Label free biosensors based on biogratings patterned on microfibersAugusto Juste-Dolz1, Martina Delgado-Pinar2,*, Miquel Avellà-Oliver1,4, Estrella Fernández1

Daniel Pastor3, Miguel V.Andrés2, Ángel Maquieira1,41 Instituto Universitario de Investigación de Reconocimiento Molecular y Desarrollo Tecnológico (Universitat Poltècnica de València-Universitat de València)2 Laboratory of Fiber Optics - Institut de Ciències dels Materials (Universitat de València) * martina.delgado@uv.es3 Photonic Research Labs (Universitat Politècnica de València) 4 Departament de Química (Universitat Politècnica de València)

Bio-Bragg gra�ngs (BBGs): fabrica�on

1 - Microfibers of 3-5 �m were fabricated by the fuse-and-pull-technique.2 - BSA proteins are a�ached onto the surface by microcontact prin�ng.3 - IgGs present in the medium bind to the bioreceptors, conforming the BBG.

1 2 3

�: 556 ± 1 nm FESEM image: BBG in a taper of 5 �m

Abstract: we present the design, fabrica�on and proof of concept of a label free, photonic biosensor based on a bio-Bragg gra�ng (BBG) that is imprinted on the surface of a microfiber. The biosensor was tested using a BSA-IgG model, and experimental detec�on and quan�fica�onlimits of 0.1 �g·mL-1 and 0.4 �g·mL-1, respec�vely, of unlabelled IgG in label-free condi�ons are obtained.

ConclusionsWe presented a photonic biosensor that combines the ability to pa�ern a pe-riodic network of bioreceptors on the surface of a microfiber, with the sensing capacity of microfibers due to its significant evanescent op�cal field.

Different devices were individually fabricated and tested to perform a BSA-IgGdose-response immunoassay, and promising LOD and LOQ were obtained inlabel free condi�ons.

Mul�plexing of different BBGs in a single device has been demonstrated.

Opera�on principle

reference FBG 2 - BSA BBG 3 - BSA-IgG BBG

�R

The incipient BBG formed by the BSA proteins are detected in reflec�on asa weak gra�ng, at its Bragg wavelength. As the IgGs bind to the bioreceptors, the reflec�vity of the BBG increases. Quan�fica�on of the concentra�on ofIgG is possible by means of the measurement of the increasing �R. A conven�onal FBG was introduced in the setup as a reference, to monitor possible loss introduced during the different steps of fabrica�on.

Input light

Reflected light

Pa�erned bioreceptors

Evanescent op�cal field

Microfiber

Op�miza�on of the diameter of the microfiber

Lines: calcula�onsDots: experiment

Calcula�ons Calcula�ons and experiments

Reflec�vity of the BBG as a func�on of the microfiber diameter

The microfiber diameter was set at 3 �m, as a compromise between reflec�-vity, and fragility and loss. Experiment and simula�on show good agreement.

Mul�plexing BBGs

Lines: calcula�onsDots: experiment

The stamp used for imprin�ng the BSA molecules was rotated to tune the periodof the BBG. Right: tuning of the Braggwavelength as a func�on of the rota�on angle.

Two BBGs of diferent period were fabri-cated on a single microfiber of 3 �m.The two BBGs appear well resolved in the spectrum.[IgG]: 10 �g·mL-1

R (%

)R

(%)

Dose-response immunoassay curve

LOD: 0.1 �g·mL-1LOQ: 0.4 �g·mL-1

A set of 3 �m microfibers were individually fabricated and tested to performa BSA-IgG immunoassay in label-free condi�ons. Experimental data are fi�edto a sigmoidal (logis�c four-parameters) regression, R2 = 0.997.