Highly Heterogeneous Morphology of Cobalt Oxide Nanostructures for the Development of Sensitive and Selective Ascorbic Acid Non-Enzymatic Sensor

The surface tailored metal oxide nanostructures for the development of non-enzymatic sensors are highly demanded, but it is a big task due to the wide range of complexities during the growth process. The presented study focused on the surface modification of the heterogeneous morphology of cobalt oxide (Co₃O₄) prepared by the hydrothermal method. Further surface modification was conducted with the use of sodium citrate as a reducing and surface modifying agent for the Co₃O₄ nanostructures through the high density of oxygenated terminal groups from the citrate ions. The citrate ions enabled a significant surface modification of the Co₃O₄ nanostructures, which further improved the electrochemical properties of the Co₃O₄ material toward the design of the non-enzymatic ascorbic acid sensor in a phosphate buffer solution of pH 7.4. The morphology and crystal arrays of the Co₃O₄ nanostructures were studied by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) techniques. These physical characterizations showed the highly tailored surface features of Co₃O₄ nanostructures and a significant impact on the crystal properties. The electrochemical activity of Co₃O₄ was studied by chronoamperometry, linear sweep voltammetry, and cyclic voltammetry (CV) for the detection of ascorbic acid. The linear range of the proposed sensor was measured from 0.5 mM to 6.5 mM and a low limit of detection of 0.001 mM was also estimated. The presented Co₃O₄ nanostructures exhibited significant surface roughness and surface area, consequently playing a vital role toward the selective, sensitive, and stable detection of ascorbic acid. The use of a low cost surface modifying agent such as sodium citrate could be of great interest for the surface roughness and high surface area of nanostructured materials for the improved electrochemical properties for the biomedical, energy storage, and conversion systems.

Carbon dots surface chemistry drives fluorescent properties: New tools to distinguish isobaric peptides

The possibility to design rational carbon dots surface functionalization for specific analytical and bioanalytical applications is hindered by the lack of a full knowledge of the surface chemical features driving fluorescent properties. In this model study, we have synthesized four different peptides, three of which are isobaric and not distinguishable by common MSMS experiments. After having characterized the peptides conformations by CD analyses, we have covalently bonded all four peptides to carbon dots by using different experimental procedures, which produce different functional groups on the carbon dots surface. The peptide orientations obtained on the differently functionalized surface of the nanoparticles were different and produced different fluorescent responses. The reported results indicate the possibility to design amino and carboxyl enriched surface carbon dots to answer specific chemical requirements, paving the way for the use of these nanoparticles as a versatile and useful new chemical and biochemical tool.

Fluorescent Mechanism in Zero-Dimensional Carbon Nanomaterials: A Review

Fluorescent carbon dots (CDs) have acquired growing interest from different areas over decades. Their fascinating property of tunable fluorescence by changing the excitation wavelength has attracted researchers worldwide. Understanding the mechanisms behind fluorescence is of great importance, as they help with the synthesis and applications, significantly when narrowed down to applications with color-tunable mechanisms. But, due to a lack of practical and theoretical information, the fluorescence mechanisms of CDs remain unknown, preventing the production of CDs with desired optical qualities. This review focuses on the PL mechanisms of carbon dots. The quantum confinement effect determined the carbon core, the surface and edge states determined by various surface defects and the connected functional/chemical groups on the surface/edges, the molecular state solely determined the fluorophores in the interior or surface of the CDs, and the Crosslink Enhanced Emission Effect are the currently confirmed PL mechanisms.

Preparation of boronic acid-modified polymer dots under mild conditions and their applications in pH and glucose detection

For the first time, boronic acid-modified polymer dots (B-PDs) were fabricated by a "synthesis-modification integration" route using polyethylenimine (PEI) and phenylboronic acid as precursors. Under optimized preparation conditions, the B-PDs exhibited an average size of 2.2 nm, good water solubility, and high fluorescence quantum yield of 8.69%. The B-PDs showed reversible fluorescence response in acid solutions (blue emissions) and alkaline solutions (green emissions). The fluorescence emissions of B-PDs demonstrated an obvious red shift with varying the pH value from 1 - 13. Moreover, glucose could assemble on the surface of B-PDs due to the reversible reaction between boronic acid and cis-diols, which resulted in a blue shift of emission wavelength and an obvious increase of FL intensity at λ_ex = 380 nm based on the aggregation-induced enhancement effect. The glucose sensing method was thus developed in the range 0.0001 - 1.0 mol L^-1. Applications to real human blood and glucose injection samples demonstrated satisfactory results. The B-PDs based on the analytical method display good selectivity, wide detection range, and simplicity in preparation and detection, implying promising applications as a practical platform for biosensing.

