Long period and fiber Bragg gratings written within the same fiber for sensing purposes

Opto 2011Photonics West, San Francisco, California,

USA

Long period and fiber Bragg gratings written within the same fiber for sensing purposesFrancesco Baldini, Massimo Brenci, Ambra

Giannetti, Cosimo TronoInstitute of Applied Physics, National Research

Council, Florence – Italy

Francesco Chiavaioli, Marco MugnainiDept. Information Engineering, Univ. of Siena, Italy

Opto 2011Photonics West, San Francisco, California,

USA

introduction experimental setup grating manufacture the flow cell grating characterisation experimental results conclusions

OutlineOutline

Opto 2011Photonics West, San Francisco, California,

USA

Measurements of refractive index in biological fluids are being used since many years for the quantitative measurements of analytes, by means of the use of chemical/biochemical recognition layers deposited on suitable substrates

surface plasmon resonance interferometric configurations resonating structures Long period gratings have been recently proposed for chemical and biochemical sensing. These sensors have high sensitivity to external refractive index in addition to all the other benefits offered by the optical fibre sensors but they are also sensitive to temperature and strain

IntroductionIntroduction

Opto 2011Photonics West, San Francisco, California,

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Experimental setupExperimental setup

Opto 2011Photonics West, San Francisco, California,

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Grating manufacture (LPG)Grating manufacture (LPG)

• fiber: Photosensitive B/Ge co-doped optical fiber (Fibercore PS1250/1500)

• source: UV excimer laser source (KrF @ 248 nm)

• LPG writing by point-to-point technique• fibre mounted on a motorized translation stage and irradiated by a laser spot appropriately shaped and focused by means of a variable micrometric slit and a cylindrical lens.

• possibility to choose the grating period, the number of shots for each step and the total number of step (grating length) thanks to an ad-hoc software which drives all the process

Opto 2011Photonics West, San Francisco, California,

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Grating manufacture (FBG)Grating manufacture (FBG)FBG are written by the phase-mask technique• Fiber: photosensitive B/Ge co-doped optical fiber (Fibercore PS1250/1500)

• Source: UV excimer laser source (KrF @ 248 nm)

• Phase mask pitch: 1059.9 nm

Opto 2011Photonics West, San Francisco, California,

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Transmission spectrum

FBG Length: 1 cmPeriod: 530 nmλres: 1534 nm FWHM: 0.26 nmtransmission loss: 10 dB

LPG Length: 2.46 cm Period: 615 μmλres: 1567 nm FWHM: 6.5 nmtransmission loss: 15 dB

Opto 2011Photonics West, San Francisco, California,

USA

The flow-cellThe flow-cell

Opto 2011Photonics West, San Francisco, California,

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The flow-cellThe flow-cell

Opto 2011Photonics West, San Francisco, California,

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GGrating characterisation - strainrating characterisation - strain

pm/ 0.04 pm/ 1.25 FBGsk pm / 0.01 pm / 0.32 LBG

sk

Opto 2011Photonics West, San Francisco, California,

USA

GGrating characterisation - strainrating characterisation - strain

Opto 2011Photonics West, San Francisco, California,

USA

GGrating characterisation - temperaturerating characterisation - temperature

1533,82

1533,86

1533,9

1533,94

1533,98

1534,02

1534,06

1534,1

1534,14

1564,5

1564,8

1565,1

1565,4

1565,7

1566

1566,3

1566,6

1566,9

13:00 13:20 13:40 14:00 14:20 14:40 15:00 15:20 15:40

FBG resonance w

avele

ngth (nm)

LPG resonance w

avele

ngth (nm)

Tim e (hh:m m )

LPGFBG

21.1 °C

21.1 °C

22.03 °C

22.03 °C

22.83 °C

23.64 °C

24.53 °C

25.54 °C

26.28 °C

22.83 °C

23.64 °C

24.53 °C

25.54 °C

26.28 °C

Opto 2011Photonics West, San Francisco, California,

USA

GGrating characterisation - temperaturerating characterisation - temperature

Opto 2011Photonics West, San Francisco, California,

USA

Refractive index measurementsRefractive index measurements

• mixture of glycerol and water • flow rate of about 0.5 mL/min for approximately 4 minutes

• stopped pump and acquisition of FBG and LPG minima extrapolated by the Gaussian (FBG) and Lorentzian (LPG) fit averaged on a period of about 10 minutes

Opto 2011Photonics West, San Francisco, California,

USA

Refractive index measurementsRefractive index measurements

Refractive Index Range

Δλ(nm) Value (nm/RIU) Resolution (RIU)

Minimum sensitivity 1 – 1.334 -0.3635 1.1 5 x 10-3

Intermediate Sensitivity 1.435 – 1.451 -5.5828 195 4 x 10-5

Maximum Sensitivity 1.454 – 1.456 -

13.4463 3120 2 x 10-5

Opto 2011Photonics West, San Francisco, California,

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First results on IgG/anti- IgG bioassayFirst results on IgG/anti- IgG bioassay

deposition of an Eudragit layer on the LPG surface

activation of the surface by EDC/NHS covalent binding of the IgG antibody (1 mg/mL)

passivation of the surface with BSA (3% in PBS)

interaction with the anti-IgG antibody

non specific interaction anti-PSA antibody (10 μg/mL)

Opto 2011Photonics West, San Francisco, California,

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Conclusions

Realization of cascaded LPG and FBG gratings

Design and realization of a stabilised flow-cell

Refractive index measurement with a resolution of the order of 10-5 RIU

Preliminary IgG/anti-IgG assay