Methods, structures, devices and systems are disclosed for implementing a photothermal therapy using nanostructures. In one aspect, a device to produce a photothermal effect includes a particle having a molecular layer functionalized onto the external surface of the particle and structured to attach to one or more targeting molecules capable of binding to a receptor site of a cell, in which the particle is configured to absorb light energy at a particular wavelength to produce a plasmon resonance effect that causes the particle to emit heat energy. In some implementations, the device is deployed in an organism having a tumor that includes a plurality of the cell and binds to the receptor site of the tumor by the targeting molecules, in which the light energy is emitted at a region of the organism that contains the tumor and the heat energy causes cellular death of the tumor cell.