Synthetic Developments of Nontoxic Quantum Dots

Effect of Polymer and Cell Membrane Coatings on Theranostic Applications of Nanoparticles: A Review

The recent decade has witnessed a remarkable surge in the field of nanoparticles, from their synthesis, characterization, and functionalization to diverse applications. At the nanoscale, these particles exhibit distinct physicochemical properties compared to their bulk counterparts, enabling a multitude of applications spanning energy, catalysis, environmental remediation, biomedicine, and beyond. This review focuses on specific nanoparticle categories, including magnetic, gold, silver, and quantum dots (QDs), as well as hybrid variants, specifically tailored for biomedical applications. A comprehensive review and comparison of prevalent chemical, physical, and biological synthesis methods are presented. To enhance biocompatibility and colloidal stability, and facilitate surface modification and cargo/agent loading, nanoparticle surfaces are coated with different synthetic polymers and very recently, cell membrane coatings. The utilization of polymer- or cell membrane-coated nanoparticles opens a wide variety of biomedical applications such as magnetic resonance imaging (MRI), hyperthermia, photothermia, sample enrichment, bioassays, drug delivery, etc. With this review, the goal is to provide a comprehensive toolbox of insights into polymer or cell membrane-coated nanoparticles and their biomedical applications, while also addressing the challenges involved in translating such nanoparticles from laboratory benchtops to in vitro and in vivo applications. Furthermore, perspectives on future trends and developments in this rapidly evolving domain are provided.

Not all silicon quantum dots are equal: photostability of silicon quantum dots with and without a thick amorphous shell

Luminescent colloidal silicon quantum dots (SiQDs) are sustainable alternatives to metal-based QDs for various optical applications. While the materials are reliant on their photoluminescence efficiency, the relationship between the structure and photostability of SiQDs is yet to be well studied. An amorphous silicon (a-Si) shell was recently discovered in SiQDs prepared by thermally-processed silicon oxides. As a-Si is known as a source of defects upon UV irradiation, the disordered shell could potentially have an adverse effect on the optical properties of nanoparticles. Herein, the photostability of ∼5 nm diameter SiQDs with an amorphous shell was compared with that of over-etched SiQDs of equivalent dimensions that bore an a-Si shell of negligible thickness. An UV-induced degradation study was conducted by subjecting toluene solutions of SiQDs to 365 nm light-emitting diodes (LEDs) under an inert atmosphere for predetermined times up to 72 hours. The structure, composition, and optical responses of the exposed SiQDs were evaluated.

Recent advances of ratiometric sensors in food matrices: mycotoxins detection

The public health problem caused by mycotoxins contamination has received a great deal of attention worldwide. Mycotoxins produced by filamentous fungi widely distributed in foodstuffs can cause adverse impacts on humans and livestock, posing serious health threats. Particularly worth mentioning is that mycotoxins can accumulate in organisms and be enriched through the food chain. Improving early trace detection and control from the source is a more desirable approach than the contaminated food disposal process to ensure food safety. Conventional sensors are susceptible to interference from various components in intricate food matrices when detecting trace mycotoxins. The application of ratiometric sensors avoids signal fluctuations, and reduce background influences, which casts new light on developing sensors with superior performance. This work is the first to provide an overview of the recent progress of ratiometric sensors in the detection of mycotoxins in intricate food matrices, and highlight the output types of ratiometric signal with respect to accurate quantitative analysis. The prospects of this field are also included in this paper and are intended to have key ramifications on the development of sensing detection conducive to food safety.

Transcriptome analysis reveals the molecular mechanisms by which carbon dots regulate the growth of Chlamydomonas reinhardtii

Carbon dots (CDs) have attracted increasing attention for their ability to artificially improve photosynthesis. Microalgal bioproducts have emerged as promising sources of sustainable nutrition and energy. However, the gene regulation mechanism of CDs on microalgae remains unexplored. The study synthesized red-emitting CDs and applied them to Chlamydomonas reinhardtii. Results showed that 0.5 mg/L-CDs acted as light supplements to promote cell division and biomass in C. reinhardtii. CDs improved the energy transfer of PS II, photochemical efficiency of PS II, and photosynthetic electron transfer. The pigment content and carbohydrate production slightly increased, while protein and lipid contents significantly increased (by 28.4% and 27.7%, respectively) in a short cultivation time. Transcriptome analysis identified 1166 differentially expressed genes. CDs resulted in faster cell growth by up-regulating the expression of genes associated with cell growth and death, promoting sister chromatid separation, accelerating the mitotic process and shortening the cell cycle. CDs improved the ability of energy conversion by up-regulating photosynthetic electron transfer-related genes. Carbohydrate metabolism-related genes were regulated and provided more available pyruvate for the citrate cycle. The study provides evidence for the genetic regulation of microalgal bioresources by artificially synthesized CDs.

