A lens-less optical fiber designed for enhanced-fluorescence biosensor applications is presented. In order to obtain the enhanced sensor performances, two elements are essential: a planar antenna that redirects fluorescence emission into a narrow cone and an automated fiber-based optical system for multi-spot analysis. In particular, the potential early diagnosis of sepsis via C-reactive protein (CRP) detection is here demonstrated, reaching a limit of detection of 1.5 ng/mL), which is in the clinical range of interest for such biomarker. Upon the combination with other sepsis biomarkers, the presented sensor can become relevant for the early diagnosis of sepsis. These results validate the developed prototype as a simple, affordable, easy-to-operate, plug&play device with fast turnaround times, compatible with standardized micro-well arrays, and potentially suitable for POC applications with respect to the diagnosis of sepsis. It is also suitable for implementation with other biomarkers and liquid environments.
A major challenge in photonic quantum technologies is two-photon interference from distinct quantum emitters on the same chip. Here, we show and discuss recent results on Hong–Ou–Mandel interference experiments using couples of single organic molecules within few tens of microns, yielding post-selected visibilities of up to 97%. In particular, we discuss the potential interest for future realizations of measurement-device independent quantum key distribution protocols for information-theoretic secure communication.
Sepsis, defined as the systemic inflammatory response to a confirmed or suspected source of infection, is the most severe infection-related condition and its identification can be particularly difficult in the initial stages. The importance of having a Point-of-care testing platform capable of measuring sepsis biomarkers for a secure early-stage diagnosis is evident to reduce delay in treatment and hence recovery period for the patient.
We will report on a simple and cost-effective device which also shows high portability. It is based on the optical detection of labeled essays through a fully-automated fiber probe. Efficient signal collection is obtained by replacing the standard glass substrate with a planar metallo-dielectric multilayer which funnels the emission into a narrow cone around the polar axis [1]. Optical interrogation is implemented with a minimized epi-fluorescence monolithic system directly connected to the fiber.
On one hand, optical probes provide the ability to detect low quantities of target molecules without direct contact to the sample; on the other hand, nano-photonics promises to overcome the limitations related to bulk optics with precise and fragile alignment procedures.
We will report on preliminary results obtained for a reference dry essays (IgG/anti-IgG) marked with ATTO647N, which demonstrates sensitivity overcoming the requirements for CRP-based sepsis detection. We will also discuss optimization steps which are expected to bring sensitivity beyond the level required for PRC-based sepsis detection. The proposed device is also prone to implementation in microfluidic-based protocols.
[1] Checcucci S, Lombardi P., Rizvi S., Sgrignuoli F., Gruhler N., Dieleman F.B.C., Cataliotti F.S., Pernice W.H.P., Agio M., and Toninelli C., Beaming light from a quantum emitter with a planar optical antenna, Light: Science and Applications, Vol. 6, e16245 (2017).
Sepsis, defined as the systemic inflammatory response to a confirmed or suspected source of infection, is the most severe infection-related condition and its identification can be particularly difficult in the initial stages. The importance of having a POCT platform capable of measuring sepsis biomarkers for a secure early-stage diagnosis is evident since traditional methods of pathogen determination delay treatment and also increase the recovery period for the patient. The biggest advantage of optical probes is the ability to detect low quantities of target molecules without direct contact to the sample. Nanophotonics-based sensing promises to build on the advantages of optical sensing, while overcoming its limitations by providing a high sensitivity, specificity, dynamic range, as well as the possibility for easy integration into simple and affordable devices. The project FASPEC (Fiber-based planar antennas for biosensing and diagnostics) aims at developing and prototyping a high-performance fluorescence-based molecular assay for in-vitro diagnostics that integrates lab-on-a-chip and optical readout functionalities within a single, fully automated platform. The key biophotonics innovation of the project is the replacement of the bulk optics used for collecting the fluorescence signal with a suitably designed optofluidic chip. The latter shall function as an optical antenna to direct fluorescence towards the sensor head, hence enhancing the sensitivity of the fluorescence-based assay by orders of magnitude. Application-specific lab-on-a-chip systems equipped with our high-throughput and ultrasensitive detection scheme have been envisioned.
KEYWORDS: Signal detection, Single photon, Mirrors, Waveguides, Digital breast tomosynthesis, Molecules, Silica, Optical design, Light wave propagation, Structural design
We employ mirror enhanced grating couplers as convenient output ports for ridge Si3N4 waveguide to detect single photons emitted from Dibenzoterrylene (DBT) molecules coupled into propagating modes at room temperature. The coupling ports are designed for waveguide structures on transparent silica substrates for light extraction from the chip backside. Thus the coupling ports enable contact free readout of the waveguide devices by imaging through the silica substrate.
