Detection of DNA hybridization on chemically modified graphene platforms

Biosensing of single-nucleotide polymorphism: Technological advances and their transformative applications on health

Single nucleotide polymorphisms (SNPs) are important genetic changes related to many diseases such as breast cancer, Alzheimer's disease, and β-thalassemia. Because of the increased interest in biosensor technologies, there has been a notable surge in the creation of new techniques to identify these changes in recent years. These new methods are highly accurate and sensitive, cost-effective and fast, making them ideal for use in clinical analysis. The non-invasive nature of biosensing techniques further enhances their integration into clinical protocols and point-of-care diagnostics. Several electrochemical, optical, and mass-based biosensors are carefully examined in this extensive review; each is distinguished by unique sensing platforms and techniques. This review presents in-depth discussions of linear dynamic ranges, detection limits, and real-world applications of contemporary research in the diagnosis of biological substrate disorders.

A highly selective and sensitive electrochemical sensor for tetracycline resistant genes detection based on the non-covalent interaction of graphene oxide and nucleobase

Antibiotic resistance genes (ARGs) are causing worldwide environmental problems, however, the traditional analytical methods and test equipment for them are time-consuming and expensive. The electrochemical sensor using the non-covalent bond between graphene oxide (GO) and single-stranded tet (ss-tet) was established for specific tetracycline resistance genes (tet, composed of ss-tet and complementary ss-tet (ss-tet') in water) detection, which preparation time was only 35 min and far less than most reported sensors based on covalent bond. As the result of the detection for tet, the developed sensor not only had the low detection limit of 50.0 pM (8.1 × 102 copies·mL-1), the short detection time within 42 min, but also had satisfactory stability, excellent reproducibility, and highly selectivity (RSD < 4.43 %). Besides, it also had acceptable accuracy comparing to the real-time quantitative polymerase chain reaction (RT-qPCR) and PCR array in tet detection. Noticeably, it also had been successfully applied to tetA detection in different water samples. In brief, the prepared non-covalent bond sensor is simple, rapid, and suitable for highly selective and sensitive detection of the ARGs in actual water.

Electrochemical Detection Platform Based on RGO Functionalized with Diazonium Salt for DNA Hybridization

In this paper, we propose an improved electrochemical platform based on graphene for the detection of DNA hybridization. Commercial screen-printed carbon electrodes (SPCEs) were used for this purpose due to their ease of functionalization and miniaturization opportunities. SPCEs were modified with reduced graphene oxide (RGO), offering a suitable surface for further functionalization. Therefore, aryl-carboxyl groups were integrated onto RGO-modified electrodes by electrochemical reduction of the corresponding diazonium salt to provide enough reaction sites for the covalent immobilization of amino-modified DNA probes. Our final goal was to determine the optimum conditions needed to fabricate a simple, label-free RGO-based electrochemical platform to detect the hybridization between two complementary single-stranded DNA molecules. Each modification step in the fabrication process was monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using [Fe(CN)6]3-/4- as a redox reporter. Although, the diazonium electrografted layer displayed the expected blocking effect of the charge transfer, the next steps in the modification procedure resulted in enhanced electron transfer properties of the electrode interface. We suggest that the improvement in the charge transfer after the DNA hybridization process could be exploited as a prospective sensing feature. The morphological and structural characterization of the modified electrodes performed by scanning electron microscopy (SEM) and Raman spectroscopy, respectively, were used to validate different modification steps in the platform fabrication process.

Blocking the Nanopores in a Layer of Nonconductive Nanoparticles: Dominant Effects Therein and Challenges for Electrochemical Impedimetric Biosensing

Blockage of a nanopore by an analyte molecule has emerged as a promising concept for electrochemical biosensing. Nanoporous structures can be formed on the electrode surface simply by packing spherical nanoparticles in a dense planar arrangement. Modification of the nanoparticles with human serum albumin (HSA) and its interaction with the corresponding antibody (anti-HSA) can induce nanopore-blockage which significantly hinders permeation of the redox probe ([Fe(CN₆)]^4-/3-). Interfaces of different parameters were studied using Electrochemical Impedance Spectroscopy (EIS), and counterintuitively, the influence of charge of the nanoparticles and other immobilized entities played a substantial role in the measurement. Our study reveals dominant effects including the presence of mixed output signal and resolves corresponding EIS biosensing-related challenges. Consequently, blocking the nanopores was introduced as an efficient technique which enables the application of EIS-based biosensing to real-world analytical issues.

Impact of nano-morphology, lattice defects and conductivity on the performance of graphene based electrochemical biosensors

Diverse properties of graphenic materials have been extensively explored to determine properties that make good electrochemical nanomaterial-based biosensors. These are reviewed by critically examining the influence of graphene nano-morphology, lattice defects and conductivity. Stability, reproducibility and fabrication are discussed together with sensitivity and selectivity. We provide an outlook on future directions for building efficient electrochemical biosensors.