Molecule(s) of Interest: I. Ionic Liquids-Gateway to Newer Nanotechnology Applications: Advanced Nanobiotechnical Uses', Current Status, Emerging Trends, Challenges, and Prospects

Ionic liquids are a potent class of organic compounds exhibiting unique physico-chemical properties and structural compositions that are different from the classical dipolar organic liquids. These molecules have found diverse applications in different chemical, biochemical, biophysical fields, and a number of industrial usages. The ionic liquids-based products and procedural applications are being developed for a number of newer industrial purposes, and academic uses in nanotechnology related procedures, processes, and products, especially in nanobiotechnology and nanomedicine. The current article overviews their uses in different fields, including applications, functions, and as parts of products and processes at primary and advanced levels. The application and product examples, and prospects in various fields of nanotechnology, domains of nanosystem syntheses, nano-scale product development, the process of membrane filtering, biofilm formation, and bio-separations are prominently discussed. The applications in carbon nanotubes; quantum dots; and drug, gene, and other payload delivery vehicle developments in the nanobiotechnology field are also covered. The broader scopes of applications of ionic liquids, future developmental possibilities in chemistry and different bio-aspects, promises in the newer genres of nanobiotechnology products, certain bioprocesses controls, and toxicity, together with emerging trends, challenges, and prospects are also elaborated.

Diffusion-Limited Kinetics of Isovalent Cation Exchange in III-V Nanocrystals Dispersed in Molten Salt Reaction Media

The goal of this work is to determine the kinetic factors that govern isovalent cation exchange in III-V colloidal quantum dots using molten salts as the solvent and cation source. We focus on the reactions of InP + GaI₃→ In_1-xGa_xP and InAs + GaI₃→ In_1-xGa_xAs to create technologically important ternary III-V phases. We find that the molten salt reaction medium causes the transformation of nearly spherical InP nanocrystals to tetrahedron-shaped In_1-xGa_xP nanocrystals. Furthermore, we determine that the activation energy for the cation exchange reaction is 0.9 eV for incorporation of Ga into InP and 1.2 eV for incorporation of Ga into InAs, both much lower than the measured values in bulk semiconductors. Next, we use powder XRD simulations to constrain our understanding of the structure of the In_1-xGa_xP nanocrystals. Together our results reveal several important features of molten salt-mediated cation exchange and provide guidance for future development of these materials.

Sequential, low-temperature aqueous synthesis of Ag-In-S/Zn quantum dots via staged cation exchange under biomineralization conditions

The development of high quality, non-toxic (i.e., heavy-metal-free), and functional quantum dots (QDs) via 'green' and scalable synthesis routes is critical for realizing truly sustainable QD-based solutions to diverse technological challenges. Herein, we demonstrate the low-temperature all-aqueous-phase synthesis of silver indium sulfide/zinc (AIS/Zn) QDs with a process initiated by the biomineralization of highly crystalline indium sulfide nanocrystals, and followed by the sequential staging of Ag⁺ cation exchange and Zn²⁺ addition directly within the biomineralization media without any intermediate product purification. Therein, we exploit solution phase cation concentration, the duration of incubation in the presence of In₂S₃ precursor nanocrystals, and the subsequent addition of Zn²⁺ as facile handles under biomineralization conditions for controlling QD composition, tuning optical properties, and improving the photoluminescence quantum yield of the AIS/Zn product. We demonstrate how engineering biomineralization for the synthesis of intrinsically hydrophilic and thus readily functionalizable AIS/Zn QDs with a quantum yield of 18% offers a 'green' and non-toxic materials platform for targeted bioimaging in sensitive cellular systems. Ultimately, the decoupling of synthetic steps helps unravel the complexities of ion exchange-based synthesis within the biomineralization platform, enabling its adaptation for the sustainable synthesis of 'green', compositionally diverse QDs.

Controlled synthesis of silver-based ternary quantum dots with outstanding luminescence

Quantum dots (QDs) have attracted much attention over the past decades due to their outstanding properties. However, obtaining QDs with excellent photoluminescence and quantum yields (QYs) from their aqueous synthesis is still a big concern. We herein present a green and facile synthesis of AgInS (AIS) QDs and AgInS-ZnS (AIS-ZnS) core-shell QDs using a combination of two capping agents (glutathione and sodium citrate). The temporal evolution of the optical properties is investigated by varying the reaction time and pH of the solution. The results show that the fluorescence intensity of the QDs increases as the reaction time increase, while the emission position blue-shift as the pH of the solution increase. An outstanding photoluminescence quantum yield (PLQY) of 90% is obtained at optimized synthetic conditions. The Fourier transform Infrared studies confirm efficient passivation of the QDs by the capping agents. The XRD analysis reveals that all the materials crystallize in the tetragonal crystalline phase, while the TEM micrographs of AIS-ZnS QDs reveal a spherical shape. The EDS analysis confirms the presence of Silver, Indium, Sulphide, and Zinc elements. The reported synthetic route is facile and eco-friendly.

Quantum dots and photodynamic therapy in COVID ‐19 treatment

Viral diseases are regarded as a global burden. The eradication of viral diseases is always a challenging task in medical research due to the high infectivity and mutation capability of the virus. The ongoing COVID‐19 pandemic is still not under control even after several months of the first reported case and global spread. In the pursuit of a promising strategy, carbon dots could be considered as potential nanostructure against this viral pandemic. Carbon dots are photoluminescent carbon nanoparticles, smaller than 10 nm in dimension with a very attractive photostable and biocompatible properties which can be surfaced modified or functionalized. These photoluminescent tiny particles have captured much attention owing to their functionalization property and biocompatibility. Photodynamic therapy (PDT) is a technique that is widely used in cancer treatment and against various microbes. In this technique, a light‐induced photosensitizer generates reactive oxygen species (ROS), ultimately killing the target cells. Considering these facts, an attempt has been made to review the current literature on viral inactivation using PDT approach. Accordingly, the mechanism of PDT action has been discussed, along with an update on the use of various photosensitizers (PSs) and nanoparticles. The capsid proteins and nucleic acid (RNA) of SARS‐CoV‐2 can be a possible target for PDT.

