Optimization of SiON Ring Resonator-Based Biosensors for Aflatoxin M1 Detection.

In this article, we designed and studied silicon oxynitride (SiON) microring-based photonic structures for biosensing applications. We designed waveguides, directional couplers, and racetrack resonators in order to measure refractive index changes smaller than 10-6 refractive index units (RIU). We tested various samples with different SiON refractive indexes as well as the waveguide dimensions for selecting the sensor with the best performance. Propagation losses and bending losses have been measured on test structures, along with a complete characterization of the resonator's performances. Sensitivities and limit of detection (LOD) were also measured using glucose-water solutions and compared with expected results from simulations. Finally, we functionalized the resonator and performed sensing experiments with Aflatoxin M1 (AFM1). We were able to detect the binding of aflatoxin for concentrations as low as 12.5 nm. The results open up the path for designing cost-effective biosensors for a fast and reliable sensitive analysis of AFM1 in milk.

Investigation of non-specific signals in nanoporous flow-through and flow-over based sensors.

Porous materials are ideal hosts to fabricate high sensitivity devices. Their large specific area and the possibility to modify the type and the strength of the matrix-analyte interactions allow the realization of sensors with finely tailored characteristics. In this article, we investigate how mass transport across the nanoporous structure influences the response due to the non-specific signal by comparing flow-through versus flow-over geometries. We observed a systematic overestimation of the sensitivity for porous substrate devices made of closed-ended pores compared with open-ended pore ones. Our analysis shows that such an effect is due to (unbound) analytes or contaminants that remain trapped within the pores and are not removed by rinsing of the sample. This result was verified by measuring similar samples in both flow through and flow over configurations, as well as their residual response after blockage of all their active sites. We also notice that sensors based on free-standing membranes show similar results independent of the fact that mass transport is induced by either an external pressure source or simply by Brownian motions.

Integration, photostability and spontaneous emission rate enhancement of colloidal PbS nanocrystals for Si-based photonics at telecom wavelengths.

We experimentally investigate PbS nanocrystal (NC) photoluminescence (PL) coupled to all-integrated Si-based ring resonators and waveguides at telecom wavelengths. Dissolving the NCs into Novolak polymer significantly improves their stability in ambient atmosphere. Polymer-NC blends of various NC concentrations can be applied to and removed from the same device. For NC concentrations up to 4vol%, the spontaneous emission rate into ring-resonator modes is enhanced by a factor of ~13 with respect to that into a straight waveguide. The PL intensity shows a linear dependence on the excitation intensity up to 1.64kW/cm(2) and stable quality factors of ~2500.

Optical characterization of a SCISSOR device.

Here, we report on the design, fabrication and characterization of single-channel (SC-) and dual-channel (DC-) side-coupled integrated spaced sequences of optical resonators (SCISSOR) with a finite number (eight) of microring resonators using submicron silicon photonic wires on a silicon-on-insulator (SOI) wafer. We present results on the observation of multiple resonances in the through and the drop port signals of DC-SCISSOR. These result from the coupled resonator induced transparency (CRIT) which appears when the resonator band (RB) and the Bragg band (BB) are nearly coincident. We also observe the formation of high-Q (> 23000) quasi-localized modes in the RB of the drop transmission which appear when the RB and BB are well separated from each other. These multiple resonances and quasi-localized modes are induced by nanometer-scale structural disorders in the dimension of one or more rings. Finally, we demonstrate the tunability of RB (and BB) and localized modes in the DC-SCISSOR by thermo-optical or free-carrier refraction.

Photoluminescence of hydrophilic silicon nanocrystals in aqueous solutions.

Stable aqueous solutions of undecylenic-acid-grafted silicon nanocrystals (Si-nc) were prepared. The time evolution of the photoluminescence properties of these hydrophilic silicon nanocrystals has been followed on different timescales (hours and days). On a short timescale (hours), Si-nc tend to agglomerate while the PL lineshape and intensity are stable. Agglomeration can be reduced by using suitable surfactants. On a long timescale (days), oxidation of Si-nc occurs even in the presence of surfactants. These two observations render Si-nc very useful as a labeling agent for biosensing.

Ultrafast all-optical switching in a silicon-nanocrystal-based silicon slot waveguide at telecom wavelengths.

We demonstrate experimentally all-optical switching on a silicon chip at telecom wavelengths. The switching device comprises a compact ring resonator formed by horizontal silicon slot waveguides filled with highly nonlinear silicon nanocrystals in silica. When pumping at power levels about 100 mW using 10 ps pulses, more than 50% modulation depth is observed at the switch output. The switch performs about 1 order of magnitude faster than previous approaches on silicon and is fully fabricated using complementary metal oxide semiconductor technologies.

NanoSi low loss horizontal slot waveguides coupled to high Q ring resonators.

Si-based horizontal slot waveguides coupled to ring resonators have been fabricated and characterised. The central layer of the slot has been filled by Silicon nanocrystals (Si-nc) obtained by deposition of silicon rich silicon oxide and then thermal annealing. A comparison of various deposition and annealing parameters to form the Si-nc is performed. Propagation losses as low as 3 dB/cm and ring resonator quality factor of 30,000 have been achieved at 1550 nm.

Asymmetric Mach-Zehnder Interferometer Based Biosensors for Aflatoxin M1 Detection.

In this work, we present a study of Aflatoxin M1 detection by photonic biosensors based on Si3N4 Asymmetric Mach-Zehnder Interferometer (aMZI) functionalized with antibodies fragments (Fab'). We measured a best volumetric sensitivity of 104 rad/RIU, leading to a Limit of Detection below 5 × 10(-7) RIU. On sensors functionalized with Fab', we performed specific and non-specific sensing measurements at various toxin concentrations. Reproducibility of the measurements and re-usability of the sensor were also investigated.