Redox-Active Ultrathin Template of Silk Fibroin: Effect of Secondary Structure on Gold Nanoparticle Reduction

Abstract

We report on an application of silk as an ultrathin redox-active template for controllable, one-step synthesis of gold nanoparticles via control over silk secondary structure. We found that both silk I and silk II molecular layers can facilitate gold nanoparticle formation at ambient conditions, indicating that tyrosine groups are available for metal ion reduction in both forms of silk. We suggest that the presence of β-sheets in silk II facilitates tyrosine ordering thereby resulting in well-dispersed, uniform nanoparticles with diameters of less than 6 nm. In addition, the mineralization does not result in transformation of the silk I secondary structure to silk II. In fact, the silk I structure is stabilized from further transformation into silk II even upon drying. These results are critical for developing a better understanding of silk interfacial behavior and offer an opportunity to design a new class of nanocomposites that combine the beneficial features of silk with those of the nanoparticles.

Flexible Silk–Inorganic Nanocomposites: From Transparent to Highly Reflective

“…[35] Indeed, silk deposited from aqueous solutions as silk I (random coil) is partially transferred into silk II (random coils þ ß sheets) followed by the strengthening of interlayer interactions. [61] In the case of composite membranes, the additional interactions between silk and its counterparts contribute to the interlayer binding leading to reinforced mechanical properties. Moreover, our results indicate that methanol, which enhances crystallization of silk and induces chain rearrangement, [36] does not effect the silk/nanofiller interfaces as the methanol-treated films remain stable in solution for the same amount of time as the films without methanol treatment.…”

Silk‐on‐Silk Layer‐by‐Layer Microcapsules

“…[ 46 , 73 ] Multilayered silk fi lm was prepared on an ATR crystal as described in a previous publication. [ 47 ] Zeta-Potential Measurements: Surface potentials of bare and coated silica particles were measured from aqueous solutions on Zetasizer Nano-ZS equipment (Malvern). Each value of the zeta-potential was obtained at ambient conditions by averaging three independent measurements of 35 sub-runs each.…”

“…The shell thickness determined this way increased stepwise from 10 ± 2 to 54 ± 11 nm which is a critical confi rmation of an organized LbL assembly with the average increment close to that known Olga Shchepelina , Irina Drachuk , Maneesh K. Gupta , Jeffrey Lin , and Vladimir V. Tsukruk * fi lm deposited by spin-assisted LbL was thoroughly described in our previous publication, where four major bands were described: two of them centered at 1688 and 1623 cm − 1 and associated with β -sheets and two bands at 1645 and 1661 cm − 1 attributed to random coils ( Figure 3 ). [ 47 ] Methanol treatment during capsule preparation induces the conformational transition from silk I to silk II by dehydration, which promotes the formation of a hydrogen bonding network and β -sheet formation. Thus, we can conclude that treatment with HF does not change mixed (random and β -sheet) secondary structures typical for conventional silk LbL fi lms.…”

Written‐in Conductive Patterns on Robust Graphene Oxide Biopaper by Electrochemical Microstamping

“…These robust biopapers with excellent wet stability that facilitates the writing-in technique were assembled by replacing synthetic binders with a heterogeneous hydrophilic-hydrophobic biopolymer "binder"-silk fibroin, which matches the random domain surface functionalities of graphene oxides. [30][31][32] Moreover, in contrast to other synthetic binders, silk fibroin is mechanically strong, optically transparent, biocompatible, biodegradable, and can serve as an additional reducing agent. [33,34] Vacuum-assisted filtration was used to fabricate layered "paper" from the homogeneous mixture of graphene oxide and silk fibroin similar to literature methods but with special efforts to prevent fast coagulation of biopolymer solution (see Experimental Section and Supporting Information).…”