DNA immobilisation and hydrogel matrix formation in suspended-core optical fibre

Recently, microstructured optical fibres (MOFs) have been proposed for sensing [1-3] in a number of new applications made possible by their unique cladding structure. The analyte can be introduced into the fibre voids, where confinement of the sample within the optical mode enhances its interaction with the optical field and allows tailoring of the sensor length. In order to maximize the light interaction with the sample, the sample should be reasonably uniformly distributed inside the fibre so that variations in the refractive index do not inhibit light guidance. Therefore, we have proposed the use of a specifically designed hydrogel for anchoring the analyte within a fibre and we have reported previously such hydrogel formation within a hollow-core photonic crystal fibre (HC-PCF) [3]. In this paper we extend our earlier work to a suspended-core optical fibre with an incircle core diameter of 1.2m, shown in Fig.1 (a). We believe that it will be possible to achieve more effective hydrogel coverage in suspended-core fibre than in HC-PCF. The improved guidance of the light used for the photo-polymerization step of hydrogel formation should produce a hydrogel matrix over a greater length of fibre. Moreover, it is expected that the hydrogel matrix will only partially fill the cladding holes, which should help retain the guiding properties of the fibre at the wavelengths of interest and thus enhance the interaction length. Furthermore, the incomplete filling of the voids in the fibre structure should promote access by the analyte to the hydrogel matrix, which will improve the efficiency of DNA probe hybridisation. In this paper, we show for the first time the formation of a hydrogel matrix in a suspended-core fibre and demonstrate its ability to immobilize a DNA probe.