Nanodiamonds
Nanodiamonds are diamond-structured particles measuring less than 10 nanometers in diameter which result as a residue from a TNT or Hexogen explosion in a contained space. Nanodiamonds have excellent mechanical and optical properties, high surface areas and tunable surface structures. Nanodiamonds have a wide range of potential applications in tribology, drug delivery, bio imaging and tissue engineering, for biomedical applications as they are also non-toxic, as protein mimics and also a filler material for nano composites. Nanodiamonds have perfect mechanical performance and widely used in various industries such as spaceflight, aero plane manufacture, information industry, precision machinery, optical instrument, automobile manufacture, chemical plastics and lubricant etc.
Measuring magnetic fields
Researchers at the University of California, Santa Barbara have developed an electron spin resonance technique involving nanodiamonds and lasers to measure local magnetic fields in liquid environments.
Technique
The technique relies on measuring the electron spin resonance of the NV centres in nanodiamonds which been trapped using optical tweezers. NV centres in nanodiamonds are trapped using a single laser beam that is so tightly focused and dielectric particles are pulled to the beam focus rather than being pushed forwards by the beam. The particles are thus held in the focus, optically levitated and trapped. By moving the laser focus with respect to the fluidic environment the position of placing the particles can be chosen using an all-optical technique without a need for wires or physical contacts.
The electron spin resonance is employed to measure the energy-level structure of the NV centres using Zeeman effect to monitor the magnetic fields detected by the NV sensors in the nanodiamonds.
Uses 
The method could be used to monitor a wide range of phenomena that occur in biological cellular processes, study devices like electrochemical cells, understanding biological electrochemical cells, surface catalysis or lipid membranes to visualize important biological and chemical structures that may be difficult to probe with conventional techniques and even image electromagnetic fields around neurons in the brain.
The nitrogen-vacancy (NV) centre in diamond has a long spin coherence time even at room temperature and so the quantum spins in the defect take time to flip from their original positions allowing them to be read out reliably and reinitialized when needed. The structures can thus be employed as quantum probes to detect magnetic fields in their surroundings. The nanodiamonds can be placed with nanometre precision at any location in a sample and moved around at will for sensing, tracking and tagging in submicron biophysical systems.