Graphene-based aptasensors: from molecule-interface interactions to sensor design and biomedical diagnostics

Bio(sensors) based on molecularly imprinted polymers and silica materials used for food safety and biomedical analysis: Recent trends and future prospects

In recent decades, analytical techniques have increasingly focused on the precise quantification. Achieving this goal has been accomplished with conventional analytical approaches that typically require extensive pretreatment methods, significant reagent usage, and expensive instruments. The need for rapid, simple, and highly selective identification platforms has become increasingly pronounced. Molecularly imprinted polymer (MIP) has emerged as a promising avenue for developing advanced sensors that can potentially surpass the limitations of conventional detection methods. In recent years, the application of MIP-silica materials-based sensors has garnered significant attention owing to their distinctive characteristics. These types of probes hold a distinct advantage in their remarkable stability and durability, all of which provide a suitable sensing platform in severe environments. Moreover, the substrate composed of silica materials offers a vast surface area for binding, thereby facilitating the efficient detection of even minuscule concentrations of targets. As a result, sensors based on MIP-silica materials have the potential to be widely applied in various industries, including medical diagnosis, and food safety. In the present review, we have conducted an in-depth analysis of the latest research developments in the field of MIPs-silica materials based sensors, with a focus on succinctly summarizing and elucidating the most crucial findings. This is the first comprehensive review of integration MIPs with silica materials in electrochemical (EC) and optical probes for biomedical analysis and food safety.

Mercury (II) sensing using a simple turn-on fluorescent graphene oxide based aptasensor in serum and water samples

A simple, highly sensitive, and selective fluorometric aptasensing platform based on aptamer and graphene oxide (GO) is proposed for the determination of mercury (II) ion (Hg2+). In the designed assay, two aptamer probes, a carboxy-fluorescein (FAM) labeled aptamer (aptamer A) and its complementary (aptamer B) with partial complement containing several mismatches and GO as the quencher were used. In the absence of Hg2+, both A and B aptamers were adsorbed on the surface of GO by π-π-stacking, leading to fluorescence quenching of FAM due to fluorescence resonance energy transfer (FRET). Upon exposure to Hg2+, the A and B aptamer strands bind Hg2+ and form T-Hg2+-T complexes, leading to the formation of a stable double-stranded aptamer. The double-stranded aptamer is detached from the GO surface, resulting in the recovery of FAM fluorescence. The fluorescence intensity (FI) of the developed sensor was correlated with the Hg2+ concentration under optimized experimental conditions in two wide linear ranges, even in the presence of 10 divalent cations as interferences. The linear ranges were obtained from 200.0 to 900.0 fM and 5.0 to 33.0 pM, a limit of detection (LOD) of 106.0 fM, and a limit of quantification (LOQ) of 321.3 fM. The concentration of Hg2+ was determined in five real samples containing three water and two serum samples, using spiking and standard addition methods and the results were compared with the spiked amounts and atomic absorption (AAS) as standard method respectively, with acceptable recoveries. Furthermore, in the standard addition method, to overcome the effects of matrix influence of real samples in quantitative predictions, the excitation-emission matrix (EEM) data for samples was simultaneously analyzed by multivariate curve resolution with alternating least squares (MCR-ALS) as a second-order standard addition method (SOSAM).

Interplay of graphene-DNA interactions: Unveiling sensing potential of graphene materials

Graphene-based materials and DNA probes/nanostructures have emerged as building blocks for constructing powerful biosensors. Graphene-based materials possess exceptional properties, including two-dimensional atomically flat basal planes for biomolecule binding. DNA probes serve as excellent selective probes, exhibiting specific recognition capabilities toward diverse target analytes. Meanwhile, DNA nanostructures function as placement scaffolds, enabling the precise organization of molecular species at nanoscale and the positioning of complex biomolecular assays. The interplay of DNA probes/nanostructures and graphene-based materials has fostered the creation of intricate hybrid materials with user-defined architectures. This advancement has resulted in significant progress in developing novel biosensors for detecting DNA, RNA, small molecules, and proteins, as well as for DNA sequencing. Consequently, a profound understanding of the interactions between DNA and graphene-based materials is key to developing these biological devices. In this review, we systematically discussed the current comprehension of the interaction between DNA probes and graphene-based materials, and elucidated the latest advancements in DNA probe-graphene-based biosensors. Additionally, we concisely summarized recent research endeavors involving the deposition of DNA nanostructures on graphene-based materials and explored imminent biosensing applications by seamlessly integrating DNA nanostructures with graphene-based materials. Finally, we delineated the primary challenges and provided prospective insights into this rapidly developing field. We envision that this review will aid researchers in understanding the interactions between DNA and graphene-based materials, gaining deeper insight into the biosensing mechanisms of DNA-graphene-based biosensors, and designing novel biosensors for desired applications.

Colorimetric Sensors for Chemical and Biological Sensing Applications

Colorimetric sensors have been widely used to detect numerous analytes due to their cost-effectiveness, high sensitivity and specificity, and clear visibility, even with the naked eye. In recent years, the emergence of advanced nanomaterials has greatly improved the development of colorimetric sensors. This review focuses on the recent (from the years 2015 to 2022) advances in the design, fabrication, and applications of colorimetric sensors. First, the classification and sensing mechanisms of colorimetric sensors are briefly described, and the design of colorimetric sensors based on several typical nanomaterials, including graphene and its derivatives, metal and metal oxide nanoparticles, DNA nanomaterials, quantum dots, and some other materials are discussed. Then the applications, especially for the detection of metallic and non-metallic ions, proteins, small molecules, gas, virus and bacteria, and DNA/RNA are summarized. Finally, the remaining challenges and future trends in the development of colorimetric sensors are also discussed.

