The authors describe an electrochemical sensor for hydrogen peroxide (H2O2). It was constructed by consecutive, selective modification of a glassy carbon electrode (GCE) with Prussian Blue (PB), layered molybdenum disulfide (MoS2), and reduced graphene oxide (rGO). The properties of the modified GCE were characterized via high-resolution transmission electron microscopy, UV-vis spectroscopy and X-ray diffraction. The electrochemical properties of the electrode were studied using cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibits excellent electrocatalytic activity for the reduction of hydrogen peroxide in comparison to GCEs modified with MoS2-rGO or PB only. Response is linear in the 0.3 μM to 1.15 mM H2O2 concentration range at a working analytical voltage of 0.1 V, with a 0.14 μM detection limit. The electrochemical sensitivity is 2883.5 μA·μM?1·cm?2, and response is fast (<10 s). The sensor is selective, stable and reproducible. This is attributed to the efficient electron transport properties of the MoS2-rGO composite and the high loading with PB.
Graphic abstract Prussian Blue nanoparticles were deposited on MoS2-rGO modified glassy carbon electrode by electrochemical method. This sensor was used for the detection of H2O2 in tap water and river water.
The authors describe the preparation of a molecularly imprinted polymer (MIP) film on the surface of electrodeposited hollow nickel nanospheres (hNiNS), and the use of this nanocomposite in an electrochemical sensor for dopamine (DA). The use of the 3-dimensional hNiNS as a support material enlarges the sensing area and conductivity, while the MIP film warrants improved selectivity for DA. Quantification based on the “MIP/gate effect” was performed by employing hexacyanoferrate as the electrochemical probe. Scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy were applied to characterize the sensor materials. The electropolymerization condition such as pH value, functional monomer and ratio of template to monomer were optimized. By using dopamine (DA) as a model analyte, the sensor, if operated at 0.1 V vs. SCE, has fairly low detection limit of 1.7?×?10?14 M (at an S/N ratio of 3), two wide assay ranges of 5?×?10?14 to 1?×?10?12 M and 1?×?10?12 to 5?×?10?11 M, and superb selectivity.
Graphical Abstract An electrochemical sensor platform with a novel composite film composed of hollow nickel nanospheres (hNiNS) and molecularly imprinted polymer (MIP) was developed via a facile double-elecrodeposition method. The synergistic effects of hNiNS and MIP guarantee the ultrahigh sensitivity (down to 10?2 ppt) and selectivity of the sensor.
A magnetic glassy carbon electrode (mGCE) was modified with a ternary composite prepared from Prussian blue (PB), magnetite (Fe3O4) nanoparticles, and reduced graphene oxide (rGO) in order to obtain an amperometric sensor for hydrazine. The utilization of Fe3O4 facilitates the magnetic immobilization and separation of sensing material, while the use of rGO enhances sensitivity. The surface coverage and the stability of the PB on the modified electrode were considerably improved. The electro-oxidative response to hydrazine was investigated with this modified mGCE using cyclic voltammetry and amperometric. The sensor, typically operated at a voltage of 0.2 V (vs. SCE), displays superior response hydrazine, with a response time of 4 s, a sensitivity of 97.73 μA μM?1 cm?2 and a 13.7 nM detection limit.
Graphical abstract A magnetic glassy carbon electrode was modified with a ternary composite prepared from Prussian blue, magnetite nanoparticles, and reduced graphene oxide to obtain a selective amperometric sensor for dissolved hydrazine.
An electrochemical sensor for H2O2 was developed based on electrochemically deposited Prussian blue (PB) nanoparticles doped poly(3,4-ethylenedioxythiophene) (PEDOT). The PEDOT/PB composite was composed of PEDOT wrapped PB nanoparticles, where the conducting polymer PEDOT not only protected the PB particles to warrant high stability, but also connected them to enhance the electron transfer. Owing to the excellent conductivity of PEDOT and unique electrocatalytic activity of PB, the PEDOT/PB modified electrode exhibited good catalytic activity toward the electrochemical reduction of H2O2, and was used for the detection of H2O2 in concentrations ranging from 0.5 to 839 μM, with a detection limit of 0.16 μM. Moreover, the sensor also demonstrated excellent reproducibility, selectivity and long-term stability, showing great promise for the fabrication of electrochemical sensors and H2O2 related biosensors.
Graphical abstract An electrochemical non-enzymatic sensor for hydrogen peroxide with excellent stability was developed. It is based on conducting polymer PEDOT doped with Prussian blue nanoparticles.
