Influence of carbon dot synthetic parameters on photophysical and biological properties

Ultrasensitive Dual Fluorophore-Conjugated Carbon Dots for Intracellular pH Sensing in 3D Tumor Models

The dysregulation of pH has been linked to the onset of chronic conditions, such as cancer and neurological diseases. Consequently, the development of a highly sensitive tool for intracellular pH sensing is imperative to investigate the interplay between pH and the biochemical changes accompanying disease pathogenesis. Here, we present the development of a ratiometric fluorescent nanoprobe, NpRhoDot, designed for precisely measuring pH levels. We demonstrate its efficacy in sensitively reporting intracellular pH in monolayer A549 lung cancer cells, primary fibroblast cells, and 3D tumor spheroids derived from the DLD-1 colorectal adenocarcinoma cell line. NpRhoDot leverages a novel design, where stable carbon dots are functionalized with a pH-responsive ratiometric fluorescent probe comprising a naphthalimide-rhodamine moiety, NpRho1. This design confers NpRhoDot with the high pH sensitivity characteristics of organic fluorescent probes, along with excellent photostability up to 1 h and biocompatibility of carbon dots. Through one-photon and two-photon fluorescence microscopy, we validate the reliability of NpRhoDot for biosensing intracellular pH in monolayer and three-dimensional tumor models from pH 4 to 7.

In-Brain Multiphoton Imaging of Vaterite Cargoes Loaded with Carbon Dots

Biocompatible fluorescent agents are key contributors to the theranostic paradigm by enabling real-time in vivo imaging. This study explores the optical properties of phenylenediamine carbon dots (CDs) and demonstrates their potential for fluorescence imaging in cells and brain blood vessels. The nonlinear absorption cross-section of the CDs was measured and achieved values near 50 Goeppert-Mayer (GM) units with efficient excitation in the 775-895 nm spectral range. Mesoporous vaterite nanoparticles were loaded with CDs to examine the possibility of a biocompatible imaging platform. Efficient one- and two-photon imaging of the CD-vaterite composites uptaken by diverse cells was demonstrated. For an in vivo scenario, CD-vaterite composites were injected into the bloodstream of a mouse, and their flow was monitored within the blood vessels of the brain through a cranial window. These results show the potential of the platform for high-brightness biocompatible imaging with the potential for both sensing and simultaneous drug delivery.

Intravitreal therapeutic nanoparticles for age-related macular degeneration: Design principles, progress and opportunities

Age-related macular degeneration (AMD) is a leading cause of vision loss in the elderly. The current standard treatment for AMD involves frequent intravitreal administrations of therapeutic agents. While effective, this approach presents challenges, including patient discomfort, inconvenience, and the risk of adverse complications. Nanoparticle-based intravitreal drug delivery platforms offer a promising solution to overcome these limitations. These platforms are engineered to target the retina specifically and control drug release, which enhances drug retention, improves drug concentration and bioavailability at the retinal site, and reduces the frequency of injections. This review aims to uncover the design principles guiding the development of highly effective nanoparticle-based intravitreal drug delivery platforms for AMD treatment. By gaining a deeper understanding of the physiology of ocular barriers and the physicochemical properties of nanoparticles, we establish a basis for designing intravitreal nanoparticles to optimize drug delivery and drug retention in the retina. Furthermore, we review recent nanoparticle-based intravitreal therapeutic strategies to highlight their potential in improving AMD treatment efficiency. Lastly, we address the challenges and opportunities in this field, providing insights into the future of nanoparticle-based drug delivery to improve therapeutic outcomes for AMD patients.

