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.
Electrochemical DNA sensors represent a simple, accurate and economical platform for DNA detection. Gold nanoparticles are known to be efficient labels in electrochemical sensors and to be viable materials to modify the surface of electrodes thereby to enhance the detection limit of the sensor. For surface modification, gold nanoparticles are used in combination with nanomaterials like graphene, graphene oxide, or carbon nanotubes to improve electrochemical performance in general. This review (with 116 refs.) mainly covers the advances made in recent years in the use of gold nanoparticles in DNA sensing. It is divided into the following main sections: (a) An introduction covers aspects of electrochemical sensing of DNA and of appropriate nanomaterials in general. (b) The use of gold nanoparticles in DNA is specifically addressed next, with subsections on AuNPs acting as electrochemical labels, electron transfer mediators, signal amplifiers, carriers of electroactive molecules, catalysts, immobilization platforms, on silver enhancement strategies, on AuNPs modified with carbonaceous materials (such as graphenes and nanotubes), and on multiple amplification schemes. The review concludes with a discussion of current challenges and trends in terms of highly sensitive DNA based sensing using AuNPs.
Graphical abstract The review describes the state of the art in the use of gold nanoparticles in the electrochemical DNA sensors and contains sections on the use of AuNPs as labels, signal amplifiers, carriers of electroactive molecules, catalyst, immobilization platform, and on silver enhancement and multiple amplification strategies.
We describe a label-free electrochemical immunosensor for the carcinoembryonic antigen (CEA). It is based on a nanocomposite consisting of electrochemically reduced graphene oxide, gold nanoparticles (AuNPs), and poly(indole-6-carboxylic acid). Coupled to nanoparticle-amplification techniques and modified with ionic liquid (IL), this immunoassay shows high sensitivity and good selectivity for CEA. At the best working voltage of 0.95 V (vs. Ag/AgCl), the lower detection limit is 0.02 ng·mL?1, and the response to CEA is linear in the range from 0.02 to 90 ng·mL?1. The method was applied to the determination of CEA in spiked serum samples and gave recoveries in the range from 98.5 % to 102 %.
Graphical abstract A label-free electrochemical immunosensor was fabricated for the carcinoembryonic antigen (CEA) with a detection limit of 0.02 ng·mL?1. It is based on a nanocomposite consisting of electrochemically reduced graphene oxide (erGO), gold nanoparticles (Au NP), and poly(indole-6-carboxylic acid) (PICA).
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.
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.
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.
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.
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.
The incorporation of nanomaterials into electrochemical sensors is an attractive approach towards the improvement of the sensitivity of amperometry and also can provide improved sensor selectivity and stability. This review (with 137 references) details the current state of the art and new trends in nanomaterial-based electrochemical sensing of hydrogen peroxide (H2O2), hydrogen sulfide (H2S) and nitric oxide (NO) in cells or released by cells. The article starts with a discussion of the significance of the three analytes, and this is followed by three sections that summarize the electrochemical detection schemes for H2O2, H2S and NO. Each section first summarizes the respective physiological roles, and then reviews electrochemical sensors based on the use of carbon nanomaterials, noble metal nanomaterials, metal oxide nanomaterials, and layered doubled hydroxides. The materials are compiled in three tables along with figures of merit for the various sensors.
Graphical abstract Nanomaterial-based electrochemical sensors for Reactive oxygen species (H2O2), Reactive nitrogen species (NO) and Reactive hydrogen sulfide species (H2S) inside cells or released by cells.
Two-dimensional (2D) nanomaterials are promising building blocks for sensors due to their unique physical, chemical, electronic, and optical properties. This review (with 253 references) first summarizes the historical developments of 2D nanomaterials and discusses the advantages of 2D nanomaterials when applied for constructing sensors. Next, their properties are discussed, with subsections on electronic, optical, mechanical and chemical properties. This is followed by an overview on methods for syntheses and the effects of positive and/or negative charges on the properties and in sensing applications. Then, recent advances in 2D nanomaterial-based electrochemical, fluorometric, colorimetric, electrochemiluminescent, photoelectrochemical, and field-effect transistor sensors are discussed. The discussion also includes the preparation of sensing elements, the roles of such nanomaterials, and assay strategies. Finally, on the basis of the current achievements in the field of 2D nanomaterials, the perspectives on the challenges and opportunities for the exploration of 2D nanomaterial-based sensors are put forward.
