Here comes the nanobots, not quite

Nanorobotics is the emerging technology field creating machines or robots whose components are at or close to the scale of a nanometer (10−9 meters). More specifically, nanorobotics refers to the nanotechnology engineering discipline of designing and building nanorobots, with devices ranging in size from 0.1–10 micrometers and constructed of nanoscale or molecular components. The names nanobots, nanoids, nanites, nanomachines or nanomites have also been used to describe these devices currently under research and development.
Nanomachines are largely in the research-and-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 and destroy cancer cells.
Another potential application is the detection of toxic chemicals, and the measurement of their concentrations, in the environment. Rice University has demonstrated a single-molecule car developed by a chemical process and including buckyballs for wheels. It is actuated by controlling the environmental temperature and by positioning a scanning tunneling microscope tip.

Another definition is a robot that allows precision interactions with nanoscale objects, or can manipulate with nanoscale resolution. Such devices are more related to microscopy or scanning probe microscopy, instead of the description of nanorobots as molecular machine. Following the microscopy definition even a large apparatus such as an atomic force microscope can be considered a nanorobotic instrument when configured to perform nanomanipulation. For this perspective, macroscale robots or microrobots that can move with nanoscale precision can also be considered nanorobots.
Previous research by Stanford University had revealed the potential for gold nanoparticles to "tag" cancerous cells. The nanoparticles were coated in imaging reagents before being introduced to brain tumour patients. "We hypothesised that these particles, injected intravenously, would preferentially home in on tumours but not healthy brain tissue," said lead radiologist on the case Sam Gambhir. This, he added, is down to the fact that, "the tiny blood vessels that feed a brain tumour are leaky, so we hoped that the spheres would bleed out of these vessels and lodge in nearby tumour material." They did just that. Using MRI, photoacoustic and Raman imaging, the coated particles could be picked out and act as a map of the brain tumours. All that was left to do was activate the gold nanoparticles so that they could go from passive mapping tools to weapons.

The treatment involves introducing radioactive gold nanoparticles directly to a prostate tumour, causing it to shrink. Sandra Axiak-Bechtel, an assistant professor of oncology at the University of Missouri (MU) College of Veterinary Medicine explains: "We deliver the gold nanoparticles using CT guided injection; they are radioactive; and the gum arabic coating keeps the nanoparticles from aggregating (normally, with no coating, the nanoparticles clump together; with gum Arabic, they can freely diffuse through the tumour without any clumping). Because the nanoparticles are so small, the injection appears as a purple liquid, and because dog prostate tumors are so large, we inject in multiple different sites."

Thus far, it has produced no side effects in the dogs taking part and has also been successful in shrinking tumours in mice. The doses required are thousands of times smaller than those used in chemotherapy, and it can also be introduced directly to the tumour, rather than passing into disease-free tissue and organs. The side effects are monitored by taking blood tests looking for "systemic toxicity" and using CT scans to look for "local toxicity" (swelling, infection) some four weeks after treatment. researchers found no statistically significant differences in bloodwork parameters for bone marrow, kidneys, and liver. In dogs that had a CT scan four weeks after treatment, there was no evidence of tumour swelling or infection.
Another method of a medical cure is to use magnetic fields on nanoparticles, a MRI machine can be used for robotic navigation, you must know something about how it works. The bulk of the machine is a powerful, doughnut-shaped superconducting magnet that generates a magnetic field up to about 60 000 times as strong as Earth’s. In medical imaging, the field’s purpose is to align the spin of protons—the nuclei of hydrogen atoms—in the body. (A spinning proton acts as a sort of bar magnet; like a compass needle, it points in the direction of a surrounding field.) Tucked inside the big magnet is the RF coil, which transmits radio-frequency waves. When the frequency of a wave pulse matches the spin rate of the protons, the spin “flips” direction by 90 degrees. When the pulse ends, the protons relax back to their original alignment, a lower energy state. The lost energy departs as a radio signal, which is picked up by a receiver. The density of signals gives information about the molecular makeup of bodily tissues—distinguishing bone from blood, white matter from gray matter, tumors from healthy tissue.

Knowing where in the body the signals originate requires yet another set of coils. Sandwiched between the main magnet and the RF coil, the gradient coils generate a magnetic field that makes the main field stronger in some places and weaker in others. This variation changes the frequency of the protons’ signals depending on their location in the field, which allows a computer to calculate their location in the body. By pulsing the gradient and RF coils on and off in various configurations, the machine produces a three-dimensional picture. It’s the gradient field that typically makes metal objects problematic in an MRI machine. Because the magnetic force the field exerts is uneven, it can slingshot an object through the body.

Sad to say nanobots haven't achieved the level of sophistication most people would assume when looking at the photos in this article. The main success is that nanoparticles if its gold or ferro magnetic can be injected into the main diseased area and the particle (some of which will be absorbed into the affected cell)  can be heated up or have an active chemo ingredient which shrinks tumours or other forms of cancer. Bots can't navigate themselves or have the recognition skills of white blood-cells just yet. Futurists like Ray kurzweil might have ambitious hopes for a micro robot actively repairing your body, but the truth is its early days for any kind of robot. The need for a power source and computational intelligence is difficult in the normal world so nano machines will have to wait within the realms of science fiction. Despite the debunking of micro medical bots, there is advancement in small components such as nano switches and dancing robots on chips. Nanomachines on silicon surfaces controlled my electromagnetic fields or electrical changes, can be controlled in this case for a football game. Using exterior intelligence you can manipulate a complex football game but without the operator the game would not even start.
In the many many many years to come we might have more passive systems for nanoparticles with will help for medical purposes, but its a long road to reach the realms of science fiction and repair bots.
Passive systems are more feasible they might allow a slow release of drugs over time or as a diagnostic tool which sends back images or data back to the doctor. Its likely that nano scale particles will be used as a method to fight different types of cancer, or as a diagnostic tool for identifying blocked blood arteries or internal bleeding.
Considering the possibilities for a passive ways nanoparticles can help, the use of nano sized particle in drug form or using essential minerals to revitalize cells from cell death could be reachable within a few years. Possibly robots could one day exist as servants, but on a nanoscale repairing the human body is more complex than anyone can imagine...