The development of complex oxides over the past fifteen years has raised the prospect for new classes of electronic devices. In particular, it has been discovered that a high-mobility two-dimensional electron gas (2DEG) can be formed at the interface between two high-k insulators: LaAlO3 and SrTiO3. More interestingly, in samples with 3-unit-cell LaAlO3 (LAO) film grown on SrTiO3 (STO) substrate, a biased conducting atomic force microscope probe can locally and reversibly control the interfacial metal-insulator transition. This method is capable of patterning arbitrary conducting structures at LAO/STO interfaces with a spatial resolution of only a few nanometers. Based on such technique, various on demand functional nanoelectronic structures such as transistors, diodes and photodetectors have been produced and studied. In the meanwhile, another tempting application lies in the potential of making nanoplasmonic circuits. Doped STO and interfacial 2DEG can support fundamentally different plasmon modes, making the complex oxide interfaces a rich platform for studying plasmonic properties. In addition, we are also exploring the possibility of controlling plasmons based on high mobility Dirac fermions in graphene by integrating graphene with LAO/STO interfaces.