Preventing biofilm formation and eradicating pathogenic bacteria by Zn doped histidine derived carbon quantum dots

Bacterial infections are of major medical concern due to antibiotic resistance. Carbon quantum dots (CDs) have emerged as potentially excellent biomaterials for multifunctional applications due to their low toxicity, outstanding water solubility, high fluorescence, and high biocompatibility. All of these properties allow CDs to be exceptional biomaterials for inhibiting the growth of bacteria and stopping biofilm formation due to their strong binding affinity, cell wall penetration, and solubilizing biofilm in water. Here, we describe a strategy for one-pot synthesis of histidine-derived zinc-doped N-doped CDs (Zn-NCDs) by a hydrothermal method for inhibiting the growth of both Gram-positive and Gram-negative bacteria without harming mammalian cells. The NCDs and Zn-NCDs showed uniform sizes (∼6 nm), crystallinity, good photostability, high quantum yield (76%), and long decay time (∼5 ns). We also studied their utilization for live cell bio-imaging and the antimicrobial properties towards the Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa. Importantly, the Zn-NCDs could penetrate the biofilm and bacterial cell wall to effectively inhibit the growth of bacteria and subsequently inhibit biofilm formation. Thus, the structure, chemical composition, and low toxicity properties of the newly-developed Zn-NCDs exemplify a promising novel method for the preparation of nano-level antibacterial drugs.

High Quantum Yield Amino Acid Carbon Quantum Dots with Unparalleled Refractive Index

Carbon quantum dots (CQDs) are one of the most promising types of fluorescent nanomaterials due to their exceptional water solubility, excellent optical properties, biocompatibility, chemical inertness, excellent refractive index, and photostability. Nitrogen-containing CQDs, which include amino acid based CQDs, are especially attractive due to their high quantum yield, thermal stability, and potential biomedical applications. Recent studies have attempted to improve the preparation of amino acid based CQDs. However, the highest quantum yield obtained for these dots was only 44%. Furthermore, the refractive indices of amino acid derived CQDs were not determined. Here, we systematically explored the performance of CQDs prepared from all 20 coded amino acids using modified hydrothermal techniques allowing more passivation layers on the surface of the dots to optimize their performance. Intriguingly, we obtained the highest refractive indices ever reported for any CQDs. The values differed among the amino acids, with the highest refractive indices found for positively charged amino acids including arginine-CQDs (∼2.1), histidine-CQDs (∼2.0), and lysine-CQDs (∼1.8). Furthermore, the arginine-CQDs reported here showed a nearly 2-fold increase in the quantum yield (∼86%) and a longer decay time (∼8.0 ns) compared to previous reports. In addition, we also demonstrated that all amino acid based CQD materials displayed excitation-dependent emission profiles (from UV to visible) and were photostable, water-soluble, noncytotoxic, and excellent for high contrast live cell imaging or bioimaging. These results indicate that amino acid based CQD materials are high-refractive-index materials applicable for optoelectronic devices, bioimaging, biosensing, and studying cellular organelles in vivo. This extraordinary RI may be highly useful for exploring cellular elements with different densities.

BSA-assisted hydrothermal conversion of MoS2 nanosheets into quantum dots with high yield and bright fluorescence for constructing a sensing platform via dual quenching effects

