Self-Enhanced Carbonized Polymer Dots for Selective Visualization of Lysosomes and Real-Time Apoptosis Monitoring

Green synthesis and multifaceted applications: challenges and innovations in carbon dot nanocomposites

This paper describes the potential of carbon dot nanocomposites (CDs) synthesized from waste materials by top-down and bottom-up state-of-the-art approaches. Through sustainable practices, wastes are converted into valuable nanomaterials, solving environmental problems and pioneering advances in nanotechnology. In this paper, an overview of the synthesis aspects of CDs is presented with the formation of their versatile nanocomposites and metal/metal oxide elements. The phase of this paper has been devoted to elaborate study of the multifaceted applications of CDs in various sectors, ranging from electronics and biomedicine to environmental remediation. Although having huge potential, CDs application is presently hampered due to limitations on scalability, stability, and reproducibility. In this review paper, most profound insights have been drawn into overcoming these barriers for clear routes toward future innovations. The present research being undertaken in this area has, therefore, underscored sustainable nanotechnology to resolve global problems and achieving technological development through green synthesis. Necessitating the efficient sewage disposal systems ensuring minimum toxin generation.

Optimization of Preparation Technology for PET-Based Carbon Dots by Response Surface Method and Its Application

The preparation of polyethylene terephthalate(PET)-based Carbon Dots (PET-CDs) using one-step hydrothermal method with PET waste, pyromellitic acid (PMA) and ammonia (NH3·H2O) as precursors is a high-value utilization strategy for PET waste, offering significant application potential. To achieve efficient recycling of PET waste, response surface methodology was adopted for to optimize the precursor ratio during the synthesis of PET-CDs with fluorescence quantum yield (QY) as the key performance indicator. The optimal preparation conditions were determined to be: 1.180 g of PET, 3.287 g of PMA, 8.969 mL of NH3·H2O, a reaction temperature of 260 °C, and a reaction time of 12 h. The as-prepared PET-CDs exhibit excitation-independent emission properties in the range from 360 nm to 440 nm, with the optimal excitation wavelength of 410 nm and the optimal emission wavelength was 485 nm, resulting in a QY of 83.34%. Structurally, PET-CDs exhibit a spherical morphology, featuring amino and carboxyl groups on their surface, with the particle size ranging from 1.61 to 4.92 nm and an average particle size of 2.88 nm. The prepared PET-CDs can be utilized in light-blocking films (LBFs) and fluorescence anti-counterfeiting technologies. The intensity of light passing through the LBFs significantly is decreased in the ultraviolet and blue light wavelength ranges, with performance comparable to commercial anti-blue light glasses. Additionally, the PET-CDs solution can be adopted for printing patterns that are visible under ultraviolet excitation and are not visible in visible light, demonstrating that PET-CDs can be employed in fluorescence anti-counterfeiting measures.

Semiconducting polymer dots for multifunctional integrated nanomedicine carriers

The expansion applications of semiconducting polymer dots (Pdots) among optical nanomaterial field have long posed a challenge for researchers, promoting their intelligent application in multifunctional nano-imaging systems and integrated nanomedicine carriers for diagnosis and treatment. Despite notable progress, several inadequacies still persist in the field of Pdots, including the development of simplified near-infrared (NIR) optical nanoprobes, elucidation of their inherent biological behavior, and integration of information processing and nanotechnology into biomedical applications. This review aims to comprehensively elucidate the current status of Pdots as a classical nanophotonic material by discussing its advantages and limitations in terms of biocompatibility, adaptability to microenvironments in vivo, etc. Multifunctional integration and surface chemistry play crucial roles in realizing the intelligent application of Pdots. Information visualization based on their optical and physicochemical properties is pivotal for achieving detection, sensing, and labeling probes. Therefore, we have refined the underlying mechanisms and constructed multiple comprehensive original mechanism summaries to establish a benchmark. Additionally, we have explored the cross-linking interactions between Pdots and nanomedicine, potential yet complete biological metabolic pathways, future research directions, and innovative solutions for integrating diagnosis and treatment strategies. This review presents the possible expectations and valuable insights for advancing Pdots, specifically from chemical, medical, and photophysical practitioners' standpoints.

