A review on electrochemical detection of serotonin based on surface modified electrodes

Electrochemically Grown Hole-Rich NiO(OH) Thin Films toward Hole-Mediated Very Fast and Selective Enzyme-Free Electrochemical Sensing of Dopamine under Simulated Environment

This work aimed to develop an enzyme-free semiconductor-assisted electrochemical technique for the selective detection of the neurotransmitter dopamine. In this case, electrochemically grown nickel oxyhydroxide [NiO(OH)] thin films were chosen to fabricate the sensing platform, i.e., the electrodes. Chronoamperometry was used to deposit the films on indium tin oxide (ITO) coated glass substrates. The films were thoroughly characterized to establish their structure, composition, phase purity, and electrochemical attributes. Electrochemical sensing characteristics were investigated by means of cyclic and differential pulse voltammetry, steady-state amperometry, and electrochemical impedance spectroscopy. The effects of several interfering agents like glucose, sodium chloride, methanol, hydrogen peroxide, and paracetamol were also studied on the detection attributes of dopamine. Significantly high value of sensitivity (11.87 μA μM-1 cm-2) was obtained for dopamine sensing that was associated with a limit of detection (LoD) of 0.22 μM of dopamine. However, the sensitivity (2.51 μA μM-1 cm-2) and LoD (1.20 μM) obtained for serotonin were inferior compared to those of dopamine. The performance of the electrode toward dopamine sensing was not compromised either in the presence of only serotonin or a series of other electroactive interfering agents, which makes the electrode very much dopamine selective. The dopamine response time was 200 ms, which is notably fast. Extensive studies on the effect of temperature, pH and scan rate on the detection of dopamine by the developed electrode material have also been carried out. The developed electrodes were also found to be notably stable for dopamine detection with a decay of only 6.6% in oxidation peak current density after the 50th cycle. Real-life application of the developed electrode material was checked with urine samples from adult male humans and yielded encouraging results.

Cu2MoS4 Nanocatalyst-Based Electrochemical Sensor for Ofloxacin Electro-Oxidation: Delineating the Combined Roles of Crystallinity and Morphology on the Analytical Performance

In this study, we demonstrate the influence of crystallinity and morphology on the analytical performance of various Cu2MoS4 (CMS) nanocatalysts-based electrochemical sensors for the high-efficiency detection of Ofloxacin (OFX) antibiotic. The electrochemical kinetics parameters including peak current response (ΔIp), peak-to-peak separation (ΔEp), electrochemically active surface area (ECSA), electron-transfer resistance (Rct), were obtained through the electrochemical analyses, which indicate the single-crystalline nature of CMS nanomaterials (NMs) is beneficial for enhanced electron-transfer kinetics. The morphological features and the electrochemical results for OFX detection substantiate that by tuning the tube-like to plate-like structures of the CMS NMs, it might noticeably enhance multiple adsorption sites and more intrinsic active catalytic sites due to the diffusion of analytes into the interstitial spaces between CMS nanoplates. As results, highly single-crystalline and plate-shaped morphology structures of CMS NMs would significantly enhance the electrocatalytic OFX oxidation in terms of onset potential (Eonset), Tafel slope, catalytic rate constant (kcat), and adsorption capacity (Γ). The CMS NMs-based electrochemical sensing platform showed excellent analytical performance toward the OFX detection with two ultra-wide linear detection concentration ranges from 0.25-100 and 100-1000 μM, a low detection limit of 0.058 μM, and an excellent electrochemical sensitivity (0.743 μA μM-1 cm-2).

A label-free fluorescence aptamer sensor for point-of-care serotonin detection

Serotonin, a pivotal neurotransmitter regulating various physiological functions, plays a crucial role in disease diagnosis, necessitating precise monitoring of its levels in biological fluids for accurate assessment. Aptamers, known for their high specificity and affinity, have emerged as innovative molecular probes for serotonin analysis. However, existing serotonin aptamer sensing platforms exhibit limitations in terms of portability and rapid detection capabilities. In this study, we introduce a novel, portable, label-free serotonin aptamer sensor utilizing a dye replacement strategy, achieving a short sample-to-result turnaround time and convenient signal readout through a smartphone. The performance of this aptamer sensor was thoroughly assessed across diverse physiological media, demonstrating robust stability in buffer, urine, and serum. Importantly, the detection limit was in the nanomolar range, emphasizing its suitability for the rapid, sensitive, and user-friendly detection of serotonin. This research pioneers an approach for the development of a point-of-care testing (POCT) system for serotonin with practical implications, particularly in resource-limited settings.

In vitro selection of a trans aptamer complex for target-responsive fluorescence activation

BACKGROUND

Most biological molecular complexes consist of multiple functional domains, yet rationally constructing such multifunctional complexes is challenging. Aptamers, the nucleic acid-based functional molecules, can perform multiple tasks including target recognition, conformational changes, and enzymatic activities, while being chemically synthesizable and tunable, and thus provide a basis for engineering enhanced functionalities through combination of multiple units. However, the conventional approach of simply combining aptamer units in a serial manner is susceptible to undesired crosstalk or interference between the aptamer units and to false interactions with non-target molecules; besides, the approach would require additional mechanisms to separate the units if they are desired to function independently. It is clearly a challenge to develop multi-aptamer complexes that preserve independent functions of each unit while avoiding undesired interference and non-specific interactions.

RESULTS

By directly in vitro selecting a 'trans' aptamer complex, we demonstrate that one aptamer unit ('utility module') can remain hidden or 'inactive' until a target analyte triggers the other unit ('sensing module') and separates the two aptamers. Since the operation of the utility module occurs free from the sensing module, unnecessary crosstalk between the two units can be avoided. Because the utility module is kept inactive until separated from the complex, non-specific interactions of the hidden module with noncognate targets can be naturally prevented. In our demonstration, the sensing module was selected to detect serotonin, a clinically important neurotransmitter, and the target-binding-induced structure-switching of the sensing module reveals and activates the utility module that turns on a fluorescence signal. The aptamer complex exhibited a moderately high affinity and an excellent specificity for serotonin with ∼16-fold discrimination against common neurotransmitter molecules, and displayed strong robustness to perturbations in the design, disallowing nonspecific reactions against various challenges.

