Electroactive nanocarbon materials as signaling tags for electrochemical PCR.

Electrochemical polymerase chain reaction (PCR) represents a valid alternative to the optical-based PCR due to reduced costs of signaling labels, use of simpler instrumentation, and possibility of miniaturization and portability of the systems, which can facilitate decentralized detection. The high intrinsic electroactivity and strong linear relationship between the material concentration and its redox signal suggest a possible use of oxidized nanocarbon materials as electroactive tags for PCR. Herein, we compared three different nanographene oxide materials namely nGO-1, nGO-2 and nGO-3 as signaling tags for the detection of genetically modified organisms (GMO) by electrochemical PCR. The three materials differ in size, chemical composition as well as type and amount of oxygen functionalities verified by extensive characterization with X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM) and electrochemical methods. A sense primer sequence belonging to the Cauliflower Mosaic Virus 35S promoter (a common genetic marker for GMO screening) was used to conjugate to the nanocarbon materials by carbodiimide chemistry before PCR amplification with a biotinylated antisense strand. Finally, the amplified electroactive PCR product was detected, where the reduction signal derived from the electrochemically reducible oxygenated functionalities on the nanocarbon material surface was directly correlated to the presence of GMO. Overall, we were able to correlate the different material characteristics with their performance as electroactive labels and identify the nanocarbon material that exhibits the highest potential to be used as innovative electroactive label for PCR in the amplification and detection of the selected target sequence.

How 3D printing can boost advances in analytical and bioanalytical chemistry.

3D printing fabrication methods have received lately an enormous attention by the scientific community. Laboratories and research groups working on analytical chemistry applications, among others, have advantageously adopted 3D printing to fabricate a wide range of tools, from common laboratory hardware to fluidic systems, sample treatment platforms, sensing structures, and complete fully functional analytical devices. This technology is becoming more affordable over time and therefore preferred over the commonly used fabrication processes like hot embossing, soft lithography, injection molding and micromilling. However, to better exploit 3D printing fabrication methods, it is important to fully understand their benefits and limitations which are also directly associated to the properties of the materials used for printing. Costs, printing resolution, chemical and biological compatibility of the materials, design complexity, robustness of the printed object, and integration with commercially available systems represent important aspects to be weighted in relation to the intended task. In this review, a useful introductory summary of the most commonly used 3D printing systems and mechanisms is provided before the description of the most recent trends of the use of 3D printing for analytical and bioanalytical chemistry. Concluding remarks will be also given together with a brief discussion of possible future directions.

Electrochemical Biosensor with Enhanced Antifouling Capability for COVID-19 Nucleic Acid Detection in Complex Biological Media.

Biofouling caused by the accumulation of biomolecules on sensing surfaces is one of the major problems and challenges to realize the practical application of electrochemical biosensors, and an effective way to counter this problem is the construction of antifouling biosensors. Herein, an antifouling electrochemical biosensor was constructed based on electropolymerized polyaniline (PANI) nanowires and newly designed peptides for the detection of the COVID-19 N-gene. The inverted Y-shaped peptides were designed with excellent antifouling properties and two anchoring branches, and their antifouling performances against proteins and complex biological media were investigated using different approaches. Based on the biotin-streptavidin affinity system, biotin-labeled probes specific to the N-gene (nucleocapsid phosphoprotein) of COVID-19 were immobilized onto the peptide-coated PANI nanowires, forming a highly sensitive and antifouling electrochemical sensing interface for the detection of COVID-19 nucleic acid. The antifouling genosensor demonstrated a wide linear range (10-14 to 10-9 M) and an exceptional low detection limit (3.5 fM). The remarkable performance of the genosensor derives from the high peak current of PANI, which is chosen as the sensing signal, and the extraordinary antifouling properties of designed peptides, which guarantee accurate detection in complex systems. These crucial features represent essential elements for future rapid and decentralized clinical testing.

Electrochemical Exfoliation of MoS2 Crystal for Hydrogen Electrogeneration.

Transition metal dichalcogenides (TMDs) have recently emerged within the group of 2D materials due to their electrical, catalytic and optical properties significantly enhanced and useful when down-sized to single layer. In particular, MoS2 has attracted much attention due to its semiconducting nature with a useful band gap when present as single layer, the enhanced photoluminescence, but also importantly the excellent catalytic properties towards the electrochemical hydrogen evolution. We present here the preparation of thin layers MoS2 nanosheets with enhanced catalytic properties towards the hydrogen evolution reaction by means of an easy and fast electrochemical top-down exfoliation procedure in aqueous solution from a naturally occurring MoS2 crystal. After structural and chemical characterization with STEM, AFM, XPS and Raman spectroscopy electrochemical investigations were performed to test catalytic properties in acidic solution for the electrogeneration of hydrogen and compare it to MoS2 nanosheets obtained through the widely employed chemical Li intercalation/exfoliation. Electrochemically exfoliated MoS2 shows lower Tafel slope than its counterpart obtained with chemical exfoliation.

Covalent Functionalization of Exfoliated Arsenic with Chlorocarbene.

Few-layer and monolayer arsenic (arsenene) materials have been attracting great attention mainly from a theoretical perspective. Chemical modification of these materials would expand significantly the range of their applications. Here, we describe a chlorocarbene-mediated modification of exfoliated layered arsenic materials. Carbene-based species are highly reactive and offer further possibilities of functionalization. Our approach for modifying the arsenic surface by chlorocarbene generated from organolithium and dichloromethane resulted in a large surface coverage and a highly luminescent functionalized material, opening the door for its application in modern optoelectronic devices.

Exfoliation of layered materials using electrochemistry.

After the isolation and discovery of the extraordinary properties of graphene, tremendous interest has been directed towards other layered materials. Known also as van der Waals solids, these materials can offer a much wider range of properties than graphene when exfoliated to single or few-layer sheets with benefits for several different applications. Similar to graphene, a key aspect for the actual application of these materials is certainly represented by the development of efficient fabrication methods able to produce a large quantity of individual sheets of good quality. Electrochemically-assisted exfoliation of bulk crystals represents one of the most promising methods for mass-production of graphene and also other 2D material sheets due to the mild operational conditions, short time, simple instrumentation and high yield of individual layers obtained. We review here the latest and most representative electrochemically-assisted methods of exfoliation of layered materials categorized by the intercalation ion employed. A separate section is also included and dedicated to the recent bipolar electrochemical procedures which through different mechanistic avenues recently demonstrated efficient reduction of both lateral size and thickness of bulk particles of layered materials dispersed in solution. A summary discussion along with future perspectives is also provided in the last section.

Detection of Amphipathic Viral Peptide on Screen-Printed Electrodes by Liposome Rupture Impact Voltammetry.

Detection of infectious viruses and disease biomarkers is of utmost importance in clinical screening for effective identification and treatment of diseases. We demonstrate here the use of liposome rupture impact voltammetry for the qualitative detection of model amphipathic viral peptide on a screen-printed electrode. This novel, proof-of-concept method was proposed for the quick and reliable detection of viruses by nonfaradaic liposome rupture impact voltammetry with the aid of 1,2-dioleoyl-sn-glycero-3-phosphocholine liposomes. This provides an avenue for the development of future on-site, point-of-care detection devices for medical and biological applications.

3D Printed Electrodes for Detection of Nitroaromatic Explosives and Nerve Agents.

Three-dimensional (3D) printing has proven to be a versatile and useful technology for specialized applications in industry and also for scientific research. We demonstrate its potential use toward the electrochemical detection of nitroaromatic compounds 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), and fenitrothion (FT). The detection of these compounds is of utmost importance in military and forensic applications. Stainless steel electrodes were fabricated by 3D printing, and the surface was electroplated with gold. The electrochemical performance of the 3D printed electrodes was compared to that of the conventionally employed glassy carbon electrode (GCE) and proved to be more sensitive toward the detection of all three nitroaromatic compounds. 3D printing of customizable electrodes provides a viable alternative to traditional electrodes for the analysis of samples with electrochemical methods.

Electrochemical Exfoliation of Layered Black Phosphorus into Phosphorene.

Among 2D materials that recently have attracted enormous interest, black phosphorus (BP) is gaining a rising popularity due to its tunable band-gap structure, which is strongly correlated to the thickness and can enable its use in optoelectronic and electronic applications. It is therefore important to provide a facile and scalable methodology to prepare single or few-layer BP nanosheets. We propose herein a simple and fast top-down method to exfoliate a BP crystal into nanosheets of reduced thickness by using electrochemistry. The application of an anodic potential to the crystal in an acidic aqueous solution allows control over the exfoliation efficiency and quality of the nanosheets produced. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and scanning transmission electron microscopy (STEM) have been applied to fully characterize the exfoliated material, which presented significantly reduced layer thickness compared to the starting bulk material.

Chemically Reduced Graphene Oxide for the Assessment of Food Quality: How the Electrochemical Platform Should Be Tailored to the Application.

Graphene platforms have been drawing considerable attention in electrochemistry for the detection of various electroactive probes. Depending on the chemical composition and properties of the probe, graphene materials with diverse structural features may be required to achieve an optimal electrochemical performance. This work comprises a comparative study on three chemically modified graphenes, obtained from the same starting material and with different oxygen functionalities and structural defects (graphene oxide (GO), chemically reduced graphene oxide (CRGO), and thermally reduced graphene oxide (TRGO)) towards the electrochemical detection of quinine, an important flavoring agent present in tonic-based beverages. In general, the reduced graphenes, namely CRGO and TRGO, showed enhanced performance in terms of calibration sensitivity and selectivity, due to the improved heterogeneous electron-transfer rates on their surfaces. In particular, CRGO provided the best overall electrochemical performance, which can be attributed to its higher density of structural defects and reduced amount of oxygen functionalities. For this reason, CRGO was employed for the electrochemical detection of quinine in commercial tonic drink samples, showing high sensitivity and selectivity, and therefore representing a valid low-cost alternative to more complicated and time consuming traditional analytical methods.

Exfoliation of Layered Topological Insulators Bi2Se3 and Bi2Te3 via Electrochemistry.

Among layered materials, topological insulators such as Bi2Se3 and Bi2Te3 are lately attracting much attention due to particular electronic properties and, especially with Bi2Te3, excellent thermoelectric properties. Methods of preparation of few-layered nanosheets of Bi2Se3 and Bi2Te3 range from the bottom-up chemical vapor deposition or hydrothermal synthesis from oxide precursors to the top-down mechanical exfoliation and liquid-based exfoliation supported by sonication from the natural bulk crystals. Here, we propose a simple and rapid electrochemical approach to exfoliate natural Bi2Se3 and Bi2Te3 crystals in aqueous media to single/few-layer sheets. The exfoliated materials have been characterized by scanning transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, high-resolution transmission electron microscopy, and Raman spectroscopy in addition to evaluation of their electrochemical properties. This electrochemical procedure represents a simple, reagent-free, and scalable method for the fabrication of single/few-layer sheets of these materials.

Phenols as probes of chemical composition of graphene oxide.

Graphene oxide (GO) can be conveniently used as a starting material for the preparation of selective and sensitive electrochemical sensing systems. The amount of oxygen groups present on the material can be precisely tuned by reduction methodologies which allow the selection of the optimal C/O ratio for specific analytes. An electrochemical reduction procedure is used in this work to alter the oxygen content of the GO starting material and investigate the effects on the electrochemical detection of phenolic compounds selected with different hydroxyl groups: phenol, catechol, hydroquinone and phloroglucinol. Cyclic voltammetry has been used to measure the alteration of the oxidation signal upon tuning the oxygen content of the graphene based electrode material.

Nitroaromatic explosives detection using electrochemically exfoliated graphene.

Detection of nitroaromatic explosives is of paramount importance from security point of view. Graphene sheets obtained from the electrochemical anodic exfoliation of graphite foil in different electrolytes (LiClO4 and Na2SO4) were compared and tested as electrode material for the electrochemical detection of 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in seawater. Voltammetry analysis demonstrated the superior electrochemical performance of graphene produced in LiClO4, resulting in higher sensitivity and linearity for the explosives detection and lower limit of detection (LOD) compared to the graphene obtained in Na2SO4. We attribute this to the presence of oxygen functionalities onto the graphene material obtained in LiClO4 which enable charge electrostatic interactions with the -NO2 groups of the analyte, in addition to π-π stacking interactions with the aromatic moiety. Research findings obtained from this study would assist in the development of portable devices for the on-site detection of nitroaromatic explosives.

3D-printing technologies for electrochemical applications.

Since its conception during the 80s, 3D-printing, also known as additive manufacturing, has been receiving unprecedented levels of attention and interest from industry and research laboratories. This is in addition to end users, who have benefited from the pervasiveness of desktop-size and relatively cheap printing machines available. 3D-printing enables almost infinite possibilities for rapid prototyping. Therefore, it has been considered for applications in numerous research fields, ranging from mechanical engineering, medicine, and materials science to chemistry. Electrochemistry is another branch of science that can certainly benefit from 3D-printing technologies, paving the way for the design and fabrication of cheaper, higher performing, and ubiquitously available electrochemical devices. Here, we aim to provide a general overview of the most commonly available 3D-printing methods along with a review of recent electrochemistry related studies adopting 3D-printing as a possible rapid prototyping fabrication tool.

Graphene and its electrochemistry - an update.

The electrochemistry of graphene and its derivatives has been extensively researched in recent years. In the aspect of graphene preparation methods, the efficiencies of the top-down electrochemical exfoliation of graphite, the electrochemical reduction of graphene oxide and the electrochemical delamination of CVD grown graphene, are currently on par with conventional procedures. Electrochemical analysis of graphene oxide has revealed an unexpected inherent redox activity with, in some cases, an astonishing chemical reversibility. Furthermore, graphene modified with p-block elements has shown impressive electrocatalytic performances in processes which have been historically dominated by metal-based catalysts. Further progress has also been achieved in the practical usage of graphene in sensing and biosensing applications. This review is an update of our previous article in Chem. Soc. Rev. 2010, 39, 4146-4157, with special focus on the developments over the past two years.

Electrochemically Exfoliated Graphene and Graphene Oxide for Energy Storage and Electrochemistry Applications.

Top-down methods are of key importance for large-scale graphene and graphene oxide preparation. Electrochemical exfoliation of graphite has lately gained much interest because of the simplicity of execution, the short process time, and the good quality of graphene that can be obtained. Here, we test three different electrolytes, that is, H2 SO4 , Na2 SO4 , and LiClO4 , with a common exfoliation procedure to evaluate the difference in structural and chemical properties that result for the graphene. The properties are analyzed by means of scanning transmission electron microscopy (STEM), Raman spectroscopy, and X-ray photoelectron spectroscopy. We then tested the graphene materials for electrochemical applications, measuring the heterogeneous electron transfer (HET) rates with a Fe(CN)6 (3-/4-) redox probe, and their capacitive behavior in alkaline solutions. We correlate the electrochemical features with the presence of structural defects and oxygen functionalities on the graphene materials. In particular, the use of LiClO4 during the electrochemical exfoliation of graphite allowed the formation of highly oxidized graphene with a C/O ratio close to 4.0 and represents a possible avenue for the mass production of graphene oxide as valid alternative to the current laborious and dangerous chemical procedures, which also have limited scalability.

Improving the Analytical Performance of Graphene Oxide towards the Assessment of Polyphenols.

The presence of oxygen functionalities on graphene surface has enormous influence on its electrochemical and electroanalytical properties. The oxygen-containing groups on graphene platforms can strongly affect the electrochemical response, being either detrimental for the heterogeneous charge transfer or promoting a favourable interaction with the specific analyte. In this study, by electrochemically reducing graphene oxide material at increasing negative potentials (from -0.25 to -1.50 V) we obtained eight electrochemically reduced graphene oxide (ERGO) platforms carrying a decreasing amount of oxygen functionalities. Subsequently, we analysed the electroanalytical response of each ERGO material for the detection of gallic acid, a standard polyphenol that is correlated to the antioxidant activity of food and beverages. The graphene platform providing the best electroanalytical performance in terms of sensitivity, selectivity and linearity of response was then employed for the analysis of commercial fruit juice samples. Herein we demonstrated that graphene materials can be electrochemically tuned to optimise their electrochemical response towards the detection of biologically important analytes.

Anti-MoS2 Nanostructures: Tl2S and Its Electrochemical and Electronic Properties.

Layered transition metal dichalcogenides are catalytically important compounds. Unlike the mounting interest in transition metal dichalcogenides such as MoS2 and WS2 for electrochemical applications, other metal chalcogenides with layered structure but different chemical composition have received little attention among the scientific community. One such example is represented by thallium(I) sulfide (Tl2S), a Group 13 chalcogenide, which adopts the peculiar anti-CdCl2 type structure where the chalcogen is sandwiched between the metal layers. This is the exact opposite of a number of transition metal dichalcogenides like 1T-MoS2 adopting the regular CdCl2 structure type. The electronic structure of Tl2S thus differs from MoS2. Such structure may provide a useful insight and understanding toward its electrochemical behavior in relation to the electrochemical properties of MoS2. We thus investigated the intrinsic electroactivity of Tl2S and its implications for sensing and energy generation, specifically the electrocatalytic properties toward the hydrogen evolution reaction (HER). We show that Tl2S exhibits four distinct redox signals at ca. 0.4 V, -0.5 V, -1.0 V and -1.5 V vs Ag/AgCl as a result of its inherent cathodic and anodic processes. We also demonstrate that Tl2S possesses slow electron transfer abilities with a rate (k(0)obs) as low as 6.3 × 10(-5) cm s(-1). Tl2S displays a competent performance as a HER electrocatalyst compared to a conventional glassy carbon electrode. However, the poor conductivity of Tl2S renders the HER electrocatalytic behavior second-rate compared to MoS2. Furthermore, we investigated the electronic properties of Tl2S and found that Tl2S exhibits an unusually narrow band dispersion around the Fermi level. We show here that anti-MoS2 structure of Tl2S is accompanied by highly unusual features.