GABA Detection with Nano-ITIES Pipet Electrode: A New Mechanism, Water/DCE–Octanoic Acid Interface

Abstract

Interface between two immiscible electrolyte solutions (ITIES) supported on the orifice of a pipet have become a powerful platform to detect a broad range of analytes. We present here the detection of γ-aminobutyric acid (GABA) with the nanoITIES pipet electrodes for the first time. GABA has a net charge of zero in an aqueous solution at pH ≈ 7, and it has not previously been detected at ITIES. In this work, we demonstrated GABA detection at ITIES in an aqueous solution at pH ≈ 7, where we introduced a novel detection strategy based on “pH modulation from the oil phase”. To the best of our knowledge, this is the first report of such. Current increases linearly with increasing concentrations of GABA, ranging from 0.25 mM to 1.0 mM. The measured half-wave transfer potential of GABA is −0.401 ± 0.010 V (n = 22) vs E1/2,TBA. The measured diffusion coefficient for GABA detection at nanoITIES pipet electrode is 6.09 (±0.58) × 10−10 m2/s (n = 5). Experimental results indicate that protons generated from octanoic acid dissociation in the oil phase do not come out from the oil phase into the aqueous phase; neither were protons produced in the aqueous phase. NanoITIES pipet electrodes with radii of 320–340 nm were used in the current study. This new strategy and knowledge presented here lays the groundwork for the future development of ITIES pipet electrodes, especially for the detection of electrochemically nonredox active analytes.

A Newly Synthesized Tris(crown ether) Ionophore for Assisted Ion Transfer at NanoITIES Electrodes

“…0.7 mm, length=7.5 cm) using a P‐2000 capillary puller (Sutter Instrument Co., Novato, CA). The nanopipets were fabricated using procedures as previously reported …”

“…An Ag wire (diameter=250 μm) coated with AgCl (through an oxidation reaction in saturated KCl solution) was placed in the aqueous phase as an outside reference electrode. A two electrode configuration was used as reported previously, where a potential was applied between the inner Pt wire and the outer Ag/AgCl reference electrode . Positive potential is for positive ion transfer from water to oil (1, 2‐DCE), seen as positive current.…”

“…Ions transfer either directly across ITIES without an ionophore, or through its complexation with an ionophore, which is known as the assisted ion transfer . A commonly used ionophore in ITIES is dibenzo‐18‐crown‐6 (DB18C6) . Although great progress has been made in synthesizing ionophores with multiple crown either moieties for ion selective electrodes, such ionophores have yet to be tested for amperometric ion detection at ITIES electrodes.…”

A Nanopipette Platform for Delivering Nanoliter Volumes of Acetylcholine

“…The TFAB salt of TDDA (TDDATFAB) was prepared by metathesis. [37][38][39] Potassium tetrakis(pentafluorophenyl)borate was purchased from Boulder Scientific Company (Mead, CO). Magnesium sulfate (MgSO 4 ) and HEPES were purchased from Fisher Scientific (Hampton, NH).…”

“…Details on nanoITIES electrodes fabrication and characterization can be found in recent publications from our group. [37][38][39] Delivery experiments.-A Nanopipette delivery probe as described above was immersed into the aqueous cellular medium, the artificial seawater (ASW), after which a voltage was applied to induce the delivery of ACh. To prevent an unwanted ingress during the immersion process, a retaining voltage of 0.8 V vs Ag/AgCl was applied while the pipette was lowered into the ASW.…”