A nanothermometer is disclosed. In various embodiments, a nanothermometer comprises a nanoparticle such as a gold nanoparticle, a fluorophore, and a linker, such as a peptide linker, extending between the nanoparticle and the fluorophore, whereby the fluorophore is self-quenched. The linker can comprise one or more cysteines. An unheated thermometer shows little or no fluorescence. Upon heating, fluorophore-linker conjugates are released from the nanoparticle, thereby unquenching the fluorescence. An increase in fluorescence results. In some embodiments, the increase in fluorescence can be irreversible. Methods of measuring temperature of a sample such as a biological sample, and methods of synthesizing a nanothermometer, are also disclosed. A molecular thermometer is also disclosed.