Label-free and selective nonlinear fiber-optical biosensing

Abstract

We demonstrate that the inherent nonlinearity of a microstructured optical fiber (MOF) may be used to achieve label-free selective biosensing, thereby eliminating the need for post-processing of the fiber. This first nonlinear biosensor utilizes a change in the modulational instability (MI) gain spectrum (a shift of the Stokes- or anti-Stokes wavelength) caused by the selective capture of biomolecules by a sensor layer immobilised on the walls of the holes in the fiber. We find that such changes in the MI gain spectrum can be made detectable, and that engineering of the dispersion is important for optimizing the sensitivity. The nonlinear sensor shows a sensitivity of around 10.4 nm/nm, defined as the shift in resonance wavelength per nm biolayer, which is a factor of 7.5 higher than the hitherto only demonstrated label-free MOF biosensor.

Refractive Index Sensing in an All-Solid Twin-Core Photonic Bandgap Fiber

“…From (3), the coupling wavelength, , is defined by (5) and therefore the sensitivity of spectral sensing scheme is (6) III. CONCLUSION…”

“…For the spectral sensing scheme, the sensitivity [given by (6)] is maximized when is independent of wavelength, i.e., at the long wavelength edge of the bandgap, and increases with the number of coupling lengths. An example was given of a sensor one coupling length long, in this case 334…”

“…The best sensitivities of label-free MOF biosensors to date have been reported in devices in which the analyte modifies the phase matching, or peak coupling wavelength, between coupled modes. For example, Rindorf et al demonstrated a sensitivity of 1.4 nm shift of a long-period grating resonance per nm biolayer (1.4 nm/nm) [5], and Ott et al [6] predicted a sensitivity of 10.4 nm/nm in a four-wave mixing-based label-free biosensor. Wu et al [9] recently demonstrated a sensitivity of 30 100 nm per refractive index unit (nm/RIU) in a refractive index guiding twin-core silica MOF operating just above cutoff of the selectively filled analyte channel, shown schematically in Fig.…”

Nonlinear fiber-optic strain sensor based on four-wave mixing in microstructured optical fiber

“…The fiber-optic FWM sensor technology can offer high sensitivity due to the extreme sensitivity of FWM to the dispersion profile [7] and it does not require fiber postprocessing. It was recently verified that highly sensitive refractive index sensing, and thus also biosensing, can indeed be achieved with the FWM technique [6,8].…”

“…It has been proposed to instead use the Stokes and anti-Stokes lines generated by nonlinear degenerate four-wave mixing (FWM) [5] in a microstructured optical fiber (MOF) to achieve highly efficient sensing of materials infiltrated into the holes [6]. The fiber-optic FWM sensor technology can offer high sensitivity due to the extreme sensitivity of FWM to the dispersion profile [7] and it does not require fiber postprocessing.…”