A molecularly imprinted polymer (MIP) and a nanocomposite prepared from gold nanoparticles (AuNP) and poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) were deposited on a screen-printed carbon electrode (SPCE). The nanocomposite was prepared by one-pot simultaneous in-situ formation of AuNPs and PEDOT:PSS and was then inkjet-coated onto the SPCE. The MIP film was subsequently placed on the modified SPCE by co-electrodeposition of o-phenylenediamine and resorcinol in the presence of the antibiotic nitrofurantoin (NFT). Using differential pulse voltammetry (DPV), response at the potential of ~ 0.1 V (vs. Ag/AgCl) is linear in 1 nM to 1000 nM NFT concentration range, with a remarkably low detection limit (at S/N?=?3) of 0.1 nM. This is two orders of magnitude lower than that of the control MIP sensor without the nanocomposite interlayer, thus showing the beneficial effect of AuNP-PEDOT:PSS. The electrode is highly reproducible (relative standard deviation 3.1% for n?=?6) and selective over structurally related molecules. It can be re-used for at least ten times and was found to be stable for at least 45 days. It was successfully applied to the determination of NFT in (spiked) feed matrices and gave good recoveries.
Graphical abstract Schematic representation of a voltammetric sensor for the determination of nitrofurantoin. The sensor is based on a screen-printed carbon electrode (SPCE) modified with an inkjet-printed gold nanoparticles-poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) nanocomposite and a molecularly imprinted polymer.
Three-dimensional structures comprising polypyrrole nanowires (PPyNWs) and molecularly imprinted polymer (MIP) were prepared by electropolymerization on the surfaces of a glassy carbon electrode (GCE). The modified GCE possesses both large surface area and good electrocatalytic activity for oxidizing dopamine (DA), and this leads to high sensitivity. The electropolymerized MIP has a large number of accessible surface imprints, and this makes the GCE more selective. Under optimal conditions and at a working voltage of typically 0.23 V (vs. SCE), the calibration plot is linear in the 50 nM to 100 μM DA concentration range, and the limit of detection is 33 nM. The sensor has been successfully applied to the analysis of DA in injections.
Graphical abstract Schematic of a three-dimensional nanocomposite based dopamine sensing platform based on the use of a molecularly imprinted polymer and poly(pyrrole) nanowires. The modified polypyrrole nanowires and molecularly imprinted polymer endowed high electrocatalytic capacity and good selectivity for dopamine recognition, respectively.
An electrochemical quercetin (QR) sensor is described that is based on the use of magnetic reduced graphene oxide (MrGO) incorporated into a molecularly imprinted polymer (MIP) on the surface of a screen-printed electrode (SPE). The MrGO consists of reduced graphene oxide (rGO), magnetite (Fe3O4) and silver nanoparticles (Ag). The analyte (QR) is electrostatically adsorbed on the surface of the MrGO. Finally, the MIP was deposited via in-situ polymerization. The composite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy and Vibrating sample magnetometry. The morphologies and electrochemical properties of different electrodes were characterized by Field emission scanning electron microscopy, Electrochemical impedance spectroscopy and differential pulse voltammetry. Under optimal conditions, the modified electrode has a linear response in the 20 nM to 250 μM QR concentration range. The limit of detection is 13 nM (at an S/N ratio of 3). The electrode is selective, stable, regenerable and reliable. It was applied to the determination of QR in spiked pharmaceutical samples and gave satisfactory results.
Graphical abstract Schematic presentation of a method for sensing quercetin. It is based on the use of screen printed electrode modified with magnetized reduced graphene oxide and a molecularly imprinted polymer.
The authors describe an electrochemical sensor for the neonicotinoid insecticide imidacloprid (IMI) based on Pt-In catalytic nanocomposite film and Bromophenol blue amplification. The Pt-In nanocomposite film was deposited on the surface of a modified glassy carbon electrode. The composite molecularly imprinted polymer (MIP) was prepared by electro-polymerization using bromophenol blue doped o-aminophenol as functional monomer and 4-tert-butylcalix[6]arene-IMI supramolecular inclusion complex as template molecule. The experimental results showed that the current intensity of IMI was clearly amplified in the potential range from ?0.3 to ?1.8 V, because of the double amplification, based on the Pt-In film and Bromophenol blue catalysis. Moreover, the double recognition ability of the sensor, which relied on the MIP and the vacuum structure of 4-tert-butylcalix[6]arene, effectively increased the specific recognition performance. The feasibility of its practical applications has been demonstrated by the analysis of vegetable samples.