Structure and Interface Modification of Carbon Dots for Electrochemical Energy Application

Carbon dots (CDs) as new nanomaterials have attracted much attention in recent years due to their unique characteristics. Notably, structure and interface modification (carbon core, edge, defects, and functional groups) of CDs have been considered as valid methods to regulate their properties, which contain electron transfer effect, electrochemical activity, fluorescence luminescent, and so on. Additionally, CDs with ultrasmall size, excellent dispersibility, high specific surface area, and abundant functional groups can guarantee positive and extraordinary effects in electrical energy storage and conversion. Therefore, CDs are used to couple with other materials by constructing a special interface structure to enhance their properties. Here, diverse structural and interfacial modifications of CDs with various heteroatoms and synergy effects are systematically analyzed. And not only several main syntheses of CDs-based composites (CDs/X) are summarized but also the merit and demerit of CDs/X in electrical energy storage are discussed. Finally, the applications of CDs/X in energy storage devices (supercapacitors, batteries) and electrocatalysts for practical applications are discussed. This review mainly provides a comprehensive summary and future prospect for synthesis, modification, and electrochemical applications of CDs.

Carbon dots for cancer nanomedicine: a bright future

Cancer remains one of the main causes of death in the world. Early diagnosis and effective cancer therapies are required to treat this pathology. Traditional therapeutic approaches are limited by lack of specificity and systemic toxicity. In this scenario, nanomaterials could overcome many limitations of conventional approaches by reducing side effects, increasing tumor accumulation and improving the efficacy of drugs. In the past few decades, carbon nanomaterials (i.e., fullerenes, carbon nanotubes, and carbon dots) have attracted significant attention of researchers in various scientific fields including biomedicine due to their unique physical/chemical properties and biological compatibility and are among the most promising materials that have already changed and will keep changing human life. Recently, because of their functionalization and stability, carbon nanomaterials have been explored as a novel tool for the delivery of therapeutic cancer drugs. In this review, we present an overview of the development of carbon dot nanomaterials in the nanomedicine field by focusing on their synthesis, and structural and optical properties as well as their imaging, therapy and cargo delivery applications.

Microwave-Assisted Synthesis of Carbon Dot - Iron Oxide Nanoparticles for Fluorescence Imaging and Therapy

Fluorescence microscopy is commonly used to image specific parts of a biological system, and is applicable for early diagnosis of cancer. Current fluorescent probes, such as organic dyes and quantum dots, suffer from poor solubility and high toxicity, respectively, demonstrating a need for a colloidal stable and non-toxic fluorescent probe. Here we present an iron oxide and carbon dot (CD) based nanoparticle (CNPCP) that displays optical properties similar to those of conventional fluorescent probe and also exhibits good biocompatibility. Fluorescent CDs were synthesized from glucosamine onto chitosan - polyethylene glycol (PEG) graft copolymer using microwave irradiation. These NPs were monodispersed in aqueous environments and displayed excitation-dependent fluorescence; they demonstrated good size stability and fluorescence intensity in biological media. In vitro evaluation of CNP as fluorescent probes in cancer cell lines showed that these NPs caused little toxicity, and allowed fast and quantitative imaging. Model therapeutic doxorubicin (DOX) was conjugated onto the NPs (CNPCP-DOX) to demonstrate the multifunctionality of the NPs, and in vitro studies showed that CNPCP-DOX was able to kill cancer cells in a dose dependent manner. These results indicate the potential of using CNPCPs as fluorescent probes capable of delivering chemotherapeutics.

You Don't Learn That in School: An Updated Practical Guide to Carbon Quantum Dots

Carbon quantum dots (CQDs) have started to emerge as candidates for application in cell imaging, biosensing, and targeted drug delivery, amongst other research fields, due to their unique properties. Those applications are possible as the CQDs exhibit tunable fluorescence, biocompatibility, and a versatile surface. This review aims to summarize the recent development in the field of CQDs research, namely the latest synthesis progress concerning materials/methods, surface modifications, characterization methods, and purification techniques. Furthermore, this work will systematically explore the several applications CQDs have been subjected to, such as bioimaging, fluorescence sensing, and cancer/gene therapy. Finally, we will briefly discuss in the concluding section the present and future challenges, as well as future perspectives and views regarding the emerging paradigm that is the CQDs research field.

