This study presents a gas vapor sensing approach based on a long tapered side-hole optical fiber (S-H OF) interrogated spectrally in the near-infrared region (1200-1800 nm). The tapered S-H OF section was fusion-spliced to standard single-mode fibers (SMFs) and connected to a supercontinuum source and an optical spectrum analyzer (OSA). The sensing experiments were conducted in a sealed, thermally isolated chamber, where the tapered fiber was exposed to vapors of aqueous ammonia (NH3·H2O) and trimethyl phosphate (TMP) generated from 200 μl liquid samples. Initially,measurements were performed without any functional layer, followed by tests with two biopolymer coatings applied separately: DNA-DODA and DNA-(S)-TMA. The optical power variation (ΔOP) as a function of wavelength and time was recorded for each configuration and compared to the reference fiber without coating. Among the tested biopolymer coatings, DNA–DODA produced the largest optical power changes under exposure to NH3·H2O vapors (ΔOP = 3.84 dBm near 1463 nm and ΔOP = 1.75 dBm near 1504 nm), whereas DNA-(S)-TMA exhibited the strongest response to TMP vapors (ΔOP = 1.19 dBm near 1510 nm and ΔOP = 2.46 dBm near 1780 nm). These findings indicate that the two DNA-based coatings interact differently with the analyzed vapors, enabling analyte-dependent response characteristics. The results highlight the potential of tapered S-H OFs combined with biopolymer functionalization for selective gas vapor detection, offering a simple and effective alternative to more complex sensing architectures.