Simultaneous voltammetry detection of dopamine and uric acid in human serum and urine with a poly(procaterol hydrochloride) modified glassy carbon electrode

Integrating carbon dots and gold/silver core-shell nanoparticles to achieve sensitive detection of dopamine with fluorometric/colorimetric dual signal

Dopamine (DA) is a potent neuromodulator in the brain that affects a wide range of motivated behaviors. Abnormal concentration of DA is related to a variety of diseases. Hence, it is imperative to establish a rapid and precise method for quantifying DA. In this work, we integrate orange-yellow emissive carbon dots (CDs) with target-induced silver deposition on gold nanoparticles (Au NPs), forming gold/silver core-shell nanoparticles (Au@Ag NPs), to construct a fluorometric and colorimetric dual-signal sensor for sensitive detection of DA. Au NPs and silver ions (Ag+) have minimal effect on the fluorescence of CDs. DA can reduce the silver ions to Ag(0) on the surface of the Au NPs to form a silver shell, resulting in the blue-shift of the absorbance peak from 520 to 416 nm, which overlaps with the excitation spectrum of CDs. As a result, the system color turns from pink to orange-yellow, and the fluorescence of CDs is quenched due to the strong inner filter effect. The linear range of the colorimetry is 0.5-18 μM with a limit of detection (LOD) of 0.41 μM, while the linear range for the fluorometry method is 0.5-14 μM with a LOD of 0.021 μM. This method demonstrates notable advantages including a low detection limit, rapid response time, and straightforward operation in practical samples, showing great potential in biomedical analysis.

A colorimetric detection of dopamine in urine and serum based on the CeO2 @ZIF-8/Cu-CDs laccase-like nanozyme activity

This study reports a sensitive and selective colorimetric approach for the analysis of dopamine (DA) based on CeO2 @ZIF-8/Cu-CDs laccase-like nanozymes activity. The CeO2 @ZIF-8/Cu-CDs was synthesized using cerium oxide (CeO2 ) and copper-doped carbon dots (Cu-CDs) with 2-methylimidazole by a facilely hydrothermal approach. The CeO2 @ZIF-8/Cu-CDs exhibited excellent laccase-like nanozymes activity and can oxidize the colorless substrate (DA) to red product with 4-aminoantipyrine as the chromogenic agent. The Michaelis-Menten constant (Km ) and the maximal velocity (Vmax ) of CeO2 @ZIF-8/Cu-CDs are 0.20 mM and 1.48 μM/min, respectively. The detection method has a linear range of 0.05-7.5 μg/mL and a detection limit as low as 8.5 ng/mL with good reproducibility. The developed colorimetric sensor was applied to rapid and precise quantitative evaluation of DA levels in serum and urine samples. This study presents a new approach for detecting biological molecules by utilizing the controlled regulation of nanozymes' laccase-like activity.

Square-wave voltammetry of human blood serum

A study on voltammetric analysis of blood serum diluted in a phosphate buffer is presented using advanced square-wave voltammetry at an edge plane pyrolytic graphite electrode. The results demonstrate that even in a complex medium like human blood serum, electrochemical characterization can be achieved through the use of advanced voltammetric techniques in conjunction with an appropriate commercially available electrode, such as the edge plane pyrolytic graphite electrode, which boosts superior electrocatalytic properties. Without undergoing any chemical treatment of the serum sample, the square-wave voltammetry technique reveals, for the first time, the electrode reactions of uric acid, bilirubin, and albumin in a single experiment, as represented by well-defined, separated, and intense voltammetric signals. All electrode processes are surface-confined, indicating that the edge plane sites of the electrode serve as an ideal platform for the competitive adsorption of electroactive species, despite the extensive chemical complexity of the serum samples. The speed and differential nature of square-wave voltammetry are crucial for obtaining an outstanding resolution of the voltammetric peaks, maintaining the quasi-reversible nature of the underlying electrode processes, while reducing the impact of follow-up chemical reactions that are coupled to the initial electron transfer for all three detected species, and minimizing fouling of the electrode surface.