With large surface-responsive and excitation-dependent fluorescence, two-dimensional fluorescent quantum dots (QDs) have been receiving tremendous attention to develop their facile synthetic approaches and/or expand their promising applications. Here, a two-step strategy is demonstrated for high-yield production of MoS₂ QDs from MoS₂ powder through first sonication-driven exfoliation and subsequent hydrothermal splitting with the assistance of bovine serum albumin (BSA). Experimentally, ∼100 nm-sized MoS₂ nanosheets are ultrasonically exfoliated from MoS₂ powder in a BSA solution, and further hydrothermally split into ∼ 8.2 nm-sized QDs (NQDs) at 200 °C. In addition to their excellent stability/dispersibility in aqueous solution, the resultant MoS₂ NQDs also exhibit much brighter blue fluorescence than those synthesized by other methods. The strong fluorescence is significantly quenched by p-nitrophenol for constructing a sensitive sensor with high selectivity, which is attributed to dual quenching effects from inner filter effect (IFE) and fluorescence resonance energy transfer (FRET). Interestingly, with the increment of pH from 5 to 10, the ratio of IFE in fluorescence quenching gradually decreases accompanied by an increment of FRET ratio, resulting in the high sensitivity and responsivity for detecting p-nitrophenol at a wide range of pH. Clearly, the MoS₂ NQD-based sensing approach demonstrates a promising potential for selective detection and fast analysis of pollutants in environment monitoring and security screening.

Carbon dot-based therapeutics for combating drug-resistant bacteria and biofilm infections in food preservation

Drug-resistant bacteria are caused by antibiotic abuse and/or biofilm formation and have become a threat to the food industry. Carbon dot (CD)-based nanomaterials are a very promising tools for combating pathogenic and spoilage bacteria, and they possess exceptional and adjustable photoelectric and chemical properties. In view of the rapid development of CD-based nanomaterials and their increasing popularity in the food industry, a comprehensive and updated review is needed to summarize their antimicrobial mechanisms and applications in foods. This review discusses the synthesis of CDs, antimicrobial mechanisms, and their applications for extending the shelf life of food. It includes the synthesis of CDs using small molecules, polymers, and biomass. It also discusses the different antimicrobial mechanisms of CDs and their use as antibacterial agents and carriers/ligands. CD-based materials have proven effective against pathogenic and spoilage bacteria in food by inhibiting planktonic bacteria and biofilms. Optimization of the production parameters of CDs can help them achieve a full-spectral response, but degradability still requires further research.

Development of Doped Carbon Quantum Dot-Based Nanomaterials for Lubricant Additive Applications

The development of advanced lubricants is essential for the pursuit of energy efficiency and sustainable development. In order to improve the properties of lubricating fluids, high-performance lubricating additives are required. In recent research studies, carbon nanomaterials such as fullerenes, carbon nanotubes, and graphene have been examined as lubricating additives to water or oil. Lubricating oils are well known for the presence of additives, especially friction-reducers and anti-wear additives. As part of this work, we have studied the advancement in the research and development of carbon dot (CD)-based lubricant additives by presenting a number of several applications of CD-based additives. We have also highlighted the friction-reducing properties and anti-wear properties of CDs and their lubrication mechanism along with some challenges and future perspectives of CDs as an additive. CDs are carbon nanomaterials that are synthesized from single-atom-thick sheets containing a large number of oxygen-containing functional groups; they have gained increasing attention as friction-reducing and antiwear additives. CDs have gradually been revealed to have exceptional tribological properties, particularly acting as additives to lubricating base oils. In our final section, we discuss the main challenges, future research directions, and a number of suggestions for a complete functionalized or hybrid doped CD-based material.

Organic quantum dots: An ultrasmall nanoplatform for cancer theranostics

Tumours are the second leading cause of death globally, generating alterations in biological interactions and, as a result, malfunctioning of crucial genetic traits. Technological advancements have made it possible to identify tumours at the cellular level, making transcriptional gene variations and other genetic variables more easily investigated. Standard chemotherapy is seen as a non-specific treatment that has the potential to destroy healthy cells while also causing systemic toxicity in individuals. As a result, developing new technologies has become a pressing necessity. QDs are semiconductor particles with diameters ranging from 2 to 10 nanometers. QDs have grabbed the interest of many researchers due to their unique characteristics, including compact size, large surface area, surface charges, and precise targeting. QD-based drug carriers are well known among the many nanocarriers. Using QDs as a delivery approach enhances solubility, lengthens retention time, and reduces the harmful effects of loaded medicines. Several varieties of quantum dots used in drug administration are discussed in this article, along with their chemical and physical characteristics and manufacturing methods. Furthermore, it discusses the role of QDs in biological, medicinal, and theranostic applications.

