Electrochemical serotonin monitoring of poly(ethylenedioxythiophene):poly(sodium 4-styrenesulfonate)-modified fluorine-doped tin oxide by predeposition of self-assembled 4-pyridylporphyrin

Superlative and Selective Sensing of Serotonin in Undiluted Human Serum Using Novel Polystyrene Sulfonate Conductive Polymer

In the past 5 years, real-time health monitoring has become ubiquitous with the development of watches and rings that can measure and report on the physiological state. As an extension, real-time biomarker sensors, such as the continuous glucose monitor, are becoming popular for both health and performance monitoring. However, few real-time sensors for biomarkers have been made commercially available; this is primarily due to problems with cost, stability, sensitivity, selectivity, and reproducibility of biosensors. Therefore, simple, robust sensors are needed to expand the number of analytes that can be detected in emerging and existing wearable platforms. To address this need, we present a simple but novel sensing material. In short, we have modified the already popular PEDOT/PSS conductive polymer by completely removing the PEDOT component and thus have fabricated a polystyrene sulfonate (PSS) sensor electrodeposited on a glassy carbon (GC) base (GC-PSS). We demonstrate that coupling the GC-PSS sensor with differential pulse voltammetry creates a sensor capable of the selective and sensitive detection of serotonin. Notably, the GC-PSS sensor has a sensitivity of 179 μA μM-1 cm-2 which is 36x that of unmodified GC and an interferent-free detection limit of 10 nM, which is below the concentrations typically found in saliva, urine, and plasma. Notably, the redox potential of serotonin interfacing with the GC-PSS sensor is at -0.188 V versus Ag/AgCl, which is significantly distanced from peaks produced by common interferants found in biofluids, including serum. Therefore, this paper reports a novel, simple sensor and polymeric interface that is compatible with emerging wearable sensor platforms.

A Disposable Screen Printed Electrodes with Hexagonal Ni(OH)2 Nanoplates Embedded Chitosan Layer for the Detection of Depression Biomarker

Serotonin (5-hydroxytryptamine (5-HT)) is one of the important neurotransmitters which is released from the endocrine system. An abnormal level of this biomarker leads to several neurological diseases. The accurate assessment of serotonin is the utmost option to start treatment in the early stages of the disease. The current work is focused on the development of a disposable, screen-printed electrochemical sensor for the depression biomarker, serotonin in the physiological pH medium (pH 7.4) with the aid of a hexagonal, Ni(OH)₂-nanoplate (NH-HNP)-embedded chitosan (Chit) and modified, screen-printed carbon electrode (SPCE). Initially, hexagonal nanoplates of Ni(OH)₂ were synthesized by an eco-friendly and simple hydrothermal method. The prepared materials were well characterized by advanced analytical techniques to examine the physicochemical properties of the synthesized Ni(OH)₂ hexagonal nanoplates. From the cyclic voltametric (CV) analysis, it was found that the oxidative current response of 5-HT at a NH-HNP-modified SPCE has about fivefold higher current values than over bare SPCE. The scan rate studies of NH-HNP-Chit/SPCE electrodes revealed that the oxidation mechanism of 5-HT is controlled by the diffusion behavior of the analyte. Differential pulse voltammetric tests of the NH-HNP-Chit/SPCE electrode exhibited a linear response in the dynamic concentration range of 0.1 to 30 µM, with a detection limit of about 60 nM. The sensor response is very reproducible from electrode to electrode, and the deactivation or surface-fouling of the sensor was not observed within the several experimental measurements. The sensor exhibited excellent storage stability over a period of twenty days. Finally, the fabricated, disposable SPCE sensor has shown respectable activity for the detection of depression biomarker 5-HT from synthetic urine and saliva samples.

A serotonin voltammetric biosensor composed of carbon nanocomposites and DNA aptamer

A sensitive and selective voltammetric biosensor composed of layer-by-layer (LbL) self-assembly of positively charged poly(diallyldimethylammonium)-wrapped oxidized single-walled carbon nanotubes (PDDA-oSWCNTs), negatively charged serotonin (5-hydroxytryptamine, 5-HT)-specific aptamer, and tyrosinase on Au nanoparticles deposited screen printed carbon electrode was developed for measurement of 5-HT. Surface characteristics of 5-HT biosensor were explored using scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The respective effects of 5-HT-specific aptamer and oSWCNTs on the detection of 5-HT were investigated by differential pulse voltammetry (DPV). The peak current at the potential of 0.29 V (vs. Ag/AgCl) increased with respect to 5-HT concentration resulting in two dynamic ranges from 0.05 to 0.5 and 1 to 20 μM with a limit of detection of 2 nM from the LbL biosensor in buffer solution, which were better than those without the LbL of aptamer and oSWCNTs. The developed biosensor was applied to the direct determination of 5-HT concentrations in undiluted healthy control and Internet gaming disorder serum samples. The results were verified by comparison with those from liquid chromatography-mass spectrometric analyses.

