Tear-based MMP-9 detection: A rapid antigen test for ocular inflammatory disorders using vanadium disulfide nanowires assisted chemi-resistive biosensor

A sensitive, non-invasive, and biomarker detection in tear fluids for inflammation in potentially blinding eye diseases could be of great significance as a rapid diagnostic tool for quick clinical decisions. In this work, we propose a tear-based MMP-9 antigen testing platform using hydrothermally synthesized vanadium disulfide nanowires. Also, various factors contributing to baseline drifts of the chemiresistive sensor including nanowire coverage on the interdigitated microelectrode of the sensor, sensor response duration, and effect of MMP-9 protein in different matrix solutions were identified. The drifts on the sensor baseline due to nanowire coverage on the sensor were corrected using substrate thermal treatment providing a more uniform distribution of nanowires on the electrode which brought the baseline drift to 18% (coefficient of variations, CV = 18%). This biosensor exhibited sub-femto level limits of detection (LODs) of 0.1344 fg/mL (0.4933 fmoL/l) and 0.2746 fg/mL (1.008 fmoL/l) in 10 mM phosphate buffer saline (PBS) and artificial tear solution, respectively. For a practical tear MMP-9 detection, the proposed biosensor response was validated with multiplex ELISA using tear samples from five healthy controls which showed excellent precision. This label-free and non-invasive platform can serve as an efficient diagnostic tool for the early detection and monitoring of various ocular inflammatory diseases.

Recent Advances in Nanomaterial-Based Aptasensors in Medical Diagnosis and Therapy

Rapid and accurate diagnosis of various biomarkers associated with medical conditions including early detection of viruses and bacteria with highly sensitive biosensors is currently a research priority. Aptamer is a chemically derived recognition molecule capable of detecting and binding small molecules with high specificity and its fast preparation time, cost effectiveness, ease of modification, stability at high temperature and pH are some of the advantages it has over traditional detection methods such as High Performance Liquid Chromatography (HPLC), Enzyme-linked Immunosorbent Assay (ELISA), Polymerase Chain Reaction (PCR). Higher sensitivity and selectivity can further be achieved via coupling of aptamers with nanomaterials and these conjugates called "aptasensors" are receiving greater attention in early diagnosis and therapy. This review will highlight the selection protocol of aptamers based on Traditional Systematic Evolution of Ligands by EXponential enrichment (SELEX) and the various types of modified SELEX. We further identify both the advantages and drawbacks associated with the modified version of SELEX. Furthermore, we describe the current advances in aptasensor development and the quality of signal types, which are dependent on surface area and other specific properties of the selected nanomaterials, are also reviewed.

Novel fluorescent biosensor for carcinoembryonic antigen determination via atom transfer radical polymerization with a macroinitiator

A novel fluorescence method for CEA via β-CD and BIBB-initiated atom transfer radical polymerization (ATRP) was reported.

Theoretical Insight on the Biosensing Applications of 2D Materials

The research on the design of efficient, reliable, and cost-effective biosensors is expanding given its high demand in various fields such as health care, environmental surveillance, agriculture, diagnostics, industries, and so forth. In the last decade, various fascinating and interesting 2D materials with extraordinary properties have been experimentally synthesized and theoretically predicted. 2D materials have been explored for the sensing of different biomolecules because of their large surface area and strong interaction with different biomolecules. Theoretical simulations can bring important insight on the interaction of biomolecules on 2D materials, charge transfer, orbital interactions, and so forth and may play an important role in the development of efficient biosensors. Quantum simulation techniques, such as density functional theory (DFT), are very powerful and are gaining popularity especially with the advent of high-speed computing facilities. This review article provides theoretical insight regarding the interaction of various biomolecules on different 2D materials and the charge transfer between the biomolecules and 2D materials leading to electrochemical signals, which can then provide experimentalists the useful design parameters for fabrication of biosensors. It also includes an overview of quantum simulations, use of the DFT method for simulating biomolecules on 2D materials, parameters obtained from theoretical simulations and sensitivity, and limitations of computational techniques for sensing biomolecules on 2D materials. Furthermore, this review summarizes the recent work in first-principles investigation of 2D materials for the purpose of biomolecule sensing. Beyond the traditional graphene or 2D transition-metal dichalcogenides, some novel and recently proposed 2D materials such as pentagraphene, haeckelite, MXenes, and so forth which have exhibited good sensing applications have also been highlighted.

