The authors describe a nonenzymatic glucose sensor that was obtained by electrochemical deposition and oxidization of metallic nickel on the surface of nitrogen-doped reduced graphene oxide (N-RGO) placed on a glassy carbon electrode (GCE). An analysis of the morphology and chemical structure indicated the composite to possess a well-defined vermicular Ni(OH)2 nanorods combined with N-RGO. The electrochemical performance of the modified GCE with respect to the detection of glucose in 0.1 M NaOH was investigated by cyclic voltammetry and amperometry. The wrinkle and protuberance of N-RGO for loading of nanostructured Ni(OH)2 are found to increase electrical conductivity, surface area, electrocatalytical activity and stability. The modified GCE displays a high electrocatalytic activity towards the oxidation of glucose in 0.1 M NaOH solution. The lower detection limit is 0.12 μM at an applied potential of +0.45 V (vs Ag/AgCl) (S/N=3), and the sensitivity is 3214 μA mM?1 cm?2. The modified GCE possesses long-term stability, good reproducibility and high selectivity over fructose, sucrose and lactose.
Graphical abstract The composite of vermicular Ni(OH)2 nanorods combined with N-doped reduced graphene oxide is a viable catalyst for non-enzymatic electrochemical sensing of glucose.
Various kinds of nanomaterials have been described in recent years that represent stable and low-cost alternatives to biomolecules (such as enzymes) for use in (bio)analytical methods. The materials typically include, metal/metal oxides, metal complexes, nanocomposites, porphyrins, phthalocyanines, smart polymers, and carbonaceous nanomaterials. Due to their biomimetic and other properties, such nano-materials may replace natural enzymes in chemical sensors, biosensors, and in various kinds of bioassays. This overview (with 252 references) highlights the analytical potential of such nanomaterials. It is divided into sections on (a) the types of nanomaterials according to their intrinsic nature, (b) non-enzymatic sensor designs (including electrochemical, colorimetric, fluorescent and chemiluminescent methods), and (c), applications of non-enzymatic sensors in the biomedical, environmental and food analysis fields. We finally address current challenges and future directions.
Graphical abstract This review discusses different types of nanomaterials, which are explored as a potential biomimetic material to replace the natural enzyme in the field of biosensors, and have found widespread applications in biomedical, food and environmental analysis.
Gold nanorods (AuNRs) show high potential in electrochemical sensing owing to their excellent conductivity, electrocatalytic activity, selectivity and sensitivity. This review (with 99 refs.) summarizes the performance of AuNR-based electrochemical sensors based on the use of advanced nanocomposites. Following an introduction into the fields of biosensors and nanomaterials, the article summarizes the advantages and limitations of conventional analytical methods. A third section overviews the methods for preparation and characterization of AuNRs and nanocomposites including bimetallic nanorods, gold-metal oxide, gold-carbon nanotubes, gold-polymer, gold-graphene, gold-CNT and gold-enzymes conjugates. Their electrochemistry is treated next, with aspects related to the effects of rod size and shape, of thiol coatings on voltammetric signals, and on the behavior of 1-D AuNRs and respective arrays. Section 5 gives examples for non-enzymatic sensors for simple biomolecules, with subsections on sensors for hydrogen peroxide, nitric oxide, glucose, dopamine, NAD/NADH, cysteine, and some drugs. Section 6 covers enzyme-based sensors, with examples on sensors using peroxidases, oxidases and the like. The next sections cover DNA biosensors (such as for DNA biomarkers) and immunosensors, mainly for tumor markers. Possibilities for improving sensor performance are presented at the end of the review.
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.
This review (with (318) refs) describes progress made in the design and synthesis of morphologically different metal oxide nanoparticles made from iron, manganese, titanium, copper, zinc, zirconium, cobalt, nickel, tungsten, silver, and vanadium. It also covers respective composites and their function and application in the field of electrochemical and photoelectrochemical sensing of chemical and biochemical species. The proper incorporation of chemical functionalities into these nanomaterials warrants effective detection of target molecules including DNA hybridization and sensing of DNA or the formation of antigen/antibody complexes. Significant data are summarized in tables. The review concludes with a discussion or current challenge and future perspectives.