SIGNIFICANCE

This work represents the first example of a trans aptamer complex that was in vitro selected de novo. The trans aptamer complex selected by our strategy does not require chemical modifications or immediate optimization processes to function, because the complex is directly selected to perform desired functions. This strategy should be applicable to a wide range of functional nucleic acid moieties, which will open up diverse applications in biosensing and molecular therapeutics.

Ratiometric electrochemical aptasensor based on split aptamer and Au-rGO for detection of aflatoxin M1

A novel ratiometric electrochemical aptasensor based on split aptamer and Au-reduced graphene oxide (Au-rGO) nanomaterials was proposed to detect aflatoxin M1 (AFM1). In this work, Au-rGO nanomaterials were coated on the electrode through the electrodeposition method to increase the aptamer enrichment. We split the aptamer of AFM1 into 2 sequences (S1 and S2), where S1 was immobilized on the electrode due to the Au-S bond, and S2 was tagged with methylene blue (MB) and acted as a response signal. A complementary strand to S1 (CS1) labeled with ferrocene (Fc) was introduced as another reporter. In the presence of AFM1, CS1 was released from the electrode surface due to the formation of the S1-AFM1-S2 complex, leading to a decrease in Fc and an increase in the MB signal. The developed ratiometric aptasensor exhibited a linear range of 0.03 μg L-1 to 2.00 μg L-1, with a detection limit of 0.015 μg L-1 for AFM1 detection. The ratiometric aptasensor also showed a linear relationship from 0.2 μg L-1 to 1.00 μg L-1, with a detection limit of 0.05 μg L-1 in natural milk after sample pretreatment, indicating the successful application of the developed ratiometric aptasensor. Our proposed strategy provides a new way to construct aptasensors with high sensitivity and selectivity.

A low-cost voltammetric sensor based on multi-walled carbon nanotubes for highly sensitive and accurate determination of nanomolar levels of the anticancer drug Ribociclib in bulk and biological fluids

In this study, we present the development and comprehensive characterization of the first electrochemical sensor utilizing multi-walled carbon nanotubes (MWCNTs) for the sensitive and precise detection of Ribociclib (RIBO), an important anticancer drug. The sensor underwent systematic optimization, focusing on critical parameters such as pH, deposition potential, and cumulative time to enhance its electrocatalytic activity and expand the linear range for RIBO determination. The MWCNTs/GCE sensor exhibited excellent reproducibility and repeatability, ensuring reliable and consistent results. The applicability and feasibility of the sensor for real sample analysis were extensively evaluated by analyzing human serum, urine, and tablet samples using the standard addition method. The obtained percent recovery values demonstrated the sensor's exceptional accuracy and precision. Furthermore, interference studies revealed the sensor's remarkable selectivity, with minimal impact from common interfering substances. The developed sensor displayed a wide linear range of 0.01 μM to 5.0 μM, with a limit of detection (LOD) and limit of quantification (LOQ) calculated to be 0.69 nM and 2.31 nM, respectively, affirming its high sensitivity for detecting low RIBO concentrations. The MWCNTs/GCE sensor demonstrates substantial promise for diverse practical applications with its simplicity, cost-effectiveness, and excellent analytical performance.

Development of a highly sensitive aptamer-based electrochemical sensor for detecting saxitoxin based on K3Fe(CN)6 regulated silver nanoparticles

BACKGROUND

Saxitoxin (STX) is the most toxic marine toxin, which can pose several adverse effects on human health. High sensitivity, fast response, and low-cost detection of STX contamination are of significance to reducing the fishery and seafood industries' loss. Among the various types of biosensors, the electrochemical biosensors have been extensively studied in the detection of STX, but the electrode surface modification material is easy to fall off, resulting in unstable electrochemical signals and poor reproducibility. It is imperative to have a ratiometric electrochemical biosensor for STX.

RESULTS

In this study, we developed a novel aptamer-based electrochemical sensor (AECs) for the sensitive detection of STX based on a K3Fe(CN)6 regulated silver nanoparticles (Ag NPs) modified with aptamer. The AECs was constructed by immobilizing aptamer on Ag NPs surfaces. Under optimized conditions, the AECs showed a linear response towards STX in the range from 0.04 to 0.15 μM with the regression equation of Y = -8.0 + 233.7 X (R2 = 0.9956). The limit of detection (LOD) was calculated to be 1 nM (based on 3 N/S), which is significantly lower than the regulatory limits for STX in seafood. Moreover, the AECs showed excellent sensitivity, reproducibility and stability, as well as the detection in samples with acceptable recovery ranged from 71.2 % to 93.8 %, demonstrating its broad application prospects in detection of STX in seafood samples.

SIGNIFICANCE

This work proposed an AECs to achieve sensitive detection of STX. A reaction system of K3Fe(CN)6 etched Ag NPs was introduced and used as the signal source to avoid the instability of the electrochemical signal, which can produce a ratiometric electrochemical signal output mode, improving the stability and sensitivity of electrochemical detection of STX.

The High-Precision Liquid Chromatography with Electrochemical Detection (HPLC-ECD) for Monoamines Neurotransmitters and Their Metabolites: A Review

This review highlights the advantages of high-precision liquid chromatography with an electrochemical detector (HPLC-ECD) in detecting and quantifying biological samples obtained through intracerebral microdialysis, specifically the serotonergic and dopaminergic systems: Serotonin (5-HT), 5-hydroxyindolacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), dopamine (DA), 3-metoxytryptamin (3-MT) and homovanillic acid (HVA). Recognized for its speed and selectivity, HPLC enables direct analysis of intracerebral microdialysis samples without complex derivatization. Various chromatographic methods, including reverse phase (RP), are explored for neurotransmitters (NTs) and metabolites separation. Electrochemical detector (ECD), particularly with glassy carbon (GC) electrodes, is emphasized for its simplicity and sensitivity, aimed at enhancing reproducibility through optimization strategies such as modified electrode materials. This paper underscores the determination of limits of detection (LOD) and quantification (LOQ) and the linear range (L.R.) showcasing the potential for real-time monitoring of compounds concentrations. A non-exhaustive compilation of literature values for LOD, LOQ, and L.R. from recent publications is included.

