Long term stability of nanowire nanoelectronics in physiological environments

Abstract

Nanowire nanoelectronic devices have been exploited as highly sensitive subcellular resolution detectors for recording extracellular and intracellular signals from cells, as well as from natural and engineered/cyborg tissues, and in this capacity open many opportunities for fundamental biological research and biomedical applications. Here we demonstrate the capability to take full advantage of the attractive capabilities of nanowire nanoelectronic devices for long term physiological studies by passivating the nanowire elements with ultrathin metal oxide shells. Studies of Si and Si/aluminum oxide (Al2O3) core/shell nanowires in physiological solutions at 37 °C demonstrate long-term stability extending for at least 100 days in samples coated with 10 nm thick Al2O3 shells. In addition, investigations of nanowires configured as field-effect transistors (FETs) demonstrate that the Si/Al2O3 core/shell nanowire FETs exhibit good device performance for at least 4 months in physiological model solutions at 37 °C. The generality of this approach was also tested with in studies of Ge/Si and InAs nanowires, where Ge/Si/Al2O3 and InAs/Al2O3 core/shell materials exhibited stability for at least 100 days in physiological model solutions at 37 °C. In addition, investigations of hafnium oxide-Al2O3 nanolaminated shells indicate the potential to extend nanowire stability well beyond 1 year time scale in vivo. These studies demonstrate that straightforward core/shell nanowire nanoelectronic devices can exhibit the long term stability needed for a range of chronic in vivo studies in animals as well as powerful biomedical implants that could improve monitoring and treatment of disease.

Figure 1

Core/shell stabilization of nanowire devices in physiological environments. (A) Schematic illustration of long-time evolution of Si-nanowire FET devices with and without Al₂O₃ protective shell in physiological mimicking 1× PBS (pH 7.4) at 37 °C. TEM images of (B) a Si nanowire with native surface oxide, and (C) a Si nanowire with a 5 nm thick Al₂O₃ shell. The Al₂O₃ was annealed at 400 °C for 1 min prior to sample preparation.

Figure 2

Nanowire stability in solution. (A) Schematic illustrating the experiment methodology. (B–D) Dark-field microscope images showing morphology evolution of Si nanowires with different Al₂O₃ shell thickness in (B) 1× PBS at 37 °C, (C) 1× PBS at room temperature, and (D) Neurobasal at 37 °C.

Figure 3

Si and Si/Al₂O₃ nanowire FET devices stability in solution at 37 ^oC. Time-dependent evolution of the normalized conductance and transconductance for (A) Si nanowire and (B) Si/Al₂O₃ core/shell nanowire (10 nm thick shell) FET devices in 1× PBS at 37 °C. The averages were determined at solution gate voltage = 0 V from 30 devices in both (A) and (B).

Figure 4

Stabilization of semiconductor nanowires with Al₂O₃ shells. Dark-field microscope images showing time-dependent evolution of (A) Ge/Si core/shell nanowires and (B) InAs nanowires with and without Al₂O₃ shells in 1× PBS at 37 °C.