A Strategic Review on Carbon Quantum Dots for Cancer-Diagnostics and Treatment

The understanding of the genesis of life-threatening cancer and its invasion calls for urgent development of novel technologies for real-time observations, early diagnosis, and treatment. Quantum dots (QDs) grabbed the spotlight in oncology owing to their excellent photostability, bright fluorescence, high biocompatibility, good electrical and chemical stability with minimum invasiveness. Recently, carbon QDs (CQDs) have become popular over toxic inorganic QDs in the area of bioimaging, biosensing, and drug delivery. Further, CQDs derived from natural sources like biomolecules and medicinal plants have drawn attention because of their one-pot, low-cost and ease of synthesis, along with remarkable tunable optical properties and biocompatibility. This review introduces the synthesis and properties of CQDs derived from natural sources, focusing on the applicability of CQD-based technologies as nano-theranostics for the diagnosis and treatment of cancer. Furthermore, the current issues and future directions for the transformation of CQDs-based nanotechnologies to clinical applications are highlighted.

Construction of N-CDs and Calcein-Based Ratiometric Fluorescent Sensor for Rapid Detection of Arginine and Acetaminophen

In our study, a unique ratiometric fluorescent sensor for the rapid detection of arginine (Arg) and acetaminophen (AP) was constructed by the integration of blue fluorescent N-CDs and yellowish-green fluorescent calcein. The N-CD/calcein ratiometric fluorescent sensor exhibited dual emission at 435 and 519 nm under the same excitation wavelength of 370 nm, and caused potential Förster resonance energy transfer (FRET) from N-CDs to calcein. When detecting Arg, the blue fluorescence from the N-CDs of the N-CD/calcein sensor was quenched by the interaction of N-CDs and Arg. Then, the fluorescence of our sensor was recovered with the addition of AP, possibly due to the stronger association between AP and Arg, leading to the dissociation of Arg from N-CDs. Meanwhile, we observed an obvious fluorescence change from blue to green, then back to blue, when Arg and AP were added, exhibiting the “on–off–on” pattern. Next, we determined the detection limits of the N-CD/calcein sensor to Arg and AP, which were as low as 0.08 μM and 0.02 μM, respectively. Furthermore, we discovered that the fluorescence changes of the N-CD/calcein sensor were only responsible for Arg and AP. These results suggested its high sensitivity and specificity for Arg and AP detection. In addition, we have successfully achieved its application in bovine serum samples, indicating its practicality. Lastly, the logic gate was generated by the N-CD/calcein sensor and presented its good reversibility. Overall, we have demonstrated that our N-CD/calcein sensor is a powerful sensor to detect Arg and AP and that it has potential applications in biological analysis and imaging.

Synthesis of Doped/Hybrid Carbon Dots and Their Biomedical Application

Carbon dots (CDs) are a novel type of carbon-based nanomaterial that has gained considerable attention for their unique optical properties, including tunable fluorescence, stability against photobleaching and photoblinking, and strong fluorescence, which is attributed to a large number of organic functional groups (amino groups, hydroxyl, ketonic, ester, and carboxyl groups, etc.). In addition, they also demonstrate high stability and electron mobility. This article reviews the topic of doped CDs with organic and inorganic atoms and molecules. Such doping leads to their functionalization to obtain desired physical and chemical properties for biomedical applications. We have mainly highlighted modification techniques, including doping, polymer capping, surface functionalization, nanocomposite and core-shell structures, which are aimed at their applications to the biomedical field, such as bioimaging, bio-sensor applications, neuron tissue engineering, drug delivery and cancer therapy. Finally, we discuss the key challenges to be addressed, the future directions of research, and the possibilities of a complete hybrid format of CD-based materials.