One-step synthesis of orange-red emissive carbon dots: photophysical insight into their excitation wavelength-independent and dependent luminescence

A low-temperature method was developed to synthesize orange-red luminescence phosphor-doped carbon dots (CDs) without complicated purification procedures. These CDs showed excitation wavelength-independent narrow emission (photo-luminescence quantum yield, Φf ∼ 12 to 22%) with single exponential time-resolved decay in weakly polar/non-polar solvents, indicating the presence of one kind of chromophore. In contrast, the same CDs showed excitation wavelength-dependent broad emission (Φf ∼ 1 to 8%) with multi-exponential fluorescence decay in polar solvents. These CDs exhibited poor solubility in polar solvents, resulting in CD aggregates contributed by excitation wavelength-dependent weak luminescence. The CDs embedded in polymethyl methacrylate (PMMA) polymer film displayed bright orange-red fluorescence under UV 365 nm illumination, indicating their potential application in solid-state luminescence. Further, an analytical method was developed for the naked-eye detection of trifluoracetic acid (red emission) and triethylamine (green emission) under UV 365 nm illumination with reversible two switch-mode luminescence. Additionally, this efficient orange-red luminescence of CDs was utilized for possible bioimaging applications with negligible cytotoxicity in 3T3 mouse fibroblast cells.

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Two-Pronged Approach: Synergistic Tuning of the Surface and Carbon Core to Achieve Yellow Emission in Lignin-Based Carbon Dots

In this study, yellow emissive lignin-based carbon dots (Y-CDs) were successfully prepared through a synergistic approach to adjust its surface and carbon core states. The lignin was initially effectively oxidized and carboxymethylated to impart abundant -COOH onto the precursor, which eventually adjusts the surface state of the CDs. Subsequently, α-naphthol was employed during the solvothermal treatment of lignin with the aim of elevating the sp2 domain content in the CDs and, thus, adjusting its carbon core state. The obtained Y-CDs possessed abundant carboxyl groups and nanoscale spherical shape with an average diameter of 5.21 nm. Meanwhile, the energy gap of Y-CDs was 2.46 eV and the optimal emission wavelength was 561 nm under the excitation wavelength of 410 nm. Synergistic adjusting carbon core and surface of the Y-CDs would alter the surface charge distribution and promote the delocalization of π electrons, and thus lead to a red shifting with the emission wavelength of 154 nm. Furthermore, a shape memory film with excellent recovery performance and fluorescent properties was designed by embedding the Y-CDs into polyvinyl alcohol (PVA) polymer. The incorporation of Y-CDs could impart the film with considerable high-value applications in the fields of intelligent sensing, biomedicine, and tissue engineering.

N-doped carbon nanomaterials as fluorescent pH and metal ion sensors for imaging

Herein we describe the facile synthesis of new N-doped carbon nanoparticles (CNPs) obtained from 1,10-phenanthroline by the solvothermal method. Characterization of CNPs were carried out with transmission electron microscope (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectra (FTIR), UV-vis absorption spectra, and luminescence spectra. CNPs were pH sensitive and exploited as fluorescent chemosensors and imaging agents for Al(III) and Zn(II) ions in real-life samples. Remarkably, we show that CNPs can be used for the detection of Al(III) and Zn(II) ions in water samples. Accordingly, the results indicate that CNPs are highly effective in detecting Zn(II) content of cosmetic creams. We also demonstrated that the CNPs could be used for in vitro imaging of Al(III) and Zn(II) in Human Larynx Squamous Cell Carcinoma (Hep-2). Finally, Al(III) imaging in Angelica Officinalis root tissue was also achieved successfully. The CNPs are promising as luminescent multianalyte (pH, Al(III) and Zn(II)) sensors.

Yellow emissive nitrogen-doped carbon dots as a fluorescence probe for the sensitive and selective detection of silver ions

In this work, yellow emissive carbon dots (Y-CDs) were prepared via a simple hydrothermal method using catechol and hydrazine hydrate as the carbon and nitrogen sources, respectively. The average particle size was 2.99 nm. The Y-CDs demonstrate excitation-dependent emission properties, and the maximum emission wavelength is 570 nm at E x = 420 nm. The fluorescence quantum yield is calculated to be 28.2%. Ag+ could quench the fluorescence of Y-CDs with high selectivity. The quenching mechanism was further explored by various characterization techniques. A sensitive fluorescent probe for Ag+ detection was established based on Y-CDs with a linear range of 3-300 μM. The detection limit was calculated to be 1.1 μM. The proposed method shows satisfactory results in real water samples without interference by coexistence.