Construction of a nano dispersed Cr/Fe-polycrystalline sensor via high-energy mechanochemistry for simultaneous electrochemical determination of dopamine and uric acid

A bimetallic polycrystalline sensor (Cr/Fe-SNCM) having nanosized and high dispersion was designed and used for the electrochemical simultaneous determination of dopamine (DA) and uric acid (UA). Catalytic nanosized Cr/Fe were highly anchored on N/S/O-contained porous carbon with high dispersion and polycrystalline Cr/Fe via energetic mechanochemical method and high-temperature carbonization. The obtained Cr/Fe-SNCM exhibited high graphitized carbon supporter and endowed high electron transport and signal output for the whole sensor. Moreover, highly dispersed Cr/Fe sites and the polycrystalline form (metal-N/S/O) efficiently enhanced the catalytic reaction, leading to a limits of detection (based on the 3σ/m criterion) of 25.8 and 22.5 nM for DA and UA, respectively. This is 1-2 orders of magnitude lower than many state-of-the-art reported sensors. The Cr/Fe-SNCM_1.0 sensor exhibited wide working range (0.1 to 10.0 μM), high recovery (96-103%) and low relative standard deviation (RSD = 3.2-4.7%) for DA and UA in real serum samples, possessing high significance for practical large-scale applications.

Simultaneous Determination of Dopamine and Uric Acid in Real Samples Using a Voltammetric Nanosensor Based on Co-MOF, Graphene Oxide, and 1-Methyl-3-butylimidazolium Bromide

A chemically modified carbon paste electrode, based on a CoMOF-graphene oxide (GO) and an ionic liquid of 1-methyl-3-butylimidazolium bromide (CoMOF-GO/1-M,3-BB/CPE), was fabricated for the simultaneous determination of dopamine (DA) and uric acid (UA). The prepared CoMOF/GO nanocomposite was characterized by field emission-scanning electron microscopy (FE-SEM), the X-ray diffraction (XRD) method, a N₂ adsorption-desorption isotherm, and an energy dispersive spectrometer (EDS). The electrochemical sensor clearly illustrated catalytic activity towards the redox reaction of dopamine (DA), which can be authenticated by comparing the increased oxidation peak current with the bare carbon paste electrode. The CoMOF-GO/1-M,3-BB/CPE exhibits a wide linear response for DA in the concentration range of 0.1 to 300.0 µM, with a detection limit of 0.04 µM. The oxidation peaks' potential for DA and uric acid (UA) were separated well in the mixture containing the two compounds. This study demonstrated a simple and effective method for detecting DA and UA in real samples.

Gold-Modified Molecularly Imprinted N-Methacryloyl-(l)-phenylalanine-containing Electrodes for Electrochemical Detection of Dopamine

A molecularly imprinted polymer-based pencil graphite electrode (MIP PGE) sensor, modified with gold nanoparticles, was utilized for the detection of dopamine in the presence of other biochemical compounds using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), depending on its strong electroactivity function. The pulse voltammetry methods recorded the highest response. In addition to the high oxidation rate of DA and the other biomolecule interferences available in the sample matrix used, which cause overlapping voltammograms, we aimed to differentiate them in a highly sensitive limit of detection range. The calibration curves for DA were obtained using the CV and DPV over the concentration range of 0.395–3.96 nM in 0.1 M phosphate buffer solution (PBS) at pH 7.4 with a correlation coefficient of 0.996 and a detection limit of 0.193 nM. The electrochemical technique was employed to detect DA molecules quantitatively in human blood plasma selected as real samples without applying any pre-treatment processes. MIP electrodes proved their ability to detect DA with high selectivity, even with epinephrine and norepinephrine competitor molecules and interferences, such as ascorbic acid (AA). The high level of recognition achieved by molecularly imprinted polymers (MIPs) is essential for many biological and pharmaceutical studies.