Ultrasonic-Assisted Synthesis of N-Doped, Multicolor Carbon Dots toward Fluorescent Inks, Fluorescence Sensors, and Logic Gate Operations

Over past decades, the multicolor carbon dots (M-CDs) have attracted enormous attentions due to their tunable photoluminescence and versatile applications. Herein, the nitrogen-doped (N-doped) M-CDs including green, chartreuse, and pink emissive CDs are successfully synthesized by ultrasonic treatment of kiwifruit juice with different additive reagents such as ethanol, ethylenediamine, and acetone. Owing to their strong fluorescence upon irradiation with 365 nm UV light, the highly water-soluble M-CDs present great potential in the anticounterfeit field as fluorescent inks. Particularly, the resulting green emission CDs (G-CDs) with excellent fluorescence and stability are applied as a label-free probe model for “on–off” detection of Fe3+. The fluorescence of G-CDs is significantly quenched by Fe3+ through static quenching. The nanoprobe demonstrates good selectivity and sensitivity toward Fe3+ with a detection limit of ~0.11 μM. Besides, the quenched fluorescence of G-CDs by Fe3+ can be recovered by the addition of PO43− or ascorbic acid (AA) into the CDs/Fe3+ system to realize the “off–on” fluorescent process. Furthermore, NOT and IMPLICATION logic gates are constructed based on the selection of Fe3+ and PO43− or AA as the inputs, which makes the G-CD-based sensors utilized as various logic gates at molecular level. Therefore, the N-doped M-CDs hold promising prospects as competitive candidates in monitoring the trace species, applications in food chemistry, anticounterfeit uses, and beyond.

Nanosensors Based on Structural Memory Carbon Nanodots for Ag+ Fluorescence Determination

Ag⁺ pollution is of great harm to the human body and environmental biology. Therefore, there is an urgent need to develop inexpensive and accurate detection methods. Herein, lignin-derived structural memory carbon nanodots (C_SM-dots) with outstanding fluorescence properties were fabricated via a green method. The mild preparation process allowed the C_SM-dots to remain plentiful phenol, hydroxyl, and methoxy groups, which have a specific interaction with Ag⁺ through the reduction of silver ions. Further, the sulfur atoms doped on C_SM-dots provided more active sites on their surface and the strong interaction with Ag nanoparticles. The C_SM-dots can specifically bind Ag⁺, accompanied by a remarkable fluorescence quenching response. This “turn-off” fluorescence behavior was used for Ag⁺ determination in a linear range of 5–290 μM with the detection limit as low as 500 nM. Furthermore, findings showed that this sensing nano-platform was successfully used for Ag⁺ determination in real samples and intracellular imaging, showing great potential in biological and environmental monitoring applications.

Synthesis and modification of carbon dots for advanced biosensing application

There has been an explosion of interest in the use of nanomaterials for biosensing applications, and carbonaceous nanomaterials in particular are at the forefront of this explosion. Carbon dots (CDs), a new type of carbon material, have attracted extensive attention due to their fascinating properties, such as small particle size, tunable optical properties, good conductivity, low cytotoxicity, and good biocompatibility. These properties have enabled them to be highly promising candidates for the fabrication of various high-performance biosensors. In this review, we summarize the top-down and bottom-up synthesis routes of CDs, highlight their modification strategies, and discuss their applications in the fields of photoluminescence biosensors, electrochemiluminescence biosensors, chemiluminescence biosensors, electrochemical biosensors and fluorescence biosensors. In addition, the challenges and future prospects of the application of CDs for biosensors are also proposed.

Preparation of N/S doped carbon dots and their application in nitrite detection

Detection of carcinogens is generally recognized to be meaningful, especially for nitrites (NO₂⁻). Here blue-green fluorescent carbon dots (CDs) were successfully synthesized by using p-aminobenzenesulfonic acid, and their surfaces were identified to be abundant in the functional groups of amino, hydroxyl, and sulfuric acid. Importantly, the sulfuric acid group and aromatic primary ammonia groups on the surfaces of CDs showed the interactions with the nitrites to cause fluorescence quenching. The novel CDs showed high sensitivity and selectivity for NO₂⁻ detection with a low detection limit of 0.03 mM in water due to the fluorescence quenching effect of the CDs. Consequently, the proposed CDs here may provide a new way of monitoring NO₂⁻ in the target samples.

