The discovery and use of fluorescent proteins has been of extreme importance in biological imaging of cells, tissues, and organs. In order to address some of the limitations of fluorescent tags, second harmonic generation can be used. Second harmonic generating nanoprobes allow nontoxic, long-term imaging that, with proper functionalization, can be utilized for biological imaging applications. As a proof of principle, commercial tetragonal barium titanate nanoparticles were functionalized to expose surface amine groups, which could...