Ji-ryang Jang

Highly Sensitive Reduced Graphene Oxide Impedance Sensor Harnessing π‑Stacking Interaction Mediated Direct Deposition of Protein Probes

Graphene-based electrochemical impedance sensors have recently received much attention due to their outstanding sensing capability and economic viability. In this study, we present a novel means of constructing an impedance sensing platform via harnessing intrinsic π-stacking interactions between probe protein molecules and reduced graphene oxide (RGO) substrate, obviating the need for introducing external chemical groups often required for covalent anchoring of the probes. To achieve this goal, protein molecules used as a probe were denatured to render their hydrophobic residues exposed in order to facilitate their direct π-stacking interactions with the surface of RGO nanosheets. The protein molecules in denatured form, which would otherwise have difficulty in undergoing π-stacking interactions with the RGO surface, were found to uniformly cover the RGO nanosheets at high density, conducive to providing a graphene-based impedance sensing platform capable of detecting a probe-specific analyte at high sensitivity. The proof-of-concept performance of thus-constructed RGO-based impedance sensors was demonstrated via selective detection of biological binding events of antigen-antibody reaction at a femtomolar range. Notably, since the π-stacking interaction can occur on the entire RGO surface, it can desirably exclude a backfill process indispensable for the conventional biosensors to suppress background noise signals. Since the procedure of π-stacking mediated direct deposition of on-purpose denatured protein probes onto the RGO surface is facile and straightforward, the proposed strategy is anticipated to extend its applicability for fabrication of high performance graphene-based bio or chemical sensors.

The interplay of peptide sequence and local structure in TiO2 biomineralization

Using cyclic constrained TiO(2) binding peptides STB1 (CHKKPSKSC), RSTB1 (CHRRPSRSC) and linear peptide LSTB1 (AHKKPSKSA), it was shown that while affinity of the peptide to TiO(2) is essential to enable TiO(2) biomineralization, other factors such as biomineralization kinetics and peptide local structure need to be considered to predict biomineralization efficacy. Cyclic and linear TiO(2) binding peptides show significantly different biomineralization activities. Cyclic STB1 and RSTB1 could induce TiO(2) precipitation in the presence of titanium(IV)-bis-ammonium-lactato-dihydroxide (TiBALDH) precursor in water or tris buffer at pH 8. In contrast, linear LSTB1 was unable to mineralize TiO(2) under the same experimental conditions despite its high affinity to TiO(2) comparable with STB1 and/or RSTB1. LSTB1 being a flexible molecule could not render the stable condensation of TiBALDH precursor to form TiO(2) particles. However, in the presence of phosphate buffer ions, the structure of LSTB1 is stabilized, leading to efficient condensation of TiBALDH and TiO(2) particle formation. This study demonstrates that peptide-mediated TiO(2) mineralization is governed by a complicated interplay of peptide sequence, local structure, kinetics and the presence of mineralizing aider such as phosphate ions.

Harnessing denatured protein for controllable bipolar doping of a monolayer graphene.

In this work, we demonstrated tunable p- and/or n-type doping of chemical vapor deposition-grown graphene with the use of protein bovine serum albumin (BSA) as a dopant. BSA undergoes protonation or deprotonation reaction subject to solution pH, thereby acting as either an electron donor or an electron acceptor on the graphene surface layered with denatured BSA through π-stacking interaction. This direct annealing of graphene with denatured BSA of amphoteric nature rendered facilitated fabrication of a p- and/or n-type graphene transistor by modulating pH-dependent net charges of the single dopant. Following AFM confirmation of the BSA/graphene interface assembly, the carrier transport properties of BSA-doped graphene transistors were assessed by I-V measurement and Raman spectra to show effective charge modulation of the graphene enabled by BSA doping at various pH conditions. The protein-mediated bipolar doping of graphene demonstrated in our work is simple, scalable, and straightforward; the proposed scheme is therefore expected to provide a useful alternative for fabricating graphene transistors of novel properties and promote their implementation in practice.

Incorporation of a Metal Oxide Interlayer using a Virus-Templated Assembly for Synthesis of Graphene-Electrode-Based Organic Photovoltaics.

UNLABELLED Transition metal oxide (TMO) thin films have been exploited as interlayers for charge extraction between electrodes and active layers in organic photovoltaic (OPV) devices. Additionally, graphene-electrode-based OPVs have received considerable attention as a means to enhance device stability. However, the film deposition process of a TMO thin-film layer onto the graphene electrode is highly restricted owing to the hydrophobic nature of the graphene surface; thus, the preparation of the device should rely on a vacuum process that is incompatible with solution processing. In this study, we present a novel means for creating a thin tungsten oxide (WO3 ) interlayer on a graphene electrode by employing an engineered biotemplate of M13 viruses, whereby nondestructive functionalization of the graphene and uniform synthesis of a WO3 thin interlayer are concurrently achieved. As a result, the incorporated virus-templated WO3 interlayer exhibited solar-conversion efficiency that was 20 % higher than that of conventional OPVs based on the use of a (3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) interlayer. Notably, bilayer-structured OPVs with synergistically integrated WO3 /PEDOT:PSS achieved >60 % enhancement in device performance.