Recent advances of graphene-biomacromolecule nanocomposites in medical applications

In recent years, graphene-based composites have received increasing attention due to their high biocompatibility, large specific surface area, high electrical conductivity and unique mechanical properties. The combination of biomacromolecules and graphene provides a promising route for the preparation of novel graphene-based nanocomposites. Novel graphene-based nanocomposites with unique functions could be applied to medicine, biology, biosensors, environmental science, energy storage and other fields. Graphene-biomacromolecule nanocomposites have excellent biocompatibility, outstanding biofunctionality and low cytotoxicity, and have more advantages and development prospects than other traditional graphene-based materials in biological and biomedical fields. In this work, we summarize the research on the covalent and non-covalent interactions between different biomacromolecules (peptides, DNA/RNA, proteins and enzymes) and graphene, as well as the synthesis methods of novel functionalized graphene-biomacromolecule composites in recent years. We mainly introduce the recent advances (last 5 years) of graphene-biomacromolecule nanocomposites in medical applications, such as medical detection and disease treatment. We hope that this review will help readers to understand the methods and mechanisms of biomolecules modifying the surface of graphene, as well as the synthesis and application of graphene-based nanocomposites, which will promote the future developments of graphene-biomolecule composites in biomedicine, tissue engineering, materials engineering, and so on.

Progress and challenges of graphene and its congeners for biomedical applications

Nanomaterials by virtue of their small size and enhanced surface area, present unique physicochemical properties that enjoy widespread applications in bioengineering, biomedicine, biotechnology, disease diagnosis, and therapy. In recent years, graphene and its derivatives have attracted a great deal of attention in various applications, including photovoltaics, electronics, energy storage, catalysis, sensing, and biotechnology owing to their exceptional structural, optical, thermal, mechanical, and electrical. Graphene is a two-dimensional sheet of sp2 hybridized carbon atoms of atomic thickness, which are arranged in a honeycomb crystal lattice structure. Graphene derivatives are graphene oxide (GO) and reduced graphene oxide (rGO), which are highly oxidized and less oxidized forms of graphene, respectively. Another form of graphene is graphene quantum dots (GQDs), having a size of less than 20 nm. Contemporary graphene research focuses on using graphene nanomaterials for biomedical purposes as they have a large surface area for loading biomolecules and medicine and offer the potential for the conjugation of fluorescent dyes or quantum dots for bioimaging. The present review begins with the synthesis, purification, structure, and properties of graphene nanomaterials. Then, we focussed on the biomedical application of graphene nanomaterials with special emphasis on drug delivery, bioimaging, biosensing, tissue engineering, gene delivery, and chemotherapy. The implications of graphene nanomaterials on human health and the environment have also been summarized due to their exposure to their biomedical applications. This review is anticipated to offer useful existing understanding and inspire new concepts to advance secure and effective graphene nanomaterials-based biomedical devices.

An overview of advancement in aptasensors for influenza detection

INTRODUCTION

The platforms for early identification of infectious diseases such as influenza has seen a surge in recent years as delayed diagnosis of such infections can lead to dreadful effects causing large numbers of deaths. The time taken in detection of an infectious disease may vary from a few days to a few weeks depending upon the choice of the techniques. So, there is an urgent need for advanced methodologies for early diagnosis of the influenza.

AREAS COVERED

The emergence of "Aptasensor" synergistically with biosensors for diagnosis has opened a new era for sensitive, selective and early detection approaches. This review described various conventional as well as advanced methods based on artificial immunogenic nucleotide sequences complementing a part of the virus, i.e., aptamers based aptasensors for influenza diagnosis and the challenges faced in their commercialization.

EXPERT OPINION

Although numerous traditional methods are available for influenza detection but mostly associated with low sensitivity, specificity, high cost, trained personnel, and animals required for virus culture/ antibody raising as the major drawbacks. Aptamers can be manufactured invitro as 'chemical antibodies' at commercial level, no animal required. Following these advantages, aptamers can pave the way for an efficient diagnostic technique as compared to other existing conventional methods..

Fluorescent Biosensors for the Detection of Viruses Using Graphene and Two-Dimensional Carbon Nanomaterials

Two-dimensional carbon nanomaterials have been commonly employed in the field of biosensors to improve their sensitivity/limits of detection and shorten the analysis time. These nanomaterials act as efficient transducers because of their unique characteristics, such as high surface area and optical, electrical, and magnetic properties, which in turn have been exploited to create simple, quick, and low-cost biosensing platforms. In this review, graphene and two-dimensional carbon material-based fluorescent biosensors are covered between 2010 and 2021, for the detection of different human viruses. This review specifically focuses on the new developments in graphene and two-dimensional carbon nanomaterials for fluorescent biosensing based on the Förster resonance energy transfer (FRET) mechanism. The high-efficiency quenching capability of graphene via the FRET mechanism enhances the fluorescent-based biosensors. The review provides a comprehensive reference for the different types of carbon nanomaterials employed for the detection of viruses such as Rotavirus, Ebola virus, Influenza virus H3N2, HIV, Hepatitis C virus (HCV), and Hepatitis B virus (HBV). This review covers the various multiplexing detection technologies as a new direction in the development of biosensing platforms for virus detection. At the end of the review, the different challenges in the use of fluorescent biosensors, as well as some insights into how to overcome them, are highlighted.

Green syntheses of graphene and its applications in internet of things (IoT)-a status review

Internet of Things (IoT) is a trending technological field that converts any physical object into a communicable smarter one by converging the physical world with the digital world. This innovative technology connects the device to the internet and provides a platform to collect real-time data, cloud storage, and analyze the collected data to trigger smart actions from a remote location via remote notifications, etc. Because of its wide-ranging applications, this technology can be integrated into almost all the industries. Another trending field with tremendous opportunities is Nanotechnology, which provides many benefits in several areas of life, and helps to improve many technological and industrial sectors. So, integration of IoT and Nanotechnology can bring about the very important field of Internet of Nanothings (IoNT), which can re-shape the communication industry. For that, data (collected from trillions of nanosensors, connected to billions of devices) would be the 'ultimate truth', which could be generated from highly efficient nanosensors, fabricated from various novel nanomaterials, one of which is graphene, the so-called 'wonder material' of the 21st century. Therefore, graphene-assisted IoT/IoNT platforms may revolutionize the communication technologies around the globe. In this article, a status review of the smart applications of graphene in the IoT sector is presented. Firstly, various green synthesis of graphene for sustainable development is elucidated, followed by its applications in various nanosensors, detectors, actuators, memory, and nano-communication devices. Also, the future market prospects are discussed to converge various emerging concepts like machine learning, fog/edge computing, artificial intelligence, big data, and blockchain, with the graphene-assisted IoT field to bring about the concept of 'all-round connectivity in every sphere possible'.

