A novel and sensitive electrochemical DNA biosensor based on Fe@Au nanoparticles decorated graphene oxide

Electrochemical investigations and antimicrobial activity of Au nanoparticles photodeposited on titania nanoparticles

Titanium oxide nanopowder (TiO2 NPs) was synthesized via anodization in 0.7 M perchloric acid then annealed in nitrogen at 450 °C for 3 h to prepared the Titanium Oxide Nitrogen annealed nanoparticles (TiO2 NPs-N2) powder as catalytic support. Using a photodeposition process, gold was added with isopropanol as a sacrificial donor and H[AuCl4] acid, producing gold nanoparticles on nitrogen-annealed titanium oxide nanoparticles (Au-NPs on TiO2-NPs-N2). The mass loading of Au NPs was 2.86 × 10-4 (g/cm2). TEM images of Au NPs on TiO2-NPs-N2 suggest circular particles with a tendency to agglomerate. Cyclic voltammetry (CV) was used to investigate the electrocatalytic performance of the Au NPs/TiO2-NPs-N2 catalysts in ferrocyanide, KOH, and H2SO4, and the results were compared to those of a polycrystalline Au electrode that is readily accessible in the market. In KOH, H2SO4, and (2 M KOH + 0.1 M glycerol) solutions, the Au NPs/TiO2-NPs-N2 electrode displayed a startlingly high electrocatalytic performance. Using CV, the electrocatalytic oxygen reduction reaction (ORR) of Au NPs/TiO2-NPs-N2 and Au-NPs against glycerol oxidation in basic media was studied. The results indicated that Au NPs/TiO2-NPs-N2 is a promising support material for improving the electrocatalytic activity for acidic and basic oxidation. The electrode made of Au NPs/TiO2-NTs-N2 has steady electrocatalytic activity and may be reused repeatedly. TiO2 NPs and Au NPs/TiO2NPs-N2 showed satisfactory antibacterial activity against some human pathogenic bacteria using the disc diffusion method.

Development of a New Route for the Immobilization of Unmodified Single-Stranded DNA on Chitosan Beads and Detection of Released Guanine after Hydrolysis

In this work, chitosan beads were used as a cost-effective platform for the covalent immobilization of unmodified single-stranded DNA, using glutaraldehyde as a cross-linking agent. The immobilized DNA capture probe was hybridized in the presence of miRNA-222 as a complementary sequence. The target was evaluated based on the electrochemical response of the released guanine, using hydrochloride acid as a hydrolysis agent. Differential pulse voltammetry technique and screen-printed electrodes modified with COOH-functionalized carbon black were used to monitor the released guanine response before and after hybridization. The functionalized carbon black provided an important signal amplification of guanine compared to the other studied nanomaterials. Under optimal conditions (6 M HCl at 65 °C for 90 min), an electrochemical-based label-free genosensor assay exhibited a linear range between 1 nM and 1 µM of miRNA-222, with a detection limit of 0.2 nM of miRNA-222. The developed sensor was successfully used to quantify miRNA-222 in a human serum sample.

Smart Graphene-Based Electrochemical Nanobiosensor for Clinical Diagnosis: Review

