Tatevik Chalyan

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.

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.

A SiON Microring Resonator-Based Platform for Biosensing at 850 nm

In this paper, we report on the design, fabrication, and characterization of a photonic circuit for biosensing applications. Silicon oxynitride with a bulk refractive index of 1.66 is the core-layer material. The photonic circuit is optimized for a wavelength of ~850 nm, which allows on-chip integration of the light source via cost effective vertical-cavity surface-emitting lasers and of the detector by using standard silicon photodetectors. Design as well as fabrication processes are explained in details. The best characteristics for the single optical components in the photonic circuit are: for single-mode channel waveguides with dimensions of 350 nm × 950 nm; propagation losses of 0.8 dB/cm; bending losses of 0.1 dB/90°-bend (radius of curvature 100 μm); 49/51 splitting ratio for 3-dB power splitters (directional couplers); quality factors up to 1.3 × 105 for microring resonators. Volumetric sensing yields a bulk sensitivity of 80 nm/RIU and a limit of detection of 3 × 10-6 RIU. Therefore, SiON-based photonic circuits represent a reliable material platform for biosensing in the short-wave near infrared region.

Biosensors based on Si3N4 asymmetric Mach-Zehnder interferometers

In this work, we present a study on photonic biosensors based on Si3N4 asymmetric Mach-Zehnder Interferometers (aMZI) for Aflatoxin M1 (AFM1) detection. AFM1 is an hepatotoxic and a carcinogenic toxin present in milk. The biosensor is based on an array of four Si3N4 aMZI that are optimized for 850nm wavelength. We measure the bulk Sensitivity (S) and the Limit of Detection (LOD) of our devices. In the array, three devices are exposed and have very similar sensitivities. The fourth aMZI, which is covered by SiO2, is used as an internal reference for laser (a VCSEL) and temperature fluctuations. We measured a phase sensitivity of 14300±400 rad/RIU. To characterize the LOD of the sensors, we measure the uncertainty of the experimental readout system. From the measurements on three aMZI, we observe the same value of LOD, which is ≈ 4.5×10−7 RIU. After the sensor characterization on homogeneous sensing, we test the surface sensing performances by flowing specific Aflatoxin M1 and non-specific Ochratoxin in 50 mM MES pH 6.6 buffer on the top of the sensors functionalized with Antigen-Recognising Fragments (Fab’). The difference between specific and non-specific signals shows the specificity of our sensors. A moderate regeneration of the sensors is obtained by using glycine solution.

Photonic biosensors for Fab'-AFM1 interaction study in real milk (Conference Presentation)

Aspergillus is known as one of the most frequent toxigenic fungi in Europe. It produces aflatoxin B1 transformed into aflatoxin M1 (AFM1) present in milk. The International Agency for Research on Cancer (IARC) has included AFM1 in the group I human carcinogens. Acceptable maximum level of AFM1 in milk according to EU regulation is 50 ppt equivalent to 15.2×10-2 nM (the molecular weight of AFM1 is 328.27 g/mol). Up to now, the most used techniques for AFM1 detection in milk are time consuming Enzyme-Linked Immuno-Sorbent Assay (ELISA) and high-performance liquid chromatography associated to fluorescence (HPLC). Silicon photonics based biosensors such as Mach-Zehnder Interferometers and Microring Resonators thanks to their ability to be miniaturize and integrated with electronics and microfluidics in lab-on-a-chip devices, are new candidates to become faster, cheaper and more accurate tools for AFM1 detection in milk. Here, we validate photonic AFM1 biosensors based on an array of four Si3N4 asymmetric Mach-Zehnder Interferometers (aMZI) functionalized by F(ab’)2 fragments and passivated with casein. Analyses of AFM1 binding by Fab’ in MES buffer and in real milk samples, using different concentrations of AFM1, are performed. The dependence of the phase shifts to the AFM1 concentration allows to calculate the association and dissociation rate constants. The proposed biosensor is capable to detect AFM1 concentration down to 50 ppt. For the average dissociation constant (KD) of AFM1-Fab’ interaction, values of (1.8÷5)×10-8 M in MES buffer and 0.8×10-9 M in milk samples are measured. These are in the same order of magnitude as published results. The difference of one order of magnitude between KD in MES buffer and in milk might be caused by the fact that during the preparation of milk samples, an additional concentration of salt is added to the solution which yields a stronger ionic interaction to occur. Finally, the specificity of the interaction is confirmed by using blank solutions that are free from AFM1.

