Gold Enhanced Hemoglobin Interaction in a Fabry–Pérot Based Optical Fiber Sensor for Measurement of Blood Refractive Index

A Fabry-Pérot based optical fiber sensor to measure the oxygen concentration through monitoring the change of refractive index in red blood cells is reported. The optical fiber sensor with a diameter of 220 μm is made entirely of fused silica glass fibers, which can be integrated within standard brachytherapy seed delivery needle to be used in vivo. Isopropanol solution and pig blood are prepared to produce refractive index in the range 1.344-1.365. Gold is coated to a thickness of 100 nm at the tip of the sensor to enhance the interaction between hemoglobin and light. A fast Fourier transform algorithm is used to analyze the phase angle from the reflected output spectrum. The gold-coated sensor has up to almost ten times higher sensitivity to hemoglobin concentration in blood solutions compared to isopropanol solutions. A sensitivity of 9.82 rad/RIU with a refractive index resolution of 2.09 × 10
^-3
RIU is achieved for the sensor with a 16 μm thickness diaphragm.