Publication:

Femtomolar detection by nanocoated fiber label-free biosensors

The advent of optical fibre-based biosensors combined with that of nanotechnologies has provided an oppor-tunity for developing in situ, portable, lightweight, versatile and high-performance optical sensing platforms. We report on the generation of lossy mode resonances by the deposition of nm-thick metal oxide films on optical fibres, which makes it possible to measure precisely and accurately the changes in optical properties of the fibre-surrounding medium with very high sensitivity compared to other technology platforms, such as long period gratings or surface plasmon resonances, the gold standard in label-free and real-time biomolecular interaction analysis. This property, combined with the application of specialty structures such as D-shaped fibres, permits enhancing the light-matter interaction. SEM and TEM imaging together with X-EDS tool have been utilised to characterise the two films used, i.e. indium tin oxide and tin dioxide. More-over, the experimental transmission spectra obtained after the deposition of the nanocoatings have been numerically cor-roborated by means of wave propagation methods. With the use of a conventional wavelength interrogation system and ad-hoc developed microfluidics, the shift of the lossy mode resonance can be reliably recorded in response to very low analyte concentrations. Repeated experiments confirm a big leap in performance thanks to the capability to detect femtomolar concentrations in human serum, improving the detection limit by three orders of magnitude when compared with other fibre-based configurations. The biosensor has been regenerated several times by injecting sodium dodecyl sul-phate, which proves the capability of sensor to be reused.