We report our observations on the catalytic effect of nitrogen in the growth of diamond on top of a diamond anvil substrate by microwave plasma chemical vapor deposition technique. The diamond deposition experiments were carried out by varying the nitrogen content in the range 0-3500ppm in a standard hydrogen/methane/oxygen plasma. We employ isotopically enriched C-13 methane gas as the source of carbon in the plasma to clearly distinguish the grown diamond layer from the underlying substrate using Raman spectroscopy. The measured diamond growth rate shows a sharp peak at a nitrogen content of 1000ppm in our growth experiments carried out at 1212C and atomic force microscopy reveals a dramatic change in surface morphology. Thermodynamic calculations of the plasma show that this growth enhancement could be the result of a competition between the CN and CH3 radicals in the plasma. Finally, we show an application of this 'unique chemistry' by synthesizing several designer diamonds with embedded sensors for high-pressure materials research experiments.