Detection of carcinogens is generally recognized to be meaningful, especially for nitrites (NO₂⁻).

Fluorescent-Nitrogen-Doped Carbon Quantum Dots Derived from Citrus Lemon Juice: Green Synthesis, Mercury(II) Ion Sensing, and Live Cell Imaging

In this study, we report a green and economical hydrothermal synthesis of fluorescent-nitrogen-doped carbon quantum dots (NCQDs) using citrus lemon as a carbon source. The prepared NCQDs possess high water solubility, high ionic stability, resistance to photobleaching, and bright blue color under ultraviolet radiation with a high quantum yield (∼31%). High-resolution transmission electron microscopy (HRTEM) results show that the prepared NCQDs have a narrow size distribution (1-6 nm) with an average particle size of 3 nm. The mercury ion (Hg2+) sensing efficiency of the NCQDs was studied, and the result indicated that the material has high sensitivity, high precision, and good selectivity for Hg2+. The limit of detection (LOD) is 5.3 nM and the limit of quantification (LOQ) is 18.3 nM at a 99% confidence level. The cytotoxicity was evaluated using MCF7 cells, and the cell viabilities were determined to be greater than 88% upon the addition of NCQDs over a wide concentration range from 0 to 2 mg/mL. Based on the low cytotoxicity, good biocompatibility, and other revealed interesting merits, we also applied the prepared NCQDs as an effective fluorescent probe for multicolor live cell imaging.

Fluorescent protein nanoparticles: Synthesis and recognition of cellular oxidation damage

Intracellular reactive oxygen species (ROS) generation are associated with many diseases. Lots of studies focus on the detection of intracellular ROS by small fluorescent molecules. However, ROS recognized by biocompatible nanoparticles are relatively less reported. It is widely known that albumin-based nanomaterials possess unique advantages in biomedical applications because they are biodegradable and biocompatible. Herein, fluorescent protein nanoparticles (PNPs) were prepared using BSA as a starting material without introducing extra fluorescent molecules. The blue fluorescent PNPs were well characterized by FL, FTIR, CD, TEM, DLS, etc. It was revealed that the PNPs exhibited two types of emissive centers through FL spectra and the fluorescence lifetimes. Further mechanism study indicated that the fluorescence of the PNPs was mainly derived from three kinds of aromatic amino acids, namely tryptophan, tyrosine and phenylalanine. Moreover, the fluorescence properties of the PNPs were tightly related to pH. The PNPs displayed excellent stabilities under harsh conditions as well as physiological conditions. In addition, the PNPs (200 μg/mL) were nontoxic to HeLa and GES-1 cell lines, showing good biocompatibility. The cellular uptake of PNPs was occurred only when the cells were stressed with glucose oxidase or H₂O₂, thereafter the bright blue fluorescence was observed, indicating that it could be utilized for the recognition of cellular oxidation damage. These findings will offer novel clues for the future synthesis of even brighter protein nanoparticles and their biomedical applications.

Tribological Anti-Wear and Extreme-Pressure Performance of Multifunctional Metal and Nonmetal Doped C-based Nanodots

Carbon nanodots (CDs) are extensively explored due to their little toxicity, excellent water solubility, and biocompatibility. Particularly, fluorescent CDs have received ever-increasing attention. Nevertheless, up to now, only a few findings have been dedicated to measuring the tribological properties of doped CDs, especially Ga doped CDs (Ga@CDs and nitrogen doped CDs (N@CDs)), and to compare their tribological properties with CDs. Here, we describe a strategy for the low-cost one-pot synthesis of CDs for tribological study. The presented research for the first time describes tribological properties and indicates a possible application of the multifunctional CDs (N@CDs, Ga@CDs, and CDs) as highly specific materials for various tests of engine oils and hydraulic oils. Further, it is stated that the doping of the CDs with various elements can tailor demanding tribological performances like anti-wear and extreme-pressure performances.