Optimized grating structures provide maximum out-coupling efficiency at 785nm (the central emission wavelength of DBT) with a bandwidth of 50 nm and fulfill mode-matching to a Gaussian mode in free space (FWHM ≈ 4μm). Covering fully etched grating devices with a Hydrogen silsesquioxane buffer layer and a gold mirror increase the coupling efficiency compared to bare grating structures. The maximum single coupler efficiency predicted by finite element simulations is 90% which reduces to 60% when adapted to fabrication constrains, whereas the average measured coupling efficiency is 35±5%.
We employ such grating ports to read out optical waveguides designed for single-mode operation at λ=785 nm. DBT molecules are coupled evanescently to the waveguides and transport emitted single photon signals to the coupling region upon optical pumping. Using a Hanbury Brown and Twiss setup we observe pronounced antibunching with g(2)(0)=0.50±0.05 from the grating couplers by excitation (λ=767nm) of a single DBT molecule which confirms the quantum nature of the outcoupled fluorescent light.
Efficient quantum light sources and non-linear optical elements at the few photon level are the basic
ingredients for most applications in nano and quantum technologies. On the other hand, a scalable platform for quantum ICT typically requires reliable light matter interfaces and on-chip integration. In this work we demonstrate the potential of a novel hybrid technology which combines single organic molecules as quantum emitters and dielectric chips [1].
Dibenzoterrylene molecules in anthracene crystals (DBT:Ac) are particularly suitable quantum systems for this task, since they exhibit long-term photostability in thin samples [2], easy fabrication methods and life-time limited emission at cryogenic temperatures [3].
We demonstrate at room temperature the emission of single photons from DBT molecules into ridge waveguides with a branching ratio up to 40%. The overall single-photon source efficiency, including emission into the guided mode, propagation losses, and emission into a quasi-gaussian mode in free space, is estimated around 16%. These results are competitive with state-of-the-art single photon emission into propagating guided modes from solid state systems [4], while offering a novel platform with unprecedented versatility.
References
[1] P. Lombardi et al., Arxiv: 1701.00459v1 (2017).
[2] C. Toninelli et al., Opt. Express 18, 6577 (2010).
[3] A. A. L. Nicolet et al., ChemPhysChem 8, 1929 (2007).
[4] I. Zadeh et al., Nano Lett. 16, 2289 (2016); R. S. Daveau et al., Arxiv: 1610.08670v1 (2016).
[5] J. Hwang et. al., New J. Phys. 13, 085009 (2011); H.-W. Lee et al., Phys. Rev. A 63, 012305 (2000).
We report on optical analogues of well-known electronic phenomena such as Bloch oscillations and electrical Zener breakdown. We describe and detail the experimental observation of Bloch oscillations and resonant Zener tunneling of light waves in static and time-resolved transmission measurements performed on optical superlattices. Optical superlattices are formed by one-dimensional photonic structures (coupled microcavities) of high optical quality and are specifically designed to represent a tilted photonic crystal band. In the tilted bands condition the miniband of degenerate cavity modes turns into an optical Wannier-Stark ladder (WSL). This allows an ultrashort light pulse to bounce between the tilted photonic band edges and hence to perform Bloch oscillations, the period of which is defined by the frequency separation of the WSL states. When the superlattice is designed such that two minibands are formed within the stop band, at a critical value of the tilt of photonic bands the two WSLs couple within the superlattice structure. This results in a formation of a resonant tunneling channel in the minigap region, where the light transmission boosts from 0.3% to over 43%. The latter case describes the resonant Zener tunneling of light waves.
KEYWORDS: Strontium, Spectroscopy, Laser sources, Visible radiation, Optical testing, Global Positioning System, Laser development, Solid state lasers, Solid state physics, Control systems
We present a new laser setup suited for high precision spectroscopy on atomic strontium. The source is used for an absolute frequency measurement of the visible 5s21S0-5s5p3P1 intercombination line of strontium which is considered a possible candidate for a future optical frequency standard. The optical frequency is measured with an optical comb generator referenced to the SI through a GPS signal. We developed also an all solid state blue laser source that will be used for laser cooling of strontium, which will result in a better control on the systematic effects and a great improvement in the precision of the measurement.
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