Quantum-dot cellular automaton (QCA) is a novel nanotechnology that provides a very different computation platform than traditional CMOS, in which polarization of electrons indicates the digital information. This paper demonstrates designing combinational circuits based on quantum-dot cellular automata (QCA) nanotechnology, which offers a way to implement logic and all interconnections with only one homogeneous layer of cells. In this paper, the authors have proposed a novel design of XOR gate. This model proves designing capabilities of combinational circuits that are compatible with QCA gates within nano-scale. Novel adder circuits such as half adders, full adders, which avoid the fore, mentioned noise paths, crossovers by careful clocking organization, have been proposed. Experiment results show that the performance of proposed designs is more efficient than conventional designs. The modular layouts are verified with the freely available QCA Designer tool.