Au/ZnO hybrid nanocatalysts impregnated in N-doped graphene for simultaneous determination of ascorbic acid, acetaminophen and dopamine

A High-Performance Electrochemical Sensor Based on Ni-Pt Bimetallic Nanoparticles Doped Metal Organic Framework ZIF-8 for the Detection of Dopamine

In this paper, microporous Zn-based zeolitic imidazolate framework with the sodalite cage structure (SOD-ZIF-8) was synthesized by the solvothermal method. Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and N2 adsorption were employed to characterize the synthesized material. An ultra-sensitive electrochemical sensor based on highly dispersed bimetallic Ni-Pt nanoparticles immobilized on zeolitic metal-organic framework ZIF-8 for dopamine quantification is introduced for the first time. The as-prepared Ni-Pt@ZIF-8 composite was deposited onto a glassy carbon electrode (GCE), serving as a sensor that exhibits superior properties for the detection of dopamine (DA). A Box-Behnken design was employed, and response surface methodology (RSM) was applied to investigate the impact of various experimental parameters on dopamine detection. The parameters optimized in this study included pH, drying time (hours), drop volume for deposition (μL), and accumulation time (minutes). The Box-Behnken experimental design enabled the systematic optimization of these factors to enhance the sensor's performance. Benefiting from the synergy of ZIF-8 and Ni-Pt bimetallic nanoparticles, the Ni-Pt@ZIF-8 composite exhibited high sensitivity towards dopamine, achieving a low detection limit of 1.0 nM. The sensor's linear response to dopamine (1 nM to 10 μM), resistance to interference, and high recovery in human serum, coupled with its simple fabrication, make it a promising tool for real-world dopamine detection.

Green synthesis of curcumin-silver nanoparticle and its modified electrode assisted amperometric sensor for the determination of paracetamol

Contamination of paracetamol, a primary analgesic was wide spread in the water system that affects the eco-system. High-dosage of paracetamol to humans cause organ damages and showed adverse effect. It is important to monitor the paracetamol concentration in environmental and human samples periodically. Conventional methods associated with chromatography is found to be high-cost, time consuming and requires high-end instrumentation, Herein, we investigated the role of curcumin during bio-synthesis of silver nanoparticles. The curcumin functionalized silver nanoparticles were further chemically modifying on the electrode surface and the resulting modified electrode was applied for electrocatalytic oxidation of paracetamol. The experimental finding proved that the modified electrode is capable of sensing paracetamol by applying oxidation potential 0.4 V. Both the synthesised material and modified electrode surface were characterized for its physic-chemical properties using spectroscopy and microscopy techniques. The HR-TEM, FESEM and AFM results showed that the distribution of nanoparticle with the size range from 25 to 70 nm and the UV-Vis and Raman spectrophotometer characterization confirms the coordination between SNP and curcumin. Under optimized condition, in 0.1 M NH₄Cl (pH 7) at the scan rate of 50 mVs^-1. The modified electrode enhanced the sensitivity towards the detection of paracetamol in trace level. The modified electrode is capable of sensing paracetamol in a linear range between 0.59 × 10^-6 and 342.1 × 10^-6 M, with LOD of 0.29 μM, and linear regression equation of y = 0.092x+502.6 with a correlation coefficient of R² = 0.996.

Detection of ascorbic acid based on its quenching effect on luminol-artemisinin chemiluminescence

We find that luminol can react with artemisinin (ART) to produce chemiluminescence (CL) in the absence of a catalyst and ascorbic acid (AA) can quench luminol-ART CL. Based on its efficient inhibition effect on luminol-ART CL, a new AA detection method is established. The calibration curve for the determination of AA is in the linear range of 5 × 10^-7 M to 1 × 10^-4 M with a detection limit of 50 nM, which is more sensitive than many other reported methods. This CL approach was utilized to detect AA in vitamin C tablets by applying the standard addition method, and the recoveries of 104.0%, 96.8% and 103.4% were obtained, respectively, at concentrations of 1 μM, 5 μM and 10 μM with a RSD value of less than 3.6%. This developed method for AA assay is distinguished by its fastness, reproducibility, easy operation and good selectivity.

Flexible and disposable gold nanoparticles-N-doped carbon-modified electrochemical sensor for simultaneous detection of dopamine and uric acid

Catalytic and electrocatalytic applications of supported metal nanoparticles are hindered due to an aggregation of metal nanoparticles and catalytic leaching under harsh operations. Hence, stable and leaching free catalysts with high surface area are extremely desirable but also challenging. Here we report a gold nanoparticles-hosted mesoporous nitrogen doped carbon matrix, which is prepared using bovine serum albumin (BSA) through calcination. BSA plays three roles in this process as a reducing agent, capping agent and carbon precursor, hence the protocol exhibits economic and sustainable. Gold nanoparticles at N-doped BSA carbon (AuNPs@NBSAC)-modified three-electrode strip-based flexible sensor system has been developed, which displayed effective, sensitive and selective for simultaneous detection of uric acid (UA) and dopamine (DA). The AuNPs@NBSAC-modified sensor showed an excellent response toward DA with a linear response throughout the concentration range from 1 to 50 μM and a detection limit of 0.05 μM. It also exhibited an excellent response toward UA, with a wide detection range from 5 to 200 μM as well as a detection limit of 0.1 μM. The findings suggest that the AuNPs@NBSAC nanohybrid reveals promising applications and can be considered as potential electrode materials for development of electrochemical biosensors.