Development and perspectives of rapid detection technology in food and environment

Food safety become a hot issue currently with globalization of food trade and food supply chains. Chemical pollution, microbial contamination and adulteration in food have attracted more attention worldwide. Contamination with antibiotics, estrogens and heavy metals in water environment and soil environment have also turn into an enormous threat to food safety. Traditional small-scale, long-term detection technologies have been unable to meet the current needs. In the monitoring process, rapid, convenient, accurate analysis and detection technologies have become the future development trend. We critically synthesizing the current knowledge of various rapid detection technology, and briefly touched upon the problem which still exist in research process. The review showed that the application of novel materials promotes the development of rapid detection technology, high-throughput and portability would be popular study directions in the future. Of course, the ultimate aim of the research is how to industrialization these technologies and apply to the market.

Optical properties of organosilicon compounds containing sigma-electron delocalization by quasiparticle self-consistent GW calculations

We investigate theoretically the electronic and optical absorption properties of two sub-classes of oligosilanes: (i) Si(CH₃)₄, Si₄(CH₃)₈, and Si₈(CH₃)₈ that contain Si dot, ring and cage, respectively, and exhibit typical SiC and SiSi bonds; and (ii) persilastaffanes Si₇H₆(CH₃)₆ and Si₁₂H₆(CH₃)₁₂, which contain extended delocalized σ-electrons in SiSi bonds over three-dimensional Si frameworks. Our modeling is performed within the GW approach up to the partially self-consistent GW₀ approximation, which is more adequate for reliably predicting the optical band gaps of materials. We examine how the optical properties of these organosilicon compounds depend on their size, geometric features, and Si/C composition. Our results indicate that the present methodology offers a viable way of describing the optical excitations of tailored functional Si-C-based clusters and molecular optical tags with potential use as efficient light absorbers/emitters in molecular optical devices.

Synthesis of Multi-Functional Carbon Quantum Dots for Targeted Antitumor Therapy

Carbon dots are nano-sized photoluminescence materials which have good biocompatibility and low cytotoxicity, while the previously synthesized carbon dots lack tumor targeting capability and therapy function so that it cannot achieve the purpose of diagnosis and treatment. Herein, a new kind of multi-functional carbon dots (GFCDs) is promising to be applied in tumor cells imaging and clinical targeted therapy. Gallic acid (GA) was used as the carbon resource and antitumor active molecule, folic acid (FA) was used as the nitrogen resource and tumor targeting molecule, and citric acid monohydrate (CA) was used as the auxiliary carbon source. Multi-functional GACDs were synthesized by a simple one-step microwave-assisted procedure and analyzed with UV - vis spectrophotometer, fourier transform infrared spectrometer, transmission electron microscopy and X-ray photoelectron spectrometer. Results show that the diameter of GFCDs is about 3 nm. And GFCDs are pale-yellow under natural light which turn blue under 360 nm UV lamp. Besides ester bond is the connecting mode between functional molecules. In addition, the results of in vitro cell imaging experiments and in vivo antitumor experiments demonstrate the targeting imaging and antitumor abilities towards Hela cells. The synthesis route and properties of GFCDs.

Design of experiments a powerful tool to improve the selectivity of copper antimony sulfide nanoparticles synthesis

Design of experiments to find the main factors governing phase compositions and nanoparticle size.

Synthesis, characterization and biocompatibility studies of carbon quantum dots from Phoenix dactylifera

In the present study, Carbon Quantum Dots (CQDs) were synthesized from Phoenix dactylifera (Date palm fruit) using microwave-assisted pyrolysis and were characterized for its various properties. The synthesized CQD sample exhibited a narrow absorbance peak at 270 nm in UV-Vis spectrum that indicated generation of narrow sized particles. The FTIR analysis of the crude CQDs and dialysed sample revealed the various functional groups involved in the formation of CQDs. TEM data revealed the nature of CQDs to be quasi-spherical and spatially distributed. Biocompatibility of the CQDs was studied using various model systems. CQDs displayed no cytotoxic and anti-clonogenic property when exposed to WRL-68 cell line whereas a slight toxicity was evident in HT1080 post 24 h of incubation suggesting the tremendous potential of the CQDs in the synergistic killing of cancer cells. Phytotoxicity assessment in four different seedlings revealed the non-toxic nature of CQDs. Further these CQDs were found to possess high biocompatibility imposing no inhibition in microbial growth and zilch effect on the development of zebrafish embryos. Thus these CQDs can find immense potential applications in fields of biomedicine as biomolecule detection, drug carriers, fluorescent tracers and in controlling the drug release.

Evolution and Synthesis of Carbon Dots: From Carbon Dots to Carbonized Polymer Dots

Despite the various synthesis methods to obtain carbon dots (CDs), the bottom-up methods are still the most widely administrated route to afford large-scale and low-cost synthesis. However, as CDs are developed with increasing reports involved in producing many CDs, the structure and property features have changed enormously compared with the first generation of CDs, raising classification concerns. To this end, a new classification of CDs, named carbonized polymer dots (CPDs), is summarized according to the analysis of structure and property features. Here, CPDs are revealed as an emerging class of CDs with distinctive polymer/carbon hybrid structures and properties. Furthermore, deep insights into the effects of synthesis on the structure/property features of CDs are provided. Herein, the synthesis methods of CDs are also summarized in detail, and the effects of synthesis conditions of the bottom-up methods in terms of the structures and properties of CPDs are discussed and analyzed comprehensively. Insights into formation process and nucleation mechanism of CPDs are also offered. Finally, a perspective of the future development of CDs is proposed with critical insights into facilitating their potential in various application fields.

