True Picomolar Neurotransmitter Sensor Based on Open-Ended Carbon Nanotubes

Abstract

Neurotransmitters are important chemicals in human physiological systems for initiating neuronal signaling pathways and in various critical health illnesses. However, concentration of neurotransmitters in the human body is very low (nM or pM level) and it is extremely difficult to detect the fluctuation of their concentrations in patients using existing electrochemical biosensors. In this work, we report the performance of highly densified carbon nanotubes fiber (HD-CNTf) crosssections called rods (diameter ∼ 69 μm, and length ∼ 40 μm) as an ultrasensitive platform for detection of common neurotransmitters. HD-CNTf rods microelectrodes have open-ended CNTs exposed at the interface with electrolytes and cells and display a low impedance value, i.e., 1050 Ω. Their fabrication starts with dry spun CNT fibers that are encapsulated in an insulating polymer to preserve their structure and alignment. Arrays of HD-CNTf rods microelectrodes were applied to detect neurotransmitters, i.e., dopamine (DA), serotonin (5-HT), epinephrine (Epn), and norepinephrine (Norepn), using square wave voltammetry (SWV) and cyclic voltammetry (CV). They demonstrate good linearity in a broad linear range (1 nM to 100 μM) with an excellent limit of detection, i.e., 32 pM, 31 pM, 64 pM, and 9 pM for DA, 5-HT, Epn, and Norepn, respectively. To demonstrate practical application of HD-CNTf rod arrays, detection of DA in human biological fluids and real time monitoring of DA release from living pheochromocytoma (PC12) cells were performed.

Amorphous Carbon Film with Self‐modified Carbon Nanoparticles Synthesized by Low Temperature Carbonization of Phenolic Resin for Simultaneous Sensing of Dopamine and Uric Acid

“…The slope of the line for DA and UA was 55 and 41 mV pH À 1 , respectively, which was close to the Nernst value [13,[51][52][53]. Therefore, the number of protons involved equalled the number of electrons throughout the oxidation process [54][55].…”

“…Sensitivity is equal to the slope of the linear curve between concentration and peak current density [10]. Limit of detection (LOD) was KS b /m (2), where m is the slope of the analytical curve in the low concentration range, and S b is the blank standard deviation, and K is the constant related to the confidence concentration (K = 3) [8,13]. Parameters of DPV: Incr E = 4 mV, amplitude = 20 mV, pulse width = 0.05 s, pulse period = 0.2 s, sensitivity = 10 À 6 A/V.…”

“…The response peak current density as a function of concentrations is shown in Figure 5b (DA) and Figure 5d (UA). In the case of increasing concentrations of DA and fixing UA (Figure 5a), the line equation was Y(μA cm 2 ) = 2.953 + 0.74 X(μM), R 2 = 0.981 (13). The initial linear range was utilised to calculate the sensitivity and LOD of DA, and was found to be 0.738 μA cm À 2 μM À 1 , 0.398 μM.…”

“…A number of methods have been developed to detect UA and DA [11][12]. Among them, electrochemical detection is becoming the best method for detecting DA and UA, primarily due to its simple operation, fast response, high sensitivity, and excellent selectivity [13][14][15][16]. However, the proximity of oxidation potential is remaining a problem concerned with the simultaneous detection of DA and UA, illustrated by the mixed peak.…”

Grand Challenges in Nanomaterial-Based Electrochemical Sensors

“…Due to the innovation of nanomaterial-modified surfaces, LODs with values as low as picomole and femtomole levels have been achieved in the case of some ultra-sensitive sensors (Suherman et al, 2017;Li X. et al, 2018;Ponnaiah et al, 2018;Alizadeh et al, 2019;Wu et al, 2019;Gupta et al, 2020). For example, a sensor modified with open-ended CNTs was reported to have picomolar levels of sensitivity for the detection of neurotransmitters (Gupta et al, 2020). An ultrasensitive sensor for the detection of Hg 2+ was developed by modification of a glassy carbon electrode with silver nanoparticles resulting in picomolar level LOD values (Suherman et al, 2017).…”