Conducting polymers possess good conductivity, can be easily modified, have a particular redox activity. Noble metal nanomaterials, in turn, possess high conductivity, catalytic properties and large surface-to-volume ratios. Synergistic materials consisting of both conducting polymer and metal nanomaterial therefore are most useful materials for use in electrochemical immunosensors with improved sensitivity and specificity. This review (with 75 references) gives an overview on advances in conducting polymer based noble metal nanomaterial hybrids for amperometric immunoassay of the 13 most common tumor markers. The review is divided into the following sections: (1) Polyaniline based noble metal nanomaterial hybrids; (2) Polyaniline derivative-based noble metal nanomaterial hybrids; (3) Polypyrrole-based noble metal nanomaterial hybrids. A final section covers future perspectives regarding challenges on the design of electrochemical immunoassays.
Graphical abstract Advances on conducting polymer and noble metal nanomaterial hybrids for amperometric immunoassay of tumor marker are reviewed. Future perspectives regarding challenges on the construction of electrochemical immunosensing interface for tumor marker are discussed.
The authors describe a composite material prepared from carbon nanohorns and poly(2-aminopyridine) that was obtained by electrochemical polymerization of 2-aminopyridine on carbon nanohorns. The material was used to modify a glassy carbon electrode (GCE) to obtain a sensor for non-enzymatic determination of hydrogen peroxide. The modified GCE was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The modified electrode is shown to display excellent electrical conductivity and catalytic activity towards hydrogen peroxide, mainly due to the large specific surface area of carbon nanohorns, the good electron charge transfer properties resulting from the use of poly(2-aminopyridine), and their synergistic effect. The response of the modified GCE (best operated at a working potential of ?0.45 V vs. SCE) to H2O2 is linear in the 0.05 to 8 mM concentration range. The limits of detection (LOD) and quantitation (LOQ) are 3.6 μM and 12.4 μM, respectively. The electrode is selective, stable and reproducible, this making it a promising tool for non-enzymatic determination of hydrogen peroxide.
This review (with 340 refs) focuses on methods for specific and sensitive detection of metabolites for diagnostic purposes, with particular emphasis on electrochemical nanomaterial-based sensors. It also covers novel candidate metabolites as potential biomarkers for diseases such as neurodegenerative diseases, autism spectrum disorder and hepatitis. Following an introduction into the field of metabolic biomarkers, a first major section classifies electrochemical biosensors according to the bioreceptor type (enzymatic, immuno, apta and peptide based sensors). A next section covers applications of nanomaterials in electrochemical biosensing (with subsections on the classification of nanomaterials, electrochemical approaches for signal generation and amplification using nanomaterials, and on nanomaterials as tags). A next large sections treats candidate metabolic biomarkers for diagnosis of diseases (in the context with metabolomics), with subsections on biomarkers for neurodegenerative diseases, autism spectrum disorder and hepatitis. The Conclusion addresses current challenges and future perspectives.
Graphical abstract This review focuses on the recent developments in electrochemical biosensors based on the use of nanomaterials for the detection of metabolic biomarkers. It covers the critical metabolites for some diseases such as neurodegenerative diseases, autism spectrum disorder and hepatitis.
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.
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.
The authors describe a method for increasing the peroxidase-like catalytic properties of copper nanoclusters (Cu-NCs) that are used in non-enzymatic assays. The Cu-NCs were prepared by utilizing 6-thio-β-cyclodextrin as both the template and as effective modulators for increasing the peroxidase-like properties of the Cu-NCs. The β-CD-coated Cu-NCs have an average diameter of 2 nm, are stable in aqueous solutions, display strong fluorescence with excitation/emission peak wavelengths of 360/450 nm, and possess peroxidase-like catalytic activity which makes them a useful enzyme mimic. We have applied the findings to non-enzymatic photometric determination (at 650 nm) of (a) H2O2 in the concentration range of 0.02 to 10 mM using the β-CD/Cu-NC assisted oxidation of tetramethylbenzidine by H2O2, and (b) glucose in the concentration range of 0.04 to 20 mM after addition of glucose oxidase and formation of H2O2. The detection limits (at an S/N ratio of 3) are 0.2 μM for H2O2 and 0.4 μM for glucose. The β-CD coating is found to result in a strong increase in the reaction rate, probably because the cavity of β-CD acts as a pocket for the recognition and catalysis of substrate. Hence, the binding specificity becomes similar to that of natural enzymes.