Semiconductor Quantum Dots: An Emerging Candidate for CO2 Photoreduction

As one of the most critical approaches to resolve the energy crisis and environmental concerns, carbon dioxide (CO₂ ) photoreduction into value-added chemicals and solar fuels (for example, CO, HCOOH, CH₃ OH, CH₄ ) has attracted more and more attention. In nature, photosynthetic organisms effectively convert CO₂ and H₂ O to carbohydrates and oxygen (O₂ ) using sunlight, which has inspired the development of low-cost, stable, and effective artificial photocatalysts for CO₂ photoreduction. Due to their low cost, facile synthesis, excellent light harvesting, multiple exciton generation, feasible charge-carrier regulation, and abundant surface sites, semiconductor quantum dots (QDs) have recently been identified as one of the most promising materials for establishing highly efficient artificial photosystems. Recent advances in CO₂ photoreduction using semiconductor QDs are highlighted. First, the unique photophysical and structural properties of semiconductor QDs, which enable their versatile applications in solar energy conversion, are analyzed. Recent applications of QDs in photocatalytic CO₂ reduction are then introduced in three categories: binary II-VI semiconductor QDs (e.g., CdSe, CdS, and ZnSe), ternary I-III-VI semiconductor QDs (e.g., CuInS₂ and CuAlS₂ ), and perovskite-type QDs (e.g., CsPbBr₃ , CH₃ NH₃ PbBr₃ , and Cs₂ AgBiBr₆ ). Finally, the challenges and prospects in solar CO₂ reduction with QDs in the future are discussed.

Rhenium (I) Complexes as Probes for Prokaryotic and Fungal Cells by Fluorescence Microscopy: Do Ligands Matter?

Re(I) complexes have exposed highly suitable properties for cellular imaging (especially for fluorescent microscopy) such as low cytotoxicity, good cellular uptake, and differential staining. These features can be modulated or tuned by modifying the ligands surrounding the metal core. However, most of Re(I)-based complexes have been tested for non-walled cells, such as epithelial cells. In this context, it has been proposed that Re(I) complexes are inefficient to stain walled cells (i.e., cells protected by a rigid cell wall, such as bacteria and fungi), presumably due to this physical barrier hampering cellular uptake. More recently, a series of studies have been published showing that a suitable combination of ligands is useful for obtaining Re(I)-based complexes able to stain walled cells. This review summarizes the main characteristics of different fluorophores used in bioimage, remarking the advantages of d⁶-based complexes, and focusing on Re(I) complexes. In addition, we explored different structural features of these complexes that allow for obtaining fluorophores especially designed for walled cells (bacteria and fungi), with especial emphasis on the ligand choice. Since many pathogens correspond to bacteria and fungi (yeasts and molds), and considering that these organisms have been increasingly used in several biotechnological applications, development of new tools for their study, such as the design of new fluorophores, is fundamental and attractive.

Endocytosis and Lack of Cytotoxicity of Alkyl-Capped Silicon Quantum Dots Prepared from Porous Silicon

Freely-dissolved silicon quantum dots were prepared by thermal hydrosilation of 1-undecene at high-porosity porous silicon under reflux in toluene. This reaction produces a suspension of alkyl-capped silicon quantum dots (alkyl SiQDs) with bright orange luminescence, a core Si nanocrystal diameter of about 2.5 nm and a total particle diameter of about 5 nm. Previous work has shown that these particles are rapidly endocytosed by malignant cell lines and have little or no acute toxicity as judged by the standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for viability and the Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay for apoptosis. We have extended this work to the CACO-2 cell line, an established model for the human small intestinal mucosa, and demonstrate that neither acute nor chronic (14 days) toxicity is observed as judged by cell morphology, viability, ATP production, ROS production and DNA damage (single cell gel electrophoresis) at doses of 50–200 μg mL−1. Quantitative assessment of the extent of uptake of alkyl SiQDs by CACO-2, HeLa, HepG2, and Huh7 cell lines by flow cytometry showed a wide variation. The liver cell lines (HepG2 and Huh7) were the most active and HeLa and CACO-2 showed comparable activity. Previous work has reported a cholesterol-sensitivity of the endocytosis (HeLa), which suggests a caveolin-mediated pathway. However, gene expression analysis by quantitative real–time polymerase chain reaction (RT-PCR) indicates very low levels of caveolins 1 and 2 in HepG2 and much higher levels in HeLa. The data suggest that the mechanism of endocytosis of the alkyl SiQDs is cell-line dependent.

Recent Advancements in Doped/Co-Doped Carbon Quantum Dots for Multi-Potential Applications

Carbon quantum dots (CQDs)/carbon nanodots are a new class of fluorescent carbon nanomaterials having an approximate size in the range of 2–10 nm. The majority of the reported review articles have discussed about the development of the CQDs (via simple and cost-effective synthesis methods) for use in bio-imaging and chemical-/biological-sensing applications. However, there is a severe lack of consolidated studies on the recently developed CQDs (especially doped/co-doped) that are utilized in different areas of application. Hence, in this review, we have extensively discussed about the recent development in doped and co-doped CQDs (using elements/heteroatoms—e.g., boron (B), fluorine (F), nitrogen (N), sulphur (S), and phosphorous (P)), along with their synthesis method, reaction conditions, and/or quantum yield (QY), and their emerging multi-potential applications including electrical/electronics (such as light emitting diode (LED) and solar cells), fluorescent ink for anti-counterfeiting, optical sensors (for detection of metal ions, drugs, and pesticides/fungicides), gene delivery, and temperature probing.

