Selective Sodium Sensing with Gold-Coated Silicon Nanowire Field-Effect Transistors in a Differential Setup

Abstract

Ion-sensitive field-effect transistors based on silicon nanowires with high dielectric constant gate oxide layers (e.g., Al2O3 or HfO2) display hydroxyl groups which are known to be sensitive to pH variations but also to other ions present in the electrolyte at high concentration. This intrinsically nonselective sensitivity of the oxide surface greatly complicates the selective sensing of ionic species other than protons. Here, we modify individual nanowires with thin gold films as a novel approach to surface functionalization for the detection of specific analytes. We demonstrate sodium ion (Na(+)) sensing by a self-assembled monolayer (SAM) of thiol-modified crown ethers in a differential measurement setup. A selective Na(+) response of ≈-44 mV per decade in a NaCl solution is achieved and tested in the presence of protons (H(+)), potassium (K(+)), and chloride (Cl(-)) ions, by measuring the difference between a nanowire with a gold surface functionalized by the SAM (active) and a nanowire with a bare gold surface (control). We find that the functional SAM does not affect the unspecific response of gold to pH and background ionic species. This represents a clear advantage of gold compared to oxide surfaces and makes it an ideal candidate for differential measurements.

Competing surface reactions limiting the performance of ion-sensitive field-effect transistors

“…[3,4] In particular, silicon nanowire FETs (SiNWFETs) have been used successfully for different sensing experiments. Although successful chemical sensing [5,6,7,8,9,10,11], label-free biosensing [12,3,13,4,14,15,16,17] and the recording of intracellular action potentials [18] have been demonstrated, the only commercial application is still pH sensing [3,19,20,21,22]. The reason for this development lies in the use of bare, high quality oxide surfaces such as Al 2 O 3 or HfO 2 which exhibit a high number of surface hydroxyl groups.…”

Gating Hysteresis as an Indicator for Silicon Nanowire FET Biosensors

“…Devices with close to ideal Nernstian sensitivity were obtained using this oxide material [32,43]. Each FET had up to 10 3 parallel nanowire channels.…”

'Active Surfaces' as Possible Functional Systems in Detection and Chemical (Bio) Reactivity

“…[54][55][56][57][58][59] due to their high sensitivity, [60,61] ease of use, and potential scalability. [62] At the core of the ISFET lies the principle of the classical Metal-Oxide Semiconductor Field functionality.…”

“…ionic receptors for Na + , [59] K + , [64] Ca 2+ [65] and F -. [66] For this purpose, the dielectric layer of SiNWs is coated with an additional thin gold layer to take advantage of gold chemistry and engineer the surface with self-assembled monolayers of thiol-terminated functional molecules.…”