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Modified optical fiber tips with micrometer/sub micrometer dimensions are very promising in the field of Tip enhanced Raman Scattering (TERS), Surface Enhance Raman Scattering (SERS), optical trapping, plasmonic sensor etc. A unique axicon fabricated on the optical fiber tip by simple chemical etching in 48% Hydrofluoric acid (HF) followed by thin film gold (Au) coating by magnetron sputtering is demonstrated for anti-BSA and BSA binding. The dimension of conical axicon is ~2 μm apex at the core of fiber, opening diameter of ~70 μm at the tip and total length of ~300 μm. The inner surface of the hollow negative axicon is coated with thin film of gold. The dielectric tip experiences notable optical field enhancement due to the plasmonic coating. Further, such tip generates non-diffracting Bessel beam which has several advantages including collimation. To monitor the binding process of protein bovine serum albumin (BSA) and anti-BSA, the tip is processed for anti-BSA binding on the surface of the negative axicon. The tip is further tested to bind BSA of different concentrations. For every change in concentration of the BSA, time response curve with respect to variation in wavelength shift was recorded. The tip has shown sensitivity to protein binding process for BSA concentrations of range 10-12 mg/ml to 10-4 mg/ml. The sensor saturates for higher concentration of protein BSA around 10-4 mg/ml. The sensor tends to be very sensitive to proteins of different concentration. This deep seated negative axicon tip based probe can be used for sensing low volumetric bio-samples.
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