Superparamagnetic graphene quantum dot as a dual-modality contrast agent for confocal fluorescence microscopy and magnetomotive optical coherence tomography

A magnetic graphene quantum dot (MGQD) nanoparticle, synthesized by hydrothermally reducing and cutting graphene oxide-iron oxide sheet, was demonstrated to possess the capabilities of simultaneous confocal fluorescence and magnetomotive optical coherence tomography (MMOCT) imaging. This MGQD shows low toxicity, significant tunable blue fluorescence and superparamagnetism, which can thus be used as a dual-modality contrast agent for confocal fluorescence microscopy (CFM) and MMOCT. The feasibility of applying MGQD as a tracer of cells is shown by imaging and visualizing MGQD labeled cells using CFM and our in-house MMOCT. Since MMOCT and CFM can offer anatomical structure and intracellular details, respectively, the MGQD for cell tracking could provide a more comprehensive diagnosis.

Sensing with photoluminescent semiconductor quantum dots

Fluorescent sensors benefit from high signal-to-noise and multiple measurement modalities, enabling a multitude of applications and flexibility of design. Semiconductor nanocrystal quantum dots (QDs) are excellent fluorophores for sensors because of their extraordinary optical properties. They have high thermal and photochemical stability compared to organic dyes or fluorescent proteins and are extremely bright due to their large molar cross-sections. In contrast to organic dyes, QD emission profiles are symmetric, with relatively narrow bandwidths. In addition, the size tunability of their emission color, which is a result of quantum confinement, make QDs exceptional emitters with high color purity from the ultra-violet to near infrared wavelength range. The role of QDs in sensors ranges from simple fluorescent tags, as used in immunoassays, to intrinsic sensors that utilize the inherent photophysical response of QDs to fluctuations in temperature, electric field, or ion concentration. In more complex configurations, QDs and biomolecular recognition moieties like antibodies are combined with a third component to modulate the optical signal via energy transfer. QDs can act as donors, acceptors, or both in energy transfer-based sensors using Förster resonance energy transfer (FRET), nanometal surface energy transfer (NSET), or charge or electron transfer. The changes in both spectral response and photoluminescent lifetimes have been successfully harnessed to produce sensitive sensors and multiplexed devices. While technical challenges related to biofunctionalization and the high cost of laboratory-grade fluorimeters have thus far prevented broad implementation of QD-based sensing in clinical or commercial settings, improvements in bioconjugation methods and detection schemes, including using simple consumer devices like cell phone cameras, are lowering the barrier to broad use of more sensitive QD-based devices.

Design of Carbon Dots for Metal-free Photoredox Catalysis

The photoreduction potential of a set of four different carbon dots (CDs) was investigated. The CDs were synthesized by using two different preparation methods-hydrothermal and pyrolytic-and two sets of reagents-neat citric acid and citric acid doped with diethylenetriamine. The hydrothermal syntheses yielded amorphous CDs, which were either nondoped (a-CDs) or nitrogen-doped (a-N-CDs), whereas the pyrolytic treatment afforded graphitic CDs, either non-doped (g-CDs) or nitrogen-doped (g-N-CDs). The morphology, structure, and optical properties of four different types of CDs revealed significant differences depending on the synthetic pathway. The photocatalytic activities of the CDs were investigated as such, that is, in the absence of any other redox mediators, on the model photoreduction reaction of methyl viologen. The observed photocatalytic reaction rates: a-N-CDs ≥ g-CDs > a-CDs ≥ g-N-CDs were correlated with the presence/absence of fluorophores, to the graphitic core, and to quenching interactions between the two. The results indicate that nitrogen doping reverses the photoredox reactivity between amorphous and graphitic CDs and that amorphous N-doped CDs are the most photoredox active, a yet unknown fact that demonstrates the tunable potential of CDs for ad hoc applications.

Luminescent, low-toxic and stable gradient-alloyed Fe:ZnSe(S)@ZnSe(S) core:shell quantum dots as a sensitive fluorescent sensor for lead ions

In this paper, an aqueous-based approach is introduced for facile, fast, and green synthesis of gradient-alloyed Fe-doped ZnSe(S)@ZnSe(S) core:shell quantum dots (QDs) with intense and stable emission. Co-utilization of co-nucleation and growth doping strategies, along with systematic optimization of emission intensity, provide a well-controllable/general method to achieve internally doped QDs (d-dots) with intense emission. Results indicate that the alloyed ZnSe(S)@ZnSe(S) core:shell QDs have a gradient structure that consists of a Se-rich core and a S-rich shell. This gradient structure cannot only passivate the core d-dots by means of the wider band gap S-rich shell, but also minimizes the lattice mismatch between alloyed core-shell structures. Using this novel strategy and utilizing the wider band gap S-rich shell can obviously increase the cyan emission intensity and also drastically improve the emission stability against chemical and optical corrosion. Furthermore, the cytotoxicity experiments indicate that the obtained d-dots are nontoxic nanomaterials, and thus they can be considered as a promising alternative to conventional Cd-based QDs for fluorescent probes in biological fields. Finally, it is demonstrated that the present low-toxicity and gradient-alloyed core:shell d-dots can be used as sensitive chemical detectors for Pb²⁺ ions with excellent selectivity, small detection limit, and rapid response time.

