In fluorophore mediated biosensing and bioimaging, fluorescence emission level control can be beneficial. For example, fluorescence enhancement can improve the sensitivity, and fluorescence quenching caused by a particular molecule can be used to detect that molecule. Since fluorescence is emitted during electron energy transition of a fluorophore, it may be altered when the fluorophore is placed in a plasmon field generated by free electron oscillations. Nanometal particles (NMP) possessing strong surface plasmon field can be effectively used for this fluorescence level control. The field strength is the highest at the surface of the particle and decays exponentially with the distance from the surface and the fluorescence change by NMPs depends on the plasmon field strength where the fluorohpore is placed. In other words, the level of fluorescence may be controlled by controlling the distance between the particle surface and the fluorophore.

One way of controlling the distance is placing a molecular spacer between a particle and a fluorohpore. Here we have correlated the fluorescence emission level (i.e. enhancement or quenching) with the spacer length between a fluorophore and an NMP. The information obtained may be effectively utilized for optimal design of fluorophore mediated biosensing and bioimaging.