Solvatochromic Dyes Increase the Sensitivity of Nanosensors

Organic dyes can be chemically tailored to bind specific molecules and act as molecular sensors or probes. However, they bleach, and most of them fluoresce in the UV–vis range. In contrast, nanomaterials such as single-wall carbon nanotubes (SWCNTs) fluoresce in the near-infrared (NIR) tissue transparency window and are extremely stable. Here, we combine solvatochromic dyes with SWCNTs to create molecular sensors and increase their sensitivity. We find that the dyes trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (t-DSMI) and Reichardt’s dye (Betaine 30) increase the fluorescence responses of DNA-modified SWCNTs to target analytes. With t-DSMI the fluorescence of (GC)₁₅-SWCNT decreases 4 times more in response to pH changes compared to SWCNTs alone. Betaine 30 also boosts the sensitivity of T₂₀-SWCNT for the lipid linoleic acid (LA) more than 2-fold. A kinetic model shows that not the affinity for the analyte but mainly the fluorescence change is increased by the presence of the solvatochromic dyes. This approach provides a flexible design framework to increase the sensitivity of SWCNTs-based biosensors and combines the best of two worlds.