Tuning the Luminescence of Microwave-Assisted N-Doped Fluorescent Carbon Dots: Bioimaging Applications and Label-Free Anti-Cancer Drug Delivery

Nanosized fluorescent carbon dots (Cdots) have gained a lot of attention in the recent years because of their superior properties, such as good biocompatibility, low toxicity, excellent chemical stability, resistance to photobleaching, and ease of chemical modification. Cdots are promising candidates for considerable applications in various fields: sensors, bioimaging, and drug delivery. Specifically, nitrogen-doped Cdots have attracted a huge interest because of their applicability in bioimaging and drug delivery. Conventional methods for the synthesis of Cdots have drawbacks, such as the use of organic solvents, the presence of side products, and the time required for synthesis. Keeping all these points in mind, herein, we report green methodology for the synthesis of water-soluble, blue-emitting, nitrogen-doped multifunctional Cdots under microwave irradiation within 3 min. The Cdots were prepared using citric acid and arginine as source materials and were characterized using various physicochemical techniques. A pH-responsive drug delivery system was then designed using anticancer drug doxorubicin and the synthesized Cdots. The biocompatibility of synthesized Cdots was analyzed against L929 normal cell line. The Cdots-DOX conjugates exhibited efficient anticancer activity against HeLa cells and also acted as excellent bioimaging agents.

Sustainable Nanomaterials for Biomedical Applications

Significant progress in nanotechnology has enormously contributed to the design and development of innovative products that have transformed societal challenges related to energy, information technology, the environment, and health. A large portion of the nanomaterials developed for such applications is currently highly dependent on energy-intensive manufacturing processes and non-renewable resources. In addition, there is a considerable lag between the rapid growth in the innovation/discovery of such unsustainable nanomaterials and their effects on the environment, human health, and climate in the long term. Therefore, there is an urgent need to design nanomaterials sustainably using renewable and natural resources with minimal impact on society. Integrating sustainability with nanotechnology can support the manufacturing of sustainable nanomaterials with optimized performance. This short review discusses challenges and a framework for designing high-performance sustainable nanomaterials. We briefly summarize the recent advances in producing sustainable nanomaterials from sustainable and natural resources and their use for various biomedical applications such as biosensing, bioimaging, drug delivery, and tissue engineering. Additionally, we provide future perspectives into the design guidelines for fabricating high-performance sustainable nanomaterials for medical applications.

Ratiometric Sensing of Intracellular pH Based on Dual Emissive Carbon Dots

Accurate monitoring of intracellular pH in living cells is critical for developing a better understanding of cellular activities. In the current study, label-free carbon dots (p-CDs), which were fabricated using a straightforward one-pot solvothermal treatment of p-phenylenediamine and urea, were employed to create a new ratiometric pH nanosensor. Under single-wavelength excitation (λ_ex = 500 nm), the p-CDs gave dual emission bands at 525 and 623 nm. The fluorescent intensity ratio (I₅₂₅/I₆₂₃) was linearly related to pH over the range 4.0 to 8.8 in buffer solutions, indicating that the ratiometric fluorescence nanoprobe may be useful for pH sensing. In pH measurements, the p-CDs also demonstrated outstanding selectivity, reversibility, and photostability. Owing to the advantages outlined above, the nanoprobe was used to monitor the pH of HeLa cells effectively. The label-free CD-based ratiometric nanoprobe features comparatively easy manufacturing and longer excitation and emission wavelengths than the majority of previously reported CD-based ratiometric pH sensors, which is ultimately beneficial for applications in biological imaging.

