A facile electrochemical sensor for dopamine detection was successfully fabricated by the modification of gold nanoparticles (AuNPs) and poly(hydroquinone) film on three-dimensional nickel foam. The results of scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry measurements demonstrated the successfully preparation of the sensor. The effect factors of electrodeposition time of AuNPs, polymerization pH, cycles of polymerization and rate of polymerization were optimized for the sensor preparation. Under the optimized conditions, the prepared sensor exhibited selective and sensitive detection capacities toward dopamine. The linear response to dopamine ranged from 1.0 × 10− 7 mol/L to 1.0 × 10− 5 mol/L with a detection limit of 4.19 × 10− 8 mol/L. Moreover, the sensor could be applied in the detection of dopamine in real samples with satisfactory results.

In this work, a sensitive and reliable electrochemical platform was developed for catechol (CC) and hydroquinone (HQ) individual and sensitive simultaneous detection. Due to the outstanding advantages of low cost, excellent flexibility, large surface area, and good conductivity, an exfoliated graphite paper (EGP) was used as a supported electrode for gold nanoparticles (AuNPs) electrodeposition to fabricate a sensor (AuNPs/EGP). Scanning electron microscope and cyclic voltammetry results revealed that AuNPs/EGP was successfully prepared with multi-layered structure and enhanced electron transfer ability. Under the optimized conditions, the sensor showed wide linear range for CC and HQ detection of 5.0  ×  10−7 - 1.0  ×  10−4 mol/L and 7.0  ×  10−8 - 1.0  ×  10−4 mol/L with limitation of detection (S/N = 3) of 4.13 × 10−8 mol/L and 2.73  ×  10−8 mol/L, respectively. And the proposed sensing platform was successfully applied to the simultaneous determination of CC and HQ in real samples of three kinds of water with reliable recovery. The low cost, facile preparation, and attractive electrochemical performances made the graphite paper based sensor promise perspectives in the field of electroanalysis.

•A dual-signal strategy for QR electrochemical detection was developed.•Dual-signal was generated from the replacement of the included HQ in CD cavity by QR.•Dual current signals, ∆|IHQ|+∆|IQR|, exhibited improved sensitivity for QR detection.•The sensor possessed good selectivity for QR detection.•The dual-signal strategy facilitates the present approach promising.A dual-signal strategy was developed in the present work for quercetin (QR) electrochemical recognition and detection. Mercapto-β-cyclodextrin (HS-β-CD) self-assembled on gold nanoparticles and multi-walled carbon nanotubes modified electrode surface to fabricate an electrochemical sensor. Scanning electron microscope, electrochemical impedance spectroscopy, and cyclic voltammetry were employed to characterize the preparation process of the sensor. Hydroquinone (HQ) was chosen as an electrochemical marker for QR detection due to its small molecular size for the formation of inclusion with HS-β-CD. The results of UV–vis and differential pulse voltammetry demonstrate that the added QR can replace the included HQ in CD cavities, resulting in the dual-signal in electrochemical experiments composed of the decrease of oxidized current of HQ and the increase of oxidized current of QR. Compared with the sensor for QR detection in the absence of HQ, the sensor based dual-signal strategy exhibited a higher sensitivity with a wider detection range from 5.0×10−9 to 7.0×10−6 mol/L. With good selectivity, reproducibility, and stability, the sensor was applied for real samples detection with satisfactory results. The proposed dual-signal strategy can be readily extended to the selective recognition and sensitive detection of other molecules.

The authors report on a ratiometric electrochemical sensor for paracetamol (PR) which was fabricated by successively electropolymerizing a layer of Prussian blue (PB) and a layer of molecularly imprinted polypyrrole (MIP) on the surface of a glassy carbon electrode (GCE). The binding of PR molecules to the MIP has two effects: The first is an increase of the oxidation current for PR at 0.42 V (vs. SCE), and the second is a decrease in the current for PB (at 0.18 V) due to partial blocking of the channels which results in reduced electron transmissivity. Both currents, and in particular their ratio, can serve as analytical information. Under optimized conditions, the sensor displays enhanced sensitivity for PR in the 1.0 nM to 0.1 mM concentration range and a 0.53 nM lower limit of detection. The sensor was applied to the determination of PR in tablets and urines where it gave recoveries in the range between 94.6 and 104.9 %. This dual-signal (ratiometric) detection scheme (using electropolymerized Prussian Blue and analyte-specific MIP) in our perception has a wide scope in that it may be applied to numerous other electroactive species for which specific MIP can be made available.