The technological improvement in the field of physics, chemistry, electronics, nanotechnology, biology, and molecular biology has contributed to the development of various electrochemical biosensors with a broad range of applications in healthcare settings, food control and monitoring, and environmental monitoring. In the past, conventional biosensors that have employed bioreceptors, such as enzymes, antibodies, Nucleic Acid (NA), etc., and used different transduction methods such as optical, thermal, electrochemical, electrical and magnetic detection, have been developed. Yet, with all the progresses made so far, these biosensors are clouded with many challenges, such as interference with undesirable compound, low sensitivity, specificity, selectivity, and longer processing time. In order to address these challenges, there is high need for developing novel, fast, highly sensitive biosensors with high accuracy and specificity. Scientists explore these gaps by incorporating nanoparticles (NPs) and nanocomposites (NCs) to enhance the desired properties. Graphene nanostructures have emerged as one of the ideal materials for biosensing technology due to their excellent dispersity, ease of functionalization, physiochemical properties, optical properties, good electrical conductivity, etc. The Integration of the Internet of Medical Things (IoMT) in the development of biosensors has the potential to improve diagnosis and treatment of diseases through early diagnosis and on time monitoring. The outcome of this comprehensive review will be useful to understand the significant role of graphene-based electrochemical biosensor integrated with Artificial Intelligence AI and IoMT for clinical diagnostics. The review is further extended to cover open research issues and future aspects of biosensing technology for diagnosis and management of clinical diseases and performance evaluation based on Linear Range (LR) and Limit of Detection (LOD) within the ranges of Micromolar µM (10^-6), Nanomolar nM (10^-9), Picomolar pM (10^-12), femtomolar fM (10^-15), and attomolar aM (10^-18).

Electrochemical DNA Biosensor Based on Immobilization of a Non-Modified ssDNA Using Phosphoramidate-Bonding Strategy and Pencil Graphite Electrode Modified with AuNPs/CB and Self-Assembled Cysteamine Monolayer

The present paper describes an alternative approach to the traditionally used covalent immobilization methods that require cost-intensive and complicated chemistry modification of a single-stranded DNA (ssDNA) capture probe. The low-cost pencil graphite electrode (PGE) modified with carbon black (CB) and gold nanoparticles (AuNPs) was used as an electrochemical platform and the non-modified ssDNA was immobilized on a self-assembled cysteamine modified AuNPs/CB-PGE through a phosphoramidate bond between the 5'-terminal phosphate group of ssDNA and the primary amine group of cysteamine. The microRNA-21 was used as a target model in the fabrication of this electrochemical DNA biosensor and the hybridization process with the complementary probe was monitored by differential pulse voltammetry using methylene blue (MB) as an electrochemical hybridization indicator. The decreased reduction peak current of MB shows a good linear correlation with the increased concentration of microRNA-21 target sequences because the MB signal is determined by the amount of exposed guanine bases. The linear range of the fabricated DNA biosensor was from 1.0 × 10^-8 to 5.0 × 10^-7 M with a detection limit of 1.0 × 10^-9 M. These results show that the covalent immobilization of a non-modified ssDNA capture probe through a phosphoramidate-bonding strategy could serve as a cost-effective and versatile approach for the fabrication of DNA biosensors related to a wide range of applications that cover the fields of medical diagnostic and environmental monitoring. The fabricated electrochemical DNA biosensor was used to analyze microRNA-21 in a (spiked) human serum sample and it showed satisfactory and encouraging results as an electrochemical DNA biosensor platform.

Graphene and Its Derivatives: Synthesis and Application in the Electrochemical Detection of Analytes in Sweat

Wearable sensors and invasive devices have been studied extensively in recent years as the demand for real-time human healthcare applications and seamless human-machine interaction has risen exponentially. An explosion in sensor research throughout the globe has been ignited by the unique features such as thermal, electrical, and mechanical properties of graphene. This includes wearable sensors and implants, which can detect a wide range of data, including body temperature, pulse oxygenation, blood pressure, glucose, and the other analytes present in sweat. Graphene-based sensors for real-time human health monitoring are also being developed. This review is a comprehensive discussion about the properties of graphene, routes to its synthesis, derivatives of graphene, etc. Moreover, the basic features of a biosensor along with the chemistry of sweat are also discussed in detail. The review mainly focusses on the graphene and its derivative-based wearable sensors for the detection of analytes in sweat. Graphene-based sensors for health monitoring will be examined and explained in this study as an overview of the most current innovations in sensor designs, sensing processes, technological advancements, sensor system components, and potential hurdles. The future holds great opportunities for the development of efficient and advanced graphene-based sensors for the detection of analytes in sweat.