Fluorescent metal-doped carbon dots for neuronal manipulations

There is a growing need for biocompatible nanocomposites that may efficiently interact with biological tissues through multiple modalities. Carbon dots (CDs) could serve as biocompatible fluorescence nanomaterials for targeted tissue/cell imaging. Important goals toward this end are to enhance the fluorescence quantum yields of the CDs and to increase their targetability to cells. Here, sonochemistry was used to develop a one-pot synthesis of CDs, including metal-doped CDs (M@CDs), demonstrating how various experimental parameters, such as sonication time, temperature, and power of sonication affect the size of the CDs (2-10 nm) and their fluorescence properties. The highest measured quantum yield of emission was ∼16%. Similarly, we synthesized CDs doped with different metals (M@CDs) including Ga, Sn, Zn, Ag, and Au. The interaction of M@CDs with neuron-like cells was examined and showed efficient uptake and low cytotoxicity. Moreover, the influence of the M@CDs on the improvement of neurites during initiation and elongation growth phases were compared with pristine CDs. Our research demonstrates the use of M@CDs for imaging and for neuronal interactions. The M@CD nanocomposites are promising due to their biocompatibility, photo-stability and potential selective affinity, paving the way for multifunctional biomedical applications.

Biomolecule-derived quantum dots for sustainable optoelectronics

The diverse chemical functionalities and wide availability of biomolecules make them essential and cost-effective resources for the fabrication of zero-dimensional quantum dots (QDs, also known as bio-dots) with extraordinary properties, such as high photoluminescence quantum yield, tunable emission, photo and chemical stability, excellent aqueous solubility, scalability, and biocompatibility. The additional advantages of scalability, tunable optical features and presence of heteroatoms make them suitable alternatives to conventional metal-based semiconductor QDs in the field of bioimaging, biosensing, drug delivery, solar cells, photocatalysis, and light-emitting devices. Furthermore, a recent focus of the scientific community has been on QD-based sustainable optoelectronics due to the primary concern of partially mitigating the current energy demand without affecting the environment. Hence, it is noteworthy to focus on the sustainable optoelectronic applications of biomolecule-derived QDs, which have tunable optical features, biocompatibility and the scope of scalability. This review addresses the recent advances in the synthesis, properties, and optoelectronic applications of biomolecule-derived QDs (especially, carbon- and graphene-based QDs (C-QDs and G-QDs, respectively)) and discloses their merits and disadvantages, challenges and future prospects in the field of sustainable optoelectronics. In brief, the current review focuses on two major issues: (i) the advantages of two families of carbon nanomaterials (i.e. C-QDs and G-QDs) derived from biomolecules of various categories, for instance (a) plant extracts including fruits, flowers, leaves, seeds, peels, and vegetables; (b) simple sugars and polysaccharides; (c) different amino acids and proteins; (d) nucleic acids, bacteria and fungi; and (e) biomasses and their waste and (ii) their applications as light-emitting diodes (LEDs), display systems, solar cells, photocatalysts and photo detectors. This review will not only bring a new paradigm towards the construction of advanced, sustainable and environment-friendly optoelectronic devices using natural resources and waste, but also provides critical insights to inspire researchers ranging from material chemists and chemical engineers to biotechnologists to search for exciting developments of this field and consequently make an advance step towards future bio-optoelectronics.