Recent trends in nanomaterial-based signal amplification in electrochemical aptasensors

Ultrasensitive biosensors have become a necessity in the world of scientific research, and several signal enhancement strategies have been employed to attain exceptionally low detection limits. Nanotechnology turns out to be a strong contender for signal amplification, as they can be employed as platform modifiers, catalysts, carriers or labels. Here, we have described the most recent advancements in the utilization of nanomaterials as signal amplification components in aptamer-based electrochemical biosensors. We have briefly reviewed the methods that utilized nanomaterials, namely gold and carbon, as well as nanocomposites such as: graphene, carbon nanotubes, quantum dots, and metal-organic frameworks.

Nanomaterial application in bio/sensors for the detection of infectious diseases

Infectious diseases are a potential risk for public health and the global economy. Fast and accurate detection of the pathogens that cause these infections is important to avoid the transmission of the diseases. Conventional methods for the detection of these microorganisms are time-consuming, costly, and not applicable for on-site monitoring. Biosensors can provide a fast, reliable, and point of care diagnostic. Nanomaterials, due to their outstanding electrical, chemical, and optical features, have become key players in the area of biosensors. This review will cover different nanomaterials that employed in electrochemical, optical, and instrumental biosensors for infectious disease diagnosis and how these contributed to enhancing the sensitivity and rapidity of the various sensing platforms. Examples of nanomaterial synthesis methods as well as a comprehensive description of their properties are explained. Moreover, when available, comparative data, in the presence and absence of the nanomaterials, have been reported to further highlight how the usage of nanomaterials enhances the performances of the sensor.

Computational Insights into Molecular Adsorption Characteristics of Methylated DNA on Graphene Oxide for Multicancer Early Detection

DNA methylation is an epigenetic modification involving the transfer of a methyl group to cytosine residues of a DNA molecule. Altered DNA methylation of certain genes is associated with several diseases including cancer. Nanomaterials, such as graphene oxide (GO), offer great potential as sensing elements for methylated DNA (mDNA) detection due to their distinct properties. Understanding molecular interactions between mDNA and GO can make provision for developing a universal cancer screening test. Molecular dynamics (MD) simulation and density functional theory (DFT) calculation have been employed for investigating their detailed macro- and microscale interactions. Based upon the MD simulation, different adsorption levels of methylated and unmethylated DNAs on GO were represented by a contacting surface area (CSA), which depends on surrounding conditions (in water or a MgCl₂ solution). In water, the CSAs of the methylated and unmethylated single-stranded DNA (ssDNA) were ≈13 and ≈5 nm², respectively, representing more preferable adsorption on GO for the methylated ssDNA. In the presence of divalent ions (Mg²⁺), the CSAs of both methylated and unmethylated DNA molecules were ≈8 nm², suggesting that there was no significant difference in adsorption in a saline solution. To reveal the electrical property of GO covered by either methylated or unmethylated DNA, its electronic structure was investigated by the DFT calculation. The energy gaps of pristine graphene (pG) and GO adsorbed by 5-methylcytosine (5mC) were 1.6 and 12.9 meV, respectively, while cytosine adsorption resulted in lower energy gaps (1.2 meV for pG and 9.5 meV for GO). When comparing methylated DNA-covered GO with that covered with unmethylated DNA, remarkable differences in electrical conductivity, which were caused by the electronic structure of GO, were observed. These findings will provide a new route for an efficient detection method of DNA methylation, which can further be used to develop a universal cancer test.

Molecular patterns of oligopeptide hydrocarbons on graphite

Graphitic materials including graphene, carbon nanotubes and fullerenes, are promising for use in nanotechnology and biomedicine. Non-covalent functionalization by peptides and other organic molecules allows changing the properties of graphitic surfaces in a controlled manner and represents a big potential for fundamental research and applications. Recently described oligopeptide-hydrocarbon derivative N,N'-(decane-1,10-diyl)bis(tetraglycineamide) (GM) is highly prospective for the development of graphitic interfaces in biosensor application as well as in structural biology for improving the quality of high-resolution atomic force microscopy (AFM) visualization of individual biomacromolecules. However, molecular organization of GM on graphitic surfaces is still unknown. In this work, the molecular model of GM at the water/highly oriented pyrolytic graphite (HOPG) interface has been developed basing on the high-resolution AFM and full-atom molecular modeling data. This model explains two periodicities observed in AFM images by GM self-assembly on a HOPG surface with formation of the stacks with the lateral shifts. The obtained results reveal the particular patterns and dynamics of GM molecules adsorbed on graphite and unravel the puzzle of peptide self-assembly on graphitic surfaces.

Dual sensitive and rapid detection of glycated human serum albumin using a versatile lead/graphene nanocomposite probe as a fluorescence-electrochemical aptasensor

Monitoring of glycated human serum albumin (GHSA) as a glycemic marker for screening and monitoring of diabetes mellitus is widely practiced for patients with conditions that affect red blood cells. In this study, a complex comprising Pb ions adsorbed on graphene oxide (GO-Pb) was fabricated and utilized as a versatile probe in a fluorescence-electrochemical aptasensor for GHSA quantification. To simplify the aptasensor, the GO-Pb complex probe was prepared via an ion adsorption process. After modification with a fluorophore-labeled aptamer, the GO-Pb complex served as an excellent energy acceptor in fluorescence-based analysis, as well as generating a high current in the electrochemical transducer. Additionally, the proposed platform can detect GHSA via the dual technique from a single sample, allowing for precise and accurate results. Under optimal conditions, the fluorescence-electrochemical aptasensor exhibited a linear relationship with GHSA concentrations from 0.001 to 80 μg mL^-1 and from 0.005 to 10 μg mL^-1 for fluorescence and electrochemical detection, respectively. The corresponding detection limits were 8.80 ng mL^-1 and 0.77 ng mL^-1, respectively. The proposed aptasensor additionally displayed good selectivity and excellent stability. Moreover, its successful application in the analysis of clinical samples further demonstrated its utility. Therefore, the proposed platform has significant potential as a novel, facile, highly responsive, and low-cost monitoring method for the development of diabetes mellitus diagnostic devices intended for a clinical setting.