Polyoxometalate-based materials in extraction, and electrochemical and optical detection methods: A review

Polyoxometalates (POMs) as metal-oxide anions have exceptional properties like high negative charges, remarkable redox abilities, unique ligand properties and availability of organic grafting. Moreover, the amenability of POMs to modification with different materials makes them suitable as precursors to further obtain new composites. Due to their unique attributes, POMs and their composites have been utilized as adsorbents, electrodes and catalysts in extraction, and electrochemical and optical detection methods, respectively. A survey of the recent progress and developments of POM-based materials in these methods is therefore desirable, and should be of great interest. In this review article, POM-based materials, their properties as well as their identification methods, and analytical applications as adsorbents, electrodes and catalysts, and corresponding mechanisms of action, where relevant, are reviewed. Some current issues of the utilization of these materials and their future prospects in analytical chemistry are discussed.

Electrochemical Biosensor Using Nitrogen-Doped Graphene/Au Nanoparticles/DNAzyme for Ca2+ Determination

An electrochemical biosensor for detecting Ca²⁺ concentration was proposed using glass carbon electrodes (GCEs) modified with nitrogen-doped graphene (NGR), gold nanoparticles (AuNPs) and DNAzyme. The resistance signal was amplified through two methods: electrochemical reduction of AuNPs on the NGR surface to increase the specific surface area of the electrode and strengthen the adsorption of DNAzyme; and increasement of the DNAzyme base sequence. The process of electrode modification was characterized by scanning electron microscopy, Raman spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Experimental parameters’ influence, such as the deposition time of gold nanoparticles and the detection time, were assessed by electrochemical methods. The linear ranges of the electrochemical biosensor were in the range from 5 × 10⁻⁶ to 5 × 10⁻⁵ and 5 × 10⁻⁵ to 4 × 10⁻⁴ M, with a detection limit of 3.8 × 10⁻⁶ M. The concentration of Ca²⁺ in the serum of dairy cows was determined by the biosensor with satisfactory results, which could be potentially used to diagnose subclinical hypocalcemia.

Electrochemical Sensor for Directional Recognition and Measurement of Antibiotic Resistance Genes in Water

The establishment of rapid targeted identification and analysis of antibiotic resistance genes (ARGs) is very important. In this study, an electrochemical sensor, which can detect ARGs was obtained by modifying the sulfhydryl single-stranded DNA probe onto the thin-film gold electrode through self-assembly. The sensor can perform a hybridization reaction with a target sequence to obtain an electrochemical impedance spectroscopy signal. The results showed that when the concentration of the probe used to modify thin-film gold electrodes during preparation was 1 μM, the hybridization time was 1 h, and the hybridization temperature was 35 °C, the self-assembled sensor showed good detection performance for the ARGs encoding β-lactam hydrolase. The measurement ARG concentration linear range is 6.3-900.0 ng/mL, and the R² is 0.9992. The sensor shows good specific recognition ability for single-base, double-base, and three-base mismatch DNA. In addition, after 30 days of storage at 4 °C, the accurate identification and analysis of ARGs can still be maintained.

Evolution of nucleic acids biosensors detection limit III

This review is an update of two previous ones focusing on the limit of detection of electrochemical nucleic acid biosensors allowing direct detection of nucleic acid target (miRNA, mRNA, DNA) after hybridization event. A classification founded on the nature of the electrochemical transduction pathway is established. It provides an overall picture of the detection limit evolution of the various sensor architectures developed during the last three decades and a critical report of recent strategies.

