Wavelength shift in a whispering gallery microdisk due to bacterial sensing: a theoretical approach

Whispering gallery mode microcavities have recently been studied as a means to achieve real-time label-free detection of biological targets such as virus particles, specific DNA sequences, or proteins. Binding of a biomolecule to the surface of a microresonator will increase its path length, leading to a shift in the resonance frequency according to the reactive sensing principle. In this paper, we develop a theoretical expression that will link the reactive shift to the bacteria and microdisk parameters and help quantify the number of bacteria that bind to the surface of a 200μm-diameter silica microdisk

Flatness-Based Control of Electrostatically Actuated MEMS With Application to Adaptive Optics: A Simulation Study

International audienceTypical adaptive optics (AO) applications require continual measurement and correction of aberrated light and form closed-loop control systems. One of the key components in microelectromechanical system (MEMS) based AO systems is the parallel-plate microactuator. Being electrostatically actuated, this type of devices is inherently instable beyond the pull-in position when they are controlled by a constant voltage. Therefore extending the stable travelling range of such devices forms one of the central topics in the control of MEMS. In addition, though certain control schemes, such as charge control and capacitive feedback, can extend the travelling range to the full gap, the transient behavior of actuators is dominated by their mechanical dynamics. Thus, the performance may be poor if the natural damping of the devices is too low or too high. This paper presents an alternative for the control of parallel-plate electrostatic actuators, which is based on an essential property of nonlinear systems, namely differential flatness, and combines the techniques of trajectory planning and robust nonlinear control. It is, therefore, capable of stabilizing the system at any point in the gap while ensuring desired performances. The proposed control scheme is applied to an AO system and simulation results demonstrate its advantage over constant voltage contro

Simultaneous measurement of quality factor and wavelength shift by phase shift microcavity ring down spectroscopy

Optical resonant microcavities with ultra high quality factors are widely used for biosensing. Until now, the primary method of detection has been based upon tracking the resonant wavelength shift as a function of biodetection events. One of the sources of noise in all resonant-wavelength shift measurements is the noise due to intensity fluctuations of the laser source. An alternative approach is to track the change in the quality factor of the optical cavity by using phase shift cavity ring down spectroscopy, a technique which is insensitive to the intensity fluctuations of the laser source. Here, using biotinylated microtoroid resonant cavities, we show simultaneous measurement of the quality factor and the wavelength shift by using phase shift cavity ring down spectroscopy. These measurements were performed for disassociation phase of biotin-streptavidin reaction. We found that the disassociation curves are in good agreement with the previously published results. Hence, we demonstrate not only the application of phase shift cavity ring down spectroscopy to microcavities in the liquid phase but also simultaneous measurement of the quality factor and the wavelength shift for the microcavity biosensors in the application of kinetics measurements

Chalcogenide Fabry–Perot Fiber Tunable Filter

We demonstrate the first mid-infrared compatible all-fiber Fabry-Perot filter. It consists of chalcogenide fibers terminated with high-reflective coatings made of germanium and calcium fluoride. In addition to the transmission compatibility with mid-infrared wavelength, the filter has both tunability and free spectral range >350 nm as well as a finesse of 27. To demonstrate the application of the filter, a thulium-doped fiber laser is built and shows continuous tunability from 1.835 to 1.920 μm

Tests of achromatic phase shifters performed on the SYNAPSE test bench: a progress report

The achromatic phase shifter (APS) is a component of the Bracewell nulling interferometer studied in preparation for future space missions (viz. Darwin/TPF-I) focusing on spectroscopic study of Earth-like exo-planets. Several possible designs of such an optical subsystem exist. Four approaches were selected for further study. Thales Alenia Space developed a dielectric prism APS. A focus crossing APS prototype was developed by the OCA, Nice, France. A field reversal APS prototype was prepared by the MPIA in Heidelberg, Germany. Centre Spatial de Li\`ege develops a concept based on Fresnel's rhombs. This paper presents a progress report on the current work aiming at evaluating these prototypes on the SYNAPSE test bench at the Institut d'Astrophysique Spatiale in Orsay, France

Congenital Transmission of Chagas Disease in Latin American Immigrants in Switzerland

International migration has changed the epidemiologic patterns of Chagas disease. Recently, 2 cases of Chagas disease transmitted from Latin American women to their newborns were diagnosed in Geneva, Switzerland. A retrospective study to detect Chagas disease showed a prevalence of 9.7% among 72 Latin American women tested during pregnancy in Switzerland

Selective in-plane Fabry-Pérot gas sensor functionalized with polymer

Smell is one of the last senses still not completely replicated. Artificial gas sensors do manage to reach enough sensitivity but selectivity is still an issue. However, it is essential to several industries and smart cities. In this work, the selectivity of a previously reported optical gas sensor is demonstrated using three polymers for functionalization. Different sensitivities are obtained for toluene, 1-butanol, limonene and valeric acid

Gas sensing with SU-8 whispering gallery mode resonators

We present an optical gas sensor using SU-8 microdisk whispering gallery mode resonators. Sensitivities were measured for different vapor phases: water, toluene, limonene and valeric acid. The highest reported sensitivity is 18.98 pm/ppm

High-throughput volume refractive index distribution measurement through mechanical deformation of single cells

This paper reports a high-throughput microphotonic biosensor measuring volume refractive index distribution through mechanical deformation of single cells. Preliminary results suggest that different cell states can be distinguished. This feature could readily add novel parameters for cell analysis without resorting to nucleic acid dies