formation. Endonucleases of KpnI and StuI resulted in changes in plasmonic wavelength

values because of the cleavage of certain sequences in tsDNA. Through this, the developed

biologic gate performed an OR and XOR logic operation.

Willner’s group developed a biologic gate using GO and two types of DNA modified

with two different fluorescent materials, respectively [51]. The “AND” biologic gate was

initiated by hybridizing these two types of fluorescent modified DNA with com­

plementary DNA (cDNA) and forming a loop structure. Due to the formation of the loop

structure, fluorescent modified DNA generated a strong fluorescence signal because of

detachment from the GO, which is capable of quenching the fluorescent signal. However,

in the presence of target DNA, which had a stronger binding affinity for the cDNA than

the fluorescent modified DNA, the fluorescent modified DNA was adsorbed on the GO

surface and the fluorescence signal was re-quenched. Using this reaction mechanism, a

biological operation was processed using different binding affinities between each single-

stranded DNA. Bi’s group developed a biologic gate composed of AuNP modified with

single-stranded DNA, dumbbell probe (DP), and duplex-specific nuclease (DSN) through

the conformational change of DP using different binding affinities between nucleic acids

and degradation by DSN [52]. In summary, the unique properties of nucleic acids in­

cluding complimentary bonds between nucleic acids and differences in binding affinity

are suitable for implementing biologic functions and processing of complex functions on

the device by combining with functional nanomaterials.

17.5.3 Biotransistor

The performance of the computing system is closely related to transistor density. To

improve the integration level of the transistor, it is necessary to manufacture ultra-

compact transistors. To develop these transistors using biomaterials with nanomaterials,

Yin’s group manufactured a precise CNT transistor array using DNA as a template [53].

Here, the parallel CNT arrays with a uniform nanometer-sized spacing were constructed

by using DNA brick-based nanotrenches to align DNA-wrapped CNTs. For this, the

supramolecular assembly method was used to generate a scaffold composed of com­

pacted DNA. In the fabricated scaffold, some part of the DNA was located on the surface

to hybridize with other DNA that was immobilized on the surface of the CNT. By placing

the CNT on the scaffold, the directionality of individual CNT was precisely controlled.

Moreover, by programming the DNA template differently, CNT was arrayed with uni­

form spacing of 16.8, 12.6, and 10.4 nm using the electrostatic repulsion between DNA

and negatively charged CNT with high stability. In addition, this method enabled the

fabrication of millions of parallel CNT arrays at the same time, which demonstrated the

functionality of the biotransistor.

In addition, Kim’s group patterned the chemically modified graphene and bottom-up

self-assembly of DNA origami to develop a few nanometer-level DNA-based bio­

transistors [54]. It was confirmed that a rectangular DNA origami structure with a size of

2 nm × 70 nm × 90 nm was deposited on patterned nitrogen-doped reduced GO (NrGO)

without folding or overlapping structures. The nucleic acid-based biotransistors have the

potential for developing biosensors by using the property of nucleic acids to hybridize

with aptamers or complementary sequences that selectively bind to target molecules [55].

For example, Han’s group developed a graphene-based FET for miRNA detection

(Figure 17.6c) [49]. In this study, the complementary sequence of the target miRNA was

located at the 3’ end of the probe DNA, and 10 adenine bases were designed at the 5’ end

for attachment to the graphene channel via π-π interactions. By investigating the shift of

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Bioelectronics