Optical probes enable real-time monitoring of biomarkers in vitro, in vivo, and in cells. Probes based on the fluorescence of semiconducting single-walled carbon nanotubes (SWCNTs) specifically benefit from photostable near-infrared light emissions that are minimally absorbed by biological tissue. SWCNTs are often solubilized by DNA to enable the optical detection of specific bioanalytes. Despite efforts to engineer the selectivity of the DNA sequences towards only specific analytes of interest, these DNA-wrapped sensors are prone to optical perturbations from fluctuations in pH. In this work, we explore the fluorescence effects of DNA-SWCNT in varying pH. We observe a substantial pH effect that varies with the DNA sequence and exploit this pH sensitivity for applications in cancer detection. Using xeno nucleic acids (XNAs), we further engineer optical sensors that show resilience towards fluctuations in pH, enabling the detection of biomarkers in the absence of contributions from varying pH effects.