Fabrication strategies and surface tuning of hierarchical gold nanostructures for electrochemical detection and removal of toxic pollutants

The intensive research on the synthesis and characterization of gold (Au) nanostructures has been extensively documented over the last decades. These investigations allow the researchers to understand the relationships between the intrinsic properties of Au nanostructures such as particle size, shape, morphology, and composition to synthesize the Au nano/hybrid nanostructures with novel physicochemical properties. By tuning the properties above, these nanostructures are extensively employed to detect and remove trace amounts of toxic pollutants from the environment. This review attempts to document the achievements and current progress in Au-based nanostructures, general synthetic and fabrication strategies and their utilization in electrochemical sensing and environmental remediation applications. Additionally, the applications of Au nanostructures (e.g., as adsorbents, sensing platforms, catalysts, and electrodes) and advancements in the field of electrochemical sensing of different target analytes (e.g., proteins, nucleic acids, heavy metals, small molecules, and antigens) are summarized. The literature survey concludes the existing methods for the detection of toxic contaminants at various concentration levels. Finally, the existing challenges and future research directions on electrochemical sensing and degradation of toxic contaminants using Au nanostructures are defined.

Amperometric determination of ecotoxic N-methyl-p-aminophenol sulfate in photographic solution and river water samples based on graphene oxide/CeNbO4 nanocomposite catalyst

The electronic conductivity of the metal oxides is generally increased by hybridization of highly conductive carbon supportive materials. In this present work, we have demonstrated a novel one-pot preparation of cerium niobate (CeNbO₄) nanoparticles embedded with graphene oxide (GO/CeNbO₄) composite, for ultrasensitive detection of the photographic developing agent, metol (MTL). The as-prepared GO/CeNbO₄ was analyzed by various characterization techniques. The intensive characterization techniques were used to affirm the detailed structural moiety, size, morphology, and surface area of GO/CeNbO_4. The GO/CeNbO₄ modified glassy carbon electrode (GCE) affords a superior electrocatalytic activity toward MTL. The obtained amperometric response on the GO/CeNbO₄/GCE holding an extremely low level detection of 10 nM and superior sensitivity of 10.97 µA µM^-1 cm^-2 toward MTL detection. Besides, the GO/CeNbO₄/GCE also gives excellent selectivity, stability, repeatability, and reproducibility. We achieved excellent recovery results in real photographic solution and river water samples analysis with great accuracy. This work offers a novel insight into the growth of the carbon-based niobate family with electrochemical sensor applications.

Novel nucleic acid origami structures and conventional molecular beacon-based platforms: a comparison in biosensing applications

Nucleic acid nanotechnology designs and develops synthetic nucleic acid strands to fabricate nanosized functional systems. Structural properties and the conformational polymorphism of nucleic acid sequences are inherent characteristics that make nucleic acid nanostructures attractive systems in biosensing. This review critically discusses recent advances in biosensing derived from molecular beacon and DNA origami structures. Molecular beacons belong to a conventional class of nucleic acid structures used in biosensing, whereas DNA origami nanostructures are fabricated by fully exploiting possibilities offered by nucleic acid nanotechnology. We present nucleic acid scaffolds divided into conventional hairpin molecular beacons and DNA origami, and discuss some relevant examples by focusing on peculiar aspects exploited in biosensing applications. We also critically evaluate analytical uses of the synthetic nucleic acid structures in biosensing to point out similarities and differences between traditional hairpin nucleic acid sequences and DNA origami.

Biosensing platform on ferrite magnetic nanoparticles: Synthesis, functionalization, mechanism and applications

Ferrite magnetic nanoparticles (FMNPs) are gaining popularity to design biosensors for high-performance clinical diagnosis. The fusion of information shows that FMNPs based biosensors require well-tuned FMNPs as detection probes to produce large and specific biological signals with minimal non-specific binding. Nevertheless, there is a noticeable lacuna of information to solve the issues related to suitable synthesis route, particle size reduction, functionalization, sensitivity towards targeted intercellular biological tiny particles, and lower signal-to-noise ratio. Therefore it allows exploring unique characteristics of FMNPs to design a suitable sensing device for intracellular measurements and diseases detection. This review focuses on the extensively used synthesis routes, their advantages and limitations, crystalline structure, functionalization, along with recent applications of FMNPs in biosensors, taking into consideration their analytical figures of merit and range of linearity. This work also addresses the current progress, key factors for sensitivity, selectivity and productivity improvement along with the challenges, future trends and perspectives of FMNPs based biosensors.

