Carbon Dots-AS1411 Aptamer Nanoconjugate for Ultrasensitive Spectrofluorometric Detection of Cancer Cells

An ultrasensitive paper-based SERS sensor for detection of nucleolin using silver-nanostars, plastic antibodies and natural antibodies

A state-of-the-art, ultrasensitive, paper-based SERS sensor has been developed using silver nanostars (AgNSs) in combination with synthetic and natural antibodies. A key component of this innovative sensor is the plastic antibody, which was synthesized using molecularly imprinted polymer (MIP) technology. This ground-breaking combination of paper substrates/MIPs with AgNSs, which is similar to a sandwich immunoassay, is used for the first time with the aim of SERS detection and specifically targets nucleolin (NCL), a cancer biomarker. The sensor device was carefully fabricated by synthesizing a polyacrylamide-based MIP on cellulose paper (Whatman Grade 1 filter) by photopolymerization. The binding of NCL to the MIP was then confirmed by natural antibody binding using a sandwich assay for quantitative SERS analysis. To facilitate the detection of NCL, antibodies were pre-bound to AgNSs with a Raman tag so that the SERS signal could indicate the presence of NCL. The composition of the sensory layers/materials was meticulously optimized. The intensity of the Raman signal at ∼1078 cm-1 showed a linear trend that correlated with increasing concentrations of NCL, ranging from 0.1 to 1000 nmol L-1, with a limit of detection down to 0.068 nmol L-1 in human serum. The selectivity of the sensor was confirmed by testing its analytical response in the presence of cystatin C and lysozyme. The paper-based SERS detection system for NCL is characterized by its simplicity, sustainability, high sensitivity and stability and thus embodies essential properties for point-of-care applications. This approach is promising for expansion to other biomarkers in various fields, depending on the availability of synthetic and natural antibodies.

Formulation optimization of lyophilized aptamer-gold nanoparticles: Maintained colloidal stability and cellular uptake

Anti-nucleolin (NCL) aptamer AS1411 is the first anticancer aptamer tested in clinical trials. Gold nanoparticles (AuNP) have been widely exploited for various biomedical applications due to their unique functional properties. In this study, we evaluated the colloidal stability and targeting capacity of AS1411-funtionalized AuNP (AuNP/NCL-Apt) against MCF-7 breast cancer cell line before and after lyophilization. Trehalose, mannitol, and sucrose at various concentrations were evaluated to determine their cryoprotection effects. Our results indicate that sucrose at 10 % (w/v) exhibits the best cryoprotection effect and minimal AuNP/NCL-Apt aggregation as confirmed by UV-Vis spectroscopy and dynamic light scattering (DLS) measurements. Moreover, the lyophilized AuNP/NCL-Apt at optimized formulation maintained its targeting and cytotoxic functionality against MCF-7 cells as proven by the cellular uptake assays utilizing flow cytometry and confocal laser scanning microscopy (CLSM). Quantitative PCR (qPCR) analysis of nucleolin-target gene expression also confirmed the effectiveness of AuNP/NCL-Apt. This study highlights the importance of selecting the proper type and concentration of cryoprotectant in the typical nanoparticle lyophilization process and contributes to our understanding of the physical and biological properties of functionalized nanoparticles upon lyophilization.

A narrative review on the role of carbon nanoparticles in oncology

The lymphatic system is the first site of metastasis for most tumors and is a common reason for the failure of cancer therapy. The lymphatic system's anatomical properties make it difficult to deliver chemotherapy agents at therapeutic concentrations while avoiding systemic toxicity. Carbon nanoparticles offer a promising alternative for identifying and transporting therapeutic molecules. The larger diameter of lymphatic vessels compared to the diameter of blood vessels, allows carbon nanoparticles to selectively enter the lymphatic system once administered subcutaneously. Carbon nanoparticles stain tumor-draining lymph nodes black following intratumoral injection, making them useful in sentinel lymph node mapping. Drug-loaded carbon nanoparticles allow higher concentrations of chemotherapeutics to accumulate in regional lymph nodes while decreasing plasma drug accumulation. The use of carbon nanoparticles for chemotherapy delivery has been associated with lower mortality, fewer histopathology changes in vital organs, and lower serum concentrations of hepatocellular enzymes. This review will focus on the ability of carbon nanoparticles to target the lymphatics as well as their current and potential applications in sentinel lymph node mapping and oncology treatment regimens. This article is categorized under: Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery.

Applications of Bacteria Decorated with Synthetic DNA Constructs

The advent of DNA nanotechnology has revolutionized the way DNA has been perceived. Rather than considering it as the genetic material alone, DNA has emerged as a versatile synthetic scaffold that can be used to create a variety of molecular architectures. Modifying such self-assembled structures with bio-molecular recognition elements has further expanded the scope of DNA nanotechnology, opening up avenues for using synthetic DNA assemblies to sense or regulate biological molecules. Recent advancements in this field have lead to the creation of DNA structures that can be used to modify bacterial cell surfaces and endow the bacteria with new properties. This mini-review focuses on the ways by which synthetic modification of bacterial cell surfaces with DNA constructs can expand the natural functions of bacteria, enabling their potential use in various fields such as material engineering, bio-sensing, and therapy. The challenges and prospects for future advancements in this field are also discussed.