EDTA-bonded multi-connected carbon-dots and their Eu3+ complex: preparation and optical properties

EDTA-bonded multi-connected carbon-dots (EDTA–C-dots) were prepared from carbon dot precursors and complexed with Eu³⁺ to give Eu³⁺-coordinated EDTA-bonded multi-connected carbon dots (Eu–EDTA–C-dots). Whereas EDTA–C-dots were readily soluble in DMSO, Eu–EDTA–C-dots could not be easily dissolved in DMSO, water, or other common organic solvents. The newly prepared materials were thoroughly characterized. The X-ray diffraction results showed that no crystalline phase of Eu oxides (europium oxide or europium hydroxide) could be observed in Eu–EDTA–C-dots. The infrared and UV-Vis spectra showed that coordination with Eu³⁺ ions did not damage the structure of the EDTA–C-dots. It was found that EDTA could be easily grafted on the surface of carbon dots and EDTA had minimal influence on the photoluminescence of the carbon dot matrix. In contrast, the existence of Eu³⁺ ions strongly quenched the photoluminescence of Eu–EDTA–C-dots. The measured and fitted decay lifetime indicated that Eu–EDTA–C-dots possessed two photoluminescence decay processes, i.e., radiative recombination and non-radiative recombination.

EDTA-bonded multi-connected carbon-dots (EDTA–C-dots) were prepared from carbon dot precursors and complexed with Eu³⁺ to give Eu³⁺-coordinated EDTA-bonded multi-connected carbon dots (Eu–EDTA–C-dots).

Accelerated Bone Regeneration by Nitrogen-Doped Carbon Dots Functionalized with Hydroxyapatite Nanoparticles

We investigated the osteogenic potential of nitrogen-doped carbon dots (NCDs) conjugated with hydroxyapatite (HA) nanoparticles on the MC3T3-E1 osteoblast cell functions and in a zebrafish (ZF) jawbone regeneration (JBR) model. The NCDs-HA nanoparticles were fabricated by a hydrothermal cum co-precipitation technique. The surface structures of NCDs-HA nanoparticles were characterized by X-ray diffraction; Fourier transform infrared (FTIR), UV-vis, and laser fluorescence spectroscopies; and scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS), and NMR analyses. The TEM data confirmed that the NCDs are well conjugated on the HA nanoparticle surfaces. The fluorescent spectroscopy results indicated that the NCDs-HA exhibited promising luminescent emission in vitro. Finally, we validated the chemical structure of NCDs-HA nanoparticles on the basis of FTIR, EDS, and ³¹P NMR analysis and observed that NCDs are bound with HA by electrostatic interaction and H-bonding. Cell proliferation assay, alkaline phosphatase, and Alizarin red staining were used to confirm the effect of NCDs-HA nanoparticles on MC3T3-E1 osteoblast proliferation, differentiation, and mineralization, respectively. Reverse transcriptase polymerase chain reaction was used to measure the expression of the osteogenic genes like runt-related transcription factor 2, alkaline phosphatase, and osteocalcin. ZF-JBR model was used to confirm the effect of NCDs-HA nanoparticles on bone regeneration. NCDs-HA nanoparticles demonstrated cell imaging ability, enhanced alkaline phosphatase activity, mineralization, and expression of the osteogenic genes in osteoblast cells, indicating possible theranostic function. Further, NCDs-HA nanoparticles significantly enhanced ZF bone regeneration and mineral density compared to HA nanoparticles, indicating a therapeutic potential of NCDs-HA nanoparticles in bone regeneration and fracture healing.

Ultrafine Highly Magnetic Fluorescent γ-Fe2O3/NCD Nanocomposites for Neuronal Manipulations

In this work, we describe a low-cost, two-step synthesis of composites of nitrogen-doped carbon quantum dots (NCDs) with γ-Fe2O3 (NCDs/γ-Fe2O3), which is based on a hydrothermal cum co-precipitation method. The product is a fine powder of particles having an average diameter of 9 ± 3 nm. The physical and chemical properties of NCDs/γ-Fe2O3 were studied, as well as the superconducting quantum interference device and Mossbauer analysis of the magnetic properties of these nanocomposites. The interaction of NCDs/γ-Fe2O3 nanocomposites with neuron-like cells was examined, showing efficient uptake and low toxicity. Our research demonstrates the use of the nanocomposites for imaging and for controlling the cellular motility. The NCDs/γ-Fe2O3 nanocomposites are promising because of their biocompatibility, photostability, and potential selective affinity, paving the way for multifunctional biomedical applications.