The authors describe a sandwich-type electrochemical immunoassay for sensitive determination of the carcinoembryonic antigen (CEA). It is based on the use of iridium nanoparticles (Ir NPs) acting as electrochemical signal amplifier on the surface of a glassy carbon electrode. At first, polydopamine-reduced graphene oxide (PDA-rGO) was employed to immobilize primary antibody (Ab1) against CEA. Secondly, Ir-NPs were used as a support for the immobilization of secondary antibody (Ab2) to afford signal labels. The large surface area of PDA-rGO and the excellent electro-oxidative H2O2-sensing properties of Ir NPs result in a sensitive assay for CEA. Operated best at a working voltage of ?0.6 V (vs. SCE), the assay has a linear range that extends from 0.5 pg?mL?1 to 5 ng·mL?1, and the lower detection limit is 0.23 pg?mL?1. The immunosensor displays satisfactory reproducibility and stability, thus demonstrating a reliable immunoassay strategy for tumor biomarkers. It was applied to the determination of CEA in spiked serum samples.
Graphical abstract Schematic of an amperometric sandwich immunoassay for the carcinoembryonic antigen using a glassy carbon electrode modified with polydopamine, reduced graphene oxide and iridium nanoparticles
Carbon nanotubes, graphenes, and their hybridized composites with nanoparticles have been attempted to establish a direct electrical communication between the recognition biomolecule and its underlying electrode surface. This review (with 133 refs.) focuses on advances, strategies and technical challenges in the development of reagentless electrochemical biosensors for glucose with enhanced detection sensitivity, selectivity, and simplicity. Specifically, the review commences with a discussion of the relevance of direct electron transfer (DET) in biosensing together with the fundamental of electro-enzymology and kinetics. General aspects of glucose oxidase (GOx), the most popular enzyme with a flavin cofactor, are discussed in view of its historical and important role in the development of electrical biosensors for blood glucose. The next section assesses DET of GOx based on the Marcus theory and the Laviron formalism. The reorganizational energy of the Marcus model and the overpotential play an important role in reaction kinetics and affect the rate of electron transfer significantly. The presence of nanomaterials, particularly for graphene oxide, decreases the electron transfer distance between the enzyme redox center and the underlying electrode surface well beyond 15 Å. The improper Marcus-Hush-Chidsey integral is now simplified to estimate the rate of electron transfer with very good accuracy. Critiques, technical challenges, and future possibilities of glucose electrodes with respect to DET are also presented and discussed.
Graphical abstract This review (with 133 refs.) focuses on advances, strategies and technical challenges in the development of reagentless electrochemical biosensors for glucose with enhanced detection sensitivity, selectivity, and simplicity.
The authors describe a method for signal amplification in electrochemical aptasensors. It is based on the induction of an increased electrochemical current by the aptamer captured on a glassy carbon electrode (GCE). The phosphate groups on the aptamer backbone are brought to reaction with added molybdate to form a redox-active molybdophosphate precipitate on the surface of the GCE that generates a strong electrochemical current. To further enhance sensitivity, gold nanorods (GNRs) were selected as a support for the immobilization of aptamers. The aptasensor was applied to the determination of the cancer biomarker carcinoembryonic antigen (CEA) in a sandwich format. Antibody against CEA, CEA (antigen) and GNRs modified with CEA aptamer were sequentially captured on the GCE. The resulting aptasensor, best operated at a voltage as low as 0.18 V vs. Ag/AgCl, is highly sensitive and has a wide linear range that extends from 0.1 pg·mL?1 to 10 ng·mL?1 of CEA. This amplification strategy uses an aptamer as both the recognition probe and signal probe and therefore simplifies signal transduction. Conceivably, this detection scheme may be adapted to numerous other electrochemical bioassays if respective antibodies and aptamers are available.
Graphical abstract Schematic presentation of an electrochemical aptasensor based on aptamer induced electrochemical current for the detection of cancer biomarker carcinoembryonic antigen (CEA). Gold nanorods (GNR) are chosen for the immobilization of aptamers to increase the loading of aptamers.
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
This paper describes an electrochemiluminescent (ECL) based method for chiral recognition and detection of both glutamate (Glu) enantiomers. The luminophore luminol (Lum) was used as both the reductant and stabilizer of Ag nanoparticles (AgNP-Lum) which were combined with carbon quantum dots (C-dots) and placed on a glassy carbon electrode (GCE) along with the enzyme glutamate oxidase (GluOx). The use of these materials is found to result in strong amplification of ECL. The nanomaterials used were characterized by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR). The stepwise fabrication of the electrode was verified by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under optimized conditions and by applying a typical potential of 0.6 V, the ECL increases linearly in the 5.0 μM to 5.0 mM Glu concentration range, with a 1.6 μM lower detection limit and satisfactory selectivity. A Glu logic gate idea has been designed that is based on this enzymatic biosensor.
Graphical abstract Schematic presentation of the electrochemiluminescent (ECL) biosensor. A glassy carbon electrode (GCE) was modified with C-dots and silver nanoparticles which were deoxidized by luminol (AgNP-Lum) for enzymatic specific detection.