Anti-nucleolin Aptamer as a Boom in Rehabilitation of Breast Cancer

Breast cancer is the second leading cause of cancer-related deaths. It is important to target the complex pathways using a suitable targeted delivery system. Targeted delivery systems can effectively act on cancer cells and lead to the annihilation of tumor proliferation. They mainly employ targeting agents like aptamers linked to the formulation. Based on the expression of the receptors on the surface of the cancer cells, suitable aptamers can be developed. AS1411 is one such aptamer that has the ability to bind to the over-expressed nucleolin present in breast cancer cells. Nucleolin is a phosphoprotein that is involved in various aspects, like cell growth, differentiation and survival. Mostly they are found in the nucleolus, nucleus, cytoplasm and cell surface. The shuttling effect of the nucleolin between the nucleus and cytoplasm serves as a bonus for the AS1411 aptamer. Because of the shutting effect, the internalization of the drug compound or chemotherapeutic drug inside the cell can be achieved. In this article, we have discussed nucleolin, anti-nucleolin aptamer, namely, AS1411, and its application in exhibiting various anticancer activities, including apoptosis, anti-angiogenesis, anti-metastasis, stimulation of tumor suppressor (i.e., P53), and inhibition of tumor inducer. Further, the ways of internalization, namely macropinocytosis, are also discussed. Additionally, we have also discussed the superiority of the aptamer compared to the antibodies as well as the limitations of the aptamers. By considering all the above parameters, we hope this aptamer will be effective in the management and eradication of breast cancer cells.

A Brief Review of Carbon Dots-Silica Nanoparticles Synthesis and their Potential Use as Biosensing and Theragnostic Applications

Carbon dots (CDs) are carbon nanoparticles with sizes below 10 nm and have attracted attention due to their relatively low toxicity, great biocompatibility, water solubility, facile synthesis, and exceptional photoluminescence properties. Accordingly, CDs have been widely exploited in different sensing and biomedical applications, for example, metal sensing, catalysis, biosensing, bioimaging, drug and gene delivery, and theragnostic applications. Similarly, the well-known properties of silica, such as facile surface functionalization, good biocompatibility, high surface area, and tunable pore volume, have allowed the loading of diverse inorganic and organic moieties and nanoparticles, creating complex hybrid nanostructures that exploit distinct properties (optical, magnetic, metallic, mesoporous, etc.) for sensing, biosensing, bioimaging, diagnosis, and gene and drug delivery. In this context, CDs have been successfully grafted into diverse silica nanostructures through various synthesis methods (e.g., solgel chemistry, inverse microemulsion, surfactant templating, and molecular imprinting technology (MIT)), imparting hybrid nanostructures with multimodal properties for distinct objectives. This review discusses the recently employed synthesis methods for CDs and silica nanoparticles and their typical applications. Then, we focus on combined synthesis techniques of CD-silica nanostructures and their promising biosensing operations. Finally, we overview the most recent potential applications of these materials as innovative smart hybrid nanocarriers and theragnostic agents for the nanomedical field.

Intrinsic specificity of plain ammonium citrate carbon dots for Helicobacter pylori: Interfacial mechanism, diagnostic translation and general revelation

The exploitation of carbon dots (CDs) is now flourishing; however, more effort is needed to overcome their lack of intrinsic specificity. Herein, instead of synthesizing novel CDs, we reinvestigated three reported CDs and discovered that plain ammonium citrate CDs (AC-CDs) exhibited surprising specificity for Helicobacter pylori. Notably, we showed that the interfacial mechanism behind this specificity was due to the affinity between the high abundant urea/ammonium transporters on H. pylori outer membrane and the surface-coordinated ammonium ions on AC-CDs. Further, we justified that ammonium sulfate-citric acid CDs also possessed H. pylori-specificity owing to their NH₄⁺ doping. Thereby, we suggested that the incorporation of a molecule that could be actively transported by abundant membrane receptors into the precursors of CDs might serve as a basis for developing a plain CD with intrinsic specificity for H. pylori. Moreover, AC-CDs exhibited specificity towards live, dead, and multidrug-resistant H. pylori strains. Based on the specificity, we developed a microfluidics-assisted in vitro sensing approach for H. pylori, achieving a simplified, rapid and ultrasensitive detection with two procedures, shortened time within 45.0 ​min and a low actual limit of detection of 10.0 ​CFU ​mL⁻¹. This work sheds light on the design of more H. pylori-specific or even bacteria-specific CDs and their realistic translation into clinical practice.

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Plain ammonium citrate CDs have intrinsic specificity for Helicobacter pylori.

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Affinity of outer-membrane urea receptors to NH₄⁺ on CDs decides the specificity.

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The specific CDs coupling microfluidics confers a simplified detection of H. pylori.

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The mechanism and translation inspire the engineering of bacteria-specific CDs.

Aptamer-conjugated carbon-based nanomaterials for cancer and bacteria theranostics: A review