Graphical Abstract The peroxidase-like catalytic activity of Cu-NCs in non-enzymatic sensors is strongly enhanced by utilizing mono-6-thio-β-cyclodextrin (mono-6-SH-β-CD) as both the template molecule and the effective rate modulator.
Caspases, especially caspase-3, play a critical role in the intrinsic and extrinsic pathways of apoptosis. In addition, caspase-3 is involved in mental disorders like Alzheimer disease. Any up and down regulation of caspase-3 activity may cause cancer. This review (with 58 references) summarizes recent advances in electrochemical and electrochemiluminescent quantitation of the activity of caspase-3 based on the use of nanomaterials. The nanomaterials and nanolabels are classified in three main subgroups, namely electrochemical signal amplification strategies, amplification based on modified electrodes, and the combination of both modes. The potential of various electrochemical and electrochemiluminescence bioassays is discussed, and methods to circumvent certain limitations are oresented. Finally, current trends in the detection of caspase-3 such as system integration and the application of advanced nanomaterials are discussed.
Graphical abstract The review summarizes electrochemical methods for the quantitation of caspase-3 activity based on the use of nanomaterials and of nanomaterial based labels. It contains subsections on electrochemical signal amplification strategies, amplification based on modified electrodes, and the combination of both modes.
Cardiac troponin (cTn) is a specific and sensitive biomarker for diagnosis of myocardial injury. Hence, numerous kinds of biosensors for cTn have been reported. Electrochemical methods possess inherent advantages over other kinds of sensors because they are specific, sensitive, and simple. By combining the advantages of electrochemical biosensors with those of nanomaterials, some interesting electrochemical biosensor for cTn can be obtained where the nanomaterials trigger substantial signal amplification. This review (with 101 refs.) summarizes the state of the art in electrochemical biosensing of cTn based on the use of nanomaterials. Following an introduction into the field, the use of nanomaterials in electrochemical sensing is briefly discussed. A next section covers strategies for signal amplification by using nanomaterials, with subsections on the use of nanowires, nanotubes, graphenes, and various other nanoparticles. The article concludes with a discussion of the prospects of nanomaterial-based signal amplification and on future research directions.
Graphical abstract Illustration of electrochemical biosensing of cardiac troponin (cTn) with various kinds of nanomaterials, including nanowires, nanotubes, graphene and nanoparticles, as the signal amplification modules.
A method is described for the determination of the polarity of mixed organic solvents by using the fluorescent probe Hostasol Red (HR) desposited on the outer surface of nanosized zeolite L. Organic solvents and their mixtures can be roughly classified according to their polarity with bare eyes and fluorometrically. Emission peaks range from 520 to 640 nm. Some solvents act as quenchers. The method is studied with series of protic and nonprotic solvents, and with selected mixtures of organic solvents.
Graphical abstract The dye Hostalene Red adsorbed on nanosized zeolite shows strong fluorescence solvatochromism. This can be exploited to quickly assess the polarity of solvents and solvent mixtures.
A highly selective electrochemical sensor was fabricated based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe2O4 NPs). The nanocomposite has attractive properties such as high surface-to-volume ratio and good electrocatalytic activity towards the drugs acetaminophen (AC), epinephrine (EP), and melatonin (MT), best at working voltages of 0.35, 0.09 and 0.55 V (vs. Ag/AgCl), respectively. The linear ranges (and detection limits) are 6.5–135 (0.4) μmol L?1 for AC, 5–100 (0.7) μmol L?1 for EP, and 6.5–145 (3) μmol L?1 for MT.
Graphical abstract A novel electrochemical sensor based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe2O4) for the simultaneous detection of the acetaminophen, epinephrine and melatonin was fabricated
An electrochemical nanoaptasensor is described that is based on the use of a glassy carbon electrode (GCE) modified with electrodeposited silver nanoparticles (AgNPs). An aptamer (Apt) against trinitrotoluene (TNT) was then immobilized on the AgNPs. The addition of TNT to the modified GCE leads to decrease in peak current (typically measured at a potential of ?0.45 V vs. Ag/AgCl) of riboflavin which acts as an electrochemical probe. Even small changes in the surface (as induced by binding of Apt to TNT) alter the interfacial properties. As a result, the LOD is lowered to 33 aM, and the dynamic range extends from 0.1 fM to 10 μM without sacrificing specificity.