Multicolor emission-based nitrogen, sulfur and boron co-doped photoluminescent carbon dots for sequential sensing of Fe3+ and cysteine: RGB color sensor and live cell imaging

Herein, a simple hydrothermal synthesis is used to prepare multiple heteroatom-doped photoluminescent carbon dots (CDs) from thiourea (N and S source) and boric acid (B source) as precursors. The optical and physicochemical properties of the as-synthesized NSB-CDs were studied using UV-Vis, photoluminescence, TEM, FT-IR, XRD, Raman, and XPS analyses. The NSB-CDs exhibited excellent stability, high photostability, pH, and ionic strength tolerance; they retained their excellent stability independent of excitation. The NSB-CDs featured small sizes of approximately 3.2 ± 0.4 nm (range: 2.0-5.0 nm) as evidenced using TEM measurements. The NSB-CDs were used as a photoluminescent sensing platform to detect Fe3+ as well as cysteine (Cys) molecules. The competitive binding of Cys to Fe3+ resulted in NSB-CDs that retained their photoluminescence. For the rapid identification and quantification of Fe3+ and Cys, NSB-CDs were developed as a "switch-on" dual-function sensing platform. The linear detection range of Fe3+ was 0-20 μM (limit of detection [LOD]: 54.4 nM) and that of Cys was 0-50 μM (LOD: 4.9 nM). We also introduced a smartphone RGB analysis method for detecting low-concentration solutions based on digital images. The NSB-CDs showed no toxicity at 100 μg/mL. Photoluminescent probes for multicolor live-cell imaging can be used with NSB-CDs at this concentration, suggesting that NSB-CDs may be promising photoluminescent probes.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

The Preparation of Golgi Apparatus-Targeted Polymer Dots Encapsulated with Carbon Nanodots of Bright Near-Infrared Fluorescence for Long-Term Bioimaging

As a vital organelle in eukaryotic cells, the Golgi apparatus is responsible for processing and transporting proteins in cells. Precisely monitoring the status of the Golgi apparatus with targeted fluorescence imaging technology is of enormous importance but remains a dramatically challenging task. In this study, we demonstrate the construction of the first Golgi apparatus-targeted near-infrared (NIR) fluorescent nanoprobe, termed Golgi-Pdots. As a starting point of our investigation, hydrophobic carbon nanodots (CNDs) with bright NIR fluorescence at 674 nm (fluorescence quantum yield: 12.18%), a narrow emission band of 23 nm, and excellent stability were easily prepared from Magnolia Denudata flowers using an ultrasonic method. Incorporating the CNDs into a polymer matrix modified with Golgi-targeting molecules allowed for the production of the water-soluble Golgi-Pdots, which showed high colloidal stability and similar optical properties compared with pristine CNDs. Further studies revealed that the Golgi-Pdots showed good biocompatibility and Golgi apparatus-targeting capability. Based on these fascinating merits, utilizing Golgi-Pdots for the long-term tracking of the Golgi apparatus inside live cells was immensely successful.

Carbon dots: Types, preparation, and their boosted antibacterial activity by photoactivation. Current status and future perspectives

Carbon dots (CDs) correspond to carbon-based materials (CBM) with sizes usually below 10 nm. These nanomaterials exhibit attractive properties such us low toxicity, good stability, and high conductivity, which have promoted their thorough study over the past two decades. The current review describes four types of CDs: carbon quantum dots (CQDs), graphene quantum dots (GQDs), carbon nanodots (CNDs), and carbonized polymers dots (CPDs), together with the state of the art of the main routes for their preparation, either by "top-down" or "bottom-up" approaches. Moreover, among the various usages of CDs within biomedicine, we have focused on their application as a novel class of broad-spectrum antibacterial agents, concretely, owing their photoactivation capability that triggers an enhanced antibacterial property. Our work presents the recent advances in this field addressing CDs, their composites and hybrids, applied as photosensitizers (PS), and photothermal agents (PA) within antibacterial strategies such as photodynamic therapy (PDT), photothermal therapy (PTT), and synchronic PDT/PTT. Furthermore, we discuss the prospects for the possible future development of large-scale preparation of CDs, and the potential for these nanomaterials to be employed in applications to combat other pathogens harmful to human health. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

The role of molecular fluorophores in the photoluminescence of carbon dots derived from citric acid: current state-of-the-art and future perspectives

