This work presents a proof of concept of a novel, simple, and sensitive method of detection of dopamine, a neurotransmitter within the human brain. We propose a simple electrochemical method for the detection of dopamine using a dopamine-specific aptamer labeled with an electrochemically active ferrocene tag. Aptamers immobilized on the surface of gold screen-printed gold electrodes via thiol groups can change their secondary structure by wrapping around the target molecule. As a result, the ferrocene labels move closer to the electrode surface and subsequently increase the electron transfer. The cyclic voltammograms and impedance spectra recorded on electrodes in buffer solutions containing different concentration of dopamine showed, respectively, the increase in both the anodic and cathodic currents and decrease in the double layer resistance upon increasing the concentration of dopamine from 0.1 to 10 nM L −1 . The high affinity of aptamer-dopamine binding (KD ≈ 5 nM) was found by the analysis of the binding kinetics. The occurrence of aptamer-dopamine binding was directly confirmed with spectroscopic ellipsometry measurements.Chemosensors 2020, 8, 28 2 of 11 done on the electrochemical detection of dopamine and other neurotransmitters [2,3]. Dopamine can be very easily detected in an aqueous solution by electrochemical methods such as cyclic voltammetry since dopamine undergoes electrochemical oxidation. However, a major issue is the selectivity since complex matrices such as blood contain a range of other oxidizable compounds such as urate or ascorbate which would also generate signals, leading to inaccurate readings. Selectivity towards dopamine is therefore required.A wide range of electrode materials have been proposed to increase the selectivity of dopamine detection [2,3]. A few recent examples include the use of materials such as Nafion combined with graphite [4] or multi-walled carbon nanotubes [5] to improve the selectivity towards dopamine. Other researchers have utilized graphene-modified screen-printed electrodes [6] or graphene aerogels [7] as substrates for the selective determination of dopamine. Composites of carbon nanotubes and graphene oxide could be used to determine dopamine, nitrate, ascorbate, and urate [8]. Metal nanoparticles have also been utilized, for example palladium nanoparticles combined with graphene [9], which were used as a base of electrochemical determination of dopamine whereas a gold nanoparticle/DNA/polymer composite could be used for the simultaneous determination of dopamine, uric acid, guanine, and adenine [10]. Composites of gold nanoparticles with conducting polymers have also been used for the selective determination of dopamine [11]. Boron-doped carbon nanotubes could be used to determine levels of dopamine and ephedrine in the presence of urate [12]. Composites of graphene oxide with Bi 2 S 3 nanorods were used for the electrochemical determination of dopamine [13], and arrays of cylindrical gold nanoelectrodes could be used for both the detection of dopamine an...

A newly synthesized calix [4]arene thiourea derivative decorated with 2-(2-aminophenyl)benzothiazole unit is selected to take part important role in host-guest interactions of the macrocyclic molecules. p-tert-butylcalix [4]arene dithiourea (C[4]-DT) Langmuir-Blodgett (LB) thin films are prepared and characterized to develop a new sensing element for the detection of seven different organic vapors (dichloromethane, chloroform, acetone, benzene, carbon tetrachloride, toluene and m-xylene). The preparation of C[4]-DT-based thin films onto the different substrates was successfully and uniformly achieved with linear regressions of 0.9971 and 0.9954 for coating onto quartz glass and quartz crystal, respectively. The frequency shift (61.01 Hz) and the mass deposited onto quartz crystal (969.80 ng) were calculated for each layer. The swelling dynamics of C[4]-DT QCM chemical sensor was also illuminated by developing the early time Fick's diffusion equation. The sensing measurements can be concluded that owing to its high sensitivity (6.63 Hz/ ppm), fast response and low detection limit (0.45 ppm), this proposed C[4]-DT LB coated sensor is expected to be promising alternative chemical sensor for detection of DCM vapor.

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