Nanoprobes are a form of nanotechnology, their primary function is to facilitate the assimilation of other species into the Collectives Hive Mind. Each drone's possesses approximately 3.8 million nanoprobes (VOY - "Inside Man"). Each drones nanoprobes have a unique encoding sequence (VOY - "One") and modify themselves the specific subjects physiology (VOY - "Mortal Coil". A series of nanoprobes are typically injected into the victims bloodstream via assimilation tubules housed within the knuckles of all Borg drones. Despite how identical they may appear there are infact multiple types of nanoprobes which are released, each type fulfills a different task during the assimilation process. The Nanoprobes also grant a drastic increase to the subjects immune response allowing it to easily resist almost all known infections.
Type 01 Nanoprobe
Upon entering the blood stream these nanoprobes activate the micro-supercomputers housed within the unit upon their back, transmitting and co-ordernating the actions and progress of the other nanoprobes.
Type 02 Nanoprobe
This device is simultaniously the primary and most nanoprobe in the assimilation process, temporarily attaching itself to the lifeforms bloodcells and using the micro hypo-spray it begins injecting them with a retro-virus which beguns immediately rewriting the DNA coding of the cell, modifying multiple aspects of the lifeforms biology and assuming control over the victims cellular functions.
Type 03 Nanoprobe
Once entering the bloodstream of the victim, this device quite simply uses the micro-replicating unit mounted upon its back to replicate the materials required by type 04 nanoprobes.
Type 04 Nanoprobe
Co-ordinated by the type 01 nanoprobe these nanoprobes divide, 50% proceed immediately to the lifeforms brainstem and with the assistance of type 03 nanoprobes begin constructing the interlink node whilst the remaining 50% proceed to the lifeforms heart and with the assistance of Type 03 Nanoprobes begin constructing additional nanoprobes. The heart providing a means of immediate dispersal throughout the lifeforms entire body, think of it as the nanoprobes version of the transwarp hub.
Type 05 Nanoprobe
These nanoprobes are equipped with tine micro sutures, laser scalpels and dirmal regenerators, their purpose is to repair cellular damage including organs and blood vessels, remove blockages and attack any currently existing infections within the lifeforms blood stream/blood cells.
Species 149 possessed knowledge involving nanoprobes for the reanimation of a lifeform as long as 73 hours following death. Provided the neural pathways are intact, 70 micrograms of nanoprobes which are pre-modified to the specific subjects physiology are sufficient to reverse cellular necrosis while the cereberal cortex is stimulated with a neural electric isopulse at 1 second intervals, Nanoprobes can componsate for any cellular degredation after the technique is completed however the subject required regular doses of additional modified nanoprobes until the victims cells are capable of functioning on their own (VOY - "Mortal Coil").
Nanoprobes have two known weakness; one being the intramoleculor processors being vulnerable to intense doses of omicron radiation, destroying the nanoprobes (ENT - Regeneration). The second weakness is extreme arctic temperatures, freezing both the subject and the nanoprobes. This however does not damage the nanoprobes and will result in their reactivation immediately upon returning to a temperature of 10 to 8 degrees centigrade. (ENT - Regeneration)
The cellular antibodies of Species 8472 are capable of destroying nanoprobes, thus rendering them immune to assimilation.
Nanoprobe Weaponry Due to species 8472's physiology being able to withstand Borg nanoprobes, in 2374 during the Species 8472 war Voyager's doctor was able to modify nanoprobes to mimic the aliens cells electrochemical signatures allowing them to evade detection by their immune system while continuing to assimilate the cells.
Types of Nanoprobes
In Voyager's episode Scorpion I noticed the precise wording the doctor used "releases a SERIES of nanoprobes in-to the blood stream" that made me think there were actually more than one type of nanoprobe and did make a little more sense compared to one type that can do everything from fighting infection, healing and constructing implants all within seconds. For the types I copied off of the general structure of the collective and drone types as they would most design them to follow the same command structure as the Collective themselves.