A partially passivating core shell particle includes a luminescent nanocrystal core, and a partially passivating semiconducting core shell on a surface of the nanocrystal. The shell allows selected analytes to alter a luminescent response of the core shell particle. A quantum dot-based sensing system includes at least one partially passivating core shell particle, a light source for irradiating the partially passivating core shell particle, and a light detector for receiving emissions from the particle, wherein emissions from the core shell particle change in response to the presence of at least one analyte.