Graphical abstract Schematic presentation of a nanoaptasensor which is based on a glassy carbon electrode (GCE) modified with electrodeposited silver nanoparticles (AgNPs) and aptamer (Apt). It was applied to the detection of 2,4,6-trinitrotoluene (TNT) with the help of riboflavin (RF) as a redox probe.
A glassy carbon electrode (GCE) was modified with gold nanoparticles (AuNPs) coated on monolayer graphene (AuNP/MG) by direct in situ sputtering of AuNPs on CVD-generated graphene. This process avoids complicated polymer transfer and polymer cleaning processes and affords AuNPs with a clean surface. The monolayer graphene is ductile and well dispersed. The clean surface of the AuNPs renders this sensor superior to GCEs modified with AuNPs on reduced graphene oxide in terms of the amperometric non-enzymatic determination of hydrogen peroxide. The detection limit is 10 nM (S/N = 3) at 0.55 V (vs. SCE), which is lower than that for similar methods, and the response time is as short as 2 s. Another attractive feature of the sensor is its feasibility for large-scale production via CVD and sputtering.
Graphical abstract Gold nanoparticles deposited onto monolayered graphene generated by chemical vapor deposition (CVD) are used for electrochemical sensing of H2O2, with the detection limit of 10 nM (S/N = 3) and response time of less than 2 s.
A conducting polymer composite was prepared from nano-sized hydroxyaptite (nHAp) doped into poly(3,4-ethylenedioxythiophene) (PEDOT) and then electrodeposited on a glassy carbon electrode (GCE). The nHAp carries carboxy groups and therefore is negatively charged at moderate pH value. When doped into PEDOT (PEDOT-nHAp), it forms a uniform and stable film that exhibits low electrochemical impedance, a large specific surface, and high activity toward the electrochemical oxidation of nitrite. Under optimized conditions and at a relatively low working potential of 0.78 V (vs. SCE), the modified GCE exhibited a linear amperometric response in the 0.25 μM to 1.05 mM nitrite concentration range, and the limit of detection is as low as 83 nM.
Graphical abstract A highly sensitive nitrite sensor was developed based on conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carboxyl group functionalized hydroxyapatite nanoparticles, which exhibited a large surface area and good conductivity and stability.
This article reports on a novel aptamer-based platform for the quantitation of urea by using an aptamer with high affinity and selectivity for urea. The surface of a glassy carbon electrode (GCE) was modified by drop casting a cocktail consisting of carbon nanotubes and reduced graphene oxide (rGO) decorated with platinum-gold nanoparticles. The urea aptamer was then immobilized on the nanocomposite via covalent conjugation. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to trace the modification of the GCE. Binding of urea caused the aptamer to be folded, and this result in an inhibition of the interfacial charge transfer rate when using hexacyanoferrate as an electrochemical redox probe. The change in redox current was quantified by differential pulse voltammetry, typically at a working voltage of 0.22 V vs. Ag/AgCl. The assay has a 1.9 pM detection limit, and the response is linear up to 150 nM concentration of urea. The superior selectivity and affinity of aptamer-modified GCE makes it a most useful tool for analysis of urea present in very low concentrations.
This review (with 85 refs.) summarizes the recent literature on the adsorption of common aromatic pollutants by using modified metal-organic frameworks (MOFs). Four kinds of aromatic pollutants are discussed, namely benzene homologues, polycyclic aromatic hydrocarbons (PAHs), organic dyes and their intermediates, and pharmaceuticals and personal care products (PPCPs). MOFs are shown to be excellent adsorbents that can be employed to both the elimination of pollutants and to their extraction and quantitation. Adsorption mechanisms and interactions between aromatic pollutants and MOFs are discussed. Finally, the actual challenges of existence and the perspective routes towards future improvements in the field are addressed.
Graphical abstract Recent advance on adsorption of common aromatic pollutants including benzene series, polycyclic aromatic hydrocarbons, organic dyes and their intermediates, pharmaceuticals and personal care products by metal-organic frameworks.