Aptamers are single-stranded oligonucleotides that link to various substrates with great affinity and selectivity, including small molecules, peptides, proteins, cells, and tissues. For this reason, they can be used as imaging agents for cancer imaging techniques. Multifunctional nanomaterials combined with imaging probes and drugs are promising cancer diagnosis and treatment candidates. On the other hand, carbon-based nanomaterials (CNMs), including such as fullerene, carbon nanotubes, carbon-based quantum dots, carbon nanohorns, graphene oxide and its derivatives carbon nanodots, and nanodiamonds, are sort of smart materials that can be used in a variety of theranostic applications, including photo-triggered therapies. The remarkable physical characteristics, functionalizable chemistry, biocompatibility, and optical properties of these nanoparticles have enabled their utilization in less-invasive therapies. The theranostic agents that emerged by combining aptamers with CNMs have opened a novel alternative for personified medicine of cancer, target-specific imaging, and label-free diagnosis of a broad range of cancers, as well as pathogens. Aptamer-functionalized CNMs have been used as nanovesicles for targeted delivery of anti-cancer agents (i.e., doxorubicin and 5-fluorouracil) to tumor sites. Furthermore, these CNMs conjugated with aptamers have shown great advantages over standard CNMs to sensitively detect Mycobacterium tuberculosis, Escherichia coli, staphylococcus aureus, Vibrio parahaemolyticus, Salmonella typhimurium, Pseudomonas aeruginosa, and Citrobacter freundii. Regrettably, CNMs can form compounds defined as NOAA (nano-objects, and their aggregates and agglomerates larger than 100 nm), that accumulate in the body and cause toxic effects. Surface modification and pretreatment with albumin avoid agglomeration and increase the dispersibility of CNMs, so it is needed to guarantee the desirable interactions between functionalized CNMs and blood plasma proteins. This preliminary review aimed to comprehensively discuss the features and uses of aptamer-conjugated CNMs to manage cancer and bacterial infections.

Near-infrared carbon dots for cell imaging and detecting ciprofloxacin by label-free fluorescence sensor based on aptamer

A label-free fluorescence sensor based on near-infrared carbon dots (NIR-CDs) and aptamer is described for the highly sensitive and selective detection of ciprofloxacin (CIP). NIR-CDs were synthesized from polyethyleneimine and reduced glutathione by one-step hydrothermal method. The electrostatic interaction between the positively charged carbon dots and the negatively charged aptamer resulted in fluorescence quenching. After the addition of CIP, the specific binding between CIP aptamer and CIP was stronger, resulting in fluorescence recovery. Under the optimal experimental conditions, the recovered fluorescence intensity has a linear relationship with the concentration of CIP in the range 0.5-800 ng/mL, and the detection limit is 0.167 ng/mL. The prepared carbon dots have excellent optical properties and biocompatibility, and due to their emission characteristics in the near-infrared window, they can be used for biological imaging, which has also been confirmed in the experiment. The feasibility of the label-free fluorescence sensor for the detection of CIP is also proved by confocal fluorescence imaging. The detection results of CIP determination in milk by this sensor are satisfactory, indicating that the developed sensor has great application potential.

N-gene-complementary antisense-oligonucleotide directed molecular aggregation of dual-colour carbon dots, leading to efficient fluorometric sensing of SARS-COV-2 RNA

The early stages of the COVID-19 pandemic punctuated the need for rapid, mass testing for early detection of viral infection. Carbon dots are easily synthesized, cost-effective fluorescent nanoparticles whose surface functionalities enable facile conjugation with biorecognition elements suitable for  molecular detection of viral RNA. Herein, we report that a pair of complementary antisense oligonucleotide (ASO) sequences can lead to a highly specific molecular aggregation of dual colour carbon dots (CDs) in the presence of SARS-CoV-2 RNA. The nanoprobes used ASOs highly specific to the N-gene of SARS-COV-2. When the ASOs are conjugated to blue and yellow citric acid-derived CDs, the combination of the ASO-CD pairs facilitates aggregation-induced emission enhancement (AIEE) of the measured fluorescence after hybridization with SARS-CoV-2 RNA. We found the sensor capable of differentiating between MERS-CoV and SARS-CoV-2 samples and was found to have a limit of detection of 81 copies per μL. Additionally, we used dialysis to demonstrate that the change in emission upon aggregation is dependent on the compositional heterogeneity of the conjugated-carbon dot mixture.

A simple fluorescent strategy for liver capillary labeling with carbon quantum dot-lectin nanoprobe

Based on lycopersicon esculentum lectin that can target vascular endothelial cells and carbon quantum dots, we designed a carbon-based probe for the fluorescence labeling and imaging of hepatic blood vessels of liver tissue sections.

Graphene oxide and fluorescent aptamer based novel biosensor for detection of 25-hydroxyvitamin D3

For maintaining the healthy metabolic status, vitamin D is a beneficial metabolite stored majorly in its pre-activated form, 25-hydroxyvitamin D₃ (25(OH)D₃). Due to its important role in bone strengthening, the study was planned to quantify 25(OH)D₃ levels in our blood. Quantification techniques for 25(OH)D₃ are costly thus requiring a need for a low cost, and sensitive detection methods. In this work, an economic, and sensitive sensor for the detection of 25(OH)D₃ was developed using aptamer and graphene oxide (GO). Aptamer is an oligonucleotide, sensitive towards its target, whereas, GO with 2D nanosheets provides excellent quenching surface. Aptamer labeled with fluorescein (5’, 6-FAM) is adsorbed by π–π interaction on the GO sheets leading to quenching of the fluorescence due to Förster resonance energy transfer (FRET). However, in the presence of 25(OH)D₃, a major portion of aptamer fluorescence remains unaltered, due to its association with 25(OH)D₃. However, in the absence, aptamer fluorescence gets fully quenched. Fluorescence intensity quenching was monitored using fluorescence spectrophotometer and agarose gel based system. The limit of detection of 25(OH)D₃ by this method was found to be 0.15 µg/mL whereas when GO-COOH was used, limit of detection was improved to 0.075 µg/mL. Therefore, this method could come up as a new sensing method in the field of vitamin D detection.

