Abstract
Detecting small quantities of specific target molecules is of major importance within bioanalytics for efficient disease diagnostics. One promising sensing approach relies on combining plasmonically-active waveguides with microfluidics yielding an easy-to-use sensing platform. Here we introduce suspended-core fibres containing immobilised plasmonic nanoparticles surrounding the guiding core as a concept for an entirely integrated optofluidic platform for efficient refractive index sensing. Due to the extremely small optical core and the large adjacent microfluidic channels, over two orders of magnitude of nanoparticle coverage densities have been accessed with millimetre-long sample lengths showing refractive index sensitivities of 170 nm/RIU for aqueous analytes where the fibre interior is functionalised by gold nanospheres. Our concept represents a fully integrated optofluidic sensing system demanding small sample volumes and allowing for real-time analyte monitoring, both of which are highly relevant within invasive bioanalytics, particularly within molecular disease diagnostics and environmental science.
Highlights
The non-invasive detection of life-threatening disease is a major challenge in biomedicine, since it requires identifying pathogens of extremely low concentration or even on the single molecular level [1,2,3]
Due to the extremely small optical core and the large adjacent microfluidic channels, over two orders of magnitude of nanoparticle coverage densities have been accessed with millimetre-long sample lengths showing refractive index sensitivities of 170 nm/RIU for aqueous analytes where the fibre interior is functionalised by gold nanospheres
The fundamental working principle of NP-enhanced SCFs relies on the interaction of the propagating guided mode with the localised surface plasmon resonances (LSPRs) of the NPs, whereby the characteristics of the plasmonic resonance are impressed on the spectral distribution of the transmitted light
Summary
The non-invasive detection of life-threatening disease is a major challenge in biomedicine, since it requires identifying pathogens of extremely low concentration or even on the single molecular level [1,2,3]. Almost all fibre-integrated plasmonic sensors involve multi- or single-mode optical tapers which have been coated either with continuous metallic nanofilms [19,20] or plasmonic NPs [21,22,23] These systems have displayed refractive index (RI) sensing capabilities, the NPs are located on the outer surface of the taper, yielding non-integrated and delicate-to-handle devices with further disadvantages including the requirement for large analyte volumes with only a fraction used for the actual sensing. Three or four of these channels are arranged such to form a central micrometre-size glass core resembling the geometry of a step index fibre, with the propagating mode deeply penetrating into the channel via its evanescent field These fibres are attractive from the bioanalytical perspective, as they allow real-time probing of liquid analytes flowing through the channel regions by using the light propagating inside the fibre core. (a) microfluidic channel (b) core section microfluidic channel nano particle silica silica 10 μm
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