Electroanalysis in Pharmacogenomic Studies: Mechanisms of Drug Interaction with DNA

The review discusses electrochemical methods for analysis of drug interactions with DNA. The electroanalysis method is based on the registration of interaction-induced changes in the electrochemical oxidation potential of heterocyclic nitrogenous bases in the DNA molecule and in the maximum oxidation current amplitude. The mechanisms of DNA-drug interactions can be identified based on the shift in the electrooxidation potential of heterocyclic nitrogenous bases toward more negative (cathodic) or positive (anodic) values. Drug intercalation into DNA shifts the electrochemical oxidation potential to positive values, indicating thermodynamically unfavorable process that hinders oxidation of nitrogenous bases in DNA. The potential shift toward the negative values indicates electrostatic interactions, e.g., drug binding in the DNA minor groove, since this process does not interfere with the electrochemical oxidation of bases. The concentration-dependent decrease in the intensity of electrochemical oxidation of DNA bases allows to quantify the type of interaction and calculate the binding constants.

Laccase-Conjugated Nanostructured ZnFe2O4/rGO-Modified Electrode-Based Interfaces for Electrochemical Impedance Monitoring of Adrenaline: A Promising Biosensor for Management of Neurodegenerative Disorders

A propitious biosensor for adrenaline (AD) detection in bovine serum albumin (BSA) real samples, which can be used for diagnosis and treatment of neurodegenerative disorders, is reported here. The biosensor consists of a La/ZF/rGO/ITO bioelectrode, which is fabricated by electrophoretic deposition of zinc ferrite/reduced graphene oxide (ZF/rGO) nanohybrid followed by drop casting of laccase (La) enzymes. The material characterization and electrochemical studies revealed that the ZF/rGO nanohybrid enhanced the electroactive surface and facilitated direct electron transfer between the electrode and electrolyte interface, resulting in enhanced electrocatalytic performance. The cyclic voltammetry and electrochemical impedance spectroscopy results asserted that the ZF/rGO nanohybrid decreased the charge-transfer resistance (Rct) and increased the surface adsorption, leading to a high diffusion coefficient (D) of 0.192 cm2/s. The biosensor exhibited a high sensitivity of 0.71 Ω/μM cm2, a good linear range (0.1 to 140 μM with R2 = 0.98), and a low limit of detection (LOD) is 12.5 μM, demonstrating the synergic effect of ZF and rGO in the La/ZF/rGO/ITO bioelectrode with AD. The biosensor also exhibited high selectivity and stability (55 days) in the presence of interfering substances and in BSA samples, with a recovery percentage close to 100 ± 5% RSD, indicating its potential biosensing applications for real-world applications in disease diagnostics, monitoring, and treatment.

Easy cleaning plus stable activation of glassy carbon electrode surface by oxygen plasma

Glassy carbon (GC) electrodes are widely used in electroanalytical applications especially in bioelectrochemistry. Their use starts with an efficient surface cleaning and activation protocol, mostly based on surface polishing steps. We studied the use of an oxygen plasma exposure of GC electrodes to replace common polishing procedures. The cyclic voltammetry (CV) responses of ferrocyanide and ferrocene-dimethanol were used to compare brand new, surface-polished and plasma-treated GC electrodes. Plasma treatment induces CV responses with improved features, close to theoretical values, as compared to other methods. The plasma effects were quasi-stable over a week when electrodes were stored in water, this being explained by increased surface energy and hydrophilicity. Furthermore, when electroreduction of diazonium was performed on GC electrodes, the surface blockade could be removed by the plasma. Thus, a short oxygen plasma treatment is prone to replace polishing protocols, that display person-dependent efficiency, in most of the experiments with GC electrodes.

Electrodeposited reduced graphene oxide-PEDOT:PSS/Nafion hybrid interface for the simultaneous determination of dopamine and serotonin

The electrochemically deposited reduced graphene oxide-PEDOT:PSS/Nafion (rGO-PP/NF) hybrid material has provided a favorable interface for the simultaneous detection of dopamine (DA) and serotonin (5-HT). The rGO-PP/NF onto the Au seed layer of the flexible substrate was simple, and it was followed by the sequential electrophoretic deposition of GO, reduction at the optimal pH buffer media, electropolymerization of EDOT:PSS, and Nafion coating. The strong electron-transport capacity between rGO-PEDOT:PSS and the negatively charged Nafion matrix might allow the highly sensitive, simultaneous, and selective detection of DA and 5-HT due to its high affinity for cations. In the results of the electrochemical response, well-separated oxidation peaks were observed in a mixture that contained various concentrations of DA and 5-HT. It showed the dynamic sensing of DA and 5-HT in the ranges of 0.5-75 μM and 0.05-50 μM, respectively, and the detection limits of 0.17 and 0.16 μM, respectively. In the mixture of DA and 5-HT, the sensor had a detection limit of 0.1 μM for 5-HT and DA, and its sensitivities of DA and 5-HT were 99.3 and 86 µA/µMcm2. Furthermore, it demonstrated high selectivity, reproducibility, stability, and a recovery property in the human serum spike test that was good enough for the practical use.

Simultaneous detection of neurotransmitters and Cu2+ using double-bore carbon fiber microelectrodes via fast-scan cyclic voltammetry

There is a great demand to broaden our understanding of the multifactorial complex etiology of neurodegenerative diseases to aid the development of more efficient therapeutics and slow down the progression of neuronal cell death. The role of co-transmission and the effect of environmental factors on such diseases have yet to be explored adequately, mainly due to the lack of a proper analytical tool that can perform simultaneous multi-analyte detection in real time with excellent analytical parameters. In this study, we report a simple fabrication protocol of a double-bore carbon-fiber microelectrode (CFM) capable of performing rapid simultaneous detection of neurotransmitters and Cu2+via fast-scan cyclic voltammetry (FSCV) in Tris buffer. After imaging our CFMs via optical microscopy and scanning electron microscopy to ensure the intact nature of the two electrodes in our electrode composite, we performed a detailed analysis of the performance characteristics of our double-bore CFM in five different analyte mixtures, Cu2+-5HT, Cu2+-DA, Cu2+-AA, 5-HT-DA, and 5-HT-AA in Tris buffer, by applying different analyte-specific FSCV waveforms simultaneously. Calibration curves for each analyte in each mixture were plotted while extracting the analytical parameters such as the limit of detection (LOD), linear range, and sensitivity. We also carried out a control experiment series for the same mixtures with single-bore CFMs by applying one waveform at a time to compare the capabilities of our double-bore CFMs. Interestingly, except for the Cu2+-DA solution, all other combinations showed improved LOD, linear ranges, and sensitivity when detecting simultaneously with double-bore CFMs compared to single-bore CFMs, an excellent finding for developing this sensor for future in vivo applications.

