Optical fiber probes are generating a large interest to develop portable fluorescence spectrometers. However, the sensitivity of conventional fibers is severely limited by the high luminescence background generated in the glass and the low collection efficiency of fibers.
We solve this issue in a recent Optics Express publication by using a hollow core photonic crystal fiber probe combined with a polystyrene microsphere. Thanks to the hollow-core photonic crystal fiber, the background noise is reduced by two orders of magnitude. Thanks to the microsphere, the excitation beam is further focused and the fluorescence collection efficiency is improved. As compared to the previous state-of-the-art, we report a 200x improvement of the signal-to-noise ratio for single molecules detection events, together with a 1000x gain on the minimum detectable concentration.
Our approach takes advantage of a polystyrene microsphere directly set at the fiber end-face to focus the fiber mode down to a spot of 540 nm FHWM. These results and their application for fluorescence imaging and direct laser writing have been reported in Applied Optics.
We believe that this device offers new opportunities for remote or in vivo optical characterization together with a miniaturization of bulky microscope setups. Applications include inspection of semiconductor wafers, photolithography, laser surgery, and fluorescence sensing.
Now available from Cambridge University Press, the Optical Antennas book edited by Mario Agio and Andrea Alu.
This consistent and systematic review of recent advances in optical antenna theory and practice brings together leading experts in the fields of electrical engineering, nano-optics and nano-photonics, physical chemistry and nanofabrication. Fundamental concepts and functionalities relevant to optical antennas are explained, together with key principles for optical antenna modelling, design and characterisation. Recognising the tremendous potential of this technology, practical applications are also outlined.
A free sample preview of the chapter I wrote on aperture antennas can be found here.
The development of bright water-soluble luminescent probes is a ubiquitous problem in imaging and sensing applications. Designing fluorescent dyes typically relies on a molecular engineering approach in which photophysical properties are tuned by chemical modifications. In a letter published in Angewandte Chemie, we present a novel way of engineering luminescence by changing the photonic environment of a chromophore while maintaining its solubility. This has remained a challenge since the pioneering of this field in the 1970s, mainly because the photonic approach requires combining, in a single hybrid nanostructure, a luminescent molecule and an optical cavity that confines the electromagnetic field.
We solve this challenge by producing purified suspensions of gold nanoparticle dimers linked by a single DNA double strand exhibiting one a single dye molecule. Tuning the electromagnetic field enables unprecedented photophysical properties, such as decay rates and excitation cross-sections enhanced by more than one order of magnitude compared to an optimized, commercial chromophore.
Free access alternative pdf version of the letter can be found via arXiv:1210.6790