I expected we would be doing this using viruses, and there are viruses targeting various tissues/organs. The nanites though are just really Star Trek cool.
While nanoparticles could correspond to viral like carriers. The reason you probably wouldn't want to naively use viral particles is because any viral particle that would likely attack the body naturally would also trigger the immune system. That would decrease the efficacy and could actually increase the likelihood of side effects.
Delivery of Cas9, sgRNA, and associated complexes into cells can occur via viral and non-viral systems. Electroporation of DNA, RNA, or ribonucleocomplexes is a common technique, though it can result in harmful effects on the target cells.[43] Chemical transfection techniques utilizing lipids and peptides have also been used to introduce sgRNAs in complex with Cas9 into cells.[44][45] Types of cells that are more difficult to transfect (e.g. stem cells, neurons, and hematopoietic cells) require more efficient delivery systems, such as those based on lentivirus (LVs), adenovirus (AdV), and adeno-associated virus (AAV).[46][47][48]