Truncated Electrochemical Aptasensor with Enhanced Antifouling Capability for Highly Sensitive Serotonin Detection

Accurate determination of serotonin (ST) provides insight into neurological processes and enables applications in clinical diagnostics of brain diseases. Herein, we present an electrochemical aptasensor based on truncated DNA aptamers and a polyethylene glycol (PEG) molecule-functionalized sensing interface for highly sensitive and selective ST detection. The truncated aptamers have a small size and adopt a stable stem-loop configuration, which improves the accessibility of the aptamer for the analyte and enhances the sensitivity of the aptasensor. Upon target binding, these aptamers perform a conformational change, leading to a variation in the Faraday current of the redox tag, which was recorded by square wave voltammetry (SWV). Using PEG as blocking molecules minimizes nonspecific adsorption of other interfering molecules and thus endows an enhanced antifouling ability. The proposed electrochemical aptamer sensor showed a wide range of detection lasting from 0.1 nM to 1000 nM with a low limit of detection of 0.14 nM. Owing to the unique properties of aptamer receptors, the aptasensor also exhibits high selectivity and stability. Furthermore, with the reduced unspecific adsorption, assaying of ST in human serum and artificial cerebrospinal fluid (aCSF) showed excellent performance. The reported strategy of utilizing antifouling PEG describes a novel approach to building antifouling aptasensors and holds great potential for neurochemical investigations and clinical diagnosis.

Smartphone-based detection of levodopa in human sweat using 3D printed sensors

Parkinson's disease (PD) is one of the leading neurological disorders negatively impacting health on a global scale. Patients diagnosed with PD require frequent monitoring, prescribed medications, and therapy for extended periods as symptom severity worsens. The primary pharmaceutical treatment for PD patients is levodopa (L-Dopa) which reduces many symptoms experienced by PD patients (e.g., tremors, cognitive ability, motor dysfunction, etc.) through the regulation of dopamine levels in the body. Herein, the first detection of L-Dopa in human sweat using a low-cost 3D printed sensor with a simple and rapid fabrication protocol combined with a portable potentiostat wirelessly connected to a smartphone via Bluetooth is reported. By combining saponification and electrochemical activation into a single protocol, the optimized 3D printed carbon electrodes were able to simultaneously detect uric acid and L-Dopa throughout their biologically relevant ranges. The optimized sensors provided a sensitivity of 83 ± 3 nA/μM from 24 μM to 300 nM L-Dopa. Common physiological interferents found in sweat (e.g., ascorbic acid, glucose, caffeine) showed no influence on the response for L-Dopa. Lastly, a percent recovery of L-Dopa in human sweat using a smartphone-assisted handheld potentiostat resulted in the recovery of 100 ± 8%, confirming the ability of this sensor to accurately detect L-Dopa in sweat.

Development of an electrochemical sensor based on ternary oxide SiO2/Al2O3/SnO2 modified with carbon black for direct determination of clothianidin in environmental and food samples

This study presents the development of an electrochemical sensor, denoted as GCE/CB/SiAlSn, based on the modification of a glassy carbon electrode surface with the ternary oxide SiO2/Al2O3/SnO2 associated with carbon black, for direct determination of the neonicotinoid pesticide clothianidin in different matrices, such as environmental and food samples. Morphological characterization by the scanning electron microscopy technique, electroanalytical analyses using the cyclic voltammetry technique and differential pulse voltammetry are presented which demonstrated that the developed electrochemical platform presents high sensitivity in the electroanalytical clothianidin determination. The linear range studied was from 2.99 × 10-7 to 6.04 × 10-5 mol L-1, with an LOD of 2.47 nmol L-1. This high sensitivity was explained using the synergistic relationship between carbon black and ternary oxide that maximized the electroactive surface area of the GCE/CB/SiAlSn sensor. Interferent studies were performed that showed high selectivity of the sensor to the pesticide in the presence of Ca2+, K+, Na+, and Mg2+ and carbendazim, glyphosate, imidacloprid and thiamethoxam pesticides. The sensor was applied to real samples of tap water and apple juice obtaining recoveries from 91.0% to 103.0%.

Review on Surface-Modified Electrodes for the Enhanced Electrochemical Detection of Selective Serotonin Reuptake Inhibitors (SSRIs)

Selective serotonin re-uptake inhibitors (SSRIs) are one of the most commonly prescribed classes of antidepressants used for the treatment of moderate to severe depressive disorder, personality disorders and various phobias. This class of antidepressants was created with improved margins of safety. However, genetic polymorphism may be responsible for the high variability in patients' responses to treatment, ranging from failure to delayed therapeutic responses to severe adverse effects of treatment. It is crucial that the appropriate amount of SSRI drugs is administered to ensure the optimum therapeutic efficacy and intervention to minimise severe and toxic effects in patients, which may be the result of accidental and deliberate cases of poisoning. Determining SSRI concentration in human fluids and the environment with high sensitivity, specificity and reproducibility, and at a low cost and real-time monitoring, is imperative. Electrochemical sensors with advanced functional materials have drawn the attention of researchers as a result of these advantages over conventional techniques. This review article aims to present functional materials such as polymers, carbon nanomaterials, metal nanomaterials as well as composites for surface modification of electrodes for sensitive detection and quantification of SSRIs, including fluoxetine, citalopram, paroxetine, fluvoxamine and sertraline. Sensor fabrication, sensor/analyte interactions, design rationale and properties of functional material and the electrocatalytic effect of the modified electrode on SSRI detection are discussed.

