Development of Collagen-IV Sensor Using Optical Fiber-Based Mach-Zehnder Interferometer Structure

This study presents a label-free and efficient method for the diagnosis of collagen-IV by using an optical fiber-based Mach-Zehnder interferometer (MZI) structure. The structure of MZI is fabricated by splicing a 2.3 cm long segment of single-mode fiber (SMF) between two ~ 45 cm strands of multi-mode fibers (MMF). Owing to the mismatch of core diameters, cladding of SMF guides the light. SMF's cladding is partially etched by using 40% hydrofluoric (HF) acid so that a part of propagating energy is released that can interplay with the surroundings. The etched region is immobilized with ~ 10 nm size of gold nanoparticles (AuNPs) and ~ 50 nm size of copper oxide nanoparticles (CuO-NPs) to initiate the influence of localized surface plasmon resonance (LSPR) phenomenon. For a comparative study, two different probes are developed and analyzed. In one probe, CuO NPs are immobilized over the etched part of SMF and named as CuO-NPs probe. In other probe, a monolayer of AuNPs is sandwiched between fiber surface and CuO-NPs and termed as AuNPs/CuO-NPs probe. The characterization of NPs and developed sensor probe are performed using UV-Vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), and energy distribution spectroscopy (EDS). The sensor probes are made very specific towards collagen-IV by functionalizing them with collagenase enzyme obtained from Clostridium histolyticum. A wide range of Collagen-IV solutions of concentrations from 2 μm/ml to 40 μm/ml are sensed through the collagenase functionalized probe. The specificity of the probes are analyzed by sensing other biomolecules present in the human body.