Fiber-cap biosensors for SERS analysis of liquid samples
Optical detection techniques based on surface enhanced Raman spectroscopy (SERS) represents a powerful tool for biosensing applications. Meanwhile, due to the technological advances, different approaches have been investigated to integrate SERS substrates on the tip of optical fibres for molecular probing in liquids. To further demonstrate the perspectives offered by SERS-on-fiber technology for diagnostic purposes, in this study, novel cap-shaped SERS sensors for reversibly coupling with customized multimodal probes were prototyped via low-cost polymer casting of polydimethylsiloxane (PDMS) and further assembling of gold nanoparticles (Au NPs) of varied size and shape. To demonstrate the feasibility of liquids sensing with cap sensors using backside illumination and detection, spectra of rhodamine were acquired by coupling the caps with the fiber. As expected by UV-vis, highest SERS efficiency was observed for NPs-decorated substrates with plasmonic properties in resonance with the irradiation wavelength. Then, SERS biosensors for the specific detection of Amyloid-β (Aβ) neurotoxic biomarker were realized by covalent grafting of Aβ antibodies. As attested by fluorescence images and SERS measurements, biosensors successfully exhibited enhanced Aβ affinity compared to the bare sensors without ligands. Finally, these versatile (bio)sensors represent a powerful tool to transform any milli-sized fibers into functional (bio)sensing platforms with plasmonic and biochemical properties tailored to specific applications.