structure inside an active layer. To address this issue, here, the doping of Ag on the silk

fibroin was done for the formation of the crystal structure of the silk fibroin to promote

the carrier transmission along the direction of the formed silk fibroin. This resulted in

improved function of the biomemristor device with low operating current, low power,

and tunable performance. There was also research on the development of protein-based

biomemory utilizing multiple chain reactions between metal NPs and biomaterials. For

example, Kwon’s group reported a biological bimodal memory device that mimics the

cooperative and multimodal activation process of biological memory using a tyrosine-

rich peptide assembled film with Ag ions [34]. In this device, multiple redox reactions and

movement of Ag ions were facilitated by high proton conductivity and redox capability of

tyrosine-rich peptides. As a result, when a positive voltage was applied, Ag ions at the

top electrode were formed and migrated to the bottom electrode, showing resistive

switching characteristics similar to that of other resistive switching devices.

Wang’s group developed a resistance-switching device using graphene oxide (GO) and

egg albumen [37]. In this study, GO was used due to its unique properties such as ion

migration, redox reactions induced by electrical fields, and carrier trapping/de-trapping

characteristics. Egg albumen was used because it can form an active or dielectric layer

that is appropriate for the fabrication of resistive switching devices or transistors.

Utilizing these properties of each material, the endurance and uniformity of the device

were improved, and the resistance switching mechanism was demonstrated. As such,

nanomaterials have been applied to the development of protein-based biomemory due to

their outstanding properties, overcoming the defects of biomaterials, and improving the

function of the biomemory devices.

17.4.2 Biologic Gate/Bioprocessor

The combination of nanomaterials and proteins is frequently utilized to implement the

biologic gate functions. Fixler’s group developed a biologic gate based on AuNPs and

fluorescent molecules linked by peptides (Figure 17.5b) [35]. In this biologic gate, the

fluorescence signal generated by the fluorescence molecule (Oregon Green 488) was

quenched by the connected AuNPs. However, this signal was recovered by an increase

in the surrounding pH or when the proteinase (trypsin) decomposed the peptide.

Therefore, by combining the inputs (pH and proteinase), biologic functions (OR, AND,

NOR, NAND, XOR, and XNOR) were demonstrated through the change of emitted

fluorescent signal.

In another study, Nie’s group developed a peptide-mediated NP assembly platform

composed of AuNP and a multi-functional peptide for developing a biologic gate [38].

The multifunctional peptide was composed of two functional motifs, the Zn ion-chelating

part, and the protease substrate part. When only multifunctional peptides and AuNPs

were present in the solution, the multifunctional peptides were attached to the AuNPs to

electrically neutralize the AuNPs, which were originally negatively charged, leading to

aggregation of AuNPs. However, when Zn ions or chymotrypsin were added as inputs,

the structure of the multifunctional peptides was changed so that they cannot be attached

to the AuNPs, and the AuNPs maintained a negative charge. As a result, the AuNPs were

dispersed well, inducing the change of color. By using this phenomenon, biological op­

erations such as AND, OR, INHIBIT, NAND, and IMPLICATION were performed.

Similarly, Yang’s group developed an INHIBIT biologic gate [39]. The melamine and

human serum albumin were used as inputs for aggregation and dispersion of AuNPs,

respectively. Therefore, the INHIBIT biologic gate was demonstrated by adding only

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