Facile one-step synthesis of highly luminescent N-doped carbon dots as an efficient fluorescent probe for chromium(vi) detection based on the inner filter effect

Label-free fluorescence assay system is designed for Cr(iv) detection.

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.

Refractive-Index Tuning of Highly Fluorescent Carbon Dots

In this manuscript, we report the refractive-index (RI) modulation of various concentrations of nitrogen-doped carbon dots (N@C-dots) embedded in poly(vinyl alcohol) (PVA) polymer. The dispersion and size distribution of N@C-dots embedded within PVA have been investigated using electron microscopy. The RI of PVA-N@C-dots can be enhanced by increasing the doping concentration of highly fluorescent C-dots (quantum yield 44%). This is demonstrated using ultraviolet-visible (UV-visible), photoluminscence, Raman, and Fourier transform infrared (FTIR) spectroscopy measurements. The Mie scattering of light on N@C-dots was applied for developing the relationship between RI tuning and absorption cross section of N@C-dots. The extinction cross section of N@C-dot thin films can be rapidly enhanced by either tuning the RI or increasing the concentration of N@C-dots. The developed method can be used as effective RI contrast for various applications such as holography creation and bioimaging.

Fluorescent Nanoparticles with Tissue-Dependent Affinity for Live Zebrafish Imaging

Carbon quantum dots (CDs) are widely investigated because of their low toxicity, outstanding water solubility, and high biocompatibility. Specifically, fluorescent CDs have attracted ever-increasing interest. However, so far, only a few studies have focused on assessing the fluorescence of nitrogen-doped CDs (N@CDs) during in vivo exposure. Here, we describe a strategy for low-cost, one-pot synthesis of N@CDs. The low toxicity and suitability of the N@CDs for fluorescence imaging are validated using zebrafish (ZF) as a model. Strong fluorescence emission from ZF embryos and larvae confirms the distribution of N@CDs in ZF. The retention of N@CDs is very stable, long lasting, and with no detectable toxicity. The presence of a strong fluorescence at the yolk sac, especially in the vicinity of the intestine, suggests that a high content of N@CDs entered the digestive system. This indicates that N@CDs may have potential imaging applications in elucidating different aspects of lipoprotein and nutritional biology, in a ZF yolk lipid transport and metabolism model. On the other hand, the presence of a strong selective fluorescence at the eyes and melanophore strips at the trunk and tail region of ZF larvae suggests that N@CDs has a high melanin-binding affinity. These observations support a novel and revolutionary use of N@CDs as highly specific bioagents for eye and skin imaging and diagnosis of defects in them. N@CDs are known for their multifunctional applications as highly specific bioagents for various biomedical applications because of their exceptional biocompatibility, photostability, and selective affinity. These characteristics were validated in the developmental ZF model.

Protein-derived carbon nanodots with an ethylenediamine-modulated structure as sensitive fluorescent probes for Cu2+detection

The increasing use of fluorescent carbon nanodots (CNDs) demonstrates their advantages for sensing applications; these include superior photostability, absence of toxicity, and rapid analytical capability.

Heteroatom-doped carbon dots: synthesis, characterization, properties, photoluminescence mechanism and biological applications

Heteroatom-doped carbon dots (CDs), due to their excellent photoluminescence (PL) properties, attracted widespread attention recently and demonstrated immense promise for diverse applications, particularly for biological applications. The objective of this feature article is to provide a comprehensive overview of the recent progress in the research and development of heteroatom-doped CDs and a detailed description of the influence of single or co-doping heteroatoms on their PL behavior. The most recent understanding and critical insights into the PL mechanism of heteroatom-doped CDs are also highlighted. Moreover, potential bio-related applications of heteroatom-doped CDs in biosensing, bioimaging, and theranostics are also reviewed. This state-of-the-art review will provide a platform for understanding the intricate details of heteroatom-doped CDs, a summary of the latest progress in the field, and related applications in biology and is expected to inspire further developments in this exciting class of materials.