Hierarchical structure in poly(N-vinyl carbazole)/Fe3O4 nanocomposites and the relevant magnetic coercivity

In this study, we report the dependence of the nanoparticle dispersion on the zero-conversion initiator efficiency in the nanocomposites formed by poly(N-vinyl carbazole) (PNVK) and acrylic acid-modified iron oxide (AA-Fe₃O₄) nanoparticles via free radical solution polymerization of the precursor solution, that is, a thorough mixture of 28.5 wt% AA-Fe₃O₄ nanoparticles and the N-vinyl carbazole (NVK) monomer with the solvent dimethylformamide and azobisisobutyronitrile as an initiator. Here three different types of the dispersion state of AA-Fe₃O₄ nanoparticles in the PNVK matrix have been distinguished by a combined approach of transmission electron microscopy and small-angle X-ray scattering coupled with real-space models of the nanoparticle assemblies. When the polymerization proceeded with a higher zero-conversion initiator efficiency (f°) by pre-polymerization at 115 °C, the generation of a large amount of free radicals could efficiently induce the dominant surface-initiated polymerization of the NVK monomer with the vinyl groups of tethered acrylic acids; in this case, the constitution of "shorter multiple grafted PNVK chains" threaded AA-Fe₃O₄ nanoparticles to form particle branches and the branches were joined together from branching points along each branch, thereby forming the network structure. However, once the polymerization was conducted at a lower f° by pre-polymerization at 75 °C, a significant reduction in the generation of free radicals likely greatly reduced the efficiency in the occurrence of surface-initiated polymerization at particle surfaces; nevertheless, the self-polymerization of the NVK monomer could still take place to induce a local demixing between the polymerizing longer PNVK chains and AA-Fe₃O₄ nanoparticles via the attractive depletion mechanism, thus locally leading to the formation of small aggregates. While if the f° was controlled to be intermediate by polymerization at 100 °C, an optimal balance between the rates of the surface-initiated polymerization and the self-polymerization induced a collective construction built from the network and aggregate structures, exhibiting the structural characteristics of large aggregates. Furthermore, the magnetic coercivity of PNVK/AA-Fe₃O₄ nanocomposites was found to depend on the dispersion state of the AA-Fe₃O₄ nanoparticles, presenting a tendency towards enhanced coercivity as the dispersion state changed from large aggregates to small aggregates to network structure.

Carbon-Coated Superparamagnetic Nanoflowers for Biosensors Based on Lateral Flow Immunoassays

Superparamagnetic iron oxide nanoflowers coated by a black carbon layer (Fe3O4@C) were studied as labels in lateral flow immunoassays. They were synthesized by a one-pot solvothermal route, and they were characterized (size, morphology, chemical composition, and magnetic properties). They consist of several superparamagnetic cores embedded in a carbon coating holding carboxylic groups adequate for bioconjugation. Their multi-core structure is especially efficient for magnetic separation while keeping suitable magnetic properties and appropriate size for immunoassay reporters. Their functionality was tested with a model system based on the biotin-neutravidin interaction. For this, the nanoparticles were conjugated to neutravidin using the carbodiimide chemistry, and the lateral flow immunoassay was carried out with a biotin test line. Quantification was achieved with both an inductive magnetic sensor and a reflectance reader. In order to further investigate the quantifying capacity of the Fe3O4@C nanoflowers, the magnetic lateral flow immunoassay was tested as a detection system for extracellular vesicles (EVs), a novel source of biomarkers with interest for liquid biopsy. A clear correlation between the extracellular vesicle concentration and the signal proved the potential of the nanoflowers as quantifying labels. The limit of detection in a rapid test for EVs was lower than the values reported before for other magnetic nanoparticle labels in the working range 0-3 × 107 EVs/μL. The method showed a reproducibility (RSD) of 3% (n = 3). The lateral flow immunoassay (LFIA) rapid test developed in this work yielded to satisfactory results for EVs quantification by using a precipitation kit and also directly in plasma samples. Besides, these Fe3O4@C nanoparticles are easy to concentrate by means of a magnet, and this feature makes them promising candidates to further reduce the limit of detection.

Sensitive and selective ctDNA detection based on functionalized black phosphorus nanosheets

Circulating tumor DNA (ctDNA) identification is one of the most meaningful approaches towards early cancer diagnosis. However, effective and practical methods for analyzing this emerging class of biomarkers are still lacking. In this work, a biosensor based on nitrophenyl functionalized black phosphorus nanosheets (NP-BPs) is fabricated for sensitive and selective detection of ctDNA. In this work, a nitrophenyl functionalized black phosphorus nanosheets (NP-BPs) biosensor is fabricated for sensitive and selective detection of ctDNA. Due to the successful nitrophenyl functionalization, the NP-BPs biosensor shows higher quenching efficiency and stronger affinity towards single-stranded DNA (ssDNA), as compared with double-stranded DNA (dsDNA). Therefore, the NP-BPs biosensor exhibits 5.4-fold fluorescence enhancement when dye-labelled ssDNA probe forms dsDNA in the presence of its specific ctDNA target. This biosensor exhibits a detection limit of 50 fM and a wide linear detection range of 50 fM-80 pM, provides reliable readout in a short time (15 min). Moreover, the NP-BPs-based biosensor could be applied to discriminate single nucleotide polymorphisms in clinical serum samples. It is envisioned that the NP-BPs-based sensing platform has great potentials in early cancer diagnosis and monitoring cancer progression.

pDNA conjugated with citrate capped silver nanoparticles towards ultrasensitive bio-assay of haemophilus influenza in human biofluids: A novel optical biosensor

A sensitive and specific approach was developed for the determination of Haemophilus influenza using DNA based bio-assay. In this study, citrate capped silver nanoparticle was synthesized and employed for bioconjugation with pDNA toward target sequences detection. In this study, synthesized probe (SH-5'-AAT TTT CCA ACT TTT TCA CCT GCA T-3') of Haemophilus influenza was detected with great sensitivity and selectivity after hybridization with cDNA (5'-ATG CAG GTG AAA AAG TTG GAA AAT T-3'). Regarding to the obtained results, the low limit of quantification (LLOQ) of DNA sample was 1 ZM using 15 μL of probe and 200 μL of Cit/AgNPs. According to ultra-sensitivity of the fabricated optical DNA-based bio-assay, it has potential for bacterial determination both in clinical and environmental specimens. To evaluate the selectivity of developed DNA based biosensor, three mismatch sequences were applied. Finally, the designed genosensor is a significant diagnostic strategy for detection of Haemophilus influenza with great selectivity.

Functionalized Hybridization of 2D Nanomaterials

The discovery of graphene and subsequent verification of its unique properties have aroused great research interest to exploit diversified graphene-analogous 2D nanomaterials with fascinating physicochemical properties. Through either physical or chemical doping, linkage, adsorption, and hybridization with other functional species into or onto them, more novel/improved properties are readily created to extend/expand their functionalities and further achieve great performance. Here, various functionalized hybridizations by using different types of 2D nanomaterials are overviewed systematically with emphasis on their interaction formats (e.g., in-plane or inter plane), synergistic properties, and enhanced applications. As the most intensely investigated 2D materials in the post-graphene era, transition metal dichalcogenide nanosheets are comprehensively investigated through their element doping, physical/chemical functionalization, and nanohybridization. Meanwhile, representative hybrids with more types of nanosheets are also presented to understand their unique surface structures and address the special requirements for better applications. More excitingly, the van der Waals heterostructures of diverse 2D materials are specifically summarized to add more functionality or flexibility into 2D material systems. Finally, the current research status and faced challenges are discussed properly and several perspectives are elaborately given to accelerate the rational fabrication of varied and talented 2D hybrids.

