Surface plasmon-based nanosensor, comprising: at least one first element of metal, preferably silver or gold, or of semiconductor, the first element being excitable to surface Plasmon resonance, in particular localized surface plasmon resonance, in the presence of electromagnetic radiation from a source, and at least one second element preferably near the first element that in the presence of the electromagnetic radiation is exciton-plasmon coupled to the first element and emits electromagnetic radiation representative of the exciton-plasmon coupling, and systems and methods for sensing photons and chemical or biological agents.