Graphene-Based FRET Aptasensors

Graphene-based FRET aptasensors can be realized only by unique combinations of aptamer that can be freely functionalized by chemical modification, and graphene/graphene oxide that works as an excellent fluorescence acceptor at the same time as aptamer adsorbates. This review describes the principles of the sensor, several applications to microchannel devices, improvement of the sensing performance by molecular design of the aptamer and remarks on future prospects based on an introduction of recent works and achievements, including the author's paper. The sensor employs DNA modified with graphene/graphene oxide at the terminal as the molecular probe. This system is supported by the excellent property of DNA that does not lose the molecular recognition ability even due to a chemical modification at the terminal. I hope that this review will be useful for developing research on higher performance of graphene aptasensors in the future.

Recent Developments in Aptasensors for Diagnostic Applications

Aptamers are exciting smart molecular probes for specific recognition of disease biomarkers. A number of strategies have been developed to convert target-aptamer binding into physically detectable signals. Since the aptamer sequence was first discovered, a large variety of aptamer-based biosensors have been developed, with considerable attention paid to their potential applications in clinical diagnostics. So far, a variety of techniques in combination with a wide range of functional nanomaterials have been used for the design of aptasensors to further improve the sensitivity and detection limit of target determination. In this paper, the advantages of aptamers over traditional antibodies as the molecular recognition components in biosensors for high-throughput screening target molecules are highlighted. Aptamer-target pairing configurations are predominantly single- or dual-site binding; the design of recognition modes of each aptamer-target pairing configuration is described. Furthermore, signal transduction strategies including optical, electrical, mechanical, and mass-sensitive modes are clearly explained together with examples. Finally, we summarize the recent progress in the development of aptamer-based biosensors for clinical diagnosis, including detection of cancer and disease biomarkers and in vivo molecular imaging. We then conclude with a discussion on the advanced development and challenges of aptasensors.

Exploration of Graphene Defect Reactivity toward a Hydrogen Radical Utilizing a Preactivated Circumcoronene Model

A preexisting chemisorbed defect is well-known to increase the reactivity of graphene which is normally chemically inert. Specifically, the presence of chemisorbed hydrogen atoms forming an sp³-hybridized C-H bond is known to increase the reactivity of neighboring carbon atoms toward additional hydrogenation with wide-ranging applications from materials science to astrochemistry. In this work, static DFT and DFT-based direct dynamics simulations are used to characterize the reactivity of a graphene sheet around an existing C-H bond defect. The spin density landscape shows how to guide subsequent H atom additions, always bonding most strongly to the carbon atom with greatest spin density. Molecular dynamics of an impinging H atom under thermal conditions with defect graphene was used to determine the statistics of probable reactions. The most frequent outcome is inelastic scattering (48%) and then Eley-Rideal (ER) abstraction of the chemisorbed H atom as vibrationally hot H₂ (40%), while the least likely, but probably most interesting, result is formation of a novel C-H bond (12%). The C-H bonds always form in the β sublattice. The carbon atom in the para position shows to be most reactive toward the incoming H atom, followed by the ortho carbon, in agreement with the spin density computed in the static calculations. Globally, the graphene energy surface is repulsive, but the defects create local channels into this energy surface through which reactants can move locally through and react with the activated surface without a barrier.

Recent Advances in Aptamer Sensors

Recently, aptamers have attracted attention in the biosensing field as signal recognition elements because of their high binding affinity toward specific targets such as proteins, cells, small molecules, and even metal ions, antibodies for which are difficult to obtain. Aptamers are single oligonucleotides generated by in vitro selection mechanisms via the systematic evolution of ligand exponential enrichment (SELEX) process. In addition to their high binding affinity, aptamers can be easily functionalized and engineered, providing several signaling modes such as colorimetric, fluorometric, and electrochemical, in what are known as aptasensors. In this review, recent advances in aptasensors as powerful biosensor probes that could be used in different fields, including environmental monitoring, clinical diagnosis, and drug monitoring, are described. Advances in aptamer-based colorimetric, fluorometric, and electrochemical aptasensing with their advantages and disadvantages are summarized and critically discussed. Additionally, future prospects are pointed out to facilitate the development of aptasensor technology for different targets.

Recent Advance in the Fabrication of 2D and 3D Metal Carbides-Based Nanomaterials for Energy and Environmental Applications

Two-dimensional (2D) nanomaterials have attracted increased interest and exhibited extended applications from nanotechnology to materials science, biomedicine, tissue engineering, as well as energy storage and environmental science. With the development of the synthesis and fabrication of 2D materials, a new family of 2D materials, metal carbides (MCs), revealed promising applications in recent years, and have been utilized for the fabrication of various functional 2D and three-dimensional (3D) nanomaterials for energy and environmental applications, ascribing to the unique physical and chemical properties of MCs. In this review, we present recent advance in the synthesis, fabrication, and applications of 2D and 3D MC-based nanomaterials. For this aim, we first summarize typical synthesis methods of MCs, and then demonstrate the progress on the fabrication of 2D and 3D MC-based nanomaterials. To the end, the applications of MC-based 2D and 3D materials for chemical batteries, supercapacitors, water splitting, photodegradation, removal of heavy metals, and electromagnetic shielding are introduced and discussed. This work provides useful information on the preparation, hybridization, structural tailoring, and applications of MC-based materials, and is expected to inspire the design and fabrication of novel and functional MXene materials with improved performance.