Biosensing and Delivery of Nucleic Acids Involving Selected Well-Known and Rising Star Functional Nanomaterials

In the last fifteen years, the nucleic acid biosensors and delivery area has seen a breakthrough due to the interrelation between the recognition of nucleic acid's high specificity, the great sensitivity of electrochemical and optical transduction and the unprecedented opportunities imparted by nanotechnology. Advances in this area have demonstrated that the assembly of nanoscaled materials allows the performance enhancement, particularly in terms of sensitivity and response time, of functional nucleic acids' biosensing and delivery to a level suitable for the construction of point-of-care diagnostic tools. Consequently, this has propelled detection methods using nanomaterials to the vanguard of the biosensing and delivery research fields. This review overviews the striking advancement in functional nanomaterials' assisted biosensing and delivery of nucleic acids. We highlight the advantages demonstrated by selected well-known and rising star functional nanomaterials (metallic, magnetic and Janus nanomaterials) focusing on the literature produced in the past five years.

Ag and Au nanoparticles/reduced graphene oxide composite materials: Synthesis and application in diagnostics and therapeutics

The exceptional electrical, thermal, optical and mechanical properties have made two dimensional sp² hybridized graphene a material of choice in both academic as well as industrial research. In the last few years, researchers have devoted their efforts towards the development of graphene/polymer, graphene/metal nanoparticle and graphene/ceramic nanocomposites. These materials display excellent mechanical, electrical, thermal, catalytic, magnetic and optical properties which cannot be obtained separately from the individual components. Fascinating physical and chemical properties are displayed by noble metal nanomaterials and thus they represent model building blocks for modifying nanoscale structures for diverse applications extending from catalysis, optics to nanomedicine. Insertion of noble metal (Au, Ag) nanoparticles (NPs) into chemically derived graphene is thus of primary importance to open new avenues for both materials in various fields where the specific properties of each material act synergistically to provide hybrid materials with exceptional performances. This review attempts to summarize the different synthetic procedures for the preparation of Ag and Au NPs/reduced graphene oxide (rGO) composites. The synthesis processes of metal NPs/rGO composites are categorised into in-situ and ex-situ techniques. The in-situ approach consists of simultaneous reduction of metal salts and GO to obtain metal NPs/rGO nanocomposite materials, while in the ex-situ process, the metal NPs of desired size and shape are first synthesized and then transferred onto the GO or rGO matrix. The application of the Ag NPs and Au NPs/rGO composite materials in the area of biomedical (drug delivery and photothermal therapy) and biosensing are the focus of this review article.

A novel nucleic acid based bio-assay toward recognition of Haemophilus influenza using bioconjugation and DNA hybridization method

Haemophilus influenza (H. influenza) is a gram negative coccobacillus pathogenic microorganism. H. influenza produces beta-lactamases, and it is also able to modify its penicillin-binding proteins, so it has gained resistance to the penicillin family of antibiotics. In this work, a novel sensitive approach was established for the monitoring of H. influenza using DNA based bio-assay. For the first time, specific sequence of thiolated probe of Haemophilus influenza (SH-5'-AAT TTT CCA ACT TTT TCA CCT GCA T-3') was immobilized on the surface of gold (Au) electrode. Square wave voltammetry (SWV) was carried out in toluidine blue (TB) solution for DNA hybridization and targeting of cDNA sequence of Haemophilus influenza. Field scanning electron microscope (FE-SEM) was applied to investigation of the electrode morphology and estimate of particle size. In the optimal conditions, the planned strategy could detect target DNA (5'-ATG CAG GTG AAA AAG TTG GAA AAT T-3') down to 1 ZM with a linear range from 1 μM to 1 ZM. Moreover, engineered geno-assay selectively differentiates the complementary sequence from target sequences with one, double and three base mismatch sequences.