State of the Art and Perspectives on the Biofunctionalization of Fluorescent Metal Nanoclusters and Carbon Quantum Dots for Targeted Imaging and Drug Delivery

The interface of nanobio science and cancer nanomedicine is one of the most important current frontiers in research, being full of opportunities and challenges. Ultrasmall fluorescent metal nanoclusters (MNCs) and carbon quantum dots (CQDs) have emerged as promising fluorescent nanomaterials due to their unique physicochemical and optical properties, facile surface functionalization, good photostability, biocompatibility, and aqueous dispersity. These characteristics make them advantageous over conventional fluorophores such as organic dye molecules and semiconductor quantum dots (QDs) for the detection, diagnosis, and treatment of various diseases including cancer. Recently, researchers have focused on the biofunctionalization strategy of the MNCs and CQDs which can tailor their physicochemical and biological properties and, in turn, can empower these biofunctionalized nanoprobes for diverse applications including imaging, drug delivery, theranostics, and other biomedical applications. In this invited feature article, we first discuss some fundamental structural and physicochemical characteristics of the fluorescent biocompatible quantum-sized nanomaterials which have some outstanding features for the development of multiplexed imaging probes, delivery vehicles, and cancer nanomedicine. We then demonstrate the diverse surface engineering of these fluorescent nanomaterials with reactive target specific functional groups which can help to construct multifunctional nanoprobes with improved targeting capabilities having minimal toxicity. The promising future of the biofunctionalized fluorescent quantum-sized nanomaterials in the field of bioanalytical and biomedical research is elaborately demonstrated, showing selected recent works with relevant applications. This invited feature article finally ends with a short discussion of the current challenges and future prospects of the development of these bioconjugated/biofunctionalized nanomaterials to provide insight into this burgeoning field of MNC- and CQD-based diagnostics and therapeutic applications.

Multifunctional nanoparticles as optical biosensing probe for breast cancer detection: A review

Optical biosensors show attractive performance in medical sensing in the event of using different nanoparticles in their design. Owing to their unique optical characteristics and biological compatibility, gold nanoparticles (GNPs), silver nanoparticles (AgNPs), bimetallic nanoparticles and magnetic nanoparticles have been broadly implemented in making sensing tools. The functionalization of these nanoparticles with different components provides an excellent opportunity to assemble selective and sensitive sensing materials to detect various biological molecules related to breast cancer. This review summarizes the recent application of optical biosensing devices based on nanomaterials and discusses their pros and cons to improve breast cancer detection in real samples. In particular, the main constituent elements of these optical biosensors including recognition and transducer elements, types of applied nanostructures, analytical sensing procedures, sensor detection ranges and limit of detection (LOD), are expressed in detail.

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.

pH-responsive zwitterionic carbon dots for detection of rituximab antibody

Zwitterionic carbon dots (CDs) have received much attention as a result of good photostability, high biocompatibility, and high quantum yield. In this study, novel zwitterionic CDs were synthesized using a simple hydrothermal method of citric acid (CA) and l-histidine as carbon and nitrogen precursors, respectively. Prepared zwitterionic CDs have an average particle size of 4 nm diameter and showed green fluorescence with a peak at 530 nm when excited at 470 nm; quantum efficiency was 39.34% using rhodamine 6G as a baseline. The fluorescence intensity of zwitterionic CDs was quenched by rituximab in the range 0-400 μmol L^-1 , with a limit of detection of 27 μmol L^-1 . In addition, the synthesized zwitterionic CDs had low toxicity, good stability, and high selectivity and sensitivity sensing for rituximab, therefore zwitterionic CDs are a promising candidate for practical applications.

Organic dots (O-dots) for theranostic applications: preparation and surface engineering

Organic dots is a term used to represent materials including graphene quantum dots and carbon quantum dots because they rely on the presence of other atoms (O, H, and N) for their photoluminescence or fluorescence properties. They generally have a small size (as low as 2.5 nm), and show good photostability under prolonged irradiation. The excitation and emission wavelengths of O-dots can be tailored according to their synthetic procedure, where although their quantum yield is quite low compared with organic dyes, this is partly compensated by their large absorption coefficients. A wide range of strategies have been used to modify the surface of O-dots for passivation, improving their solubility and biocompatibility, and allowing the attachment of targeting moieties and therapeutic cargos. Hybrid nanostructures based on O-dots have been used for theranostic applications, particularly for cancer imaging and therapy. This review covers the synthesis, physics, chemistry, and characterization of O-dots. Their applications cover the prevention of protein fibril formation, and both controlled and targeted drug and gene delivery. Multifunctional therapeutic and imaging platforms have been reported, which combine four or more separate modalities, frequently including photothermal or photodynamic therapy and imaging and drug release.

Recent advances in the modification of carbon-based quantum dots for biomedical applications

Carbon-based quantum dots (CDs) are mainly divided into two sub-groups; carbon quantum dots (CQDs) and graphene quantum dots (GQDs), which exhibit outstanding photoluminescence (PL) properties, low toxicity, superior biocompatibility and facile functionalization. Regarding these features, they have been promising candidates for biomedical science and engineering applications. In this work, we reviewed the efforts made to modify these zero-dimensional nano-materials to obtain the best properties for bio-imaging, drug and gene delivery, cancer therapy, and bio-sensor applications. Five main surface modification techniques with outstanding results are investigated, including doping, surface functionalization, polymer capping, nano-composite and core-shell structures, and the drawbacks and challenges in each of these methods are discussed.

Fluorescent imaging of cytoplasmic nucleolin in live cells by a functionalized-engineered aptamer

Monitoring of over-expressed nucleolin in the cytoplasm facilitates early cancer diagnosis. Herein, we present a novel biosensing nanoscaffold based on anti-nucleolin aptamers and polymer-grafted graphene oxides for the fluorescent imaging of nucleolin in the cell cytoplasm, which can distinguish cancer cells from normal cells.

Recent advances in improving tumor-targeted delivery of imaging nanoprobes

Tumor-targeted delivery of imaging nanoprobes provides a promising approach for the precision imaging diagnosis of cancers. Nanoprobes with desired bio-nano interface properties can preferably enter tumor tissues through the vascular endothelium, penetrate into deep tissues, and detect target lesions. Surface engineering of nanoparticles offers a critical strategy to improve tumor-targeting capacities of nanoprobes. Improvements to the efficacy of targeted nanoprobes have been intensively explored and much of this work centers on the selection of suitable targeting ligands. Herein, in this review, various recent strategies based on different targeting ligands to improve tumor-targeting of imaging nanoprobes have been developed, ranging from small molecule ligands to biomimetic coatings, with highlights on emerging coating techniques using cell membranes and dual-targeting ligands. In particular, construction and surface modification methods, targeting capacities, and imaging/theranostic performance with key issues and potential questions have been described and discussed together with considerations for future development and innovations.

Recent advances in optical aptasensor technology for amplification strategies in cancer diagnostics

Aptamers are chemically synthetic single-stranded DNA or RNA molecules selected by molecular evolution. They have been widely used as attractive tools in biosensing and bioimaging because they can bind to a large variety of targets with high sensitivity and high affinity and specificity. As recognition elements, aptamers contribute in particular to cancer diagnostics by recognizing different cancer biomarkers, while they can also facilitate ultrasensitive detection by further employing signal amplification elements. Optical techniques have been widely used for direct and real-time monitoring of cancer-related biomolecules and bioprocesses due to the high sensitivity, quick response, and simple operation, which has greatly benefited cancer diagnostics. In this review, we highlight recent advances in optical platform-based sensing strategies for cancer diagnostics aided by aptamers. Limitations and current challenges are also discussed.

Multiprobe Assay for Clinical SEPT9 Methylation Based on the Carbon Dot-Modified Liquid-Exfoliated Graphene Field Effect Transistor with a Potential to Present a Methylation Panorama

The hypermethylation in the promoter region of the SEPT9 gene is associated with the development of colorectal cancer (CRC). Although its clinical significance for early diagnosis and screening of CRC has been demonstrated, the tedious operations in the conventional DNA methylation (DNAm) detection hinder its wide application. Herein, an electronic method for determining SEPT9 methylation in CRC patients is proposed by using the carbon dot-modified liquid exfoliated graphene field effect transistor (CDs-LEG-FET) as the DNAm sensor, the specifically designed probes to capture the SEPT9 gene and the immunologic recognition to recognize 5-methylcytosine (5mC) positions on the anchored sequences. The identification and nanomorphology of the as-prepared materials and devices are executed first by the characterizations of UV-vis, Raman, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electronic measurements. Then, the role of CDs in enhancing DNAm sensitivity of CD-LEG-FET is manifested by comparing it with that of CD-free LEG-FET. Third, the captured SEPT9 genes on CD-LEG-FETs by different probes are evaluated, and the optimized temperature for hybridizing the target ssDNA sequences is determined to be 48 °C. Furthermore, the detection sensitivity for the low-quantity of DNA samples is demonstrated to be as low as 2 ng. Finally, the methylation degree of the tumor and corresponding noncancerous tissue DNA samples were examined by the proposed electric method and methylight assay in parallel. The diagnostic value of the electrical assay is confirmed by using the receiver operating characteristic curves; meanwhile, the superiority of the CD-LEG-FET platform is found to present a methylation panorama of the target gene.

Regulation of cell binding and entry by DNA origami mediated spatial distribution of aptamers

Understanding the effects of surface density and distribution of ligands on their recognition and binding is critical for the regulation of cellular behaviors. However, the correlation of spatial distribution of ligands particularly with cell binding and subsequent entry has been rarely explored. Here, we describe the use of DNA origami mediated spatial distribution of aptamers to regulate receptor ligand binding. Aptamers with tunable yet accurate density and orientation are anchored by virtue of the convenience and precision of DNA origami nanoboxes (DONs) to tailor their attachments. Cell assays demonstrate that the binding of DONs depends on both the density and orientation of aptamers, in which two adjacent aptamers exhibit the highest cellular uptake. The spatial distribution dependent uptake is further validated by utilizing two human cancer cell lines expressed with different levels of membrane receptors. Additionally, anticancer doxorubicin loaded DONs show internalization dependent proliferation inhibition of tumor cells. DNA origami mediated spatial distribution of ligands not only provides a unique method to tune cellular behaviors, but also offers new insights for the optimization of targeted drug delivery for cancer treatment.

Polyethylene Glycol6000/carbon Nanodots as Fluorescent Bioimaging Agents

Photoluminescent nanomaterials have immense potential for use in biological systems due to their excellent fluorescent properties and small size. Traditional semiconductor quantum dots are heavy-metal-based and can be highly toxic to living organisms, besides their poor photostability and low biocompatibility. Nano-sized carbon quantum dots and their surface-modified counterparts have shown improved characteristics for imaging purposes. We used 1,3, 6-trinitropyrene (TNP) and polyethylene glycol6000 (PEG6000) in a hydrothermal method to prepare functional polyethylene glycol6000/carbon nanodots (PEG6000/CDs) and analyzed their potential in fluorescent staining of different types of bacteria. Our results demonstrated that PEG6000/CDs stained the cell pole and septa of gram-positive bacteria B. Subtilis and B. thuringiensis but not those of gram-negative bacteria. The optimal concentration of these composite nanodots was approximately 100 ppm and exposure times varied across different bacteria. The PEG6000/CD composite had better photostability and higher resistance to photobleaching than the commercially available FM4-64. They could emit two wavelengths (red and green) when exposed to two different wavelengths. Therefore, they may be applicable as bioimaging molecules. They can also be used for differentiating different types of bacteria owing to their ability to differentially stain gram-positive and gram-negative bacteria.

