High-Performance Conducting Polymer Nanotube-based Liquid-Ion Gated Field-Effect Transistor Aptasensor for Dopamine Exocytosis

Abstract

In this study, ultrasensitive and precise detection of a representative brain hormone, dopamine (DA), was demonstrated using functional conducting polymer nanotubes modified with aptamers. A high-performance aptasensor was composed of interdigitated microelectrodes (IMEs), carboxylated polypyrrole nanotubes (CPNTs) and DA-specific aptamers. The biosensors were constructed by sequential conjugation of CPNTs and aptamer molecules on the IMEs, and the substrate was integrated into a liquid-ion gating system surrounded by pH 7.4 buffer as an electrolyte. To confirm DA exocytosis based on aptasensors, DA sensitivity and selectivity were monitored using liquid-ion gated field-effect transistors (FETs). The minimum detection level (MDL; 100 pM) of the aptasensors was determined, and their MDL was optimized by controlling the diameter of the CPNTs owing to their different capacities for aptamer introduction. The MDL of CPNT aptasensors is sufficient for discriminating between healthy and unhealthy individuals because the total DA concentration in the blood of normal person is generally determined to be ca. 0.5 to 6.2 ng/mL (3.9 to 40.5 nM) by high-performance liquid chromatography (HPLC) (this information was obtained from a guidebook "Evidence-Based Medicine 2018 SCL " which was published by Seoul Clinical Laboratory). The CPNTs with the smaller diameters (CPNT2: ca. 120 nm) showed 100 times higher sensitivity and selectivity than the wider CPNTs (CPNT1: ca. 200 nm). Moreover, the aptasensors based on CPNTs had excellent DA discrimination in the presence of various neurotransmitters. Based on the excellent sensing properties of these aptasensors, the DA levels of exogeneous DA samples that were prepared from PC12 cells by a DA release assay were successfully measured by DA kits, and the aptasensor sensing properties were compared to those of standard DA reagents. Finally, the real-time response values to the various exogeneous DA release levels were similar to those of a standard DA aptasensor. Therefore, CPNT-based aptasensors provide efficient and rapid DA screening for neuron-mediated genetic diseases such as Parkinson's disease.Materials. Pyrrole (Py, 98%) and pyrrole-3-carboxylic acid (Py-COOH, 95%) were purchased from the Aldrich and Acros Organics. A surfactant, sodium bis(2-ethylhexyl)-sulfosuccinate (AOT, 98%) and hexane (98%) were also purchased from the Aldrich. The conjugation reagent, 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)−4methyl-morpholinium chloride (DMT-MM, 96%) was purchased from Aldrich. The aptamer was purchased from Bioneer. Inc. Fabrication of carboxylated polypyrrole nanotubes (CPNTs).CPNTs with different diameters (ca. 120 and 200 nm) were prepared by benchmarks in our previous works 51 . A surfactant, AOT (15 mmol), was dissolved in hexane (40 mL), and the solution was stirred for 30 minutes to reach equilibrium. Subsequently, aqueous FeCl 3 solution (7 M, 1 mL) was introduced into the AOT/hexane solution to generate reverse-cylindrical micelles containing iron cations 55 . Finally, a pyrrole (Py)...

Ultrasensitive Stress Biomarker Detection Using Polypyrrole Nanotube Coupled to a Field-Effect Transistor

“…Figure 2a displays SEM images of the FET system before and after conjugation of anti-cortisol IgG, respectively. The SEM images show that the bare PPy NT with a~200 nm diameter was synthesized with very homogeneous surface morphologies (left image in Figure 2a) [24]. Functionalization of anti-cortisol IgG on the PPy NT surface was also confirmed (right image in Figure 2a).…”

Electrochemical Biosensing of Dopamine Neurotransmitter: A Review

“…Another FET was functionalized with carboxylated polypyrrole nanotubes/aptamer and used to detect the dopamine secreted by living cells [149]. A very low detection limit of 100 pM was obtained, as well as a linear range going from 0.1 nM to 10 µM and a high selectivity since catechol, epinephrine, and ascorbic acid did not interfere with dopamine sensing.…”

Recent Advances of Field-Effect Transistor Technology for Infectious Diseases

“…Controlling the diameter of CPNTs was an important feature, which the authors took into account while constructing this device. It was reported that the small structures demonstrated higher sensitivity and specificity in comparison to the wider ones since they delivered a large available area [ 156 ].…”