Quantification of tramadol and serotonin by cobalt nickel tungstate in real biological samples to evaluate the effect of analgesic drugs on neurotransmitters

In this work, CoNiWO4 nanocomposite was used as an electrochemical sensor for the simultaneous electrochemical detection of tramadol and serotonin. The nanocomposite was synthesized using a hydrothermal method and characterized via XRD, SEM, TGA, Zeta, UV, and FTIR. The sensor was developed by depositing CoNiWO4-NPs onto the glassy carbon electrode surface. Tramadol and serotonin were detected by employing cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and chronoamperometry. Analytes were detected at different pH, concentrations, and scan rates. The prepared sensor showed a 0-60 µM linear range, with a LOD of 0.71 µM and 4.29 µM and LOQ of 14.3 µM and 2.3 µM for serotonin and tramadol, respectively. Finally, the modified electrode (CoNiWO4-GCE) was applied to determine tramadol and serotonin in biological samples.

Electrochemical Biosensors for Whole Blood Analysis: Recent Progress, Challenges, and Future Perspectives

Whole blood, as one of the most significant biological fluids, provides critical information for health management and disease monitoring. Over the past 10 years, advances in nanotechnology, microfluidics, and biomarker research have spurred the development of powerful miniaturized diagnostic systems for whole blood testing toward the goal of disease monitoring and treatment. Among the techniques employed for whole-blood diagnostics, electrochemical biosensors, as known to be rapid, sensitive, capable of miniaturization, reagentless and washing free, become a class of emerging technology to achieve the target detection specifically and directly in complex media, e.g., whole blood or even in the living body. Here we are aiming to provide a comprehensive review to summarize advances over the past decade in the development of electrochemical sensors for whole blood analysis. Further, we address the remaining challenges and opportunities to integrate electrochemical sensing platforms.

Resultant inward imbalanced seeding force (RIISF)-induced concave gold nanostar (CAuNS) for non-enzymatic electrocatalytic detection of serotonin and Kynurenine in human serum

CTAC-based gold nanoseed-induced concave curvature evolution of surface boundary planes from concave gold nanocube (CAuNC) to concave gold nanostar (CAuNS) has been achieved by a novel synthetic methodology simply by controlling the extent of seed used and hence the generated 'Resultant Inward Imbalanced Seeding Force (RIISF)'. The resultant CAuNS shows an excellent enhancement in catalytic activity compared to CAuNC and other intermediates as a function of curvature-induced anisotropy. Detailed characterization evaluates the presence of an enhanced number of multiple defect sites, high energy facets, larger surface area, and roughened surface which ultimately results in an increased mechanical strain, coordinately unsaturation, and multifacet-oriented anisotropic behavior suitable for positive influence on the binding affinity of CAuNSs. While different crystalline and structural parameters improve their catalytic activity, the resultant uniform three-dimensional (3D) platform shows comparatively easy pliability and well absorptivity on the glassy carbon electrode surface for increased shelf life, a uniform structure to confine a large extent of stoichiometric systems, and long-term stability under ambient conditions for making this newly developed material a unique nonenzymatic scalable universal electrocatalytic platform. With the help of various electrochemical measurements, the ability of the platform has been established by performing highly specific and sensitive detection of the two most important human bio messengers: Serotonin (STN) and Kynurenine (KYN) which are metabolites of L-Tryptophan in the human body system. The present study mechanistically surveys the role of seed-induced RIISF-modulated anisotropy in controlling the catalytic activity which offers a universal 3D electrocatalytic sensing tenet by an electrocatalytic approach.

A portable electrochemical sensing platform for serotonin detection based on surface-modified carbon fiber microelectrodes

Serotonin (5-HT) is one of the key neurotransmitters in the human body, regulating numerous physiological functions. A disruption in 5-HT homeostasis could result in serious health problems, including neurodegenerative disorders, depression, and 5-HT syndrome. Detection of 5-HT concentrations in biological fluids, such as urine, is a potential solution for early diagnosis of these diseases. In this study, we developed a novel, simple, and low-cost electrochemical sensing platform consisting of a portable workstation with customized electrodes for 5-HT detection in artificial biological fluids. Nafion/carbon nanotubes (CNTs) and electrochemically modified carbon fiber microelectrodes (Nafion-CNT/EC CFMEs) displayed improved 5-HT sensitivity and selectivity. Together with a customized Ag/AgCl reference electrode and Pt counter electrode, the portable 5-HT sensing platform had a sensitivity of 0.074 μA μM^-1 and a limit of detection (LOD) of 140 nM. This system was also assessed to measure 5-HT spiked in artificial urine samples, showing nearly full recovery rates. These satisfactory results demonstrated that the portable system exhibits outstanding performance and confirmed the feasibility of 5-HT detection, which can be used to provide point-of-care analysis in actual biological samples.

Tuning the Fe/Co ratio towards a bimetallic Prussian blue analogue for the ultrasensitive electrochemical sensing of 5-hydroxytryptamine

Lack of highly efficient, inexpensive, and easily available catalysts severely limits the practical applicability of electrochemically sensing assay towards 5-hydroxytryptamine (5-HT). Herein, four kinds of Fe-Co bimetallic Prussian blue analogues (FeCo-PBAs) with different molar ratios of Fe to Co were prepared using a simple coprecipitation method. Interestingly, Fe(III) in K₃ [Fe(CN)₆] can be reduced to Fe(II) by adding trisodium citrate dehydrate, which could offer a new clue to synthesize PBAs with Fe(II) core ions. With the optimizational FeCo-PBA synthesized at a 0.5/1 M ratio of Fe to Co as an electrocatalyst, the constructed sensor shows excellent comprehensive performance for the 5-HT assay with a high sensitivity of 0.856 μA μM^-1 and an ultralow detection limit of 8.4 nM. Under the optimum conditions, linearity was obtained in the ranges of 0.1-10.0 μM and 10.0-200.0 μM and preferable recoveries ranged from 97.8% to 103.0% with relative standard deviation (RSD) < 4.0%. The integrated properties of FeCo-PBA can be comparable to previously reported electrocatalysts for the 5-HT assay including noble metal-based and expensive carbon (graphene and carbon nanotubes)-based electrocatalysts. The proposed sensor also exhibits outstanding selectivity, reproducibility, and practicality for real sample analyses. This work is the first report on the PBA-based sensor for the 5-HT assay, verifying the practicability of this high-performance sensor for the 5-HT assay.

