Single-walled carbon nanotubes (SWCNTs) with different properties are prepared for applications. The control of the structure of the SWCNTs is important. The analysis of the structure of the pristine and functionalized SWCNTs is needed for biosensor applications. The investigation of the characteristics of the crystal structure of the substances encapsulated inside SWCNTs opens ways to revealing the parameters of the structure. The diameters of the SWCNTs are chosen precisely, and crystal structures are modified for particular applications. It becomes possible to tailor the crystal structure of the compounds in the SWCNTs with different metallicities, diameters, and numbers of walls. The aim of this work is the investigation of the crystal structure in the SWCNTs and modified SWCNTs, and the analysis of the electronic features in modified SWCNTs. The crystal structure of silver chloride inside the SWCNTs with a metallicity-mixed and semiconducting conductivity type was investigated. New one-dimensional structures were obtained inside the SWCNTs with a diameter of 1.4 nm, as revealed by scanning transmission electron microscopy (STEM). The analysis of the electronic features of filled SWCNTs gives information on doping. Raman spectroscopy showed modified electronic properties of the filled metallicity-mixed and semiconducting SWCNTs. Doping was observed in the filled SWCNTs. These data are useful for biosensor applications of filled SWCNTs.