Assigning XPS features in B,N-doped graphene: input from ab initio quantum chemical calculations

Ab initio quantum chemical calculations using large enough cluster models have been used to predict the core level binding energies of B(1s) and N(1s), including initial and final state effects, in several possible atomic arrangements in B,N-codoped graphene, such as isolated atoms, different types of B,N pairs and BN domains. To a large extent, the observed trends are dominated by initial state effects that support assigning the experimental features to the neutral samples. For the BN domains the present theoretical results are in full agreement with the experimental assignment thus providing support to the rest of the assignments. In particular, the present results strongly suggest that some of the features observed in the experiments are likely to correspond to isolated B or N atoms in graphene and, others fit well to the prediction corresponding to different types of B,N pairs. The importance of having an unambiguous, rigorous way to assign experimental features is emphasized.

Simultaneous Detection of Ascorbic Acid, Dopamine, and Uric Acid Using a Novel Electrochemical Sensor Based on Palladium Nanoparticles/Reduced Graphene Oxide Nanocomposite

A fresh strategy based on two-step electrochemical reduction for the fabrication of palladium nanoparticles/reduced oxide nanocomposite-modified glass carbon electrode (PdNPs/rGO/GCE) was established in this study. Field emission scanning electron microscopy (FESEM) images showed that spherical PdNPs were evenly distributed on the surface of rGO-modified electrode (rGO/GCE), and the introduction of PdNPs has no effect on the morphology of rGO. Electrochemical impedance spectroscopy (EIS) studies revealed that the conductivity of PdNPs/rGO/GCE was higher than that of rGO/GCE and bare GCE. The electrochemical performances of PdNPs/rGO/GCE sensor were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry using ascorbic acid (AA), dopamine (DA), and uric acid (UA) as analytes. At the optimized conditions, wide linear ranges of 0.5–3.5 mM (R² = 0.99), 3–15 μM (R² = 0.99) and 15–42 μM (R² = 0.99), and 0.3–1.4 mM (R² = 0.99) towards AA, DA, and UA in ternary mixture were observed, respectively. In addition to superior anti-interference capability, fast response (≤5 s), excellent reproducibility, and good long-term stability were also given by this sensor. These results suggested that PdNPs/rGO/GCE is promising for the simultaneous detection of AA, DA, and UA in practical application.

Molecular-scale cage-confinement pyrolysis route to size-controlled molybdenum carbide nanoparticles for electrochemical sensor

Herein, size-controllable molybdenum carbide nanoparticles (Mo₂C NPs) encapsulated by N, P-codoped carbon shells which simultaneously wrapping on the surface of carbon nanotube (Mo₂C@NPC/CNT) is synthesized through a molecular-scale cage-confinement pyrolysis route. Such confinement achieves a good coating and protection of Mo₂C and the effective control over the size of Mo₂C NPs ranging from 2.5 to 10 nm facilitates a rational investigation into their electrochemical sensor behavior at nanometer scales. The optimized structure consisting of Mo₂C nanoparticles with size of ~5 nm showed an outstanding electrochemical response toward dopamine (DA) and acetaminophen (AC) with detection limits (S/N = 3) of 0.008 μM for AC and 0.01 μM for DA.

Copper Nanowires Modified with Graphene Oxide Nanosheets for Simultaneous Voltammetric Determination of Ascorbic Acid, Dopamine and Acetaminophen

Copper nanowires (Cu NWs) were modified with graphene oxide (GO) nanosheets to obtain a sensor for simultaneous voltammetric determination of ascorbic acid (AA), dopamine (DA) and acetaminophen (AC). The nanocomposite was obtained via sonication, and its structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The electrochemical oxidation activity of the materials (placed on a glassy carbon electrode) was studied by cyclic voltammetry and differential pulse voltammetry. Due to the synergistic effect of Cu NWs and GO, the specific surface, electrochemical oxidation performance and conductivity are improved when compared to each individual component. The peaks for AA (-0.08 V), DA (+0.16 V), and AC (+0.38 V) are well separated. The sensor has wide linear ranges which are from 1-60 μM, 1-100 μM, and 1-100 μM for AA, DA, and AC, respectively, when operated in the differential pulse voltammetric mode. The detection limits are 50, 410 and 40 nM, respectively. Potential interferences by uric acid (20 μM), glucose (10 mM), NaCl (1 mM), and KCl (1 mM) were tested for AA (1 μΜ), DA (1 μΜ), and AC (1 μΜ) and were found to be insignificant. The method was successfully applied to the quantification of AA, DA, and AC in spiked serum samples.