Emerging Layered Metallic Vanadium Disulfide for Rechargeable Metal-Ion Batteries: Progress and Opportunities

Rechargeable metal-ion batteries (RMIBs), as one of the most viable technologies for electric vehicles (EVs) and large-scale energy storage (EES), have received extensive research attention for a long time. Electrode materials play a decisive role on capacity, energy, and power density, which directly affect the practical applications of RMIBs in EVs and EES. As an electrode material, layered metallic vanadium disulfide (VS₂ ) has theoretically and experimentally produced inspiring results because of its synthetic characteristics of continuously adjustable V valence, large interlayer spacing, weak interlayer interactions, and high surface activity. Herein, the synthetic strategies, theoretical metal-ion storage sites, diffusion kinetics, and experimental electrochemical reaction mechanisms of VS₂ for RMIBs are systematically introduced. Emphatically, the critical issues that affect the metal-ion storage properties of the VS₂ electrode and three major enhancement strategies, namely, optimizing the electrolyte and cutoff voltage, constructing a space-confined structure, and controlling the crystal structure are summarized, with the aim of promoting the development of transition-metal dichalcogenides. Finally, the challenges and opportunities for the future development of VS₂ in the energy-storage field are presented. It is hoped that this review can attract attention from researchers for investigations into emerging layered metallic VS₂ and provide insights toward the design of an excellent VS₂ electrode material for next-generation, high-performance RMIBs.

Highly sensitive IRS based biosensor for the determination of cytochrome c as a cancer marker by using nanoporous anodic alumina modified with trypsin

The determination of cytochrome c in the human serum sample is a regular medical investigation performed to assess cancer diseases. Herein, we used interferometric reflectance spectroscopy (IRS) based biosensor for the determination of cytochrome c. For this purpose first, the nanoporous anodic alumina (NAA) was fabricated. Then, the NAA pore walls were functionalized with 3-aminopropyl trimethoxy silane (NAA-NH₂). Subsequently, the trypsin enzyme was immobilized on the NAA pore walls. The sensing principle of proposed IRS sensor to cytochrome c is based on a change in the intensity of the reflected light to a charge-coupled device (CCD) detector after digesting of cytochrome c by immobilized trypsin enzymes on NAA-NH₂ into the heme-peptide fragment. The heme-peptide fragment then oxidized 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) to green color ABTS^·- anion radical in the presence of hydrogen peroxide. The generated green color ABTS^·- anion radical solution adsorbed the white light and therefore the intensity of the reflected light from NAA to the CCD decreased. The decrease in the intensity of the white light had a logarithmic relationship with the concentration of the cytochrome c in the range of 1-100 nM. The limit of detections (LOD) for cytochrome c was 0.5 nM. The proposed biosensor exhibited high selectivity, sensitivity, and good stability.

Facile Preparation of Organometallic Nanorods from Various Ethynyl-Substituted Molecules

A facile method to prepare one‐dimensional (1D) organometallic nanomaterials from various ethynyl‐substituted molecules is reported. The reactions of 3‐chloro‐1‐ethynylbenzene, p‐tBu‐phenylacetylene and 4‐ethynylbiphenyl with Cu⁺ ions in acetonitrile yield nanorod‐shaped copper acetylides (Cu−C≡C−R) crystals. In the case of linear alkynes, namely, propyne, 1‐pentyne and 1‐hexyne, it was found that using an aqueous ammonia/ethanol mixed solvent instead of acetonitrile is a better approach to obtain 1D nanostructures. This procedure also enables us to prepare functional 1D nanomaterials. We demonstrate the preparation of a paramagnetic nanorod from the organic radical p‐ethynylphenyl nitronyl nitroxide, and fluorescent nanorods from 9‐ethynylphenanthrene and 2‐ethynyl‐9,9′‐spirobifluorene.

Surface-Enhanced Raman Scattering-Fluorescence Dual-Mode Nanosensors for Quantitative Detection of Cytochrome c in Living Cells

During apoptosis process, the release of cytochrome c (Cyt c) is considered to be a key factor in the intrinsic pathway and is often defined as no regression point. Quantitative detection of intracellular Cyt c remains a challenge. Herein, we have developed surface-enhanced Raman scattering (SERS)-fluorescence dual-mode nanosensors for the quantitative assay of Cyt c in living cells. Dual signal detection was achieved by constructing gold nanotriangles (AuNTs) nanosensors capable of specifically recognizing Cyt c. The nanosensors were prepared by modifying the aptamer of Cyt c on AuNTs and connecting the complementary strands modified with Cy5. The AuNTs provided both enhanced SERS signals and fluorescence quenching effects. Once cells were induced by external stimulus (such as toxins) to release Cyt c, Cyt c would specifically bind to its aptamer, and the complementary strands modified with Cy5 would detach which would result in weakened SERS signal and recovery of fluorescence signal. The experimental results showed that the nanosensors not only had excellent selectivity and sensitivity but also realized real-time monitoring of Cyt c translocation event from mitochondria to cytoplasm. The SERS and fluorescence intensity showed good linear relationship with Cyt c concentration ranging from 0.044 to 9.95 μM and achieved a minimum limit of detection (LOD) of 0.02 μM in living cells. The accuracy of intracellular Cyt c quantitative results was more than 90% compared with the ELISA results.