•A new strategy based on sign-on and sign-off was proposed for PG determination was developed.•PTH and MIP showed an obvious electrocatalysis and a good recognition toward PG.•The rebound PG in imprinted cavities caused the increase of PG current and the decrease of PTH current.•The sensor exhibited good selectivity and enhanced sensitivity for PG detection.•The strategy may provide a new suitable sensing tool for electroactive compounds determination.A new strategy based on sign-on and sign-off was proposed for propyl gallate (PG) determination by an electrochemical sensor. The successively modified poly(thionine) (PTH) and molecular imprinted polymer (MIP) showed an obvious electrocatalysis and a good recognition toward PG, respectively. Furthermore, the rebound PG molecules in imprinted cavities not only were oxidized but also blocked the electron transmission channels for PTH redox. Thus, a sign-on from PG current and a sign-off from PTH current were combined as a dual-sign for PG detection. Meanwhile, the modified MIP endowed the sensor with recognition capacity. The electrochemical experimental results demonstrated that the prepared sensor possessed good selectivity and high sensitivity. A linear ranging from 5.0×10−8 to 1.0×10−4 mol/L for PG detection was obtained with a limit of detection of 2.4×10−8 mol/L. And the sensor has been applied to analyze PG in real samples with satisfactory results. The simple, low cost, and effective strategy reported here can be further used to prepare electrochemical sensors for other compounds selective recognition and sensitive detection.

A facile electrochemical sensor for hydroquinone (HQ) and catechol (CC) determination was successfully fabricated by the modification of poly(3-aminophenylboronic acid) (pAPBA) film and multi-walled carbon nanotubes (MWCNTs) on a glassy carbon electrode (pAPBA/MWCNTs/GCE). The prepared sensor was characterized by scanning electron microscope and electrochemical impedance spectroscopy. Under optimal conditions, differential pulse voltammetry was employed to quantify individual HQ and CC within the concentration range of 5.0 × 10−7–4.0 × 10−5 mol L−1 and 7.0 × 10−6–1.0 × 10−4 mol L−1, respectively. Based on the covalent binding between the boronic acid groups of pAPBA film and the cis-diol-containing molecule, a novel substitution-sensing strategy was proposed for the highly sensitive determination of CC. With the addition of CC into HQ solution, covalent interaction between CC and APBA occurred and the HQ was displaced by CC, resulting in a decrease of HQ oxidation peak current and the increase of the CC oxidation peak current. The summation of both current changes (Δ|IHQ| + Δ|ICC|) were combined for CC sensitive detection in a concentration range of 4.0 × 10−8–1.7 × 10−5 mol L−1 with a limit of detection of 4.3 × 10−9 mol L−1. The sensor was successfully applied to the determination of CC in spiked water samples.

•A imprinted sol–gel electrochemical sensor for the determination of PG was developed.•The sensor was fabricated by stepwise modifying GR-SWCNTs and MIPs.•The sensor exhibited specificity and selectivity towards PG.•The sensor could determine PG in real samples with satisfactory recovery.A novel imprinted sol–gel electrochemical sensor for the determination of propyl gallate (PG) was developed based on a composite of graphene and single walled carbon nanotubes (GR-SWCNTs). It was fabricated by stepwise modifying GR-SWCNTs and molecularly imprinted polymers and stored in 0.10 mol L−1 phosphate buffer solution pH 6.0, which endowed the sensor good sensitivity and selective recognition towards template molecules. The morphology and specific adsorption capacity of the sensor was characterized by scanning electron microscope and electrochemical methods, respectively. Under the optimized conditions, a linear range of the sensor to PG was 8.0 × 10−8–2.6 × 10−3 mol L−1 with a limit of detection of 5.0 × 10−8 mol L−1 (S/N = 3). The sensor exhibited specificity and selectivity towards template molecules as well as excellent reproducibility, regeneration and stability. Furthermore, the sensor could be applied to determine PG in edible oils, instant noodles and cookies with satisfactory results.

•A novel polymerized monomer, py–PBA, was synthesized to prepare MIP/GCE.•The present sensor possessed a high imprinted factor.•Double recognition of DA due to the specific adsorption of MIP and covalent binding between DA and PBA.•The sensor exhibited sensitive detection capacity to DA.A molecular imprinting polymer (MIP) based electrochemical sensor was successfully prepared for dopamine (DA) recognition and detection using pyrrole–phenylboronic acid (py–PBA) as a novel electropolymerized monomer. py–PBA could form cyclic boronic ester bond with DA, thus endowing a double recognition capacity of the sensor to DA in the combination of the imprinted effect of MIP. Compared with the sensor prepared using pyrrole or phenylboronic acid as electropolymerized monomer, the present sensor exhibited a remarkable high imprinted factor to DA. The influence factors including pH value, the mole ratio between monomer and template molecule, electropolymerization scan rate, and scan cycles of electropolymerization process were investigated and optimized. Under the optimal conditions, the sensor could recognize DA from its analogs and monosaccharides. A linear ranging from 5.0×10−8 to 1.0×10−5 mol/L for the detection of DA was obtained with a detection limit of 3.3×10−8 mol/L (S/N=3). The sensor has been applied to analyze DA in injection samples with satisfactory results.