Janus electrochemistry: Simultaneous electrochemical detection at multiple working conditions in a paper-based analytical device

The simultaneous detection of multiple analytes from a single sample is a critical tool for the analysis of real world samples. However, this is challenging to accomplish in the field by current electroanalytical techniques, where tuning assay conditions towards a target analyte often results in poor selectivity and sensitivity for other species in the mixture. In this work, an electrochemical paper-based analytical device (ePAD) capable of performing simultaneous electrochemical experiments in different solution conditions on a single sample was developed for the first time. We refer to the system as a Janus-ePAD after the two-faced Greek god because of the ability of the device to perform electrochemistry on the same sample under differing solution conditions at the same time with a single potentiostat. In a Janus-ePAD, a sample wicks down two channels from a single inlet towards two discreet reagent zones that adjust solution conditions, such as pH, before flow termination in two electrochemical detection zones. These zones feature independent working electrodes and shared reference and counter electrodes, facilitating simultaneous detection of multiple species at each species' optimal solution condition. The device utility and applicability are demonstrated through the simultaneous detection of two biologically relevant species (norepinephrine and serotonin) and a common enzymatic assay product (p-aminophenol) at two different solution pH conditions. Janus-ePADs show great promise as an inexpensive and broadly applicable platform which can reduce the complexity and/or number of steps required in multiplexed analysis, while also operating under the optimized conditions of each species present in a mixture.

Simultaneous determination of ascorbic acid, dopamine and uric acid by a novel electrochemical sensor based on N2/Ar RF plasma assisted graphene nanosheets/graphene nanoribbons

A novel nitrogen/argon (N₂/Ar) radio frequency (RF) plasma functionalized graphene nanosheet/graphene nanoribbon (GS/GNR) hybrid material (N₂/Ar/GS/GNR) was developed for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Various nitrogen mites introduced into GS/GNR hybrid structure was evidenced by a detailed microscopic, spectroscopic and surface area analysis. Owing to the unique structure and properties originating from the enhanced surface area, nitrogen functional groups and defects introduced on both the basal and edges, N₂/Ar/GS/GNR/GCE showed high electrocatalytic activity for the electrochemical oxidations of AA, DA, and UA with the respective lowest detection limits of 5.3, 2.5 and 5.7 nM and peak-to-peak separation potential (ΔE_P) (vs Ag/AgCl) in DPV of 220, 152 and 372 mV for AA/DA, DA/UA and AA/UA respectively. Moreover, the selectivity, stability, repeatability and excellent performance in real time application of the fabricated N₂/Ar/GS/GNR/GCE electrode suggests that it can be considered as a potential electrode material for simultaneous detection of AA, DA, and UA.

Determination of dopamine hydrochloride by host-guest interaction based on water-soluble pillar[5]arene

The supramolecular interaction between the water-soluble pillar[5]arene (WP[5]) as host and dopamine hydrochloride (DH) as guest was studied by spectrofluorometry. The fluorescence intensity of DH gradually decreased with increasing WP[5] concentration, and the possible interaction mechanism between WP[5] and DH was confirmed by ¹H NMR, 2D NOESY, and molecular modelling. Based on significant DH fluorescence, a highly sensitive and selective method for DH determination was developed for the first time. The fluorescence intensity was measured at 312nm, with excitation at 285nm. The effects of pH, temperature, and reaction time on the fluorescence spectra of the WP[5]-DH complex were investigated. A linear relationship between fluorescence intensity and DH concentration in the range of 0.07-6.2μgmL^-1 was obtained. The corresponding linear regression equation is ΔF=25.76 C+13.56 (where C denotes the concentration in μgmL^-1), with the limit of detection equal to 0.03μgmL^-1 and the correlation coefficient equal to 0.9996. This method can be used for the determination of dopamine in injection and urine samples. In addition, the WP[5]-DH complex has potential applications in fluorescent sensing and pharmacokinetics studies of DH.

Calixarene-functionalized graphene oxide composites fixed on glassy carbon electrodes for electrochemical detection

Four composite materials were prepared by grafting calixarene derivatives onto the surfaces of graphene oxide (GO) via covalent functionalization to yield covalently functionalized graphene oxides (CFGOs).

Rutin detection using highly electrochemical sensing amplified by an Au–Ag nanoring decorated N-doped graphene nanosheet

The novel Au–Ag nanorings/NG modified electrode was found to have a wide linear range from 0.05 μM to 241.2 μM (S/N = 3) with a low detection limit of 0.01 μM when it was employed for rutin detection.