Metal nanocolloids have received tremendous attention for a wide range of applications. Metal oxidation, however, has traditionally restricted the range of useful nano-metals to silver, platinum, palladium and gold. Technical low cost applications such as ink jet printing of flexible conductors and radio frequency identification (RFID) tags, however, require manufacturing costs of typically less than one cent per tag. The most evident candidate to substitute silver or gold would be copper, but nano-copper rapidly oxidizes under ambient conditions. We demonstrate how deposition of graphene bi- or trilayers on copper can be realized on a technical scale and enables full protection of the copper metal core up to 200 °C under humid air. The protected copper can then be used in domestic ink jet printers for preparation of conductive patterns under ambient conditions. References [1] N. A. Luechinger, N. Booth, G. Heness, S. Bandyopadhyay, R. N. Grass, W. J. Stark, Advanced Materials (2008), in press. [2] N. A. Luechinger, S. Loher, E. K. Athanassiou, R. N. Grass, W. J. Stark, Langmuir, 23, 3473-7 (2007). [3] N. A. Luechinger, E. K. Athanassiou, W. J. Stark, in review (2008) Figure: Flame spray synthesis (a) as a low-cost process for the production of metallic copper nanoparticles (b). Transmission electron micrograph (c) and corresponding model sketch (d) of an air-stable individual copper nanoparticle with a graphene coating. Photographs of ink-jet printed conductive copper patterns showing operating red LED's (e, f).