Use of microring resonators for biospecific interaction analysis

Integrated optical biosensors based on Mach-Zehnder Interferometers and Microring Resonators are widely used for food/drug monitoring and protein studies thank to their high intrinsic sensitivity, easy integration and miniaturization, and low cost.1, 2 In this study, we present a system to perform antibody interaction analysis using a photonic chip made of an array of six microring resonators (MRRs) based on the TriPleX platform. A compact system is presented where the input light is provided by a Vertical Cavity Surface Emitting Laser (VCSEL) pigtailed to a single mode fiber and operating at a ≈ 850nm wavelength. The output signal is detected by PIN photodetectors placed in the optical signal read-out module (the so-called OSROM) and processed by an easy-to-use Fourier Transform algorithm. Bulk sensitivity (Sb=98±2.1 nm/RIU) and Limit of Detection (LOD=(7.5± 0.5) x10-6 RIU) are measured and appeared to be very similar for the six MRRs on the same chip,3 which is an important property for multianalyte detection. An analysis of the anti-biotin interaction with immobilized biotin is performed by using different concentrations of anti-biotin antibody. The dependence of the resonance wavelength shift from the antibody concentration, as well as the association and the dissociation rate constants are calculated. For the average dissociation constant (KD) of anti-biotin antibody toward immobilized biotin, a value of (1.9±0.5) x10-7M is estimated, which is of the same order of magnitude of other published data.4 Furthermore, the specificity of the interaction is confirmed by using negative control antibodies and by performing competition with free, i.e., dissolved, biotin. In addition, the functional surface of the sensors could be regenerated for repeated measurements up to eight times by using 10 mM glycine/HCl pH 1.5.

An integrated optical biosensor platform

In recent years, new sensor systems based on optical methods have been commercialized for laboratory use by several companies.1 These systems, which enable the detection of evanescent fields (i.e., electromagnetic fields that do not propagate), have demonstrated the high sensitivity of optical methods for sensing applications and have proven to be useful in automated applications. However, many fields (e.g., clinical diagnostics, environmental monitoring, and the food industry) require small, portable, easy-to-use, and robust real-time diagnostic systems. Ideally, all the functionalities of these ‘labon-a-chip’ (LOC) devices—from sample preparation to signal delivery—would be integrated. Most devices consist of different components (e.g., microfluidics, light source, detector, sensor, and readout) that are developed using different technologies. The fabrication of a range of components and functionalities using the same technology would represent a significant contribution towards simplifying the development of compact LOC point-of-need devices. Optical sensors are particularly promising candidates for integration and fabrication using inexpensive technologies. In today’s LOC devices, the sensors are often useful for only a few measurements. Chips manufactured via CMOS processing have become so economically efficient that it is now affordable to implement a high degree of functionality on a disposable chip. The most significant recent example of this is the realization of a silicon-on-insulator-based platform, in which both the sensor and detector are designed as ring resonators. In this device, the p-i-n type detector is engineered with defects that enhance its sensitivity at wavelengths of 1.55 m.2 Another promising approach demonstrates the complete integration of a light source, Figure 1. Optical (left) and electron (right) microscope images of the main part of the photonic circuit. Microring-resonator-based sensors are monolithically integrated with silicon p-i-n (labeled PIN in the figure) photodetectors.