Electrochemical Determination of Kynurenine Pathway Metabolites-Challenges and Perspectives

In recent years, tryptophan metabolism via the kynurenine pathway has become one of the most active research areas thanks to its involvement in a variety of physiological processes, especially in conditions associated with immune dysfunction, central nervous system disorders, autoimmunity, infection, diabetes, and cancer. The kynurenine pathway generates several metabolites with immunosuppressive functions or neuroprotective, antioxidant, or toxic properties. An increasing body of work on this topic uncovers a need for reliable analytical methods to help identify and quantify tryptophan metabolites at physiological concentrations in biological samples of different origins. Recent methodological advances in the fabrication and application of electrochemical sensors promise a rise in the future generation of novel analytical systems. This work summarizes current knowledge and provides important suggestions with respect to direct electrochemical determinations of kynurenine pathway metabolites (kynurenines) in complex biological matrices. Measurement challenges, limitations, and future opportunities of electroanalytical methods to advance study of the implementation of kynurenines in disease conditions are discussed.

A novel metal organic gel with superior oxidase-like activity for efficient and sensitive chemiluminescence detection of uric acid

It is found that MIL-100(Fe) gels, as a kind of metal-organic gels (MOGs), constitutting of iron (Fe³⁺) and trimesic acid (H₃BTC), has been regarded as the efficient catalyst of luminol chemiluminescence (CL) system without the presence of extra oxidants in the present work. MIL-100(Fe) gels that have possessed mimicking oxidase-like activity can excellently enhanced luminol CL intensity by accelerating the generation of reactive oxygen species. Furthermore, with the addition of uric acid (UA), the CL signal has been dramatically inhibited under alkaline condition. Hence, the CL intensity inhibiting ratio (I₀/I_S) was proportional to the increasing concentration of UA in the rang from 10 nM to 4000 nM with the detection limit of 5.9 nM. This method has been successfully applied for analysis of UA with acceptable recoveries ranging from 97.0% to 107.9% in urine sample. These results indicates that this study open up a novel, sensitive and convenient method to detect UA in biological samples.

Electrochemical Sensors Based on Conducting Polymers for the Aqueous Detection of Biologically Relevant Molecules

Electrochemical sensors appear as low-cost, rapid, easy to use, and in situ devices for determination of diverse analytes in a liquid solution. In that context, conducting polymers are much-explored sensor building materials because of their semiconductivity, structural versatility, multiple synthetic pathways, and stability in environmental conditions. In this state-of-the-art review, synthetic processes, morphological characterization, and nanostructure formation are analyzed for relevant literature about electrochemical sensors based on conducting polymers for the determination of molecules that (i) have a fundamental role in the human body function regulation, and (ii) are considered as water emergent pollutants. Special focus is put on the different types of micro- and nanostructures generated for the polymer itself or the combination with different materials in a composite, and how the rough morphology of the conducting polymers based electrochemical sensors affect their limit of detection. Polypyrroles, polyanilines, and polythiophenes appear as the most recurrent conducting polymers for the construction of electrochemical sensors. These conducting polymers are usually built starting from bifunctional precursor monomers resulting in linear and branched polymer structures; however, opportunities for sensitivity enhancement in electrochemical sensors have been recently reported by using conjugated microporous polymers synthesized from multifunctional monomers.

A novel bromelain-MnO2 biosensor for colorimetric determination of dopamine

We report a method for determining dopamine in serum via colorimetric sensing. This new method adopts bromelain-templated MnO₂ nanosheets that possess high oxidase activity. 3,3′,5,5′-Tetramethylbenzidine (TMB) can be directly oxidized by bromelain-MnO₂ nanosheets to oxTMB products.

A flexible carbon nanotube-modified poly(styrene-butadiene)-based dopamine sensor

In this work, a multi-walled carbon nanotube-modified flexible poly(styrene-butadiene) fiber membrane material was prepared for the sensitive and selective electrochemical detection of dopamine (DA) in human serum and DA injection. The flexible fiber membrane prepared by electrospinning technology is expected to realize its application in wearable devices. The obtained conductive film-based electrochemical sensor can effectively minimize interference caused by ascorbic acid and uric acid. Under the optimized experimental conditions of differential pulse voltammetry, DA gives a linear response in the range of 1-650 μM (R² = 0.996). The detection limit of DA (signal-to noise ratio = 3) was determined to be 0.062 μM.

Molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon: fabrication, characterization and electrochemical detection of uric acid

An electrochemical sensor is described for determination of uric acid (UA). Carbon-enwrapped nickel nanoparticles (Ni@BC) were coated with polydopamine (PDA) that was molecularly imprinted with UA. The biomass carbon (BC) was synthesized by one-step solid-state pyrolysis from leaves of Firmiana platanifolia. The imprinted polymer was obtained by electrodeposition of DA as the monomer. The amount of monomer, the scan cycles, pH value and adsorption time were optimized. Furthermore, the selectivity of the MIP for UA on a glassy carbon electrode (GCE) was evaluated by selectivity tests. The differential pulse voltammetric responses to UA with and without interferents were consistent. The modified GCE has a linear response in the 0.01-30 μM UA concentration range, and the limit of detection is 8 nM. The MIP electrode was applied to the analysis of UA in urine for which the initial concentrations were determined by the phosphotungstic acid kit. Recoveries ranged from 91.3 to 113.4%, with relative standard deviations between 1.3 and 9.7% (n = 3). Graphical abstract Schematic presentation of electrochemical detection of uric acid by molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon (Ni@BC-MIP).

An electrochemical sensor based on poly(procaterol hydrochloride)/carboxyl multi-walled carbon nanotube for the determination of bromhexine hydrochloride

Poly(procaterol hydrochloride) (p-ProH) polymeric film was successfully deposited onto the carboxyl multi-walled carbon nanotube (CMWCNT) modified glass carbon electrode (GCE) to construct a p-ProH/CMWCNT composite modified GCE. Due to the synergistic effect of p-ProH and CMWCNT in the composite, the developed sensor can enormously enhance the oxidation peak current of bromhexine hydrochloride (BrH) at ca. + 0.90 V. Based on this appearance, an electrochemical method was established for the sensitive and selective determination of BrH with differential pulse voltammetry (DPV). Various conditions affecting the peak current response of BrH were studied and optimized. Under the best conditions, the oxidation peak current of BrH is linear to its concentration in two linear dynamic ranges of 0.2–1.0 μmol L⁻¹ (R = 0.9948) and 1.0–8.0 μmol L⁻¹ (R = 0.9956), with a detection limit of 0.1 μmol L⁻¹ (S/N = 3). Interference experiment indicated that the as-prepared electrochemical sensor showed wonderful selectivity to the recognition of BrH and was free from disturbance of many other electro-active substances such as dopamine, ascorbic and uric acid. Finally, the practicability of the BrH sensor was verified by the satisfactory results acquired from the BrH determination in pharmaceutical preparation and human serum.

The fabrication process of the p-ProH/CMWCNT/GCE.

A colorimetric assay system for dopamine using microfluidic paper-based analytical devices

We report the colorimetric detection of dopamine (DA) on microfluidic paper-based analytical devices (μPADs) using an oxidation-reduction method. Here, dopamine reacts with ferric chloride forming reduced Fe²⁺ that subsequently reacts with phenanthroline to form the red tris(1,10-phenanthroline)iron(II) complex. The devices were fabricated by wax printing and changes in color intensity were recorded using a common cell phone. Subsequent analysis using Photoshop software, yielded a limit of detection (LOD) for DA of 0.37 μmol/L with a linear range of 0.527-4.75 μmol/L and relative standard deviation of 0.11% (inter-day) and 0.15% (intra-day) for n = 15 paper chips. The effects of detection conditions have been investigated and are discussed. Cow serum samples and human blood serum and plasma samples were detected. The work, herein, demonstrates the potential of this method as a low cost and rapid colorimetric technique to detect DA in real samples.