Optical frequency comb based system for photonic refractive index sensor interrogation.

In this contribution, we demonstrate how an optical frequency comb can be used to enhance the functionality of an integrated photonic biosensor platform. We show that if an optical frequency comb is used to sample the spectral response of a Mach-Zehnder interferometer and if the line spacing is arranged to sample the periodic response at 120° intervals, then it is possible to combine these samples into a single measurement of the interferometer phase. This phase measurement approach is accurate, independent of the bias of the interferometer and robust against intensity fluctuations that are common to each of the comb lines. We demonstrate this approach with a simple silicon photonic interferometric refractive index sensor and show that the benefits of our approach can be obtained without degrading the lower limit of detection of 3.70×10-7 RIU.

Improved second harmonic performance in periodically poled LNOI waveguides through engineering of lateral leakage.

In this contribution, we investigate the impact of lateral leakage for linear and nonlinear optical waveguides in lithium niobate on an insulator (LNOI). Silicon nitride (SiN) loaded and direct patterned lithium niobate cross-sections are investigated. We show that lateral leakage can take place for the TE mode in LNOI ridge waveguides (X-cut lithium niobate), due to the birefringence of the material. This work gives guidelines for designing waveguides in LNOI that do not suffer from the lateral leakage effect. By applying these design considerations, we avoided the lateral leakage effect at the second harmonic wavelength of a nonlinear optical waveguide in LNOI and demonstrate a peak second harmonic generation conversion efficiency of ~1160% W-1cm-2.

Elastomeric microvalve geometry affects haemocompatibility.

This paper reports on the parameters that determine the haemocompatibility of elastomeric microvalves for blood handling in microfluidic systems. Using a comprehensive investigation of blood function, we describe a hierarchy of haemocompatibility as a function of microvalve geometry and identify a "normally-closed" v-gate pneumatic microvalve design that minimally affects blood plasma fibrinogen and von Willebrand factor composition, minimises effects on erythrocyte structure and function, and limits effects on platelet activation and aggregation, while facilitating rapid switching control for blood sample delivery. We propose that the haemodynamic profile of valve gate geometries is a significant determinant of platelet-dependent biofouling and haemocompatibility. Overall our findings suggest that modification of microvalve gate geometry and consequently haemodynamic profile can improve haemocompatibility, while minimising the requirement for chemical or protein modification of microfluidic surfaces. This biological insight and approach may be harnessed to inform future haemocompatible microfluidic valve and component design, and is an advance towards lab-on-chip automation for blood based diagnostic systems.

Shear Stress Regulates TRPV4 Channel Clustering and Translocation from Adherens Junctions to the Basal Membrane.

Localized Ca2+ influx via TRPV4 on the surface of endothelial cells greatly influences endothelial adaptation to blood flow, but how mechanical stress from blood flow controls TRPV4 integration into this physiological function is not fully understood. Here, we studied the spatial organization of TRPV4 and its relationship to the adherens junction component ß-catenin using single- and dual-color direct stochastic optical reconstruction microscopy (dSTORM). In non-stimulated endothelial cells, TRPV4 is clustered in small protein islands, as is ß-catenin. Using dual-color imaging, we found that TRPV4 and ß-catenin reside in similar islands and can be found at both the basolateral and basal membranes. Following shear stress stimulation, TRPV4 molecules formed smaller clusters, with the majority residing outside of clusters. Further shear stress stimulation changed the molecular distribution of TRPV4 molecules, limiting them to the basal membrane. This redistribution and the smaller clusters resulted in the segregation of TRPV4 from ß-catenin. Furthermore, TRPV4 trafficking was controlled by focal adhesion kinase and activation of the α5ß1 integrin. These highly differentiated spatial redistributions suggest that mechanotransduction of blood flow is controlled via a more complex hierarchy than previously thought.

Dynamic drag force based on iterative density mapping: A new numerical tool for three-dimensional analysis of particle trajectories in a dielectrophoretic system.

Dielectrophoresis is a widely used means of manipulating suspended particles within microfluidic systems. In order to efficiently design such systems for a desired application, various numerical methods exist that enable particle trajectory plotting in two or three dimensions based on the interplay of hydrodynamic and dielectrophoretic forces. While various models are described in the literature, few are capable of modeling interactions between particles as well as their surrounding environment as these interactions are complex, multifaceted, and computationally expensive to the point of being prohibitive when considering a large number of particles. In this paper, we present a numerical model designed to enable spatial analysis of the physical effects exerted upon particles within microfluidic systems employing dielectrophoresis. The model presents a means of approximating the effects of the presence of large numbers of particles through dynamically adjusting hydrodynamic drag force based on particle density, thereby introducing a measure of emulated particle-particle and particle-liquid interactions. This model is referred to as "dynamic drag force based on iterative density mapping." The resultant numerical model is used to simulate and predict particle trajectory and velocity profiles within a microfluidic system incorporating curved dielectrophoretic microelectrodes. The simulated data are compared favorably with experimental data gathered using microparticle image velocimetry, and is contrasted against simulated data generated using traditional "effective moment Stokes-drag method," showing more accurate particle velocity profiles for areas of high particle density.