In Situ Sensing of the Neurotransmitter Acetylcholine in a Dynamic Range of 1 nM to 1 mM

Abstract

The neurotransmitter acetylcholine (ACh) plays a key role in the pathophysiology of brain disorders such as Alzheimer's disease. Understanding the dynamics of ACh concentration changes and kinetics of ACh degradation in the living brain is crucial to unravel the pathophysiology of such diseases and the rational design of therapeutics. In this work, an electrochemical sensor capable of dynamic, label-free, selective, and in situ detection of ACh in a range of 1 nM to 1 mM (with temporal resolution of less than one second) was developed. The sensor was employed for the direct detection of ACh in artificial cerebrospinal fluid and rat brain homogenate, without any prior separation steps. A potentiometric receptor-doped ion-selective electrode (ISE) with selectivity for ACh was designed by taking advantage of the positive charge of ACh. The dynamic range, limit of detection (LOD), and the selectivity of the sensor were optimized stepwise by (i) screening of hydrophobic biomimetic calixarenes to identify receptors that strongly bind to ACh based on shape-selective multitopic recognition, (ii) doping of the ISE sensing membrane with an ACh-binding hydrophobic calixarene to enable selective detection of ACh in complex matrices, (iii) utilizing a hydrophilic calixarene in the inner filling solution of the ISE to buffer the concentration of ACh and, thereby, lower the LOD of the sensor, and (iv) introducing a surface treatment step prior to the measurement by placing the sensor for ∼1 min in a solution of a hydrophilic calixarene to lower the LOD of the sensor even further.

Design of Solid‐contact Ion‐selective Electrode with Graphene Transducer Layer for the Determination of Flavoxate Hydrochloride in Dosage Form and in Spiked Human Plasma

“…Calix[n]arenes are one of the most widely studied classes of molecular recognition and supramolecular hosts. They have basket-shaped aromatic electron-rich cavities whose size largely affects the selectivity and binding strength of these receptors to the target ion via cation-π interactions [50]. To study the effect of ionophore type on the degree of selectivity of the sensing membrane, calixarenes 4, 6 and 8 were incorporated as FLV ionophores.…”

“…Potentiometric technique is not only used for determination of the analyte ion concentration, but also can be applied for determination of binding constant between the guest macromolecule and the host ion. The degree of binding for organic ions can be quantitatively assessed using reference ion methods as have been reported in the literature [50,51]. Thus, a bulky hydrophobic ion is used as a reference ion that can't bind to the ionophore cavity.…”

Frontiers in electrochemical sensors for neurotransmitter detection: towards measuring neurotransmitters as chemical diagnostics for brain disorders

“…89 Mousavi et al created a potentiometric ionophore-doped ionselective electrode which did not require enzyme modication. 90 The potentiometric method measured the partition of the cationic 5-HT molecule between the sample and a hydrophobic ionselective membrane doped with calixarene, a hydrophobic molecule whose binding cavity mimics that of acetylcholinesterase. This sensor had a response time of <1 second and was used successfully in rat brain homogenates.…”

Microfabricated potentiometric sensor for personalized methacholine challenge tests during the COVID-19 pandemic

“…Cholinesterase has been historically assayed by several techniques, such as manometric ( Humiston and Wright, 1967 ; Kalow and Lindsay, 1955 ; Witter, 1962 ), titrimetric( Schwartz and Myers, 1958 ; Wilson and Cabib, 1956 ), photometric( Caraway, 1956 ; Ellman et al, 1961 ; Pohanka et al, 2009 ), fluorometric methods( Guilbault and Kramer, 1965 ; He et al, 2015 ; Li et al, 2013 ) and electrochemical methods( Cuartero et al, 2018 , 2012 ; Du et al, 2011 ; Hart et al, 1997 ; Imato and Ishibashi, 1995 ; Mousavi et al, 2018a ; Panraksa et al, 2018 ). The utilization of potentiometric methods presents some advantages over other techniques, including simplicity, rapidness and minor sample preparations.…”