Carbon dots (CDs), an emerging class of nanomaterials, have attracted considerable attention due to their intriguing photophysical properties. Despite their indisputable potential of utilization in many fascinating areas of research and life, some fundamental aspects concerning their structure and the origin of their photoluminescence (PL) properties still await clarification. The mechanism of PL emission of CDs is associated with their structure, which is dependent on the carbonization process. At the initial stages of CD synthesis via a bottom-up approach, molecular fluorophores are considered to dominate the optical characteristics of the resulting nanomaterials. In this review, the recent progress in the use of molecular state theory for explanation of the structure-property relationship in CDs is summarized. This review focuses exclusively on the molecular fluorophores existing in nanomaterials prepared from citric acid (CA) as one of the most frequent carbon sources reported for the bottom-up synthesis of CDs. Consequently, the most relevant transformations of CA and the history of molecular fluorophores derived from it are described, followed by an in-depth discussion on their relevance in understanding the specific photophysical properties of blue-, green-, and red-emitting CDs. Finally, the challenging issues and future perspectives of molecular state PL mechanism exploration in CDs are highlighted.

Electron-phonon coupling-assisted universal red luminescence of o-phenylenediamine-based carbon dots

Due to the complex core-shell structure and variety of surface functional groups, the photoluminescence (PL) mechanism of carbon dots (CDs) remain unclear. o-Phenylenediamine (oPD), as one of the most common precursors for preparing red emissive CDs, has been extensively studied. Interestingly, most of the red emission CDs based on oPD have similar PL emission characteristics. Herein, we prepared six different oPD-based CDs and found that they had almost the same PL emission and absorption spectra after purification. Structural and spectral characterization indicated that they had similar carbon core structures but different surface polymer shells. Furthermore, single-molecule PL spectroscopy confirmed that the multi-modal emission of those CDs originated from the transitions of different vibrational energy levels of the same PL center in the carbon core. In addition, the phenomenon of "spectral splitting" of single-particle CDs was observed at low temperature, which confirmed these oPD-based CDs were unique materials with properties of both organic molecules and quantum dots. Finally, theoretical calculations revealed their potential polymerization mode and carbon core structure. Moreover, we proposed the PL mechanism of red-emitting CDs based on oPD precursors; that is, the carbon core regulates the PL emission, and the polymer shell regulates the PL intensity. Our work resolves the controversy on the PL mechanism of oPD-based red CDs. These findings provide a general guide for the mechanism exploration and structural analysis of other types of CDs.

A Versatile Pep-CPDs Nanoprobe for Rapid Detection of mTBI Biomarker in Clinical Instances and Safe Fluorescence Imaging In Vivo for Improved Weight-Drop Mouse Model

Mild traumatic brain injury (mTBI) is the most common form of traumatic brain injury; however, it is the most difficult to be accurately identified in the early stage because it lacks more reliable biomarkers and detection methods. This study proposes a highly efficient system to detect a molecular biomarker for the early diagnosis of mTBI. The system was prepared by a lower cytotoxic peptide-modified fluorescent nanoprobe based on carbon polymer dots (pep-CPDs) with outstanding imaging capabilities. In vitro and in vivo tests were explored to the efficiency of pep-CPDs, inferring the good performances of cellular fluorescence imaging and in vivo imaging of mice. Moreover, an application of the versatile pep-CPDs on detecting the mTBI biomarker S100-β detection in a novel improved weight-drop mTBI mouse model and human blood samples has been successfully established. Overall, all these results indicate that the pep-CPD system is sensitive, rapid, non-toxic, and reliable for mTBI diagnosis compared with traditional detection methods. It shows a great potential in clinical and translational research and practical applications.

Non-Conventional Fluorescence and Cytotoxicity of Two Aliphatic Hyperbranched Polymer Dots Having Poly(amic acid) Structures: Implications for Labeling Nanodrug Carriers

In this study, we used one-pot A2 + B3 polymerizations to synthesize two aliphatic + alicyclic polymer dots (PDs) having non-conjugated hyperbranched structures, employing two types of dianhydrides as the A2 components, possessing bridged bicyclic alkene (PD-BT) and non-alkene (PD-ET) units, and Jeffamine T403 polyetheramine (T403) as the B3 components. We prepared PD-ET from commercially available ethylenediaminetetraacetic dianhydride (EDTAD, A2) and T403 (B3) and PD-BT from bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA, A2) and T403 (B3). These two types of PDs possessed non-conjugated hyperbranched poly(amic acid) structures with terminal amino functional groups. PD-BT and PD-ET exhibited non-conventional fluorescence with emissions at 435 and 438 nm, respectively, and quantum yields of 12.8 and 14.0%, respectively. The fluorescence intensity of PD-ET was influenced by the pH, but PD-BT was less affected because of its rigid aliphatic bridged bicyclic structure. In aqueous solutions, the sizes of the PD-BT and PD-ET nanoparticles were 3-5 nm, and their net charges can be adjusted by varying the pH. These PDs were non-cytotoxic toward human MCF-7 breast cancer cells and human keratinocyte HaCaT cells at concentrations of 50 μg mL-1 for PD-BT and 500 μg mL-1 for PD-ET. Confocal microscopic bioimaging revealed that the PDs were located within the cells after treatment for 6 h. These PDs were easy to prepare, highly water-soluble, and possessed a large number of peripheral functional groups for further modification. Combined with their non-conventional fluorescence, they appear to have potential uses in bioimaging and as drug-labeling carriers.

Simple and Green Synthesis of Carbonized Polymer dots from Nylon 66 Waste Fibers and its Potential Application

Carbonized polymer dots (CPDs) have attracted widespread attention owing to their unique properties and are usually prepared from monomers of polymers or polymers. To reduce the waste of high-value petropolymers and environmental pollution, a simple and green method for the preparation of CPDs using a hydrothermal technique based on the cross-linking enhanced emission effect was proposed, in which nylon 66 waste fibers were used as a precursor and glutaraldehyde as a cross-linking agent. The as-prepared CPDs possessed polymer/carbon hybrid structures with a 3.5 nm average diameter, and hydroxyl (-OH), carboxyl (-COOH), and amino (-NH₂) groups were present on the surface of CPDs. It can be found that the as-prepared CPDs display excitation-dependent photoluminescence emission, which is mainly attributed to the molecular state luminescence center. Because the molecular state fluorescence of CPDs could be affected by the presence of Fe³⁺ and the change of pH values, the as-prepared CPDs can be used as a probe for the detection of the concentration of Fe³⁺ and the pH variations of solution. The fluorescence intensity of CPDs was selectively quenched by Fe³⁺ in the range from 1 to 145 μM. In virtue of the static quenching of CPDs by Fe³⁺, a sensing system was fabricated for the quantitative detection of Fe³⁺, and its limit of detection was 0.1 μM. Based on the electrostatic doping/charging of CPDs, a pH sensor was fabricated. It showed that the fluorescence intensity of CPDs decreased along with the increase of pH from 2.60 to 12.6. What is more, the CPDs were found to be an alternative to traditional fluorescent inks for encryption and information storage.

Dual-Emission Carbonized Polymer Dots for Ratiometric pH Sensing, pH-Dependent Generation of Singlet Oxygen, and Imaging-Guided Dynamics Monitoring of Photodynamic Therapy

The pH environment in cancer cells has been demonstrated to display vital influences on the therapeutic effect of photodynamic therapy (PDT). It is very interesting to develop pH-responsive probes for simultaneous pH sensing and dynamics monitoring of the effects of PDT, and therefore assessing the correlation between them. In this study, a multifunctional fluorescence probe, dual-emission carbonized polymer dot (CPD) in blue and red regions, which uses ethylene imine polymer (PEI) and 4,4',4″,4‴-(porphine-5, 10, 15, 20-tetrayl) tetrakis (benzoic acid) (TCPP) as precursors through a one-step hydrothermal amide reaction, has been designed for ratiometric pH sensing, generating pH-dependent ¹O₂ for PDT of cancer cells, and investigating the dynamics effects of PDT through pH-guided imaging. The prepared CPDs were successfully used for ratiometric pH response, pH-dependent generation of ¹O₂, and dynamics monitoring PDT in HeLa cells. This study may provide an alternative strategy to prepare CPD-based theranostic integrated nanoprobes for PDT through the rational design of precursors.