When I was a child, I read a SciFi story about one guy, who built such an arm. Then using this arm under the microscope he built a set of microscopic tools, etc

When I was a child, I read a SciFi story about one guy, who built such an arm. Then using this arm under the microscope he built a set of microscopic tools, etc. Later in the story he fighting with bacteria and viruses, but because of the feedback of his microscopic arm, he was injured and almost killed by these tiny creatures.