High temperature pyrolysis can significantly improve the activity and stability of Fe-based catalysts. However, unwanted iron nanoparticles, which are proven inactive to oxygen reduction reaction (ORR), will form under this procedure. Herein, a nitrogen-rich and hindrance multifunctional 6,7-di(pyridin-2-yl)pteridine-2,4-diamine (DPPD) monomer was deliberately designed and synthesized. High content of thermally stable nitrogen in DPPD can increase the degree of coordination with iron and provide a high content of active nitrogen after pyrolysis. Distorted nitrogen-rich ferrous complex polymers were successfully prepared to keep iron ions well separated and prevent them from aggregating during the heat treatment. Carbon-supported Fe-based catalysts with different initial iron loadings from 0.2 to 4.0 wt % were obtained. Transmission electron microscopy (TEM) revealed that there were no obvious nanocrystals observed, even the initial iron loading was up to 2.0 wt %. The electrochemical performance of the Fe-based catalysts was evaluated via cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The result shows that an Fe-based catalyst with 2.0 wt % initial iron loading is the best ORR catalyst in acid media among all the iron loadings. Typically, in basic media, the catalyst with 2.0 wt % initial iron loading exhibits comparable electrocatalytic activity to commercial Pt/C material via an efficient four-electron-dominant ORR pathway coupled with better methanol tolerance as well as durability. XPS measurements confirmed that the outstanding activity of the catalyst with 2.0 wt % initial iron loading was likely attributed to higher content of pyridinic nitrogen, providing the highest density of active site structures.

•Two layers of polymer films were electropolymerized for imprinted based sensor preparation.•pABSA displayed a high catalysis for PR redox to improve the sensitivity of the sensor.•MIP endowed the sensor with good recognition capacity for PR from its interferents.•Low cost and facile preparation facilitates the present approach promising.A new strategy for a composite film based electrochemical sensor was developed in this work. A layer of conductive film of poly(p-aminobenzene sulfonic acid) (pABSA) was electropolymerized onto glassy carbon electrode surface and exhibited a high electrocatalytic active for paracetamol (PR) redox. The subsequent formation of a layer of molecular imprinted polymer (MIP) film on pABSA modified electrode endowed the sensor with plentiful imprinted cavities for PR specific adsorption. The advantages of the composite film made the prepared sensor display high sensitivity and good selectivity for PR detection and recognition. Under the optimal conditions, the sensor could recognize PR from its interferents. A linear ranging from 5.0×10−8 to 1.0×10−4 mol/L for PR detection was obtained with a detection limit of 4.3×10−8 mol/L. The sensor has been applied to analyze PR in tablets and human urine samples with satisfactory results. The simple, low cost, and efficient strategy reported here can be further used to prepare electrochemical sensors for other compounds recognition and detection.

A molecularly imprinted polymer (MIP) was prepared by self-polymerization of dopamine in the presence of bovine hemoglobin (BHb) and then deposited on the surface of an electrode modified with gold nanoparticles (AuNPs). Scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry were employed to characterize the modified electrode using the hexacyanoferrate redox system as an electroactive probe. The effects of BHb concentration, dopamine concentration, and polymerization time were optimized. Under optimized conditions, the modified electrode selectively recognizes BHb even in the presence of other proteins. The peak current for hexacyanoferrate, typically measured at + 0.17 V (vs. SCE), depends on the concentration of BHb in the 1.0 × 10−11 to 1.0 × 10−2 mg mL−1 range. Due to the ease of preparation and tight adherence of polydopamine to various support materials, the present strategy conceivably also provides a platform for the recognition and detection of other proteins.

A novel electrochemical sensor for bovine hemoglobin (BHb) recognition and detection was prepared by a surface molecularly imprinted technique. Aldehyde group-functionalized silica microspheres were modified on an Au electrode surface, and these were subsequently covalently bound with the template molecule, BHb, through imine bonds. Electropolymerization was performed to deposit polypyrrole onto the above modified electrode surface. A three-dimensional macroporous structural sensor was obtained after etching of silica and the extraction of BHb. Differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the fabrication process of the sensor using [Fe(CN)6]3−/[Fe(CN)6]4− as an electroactive probe. Since all imprinted cavities were situated at the surface of the polymers, the prepared sensor exhibited considerably fast binding kinetics. Compared to other non-template proteins, the sensor showed an excellent recognition capacity for BHb. Moreover, the prepared sensor also exhibited a dependent relationship between the concentration of BHb and the peak current of [Fe(CN)6]3−/[Fe(CN)6]4−.