Advances in the Methods for the Synthesis of Carbon Dots and Their Emerging Applications

Cutting-edge technologies are making inroads into new areas and this remarkable progress has been successfully influenced by the tiny level engineering of carbon dots technology, their synthesis advancement and impressive applications in the field of allied sciences. The advances of science and its conjugation with interdisciplinary fields emerged in carbon dots making, their controlled characterization and applications into faster, cheaper as well as more reliable products in various scientific domains. Thus, a new era in nanotechnology has developed into carbon dots technology. The understanding of the generation process, control on making processes and selected applications of carbon dots such as energy storage, environmental monitoring, catalysis, contaminates detections and complex environmental forensics, drug delivery, drug targeting and other biomedical applications, etc., are among the most promising applications of carbon dots and thus it is a prominent area of research today. In this regard, various types of carbon dot nanomaterials such as oxides, their composites and conjugations, etc., have been garnering significant attention due to their remarkable potential in this prominent area of energy, the environment and technology. Thus, the present paper highlights the role and importance of carbon dots, recent advancements in their synthesis methods, properties and emerging applications.

From cow manure to bioactive carbon dots: a light-up probe for bioimaging investigations, glucose detection and potential immunotherapy agent for melanoma skin cancer

Bioactive carbon dots (C-dots) with ca. 4 nm were successfully produced with singular photophysical properties, low-toxicity and interesting immunological response. The optical properties of the C-dots were investigated and the "light-up" behaviour enabled them to be explored in glucose detection and bioimaging experiments (mitochondrial selective probe). C-dots were not selective to the tumour region and several fluorescent spots were visualized spread on animal bodies. The histology investigations showed that cancer-bearing mice treated with C-dots presented a large number of regions with necrosis and inflammatory infiltrates, which were not identified for cancer-bearing mice without the treatment. These results suggested that C-dots have the potential to be explored as an immune therapy agent for melanoma skin cancer.

Sensor and Bioimaging Studies Based on Carbon Quantum Dots: The Green Chemistry Approach

Since carbon quantum dots have high photoluminescent efficiency, it has been a desired material in sensor and bioimaging applications. In recent years, the green chemistry approach has been preferred and the production of quantum dots has been reported in many studies using different precursors from natural, abundant, or waste sources. Hydrothermal, chemical oxidation, microwave supported, ultrasonic, solvothermal, pyrolysis, laser etching, solid-state, plasma, and electrochemical methods have been reported in the literature. In this review article, green chemistry strategies for carbon quantum dot synthesis is summarized and compared with conventional methods using methodologic and statistical data. Furthermore, a detailed discussion on sensor and bioimaging applications of carbon quantum dots produced with green synthesis approaches are presented with a special focus on the last decade.

Carbon dots: Current advances in pathogenic bacteria monitoring and prospect applications

Pathogenic bacterial infections are a significant threat to human safety and health. Recent researches on the application of nanoparticles as imaging, detecting agents have evidenced their huge potential for infectious disease management. Among these nanoparticles, carbon dots (CDs) have attracted much attention as a new and innovative nanoparticle owing to their unique optical and physicochemical properties as well as their higher biosafety. Thus, CDs are becoming superior candidates for imaging and detection of pathogenic bacteria. This review provides an overview of research advances and the mechanisms in the imaging and detection pathogenic bacteria such as "switch on" sensor, "on-off" sensor, förster resonance energy transfer (FRET), etc. Further, our discussion extends to exploring the antibacterial effects of CDs, which is considered to be a potentially promising antibacterial agent. This review would provide the basis and the direction for the further commercial applications of CDs in imaging, detecting and eliminating pathogenic bacteria. The challenges associated with CDs in monitoring of pathogenic bacteria and future directions in this field are also presented.

A Quantum Dot-Based FLIM Glucose Nanosensor

In the last few years, quantum dot (QD) nanoparticles have been employed for bioimaging and sensing due to their excellent optical features. Most studies have used photoluminescence (PL) intensity-based techniques, which have some drawbacks, especially when working with nanoparticles in intracellular media, such as fluctuations in the excitation power, fluorophore concentration dependence, or interference from cell autofluorescence. Some of those limitations can be overcome with the use of time-resolved spectroscopy and fluorescence lifetime imaging microscopy (FLIM) techniques. In this work, CdSe/ZnS QDs with long decay times were modified with aminophenylboronic acid (APBA) to achieve QD-APBA conjugates, which can act as glucose nanosensors. The attachment of the boronic acid moiety on the surface of the nanoparticle quenched the PL average lifetime of the QDs. When glucose bonded to the boronic acid, the PL was recovered and its lifetime was enhanced. The nanosensors were satisfactorily applied to the detection of glucose into MDA-MB-231 cells with FLIM. The long PL lifetimes of the QD nanoparticles made them easily discernible from cell autofluorescence, thereby improving selectivity in their sensing applications. Since the intracellular levels of glucose are related to the metabolic status of cancer cells, the proposed nanosensors could potentially be used in cancer diagnosis.

