Lab-on-tip: Protruding-shaped all-fiber plasmonic microtip probe toward in-situ chem-bio detection

Lab-on-tip technology opens a new door for optical fiber surface plasmon resonance (SPR) sensors. In this paper, we first demonstrate an ultra-compact reflective SPR microtip probe on the flat fiber end in experiment, which has a length of tens of microns and a diameter of several microns. Simulations and experiments show that this new fiber SPR microtip probe coated with a nano-goldfilm has excellent refractive index (RI) sensing characteristic and great potential for biochemical detection at single cell level. Based on the high RI sensitivity, a bio-probe assembled with Chitosan/Polysodium Styrene Sulfonate (Cs/PSS) nano-polyelectrolyte film and the sheep anti-human IgG-HRP is prepared to recognize human IgG specifically. Due to the high surface sensitivity, the SPR microtip probe exhibits an ultra-low detection limit for human IgG. Due to the high bulk sensitivity and high thermo-optical coefficient (TOC) of polydimethylsiloxane (PDMS), a reference temperature probe based on SPR microtip is proposed, which is used to compensate for the temperature cross-sensitivity of the bio-probe. This new SPR microtip probe can be used not only in optical fiber sensor, but also in Tip-Enhanced Near-Field Raman Microscopy and Scanning Near-Field Optical Microscope.