Electroluminescent aptasensor based on RuSiO2 nanoparticles for detection cytochrome c using ferrocene as quenching probe

A stable sandwiched electrochemiluminescence (ECL) aptasensor was originally constructed established upon Ru(bpy)₃²⁺-doped silica nanoparticles (RuSiO₂ NPs) with ferrocene carboxylic acid-aptamer (Fc-aptamer) to quantitatively detect cytochrome c (Cyt C). Herein, RuSiO₂ NPs and Fc-aptamer were respectively prepared through the microemulsion method and amide reaction to fabricate the ECL aptasensor. Furthermore, Fc-aptamer was used as quenching probe for quenching the ECL emission of RuSiO₂ NPs. In detail, RuSiO₂ NPs were primarily immobilized onto the electrodes by the film-forming function of chitosan. Subsequently, the aptamer was incubated onto the decorated GCE via crosslinking with glutaraldehyde (GA). After Cyt C was connected to the GCE via immunoreaction, Fc-aptamer was immobilized onto the modified electrodes owing to the specific recognition between antigens and aptamer. Ultimately, ECL signals markedly descended owing to the poor electricity conductivity of proteins and superior quenching effect of Fc-aptamer. Under optimum conditions, the designed ECL aptasensor indicated an accurate analysis for Cyt C in a rang of 0.001-100 nM with a detection limit of 0.48 pM (S/N = 3).

Modelling of adsorption and intercalation of hydrogen on/into tungsten disulphide multilayers and multiwall nanotubes

Understanding the interaction of hydrogen with layered materials is crucial in the fields of sensors, catalysis, fuel cells and hydrogen storage, among others. Density functional theory, improved by the introduction of van der Waals dispersion forces, provides an efficient and practical workbench to investigate the interaction of molecular and atomic hydrogen with WS2 multilayers and nanotubes. We find that H2 physisorbs on the surface of those materials on top of W atoms, while atomic H chemisorbs on top of S atoms. In the case of nanotubes, the chemisorption strength is sensitive to the nanotube diameter. Diffusion of H2 on the surface of WS2 encounters quite small activation barriers whose magnitude helps to explain previous and new experimental results for the observed dependence of the hydrogen concentration with temperature. Intercalation of H2 between adjacent planar WS2 layers reveals an endothermic character. Intercalating H atoms is energetically favorable, but the intercalation energy does not compensate for the cost of dissociating the molecules. When H2 molecules are intercalated between the walls of a double wall nanotube, the rigid confinement induces the dissociation of the confined molecules. A remarkable result is that the presence of a full H2 monolayer adsorbed on top of the first WS2 layer of a WS2 multilayer system strongly facilitates the intercalation of H2 between WS2 layers underneath. This opens up an additional gate to intercalation processes.

Helix structure of the double-stranded DNA for aptameric biosensing and imaging of cytochrome c

Here, a method is introduced for construction the aptameric biosensor for biosensing detection of cytochrome C (CYC) based on chain-shape structure of aptasensor by using highly dispersed silver nanoparticles (AgNPs) on acid-oxidized carbon nanotube (CNTs) substrate. The animated capture probe (ssDNA1) and CYC-aptamer (ssDNA2) was immobilized on AgNPs/CNTs surface by covalent amide bonds formed by the carboxyl groups on the nanotubes and the amino groups on the oligonucleotides and hybridization, respectively. In this protocol, the nucleic acids at both ends of the ssDNA1 were sequenced to be complementary (tailor-made ssDNA1). The helix structure of the double-stranded DNA was fabricated by hybridizing ssDNA2 with its complementary sequence (ssDNA1). CYC-aptamer could be forced to dissociate from the sensing interface after CYC triggered structure switching of the aptamer and ssDNA1 thus tend to form a chain-shape structure through the hybridization of the complementary sequences at both its ends. The proposed assay permitted to detect CYC in the linear range of 0.01-750 nM with a very low limit of detection (LOD) (1.66 pM). In addition, the specificity of this sensing system for the detection of CYC was also demonstrated by using albumin, fructose, myoglobin, and hemoglobin.