We have combined the molecular imprinting and the layer-by-layer assembly techniques to obtain molecularly imprint polymers (MIPs) for the electrochemical determination of p-nitrophenol (p-NPh). Silica microspheres functionalized with thiol groups and gold nanoparticles (Au-NPs) were assembled on a gold electrode surface layer by layer. The electrode was then immersed into a solution of pyrrole and p-NPh (the template), and electropolymerization led to the creation of a polymer-modified surface. After the removal of the silica spheres and the template, electrochemical impedance spectroscopy and differential pulse voltammetry (DPV) were employed to characterize the surface. The results demonstrated the successful fabrication of macroporous MIPs embedded with Au-NPs on the gold electrode. The effects of monomer concentration and scan rate on the performance of the electrode were optimized. Excellent recognition capacity is found for p-NPh over chemically similar species. The DPV peak current is linearly related to concentration of p-NPh in the 0.1 μM to 1.4 mM range, with a 0.1 μM limit of detection (at S/N = 3).

A novel multiporous imprinted electrochemical sensor was developed for the recognition and detection of epinephrine (EP) by combining a molecularly imprinted polymers (MIPs) film, silica nanoparticles (SiO2NPs) and multiwalled carbon nanotubes (MWNTs). A molecular imprinted polypyrrole film was electropolymerized on the surface of a SiO2NPs and MWNTs modified glassy carbon electrode (GCE) in the presence of EP. With the etching of SiO2NPs, the obtained sensor exhibited a multiporous network structure to allow for efficient mass transport, which would improve the rebinding rate and increase the efficiency of imprinted sites of the sensor. The multiporous imprinted sensor was characterized using scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) and amperometric i–t measurement. The influential factors, including the electropolymerization cycles, the scanning rate, the amount of SiO2NPs, and the incubation time of SiO2NPs in HF solution were optimized. Under the optimized conditions, the sensor could recognize EP from other structurally similar compounds. A good linearity was obtained in the range of 3.0 × 10−7–1.0 × 10−3 M with a detection limit of 3.0 × 10−8 M. The MIPs based sensor showed high sensitivity, good selectivity and satisfactory reproducibility for EP determination.

A sensitive and selective electrochemical sensor based on molecularly imprinted polymers (MIPs) was developed for caffeine (CAF) recognition and detection. The sensor was constructed through the following steps: multiwalled carbon nanotubes and gold nanoparticles were first modified onto the glassy carbon electrode surface by potentiostatic deposition method successively. Subsequently, o-aminothiophenol (ATP) was assembled on the surface of the above electrode through Au–S bond before electropolymerization. During the assembled and electropolymerization processes, CAF was embedded into the poly(o-aminothiophenol) film through hydrogen bonding interaction between CAF and ATP, forming an MIP electrochemical sensor. The morphologies and properties of the sensor were characterized by scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. The recognition and determination of the sensor were observed by measuring the changes of amperometric response of the oxidation-reduction probe, [Fe(CN)6]3−/[Fe(CN)6]4−, on modified electrode. The results demonstrated that the prepared sensor had excellent selectivity and high sensitivity for CAF, and the linear range was 5.0 × 10−10 ~ 1.6 × 10−7 mol L−1 with a detection limit of 9.0 × 10−11 mol L−1 (S/N = 3). The sensor was also successfully employed to detect CAF in tea samples.

A simple and efficient molecularly imprinted polymers (MIPs) based electrochemical sensor were proposed and prepared by electropolymerization of pyrrole in the presence of bovine hemoglobin (BHb) in an aqueous solution. The fabrication process of the sensor was characterized by differential pulse voltammetry and electrochemical impedance spectroscopy, in which [Fe(CN)6]3−/[Fe(CN)6]4− was used as an electrochemical active probe. The influence factors including electropolymerization cycles, scan rate, the concentration of pyrrole, and the extraction conditions were investigated in detailed. Under the optimized conditions, the experimental results showed that the MIPs based sensor possessed a fast rebinding dynamics and an excellent recognition capacity to BHb, compared to the other non-template proteins. Moreover, the prepared sensor also exhibited a dependent relationship between the concentration of template protein and peak current of [Fe(CN)6]3−/[Fe(CN)6]4−.