Graphene quantum dots as nanosensor for rapid and label-free dual detection of Cu2+ and tiopronin by means of fluorescence “on–off–on” switching: mechanism and molecular logic gate

(A) Schematic diagram of the interaction and dual detection of Cu2+ and MPG by means of fluorescence “on–off–on” switching. (B) Molecular logic gate and truth table constructed based on Cu2+ and MPG as inputs and emission signal as output.

Target specific aptamer-induced self-assembly of fluorescent graphene quantum dots on palladium nanoparticles for sensitive detection of tetracycline in raw milk

The excessive use of tetracyclines (TCs), a bacteriostaticantibiotic, in food products, has led to the accumulation of TCs residues in the human body, affecting human health seriously. Therefore, the development of a highly sensitive method to detect TCs in food is of utmost importance. This study reports a novel sensing strategy using aptamer-induced fluorescence fluctuation of graphene quantum dots (GQDs) and palladium nanoparticles (Pd NPs) for the rapid and label-free detection of tetracycline with a limit of detection of 45 ng.mL^-1. A novel single-step synthesis of positively charged Pd NPs and one-step green synthesis of GQDs directly from graphite has been developed. The proposed strategy provides an efficient way to detect low traces of TCs and a new technique for the development of aptamer-based sensors.

Aptamer-Based Colorimetric Probe for trans-Zeatin Detection Using Unmodified Gold Nanoparticle

Trans-Zeatin is the major active phytohormone in immature corn kernels. Herein, a highly sensitive, good selective and simple aptamer-based colorimetric method for the detection of trans-zeatin was constructed. The selected aptamer sequence binds with trans-zeatin and induces a duplex-to-aptamer structure switching. The gold nanoparticles (AuNPs) solution is stable with high-concentration salt, which is protected by red complementary DNA. In the absence of trans-zeatin, the color of AuNPs changed from red to blue because aptamer DNA and complementary DNA form double-stranded DNA. Thus, the ratio of absorbance intensities (A522/A650) of AuNPs is changed with the concentration of trans-zeatin. The color change could be observed by the naked eye. The linear range of this method covers a large variation of trans-zeatin concentration from 0.05 to 0.75 μM. The detection limit is 0.037 μM. Moreover, this method was applied successfully to detect trans-zeatin in real plant samples.

Disposable and Low-Cost Colorimetric Sensors for Environmental Analysis

Environmental contamination affects human health and reduces the quality of life. Therefore, the monitoring of water and air quality is important, ensuring that all areas are acquiescent with the current legislation. Colorimetric sensors deliver quick, naked-eye detection, low-cost, and adequate determination of environmental analytes. In particular, disposable sensors are cheap and easy-to-use devices for single-shot measurements. Due to increasing requests for in situ analysis or resource-limited zones, disposable sensors’ development has increased. This review provides a brief insight into low-cost and disposable colorimetric sensors currently used for environmental analysis. The advantages and disadvantages of different colorimetric devices for environmental analysis are discussed.

Graphene-family materials in electrochemical aptasensors

The study of graphene-based carbon nanocomposites has remarkably increased in recent years. Functionalized graphene-based nanostructures, including graphene oxide and reduced graphene oxide, have great potential as new innovative electrode materials in the fabrication of novel electrochemical sensors. Electrochemical sensors based on aptamers attracted great attention because of their high sensitivity and selectivity, and simple instrumentation, as well as low production cost. Aptamers as a potent alternative to antibodies are functional nucleic acids with a high tendency to specific analytes. Electrochemical aptasensors show specific recognition ability for a wide range of analytes. Although aptamers are selected in vitro in contrast to antibodies, they are interesting due to advantages like high stability, easy chemical modifications, and the potential to be employed in nanostructured device fabrication or electrochemical sensing devices. Recently, new nanomaterials have shown a significant impact on the production of electrochemical sensors with high efficiency and performance. This review aims to give an outline of electrochemical aptasensors based on the graphene family materials and discuss the detection mechanism in this type of aptasensors. The present review summarizes some of the recent achievements in graphene-based aptasensors and includes their recent electroanalytical applications. Graphical Abstract Graphical Abstract.

Functional Nucleic Acid Nanomaterials: Development, Properties, and Applications

Functional nucleic acid (FNA) nanotechnology is an interdisciplinary field between nucleic acid biochemistry and nanotechnology that focuses on the study of interactions between FNAs and nanomaterials and explores the particular advantages and applications of FNA nanomaterials. With the goal of building the next-generation biomaterials that combine the advantages of FNAs and nanomaterials, the interactions between FNAs and nanomaterials as well as FNA self-assembly technologies have established themselves as hot research areas, where the target recognition, response, and self-assembly ability, combined with the plasmon properties, stability, stimuli-response, and delivery potential of various nanomaterials can give rise to a variety of novel fascinating applications. As research on the structural and functional group features of FNAs and nanomaterials rapidly develops, many laboratories have reported numerous methods to construct FNA nanomaterials. In this Review, we first introduce some widely used FNAs and nanomaterials along with their classification, structure, and application features. Then we discuss the most successful methods employing FNAs and nanomaterials as elements for creating advanced FNA nanomaterials. Finally, we review the extensive applications of FNA nanomaterials in bioimaging, biosensing, biomedicine, and other important fields, with their own advantages and drawbacks, and provide our perspective about the issues and developing trends in FNA nanotechnology.