Enhanced Stability and Amplified Signal Output of Single-Wall Carbon Nanotube-Based NH3-Sensitive Electrode after Dual Plasma Treatment

Pristine nanomaterials are normally prepared using finely controlled fabrication processes. Because no imperfect nanostructure remains, they cannot be used directly as electrode substrates of functional devices. This is because perfectly organized nanostructures or nanomaterials commonly require posttreatment to generate intentionally, the kinds of desirable defects inside or on their surfaces that enable effective functionalization. Plasma treatment is an easier, simpler and more widely used way (relative to other methods) to modify a variety of nanomaterials, although plasma-functionalized nano surfaces commonly have a short lifetime. We present herein a dual plasma treatment (DPT) that significantly enhances the degree and lifetime of plasma-induced surface functional groups on single-walled carbon nanotubes (SWCNTs). The DPT process consists of two individually optimized oxygen-plasma treatments. The DPT-modified SWCNT functioned as a sensing material for ammonia gas for more than a month. It also provided more than three times the degree of functionality for amplified signal output than with a single-plasma-treated SWCNT electrode.

Conducting polymer-based electrochemical biosensors for neurotransmitters: A review

Neurotransmitters are important biochemical molecules that control behavioral and physiological functions in central and peripheral nervous system. Therefore, the analysis of neurotransmitters in biological samples has a great clinical and pharmaceutical importance. To date, various methods have been developed for their assay. Of the various methods, the electrochemical sensors demonstrated the potential of being robust, selective, sensitive, and real time measurements. Recently, conducting polymers (CPs) and their composites have been widely employed in the fabrication of various electrochemical sensors for the determination of neurotransmitters. Hence, this review presents a brief introduction to the electrochemical biosensors, with the detailed discussion on recent trends in the development and applications of electrochemical neurotransmitter sensors based on CPs and their composites. The review covers the sensing principle of prime neurotransmitters, including glutamate, aspartate, tyrosine, epinephrine, norepinephrine, dopamine, serotonin, histamine, choline, acetylcholine, nitrogen monoxide, and hydrogen sulfide. In addition, the combination with other analytical techniques was also highlighted. Detection challenges and future prospective of the neurotransmitter sensors were discussed for the development of biomedical and healthcare applications.

Poly(basic red 9) doped functionalized multi-walled carbon nanotubes as composite films for neurotransmitters biosensors

This paper discusses the electrochemical polymerization of basic dye films, which are composed of basic red 9 (BR9), on various electrodes and the enhancement of the electropolymerization by functionalized multiwall carbon nanotubes (f-MWCNTs) modification of the electrode surface. The presence of f-MWCNTs enhances the surface coverage (Γ) and stability. Poly(BR9) films were electrocatalytically active for epinephrine and serotonin oxidation. The electrocatalytic oxidation current developed from the anodic peak of the redox couple. Electrochemical impedance spectroscopy (EIS) was applied to monitor the whole process of the electrode modification. EIS can provide useful information regarding the impedance changes on the electrode surface between each step. We studied the surface morphology of the composite film using scanning electron microscopy (SEM) and atomic force microscopy (AFM), which revealed that BR9 is doped on f-MWCNTs. Cyclic voltammetry (CV) was used for the measurement of the electroanalytical properties of the analytes. The sensitivity values for the f-MWCNTs/BR9 composite film were higher than the poly(BR9) and f-MWCNTs composite film. Finally, differential pulse voltammetry (DPV) was used for the detection of a mixture of analytes at the f-MWCNTs/BR9 composite film. We simulated a more complex system with both serotonin and epinephrine present simultaneously. This system also exhibited oxidation peaks for serotonin in bovine calf serum (BCS) and epinephrine injection for real samples determination at pH 7.0 at the f-MWCNTs/BR9 composite film.