Nucleic acid-functionalized transition metal nanosheets for biosensing applications

In clinical diagnostics, as well as food and environmental safety practices, biosensors are powerful tools for monitoring biological or biochemical processes. Two-dimensional (2D) transition metal nanomaterials, including transition metal chalcogenides (TMCs) and transition metal oxides (TMOs), are receiving growing interest for their use in biosensing applications based on such unique properties as high surface area and fluorescence quenching abilities. Meanwhile, nucleic acid probes based on Watson-Crick base-pairing rules are also being widely applied in biosensing based on their excellent recognition capability. In particular, the emergence of functional nucleic acids in the 1980s, especially aptamers, has substantially extended the recognition capability of nucleic acids to various targets, ranging from small organic molecules and metal ions to proteins and cells. Based on π-π stacking interaction between transition metal nanosheets and nucleic acids, biosensing systems can be easily assembled. Therefore, the combination of 2D transition metal nanomaterials and nucleic acids brings intriguing opportunities in bioanalysis and biomedicine. In this review, we summarize recent advances of nucleic acid-functionalized transition metal nanosheets in biosensing applications. The structure and properties of 2D transition metal nanomaterials are first discussed, emphasizing the interaction between transition metal nanosheets and nucleic acids. Then, the applications of nucleic acid-functionalized transition metal nanosheet-based biosensors are discussed in the context of different signal transducing mechanisms, including optical and electrochemical approaches. Finally, we provide our perspectives on the current challenges and opportunities in this promising field.

Recent Advances in Synthesis and Biomedical Applications of Two-Dimensional Transition Metal Dichalcogenide Nanosheets

During recent decades, a giant leap in the development of nanotechnology has been witnessed. Numerous nanomaterials with different dimensions and unprecedented features have been developed and provided unimaginably wide scope to solve the challenging problems in biomedicine, such as cancer diagnosis and therapy. Recently, two-dimensional (2D) transition metal dichalcogenide (TMDC) nanosheets (NSs), including MoS₂ , WS₂ , and etc., have emerged as novel inorganic graphene analogues and attracted tremendous attention due to their unique structures and distinctive properties, and opened up great opportunities for biomedical applications, including ultrasensitive biosensing, biological imaging, drug delivery, cancer therapy, and antibacterial treatment. A comprehensive overview of different synthetic methods of ultrathin 2D TMDC NSs and their state-of-the-art biomedical applications, especially those that have appeared in the past few years, is presented. At the end of this review, the future opportunities and challenges for 2D TMDC NSs in biomedicine are also discussed.

Recent advances in cytochrome c biosensing technologies

This review is an attempt, for the first time, to describe advancements in sensing technology for cytochrome c (cyt c) detection, at point-of-care (POC) application. Cyt c, a heme containing metalloprotein is located in the intermembrane space of mitochondria and released into bloodstream during pathological conditions. The release of cyt c from mitochondria is a key initiative step in the activation of cell death pathways. Circulating cyt c levels represents a novel in-vivo marker of mitochondrial injury after resuscitation from heart failure and chemotherapy. Thus, cyt c detection is not only serving as an apoptosis biomarker, but also is of great importance to understand certain diseases at cellular level. Various existing techniques such as enzyme-linked immunosorbent assays (ELISA), Western blot, high performance liquid chromatography (HPLC), spectrophotometry and flow cytometry have been used to estimate cyt c. However, the implementation of these techniques at POC application is limited due to longer analysis time, expensive instruments and expertise needed for operation. To overcome these challenges, significant efforts are being made to develop electrochemical biosensing technologies for fast, accurate, selective, and sensitive detection of cyt c. Presented review describes the cutting edge technologies available in the laboratories to detect cyt c. The recent advancements in designing and development of electrochemical cyt c biosensors for the quantification of cyt c are also discussed. This review also highlights the POC cyt c biosensors developed recently, that would prove of interest to biologist and therapist to get real time informatics needed to evaluate death process, diseases progression, therapeutics and processes related with mitochondrial injury.

Electrochemiluminescence aptasensor of TiO2/CdS:Mn hybrids for ultrasensitive detection of cytochrome c

A novel electrochemiluminescence (ECL) aptasensor was proposed for ultrasensitive detection of cytochrome c (cyt c) using CdS:Mn quantum dot-modified TiO2 nanowires (NWs) as electrode. The Mn-doped CdS was deposited on the TiO2 NWs by successive ion layer adsorption and reaction (SILAR) as ECL emitter, on which thiol-modified aptamer of cyt c was attached via Cd-S bond. Due to the high photo-electrical transfer efficiency, the as-prepared aptasensor shows high selectivity and sensitivity towards cyt c with a detection limit of 9.5fM and a linear range from 50fM to 125pM.

Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology

The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct “beyond graphene” domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials.