Spectroscopic analysis of different body fluids has been realized by using tapered flat silver halide fiber elements as infrared biosensors. Here, a specially functionalized sensor is presented, which had been prepared by an Nhydroxysuccinimide (NHS) ester derivative containing a reactive thiol group. NHS esters are often used as coupling agents to covalently bind amine-containing biomolecules (e.g., enzymes, antibodies or peptides) for the preparation of bioanalytical sensors of high selectivity. Recently, an immuno-infrared-sensor for Alzheimer disease (AD) screening has been presented based on infrared ATR-measurements with antibody-immobilized Ge-element surfaces for the extraction and analysis of Amyloid-beta (Aβ)-monomers, oligomers, and fibrils from blood plasma and cerebrospinal fluid (CSF). Thereby the biomarker amide I maximum frequency was used for AD classification. Here, for functionalizing the silver halide surfaces different procedures have been investigated, which consider the exchange reaction of the halogen atoms by the thiol-group as one option. Other preparation methods use the chemical reduction of silver ions, either from aqueous salt solutions or of the fiber material itself. A further method uses a first printing of silver nanoparticles on top of the flattened fiber sections. The combination of specific protein immobilization via functionalized silver halide fibers with recently introduced quantum cascade laser spectrometers is very promising for device miniaturization suited for implementation into hospital laboratories or general practitioners’ offices.