Robust label-free biosensing using microdisk laser arrays with on-chip references.

Whispering-gallery mode (WGM) microdisk lasers show great potential for highly sensitive label-free detection in large-scale sensor arrays. However, when used in practical applications under normal ambient conditions, these devices suffer from temperature fluctuations and photobleaching. Here we demonstrate that these challenges can be overcome by a novel referencing scheme that allows for simultaneous compensation of temperature drift and photobleaching. The technique relies on reference structures protected by locally dispensed passivation materials, and can be scaled to extended arrays of hundreds of devices. We prove the viability of the concept in a series of experiments, demonstrating robust and sensitive label-free detection over a wide range of constant or continuously varying temperatures. To the best of our knowledge, these measurements represent the first demonstration of biosensing in active WGM devices with simultaneous compensation of both photobleaching and temperature drift.

All-polymer photonic sensing platform based on whispering-gallery mode microgoblet lasers.

We present an all-polymer photonic sensing platform based on whispering-gallery mode microgoblet lasers integrated into a microfluidic chip. The chip is entirely made from polymers, enabling the use of the devices as low-cost disposables. The microgoblet cavities feature quality factors exceeding 10(5) and are fabricated from poly(methyl methacrylate) (PMMA) using spin-coating, mask-based optical lithography, wet chemical etching, and thermal reflow. In contrast to silica-based microtoroid resonators, this approach replaces technically demanding vacuum-based dry etching and serial laser-based reflow techniques by solution-based processing and parallel thermal reflow. This enables scaling to large-area substrates, and hence significantly reduces device costs. Moreover, the resonators can be fabricated on arbitrary substrate materials, e.g., on transparent and flexible polymer foils. Doping the microgoblets with the organic dye pyrromethene 597 transforms the passive resonators into lasers. Devices have lasing thresholds below 0.6 nJ per pulse and can be efficiently pumped via free-space optics using a compact and low-cost green laser diode. We demonstrate that arrays of microgoblet lasers can be readily integrated into a state-of-the-art microfluidic chip replicated via injection moulding. In a proof-of-principle experiment, we show the viability of the lab-on-a-chip via refractometric sensing, demonstrating a bulk refractive index sensitivity (BRIS) of 10.56 nm per refractive index unit.

Dependencies of micro-pillar cavity quality factors calculated with finite element methods.

We present simulation results for optical modes in micro-pillar cavities that were computed with the finite element method and that show good agreement with experimental data. By means of this viable tool various influences on the quality factor of the fundamental mode were calculated: Firstly, the light confinement depends strongly on the absorption of the semiconductor cavity material. Here we were able to determine absolute maximum quality factors achievable in a GaAs/AlAs Bragg micro-pillar cavity. Furthermore, small pillar diameters as well as the inclination of pillar sidewalls show critical features with respect to light confinement. Additional effects of the top and bottom Bragg stacks in the pillar were calculated as well.

Localized and delocalized modes in coupled optical micropillar cavities.

Optical micropillar Bragg cavities of different diameters and coupled by a small bridge have been realized experimentally by means of a focused ion beam system. The resonator modes in these coupled microcavities are either localized in one pillar or delocalized over the whole photonic structure, a fact that could be exploited to control the coupling between two spatially separated quantum dots, i.e. placed in different pillars, via the enhanced electromagnetic field in such a coupled microcavity. A simplified two dimensional simulation has been used to predict the resonant wavelengths and design the optical modes in these coupled Bragg cavities.

Psychoneuroimmunology: an interpretation of experimental and case study evidence towards a paradigm for predictable results.

This paper surveys a number of key experiments and case studies relating to psychoneuroimmunology. It finds that most techniques to influence or even direct the immune system via the mind fall into a series of theoretical categories called passive, active and targeted effects. By examining the results of experiments and studies in the light of these categories a number of important conclusions are drawn. These conclusions explain differences in experimental results, describe those variables that appear to be central to obtaining results, and describe in detail where experimentation should be concentrated to further knowledge of psychoneuroimmunology.