A fast and facile electrochemical method for the simultaneous detection of epinephrine, uric acid and folic acid based on ZrO2/ZnO nanocomposites as sensing material

Platinum-ruthenium-iron embedded in nitrogen-doped ordered mesoporous carbon for adrenaline electrochemical sensing study

A novel nitrogen-doped ordered mesoporous carbon (OMC) pore-embedded growth Pt-Ru-Fe nanoparticles (Pt1-Ru7.5-Fex@N-OMCs) composite was designed and synthesized for the first time. SBA-15 was used as a template, and dopamine was used as a carbon and nitrogen source and metal linking reagent. The oxidative self-polymerization reaction of dopamine was utilized to polymerize dopamine into two-dimensional ordered SBA-15 template pores. Iron porphyrin was introduced as an iron source at the same time as polymerization of dopamine, which was introduced inside and outside the pores using dopamine-metal linkage. Carbonization of polydopamine, nitrogen doping and iron nanoparticle formation were achieved by one-step calcination. Then the templates were etched to form Fex@N-OMCs, and finally the Pt1-Ru7.5-Fex@N-OMCs composites were stabilized by the successful introduction of platinum-ruthenium nanoparticles through the substitution reaction. The composite uniformly embeds the transition metal nanoparticles inside the OMC pores with high specific surface area, which limits the size of the metal nanoparticles inside the pores. At the same time, the metal nanoparticles are also loaded onto the surface of the OMCs, realizing the uniform loading of metal nanoparticles both inside and outside the pores. This enhances the active sites of the composite, promotes the mass transfer process inside and outside the pores, and greatly enhances the electrocatalytic performance of the catalyst. The material shows high electrocatalytic performance for adrenaline, which is characterized by a wide linear range, high sensitivity and low detection limit, and can realize the detection of actual samples.

Common Transition Metal Oxide Nanomaterials in Electrochemical Sensors for the Diagnosis of Monoamine Neurotransmitter‐Related Disorders

Monoamine neurotransmitters are essential for learning, mental alertness, emotions, and blood flow, among other functions. Fatal neurological disorders that signal the imbalance of these biomolecules in the human system include Parkinson's disease, myocardial infarction, Alzheimer's disease, hypoglycemia, Schizophrenia, and a host of other ailments. The diagnosis of these monoamine neurotransmitter‐related conditions revolves around the development of analytical tools with high sensitivity for the four major monoamine neurotransmitters namely dopamine, epinephrine, norepinephrine, and serotonin. The application of electrochemical sensors made from notable metal oxide nanoparticles or composites containing the metal oxide nanoparticles for the detection of these monoamine neurotransmitters was discussed herein. More importantly, the feasibility of the application of the ZnO, CuO, and TiO2 nanoparticle‐based electrochemical sensors for a comprehensive diagnosis of monoamine neurotransmitter‐related conditions was critically investigated in this review.

Synthesis and characterization of ZrO2-ZnO heterojunction composite for isopropanol detection

We prepared ZrO2-ZnO heterojunction composites by a simple hydrothermal method as materials sensitive to isopropanol gas. The 5% ZrO2-ZnO sample presented a uniform rod-like structure. The optimum operating temperature, sensitivity and response/recovery times were measured to investigate the response of ZrO2-ZnO composites to isopropanol. The sensor based on 5% ZrO2-ZnO composites at an optimum temperature of 260 °C had a response to 100 ppm isopropanol of up to 172.46, which was about 3.6 times higher than that of pure ZnO. The sensor also exhibited fast response and recovery times of 5 s and 11 s, respectively. The gas-sensitive properties can be attributed to the rod-like structure, heterojunction structure and catalytic activity of ZrO2. These results would contribute in expanding the application of ZrO2 in gas sensors.

N-doped carbon Co/CoOx with laccase-like activity for detection of epinephrine

N-doped carbon Co/CoOx with laccase-like activity was directionally designed by pyrolyzing Co-coordination polymer and applied to detect epinephrine, which revealed a new preparation strategy for laccase mimics. The formation mechanism of the N-doped carbon Co/CoOx nanozyme was reconnoitered by a thermogravimetric-mass spectrometry system (TG-MS). N-doped carbon Co/CoOx exhibited outstanding laccase-like activity, and the Michaelis-Menten constant and maximum initial velocity were calculated to be 0.087 mM and 0.0089 μM s-1, respectively. Based on this principle, a simple colorimetric sensing platform was developed for the quantitative detection of epinephrine, which can be used to diagnose pheochromocytoma. In addition, the visual platform for detecting epinephrine exhibited a linear range of 3 to 20 μg mL-1 and a calculated detection limit of 0.42 μg mL-1. Therefore, the proposed colorimetric sensing platform is a promising candidate to be applied in precise early pheochromocytoma diagnosis.

In situ electrodeposition of bismuth oxide nanowires @MWNT on the carbon fiber microelectrode for the sensitively electrochemical detection of folic acid

A microminiaturized electrochemical device, BiO@CNW/CFE was fabricated based on the in situ co-electrodeposition of bismuth oxide nanowires (BiNWs) and multi-walled carbon nanotubes (MWNTs) on the surface of carbon fiber electrode (CFE). The nanostructure of BiNWs could bind MWNTs on the surface of CFE during the precipitation of bismuth at the potential of -1.1 V. The vimineous nanostructure of BiO@CNW improved the surface area and electrochemical activity of the microelectrode. With the low background noise, folic acid (FA) can be detected sensitively by BiO@CNW/CFE based on the electrochemical reduction via the method of square wave voltammetry. The linear range of FA in sodium acetate-acetic acid buffer was achieved in the range of 5.00 nM-200 nM, the detection limit was estimated to be 0.63 nM. The recoveries of FA in human serum and artificial cerebral spinal fluid were between 99% and 103%, which indicates BiO@CNW/CFE was a reliable sensor for the detection of FA in biological samples.

Terbium(iii)-based coordination polymer with millimeter-size single crystals and high selectivity and sensitivity for folic acid

Terbium(iii)-based coordination polymer with millimeter-size single crystals and high selectivity and sensitivity for folic acid.

Facile bimetallic co-amplified electrochemical sensor for folic acid sensing based on CoNPs and CuNPs

Folic acid (FA) is essential for human health, particularly for pregnant women and infants. In this work, a glassy carbon electrode (GCE) was modified by a bimetallic layer of Cu/Co nanoparticles (CuNPs/CoNPs) as a synergistic amplification element by simple step-by-step electrodeposition, and was used for sensitive detection of FA. The proposed CuNPs/CoNPs/GCE sensor was characterized by differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS) and field emission scanning electron microscopy (FESEM). Then, under optimal conditions, a linear relationship was obtained in the wide range of 110.00-1750.00 μM for the detection of FA with a limit of detection (LOD) of 34.79 μM (S/N = 3). The sensitivity was calculated as 0.096 μA μM^-1 cm^-2. Some interfering compounds including glucose (Glc), biotin, dopamine (DA), and glutamic acid (Glu) showed little effect on the detection of FA by amperometry (i-t). Finally, the average recovery obtained was in a range of 91.77-110.06%, with a relative standard deviation (RSD) less than 8.00% in FA tablets, indicating that the proposed sensor can accurately and effectively detect the FA content in FA tablets.

Design of imprinting matrix for dual template sensing via electropolymerized polythiophene films

This work presents the design of 3-thiophene acetic acid (3-TAA) polymer matrix based molecularly imprinted polymer (MIP)/reduced graphene oxide (RGO) composite for sensitive and selective detection of antipyrine (AnP) and ethionamide (ETH) simultaneously. Dual drug embedded molecularly imprinted polymer (MIP) based electrochemical sensor was developed via electropolymerization of 3-TAA. AnP and ETH were embedded inside a polymer matrix based on their 3-D orientation and interaction(s) with functional monomer(s). Their extraction from polymeric matrix generates cavities complimentary to shape and size of AnP and ETH. The extraction of templates was confirmed by differential pulse voltammetry (DPV) as well as high-performance liquid chromatography (HPLC). The designed sensor selectively captures and produces the electrochemical signal for imprinted drugs. The electrochemical behaviour of AnP and ETH was investigated by DPV technique. The sensitivity for both drug molecules was commendable on a single polymeric composite with RGO on GC electrode (LOD of 0.117 μM for AnP and 0.15 μM for ETH). Also, the sensor exhibited excellent selectivity towards AnP and ETH in the presence of other analogous interferent molecules. Thus, the designed sensor showed high sensitivity as well as high selectivity for imprinted dual drug molecules on a single platform.

Folic Acid Determination in Food Samples Using Green Synthesized Copper Oxide Nanoparticles and Electro-Poly (Methyl Orange) Sensor

Copper (II) oxide nanoparticles (CuONPs) were green synthesized using Ocimum basilicum leaves aqueous extract in which polyphenols act as reducing and stabilizing agents. The synthesized CuONPs were characterized using X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, selected area electron diffraction, and Brunauer–Emmett–Teller (BET) surface area analysis. The analyses indicated the formation of crystalline rod-like monoclinic pure CuONPs with a mean grain size of 15 nm, a surface area of 396 m2 g−1, and a total pore volume of 0.71 cm3 g−1. A glassy carbon electrode (GCE) was modified using the synthesized CuONPs and electropolymerized poly(methyl orange) (PMO). The modified PMO/CuONPs/GCE electrode was electrochemically characterized and applied for the estimation of folic acid (FA) by cyclic voltammetry, chronoamperometry, linear sweep voltammetry, and differential pulse voltammetry techniques. The influence of pH (7), scan rate (50 mV/s), supporting electrolyte (0.1 M KCl) and FA concentration has been optimized. FA is precisely determined in the range from 0.01 to 1.5 µΜ with a low detection limit (0.002 µΜ), a low quantitation limit (0.068 µΜ), high reproducibility (RSD 0.37, 10 measurements), and high stability (98% activity after 50 days). FA in food samples was determined by the new sensor with high recoveries from 93 to 108.8%.

