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”

OUTLINE

• • • • •

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

MOTIVATIONS

« …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)

• Light – matter interaction increases in the presence of small objects; • 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 ….)

OBJECTIVES

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

( millidisk )

WGMs RESONATORS

• • The Whispering Gallery phenomenon was initially described by Lord Rayleigh based on observations in St. Paul’s Cathedral in London; 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”

Lord Rayleigh (1842 – 1919

)

Whispering Gallery under the cupola of the St. Paul’s Cathedral in London L. Rayleigh , “The Problem of the Whispering Gallery,” Philosophical Magazine 20, 1001–1004 (1910).

• • Microdisks

WGMs RESONATORS

• Microspheres Microbubble • light can be resonantly guided by total internal reflection, along an equatorial plane, with long cavity lifetime and strong spatial confinement;

Field radial component for the fundamental mode Maxwell + boundary conditions: Evanescent field tail Field polar component fundamental mode for the (spherical Legendre function) Field azimuthal component (periodical function)

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 waveguide Hybrid fiber-prism

WGMs RESONATORS

Q factor measurement: experimental setup

Tunable LD d

n

=300 KHz D

n

=



1.5 GHz Modulator

• • From WGM spectral linewidth

d ν Q= ν /d ν camera Vis. LD camera Monitor Mux piezo Q

 2  (Energy stored into the cavity) Energy loss/cycle

Scope Detector d

n

SiO

2

WGMs RESONATORS

microspheres by fusion splicing

electrodes Fiber Tip D = 2R = 150 – 350 μm depending on the number of shots

• A cleaved tip of the fiber is inserted between two metal electrodes; • Arc discharges partially melts the fiber tip; • Surface tension forces produce the spherical shape.

WGMs RESONATORS

Crystalline microdisk by polishing

• 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 INTEGRATION

3.4

3.2

3.0

n =1.5 MHz, Q=1.3 x 10 8 Q = 1.3  10 8 2.8

320 360 Detuning (MHz) 400 The system is all in guided integrated optics architecture (LiNbO 3 )

!

G.Nunzi Conti et al., Opt. Express, 19, 3651 (2011)

APPLICATIONS

NL EFFECTS IN COATED MICROSPHERES

pump

PUMP-PROBE Configuration:

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.

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.

NL EFFECTS IN COATED MICROSPHERES 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

Q factor from spectral linewidth

Uncoated microsphere Coated microsphere 5.0

Q = 1.5  10 8 (@ 1550 nm) 4.5

4.0

3.5

3.0

2500 2750 3000 3250 Detuning [MHz] Q = 5  10 6 3500 3750 Coating thickness < 100 nm

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)

SiO 2 MICROSPHERES AS OPTICAL BIOSENSORS 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

.

R R ’

Wavelength Sweep Generator DFB Laser

• from the resonance condition:   

res res

 

r r

 

n n

Power Detector

SiO 2 MICROSPHERES FOR PROTEIN APTASENSORS 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 a) b) c) d) Functionalization procedure Activation Silanization Thrombin Binding Aptamer (TBA) immobilization Passivation (mercapto-ethanol 1mM 1h) OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH OH

100  m

Piranha treatment: H 2 SO 4 : H 2 O 2 4 : 1 for 3 minutes a) Mercaptopropyl trimethoxy silane 1% v/v toluene for 10 minutes at 60 °C b) Dithiol-TBA

5'-GGTTGGTGTGGTTGG- 3'

10



M in carbonate buffer 0.5M pH9 for 2 hours at 60 rpm c)

SiO 2 MICROSPHERES FOR PROTEIN APTASENSORS Q factor measurement

(@ 773 nm) bare microsphere Q = 4.0  10 7 silanized microsphere Q = 4.0  10 6 (in aqueous environment) Thrombin binding microsphere Q = 8.0  10 5 (in buffer solution) Uniform distribution of the film Coating thickness < 100 nm

L. Pasquardini et al. , J. of Biophotonics (2012)

SiO 2 MICROSPHERES FOR PROTEIN APTASENSORS Set – Up measurement Detected Proteins: Thrombin

: coagulation factor It involves many pathological diseases like: Aatherosclerosis; marker for some cancer;

VEGF G

rowth (

V

ascular

E

ndothelial

F

actor): regolator for angiogenesis;

Binding

SiO 2 MICROSPHERES FOR PROTEIN APTASENSORS

measurements showed that derivatized glass matrices: buffer and no filtered

human serum

.

Measure conditions: Thrombin concentration of 0,3mg/ml in non filtered 10% diluted human serum

3 2 1 0 6 5 4 stability VEGF165 b) 0 200 400 600 800 Time [s] 1000 1200 1400

L. Pasquardini et al. , J. of Biophotonics (2012)

FROM MICROSPHERES TO MICROBUBBLES (MB) 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 Bulk Microresonators Modulator Laser The fluidics is integrated inside the device (microbubble) & coupling system (tapered fiber) is external to the fluidics Advantage : Possibility to test liquid or gas flows inside the microbubble without disturb the microfiber alignment.

Integrated solution.

Systems based on Hollow Microresonators Modulator Laser

WHAT IS AN OPTICAL MB: THE BASIC IDEA

Antoine De Saint-Exupéry Le Petit Prince (“The Little Prince”) - 1945 M. Sumetsky et al., Opt. Lett. 35, p. 898 (2010)

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.

OPTICAL MB FABRICATION: A NEW PROCEDURE Modified Fusion 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.

A pair of electrical wires connects the electrodes to the splicer Uniform heating of the pressurized capillary is obtained by rotation of the U shaped holder around the capillary.

Parameters Outer Capillary Diameter (µm) Capillary Wall Thickness (µm) MBR Outer Diameter (µm) MBR Wall Thickness (µm) OPTICAL MICROBUBBLE RESONATORS Q factor measurement Contact - Critical coupling condition Postnova Z-DI 160481 UFE capillary 280 122 20 21 380 4 240 6 Postnova Microbubble No Contact – undercoupling condition

S. Berneschi et al., Opt. Lett. (2011)

OPTICAL MICROBUBBLE

:

REFRACTOMETRIC TEST A peristaltic pump is connected to the microbubble

Sensibility: 0.5 nm/RIU Detection Limit: 10 -6 RIU

Postnova Microbubble R outer = 190 w = 4 μm μm Different water – ethanol solutions: (4:1, 4:2, 4:3) in volume

S. Berneschi et al., Opt. Lett. (2011)

CONCLUSIONS & PERSPECTIVES

• 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) oscillators in RF systems; add-drop filters & optoelectronics • Demonstration of all – optical switch by NL coated microspheres add-drop configuration; • Demonstration of optical microsphere aptasensors for protein detection (in human serum) take the detection to the limit; • Demonstration of optical microbubble resonators possibility to use this structures for biosensing;

RELATED PROJECTS & COLLABORATIONS Aramos Project

EDA Optoelectronics Oscillators

CNRS, LAAS & Univ. de Toulouse

, France

Naomi

National Project Biosensors (protein essays)

Short term mobility program CNR FBK

(Fondazione Bruno Kessler), Trento; Ospedale di Careggi (Firenze).

Collaboration with different european Research Institutes & Universities (Moscow, Budapest, Trento,..)