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.
CdSe:Eu nanocrystals were successfully synthesized and characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectric spectroscopy. The CdSe:Eu nanocrystals showed enhanced green electrochemiluminescence (ECL) intensity when compared to pure CdSe nanocrystals. Further, the nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen (CEA) that has a linear response over the 1.0 fg·mL?1 to 100 ng·mL?1 CEA concentration range with a 0.4 fg·mL?1 detection limit. The assay was applied to the determination of CEA in human serum samples.
Graphical abstract Schematic of the assay: GCE-glassy-carbon electrode, Ab- Antibody, BSA- Bovine serum albumin, Ag- Antigen. CdSe:Eu nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen.
Peroxynitrite (PON for short) is a powerful nitrating, nitrosating and oxidative agent for cellular constituents. In vivo, PON is formed through the diffusion-controlled reaction between superoxide radical (O2?-) and nitric oxide (?NO). This critical review (with 67 refs.) covers the state of the art in nanomaterial-based (a) detection and imaging of PON inside cells and (b) monitoring of cellular events such as cellular oxidative burst by using optical or electrochemical methods. It starts with the formation, fate and pathophysiology of PON in vivo. The next part summarizes nanomaterial based electrochemical microsensors featuring nanofilms and nanostructured electrodes, nanospheres, 3D nanostructures and graphene-supported catalysts. A following chapter covers techniques based on optical nanoprobes, starting with nanomaterials used in optical detection of PON (including quantum dots, carbon dots, fluorescent organic polymer dots, rare earth nanocrystals including upconversion nanoparticles, iron oxide nanoparticles, gold nanoparticles, and fluorophore-modified nanoporous silicon). This is followed by subsections on strategies for optical detection of PON (including color changes, fluorescence quenching, activation and recovery), and on schemes for optimized spatial and temporal resolution, for improving sensitivity, selectivity, and (photo)stability. We then address critical issues related to biocompatibility, pharmacokinetics, give a number of representative practical applications and discuss challenges related to PON detection. The review concludes with a discussion of latest developments and future perspectives.
Screening serum for the presence of prostate specific antigen (PSA) belongs to the most common approach for the detection of prostate cancer. This review (with 156 refs.) addresses recent developments in PSA detection based on the use of various kinds of nanomaterials. It starts with an introduction into the field, the significance of testing for PSA, and on current limitations. A first main section treats electrochemical biosensors for PSA, with subsections on methods based on the use of gold electrodes, graphene or graphene-oxide, carbon nanotubes, hybrid nanoparticles, and other types of nanoparticles. It also covers electrochemical methods based on the enzyme-like activity of PSA, on DNA-, aptamer- and biofuel cell-based methods, and on the detection of PSA via its glycan part. The next main section covers optical biosensors, with subsections on methods making use of surface plasmon resonance (SPR), localized SPR and plasmonic ELISA-like schemes. This is followed by subsections on methods based on the use of fiber optics, fluorescence, chemiluminescence, Raman scattering and SERS, electrochemiluminescence and cantilever-based methods. The most sensitive biosensors are the electrochemical ones, with lowest limits of detection (down to attomolar concentrations), followed by mass cantilever sensing and electrochemilumenescent strategies. Optical biosensors show lower performance, but are still more sensitive compared to standard ELISA. The most commonly applied nanomaterials are metal and carbon-based ones and their hybrid composites used for different amplification strategies. The most attractive sensing schemes are summarized in a Table. The review ends with a section on conclusions and perspectives.
Graphical abstract Schematic representation of nanostructure-based biosensors for detection of prostate specific antigen using various detection schemes and biorecognition elements such as antibodies (Abs), aptamers (APT), lectins (LEC), and molecularly imprinted polymers (MIP).
Hetero-dimeric magnetic nanoparticles of the type Au-Fe3O4 have been synthesised from separately prepared, differently shaped (spheres and cubes), monodisperse nanoparticles. This synthesis was achieved by the following steps: (a) Mono-functionalising each type of nanoparticles with aldehyde functional groups through a solid support approach, where nanoparticle decorated silica nanoparticles were fabricated as an intermediate step; (b) Derivatising the functional faces with complementary functionalities (e.g. amines and carboxylic acids); (c) Dimerising the two types of particles via amide bond formation. The resulting hetero-dimers were characterised by high-resolution TEM, Fourier transform IR spectroscopy and other appropriate methods.
Graphical Abstract Nano-LEGO: Assembling two types of separately prepared nanoparticles into a hetero-dimer is the first step towards complex nano-architectures. This study shows a solid support approach to combine a gold and a magnetite nanocrystal.
