Optofluidic Sensor Based on Polymer Optical Microresonators for the Specific, Sensitive and Fast Detection of Chemical and Biochemical Species.

The accurate, rapid, and specific detection of DNA strands in solution is becoming increasingly important, especially in biomedical applications such as the trace detection of COVID-19 or cancer diagnosis. In this work we present the design, elaboration and characterization of an optofluidic sensor based on a polymer-based microresonator which shows a quick response time, a low detection limit and good sensitivity. The device is composed of a micro-racetrack waveguide vertically coupled to a bus waveguide and embedded within a microfluidic circuit. The spectral response of the microresonator, in air or immersed in deionised water, shows quality factors up to 72,900 and contrasts up to 0.9. The concentration of DNA strands in water is related to the spectral shift of the microresonator transmission function, as measured at the inflection points of resonance peaks in order to optimize the signal-over-noise ratio. After functionalization by a DNA probe strand on the surface of the microresonator, a specific and real time measurement of the complementary DNA strands in the solution is realized. Additionally, we have inferred the dissociation constant value of the binding equilibrium of the two complementary DNA strands and evidenced a sensitivity of 16.0 pm/µM and a detection limit of 121 nM.

Comparative analysis of recirculating and collimating cesium ovens.

We have performed a study of several cesium oven designs. A comparison between recirculating (or sticking-wall) and collimating (or re-emitting-wall) ovens is made in order to extract the most efficient design in terms of beam brightness. Unfortunately, non-reproducible behaviors have been observed, and the most often observed output flux is similar to the sticking-wall case, which is the lowest theoretical value of the two cases, with a beam brightness close to 1018 at. sr-1 s-1 cm-2. The reason of this universally observed behavior is unclear despite having tested several materials for the collimating tube. Conclusion on possible improved design based on sticking of cesium on several (un)cleaned surfaces is given.