Adverse Interactions of Luminescent Semiconductor Quantum Dots with Liposomes and Shewanella oneidensis

Cadmium-containing luminescent quantum dots (QD) are increasingly used in display, bioimaging, and energy technologies; however, significant concerns have been raised about their potentially adverse impact on human health and the environment. This study makes use of a broad toolkit of analytical methods to investigate and increase our understanding of the interactions of luminescent cadmium-containing (CdSe) and cadmium-free (ZnSe) QD, with and without a passivating higher bandgap energy ZnS shell, with phospholipid vesicles (liposomes), which model bacterial membranes, and with Shewanella oneidensis MR-1, an environmentally relevant bacteria. A unique feature of this study is that all QD types have the same surface chemistry, being capped with uncharged poly(ethylene glycol) ligands. This enables focusing the study on the impact of the QD core on liposomes and bacterial cells. The study reveals that QD association with liposome and bacterial cell membranes is imperative for their adverse impact on liposomes and bacterial cells. The QD' concentration-dependent association with liposomes and bacterial cells destabilizes the membranes mechanically, which leads to membrane disruption and lysis in liposomes and to bacterial cell death. The study also shows that cadmium-containing QD exhibit a higher level of membrane disruption in bacterial cells than cadmium-free QD. ZnSe QD have low membrane impact, and coating them with a ZnS shell decreases their membrane disruption activity. In contrast, CdSe QD exhibit a high level of membrane impact, and coating them with a ZnS shell does not decrease, but in fact further increases, their membrane disruption activity. This behavior might be attributed to higher affinity and association of CdSe/ZnS QD with liposomes and bacterial cells and to a contribution of dissolved zinc ions from the ZnS shell to increased membrane disruption activity.

Optical oxygen sensing with quantum dot conjugates

The ability to track and quantify changes in oxygen concentration as a function of disease progression or therapy is crucial to advance targeted chemotherapeutics. New non-invasive sensors must be developed that are small enough to penetrate into tissue and monitor dynamic changes with high resolution in real time. One way to address this challenge is with the use of nanoparticle-based sensors. This review details the design, synthesis, and characterization of optical oxygen sensors that combine a fluorescent semiconductor quantum dot (QD) with an oxygen-responsive phosphorescent molecule. The QD may have multifaceted roles in these constructs, serving as an internal standard for ratiometric sensing, as an antenna for multiphoton absorption, and as an energy transfer donor for the attendant phosphorescent molecule. Solid-state devices may be prepared by embedding the two components in a polymer matrix. Alternatively, solution-phase sensors can be synthesized by covalent conjugation, self-assembly in organic solvents, or micelle encapsulation in aqueous media. Several sensors have been used for biological imaging and oxygen sensing, demonstrating that these constructs can quantify oxygen in biological systems.

Evaluating the potential of using quantum dots for monitoring electrical signals in neurons

Success in the projects aimed at providing an advanced understanding of the brain is directly predicated on making critical advances in nanotechnology. This Perspective addresses the unique interface of neuroscience and nanomaterials by considering the foundational problem of sensing neuron membrane voltage and offers a potential solution that may be facilitated by a prototypical nanomaterial. Despite substantial improvements, the visualization of instantaneous voltage changes within individual neurons, whether in cell culture or in vivo, at both the single-cell and network level at high speed remains complex and problematic. The unique properties of semiconductor quantum dots (QDs) have made them powerful fluorophores for bioimaging. What is not widely appreciated, however, is that QD photoluminescence is exquisitely sensitive to proximal electric fields. This property should be suitable for sensing voltage changes that occur in the active neuronal membrane. Here, we examine the potential role of QDs in addressing the important challenge of real-time optical voltage imaging.

Magnetic conjugated polymer nanoparticles doped with a europium complex for biomedical imaging

Self-assembling conjugated polymer nanoparticles containing PVK and PLGA-PEG as a matrix polymer were doped with both a luminescent rare-earth complex and magnetic nanoparticles (SPIONs), giving rise to materials that are both luminescent and magnetic.

Highly photoluminescent and stable silicon nanocrystals functionalized via microwave-assisted hydrosilylation

Herein, we report a microwave-assisted hydrosilylation (MWH) reaction for the surface passivation of silicon nanocrystals (Si-NCs) with linear alkenes. The MWH reaction requires only 20 minutes and allows us to produce Si-NCs with high photoluminescence quantum yields (PLQYs), reaching 39% with an emission maximum of 860 nm. Furthermore, we investigated the effect of ligand length on the photoluminescence properties of Si-NCs. We tested six alkenes with an even number of carbon atoms (from hexene-1 to hexadecene-1). The highest PLQY combined with a long stability (test period of 6 months) was observed when capping with the shortest ligand, hexene-1. The use of microwave heating turns the hydrosilylation step into a facile and sustainable process. In order to provide insight into the emissive properties of Si-NCs surface oxidation and luminescence decay were investigated using Fourier-transform infrared spectroscopy and time-resolved photoluminescence measurements.

