We introduce novel ultra-sensitive tunable optical nanosensors based on conceptually new physical phenomena and techniques. The core foundation of these sensors is based on molecular-like behavior of hybrid systems consisting of metallic nanoparticles and semiconductor quantum dots when they interact with a laser field (activating field). Therefore, instead of using plasmons or excitons as in conventional sensors, in these nanosensors we utilize the characteristic resonances of such metamolecules (plasmonic metaresonances) caused by coherent exciton-plasmon coupling. It is shown that such resonances can be tuned by changing the intensity of the laser field responsible for activating the nanoparticle-hybrid systems. Therefore, these nanosensors are tunable with significant dynamic range and ultrahigh sensitivity. The proposed optical nanosensors can be used for real-time detection of chemical and biological substances and variation of the physical parameters of nanoscale systems (temperature, conformational changes, etc.).