Influence of Graphene Oxide Concentration when Fabricating an Electrochemical Biosensor for DNA Detection

We have investigated the influence exerted by the concentration of graphene oxide (GO) dispersion as a modifier for screen printed carbon electrodes (SPCEs) on the fabrication of an electrochemical biosensor to detect DNA hybridization. A new pretreatment protocol for SPCEs, involving two successive steps in order to achieve a reproducible deposition of GO, is also proposed. Aqueous GO dispersions of different concentrations (0.05, 0.1, 0.15, and 0.2 mg/mL) were first drop-cast on the SPCE substrates and then electrochemically reduced. The electrochemical properties of the modified electrodes were investigated after each modification step by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), while physicochemical characterization was performed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Finally, the sensing platform was obtained by the simple adsorption of the single-stranded DNA probe onto the electrochemically reduced GO (RGO)-modified SPCEs under optimized conditions. The hybridization was achieved by incubating the functionalized SPCEs with complementary DNA target and detected by measuring the change in the electrochemical response of [Fe(CN)6]3-/4- redox reporter in CV and EIS measurements induced by the release of the newly formed double-stranded DNA from the electrode surface. Our results showed that a higher GO concentration generated a more sensitive response towards DNA detection.

Mass Production of Biocompatible Graphene Using Silk Nanofibers

Mass production of high-quality graphene dispersions under mild conditions impacts the utility of the material for biomedical applications. Various proteins have been used to prepare graphene dispersions, rare sources, and expensive prices for these proteins restrict their large-scale utility for the production of graphene. Here, inexpensive silk proteins as an abundant resource in nature were used for graphene exfoliation. The silk proteins were assembled into hydrophobic nanofibers with negative charge, and then optimized for the production of graphene. Significantly higher concentrations (>8 mg mL^-1) and yields (>30%) of graphene dispersions under ambient aqueous conditions were achieved compared with previous protein-assisted exfoliation systems. The exfoliated graphene exhibited excellent stability in water and fetal bovine serum solution, cytocompatibility, and conductivity, suggesting a promising future in biomedical and bioengineering applications.

Graphene-Based Nanomaterials and Their Applications in Biosensors

Recently graphene has been drawing tremendous attention mainly due to its potential contributions to applications in biology, information technology and energy. Among these applications graphene-based biosensors have been particularly progressed caused in part by development of diverse derivatives of graphene such as graphene oxides (GOs) and graphene quantum dots (GQDs). In this chapter preparation and functionalization of the graphene and GOQs are described together with their optoelectronic properties. Recent progresses in graphene and GQD-based biosensors are also highlighted with emphasis on immunoassay which utilizes unique interaction between antigen and antibody, and oligonucleotide assay which utilizes hybridization process. Since electrical and optical features are the most prominent characteristics of graphene-based nanomaterials, biosensor systems will be focused on electrochemical and fluorescence-based detection scheme.

Reduced Graphene Oxides: Influence of the Reduction Method on the Electrocatalytic Effect towards Nucleic Acid Oxidation

For the first time a critical analysis of the influence that four different graphene oxide reduction methods have on the electrochemical properties of the resulting reduced graphene oxides (RGOs) is reported. Starting from the same graphene oxide, chemical (CRGO), hydrothermal (hTRGO), electrochemical (ERGO), and thermal (TRGO) reduced graphene oxide were produced. The materials were fully characterized and the topography and electroactivity of the resulting glassy carbon modified electrodes were also evaluated. An oligonucleotide molecule was used as a model of DNA electrochemical biosensing. The results allow for the conclusion that TRGO produced the RGOs with the best electrochemical performance for oligonucleotide electroanalysis. A clear shift in the guanine oxidation peak potential to lower values (~0.100 V) and an almost two-fold increase in the current intensity were observed compared with the other RGOs. The electrocatalytic effect has a multifactorial explanation because the TRGO was the material that presented a higher polydispersity and lower sheet size, thus exposing a larger quantity of defects to the electrode surface, which produces larger physical and electrochemical areas.

Electrochemical thrombin detection based on the direct interaction of target proteins and graphene oxide as an indicator

Target protein-directed adsorption of graphene oxide (GO) as an electroactive indicator was employed for electrochemical detection of thrombin. The method was highly sensitive and the detection limit was as low as 9.7 pg ml(-1).

An electrochemical sensor based on rhodamine B hydrazide-immobilized graphene oxide for highly sensitive and selective detection of Cu(ii)

A novel Cu²⁺ sensor based on rhodamine B hydrazide (RBH)-immobilized graphene oxide (GO) was fabricated and estimated to be a detection limit of 0.061 nM for Cu²⁺ detection.

Applications of graphene and related nanomaterials in analytical chemistry

Graphene and its related materials remain a very bright and exciting prospect in analytical chemistry.

