Fig 1.
DNA logic gate compartmentalization into a droplet and connection of the gates.
Fig 2.
Conceptual diagrams of the DNA relay mechanism.
(a–f) Logic operation using the mechanical splitting and electrical fusion of droplets (YES gate). (a) Three aqueous droplets (prepared as input, logic gate, and output) in mechanically sliding and fixed wells. (b) Contact of the input droplet to the logic gate droplet with sliding motion to form a lipid bilayer. (c) Electrical fusion by lipid bilayer rupture and mixing of single-stranded DNA (ssDNA; binary data) over the droplets: switch-on of the input. (d) Contact of the output droplet to the logic gate droplet with sliding motion to form a lipid bilayer and perform nanopore detection. (e) Electrical fusion and mixing of ssDNA (binary data) over the droplets: switch-on of the output. (f) Output droplet split-off from the logic gate droplet for use as the input droplet of the next logic gate. (g) Translocation of ssDNA, blocking by dsDNA, and no inhibition. Observation of peak-like current inhibition implies the translocation of ssDNA and the storage of ssDNA in the output droplet, leading to output 1. Observation of a long current inhibition implies the blocking of α-hemolysin nanopore by dsDNA, and no DNA strand is stored in the logic gate droplet, resulting in output 0. Alternatively, no inhibition implies no ssDNA and, therefore, the output is 0.
Fig 3.
Working principle of the NOR operation.
(a) OR gate (left panel): after the OR input droplet A is contacted by the OR gate droplet, the two droplets are fused to initiate mixing of the contents. The same procedure is performed for the OR input droplet B. The OR gate droplet and OR output droplet are fused and mixed. Then, the OR output droplet is slid to the NOT gate region. Note that the OR output droplet is used as the NOT input droplet. NOT gate (right panel): the NOT input droplet is contacted to and fused with the NOT gate droplet. The NOT output droplet is then contacted to the NOT gate droplet. Finally, the binary number in the NOT output droplet is detected by the observation of ssDNA translocation or dsDNA blocking. (b) A perspective view of the sliding well and the oil reservoir. (c) Corresponding logic circuit represented in MIL logic symbols.
Table 1.
Truth table of the NOR gate.
Fig 4.
Device images and electrical measurement.
(a) Photograph of the device. Ag/AgCl electrodes are places on the bottom of the oil reservoirs and fixed wells, which are connected to an amplifier through Ag wires beneath the reservoir layer. (b) Enlarged view of a sliding well. (c) Poly(methyl methacrylate) (PMMA) separator with a micropore installed between the sliding wells and fixed wells. (d) Electrical measurement between two droplets. The black line indicates the current–time trace. The open channel of α-hemolysin was oriented when the current was increased stepwise with conductance (G0) of 1 nS ± 20%. DNA translocation or blocking occurred when the conductance dropped to 60% below the open channel level.
Fig 5.
Experiment to determine mixing duration.
(a–c) Fluorescence images and corresponding schematics at 0, 30, and 60 min after electrical fusion of the droplets. (d) Time-course monitoring of the fluorescence intensity of the donor and acceptor droplets. Error bars: standard deviations (N = 3).
Fig 6.
Procedures and results of the NOR operation.
(a–i) Procedures of the NOR gate. (j–m) Electrical signals and outputs of the NOR operation. (j) Input (0, 0). Peak-like current inhibitions were predominant, and the readout criterion number (RTB) was 0.68 ± 0.20 (i.e., output 1). (k–m) Inputs (0, 1), (1, 0), and (1, 1), respectively. Long current inhibitions were predominant, and the RTB values were −0.36 ± 0.16, −0.76 ± 0.16, and −0.28 ± 0.08, respectively. Thus, these results exhibited output 0.