Nanorobotics is the study of robotics at the nanometer scale and includes robots that are nanoscale & large robots capable of manipulating objects that have dimensions in the nanoscale range with nanometer resolution.With the ability to position & orient nanometer scale objects,nanorobotic manipulation is a promising way to enable the assembly of nanosystems including nanorobots. Nanomachines are largely in the research & development phase,but some primitive molecular machines have been tested.An example is a sensor having a switch approximately 1.5 nanometers across,capable of counting specific molecules in a chemical sample.The first useful applications of nanomachines might be in medical technology,which could be used to identify & destroy cancer cells.Another potential application is the detection of toxic chemicals,and the measurement of their concentrations,in the environment. Since nanorobots would be microscopic in size,it would probably be necessary for very large numbers of them to work together to perform microscopic and macroscopic tasks.These nanorobots swarms,both these incapable of replication & those capable of unconstrained replication in the natural environment.