Graphical abstract A supramolecular imprinted electrochemical sensor for imidacloprid determination was prepared based on Pt-In nanocomposite film and bromophenol blue amplification. Because of the advantages of the specific recognition sites in MIPs and supramolecular chemistry, the sensor showed good selectivity for imidacloprid.
An efficient approach is demonstrated for preparing particles consisting of a silver core and a shell of molecularly imprinted polymer (Ag@MIP). The MIP is prepared by using bisphenol A (BPA) as the template and 4-vinylpyridine as the functional monomer. The Ag@MIP fulfills a dual function in that the silver core acts as a SERS substrate, while the MIP allows for selective recognition of BPA. The Ag@MIP is characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, thermogravimetric analysis and Raman spectroscopy. The Raman intensity of Ag@MIP is higher than that of bare silver microspheres. The detection limit for BPA is as low as 10?9 mol·L?1.
Graphical abstract Schematic illustration of the preparation of silver microspheres coated with a molecularly imprinted polymer (Ag@MIPs) for detecting bisphenol A (BPA) by surface enhanced Raman scattering (SERS).
The authors describe a molecularly imprinted polymer (MIP) deposited on multiwalled carbon nanotubes (MIP/MWCNTs) for separation and preconcentration of L-cysteine (L-Cys). The MIP was characterized by scanning electron microscopy, X-ray diffraction and FT-IR and via adsorption kinetics and adsorption isotherms. The MIP is shown to be a viable sorbent for L-Cys which subsequently is quantified by spectrophotometry through formation of a charge transfer complex with the DDQ reagent. The experimental parameters affecting separation efficiency and spectrophotometric determination were optimized. Under optimum conditions and at an analytical wavelength of 478 nm, the calibration plot is linear in the 4.0 to 180 ng mL?1 concentration range, and the limit of detection (at an S/N ratio of 3) is 2.3 ng mL?1. The intra-day and inter-day precision are in the range from 2.4 to 3.6%. The method was successfully applied to determination of L-Cys in spiked human serum and water samples where it gave recoveries ranging from 96.6 to 102.4%.
Graphical abstract Schematic of the preparation of a molecularly imprinted polymer coated on the multiwalled carbon nanotube (MIP/MWCNT) by functionalization of MCNTs with methacrylic acid and subsequent polymerization. The MIP/MWCNTs were successfully applied for extraction and spectrophotometric determination of L-Cys by charge transfer (CT) complexation.
A method is described for ratiometric fluorometric assays of H2O2 by using two probes that have distinct response profiles. Under the catalytic action of ferrous ion, the 615 nm emission of protein-stabilized gold nanoclusters (under 365 nm photoexcitation) is quenched by H2O2, while an increased signal is generated with a peak at 450 nm by oxidizing coumarin with the H2O2/Fe(II) system to form a blue emitting fluorophore. These decrease/increase responses give a ratiometric signal. The ratio of the fluorescences at the two peaks are linearly related to the concentration of H2O2 in the range from 0.05 to 10 μM, with a 7.7 nM limit of detection. The detection scheme was further coupled to the urate oxidase catalyzed oxidation of uric acid which proceeds under the formation of H2O2. This method provides an simple and effective means for the construction of ratiometric fluorometric (enzymatic) assays that involve the detection of H2O2.
Graphical abstract Under catalysis by ferrous ion, hydrogen peroxide quenches the luminescence of gold nanoclusters (AuNCs) and oxidizes coumarin into a fluorescent derivative, which rendered fluorescence ON and OFF at two distinct wavelengths for ratiometric measurements.
A zinc(II)-responsive ratiometric fluorescent core-shell nanoprobe (referred to as QPNPs) is described. It consist of an optimized combination of an internal reference dye (TBAP) encapsulated in the core, and a Zn(II)-specific indicator dye (PEIQ) in the shell. The nanoprobe was synthesized via single-step graft copolymerization induced by tert-butyl hydroperoxide at 80 °C. QPNPs exhibit a well-defined core-shell nanostructure and well-resolved dual emissions after photoexcitation at 380 nm. After exposure to Zn(II), the QPNPs display a green fluorescence peaking at ~500 nm that increases with the concentration of Zn(II), while the pink fluorescence of the porphine-derived reference dye peaking at ~650 nm remains unchanged. This results in color change from pink to green and thus enables Zn(II) to be detected both spectroscopically and with bare eyes. Zn(II) can be quantified with a 3.1 nM detection limit. The core-shell structured nanoprobe was also applied to real-time imaging of Zn(II) in living HeLa cells and in zebrafish. This work establishes a reliable approach to synthesize ratiometric fluorescent nanoprobes. It enables such nanoprobes to be prepared also by those not skilled in nanomaterial synthesis.