Date Pit Carbon Dots Induce Acidic Inhibition of Peroxidase and Disrupt DNA Repair in Antibacteria Resistance

Carbon nanodots (C-dots) are emerging as a new type of promising agent in anticancer, imaging, and new energy. Reports as well as the previous research indicate that certain C-dots can enhance targeted cancer therapy. However, in-depth mechanisms for such anticancer effect remain unclear. In this work, treatment provided by the date pit-derived C-dots, exhibits significant DNA damage; Annexin V/7-AAD-mediated apoptosis, and G2/M cell cycle arrest in prostate cancer cells. The application of C-dots to the cell generally leads to acidulation of the cell medium, cooperated with membrane compact. The date pit-derived C-dots are observed inhibiting the horseradish peroxidase. Moreover, the C-dots disrupt likely through nucleotide excision DNA repair at low dose during DNA ligation step suggesting the antimicrobial effect and targeting Pim-1, EGFR, mTOR, and DNA damage pathways in cancer cells. For the first time the detailed and novel mechanisms underlying the C-dots, derived from the date-pit, as an efficient, low-cost, and green nanomaterial are reveled for cancer therapy and anti-infection.

Small molecules derived carbon dots: synthesis and applications in sensing, catalysis, imaging, and biomedicine

Carbon dots (CDs) are the new fellow of carbon family having a size less than 10 nm and attracted much attention of researchers since the last decade because of their unique characteristics, such as inexpensive and facile synthesis methods, easy surface modification, excellent photoluminescence, outstanding water solubility, and low toxicity. Due to these unique characteristics, CDs have been extensively applied in different kind of scientific disciplines. For example in the photocatalytic reactions, drug-gene delivery system, in vitro and in vivo bioimaging, chemical and biological sensing as well as photodynamic and photothermal therapies. Mainly two types of methods are available in the literature to synthesize CDs: the top-down approach, which refers to breaking down a more massive carbon structure into nanoscale particles; the bottom-up approach, which refers to the synthesis of CDs from smaller carbon units (small organic molecules). Many review articles are available in the literature regarding the synthesis and applications of CDs. However, there is no such review article describing the synthesis and complete application of CDs derived from small organic molecules together. In this review, we have summarized the progress of research on CDs regarding its synthesis from small organic molecules (bottom-up approach) via hydrothermal/solvothermal treatment, microwave irradiation, ultrasonic treatment, and thermal decomposition techniques as well as applications in the field of bioimaging, drug/gene delivery system, fluorescence-based sensing, photocatalytic reactions, photo-dynamic therapy (PDT) and photo-thermal (PTT) therapy based on the available literature. Finally, the challenges and future direction of CDs are discussed.

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.

Artful and multifaceted applications of carbon dot in biomedicine

Carbon dots (C-dots) are luminescent carbon nanomaterial having good biocompatibility and low toxicity. The characteristic fluorescence emission property of C-dots establishes their role in optical imaging. C-dots which are superior to fluorescent dyes and semiconductor quantum dots act as a safer in vivo imaging probe. Apart from their bioimaging application, other applications in biomedicine such as drug delivery, cancer therapy, and gene delivery were studied. In this review, we present multifaceted applications of C-dots along with their synthesis, surface passivation, doping, and toxicity profile.

Carbon Nanomaterials in Biological Studies and Biomedicine

The "carbon nano-world" has made over the past few decades huge contributions in diverse scientific disciplines and technological advances. While dramatic advances have been widely publicized in using carbon nanomaterials such as fullerenes, carbon nanotubes, and graphene in materials sciences, nano-electronics, and photonics, their contributions to biology and biomedicine have been noteworthy as well. This Review focuses on the use of carbon nanotubes (CNTs), graphene, and carbon quantum dots [encompassing graphene quantum dots (GQDs) and carbon dots (C-dots)] in biologically oriented materials and applications. Examples of these remarkable nanomaterials in bio-sensing, cell- and tissue-imaging, regenerative medicine, and other applications are presented and discussed, emphasizing the significance of their unique properties and their future potential.

Controlled synthesis of soluble conjugated polymeric nanoparticles for fluorescence detection

Highly fluorescent soluble conjugated polymeric nanoparticles (SCPNs) were synthesized in confined nanoreactors and used for fluorescence sensing of glucose and Fe ion.

Potential prospects for carbon dots as a fluorescence sensing probe for metal ions

The well defined emission properties of CQDs have encouraged further investigation of their prospects in chemo-sensing applications for the identification of Cr³⁺ ions in aqueous media.