Quantifying the intrinsic surface charge density and charge-transfer resistance of the graphene-solution interface through bias-free low-level charge measurement

Abstract

Liquid-based bio-applications of graphene require a quantitative understanding of the grapheneliquid interface, with the surface charge density of adsorbed ions, the interfacial charge transfer resistance, and the interfacial charge noise being of particular importance. We quantified these properties through measurements of the zero-bias Faradaic charge-transfer between graphene electrodes and aqueous solutions of varying ionic strength using a reproducible, low-noise, minimally perturbative charge measurement technique. The measurements indicated that adsorbed ions had a negative surface charge density of approximately -32.8 mC m -2 and that the specific charge transfer resistance was 6.5 ± 0.3 MΩ cm 2 . The normalized current noise power spectral density for all ionic concentrations tested collapsed onto a 1/f α characteristic with α=1.1±0.2. All the results are in excellent agreement with predictions of the theory for the

Structural-functional analysis of engineered protein-nanoparticle assemblies using graphene microelectrodes

“…Because there is no extrinsic bias voltage between the solution and the microelectrode, heat dissipation (aW μm –2 ) and electrical perturbation (∼pA) to the protein structure 18 are minimized. In a previous report 15 we documented the intrinsic low noise level for microelectrode measurements in an idealized buffer solution as well as excellent agreement between the data and theoretical models of the behaviour of the electric double layer above graphene.…”

“…1a ) consisted of a graphene-based microelectrode connected to the inverting input of an electrometer 15 (Keithley 6517a). The electrostatic potential above a protein assembly in fluid, ψ f , drives a sub-picoampere faradaic current, i , through the series resistance of the charge-transfer at the graphene–solution interface 15 ( R ct ∼100 GΩ), the graphene sheet ( R □ ∼ 10 2 –10 3 Ω □ –1 ), and the graphene-gold contact 17 ( R c ∼ 10 Ω). Transferred charge accumulates on the feedback capacitor and is read out on the electrometer.…”

“…Here, we demonstrate a non-perturbing method using a graphene microelectrode 15 for structural-functional analysis of an ordered AuNP-ferritin protein assembly that differs substantively from an unstructured protein corona. Charge flowing from the AuNP through ferritin pores transfers into the graphene microelectrode and is recorded by an electrometer.…”

All-Electronic Quantification of Neuropeptide–Receptor Interaction Using a Bias-Free Functionalized Graphene Microelectrode

“…The experimental setup for Faradaic charge measurement 15 is shown in Figure 1a (see Methods for more information regarding the measurement). All measurements were conducted in full-strength phosphate buffer solution (1× PBS).…”

pH Sensing Properties of Flexible, Bias‐Free Graphene Microelectrodes in Complex Fluids: From Phosphate Buffer Solution to Human Serum

“…Here we demonstrate the use of flexible graphene microelectrodes (GEs) for rapid, bias‐free pH measurement in phosphate buffer solution (PBS), ferritin solution in PBS (0.1 × 10 −6 m ), and human serum. The GE fabrication process is based on scalable photolithographic approaches, and the measurements are conducted without using an external bias voltage, so the methodology is intrinsically low‐power and minimally perturbative. We find that the spontaneous Faradaic charge transfer between the GE and PBS is modulated by the pH.…”