Graphene impregnated electrospun nanofiber sensing materials: a comprehensive overview on bridging laboratory set-up to industry

Owing to the unique structural characteristics as well as outstanding physio-chemical and electrical properties, graphene enables significant enhancement with the performance of electrospun nanofibers, leading to the generation of promising applications in electrospun-mediated sensor technologies. Electrospinning is a simple, cost-effective, and versatile technique relying on electrostatic repulsion between the surface charges to continuously synthesize various scalable assemblies from a wide array of raw materials with diameters down to few nanometers. Recently, electrospun nanocomposites have emerged as promising substrates with a great potential for constructing nanoscale biosensors due to their exceptional functional characteristics such as complex pore structures, high surface area, high catalytic and electron transfer, controllable surface conformation and modification, superior electric conductivity and unique mat structure. This review comprehends graphene-based nanomaterials (GNMs) (graphene, graphene oxide (GO), reduced GO and graphene quantum dots) impregnated electrospun polymer composites for the electro-device developments, which bridges the laboratory set-up to the industry. Different techniques in the base polymers (pre-processing methods) and surface modification methods (post-processing methods) to impregnate GNMs within electrospun polymer nanofibers are critically discussed. The performance and the usage as the electrochemical biosensors for the detection of wide range analytes are further elaborated. This overview catches a great interest and inspires various new opportunities across a wide range of disciplines and designs of miniaturized point-of-care devices.

Plasmonic Metasensors Based on 2D Hybrid Atomically Thin Perovskite Nanomaterials

In this work, we have designed highly sensitive plasmonic metasensors based on atomically thin perovskite nanomaterials with a detection limit up to 10⁻¹⁰ refractive index units (RIU) for the target sample solutions. More importantly, we have improved phase singularity detection with the Goos–Hänchen (GH) effect. The GH shift is known to be closely related to optical phase signal changes; it is much more sensitive and sharp than the phase signal in the plasmonic condition, while the experimental measurement setup is much more compact than that of the commonly used interferometer scheme to exact the phase signals. Here, we have demonstrated that plasmonic sensitivity can reach a record-high value of 1.2862 × 10⁹ µm/RIU with the optimum configurations for the plasmonic metasensors. The phase singularity-induced GH shift is more than three orders of magnitude larger than those achievable in other metamaterial schemes, including Ag/TiO₂ hyperbolic multilayer metamaterials (HMMs), metal–insulator–metal (MIM) multilayer waveguides with plasmon-induced transparency (PIT), and metasurface devices with a large phase gradient. GH sensitivity has been improved by more than 10⁶ times with the atomically thin perovskite metasurfaces (1.2862 × 10⁹ µm/RIU) than those without (918.9167 µm/RIU). The atomically thin perovskite nanomaterials with high absorption rates enable precise tuning of the depth of the plasmonic resonance dip. As such, one can optimize the structure to reach near zero-reflection at the resonance angle and the associated sharp phase singularity, which leads to a strongly enhanced GH lateral shift at the sensor interface. By integrating the 2D perovskite nanolayer into a metasurface structure, a strong localized electric field enhancement can be realized and GH sensitivity was further improved to 1.5458 × 10⁹ µm/RIU. We believe that this enhanced electric field together with the significantly improved GH shift would enable single molecular or even submolecular detection for hard-to-identify chemical and biological markers, including single nucleotide mismatch in the DNA sequence, toxic heavy metal ions, and tumor necrosis factor-α (TNFα).

Applications of Two-Dimensional Nanomaterials in Breast Cancer Theranostics

Breast cancer is the leading cause of cancer-related mortality among women. Early stage diagnosis and treatment of this cancer are crucial to patients' survival. In addition, it is important to avoid severe side effects during the process of conventional treatments (surgery, chemotherapy, hormonal therapy, and targeted therapy) and increase the patients' quality of life. Over the past decade, nanomaterials of all kinds have shown excellent prospects in different aspects of oncology. Among them, two-dimensional (2D) nanomaterials are unique due to their physical and chemical properties. The functional variability of 2D nanomaterials stems from their large specific surface area as well as the diversity of composition, electronic configurations, interlayer forces, surface functionalities, and charges. In this review, the current status of 2D nanomaterials in breast cancer diagnosis and therapy is reviewed. In this respect, sensing of the tumor biomarkers, imaging, therapy, and theranostics are discussed. The ever-growing 2D nanomaterials are building blocks for the development of a myriad of nanotheranostics. Accordingly, there is the possibility to explore yet novel properties, biological effects, and oncological applications.

The Growing Interest in Development of Innovative Optical Aptasensors for the Detection of Antimicrobial Residues in Food Products

The presence of antimicrobial residues in food-producing animals can lead to harmful effects on the consumer (e.g., allergies, antimicrobial resistance, toxicological effects) and cause issues in food transformation (i.e., cheese, yogurts production). Therefore, to control antimicrobial residues in food products of animal origin, screening methods are of utmost importance. Microbiological and immunological methods (e.g., ELISA, dipsticks) are conventional screening methods. Biosensors are an innovative solution for the development of more performant screening methods. Among the different kinds of biosensing elements (e.g., antibodies, aptamers, molecularly imprinted polymers (MIP), enzymes), aptamers for targeting antimicrobial residues are in continuous development since 2000. Therefore, this review has highlighted recent advances in the development of aptasensors, which present multiple advantages over immunosensors. Most of the aptasensors described in the literature for the detection of antimicrobial residues in animal-derived food products are either optical or electrochemical sensors. In this review, I have focused on optical aptasensors and showed how nanotechnologies (nanomaterials, micro/nanofluidics, and signal amplification techniques) largely contribute to the improvement of their performance (sensitivity, specificity, miniaturization, portability). Finally, I have explored different techniques to develop multiplex screening methods. Multiplex screening methods are necessary for the wide spectrum detection of antimicrobials authorized for animal treatment (i.e., having maximum residue limits).

