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2 nd Conference on Centro Fermi’s Projects, Rome 19-20 April 2012 OPTICAL MICRORESONATORS & BIOPHOTONIC SENSORS PROJECT Simone Berneschi Centro Fermi Grants.

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Presentation on theme: "2 nd Conference on Centro Fermi’s Projects, Rome 19-20 April 2012 OPTICAL MICRORESONATORS & BIOPHOTONIC SENSORS PROJECT Simone Berneschi Centro Fermi Grants."— Presentation transcript:

1 2 nd Conference on Centro Fermi’s Projects, Rome 19-20 April 2012 OPTICAL MICRORESONATORS & BIOPHOTONIC SENSORS PROJECT Simone Berneschi Centro Fermi Grants CNR, Institute of Applied Physics “Nello Carrara” Project Coordinator: Stefano Pelli CNR, Institute of Applied Physics “Nello Carrara”

2 OUTLINE Motivations; Objectives; WGM microresonators: a brief overview; Applications & Results; NL effects; biosensors; Conclusions

3 MOTIVATIONS Light – matter interaction increases in the presence of small objects; « …smaller objects in nature are not just scaled replicas of similar big objects and in fact they have improved properties…» Galileo «Dialogue Concerning Two New Sciences» (1638) High Q microcavities, with strong spatial localization of the field, well respond to this principle and receive an even greater interest in many fundamental processes in photonics (e.g.: QED & NL processes; biosensing….)

4 OBJECTIVES Investigating Whispering Gallery Modes (WGMs) microcavities for: Developing highly sensitive, label free biosensors (early diagnosis); (microsphere/microbubble) Developing all-optical switch by means of NL polymeric coating; (microsphere) Studing possible integration solutions with optical planar devices. (millidisk)

5 Lord Rayleigh (1842 – 1919) The Whispering Gallery phenomenon was initially described by Lord Rayleigh based on observations in St. Paul’s Cathedral in London; L. Rayleigh, “The Problem of the Whispering Gallery,” Philosophical Magazine 20, 1001–1004 (1910). Whispering Gallery under the cupola of the St. Paul’s Cathedral in London WGMs RESONATORS a whisper spoken close to the wall can be heard all the way along the gallery, 42 m to the other side, thus the term “whispering gallery”

6 Microdisks Microspheres light can be resonantly guided by total internal reflection, along an equatorial plane, with long cavity lifetime and strong spatial confinement; WGMs RESONATORS Microbubble Field radial component for the fundamental mode Field azimuthal component (periodical function) Evanescent field tail Field polar component for the fundamental mode (spherical Legendre function) Maxwell + boundary conditions:

7 WGMs RESONATORS Efficient and robust coupling of the light to the cavity requires: phase matching and mode overlap! Approaches for efficient evanescent coupling of light into the microspheres: Prism Tapered fiber Surface waveguideHybrid fiber-prism

8 Q factor measurement: experimental setup From WGM spectral linewidth d ν Q= ν /d ν Monitor Tunable LD camera piezo Scope Modulator Mux Vis. LD Detector d d =300 KHz D =  1.5 GHz WGMs RESONATORS

9 Fiber Tip electrodes A cleaved tip of the fiber is inserted between two metal electrodes; D = 2R = 150 – 350 μm depending on the number of shots WGMs RESONATORS SiO 2 microspheres by fusion splicing Arc discharges partially melts the fiber tip; Surface tension forces produce the spherical shape.

10 Partial melting + surface tension effect cannot be applied to crystals. Polishing procedure by using a home-made lapping station. The almost spherical profile of the edges is obtained through a rotational stage whose pivot point can be finely adjusted. Polishing protocol: Grinding phase steps (abrasive disk); Fine polishing phase (diamond suspensions); WGMs RESONATORS Crystalline microdisk by polishing

11 CRYSTALLINE MICRODISK INTEGRATION G.Nunzi Conti et al., Opt. Express, 19, 3651 (2011) Q = 1.3  10 8 WGMs RESONATORS The system is all in guided integrated optics architecture (LiNbO 3 ) !


13 NL EFFECTS IN COATED MICROSPHERES pump probe Motivation: optical switch based on electronic Kerr effect (n = n 0 + n 2 I) on spherical WGMR coated by a nonlinear medium; Large resonance shift obtained on low time scales (10 -12 s) using intensities well below the damage thresholds of the polymers. All-optical switching for a probe signal I probe by a resonant pump beam I pump which change the coating refractive index and hence the resonance position. PUMP-PROBE Configuration:

14 Coated microspheres Dipping Wet layer formation Solvent evaporation Polymer: liquid crystal polyfluorene ( λ peak = 379 nm; n 2  Re (  (3) ) = 2  10 -10 cm 2 /W; β  Im (  (3) ) = = 2  10 -7 cm/W) Solution: 0.1 mg/ml of polymer in toluene NL EFFECTS IN COATED MICROSPHERES

15 Q factor from spectral linewidth Uncoated microsphere Q = 1.5  10 8 Coated microsphere Q = 5  10 6 Coating thickness < 100 nm NL EFFECTS IN COATED MICROSPHERES (@ 1550 nm)

16 NL EFFECTS IN COATED MICROSPHERES An optically induced shift of WGM of up to 250 MHz is obtained in the CW pump regime, which is nearly an order of magnitude smaller as compared to the pulsed probe regime. Such a difference of the values of the shift induced optically by the power of the pump radiation is an indicator of the nonlinear-optical mechanism of the shift. S. Soria et al. Opt. Express (2011)