Bioinspired DNA nanocockleburs for targeted delivery of doxorubicin

A variety of three-dimensional DNA assemblies have been proposed as drug carriers owing to their good biocompatibility and easy fabrication. In this study, inspired by the structure of cockleburs, a novel aptamer-tethered DNA assembly was developed for effective targeted drug delivery. The Apt-nanocockleburs were fabricated via a facile process of DNA base pairing: four complementary DNA single strands, including one aptamer-ended strand and three sticky-end strands, were applied to pair with each other. The main body of the nanocockleburs can load doxorubicin (Dox) whilst the covered aptamer spines bind to the target MCF-7 cells. The self-assembled Apt-nanocockleburs exhibit higher cell uptake as well as increased cytotoxicity to MCF-7 cells than DNA nanocockleburs without aptamers. This study provided a DNA constructing platform to produce new drug carriers with high selectivity for cancer targeted drug delivery.

AS1411 aptamer modified carbon dots via polyethylenimine-assisted strategy for efficient targeted cancer cell imaging

OBJECTIVES

Carbon dots (CDs), as a fascinating class of fluorescent carbon nanomaterials, have been proven to be powerful tools in the field of bioimaging and biosensing due to their small size, suitable photostability and favourable biocompatibility. However, the cellular uptake of free CDs lacks selectivity and the same negative charges as cell membranes may cause inefficient cell internalization. In this study, an efficient detecting and targeting nanosystem was developed based on the DNA aptamer AS1411 modified CDs with polyethyleneimine (PEI) as connecting bridge.

MATERIALS AND METHODS

Hydrothermally prepared CDs were assembled with positive-charged PEI, followed by conjugation with AS1411 through electrostatic interaction to form CDs-PEI-AS1411 nanocomplexes. The CDs, CDs-PEI and CDs-PEI-AS1411 were characterized by transmission electron microscopy (TEM), fourier transform infrared (FTIR) spectra, UV-vis spectra, zeta potential measurements and capillary electrophoresis characterizations. The cytotoxicity investigation of the CDs-PEI-AS1411 and CDs-PEI in both MCF-7 and L929 cells was carried out by the CCK-8 assay. The cellular uptake of the CDs-PEI-AS1411 was studied with confocal microscopy and flow cytometry.

RESULTS

The as-prepared nanosystem possessed good photostability and no obvious cytotoxicity. On the basis of the confocal laser scanning microscope observation and the flow cytometry studies, the cellular uptake of CDs-PEI-AS1411 nanosystem in MCF-7 cells was significantly higher than that of L929 cells, which revealed the highly selective detection ability of nucleolin-positive cells.

CONCLUSIONS

The results of this study indicated that the CDs-PEI-AS1411 nanosystem had a potential value in cancer cell targeted imaging.

Redox-Sensitive Gelatin/Silica-Aptamer Nanogels for Targeted siRNA Delivery

RNA interference (RNAi) has potential advantages over other gene therapy approaches due to its high specificity and the ability to inhibit target gene expression. However, the stability and tissue-specific delivery of siRNA remain as the biggest obstacles for RNAi therapeutics. Here, we developed such a system by conjugating gelatin-based nanogels with the nucleolin-targeted AS1411 aptamer and deoxynucleotide-substituted siRNA together (Apt-GS/siRNA) via a disulfide linker to achieve transient docking of siRNA. These Apt-GS/siRNA nanogels demonstrated favorable release of siRNA under reducing conditions owing to disulfide cleavage. Furthermore, this smart system could electively release siRNA into the cytosol in nucleolin-positive cells (A549) by a glutathione-triggered disassembly and subsequently efficient RNAi for luciferase. Besides, disulfide-equipped Apt-GS nanogels showed good biocompatibility in vitro. Taken together, this redox-responsive, tumor-targeting smart nanogels display great potential in exploiting functionalized siRNA delivery and tumor therapy.

Bioimaging Applications of Carbon Nanodots: A Review

Carbon nanodots (CNDs) is the newest member of carbon-based nanomaterials and one of the most promising for the development of new, advanced applications. Owing to their unique and unparalleled physicochemical and photoluminescent properties, they are considered to be a rising star among nanomaterials. During the last decade, many applications have been developed based on CNDs. Among others, they have been used as bioimaging agents to label cells and tissues. In this review, we will discuss the advancements in the applications of CNDs in in the field of imaging, in all types of organisms (i.e., prokaryotes, eukaryotes, and animals). Selective imaging of one type of cells over another, imaging of (bio)molecules inside cells and tumor-targeting imaging are some of the studies that will be discussed hereafter. We hope that this review will assist researchers with obtaining a holistic view of the developed applications and hit on new ideas so that more advanced applications can be developed in the near future.