Tin disulfide nanorod-graphene-β-cyclodextrin nanocomposites for sensing dopamine in rat brains and human blood serum

In the present work describes a facile synthesis of tin disulfide (SnS₂) nanorods decorated graphene-β-cyclodextrin (SnS₂/GR-β-CD) nanocomposite for robust and novel dopamine (DA) electrochemical biosensor applications. The DA biosensor was fabricated using the glassy carbon electrode (GCE) modified with SnS₂/GR-β-CD nanocomposite. The sonochemical and hydrothermal methods have been used for the synthesis of SnS₂/GR-β-CD. Different physicochemical methods were used to confirm the formation of the GR-β-CD, SnS₂, and SnS₂/GR-β-CD nanocomposite. The cyclicvoltammetric cathodic current response of DA was 5 folds higher than those observed at bare, β-CD, SnS₂-β-CD, and GR-β-CD modified GCEs. Under optimised conditions, the biosensor's DPV response current is linear to DA from the concentration of 0.01-150.76 μM. The detection limit of the biosensor was 4 nM. The SnS₂/GR-β-CD biosensor shows an excellent selectivity towards DA in the presence of common interfering species, including ascorbic acid and uric acid. Also, the as-prepared nanocomposite-modified electrode exhibited satisfactory long-term stability, sensitivity (2.49 μAμM^-1 cm^-2) along with reusability for detection of DA. The fabricated SnS₂/GR-β-CD biosensor was successfully used for the detection of DA in the rat brain and human blood serum samples.

Graphene-Based Biosensors for Detection of Biomarkers

The development of biosensors with high sensitivity and low-detection limits provides a new direction for medical and personal care. Graphene and graphene derivatives have been used to prepare various types of biosensors due to their excellent sensing performance (e.g., high specific surface area, extraordinary electronic properties, electron transport capabilities and ultrahigh flexibility). This perspective review focuses on graphene-based biosensors for quantitative detection of cancer-related biomarkers such as DNA, miRNA, small molecules and proteins by integrating with different signal outputting approaches including fluorescent, electrochemistry, surface plasmon resonance, surface enhanced Raman scattering, etc. The article also discussed their challenges and potential solutions along with future prospects.

RNase H amplified RNA probe and graphene oxide system for highly sensitive detection of (CAG)n DNA repeat sequences

Huntington's disease is a chronic progressive neurodegeneration which is caused by CAG repeat sequences expanding in the huntingtin gene. There is currently no disease-modifying treatment for the disease, and its progression can only be slowed down before the onset of symptoms. A novel fluorescent platform which contains an RNA probe and graphene oxide for detection of the biomarker of Huntington's disease, CAG repeat sequences, was constructed in this investigation. In addition, RNase H was employed in the fluorescent system to enhance the sensitivity of the detection capability. The fluorescent signal was increased through the cyclic amplified reaction, which results from RNase H, specifically digestion of the RNA strand in the complement of the RNA-DNA duplex. The designed measurement method can detect CAG repeat sequences with a detection limit of 108 pM (R² = 0.968) under which we optimized assay conditions. Furthermore, the detection limit is approximately 18 times lower than the traditional DNA and graphene oxide detection method without assistance of RNase H. Additionally, the probing platform also shows stronger ability to discriminate between the fluorescence of the target sequence and that of other non-target sequences. The results of our studies demonstrate that the RNase H amplified RNA probe and graphene oxide system exhibited excellent sensitivity and selectivity to the target of CAG repeats sequences.

Biomimetic Hydroxyapatite on Graphene Supports for Biomedical Applications: A Review

Hydroxyapatite (HA) has been widely used in fields of materials science, tissue engineering, biomedicine, energy and environmental science, and analytical science due to its simple preparation, low-cost, and high biocompatibility. To overcome the weak mechanical properties of pure HA, various reinforcing materials were incorporated with HA to form high-performance composite materials. Due to the unique structural, biological, electrical, mechanical, thermal, and optical properties, graphene has exhibited great potentials for supporting the biomimetic synthesis of HA. In this review, we present recent advance in the biomimetic synthesis of HA on graphene supports for biomedical applications. More focuses on the biomimetic synthesis methods of HA and HA on graphene supports, as well as the biomedical applications of biomimetic graphene-HA nanohybrids in drug delivery, cell growth, bone regeneration, biosensors, and antibacterial test are performed. We believe that this review is state-of-the-art, and it will be valuable for readers to understand the biomimetic synthesis mechanisms of HA and other bioactive minerals, at the same time it can inspire the design and synthesis of graphene-based novel nanomaterials for advanced applications.

Synthesis of Three-Dimensional Graphene-Based Hybrid Materials for Water Purification: A Review

Graphene-based nanostructures and nanomaterials have been widely used for the applications in materials science, biomedicine, tissue engineering, sensors, energy, catalysis, and environmental science due to their unique physical, chemical, and electronic properties. Compared to two-dimensional (2D) graphene materials, three-dimensional (3D) graphene-based hybrid materials (GBHMs) exhibited higher surface area and special porous structure, making them excellent candidates for practical applications in water purification. In this work, we present recent advances in the synthesis and water remediation applications of 3D GBHMs. More details on the synthesis strategies of GBHMs, the water treatment techniques, and the adsorption/removal of various pollutants from water systems with GBHMs are demonstrated and discussed. It is expected that this work will attract wide interests on the structural design and facile synthesis of novel 3D GBHMs, and promote the advanced applications of 3D GBHMs in energy and environmental fields.

Carbon Nanofiber-Based Functional Nanomaterials for Sensor Applications

Carbon nanofibers (CNFs) exhibit great potentials in the fields of materials science, biomedicine, tissue engineering, catalysis, energy, environmental science, and analytical science due to their unique physical and chemical properties. Usually, CNFs with flat, mesoporous, and porous surfaces can be synthesized by chemical vapor deposition and electrospinning techniques with subsequent chemical treatment. Meanwhile, the surfaces of CNFs are easy to modify with various materials to extend the applications of CNF-based hybrid nanomaterials in multiple fields. In this review, we focus on the design, synthesis, and sensor applications of CNF-based functional nanomaterials. The fabrication strategies of CNF-based functional nanomaterials by adding metallic nanoparticles (NPs), metal oxide NPs, alloy, silica, polymers, and others into CNFs are introduced and discussed. In addition, the sensor applications of CNF-based nanomaterials for detecting gas, strain, pressure, small molecule, and biomacromolecules are demonstrated in detail. This work will be beneficial for the readers to understand the strategies for fabricating various CNF-based nanomaterials, and explore new applications in energy, catalysis, and environmental science.

Highly sensitive immunodiagnostics at the point of care employing alternative recognition elements and smartphones: hype, trend, or revolution?