S-Doped carbonized polymer dots inhibit early myocardial fibrosis by regulating mitochondrial function

Myocardial fibrosis (MF) is a critical pathological lesion in the progression of various acute and chronic cardiovascular diseases. However, there is still a lack of clinically effective drugs and treatments for MF therapies. Herein, for the first time, we developed fluorescent sulfur-doped carbonized polymer dots (S-CPDs) as new nano-antioxidants to reduce the cardiomyocyte damage caused by reactive oxygen species (ROS) in the early stage of fibrotic lesions. In vitro results suggested that the pre-protection of S-CPDs significantly increased the survival rate of H9c2 cells under severe oxidative stress, inhibited the isoproterenol (ISO)-induced hypertrophy of myocardial cells through improving the content of mitochondria related proteins and adenosine triphosphate (ATP) in cells. Moreover, S-CPD administration could effectively decrease cardiac hypertrophy and promote heart function in MF rat models. The rapid internalization, high biocompatibility and fluorescence imaging potential of S-CPDs revealed their promising application prospects in the diagnoses and treatments of cardiovascular diseases.

Carbon dots with hydrogen bond-controlled aggregation behavior

Here, hydrophilic carbon dots (H-CDs) are prepared by a facile room temperature method. The strength of hydrogen bonds can be controlled by introducing proton and aprotic solvents, respectively, so as to realize the tunable aggregation state of H-CDs. Because of the ultrasensitive response to dimethyl sulfoxide (DMSO), H-CDs can serve as optical probes for detecting DMSO in a linear range of 0.005% to 0.75% and with a detection limit of 0.001%.

Milk-Derived Carbon Quantum Dots: Study of Biological and Chemical Properties Provides Evidence of Toxicity

Carbon dots (CDs) are carbon-based zero-dimensional nanomaterials that can be prepared from a number of organic precursors. In this research, they are prepared using fat-free UHT cow milk through the hydrothermal method. FTIR analysis shows C=O and C-H bond presence, as well as nitrogen-based bond like C-N, C=N and -NH2 presence in CDs, while the absorption spectra show the absorption band at 280 ± 3 nm. Next, the Biuret test was performed, with the results showing no presence of unreacted proteins in CDs. It can be said that all proteins are converted in CDs. Photo luminance spectra shows the emission of CDs is 420 nm and a toxicity study of CDs was performed. The Presto Blue method was used to test the toxicity of CDs for murine hippocampal cells. CDs at a concentration of 4 mg/mL were hazardous independent of synthesis time, while the toxicity was higher for lower synthesis times of 1 and 2 h. When the concentration is reduced in 1 and 2 h synthesized CDs, the cytotoxic effect also decreases significantly, ensuring a survival rate of 60-80%. However, when the synthesis time of CDs is increased, the cytotoxic effect decreases to a lesser extent. The CDs with the highest synthesis time of 8 h do not show a cytotoxic effect above 60%. The cytotoxicity study shows that CDs may have a concentration and time-dependent cytotoxic effect, reducing the number of viable cells by 40%.

Promise and Perspective of Nanomaterials in Antisenescence Tissue Engineering Applications

The tissue engineering approach for repair and regeneration has achieved significant progress over the past decades. However, challenges remain in developing strategies to solve the declined or impaired innate cell and tissue regeneration capacity that occurs with aging. Cellular senescence is a key mechanism underlying organismal aging and is responsible for the declined tissue regeneration capacity in the aging population. Therefore, to promote the diminished tissue regeneration ability in the aged population, it is critical to developing a feasible and promising strategy to target senescent cells. Recent advances in nanomaterials have revolutionized biomedical applications ranging from biosensing to bioimaging and targeted drug delivery. In this perspective, we review and discuss the nature and influences of cell-intrinsic and cell-extrinsic factors on reduced regenerative abilities through aging and how nanotechnology can be a therapeutic avenue to sense, rejuvenate, and eliminate senescent cells, thereby improving the tissue regeneration capacity in the aging population.