Significance of an Electrochemical Sensor and Nanocomposites: Toward the Electrocatalytic Detection of Neurotransmitters and Their Importance within the Physiological System

A prominent neurotransmitter (NT), dopamine (DA), is a chemical messenger that transmits signals between one neuron to the next to pass on a signal to and from the central nervous system (CNS). The imbalanced concentration of DA may cause numerous neurological sicknesses and syndromes, for example, Parkinson's disease (PD) and schizophrenia. There are many types of NTs in the brain, including epinephrine, norepinephrine (NE), serotonin, and glutamate. Electrochemical sensors have offered a creative direction to biomedical analysis and testing. Researches are in progress to improve the performance of sensors and develop new protocols for sensor design. This review article focuses on the area of sensor growth to discover the applicability of polymers and metallic particles and composite materials as tools in electrochemical sensor surface incorporation. Electrochemical sensors have attracted the attention of researchers as they possess high sensitivity, quick reaction rate, good controllability, and instantaneous detection. Efficient complex materials provide considerable benefits for biological detection as they have exclusive chemical and physical properties. Due to distinctive electrocatalytic characteristics, metallic nanoparticles add fascinating traits to materials that depend on the material's morphology and size. Herein, we have collected much information on NTs and their importance within the physiological system. Furthermore, the electrochemical sensors and corresponding techniques (such as voltammetric, amperometry, impedance, and chronoamperometry) and the different types of electrodes' roles in the analysis of NTs are discussed. Furthermore, other methods for detecting NTs include optical and microdialysis methods. Finally, we show the advantages and disadvantages of different techniques and conclude remarks with future perspectives.

Design and Fabrication of α-MnO2-Nanorods-Modified Glassy-Carbon-Electrode-Based Serotonin Sensor

Serotonin is a very important monoamine neurotransmitter, which takes part in biological and psychological processes. In the present scenario, design and fabrication of a serotonin electrochemical sensor is of great significance. In this study, we have synthesized α-MnO₂ via a hydrothermal synthesis method using potassium permanganate as a precursor. The physiochemical properties, such as structural and phase-purity of the prepared α-MnO₂, were investigated by various characterization techniques and methods (powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy). Furthermore, the serotonin sensor was fabricated using α-MnO₂ as an electrode modifier or electro-catalyst. The bare glassy carbon electrode (GCE) was adopted as a working substrate, and its active carbon surface was modified with the synthesized α-MnO₂. This modified GCE (α-MnO₂/GCE = MGCE) was explored as a serotonin sensor. The electrochemical investigations showed that the MGCE has excellent electro-catalytic properties towards determination of serotonin. The MGCE exhibits an excellent detection limit (DL) of 0.14 µM, along with good sensitivity of 2.41 µAµM^-1 cm^-2. The MGCE also demonstrated excellent selectivity for determination of serotonin in the presence of various electro-active/interfering molecules. The MGCE also exhibits good cyclic repeatability, stability, and storage stability.

New Trends in Fluorescent Nanomaterials-Based Bio/Chemical Sensors for Neurohormones Detection-A Review

The study of neurotransmitters and stress hormones allows the determination of indicators of the current stress load in the body. These species also create a proper strategy of stress protection. Nowadays, stress is a general factor that affects the population, and it may cause a wide range of serious disorders. Abnormalities in the level of neurohormones, caused by chronic psychological stress, can occur in, for instance, corporate employees, health care workers, shift workers, policemen, or firefighters. Here we present a new nanomaterials-based sensors technology development for the determination of neurohormones. We focus on fluorescent sensors/biosensors that utilize nanomaterials, such as quantum dots or carbon nanomaterials. Nanomaterials, owing to their diversity in size and shape, have been attracting increasing attention in sensing or bioimaging. They possess unique properties, such as fluorescent, electronic, or photoluminescent features. In this Review, we summarize new trends in adopting nanomaterials for applications in fluorescent sensors for neurohormone monitoring.

A review on nanomaterial-based electrochemical sensors for determination of vanillin in food samples

Vanillin is an organic compound that not only acts as a flavoring and fragrance enhancer in some foods, but also can have antioxidant, anti-inflammatory, anti-cancer and anti-depressant effects. Nevertheless, its excessive use can be associated with side effects on human health. Consequently, there is a need to achieve a rapid vanillin determination approach to enhance food safety. The diversity and high sensitivity of analytical approaches has led researchers to use more advanced and efficient methods providing quantitative and qualitative outcomes in complex matrices. Among these, prominent attention has been drawn to electrochemical sensors for reasons such as reliability, simplicity, cost-effectiveness, portability, selectivity, and ease of operation, especially for the determination of vanillin. Nanomaterials are a good candidate for sensor construction due to their commendable physicochemical attributes. Some advanced nanostructures with promising platforms for high-sensitivity, highly selective, and long-lasting electrochemical sensors include graphene (Gr) and its derivatives, graphite carbon nitride (g-C₃N₄), carbon nanotubes (CNTs), metal nanoparticles, metal organic frameworks, carbon nanofibers (CNFs) and quantum dots. Study about sizes, dimensions, and morphologies of nanomaterials makes strong candidates for improving sensitivity or selectivity according to electrocatalytic abilities. The low LOD and wide linear range of samples demonstrated an excellent catalytic performance towards the vanillin oxidation. Some investigations have reported the synergistic effects like great conductivity of carbon nanomaterials which improved the electrocatalytic performance of nanocomposites which demonstrated the estimable sensitivity of nanomaterial-supported electrochemical sensors for determination of vanillin concentrations. The sensors which have reported have a commendable response to practical potential and evaluated in biscuit, pudding powder, chocolate, custard specimens and etc. sensitivity, stability, reproducibility and repeatability of suggested sensor were investigated. The present review article scrutinizes recent advances in the fabrication of nanomaterial-based electrochemical sensors to detect vanillin in various food matrices.