Graphical abstract A zinc(II)-responsive core-shell nanoprobe (referred to as QPNP) is synthesized via single-step graft copolymerization. Zn(II) can be quantitated with a 3.1 nM detection limit by the QPNPs through ratiometric fluorescence strategy (PEIQ as the Zn(II) indicator and TBAP as the reference dye).
The work describes a hybrid electrochemical sensor for highly sensitive detection of the anesthetic lidocaine (LID). Porous carbon (PC) was synthesized from an isoreticular metal-organic framework-8 (IRMOF-8) and drop cast onto a glassy carbon electrode (GCE). A layer of a molecularly imprinted polymer (MIP) layer was then fabricated in situ on the modified GCE by electro-polymerization, with LID acting as the template and resorcinol as the functional monomer. Hexacyanoferrate is used as an electrochemical probe. The electrical signal (typically acquired at 0.335 V vs. SCE) increases linearly in the 0.2 pM to 8 nM LID concentration range, with a remarkable 67 fM detection limit (at an S/N ratio of 3). The sensor is stable and selective. Eventually, rapid and accurate detection of LID in spiked real samples was successfully realized.
An electrochemical non-enzymatic glucose sensor based on copper nanorods (CuNRs) was developed. The CuNRs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, and X-ray photoelectron spectroscopy. The results display a layer of rough cuprous oxide that is formed on the surface of CuNRs. The CuNR- modified glassy carbon electrode exhibits an outstanding capability in terms of nonenzymatic sensing of glucose. The sensor displays high sensitivity (1490 μA?mM?1?cm?2), fast response time (less than 5 s), a low detection limit of 8 nM (S/N = 3), long term stability, and excellent anti-fouling ability. The sensor was applied to the detection of glucose in (spiked) human serum and in black ice tea, with relative standard deviations (for n = 6) of 1.7 % and 1.9 %, respectively.
Graphical abstract The surface of Cu nanorods was covered with cuprous oxide, which increased the surface area of the nanorods and provided more catalytic active sites for the electro-oxidation of glucose. Good linearity and selectivity were obtained in glucose sensing.
A composite consisting of carbon nanotubes (CNT) and copper nanoparticles (CuNPs) was prepared by a chemical reduction method, and its structure characterized by scanning electron microscopy, transmission electron microscopy energy dispersive spectroscopy and FT-IR spectrometry. The hybrid composite was deposited on the surface of a disposable gold electrode that was manufactured from a commercial digital versatile gold disc by a drop casting method. The electrochemical properties of the modified electrode were investigated by cyclic voltammetry and differential pulse voltammetry. The sensor showed an excellent electrocatalytic activity towards oxidation of paracetamol (PA). The calibration plot (with current typically measured at 0.41 V vs. Ag/AgCl) is linear in the 0.5 to 80 μM concentration range, and the detection limit is as low as 10 nM. The sensor was successfully applied to the determination of PA in spiked water and tablet samples where it gave recoveries ranging between 95.25 and 100.5 %.
Graphical abstract Carbon nanotubes (CNT) -copper nanoparticles (CuNPs) hybrid composite was synthesized by a facile method then the nanohybrid was used as a modifier for the DVD gold electrode for improving its performance toward paracetamol electrooxidation. Cyclic voltammetry and differential pulse voltammetry were used for characterization and determination of paracetamol, respectively.
The ionic liquid 1-{3-[(2-aminoethyl)amino]propyl}-3-vinylimidazole bromide was synthesized and used to fabricate a molecularly imprinted film for electrochemical sensing of myoglobin (Myo). This film was deposited on a glassy carbon electrode modified with multi-walled carbon nanotubes by using the ionic liquid as the functional monomer, Myo as the template, N,N′-methylenebisacrylamide as the crosslinker, and a redox system containing ammonium persulfate and N,N,N′,N′-tetramethylethylenediamine as the initiator. The sensing performance of the modified electrode was investigated by using the hexacyanoferrate system as an electrochemical redox probe. The results demonstrated that the sensor possesses good selectivity and high sensitivity. The oxidation peak current at the potential of ~0.3 V (vs. SCE) was found linearly related to the myoglobin concentration in the range from 60.0 nM to 6.0 μM, with a 9.7 nM detection limit at an S/N ratio of 3. The sensor was applied to the determination of Myo in spiked serum samples where it showed average recoveries (for n = 5) of 96.5 %.