Graphical Abstract

Sensitive and Stable Electrochemical Sensor for Folic Acid Determination Using a ZIF-67/AgNWs Nanocomposite

An electrochemical sensor using silver nanowires (AgNWs)-doped with a zeolite-like metal-organic framework (ZIF-67) was developed for highly sensitive and stable determination of folic acid (FA). The ZIF-67/AgNWs nanocomposite was prepared by a one-step reaction via a template method and drop-coated onto the surface of a screen-printed carbon electrode (SPCE) to form a ZIF-67/AgNWs@SPCE electrochemical sensing platform. The electrochemical square wave voltammetry (SWV) curve for this sensing platform was measured in an electrolyte solution containing FA under the optimum experimental conditions. The redox peak current of FA (I_FA) increased with increases in the FA concentration (C_FA). There was a linear relationship between I_FA and C_FA in the range of 0.1 μM to 10 μM, and the determination limit was 30 nM. The ZIF-67/AgNWs@SPCE was used as an electrochemical sensor for FA which maintained a good stability over 7 days and showed good determination performance in real samples with a high recovery rate (100.9-102.1%, n = 6).

Nano-ZnS decorated hierarchically porous carbon electrocatalyst with multiple enzyme-like activities as a nanozyme sensing platform for simultaneous detection of dopamine, uric acid, guanine, and adenine

The simultaneous detection of multiple biological small molecules is critical for human health evaluation and disease prevention. In this study, a nano-ZnS decorated hierarchically porous carbon (ZSHPC) electrocatalyst with multiple enzyme-like activities as a nanozyme sensing platform for simultaneous derivative voltametric detection of four important biological small molecules, dopamine (DA), uric acid (UA), guanine (G), and adenine (A), is successfully synthesized via an in situ hydrothermal reaction using leaves of Cinnamomum camphora (L.) after the extraction of essential oil as a carbon source, ZnCl₂ as both zinc source and an activator, sulfuric acid as a sulfur source, and silica gel as a hard template. Activator together with the introduction of silica gel is beneficial for tuning pore structure. The in situ synthesized ZnS nanoparticles and sulfur doping improve the conductivity and cycling stability of the material. The ZSHPC electrode with multiple enzyme-like activities and oxidase-like characteristics was employed for the simultaneous detection of multiple target molecules in linear ranges of 0.3-500 μM with detection limits of 0.12 μM for DA, 0.26 μM for UA, 0.07 μM for G, and 0.075 μM for A. A derivative technique was selected for enhancing the peak resolution of the partial overlapped voltammograms and eliminating human error. Both the coefficient of determination and residual prediction deviation were used to evaluate this technique.

A highly sensitive uric acid biosensor based on vertically arranged ZnO nanorods on a ZnO nanoparticle-seeded electrode

Vertically-arranged ZnO nanorods grown on a ZnO nanoparticle-seeded FTO electrode using a hydrothermal method for highly sensitive uric acid biosensor fabrication.

Highly Sensitive Electrochemical Detection of Folic Acid by Using a Hollow Carbon Nanospheres@molybdenum Disulfide Modified Electrode

As a nutrient in body functions, folic acid (FA) plays a very important role for human health, and thus developing a highly sensitive method for its determination is of great significance. In the present work, carbon hollow nanospheres decorated with molybdenum disulfide nanosheets (CHN@MoS₂) nanomaterials were produced through a simple method and adopted to modify a glassy carbon electrode for assembling a highly sensitive electrochemical sensor of FA. After characterizing the prepared nanomaterials using scanning-/transmission-electron microscopy and Raman spectra, as well as optimizing various testing conditions, including the pH value of the buffer solution, the accumulation time and amount of nanomaterials on electrode surface, and the electrochemical determination of FA was carried out using a CHN@MoS₂ electrode. Owing to the coordinative advantages from CHN and MoS₂, the results show that CHN@MoS₂ exhibits excellent sensing responses for FA, and it has a wide linear range from 0.08 to 10.0 μM coupled with a low detection limit of 0.02 μM. Finally, the proposed method for FA detection was successfully applied in human urine analysis. The obtained results are satisfactory, revealing that the developed method based on CHN@MoS₂ nanomaterials has important applications for FA determination.