Studies of Monoamine Neurotransmitters at Nanomolar Levels Using Carbon Material Electrodes: A Review

Neurotransmitters (NTs) with hydroxyl groups can now be identified electrochemically, utilizing a variety of electrodes and voltammetric techniques. In particular, in monoamine, the position of the hydroxyl groups might alter the sensing properties of a certain neurotransmitter. Numerous research studies using electrodes modified on their surfaces to better detect specific neurotransmitters when other interfering factors are present are reviewed to improve the precision of these measures. An investigation of the monoamine neurotransmitters at nanoscale using electrochemical methods is the primary goal of this review article. It will be used to determine which sort of electrode is ideal for this purpose. The use of carbon materials, such as graphite carbon fiber, carbon fiber micro-electrodes, glassy carbon, and 3D printed electrodes are only some of the electrodes with surface modifications that can be utilized for this purpose. Electrochemical methods for real-time detection and quantification of monoamine neurotransmitters in real samples at the nanomolar level are summarized in this paper.

An electrochemical sensor-based carbon black associated with a modified mixed oxide (SiO2/TiO2/Sb2O5) for direct determination of thiamethoxam in raw honey and water samples

The study aimed to develop an electrochemical sensor based on glassy carbon, mixed oxide (SiO₂/TiO₂/Sb₂O₅), and carbon black. The material was synthesized, characterized, and used to determine thiamethoxam in raw honey and water. The morphologic structure and electrochemical performance of the sensor was characterized by scanning electron microscopy and cyclic voltammetry. Differential pulse voltammetry with a concentration of 0.1 mol L^-1 of Britton-Robinson buffer at pH 7.0 allowed the generation of a method to determine thiamethoxam in a linear range of 0.25 to 100.5 μmol L^-1 and with a limit of detection of 0.012 μmol L^-1. The system efficiently quantified traces of thiamethoxam in raw honey and tap water samples. The modified sensor did not present interferences of K⁺, Na⁺, Ca²⁺, Mg²⁺, glyphosate, imidacloprid, and carbendazim. In addition, the device showed good recovery values for thiamethoxam when applied directly to honey and water samples without any treatment, presenting an electrochemical sensor to monitor real-time hazardous substances in environmental and food matrices.

Tetrahedral DNA Framework-Programmed Electrochemical Biosenors with Gold Nanoparticles for Ultrasensitive Cell-Free DNA Detection

Tumor-associated cell-free DNA (cfDNA) is a dynamic biomarker for genetic analysis, early diagnosis and clinical treatment of cancers. However, its detection has limitations because of its low abundance in blood or other complex bodily fluids. Herein, we developed an ultrasensitive cfDNA electrochemical biosensor (E-cfDNA sensor) based on tetrahedral DNA framework (TDF)-modified gold nanoparticles (Au NPs) with an interface for cfDNA detection. By accurately controlling the numbers of base pairs on each DNA framework, three types of TDFs were programmed: 26 base pairs of TDF; 17 base pairs of TDF; and 7 base pairs of TDF (TDF-26, TDF-16 and TDF-7, respectively). We also combined the TDF with hybridization chain reaction (HCR) to achieve signal amplification. Under optimal conditions, we detected the breast cancer susceptibility gene 1 (BRCA-1), a representative cfDNA closely related to breast cancer. An ultra-low detection limit of 1 aM with a linear range from 1 aM to 1 pM by TDF-26 was obtained, which was superior to the existing methods. Each type of TDF has excellent discrimination ability, which can distinguish single mismatch. More significantly, we also detected BRCA-1 in mimic serum samples, demonstrating that the E-cfDNA sensor has potential use in clinical research.

Recent Progresses in Electrochemical DNA Biosensors for MicroRNA Detection

MicroRNAs (miRNAs), as the small, non-coding, evolutionary conserved, and post-transcriptional gene regulators of the genome, have been highly associated with various diseases such as cancers, viral infections, and cardiovascular diseases. Several techniques have been established to detect miRNAs, including northern blotting, real-time polymerase chain reaction (RT-PCR), and fluorescent microarray platform. However, it remains a significant challenge to develop sensitive, accurate, rapid, and cost-effective methods to detect miRNAs due to their short size, high similarity, and low abundance. The electrochemical biosensors exhibit tremendous potential in miRNA detection because they satisfy feature integration, portability, mass production, short response time, and minimal sample consumption. This article reviewed the working principles and signal amplification strategies of electrochemical DNA biosensors summarized the recent improvements. With the development of DNA nanotechnology, nanomaterials and biotechnology, electrochemical DNA biosensors of high sensitivity and specificity for microRNA detection will shortly be commercially accessible.

Gold Nanorods (AuNRs) and Zeolitic Imidazolate Framework-8 (ZIF-8) Core-Shell Nanostructure-Based Electrochemical Sensor for Detecting Neurotransmitters

The development of novel electrode materials for rapid and sensitive detection of neurotransmitters in the human body is of great significance for early disease diagnosis and personalized therapy. Herein, gold nanorod@zeolitic imidazolate framework-8 (AuNR@ZIF-8) core-shell nanostructures were prepared by controlled encapsulation of gold nanorods within a ZIF-8 assembly. The designed AuNR@ZIF-8 nanostructures have uniform morphology, good dispersion, a large specific surface area, and an average size of roughly 175 nm. Compared with individual ZIF-8 and AuNR-modified electrodes, the obtained core-shell-structured AuNR@ZIF-8 nanocomposite structure-modified electrode shows excellent electrocatalytic performance in the determination of dopamine (DA) and serotonin (ST). The designed AuNR@ZIF-8 exhibited a wide linear range of 0.1-50 μM and low detection limit (LOD, 0.03 μM, S/N = 3) for the determination of DA, as well as a linear range of 0.1-25 μM and low LOD (0.007 μM, S/N = 3) for monitoring ST. The improved performance is attributed to the synergistic effect of the high conductivity of AuNRs and multiple catalytic sites of ZIF-8. The good electroanalytical ability of AuNR@ZIF-8 for detection of DA and ST can provide a guide to efficiently and rapidly monitor other neurotransmitters and construct novel electrochemical sensors.