Herein, we report a microwave-assisted hydrosilylation (MWH) reaction for the surface passivation of silicon nanocrystals (Si-NCs) with linear alkenes.

Development of quantum dot-based biosensors: principles and applications

We review the recent advances in quantum dot-based biosensors and focus on quantum dot-based fluorescent, bioluminescent, chemiluminescent, and photoelectrochemical biosensors.

Effects of arginine-glycine-aspartic acid peptide-conjugated quantum dots-induced photodynamic therapy on pancreatic carcinoma in vivo

Quantum dots (QDs) conjugated with integrin antagonist arginine-glycine-aspartic acid (RGD) peptides (QDs-RGD) are novel nanomaterials with a unique optical property: a high molar extinction coefficient. Previously, we have shown that QDs-RGD demonstrate a photodynamic therapy (PDT) effect as new photosensitizers for the pancreatic cancer cell line SW1990 in vitro. Here, we investigate the application of QDs-RGD in mice bearing pancreatic tumors using PDT. To ensure that more photosensitizers accumulated in tumors, QDs-RGD were injected intratumorally. After selection of an adequate dosage for injection from analyses of biodistribution images captured by an IVIS system, PDT was initiated. Three groups were created according to different PDT procedures. In group 1, mice were injected with QDs-RGD intratumorally, and an optical fiber connected to a laser light was inserted directly into the tumor. Irradiation was sustained for 20 min with a laser light (630 nm) at 100 mW/cm2. In group 2, the laser optical fiber was placed around, and not inserted into, tumors. In group 3, PDT was conducted as in group 1 but without injection of QDs-RGD. After 28 days of observation, tumors on the back of mice in group 1 grew slowly (V/V0 =3.24±0.70) compared with the control groups, whose tumors grew quickly, and the mean V/V0 reached 6.08±0.50 (group 2) and 7.25±0.82 (group 3). Histology of tumor tissues showed more necrotic tissues, more inflammatory cells, and less vascular tissue in the PDT group than those in the control groups. These results suggest that QDs-RGD-mediated PDT, with illumination using an optical fiber inserted directly into the tumor, can inhibit the growth of SW1990 tumors with high efficiency in nude mice.

EPR and Structural Characterization of Water-Soluble Mn2+-Doped Si Nanoparticles

Water-soluble poly(allylamine) Mn²⁺-doped Si (Si_Mn) nanoparticles (NPs) were prepared and show promise for biologically related applications. The nanoparticles show both strong photoluminescence and good magnetic resonance contrast imaging. The morphology and average diameter were obtained through transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM); spherical crystalline Si NPs with an average diameter of 4.2 ± 0.7 nm were observed. The doping maximum obtained through this process was an average concentration of 0.4 ± 0.3% Mn per mole of Si. The water-soluble Si_Mn NPs showed a strong photoluminescence with a quantum yield up to 13%. The Si_Mn NPs had significant T₁ contrast with an r₁ relaxivity of 11.1 ± 1.5 mM^-1 s^-1 and r₂ relaxivity of 32.7 ± 4.7 mM^-1 s^-1 where the concentration is in mM of Mn²⁺. Dextran-coated poly(allylamine) Si_Mn NPs produced NPs with T₁ and T₂ contrast with a r₁ relaxivity of 27.1 ± 2.8 mM^-1 s^-1 and r₂ relaxivity of 1078.5 ± 1.9 mM^-1 s^-1. X-band electron paramagnetic resonance spectra are fit with a two-site model demonstrating that there are two types of Mn²⁺ in these NP's. The fits yield hyperfine splittings (A) of 265 and 238 MHz with significant zero field splitting (D and E terms). This is consistent with Mn in sites of symmetry lower than tetrahedral due to the small size of the NP's.

Bright, near infrared emitting PLGA–PEG dye-doped CN-PPV nanoparticles for imaging applications

In this publication, we describe the synthesis of near-IR emitting conjugated polymer nanoparticles with an engineered surface, and their use in biological imaging.

Facile and green one pot synthesis of zinc sulphide quantum dots employing zinc-based ionic liquids and their photocatalytic activity

Zinc-based ionic liquids are found to be suitable candidates for the preparation of ZnS QDs, whose properties depend upon the alkyl chain length of imidazolium.

Application of semiconductor quantum dots in bioimaging and biosensing

In this review we present new concepts and recent progress in the application of semiconductor quantum dots (QD) as labels in two important areas of biology, bioimaging and biosensing.

Interfacing Luminescent Quantum Dots with Functional Molecules for Optical Sensing Applications

Semiconductor quantum dots possess unique size-dependent electronic properties and are of high potential interest for the construction of functional nanodevices. Photoinduced electron- and energy-transfer processes between quantum dots and surface-bound molecular species open up attractive routes to implement chemical switching of luminescence, which is at the basis of luminescence sensing. In this article, we discuss the general principles underlying the rational design of this kind of multicomponent species. Successively, we illustrate a few prominent examples, taken from the recent literature, of luminescent chemosensors constructed by attaching molecular species to the surface of quantum dots.