Colloidal silicon crystallites in the size range of 1-12 nm, also referred to as “silicon nanocrystals” have unique optical properties that include high quantum efficiency, size-dependent emission spanning the visible to near-infrared range, and robust photostability. These features, combined with silicon’s high earth-abundance and good biocompatibility, make them an attractive option to serve as signal transduction elements in bioanalytical sensors. In this study, we combine silicon nanocrystals with a sodium-selective ionophore and a charge balancing additive in polymeric nanosensors to create a Silicon Nanocrystal NanoSensor (SiNC-NS). The SiNC-NS responded to sodium through a decrease in fluorescence intensity without the inclusion of a pH-sensitive absorbing dye which is sometimes included in analogous sensors for signal gating, leading to a sensor design with more photostable components. The SiNC-NS has a biologically relevant dynamic range of 4 – 277 mM Na+, is selective against potentially interfering cations, and its response is reversible between 0 and 2 M Na+ for at least three cycles. This work shows the first sodium-responsive silicon nanocrystal-based sensor, the first use of silicon nanocrystals in polymeric nanosensors, and demonstrates an intriguing ionophore-mediated response in silicon nanocrystals to be explored further in the future.