Opto 2011 Photonics West, San Francisco, California, USA Long period and fiber Bragg gratings written within the same fiber for sensing purposes Francesco Baldini, Massimo Brenci, Ambra Giannetti, Cosimo Trono Institute of Applied Physics, National Research Council, Florence – Italy Francesco Chiavaioli, Marco Mugnaini Dept. Information Engineering, Univ. of Siena, Italy

Opto 2011 Photonics West, San Francisco, California, USA   introduction   experimental setup   grating manufacture   the flow cell   grating characterisation   experimental results   conclusions Outline

Opto 2011 Photonics 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 strainIntroduction

Opto 2011 Photonics West, San Francisco, California, USA Experimental setup

Opto 2011 Photonics West, San Francisco, California, USA Grating manufacture (LPG) fiber: Photosensitive B/Ge co-doped optical fiber (Fibercore PS1250/1500) source: UV excimer laser source 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 2011 Photonics West, San Francisco, California, USA 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 248 nm) Phase mask pitch: nm

Opto 2011 Photonics West, San Francisco, California, USA Transmission spectrum FBGLength: 1 cm Period: 530 nm λ res : 1534 nm FWHM: 0.26 nm transmission loss: 10 dB LPGLength: 2.46 cm Period: 615 μm λ res : 1567 nm FWHM: 6.5 nm transmission loss: 15 dB

Opto 2011 Photonics West, San Francisco, California, USA The flow-cell

Opto 2011 Photonics West, San Francisco, California, USA The flow-cell

Opto 2011 Photonics West, San Francisco, California, USA Grating characterisation - strain

Opto 2011 Photonics West, San Francisco, California, USA Grating characterisation - strain

Opto 2011 Photonics West, San Francisco, California, USA Grating characterisation - temperature

Opto 2011 Photonics West, San Francisco, California, USA Grating characterisation - temperature

Opto 2011 Photonics West, San Francisco, California, USA Refractive 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 2011 Photonics West, San Francisco, California, USA Refractive index measurements Refractive Index Range Δλ(nm)Value (nm/RIU)Resolution (RIU) Minimum sensitivity1 – x Intermediate Sensitivity1.435 – x Maximum Sensitivity1.454 – x 10 -5

Opto 2011 Photonics West, San Francisco, California, USA First results on IgG/anti- IgG bioassay First 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 2011 Photonics West, San Francisco, California, USA 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 RIU   Preliminary IgG/anti-IgG assay