Implementation of cascade logic gates and majority logic gate on a simple and universal molecular platform

Abstract

Wiring a series of simple logic gates to process complex data is significantly important and a large challenge for untraditional molecular computing systems. The programmable property of DNA endows its powerful application in molecular computing. In our investigation, it was found that DNA exhibits excellent peroxidase-like activity in a colorimetric system of TMB/H₂O₂/Hemin (TMB, 3,3', 5,5'-Tetramethylbenzidine) in the presence of K⁺ and Cu²⁺, which is significantly inhibited by the addition of an antioxidant. According to the modulated catalytic activity of this DNA-based catalyst, three cascade logic gates including AND-OR-INH (INHIBIT), AND-INH and OR-INH were successfully constructed. Interestingly, by only modulating the concentration of Cu²⁺, a majority logic gate with a single-vote veto function was realized following the same threshold value as that of the cascade logic gates. The strategy is quite straightforward and versatile and provides an instructive method for constructing multiple logic gates on a simple platform to implement complex molecular computing.

Figure 1

Operation principles for the developed cascade logic gates and majority logic gate with single-vote veto. G-DNA and K⁺ has low catalytic activity and cannot cause obvious color change of the platform. The peroxidase-like activity of Cu²⁺ is related to the concentration of Cu²⁺, which is enhanced with increasing the concentration. The combinations of any two or three of G-DNA, K⁺ and Cu²⁺ exhibits excellent catalytic activity, transferring the solution color into yellow. Differently, antioxidant of TBHQ strongly inhibits the colorimetric reaction.

Figure 2

(A) UV-vis absorption spectra of the logic gate system in the absence of any input (a) and in the presence of IN1 (b), IN2 (c) and IN1 + IN2 (d). (B) The absorption intensity of the logic gate system at 452 nm (A_452nm) against various input combinations. (C) The truth table of AND logic gate. Here, IN1 and IN2 are G-DNA (400 nM) and K⁺ (20 mM), respectively. The error bar (mean ± SD) is obtained according to three independent experimental results.

Figure 3

UV-vis absorption spectra of the colorimetric system against Cu²⁺ with concentrations: 0, 1, 5, 10, 20, 25, 30, 40 μM from a to h (A) and against input combinations: (IN1 + IN3, a), (IN2 + IN3, b), (IN1 + IN2 + IN3, c) and (IN1 + IN2 + IN3 + TBHQ, d) (B). Column bar of A_452nm against input combinations (C): a’) absence of the inputs, b’) IN1, c’) IN2, d’) IN1 + IN2, e’) IN3, f’) IN1 + IN3, g’) IN2 + IN3, h’) IN1 + IN2 + IN3, i’) IN4, j’) IN1 + IN4, k’) IN2 + IN4, l’) IN1 + IN2 + IN4, m’) IN3 + IN4, n’) IN1 + IN3 + IN4, o’) IN2 + IN3 + IN4, p’) IN1 + IN2 + IN3 + IN4. Here, the IN1, IN2, IN3 and IN4 are G-DNA (400 nM), K⁺ (20 mM), Cu²⁺ (40 μM) and TBHQ (10 μM), respectively. (D) Truth table of AND-OR logic circuit. The error bar (mean ± SD) is obtained according to three independent experimental results.

Figure 4

Truth table of the cascade AND-OR-INH logic gate with corresponding logic circuit.

Figure 5

(A) Column bar of A_452nm against input combinations with logic circuit scheme. (B) The corresponding truth table of the majority logic gate. Here, the IN_M1, IN_M2 and IN_M3 are G-DNA (400 nM), K⁺ (20 mM) and Cu²⁺ (20 μM), respectively. The error bar (mean ± SD) is obtained according to three independent experimental results.