Single-walled carbon nanotubes (SWCNT) are exceptionally photostable fluorophores that emit in the near-infrared range. Their novel physical and chemical properties make them particularly appealing as optical probes for microscopy and spectroscopy. The π-electron rich side wall of SWCNT allows various biopolymers to be conjugated through π-π stacking, enabling novel applications in biology and medicine. In particular, oligonucleotides (DNA or RNA) have been widely used to functionalize SWCNT due to its specific base-pairing properties and programmability. Here we demonstrate the use of DNA-SWCNT hybrid nanomaterial in fundamental biophysics research and biomolecular sensing applications. In the first system, we show SWCNT can be used as a photo-stable imaging probe for optically tracking DNA walker's transport characteristics. DNA walkers are synthetic nanosystems that exploit the structural specificity and functional diversity of oligonucleotides to mimic intracellular protein motors. We integrated a DNA walker system onto SWCNT and demonstrated transportation of quantum dots along SWCNT track. We used localization microscopy and single-particle tracking to record the displacement time series of multiple walkers, which is then used to build the statistical distribution of speed, displacement and walking turnover time. The statistical characteristics of the system help extract time averaged and ensemble averaged walker kinetics, which provide biochemical and biophysical insights about the system. In the second system, we demonstrate using aptamer-SWCNT as a novel sensor architecture for biomolecular detection. We non-covalently functionalized SWCNT with porphyrin binding aptamers, which retains aptamer's target specificity and nanotube's optical property. We discovered the photoluminescence of aptamer-SWCNT is selectively quenched upon binding to heme, an iron-containing porphyrin present in diverse biological processes. The aptamer-SWCNT complex also serves as a quencher for the intrinsic fluorescence of porphyrins. We propose the two optical transduction signatures are induced by specific binding of aptamer to heme and non-specific adsorption of other porphyrin species on the side wall of SWCNT. Using these two properties, we developed a sensing mechanism for four porphyrin species present in the biosynthetic pathway, and demonstrated multiplexed porphyrin detection in blood plasma. Our work shows that SWCNT is a useful optical material for both fundamental biomolecular engineering research and biomedical applications.