A novel theranostic system of AS1411 aptamer-functionalized albumin nanoparticles loaded on iron oxide and gold nanoparticles for doxorubicin delivery

Recently DNA aptamers have attracted remarkable attention as possible targeting ligands since selective targeting of cancer cells is a critical step in cancer diagnosis and therapy. Here, the development of AS1411 aptamer-functionalized albumin nanoparticles loaded on iron oxide and gold nanoparticles is reported for target delivery of the well-known anticancer drug of doxorubicin (Dox). Iron oxide nanoparticles (IONPs) and gold nanoparticles (GNPs) were prepared by ultrasound-assisted and controlled seeded growth synthetic methods, respectively. The nanocarrier was synthesized by a desolvation cross-linking method and characterized by dynamic light scattering, zeta potential measurement, thermogravimetric analysis, transmission electron microscopy, as well as vibrating sample magnetometer. The synthesized nanoparticles were found to be spherical with an average diameter of 120 nm and zeta potential of about -50.3 mV. The in-vitro anti-tumor effect of the designed delivery vehicle on MCF7 and SKBR3 human cancer cells was evaluated by MTT assay. The experimental results revealed that it could significantly inhibit the proliferation of cancerous cells. Moreover, GNPs and IONPs with the coating of albumin did not show any toxicity. AS1411 aptamer-functionalized nanoparticles improved cellular uptake and efficiency to MCF7 breast cancer cells as compared to non-targeting nanoparticles because of the high affinity of mentioned aptamer toward the overexpressed nucleolin on MCF7 cell surface.

Fluorometric label-free aptasensor for detection of the pesticide acetamiprid by using cationic carbon dots prepared with cetrimonium bromide

A fluorometric aptamer-based method is described for sensitive detection of the pesticide acetamiprid. Cationic carbon dots (cCDs) with blue fluorescence were synthesized from cetrimonium bromide (CTAB) by a hydrothermal method. In the presence of the acetamiprid aptamers with a negative charge, the aptamers bind to the surface of the cCDs due to electrostatic attraction. As a result, the fluorescence of the cCDs is quenched partially (the best measurement was done at excitation/emission wavelengths of 360/445 nm). If acetamiprid is added to the above system, the aptamer binds to acetamiprid as a target with strong and specific affinity. Therefore, fluorescence increases proportionally to the acetamiprid concentrations. The aptasensor has a detection limit of 0.3 nM with a dynamic range from 1.6 to 120 nM which reveals that the method is sensitive in comparison to the other techniques. The selectivity of the method towards various pesticides was also studied and found to be adequate. The sensor was applied for the determination of acetamiprid in (spiked) wastewater, tap water, and tomatoes to underpin its practicability. Graphical abstract Cationic CDs (cCDs) were synthesized from cetrimonium bromide by a hydrothermal method. The addition of the negatively charged acetamiprid aptamer to a solution containing cCDs, the cCDs will be coated by the aptamer. This causes the blue fluorescence of the cCDs partially is quenched. If acetamiprid (ACP) is then added, the aptamer will bind to acetamiprid with strong and specific affinity. Hence, fluorescence will be gradually restored.

The advanced role of carbon quantum dots in nanomedical applications

Carbon quantum dots (CQDs) have emerged as a potential material in the diverse fields of biomedical applications due to their numerous advantageous properties including fluorescence, water solubility, biocompatibility, low toxicity, small size and ease of modification, inexpensive scale-up production, and versatile conjugation with other nanoparticles. Thus, CQDs became a preferable choice in various biomedical applications such as nanocarriers for drugs, therapeutic genes, photosensitizers, and antibacterial molecules. Further, their potentials have also been verified in multifunctional diagnostic platforms, cellular and bacterial bio-imaging, development of theranostics nanomedicine, etc. This review provides a concise insight into the progress and evolution in the field of CQD research with respect to methods/materials available in bio-imaging, theranostics, cancer/gene therapy, diagnostics, etc. Further, our discussion is extended to explore the role of CQDs in nanomedicine which is considered to be the future of biomedicine. This study will thus help biomedical researchers in tapping the potential of CQDs to overcome various existing technological challenges.

Spectrofluorometric genotyping of single nucleotide polymorphisms using carbon dots as fluorophores

In the present manuscript, a new spectrofluorometric method for the genotyping of various single nucleotide polymorphisms (SNPs) using carbon dots (CDs) is investigated. For the construction of the assay, thiolated probe DNA is self-assembled on a gold surface via sulfur‑gold chemistry and afterward, the probe is partially hybridized with a longer target DNA strand. Subsequently, the unhybridized section of the target DNA is hybridized with a capture DNA to form the DNA double-helix self-assembled monolayer on the gold surface. Finally, CDs surface amine groups are covalently attached to the 5' phosphate groups of various monobases (MB-CDs) using phosphoramidite chemistry. In this method, genotyping of SNPs is based on following the changes in fluorescence intensity of the MB-CDs suspensions before and after incubation with DNA modified gold surface. The assay is straightforward with no need for target labeling and is sensitive and low cost enough to genotype various SNPs independent of their position in a DNA double helix with an acceptable limit of detections in picomolar ranges.

Highly Biocompatible, Fluorescence, and Zwitterionic Carbon Dots as a Novel Approach for Bioimaging Applications in Cancerous Cells

Highly biocompatible, excellently photostable, nitrogen- and sulfur-containing novel zwitterionic carbon dots (CDs) were synthesized by microwave-assisted pyrolysis. The size of CDs were 2-5 nm, with an average size of 2.61 ± 0.7 nm. CDs were characterized by UV/vis spectroscopy, fluorescence spectroscopy, zeta potential, Fourier-transform infrared spectroscopy, X-ray diffraction, and time-resolved fluorescence spectroscopy. CDs were known to emit blue fluorescence when excited at 360 nm, that is, UV region, and emit in the blue region of visible spectrum, that is, at 443 nm. CDs showed excitation-independent photoluminescence behavior and were highly fluorescent even at lower concentration under UV light. These CDs were highly fluorescent in nature, with the quantum yield being as high as 80%, which is comparable to that of organic dyes. The CDs were further used to image two different oral cancer cell lines, namely, FaDu (human pharyngeal carcinoma) and Cal-27 (human tongue carcinoma). The cell viability assay demonstarted that CDs were highly biocompatible, which was further confirmed by the side scattering studies as no change in the granularity was observed even at the highest concentration of 1600 μg/mL. The generation of reactive oxygen species (ROS) was also investigated and negligible generaton of ROS was detected. In addition to that, the uptake phenomenon, cell cycle analysis, exocytosis, and cellular uptake at 4 °C and in the presence of ATP inhibitor were studied. It was found that CDs easily cross the plasma membrane without hampering the cellular integrity.