Graphical abstract By using a polymerizable ionic liquid as the functional monomer, a myoglobin imprinted polymer was fabricated on a multi-walled carbon nanotube modified glassy carbon electrode. The sensing performances of the molecularly imprinted sensor towards myoglobin demonstrated good selectivity, sensitivity and accuracy.
Under visible-light irradiation, a cathodic photoelectrochemical (PEC) sensor is presented for highly sensitive determination of Cr(VI) at a potential of ?0.25 V (vs SCE). PbS quantum dots (QDs) were capped with mercaptoacetic acid and assembled on the surface of an indium tin oxide (ITO) electrode via the linker poly(diallyl dimethyl ammonium chloride) providing a photoactive sensor. Cr(VI) accepts the photoelectrons generated by the PbS QDs. This promotes the separation of electron holes and enhances the cathodic photocurrent generated by a 470-nm LED. The sensor has 10 pM detection limit and a linear working range from 0.02 nM to 2 μM of chromate. The method was successfully applied to the determination of Cr(VI) and total chromium in spiked environmental water samples.
Graphical abstract Schematic illustration of the photocurrent enhancement response of ITO/PbS toward chromium(VI). In the presence of Cr(VI) (red line), Cr(VI) accepts the photoelectrons generated by the PbS QDs under 470-nm LED irradiation, resulting in improved photocurrent of ITO/PbS.
We describe a high-performance nitric oxide (NO) sensor by using a nanocomposite consisting of platinum-tungsten alloy nanoparticles, sheets of reduced graphene oxide and an ionic liquid (PtW/rGO-IL) that was deposited onto the surface of a glassy carbon (GC) electrode. The modified GC electrode exhibits excellent electrocatalytic activity toward the oxidation of NO with a strong peak at 0.78 V vs. Ag/AgCl due to the synergistic effects of bimetallic PtW nanoparticles, reduced graphene oxide nanosheets and an ionic liquid. The sensor possesses a detection limit as low as 0.13 nM, high sensitivity (3.01 μA μM?1 cm2), and good selectivity over electroactive interferents that may exist in biological systems. The sensor was tested to selectively distinguish NO in actual human serum and urine samples, confirming potential practical applications. In our perception, the approach described here may be extended to the fabrication of various kind of composites made from metal nanostructures, graphene and ionic liquids for medical and environmental analysis.
Graphical abstract Enhanced electrochemical sensing of nitric oxide (NO) is demonstrated by utilizing the synergistic effects of bimetallic PtW nanoparticles dispersed on reduced graphene oxide and ionic liquid nanocomposite.
The authors describe a method for the fabrication of a nanohybrid composed of carbon dots (C-dots) and gold nanoparticles (AuNPs) by in-situ reduction of C-dots and hydroauric acid under alkaline conditions. The process does not require the presence of surfactant, stabilizing agent, or reducing agent. The hybrid material was deposited in a glassy carbon electrode (GCE), and the modified GCE exhibited good electrocatalytic activity toward the oxidation of nitrite due to the synergistic effects between carbon dots and AuNPs. The findings were used to develop an amperometric sensor for nitrite. The sensor shows a linear response in the concentration range from 0.1 μmol?L-1 to 2 mmol?L-1 and a low detection limit of 0.06 μmol?L-1 at the signal-to-noise ratio of 3.
Graphical abstract Fabrication, characterization and electrochemical behavior of a glassy carbon electrode modifid with carbon dots and gold nanoparticles for sensing nitrite in lake water.
The authors describe an amperometric sensor for dopamine (DA) by employing olive-like Fe2O3 microspheres (OFMs) as the electrocatalyst for DA oxidization. The OFMs were prepared by using a protein templated method. The structure and properties of the OFMs were characterized by scanning electron microscopy, X-ray powder diffraction, energy dispersive x-ray spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The OFMs possess excellent catalytic activity towards DA oxidization due to their unique morphology. The sensor responds to DA within less than 5 s. The sensor, best operated at a voltage of +0.2 V (vs. SCE) responds linearly in the 0.2 to 115 μM DA concentration range and has a 30 nM detection limit. The selectivity, reproducibility and long-term stability of the sensor are acceptable. It performs well when applied to spiked human urine samples.
Graphical abstract Olive-like Fe2O3 microspheres (OFMs), synthesized using egg white as template, display excellent catalytic activity towards dopamine (DA) oxidization due to their unique morphology. They were applied for DA detection using the amperometric technique. The electrochemical sensor exhibited a high sensitivity and a 30 nM detection limit. DAQ: dopaquinone.