Emulsion and miniemulsion techniques in preparation of polymer nanoparticles with versatile characteristics

In recent years, polymer nanoparticles (PNPs) have found their ways into numerous applications extending from electronics to photonics, conducting materials to sensors and medicine to biotechnology. Physical properties and surface morphology of PNPs are the most important parameters that significantly affect on their exploitations and can be controlled through the synthesis process. Emulsion and miniemulsion techniques are among the most efficient and wide-spread methods for preparation of PNPs. The objective of this review is to present and highlight the recent developments in the advanced PNPs with specific properties that are produced through emulsion and miniemulsion processes.

High-Throughput 2D Heteroatom Graphene Bioelectronic Nanosculpture: A Combined Experimental and Theoretical Study

In this study, chemical vapor deposition-synthesized heteroatom graphene (HGr) bioelectronic interfaces have been developed for ultrafast, all-electronic detection and analysis of molecules by driving them through tiny holes-or atompores-in a thin lattice of the graphene sheet, including the efforts toward facilitating enhanced electrocatalytic and mapping electron transport activities. The presence of chlorine, nitrogen, and oxygen in the crystalline graphitic layers (<7) has been confirmed using Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. We report a swift bioelectrocatalytic response to step-by-step additions of the substrate with the achievement of a steady current within a few seconds. The response limit was 2.07 μM with a dynamic range of sensing from 2.07 μM to 2.97 mM. The electronic properties and adsorption energies of hydroquinone and p-benzophenone molecule adsorption on pristine, O-, N-, and Cl-doped graphene nanosheet surfaces were systematically investigated using first-principles calculations. The results revealed that the adsorption capacity was improved upon doping graphene nanosheets with O, N, and Cl atoms. Hence, Cl-doped graphene nanosheets were shown as a promising adsorbent toward hydroquinone and p-benzophenone detection.

Development of Novel Nanocomposites Based on Graphene/Graphene Oxide and Electrochemical Sensor Applications

Background:

Until now, several methods such as spectroscopic methods and chromatographic techniques have been developed for the determination of biomolecules, drug or heavy metals. Nevertheless, the crucial interference problems are present in these methods. Due to these reasons, more sensitive, favorable portability, low-cost, simple and selective sensors based on nanocomposites are needed in terms of health safety. In the development of electrochemical nanosensor, the nanomaterials such as graphene/graphene oxide, carbon and carbon nitride nanotubes are utilized to improve the sensitivity.

Objective:

The nanomaterials such as graphene/graphene oxide, carbon and carbon nitride nanotubes have important advantages such as high surface area, electrical conductivity, thermal and mechanical stability. Hence, we presented the highly selective methods for sensitive sensor applications by molecular imprinting technology in literature. This technology is a polymerization method around target molecule. This method provides the specific cavities to analyte molecule on the polymer surface. Hence, the selective sensor is easily created for biomedical and other applications. Novel electrochemical sensors based on nanocomposite whose surface is coated with Molecular Imprinting Polymer (MIP) are developed and then applied to the selective and sensitive detection in this study. Until now, we have presented several reports about nanocomposite based sensor with MIP.

DNA conformational polymorphism for biosensing applications

In this mini review, we will briefly introduce the rapid development of DNA conformational polymorphism in biosensing field, including canonical DNA duplex, triplex, quadruplex, DNA origami, as well as more functionalized DNAs (aptamer, DNAzyme etc.). Various DNA structures are adopted to play important roles in sensor construction, through working as recognition receptor, signal reporter or linking staple for signal motifs, etc. We will mainly summarize their recent developments in DNA-based electrochemical and fluorescent sensors. For the electrochemical sensors, several types will be included, e.g. the amperometric, electrochemical impedance, electrochemiluminescence, as well as field-effect transistor sensors. For the fluorescent sensors, DNA is usually modified with fluorescent molecules or novel nanomaterials as report probes, excepting its core recognition function. Finally, general conclusion and future perspectives will be discussed for further developments.