17 Wavelength Sweep Generator DFB Laser Power Detector R R ’ from the resonance condition: WGMs are morphological dependent: any change in its surrounding environment (i.e. refractive index) or on its surface (due to some chemical and/or biochemical bonding) causes a shift of the resonances and reduces the Q factor value. By measuring this shift, it is possible to obtain the refractive index change and/or the concentration of the analyte. SiO 2 MICROSPHERES AS OPTICAL BIOSENSORS

18 Aptamers: are RNA or DNA molecules (ca. 30 to 100 nucleotides) that recognize specific ligands and that are selected in vitro from vast populations of random sequences [so named in 1990 by Ellington and Szostak]. They exhibit: - comparabile affinity and specificity - more reproducibility and higher stability - reversible denaturation and ease of modification SiO 2 MICROSPHERES FOR PROTEIN APTASENSORS

19 Functionalization procedure a)Activation b)Silanization c)Thrombin Binding Aptamer (TBA) immobilization d)Passivation (mercapto-ethanol 1mM 1h) Dithiol-TBA 5'-GGTTGGTGTGGTTGG- 3' 10  M in carbonate buffer 0.5M pH9 for 2 hours at 60 rpm c) Mercaptopropyl- trimethoxy silane 1% v/v toluene for 10 minutes at 60°C b) 100  m OH Piranha treatment: H 2 SO 4 : H 2 O 2 4 : 1 for 3 minutes a) SiO 2 MICROSPHERES FOR PROTEIN APTASENSORS

20 Q factor measurement Q = 4.0  10 7 bare microsphere silanized microsphere Q = 4.0  10 6 Thrombin binding microsphere Q = 8.0  10 5 (in aqueous environment) (in buffer solution) (@ 773 nm) SiO 2 MICROSPHERES FOR PROTEIN APTASENSORS L. Pasquardini et al., J. of Biophotonics (2012) Uniform distribution of the film Coating thickness < 100 nm

21 Thrombin: coagulation factor It involves many pathological diseases like: Aatherosclerosis; marker for some cancer; Set – Up measurement Detected Proteins: VEGF (Vascular Endothelial Growth Factor): regolator for angiogenesis; SiO 2 MICROSPHERES FOR PROTEIN APTASENSORS

22 Binding measurements showed that derivatized glass microspheres can act as efficient aptasensors in complex matrices: buffer and no filtered human serum. Measure conditions: Thrombin concentration of 0,3mg/ml in non filtered 10% diluted human serum SiO 2 MICROSPHERES FOR PROTEIN APTASENSORS L. Pasquardini et al., J. of Biophotonics (2012) VEGF165 concentration of 0,3mg/ml in buffer

23 Modulator Laser Systems based on Bulk Microresonators The optical microcavity (microsphere) & coupling system (taper fiber) are immersed in a liquid medium (fluidic cell) Problems: possible instability on the resonance position due to the induced perturbations by the liquid environment on the coupling system. No integrated solution. Systems based on Hollow Microresonators Modulator Laser Advantage: Possibility to test liquid or gas flows inside the microbubble without disturb the microfiber alignment. Integrated solution. The fluidics is integrated inside the device (microbubble) & coupling system (tapered fiber) is external to the fluidics FROM MICROSPHERES TO MICROBUBBLES (MB)

24 WHAT IS AN OPTICAL MB: THE BASIC IDEA Similarly to the snake which has swallowed an elephant, an optical microbubble is a resonant microcavity structure, obtained starting from a microcapillary preform (the snake in the corresponding picture) by means of a particular fabrication process which locally increases the radial dimension of the hollow microtube (the elephant) along the axial direction. M. Sumetsky et al., Opt. Lett. 35, p. 898 (2010) Antoine De Saint-Exupéry Le Petit Prince (“The Little Prince”) - 1945

25 OPTICAL MB FABRICATION: A NEW PROCEDURE Uniform heating of the pressurized capillary is obtained by rotation of the U shaped holder around the capillary. A pair of electrical wires connects the electrodes to the splicer The electrodes were moved outside the splicer and placed in a U shaped holder able to rotate by 360° by means of a step by step motor. Modified Fusion Splicer

26 Q factor measurement Parameters Postnova Z-DI 160481 UFE capillary Outer Capillary Diameter (µm) 280122 Capillary Wall Thickness (µm) 2021 MBR Outer Diameter (µm) 380240 MBR Wall Thickness (µm) 46 Postnova Microbubble Contact - Critical coupling condition No Contact – undercoupling condition OPTICAL MICROBUBBLE RESONATORS S. Berneschi et al., Opt. Lett. (2011)

27 A peristaltic pump is connected to the microbubble R outer = 190 μm w = 4 μm R outer = 190 μm w = 4 μm Different water – ethanol solutions: (4:1, 4:2, 4:3) in volume Postnova Microbubble OPTICAL MICROBUBBLE: REFRACTOMETRIC TEST Sensibility: 0.5 nm/RIU Detection Limit: 10 -6 RIU S. Berneschi et al., Opt. Lett. (2011)

28 CONCLUSIONS & PERSPECTIVES Demonstration of optical microsphere aptasensors for protein detection (in human serum) take the detection to the limit; Possibility to obtain high Q WGM resonators in different materials and with different fabrication process; Possibility to integrate optical WGMRs in planar structures (LiNbO 3 millidisk) add-drop filters & optoelectronics oscillators in RF systems; Demonstration of all – optical switch by NL coated microspheres add-drop configuration; Demonstration of optical microbubble resonators possibility to use this structures for biosensing;

29 RELATED PROJECTS &COLLABORATIONS Aramos Project EDA Optoelectronics Oscillators Naomi National Project Biosensors (protein essays) FBK (Fondazione Bruno Kessler), Trento; Ospedale di Careggi (Firenze). CNRS, LAAS & Univ. de Toulouse, France Short term mobility program CNR Collaboration with different european Research Institutes & Universities (Moscow, Budapest, Trento,..)





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