Recognition elements based on the molecular biological techniques for detecting pesticides in food: A review

Excessive use of pesticides can cause contamination of the environment and agricultural products that are directly threatening human life and health. Therefore, in the process of food safety supervision, it is crucial to conduct sensitive and rapid detection of pesticide residues. The recognition element is the vital component of sensors and methods for fast testing pesticide residues in food. Improper recognition elements may lead to defects of testing methods, such as poor stability, low sensitivity, high economic costs, and waste of time. We can use the molecular biological technique to address these challenges as a good strategy for recognition element production and modification. Herein, we review the molecular biological methods of five specific recognition elements, including aptamers, genetic engineering antibodies, DNAzymes, genetically engineered enzymes, and whole-cell-based biosensors. In addition, the application of these identification elements combined with biosensor and immunoassay methods in actual detection was also discussed. The purpose of this review was to provide a valuable reference for further development of rapid detection methods for pesticide residues.

Assessment of Sumatriptan on Sepsis-Induced Kidney injury in the Cecal Ligation and Puncture Mice Model

Sepsis is a severe systemic inflammatory response with high mortality rate resulting from different microorganisms. Cytokines activation is essential for the immune response, but in painful conditions like sepsis, cytokines act as a double-edged sword and dysregulate immune response which is life-threatening owing to multiple organ dysfunction. The abnormality in 5-HT function is involved in pathological conditions like irritable bowel syndrome, inflammation, myocardial ischemia, itch and renal injury. Sumatriptan, a 5-HT_1B/1D agonist, has anti-inflammatory and anti-oxidative stress effects on animal models. This study was aimed to assess the effects of sumatriptan on kidney injury, the levels of pro-inflammatory cytokines and the percentage of survival in (CLP)-induced sepsis were examined.Cecal ligation and puncture (CLP) model was done on adult C57BL/6 male mice to induce Polymicrobial sepsis. Sumatriptan was injected intraperitoneally 1 h after the sepsis induction by CLP at doses of 0.1, 0.3, and 1 mg/kg in 3 treatment groups. To study the effect of sumatriptan on short-term survival, septic animals were detected 72 h after CLP. Serum levels of TNF-α, IL-1β, IL-6 and IL-10 were evaluated. To study sepsis-induced acute renal failure, kidney functional biomarkers and histopathological alterations were evaluated.Sumatriptan (0.3 mg/kg) administration significantly enhanced survival rate (P<0.01) compared to the CLP group. The beneficial effects of sumatriptan were related to a significant decrease in the pro-inflammatory cytokines and elevated level of IL-10. Sumatriptan presented protective effects on kidney biomarkers and histopathology assay.Anti-inflammatory effects of sumatriptan lead to decrease mortality rate and inflammatory cytokines in CLP induction sepsis in C57BL/6 mice.

High performance electrochemical method for simultaneous determination dopamine, serotonin, and tryptophan by ZrO2-CuO co-doped CeO2 modified carbon paste electrode

In this research, a paste containing ZrO₂-CuO-CeO₂ ternary nanocomposite and graphene (Gr) was used in constructing a carbon paste sensor for monitoring biomolecules including dopamine (Dop), serotonin (Ser) and tryptophan (Trp). The scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were utilized for ZrO₂-CuO-CeO₂ ternary nanocomposite characterization. The obtained data show that, the ZrO2-CuO-CeO₂/Gr and synergetic effect of using these three-metal oxide nanoparticles, could effectively improve the electron transfer kinetic and exhibit a high electrocatalytic activity, making it serve as a powerful tool for biomolecules analysis. The differential pulse (DP) and cycle voltammetry (CV) methods were applied for investigating electrochemical treatment of the analytes. In comparison to all of the previous voltammetric reports, this research has the lowest detection limit and widest linear range. The calibration curves in the optimum conditions were linear over the range of 0.008-7.2 and 7.2-185 μM for Dop, 0.008-7.9 and 7.9-205 μM for Ser and 0.009-8.6 and 8.6-194 μM for Trp. The calculated limit of detection (LOD) was 3.09, 3.49 and 5.32 nM for Dop, Ser and Trp, respectively. The applicability of this sensing device was tested by monitoring Dop, Ser and Trp in the human urine and plasma samples. The recovery percentage of the analysis in the real samples was between 95.6 and 104.74; also, the data of determination of Dop, Ser and Trp with ZrO₂-CuO-CeO₂/Gr/CPE was well close to HPLC data. The obtained result demonstrates that the ZrO₂-CuO-CeO₂/Gr/CPE has good selectivity, stability, reproducibility, and repeatability, and can be used for the routine analysis of Dop, Ser and Trp.

Development of a new highly sensitive serotonin sensor based on green synthesized silver nanoparticle decorated reduced graphene oxide

Electrochemical detection of serotonin (5-hydroxytryptamine, 5-HT) is proposed for the first time using a cost-effective and eco-friendly nanocomposite of AgNPs and rGO which is synthesized through an in situ green reduction process using rosemary leaf extract. The synthesized nanocomposite and the elaborate thin layers have been characterized using UV-Vis, FTIR, TEM, and EIS. The sensitivity of the developed sensor was evaluated by differential pulse voltammetry. The peak current measured at a voltage of 420 mV (vs. Ag/AgCl) increased linearly in the 0.1 nM to 100 µM concentration range. A very low limit of detection of 78 pM compared to those in recent studies reported in the literature was obtained. The innovative approach was successfully applied to the determination of serotonin in spiked artificial urine samples.

Targeted degradation of refractory organic compounds in wastewaters based on molecular imprinting catalysts

Efficient removal of low-concentration refractory pollutants is a crucial problem to ensuring water safety. The use of heterogeneous catalysis of molecular imprinting technology combined with traditional catalysts is a promising method to improve removal efficiency. Presently, the research into molecular imprinting targeting catalysts focuses mainly on material preparation and performance optimization. However, more researchers are investigating other applications of imprinting materials. This review provides recent progress in photocatalyst preparation, electrocatalyst, and Fenton-like catalysts synthesized by molecular imprinting. The principle and control points of target catalysts prepared by precipitation polymerization (PP) and surface molecular imprinting (S-MIP) are introduced. Also, the application of imprinted catalysts in targeted degradation of drugs, pesticides, environmental hormones, and other refractory pollutants is summarized. In addition, the reusability and stability of imprinted catalyst in water treatment are discussed, and the possible ecotoxicity risk is analyzed. Finally, we appraised the prospects, challenges, and opportunities of imprinted catalysts in the advanced oxidation process. This paper provides a reference for the targeted degradation of refractory pollutants and the preparation of targeted catalysts.