Ion-Selective Membrane-Coated Graphene–Hexagonal Boron Nitride Heterostructures for Field-Effect Ion Sensing

Abstract

An intrinsic ion sensitivity exceeding the Nernst–Boltzmann limit and an sp 2 -hybridized carbon structure make graphene a promising channel material for realizing ion-sensitive field-effect transistors with a stable solid–liquid interface under biased conditions in buffered salt solutions. Here, we examine the performance of graphene field-effect transistors coated with ion-selective membranes as a tool to selectively detect changes in concentrations of Ca2+, K+, and Na+ in individual salt solutions as well as in buffered Locke’s solution. Both the shift in the Dirac point and transconductance could be measured as a function of ion concentration with repeatability exceeding 99.5% and reproducibility exceeding 98% over 60 days. However, an enhancement of selectivity, by about an order magnitude or more, was observed using transconductance as the indicator when compared to Dirac voltage, which is the only factor reported to date. Fabricating a hexagonal boron nitride multilayer between graphene and oxide further increased the ion sensitivity and selectivity of transconductance. These findings incite investigating ion sensitivity of transconductance in alternative architectures as well as urge the exploration of graphene transistor arrays for biomedical applications.

Rapid and Convenient Potentiometric Method for Determining Fluorosulfate, a Byproduct of the Fumigant and Greenhouse Gas Sulfuryl Fluoride

“…The potentiometric response may depend on the pH of the sample before it is combined with the ISA due to the high mobility of hydrogen and hydroxide ions which will interfere the liquid-junction potential of the electrode. 43 , 45 , 48 , 56 Confirming this ( Figure 2 ), the slope of the fitting line ranges from −74.99 mV/decade at pH 3.0 to −40.86 mV/decade at pH 11.0. At the extreme pH values of 3.0 and 11.0, the fits are noticeably poorer, and the slopes deviate substantially from the theoretical value of −59 mV/decade compared to the corresponding fits and values at pH 5, 7, and 9.…”

“…The nitrate ion exchanger is contained within a gelled, organophilic electrode membrane. When the electrode is inserted into a solution, ion exchange will take place between the membrane and specific ions, resulting in a redox potential difference obeying the Nikolsky-Eisenman equation (eq ), a generalization of the Nernst equation, − where E is the measured electrode potential; E 0 is constant potential determined by the electrode and background electrolyte; R is the gas constant (8.314 J/K/mol); T is the absolute temperature (K); z i is the charge number of the primary ion (FSO 3 – ); F is the Faraday constant (96 487 C/mol); a i is the activity of freely dissolved FSO 3 – ; a j is the activity of interfering ion j; K ij is the potentiometric selectivity coefficient (SC) for ion j with respect to FSO 3 – ; and z j is the charge number of ion j. Here, activity was assumed equal to the ion concentration.…”

Tuning the pH Response of Monolayer Hexagonal Boron Nitride/Graphene Field-Effect Transistors

“…42 Hasan et al focused on the enhancement of ion sensors with a 2D heterostructures of monolayer graphene on hexagonal boron nitride (hBN). 43 However, there is no work reported on pH sensing with monolayer hBN as a capping layer on monolayer graphene. Using an alternative 2D material as the transducer, Wei et al used Al2O3 and hBN nanofilms as a sensing membrane to mitigate sensor drift and for enhancing the sensitivity of monolayer MoS2 field-effect transistors (FETs) as a function of solutal pH and Al2O3 thickness.…”

A Hybrid Microfluidic Electronic Sensing Platform for Life Science Applications

“…A well-established member of electrochemical sensors, the so-called ion-sensitive field-effect transistor (ISFET) sensors have been utilized in different applications for ion/charge detection in chemical solutions. The ISFETs range from carbonaceous FET sensors (e.g., graphene, carbon nanotubes) to 2D materials (e.g., MoS 2 ) [ 7 , 8 , 9 , 10 ]. Many efforts have been made to develop ISFETs based on technologically flawless silicon-based complementary metal-oxide semiconductors (CMOS) technology, resulting in different sensing structures and topologies [ 4 ] offering high-yield productions.…”