A DNA-based half-adder and half-subtractor

• Main Authors: Chun-yu Hsu, 許純瑜
• Other Authors: Chia-ning Yang
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/17420236855682608778

碩士 === 國立高雄大學 === 生物科技研究所 === 99 === As nanotechnology has become a principal research interest, nano-scale devices that can be built by either top-down or bottom-up approach are widely studied. After Adleman introduced DNA computing to solve travelling salesman problems in 1994, several works using a similar concept have been proposed theoretically and/or proved by experiments to demonstrate the possibility that designed DNA sequences can serve as elementary computing devices. The present study demonstrates two DNA-based logic circuits capable of performing addition and subtraction. A logic half-adder circuit adds two binary digits and outputs two binary digits: sum-bit and carry-bit, generated by an XOR and an AND logic gate, respectively. Likewise, a logic circuit of half-subtractor takes two binary digits for subtraction and outputs two binary digits, including borrow-bit and difference-bit by an INH and an AND logic gate, respectively. The constructed systems in this study are based on the concept of molecular beacon, which commonly serves as a DNA probe. In short, a molecular beacon is a DNA sequence labeled by a fluorophore at 5’ end and a corresponding quencher at 3’ end. Without recognizing any substrate, the DNA sequence is in a hairpin conformation (with a loop in the single-strand and a stem in the double-strand by hybridizing its two ends) and the fluorescence is quenched by the nearby quencher. Upon hybridization with a substrate whose sequence is partially or entirely complementary to the hairpin, the molecular beacon opens up and this conformational change causes the fluorophore to stay away from the quencher and shine. In the close and open forms of hairpin, the fluorescence signal is off and on and this phenomenon is perfect for “0” and “1” readings as in Boolean logic operations. The present design uses molecular beacon-like DNA strands as gate molecules whereas the substrates are used as inputs to control the on/off states of the fluorescence signal. More sophisticated arrangements allow one input strand labeled with a fluorophore to be switched between on and off states by the interplay among the gate molecule and the other input strand. We believe the present design is rather concise compared to two previously reported DNA-based Boolean circuits for half-adders.