Biogreen Synthesis of Carbon Dots for Biotechnology and Nanomedicine Applications

Over the past decade, carbon dots have ignited a burst of interest in many different fields, including nanomedicine, solar energy, optoelectronics, energy storage, and sensing applications, owing to their excellent photoluminescence properties and the easiness to modify their optical properties through doping and functionalization. In this review, the synthesis, structural and optical properties, as well as photoluminescence mechanisms of carbon dots are first reviewed and summarized. Then, we describe a series of designs for carbon dot-based sensors and the different sensing mechanisms associated with them. Thereafter, we elaborate on recent research advances on carbon dot-based sensors for the selective and sensitive detection of a wide range of analytes, including heavy metals, cations, anions, biomolecules, biomarkers, nitroaromatic explosives, pollutants, vitamins, and drugs. Lastly, we provide a concluding perspective on the overall status, challenges, and future directions for the use of carbon dots in real-life sensing.

Aluminium oxide nanoparticles induce structural changes in tau and cytotoxicity of the neuroblastoma cell line

The application of nanomaterials in the healthy system may induce some neurodegenerative diseases initiated by tau folding and neuronal cell death. Herein, aluminium oxide nanoparticles (Al₂O₃ NPs) were synthesized and characterized by XRD, TEM, DLS and zeta potential investigations. Afterwards, the interaction of Al₂O₃ NPs with tau protein was investigated by fluorescence and CD spectroscopic methods. The molecular docking and molecular dynamic were also run to explore the binding site and conformational changes of tau after interaction with Al₂O₃ cluster. Moreover, the MTT, LDH, caspase-9/-3 and flow cytometry assays were done to explore the Al₂O₃ NPs-induced cytotoxicity against SH-SY5Y cells. It was revealed that Al₂O₃ NPs bind to tau protein and form a static complex and fold the structure of tau toward a more packed structure. Molecular docking and molecular dynamic investigations revealed that NPs bind to the hydrophilic residues of the tau segments and promote some marginal structural folding of tau segment. The cellular assays displayed that Al₂O₃ NPs can elicit cell mortality through membrane leakage, caspase-9/-3 activations, and induction of both apoptosis and necrosis. This data may indicate that NPs can induce some adverse effects on the biological systems.

Exploring the conformational behaviour and aggregation properties of lipid-conjugated AS1411 aptamers

AS1411 is a nucleolin-binding aptamer which attracted great interest as active targeting ligand for the selective delivery of therapeutic agents to tumour cells. In this work we selected three AS1411 derivatives 5'-conjugated with lipophilic tails and studied their properties in view of their application in liposomial formulations and/or lipid coated-nanoparticles for targeted therapies. The conformational behaviour of these AS1411 analogs has been investigated in comparison with the unmodified aptamer by CD, UV, PAGE, SEC-HPLC, DLS and thioflavin T (ThT) fluorescence assays to get insight in their secondary structure and aggregation properties. This study has been performed in pseudo-physiological buffers mimicking the extra- and intracellular environments, and at different concentrations in the μM range, paying special attention to the effects of the lipophilic tail on the overall aptamer conformation. The 5'-lipidated AS1411 derivatives proved to fold into stable, parallel unimolecular G-quadruplex structures, forming large aggregates, mainly micelles, at conc. >10 μM. Preliminary bioscreenings on selected cancer cells showed that these derivatives are less cytotoxic than AS1411, but maintain a similar biological behaviour. This study demonstrated that lipophilic tails dramatically favour the formation of AS1411 aggregates, however not impairing the formation and thermal stability of its peculiar G4 motifs.

Fluorescence Sensing Using DNA Aptamers in Cancer Research and Clinical Diagnostics

Among the various advantages of aptamers over antibodies, remarkable is their ability to tolerate a large number of chemical modifications within their backbone or at the termini without losing significant activity. Indeed, aptamers can be easily equipped with a wide variety of reporter groups or coupled to different carriers, nanoparticles, or other biomolecules, thus producing valuable molecular recognition tools effective for diagnostic and therapeutic purposes. This review reports an updated overview on fluorescent DNA aptamers, designed to recognize significant cancer biomarkers both in soluble or membrane-bound form. In many examples, the aptamer secondary structure switches induced by target recognition are suitably translated in a detectable fluorescent signal using either fluorescently-labelled or label-free aptamers. The fluorescence emission changes, producing an enhancement (“signal-on”) or a quenching (“signal-off”) effect, directly reflect the extent of the binding, thereby allowing for quantitative determination of the target in bioanalytical assays. Furthermore, several aptamers conjugated to fluorescent probes proved to be effective for applications in tumour diagnosis and intraoperative surgery, producing tumour-type specific, non-invasive in vivo imaging tools for cancer pre- and post-treatment assessment.