An insight into the hybridization mechanism of hairpin DNA physically immobilized on chemically modified graphenes

There is an emerging interest in developing electrochemical DNA biosensors which rely on label-free protocols for the detection of DNA hybridization and polymorphism. Lately, many of them have been using DNA probes which were physically adsorbed onto different graphene platforms. In these works, the biorecognition event is monitored by electrochemical impedance spectroscopy and the detection mechanism proposed needs verification by orthogonal methods. Here, we aim to provide an insight into the mechanism behind the impedimetric signal change upon the hybridization event on graphene platforms. For this aim, we used an orthogonal electrochemical method, differential pulse voltammetry, to examine the oxidation of guanine on target DNA molecules hybridized with an inosine-substituted hairpin DNA probe. We show that the successful biorecognition event leads to desorption of dsDNA from graphenic surfaces on a wide range of graphenic surfaces, such as graphene oxide, electrochemically reduced graphene oxide and thermally reduced graphene oxide. These results confirm the previous hypothesis based on electrochemical impedance spectroscopy data. In addition, these findings also have a profound impact on the understanding of both the interactions between DNA and graphene platforms and the DNA recognition event on graphene platforms for the construction of biosensors.

Inherently electroactive graphene oxide nanoplatelets as labels for specific protein-target recognition

Graphene related materials have been widely employed as highly efficient transducers for biorecognition. Here we show a conceptually new approach of using graphene oxide nanoplatelets (50 × 50 nm) as voltammetric inherently active labels for specific protein-target molecule recognition. This proof-of-principle is demonstrated by biotin-avidin recognition, which displays that graphene oxide nanoplatelet labels show excellent selectivity. Therefore, it is expected that inherently electroactive graphene oxide nanoplatelet labels will play a similar role as electroactive gold nanoparticle labels which were developed more than a decade ago.

A molecularly imprinted polymer with incorporated graphene oxide for electrochemical determination of quercetin

The molecularly imprinted polymer based on polypyrrole film with incorporated graphene oxide was fabricated and used for electrochemical determination of quercetin. The electrochemical behavior of quercetin on the modified electrode was studied in detail using differential pulse voltammetry. The oxidation peak current of quercetin in B-R buffer solution (pH = 3.5) at the modified electrode was regressed with the concentration in the range from 6.0 × 10⁻⁷ to 1.5 × 10⁻⁵ mol/L (r² = 0.997) with a detection limit of 4.8 × 10⁻⁸ mol/L (S/N = 3). This electrode showed good stability and reproducibility. In the above mentioned range, rutin or morin which has similar structures and at the same concentration as quercetin did not interfere with the determination of quercetin. The applicability of the method for complex matrix analysis was also evaluated.

Prospects and challenges of graphene in biomedical applications

Graphene materials have entered a phase of maturity in their development that is characterized by their explorative utilization in various types of applications and fields from electronics to biomedicine. Herein, we describe the recent advances made with graphene-related materials in the biomedical field and the challenges facing these exciting new tools both in terms of biological activity and toxicological profiling in vitro and in vivo. Graphene materials today have mainly been explored as components of biosensors and for construction of matrices in tissue engineering. Their antimicrobial activity and their capacity to act as drug delivery platforms have also been reported, however, not as coherently. This report will attempt to offer some perspective as to which areas of biomedical applications can expect graphene-related materials to constitute a tool offering improved functionality and previously unavailable options.

Graphene-based electrochemical sensors

Graphene, one kind of emerging carbon nanomaterial, has attracted increasing attention recently. Due to its fascinating physical and electrochemical properties, graphene as a promising electrode material has been widely used in electrochemical sensing applications. In this review, different approaches for the fabrication of graphene and the preparation of graphene-modified electrodes for electrochemical sensors are introduced. Moreover, recent research results on different graphene-based materials as an electrochemical platform for the detection of various biomolecules and chemicals are reviewed and compared. More electrochemical studies on this novel material should show up in the near future.

Graphene-based electrodes

Graphene, the thinnest two dimensional carbon material, has become the subject of intensive investigation in various research fields because of its remarkable electronic, mechanical, optical and thermal properties. Graphene-based electrodes, fabricated from mechanically cleaved graphene, chemical vapor deposition (CVD) grown graphene, or massively produced graphene derivatives from bulk graphite, have been applied in a broad range of applications, such as in light emitting diodes, touch screens, field-effect transistors, solar cells, supercapacitors, batteries, and sensors. In this Review, after a short introduction to the properties and synthetic methods of graphene and its derivatives, we will discuss the importance of graphene-based electrodes, their fabrication techniques, and application areas.

Noble metal (Pd, Ru, Rh, Pt, Au, Ag) doped graphene hybrids for electrocatalysis

Metal decorated graphene materials are highly important for catalysis. In this work, noble metal doped-graphene hybrids were prepared by a simple and scalable method. The thermal reductions of metal doped-graphite oxide precursors were carried out in nitrogen and hydrogen atmospheres and the effects of these atmospheres as well as the metal components on the characteristics and catalytic capabilities of the hybrid materials were studied. The hybrids exfoliated in nitrogen atmosphere contained a higher amount of oxygen-containing groups and lower density of defects on their surfaces than hybrids exfoliated in hydrogen atmosphere. The metals significantly affected the electrochemical behavior and catalysis of compounds that are important in energy production and storage and in electrochemical sensing. Research in the field of energy storage and production, electrochemical sensing and biosensing as well as biomedical devices can take advantage of the properties and catalytic capabilities of the metal doped graphene hybrids.