eArch3.0 is an engineered optogenetic tool that can be used to induce membrane hyperpolarization and inhibit neuron activity; the peak activation wavelength is 520-560nm. eArch3.0 was generated by adding both an endoplasmic reticulum export signal (FCYENEV from Kir2.1) and a Golgi trafficking signal (from Kir2.1) to the C-terminal end of the naturally occurring outward proton pump encoded by the Halorubrum sodomense Archaerhodopsin-3 (aop3) gene (UniProtKB:P96787). The trafficking signal is upstream of the ER export signal and any fluorescent protein added to a particular transgene or modified endogenous locus as a tag to facilitate detection of the eArch3.0 protein is typically inserted in between the Golgi trafficking and ER export signals (PMID:22179551). For detailed kinetic and spectral properties, see PMID:22179551. For a comparison of eArch3.0 with other neuron inhibition tools, see PMID:22179551.