Immunodiagnostic tests performed at the point of care (POC) today usually employ antibodies for biorecognition and are read out either visually or with specialized equipment. Availability of alternative biorecognition elements with promising features as well as smartphone-based approaches for signal readout, however, challenge the described established configuration in terms of analytical performance and practicability. Assessing these developments' clinical relevance and their impact on POC immunodiagnostics is demanding. The first part of this review will therefore give an overview on suitable diagnostic biosensors based on alternative recognition elements (such as nucleic acid-based aptamers or engineered binding proteins) and exemplify advantages and drawbacks of these biomolecules on the base of selected assays. The second part of the review then focuses on smartphone-connected diagnostics and discusses the indispensable considerations required for successful future clinical POCT implementation. Together, the joint depiction of two of the most innovative and exciting developments in the field will enable the reader to cast a glance into the distant future of POC immunodiagnostics.

A highly sensitive electrochemical aptasensor for detection of microcystin-LR based on a dual signal amplification strategy

In this work, a sensitive and selective electrochemical aptasensor for determination of microcystin-LR (MC-LR) was developed based on a dual signal amplification system consisting of a novel ternary composite and horseradish peroxidase (HRP). The ternary composite was prepared by depositing gold nanoparticles (AuNPs) on molybdenum disulfide (MoS2) covered TiO2 nanobeads (TiONBs). MoS2 nanosheet modified TiONBs provided a large surface area for immobilization of AuNPs and biomolecules. The ternary composite also possesses an improved electron transfer and catalytic capability. To construct the aptasensor, thiolated MC-LR aptamers were immobilized on the AuNP@MoS2-TiONB modified electrode through a gold-sulfur bond. Then, biotin-cDNA with a sequence complementary to the MC-LR aptamer competed with MC-LR for binding to the immobilized aptamer. The current signal catalyzed by avidin-HRP decreased with the increase of MC-LR, based on which a linear range of 0.005-30 nM and a detection limit of 0.002 nM were obtained.

Hierarchical nanomaterials via biomolecular self-assembly and bioinspiration for energy and environmental applications

Bioinspired synthesis offers potential green strategies to build highly complex nanomaterials by utilizing the unique nanostructures, functions, and properties of biomolecules, in which the biomolecular recognition and self-assembly processes play important roles in tailoring the structures and functions of bioinspired materials. Further understanding of biomolecular self-assembly for inspiring the formation and assembly of nanoparticles would promote the design and fabrication of functional nanomaterials for various applications. In this review, we focus on recent advances in bioinspired synthesis and applications of hierarchical nanomaterials based on biomolecular self-assembly. We first discuss biomolecular self-assembly towards biological nanomaterials, in which the mechanisms and ways of biomolecular self-assembly as well as various self-assembled biomolecular nanostructures are demonstrated. Secondly, the bioinspired synthesis strategies including molecule-molecule interaction, molecule-material recognition, molecule-mediated nucleation and growth, and molecule-mediated reduction/oxidation are introduced and discussed. Meanwhile, typical examples and discussions on how biomolecular self-assembly inspires the formation of hierarchical hybrid nanomaterials are presented. Finally, the applications of bioinspired nanomaterials in biofuel cells, light-harvesting systems, batteries, supercapacitors, catalysis, water/air purification, and environmental monitoring are presented and discussed. We believe that this review will be very helpful for readers to understand the self-assembly of biomolecules and the biomimetic/bioinspired strategies for synthesizing hierarchical nanomaterials on the one hand, and on the other hand to design novel materials for extended applications in nanotechnology, materials science, analytical science, and biomedical engineering.

Controlling the Self-Assembly of Biomolecules into Functional Nanomaterials through Internal Interactions and External Stimulations: A Review

Biomolecular self-assembly provides a facile way to synthesize functional nanomaterials. Due to the unique structure and functions of biomolecules, the created biological nanomaterials via biomolecular self-assembly have a wide range of applications, from materials science to biomedical engineering, tissue engineering, nanotechnology, and analytical science. In this review, we present recent advances in the synthesis of biological nanomaterials by controlling the biomolecular self-assembly from adjusting internal interactions and external stimulations. The self-assembly mechanisms of biomolecules (DNA, protein, peptide, virus, enzyme, metabolites, lipid, cholesterol, and others) related to various internal interactions, including hydrogen bonds, electrostatic interactions, hydrophobic interactions, π⁻π stacking, DNA base pairing, and ligand⁻receptor binding, are discussed by analyzing some recent studies. In addition, some strategies for promoting biomolecular self-assembly via external stimulations, such as adjusting the solution conditions (pH, temperature, ionic strength), adding organics, nanoparticles, or enzymes, and applying external light stimulation to the self-assembly systems, are demonstrated. We hope that this overview will be helpful for readers to understand the self-assembly mechanisms and strategies of biomolecules and to design and develop new biological nanostructures or nanomaterials for desired applications.

Removing Metal Ions from Water with Graphene⁻Bovine Serum Albumin Hybrid Membrane

Here we report the fabrication of graphene oxide (GO)-based membranes covalently combined with bovine serum albumin (BSA) for metal ions detection. In this system, BSA acts as a transporter protein in the membrane and endows the membrane with selective recognition of Co2+, Cu2+, AuCl₄-, and Fe2+. Combining the metal-binding ability of BSA and the large surface area of GO, the hybrid membrane can be used as a water purification strategy to selectively absorb a large amount of AuCl₄- from HAuCl₄ solution. Moreover, BSA could reduce the membrane-immobilized AuCl₄- by adding sodium borohydride (NaBH₄). Interestingly, adsorption experiments on three kinds of metal ions showed that the GO⁻BSA membrane had good selective adsorption of Co2+ compared with Cu2+ and Fe2+. The morphology and composition changes of the membrane were observed with atomic force microscopy (AFM) and Raman spectroscopy, respectively. It is expected that this facile strategy for fabricating large-scale graphene-biomolecule membranes will spark inspirations in the development of functional nanomaterials and wastewater purification.