Читать книгу Handbook of Intelligent Computing and Optimization for Sustainable Development - Группа авторов - Страница 61

After the demonstration of DNA logic gates based on hybridization of the strands and the conformational deviations of the secondary structures, the challenge is to build large, reliable circuits. These circuits can be implemented by the set of Boolean logic functions which uses short oligonucleotides as input as well as output and thus can be cascaded to construct multilayer circuits.

The two drawbacks for which may fail are listed below:

 • the gate may be unsuccessful to release enough output signal when it is triggered;

 • the spontaneous release of the output signal may lead to gate “leak”.

These disadvantages can be repaired by signal restoration. The first drawback can be fixed by increasing a moderate output amount to the full activation level; the second drawback can be fixed by decreasing a small output amount to a negligible level.

Amplifier gate and threshold gate should be developed to implement signal restoration. The signal restoration module is composed of a threshold gate and amplifier gate. The amalgamation of it confirms the stability of digital representation of the large circuit.

The threshold gate is composed of three-input AND gate where the first input signal and the third input signal are identical. The second input signal, which is the part of threshold unit, is required only for structural reason. Here, the output is unable to surpass half the input signal. For this reason, subsequent amplification is needed for threshold gate. The system can be used as input amplifier and full translator or as fluorescence readout with slight alteration.

Amplifier gate, which is a two-gate feedback circuit, is based on feedback logic. It can linearly amplify the fluorescence output signal with time without releasing it. The two translator gates of the circuit are designed in such a way that the output of the first gate serves as the input of the second one and the output of the second gate serves as the input of the first one.

The researchers [8] have composed a larger circuit combining the predesigned subcircuits consisting of eleven gates to demonstrate modularity and scalability. The inputs to the circuit are DNA analogs of six mouse microRNAs. This experiment discloses that natural RNA sequences can also be used as the input signals logic gates instead of DNA sequences.