Surface functionalization of quantum dots for biological applications

A novel fluorescence immunoassay for the quantitative detection of florfenicol in animal-derived foods based on ZnCdSe/ZnS quantum dot labelled antibody

Florfenicol (F), an antimicrobial agent exclusive to veterinary use within the chloramphenicol class, is extensively applied as a broad-spectrum remedy for animal diseases. Despite its efficacy, concerns arise over potential deleterious residues in animal-derived edibles, posing threats to human health. This study pioneers an innovative approach, introducing a quantum dot fluorescence-based immunoassay (FLISA) for the meticulous detection of F residues in animal-derived foods and feeds. This method demonstrates heightened sensitivity, with a detection limit of 0.3 ng/mL and a quantitative detection range of 0.6-30.4 ng/mL. Method validation, applied to diverse food sources, yields recoveries from 90.4 % to 109.7 %, featuring RSDs within 1.3 % to 8.7 %, the results showed high consistency with the national standard HPLC-MS/MS detection method. These findings underscore the method's accuracy and precision, positioning it as a promising tool for swift and reliable F residue detection, with substantial implications for fortifying food safety monitoring.

Carbon Dots in Photodynamic/Photothermal Antimicrobial Therapy

Antimicrobial resistance (AMR) presents an escalating global challenge as conventional antibiotic treatments become less effective. In response, photodynamic therapy (PDT) and photothermal therapy (PTT) have emerged as promising alternatives. While rooted in ancient practices, these methods have evolved with modern innovations, particularly through the integration of lasers, refining their efficacy. PDT harnesses photosensitizers to generate reactive oxygen species (ROS), which are detrimental to microbial cells, whereas PTT relies on heat to induce cellular damage. The key to their effectiveness lies in the utilization of photosensitizers, especially when integrated into nano- or micron-scale supports, which amplify ROS production and enhance antimicrobial activity. Over the last decade, carbon dots (CDs) have emerged as a highly promising nanomaterial, attracting increasing attention owing to their distinctive properties and versatile applications, including PDT and PTT. They can not only function as photosensitizers, but also synergistically combine with other photosensitizers to enhance overall efficacy. This review explores the recent advancements in CDs, underscoring their significance and potential in reshaping advanced antimicrobial therapeutics.

Recent advances in molecularly imprinted polymers (MIPs) for visual recognition and inhibition of α-dicarbonyl compound-mediated Maillard reaction products

α-Dicarbonyl compounds (α-DCs) are important intermediates and precursors of harmful Maillard reaction products (e.g., acrylamide and late glycosylation end-products), and they exist widely in thermoprocessed sugar- or fat-rich foods. α-DCs and their end-products are prone to accumulation in the human body and lead to the development of various chronic diseases. Therefore, detection of α-DCs and their associated hazards in food samples is crucial. This paper reviews the preparation of molecularly imprinted polymers (MIPs) enabling visual intelligent responses and the strategies for recognition and capture of α-DCs and their associated hazards, and provides a comprehensive summary of the development of visual MIPs, including integration strategies and applications with real food samples. The visual signal responses as well as the mechanisms for hazard recognition and capture are highlighted. Current challenges and prospects for visual MIPs with advanced applications in food, agricultural and environmental samples are also discussed. This review will open new horizons regarding visual MIPs for recognition and inhibition of hazards in food safety.

A review on synthesis, properties, and biomedical applications of graphene quantum dots (GQDs)

A new type of 0-dimensional carbon-based materials called graphene quantum dots (GQDs) is gaining significant attention as a non-toxic and eco-friendly nanomaterial. GQDs are nanomaterials composed of sp2hybridized carbon domains and functional groups, with their lateral size less than 10 nm. The unique and exceptional physical, chemical, and optical properties arising from the combination of graphene structure and quantum confinement effect due to their nano-size make GQDs more intriguing than other nanomaterials. Particularly, the low toxicity and high solubility derived from the carbon core and abundant edge functional groups offer significant advantages for the application of GQDs in the biomedical field. In this review, we summarize various synthetic methods for preparing GQDs and important factors influencing the physical, chemical, optical, and biological properties of GQDs. Furthermore, the recent application of GQDs in the biomedical field, including biosensor, bioimaging, drug delivery, and therapeutics are discussed. Through this, we provide a brief insight on the tremendous potential of GQDs in biomedical applications and the challenges that need to be overcome in the future.

Hybridized quantum dot, silica, and gold nanoparticles for targeted chemo-radiotherapy in colorectal cancer theranostics

Multimodal nanoparticles, utilizing quantum dots (QDs), mesoporous silica nanoparticles (MSNs), and gold nanoparticles (Au NPs), offer substantial potential as a smart and targeted drug delivery system for simultaneous cancer therapy and imaging. This method entails coating magnetic GZCIS/ZnS QDs with mesoporous silica, loading epirubicin into the pores, capping with Au NPs, PEGylation, and conjugating with epithelial cell adhesion molecule (EpCAM) aptamers to actively target colorectal cancer (CRC) cells. This study showcases the hybrid QD@MSN-EPI-Au-PEG-Apt nanocarriers (size ~65 nm) with comprehensive characterizations post-synthesis. In vitro studies demonstrate the selective cytotoxicity of these targeted nanocarriers towards HT-29 cells compared to CHO cells, leading to a significant reduction in HT-29 cell survival when combined with irradiation. Targeted delivery of nanocarriers in vivo is validated by enhanced anti-tumor effects with reduced side effects following chemo-radiotherapy, along with imaging in a CRC mouse model. This approach holds promise for improved CRC theranostics.

Enzyme-Responsive Modular Peptides Enhance Tumor Penetration of Quantum Dots via Charge Reversal Strategy

Quantum dots (QDs) are colloidal semiconductor nanoparticles acting as fluorescent probes for detection, disease diagnosis, and photothermal and photodynamic therapy. However, their performance in cancer treatment is limited by inadequate tumor accumulation and penetration due to the larger size of nanoparticles compared to small molecules. To address this challenge, charge reversal nanoparticles offer an effective strategy to prolong blood circulation time and achieve enhanced endocytosis and tumor penetration. In this study, we leveraged the overexpressed γ-glutamyl transpeptidase (GGT) in many human tumors and developed a library of modular peptides to serve as water-soluble surface ligands of QDs. We successfully transferred the QDs from the organic phase to the aqueous phase within 5 min. And through systematic tuning of the peptide sequence, we optimized the fluorescent stability of QDs and their charge reversal behavior in response to GGT. The resulting optimal peptide stabilized QDs in aqueous solution with a high fluorescent retention rate of 93% after three months and realized the surface charge reversal of QDs triggered by GGT in vitro. The binding between the peptide and QD surface was investigated by using saturation transfer differential nuclear magnetic resonance (STD NMR). Thanks to its charge reversal ability, the GGT-responsive QDs exhibited enhanced cellular uptake in GGT-expressing cancer cells and deeper penetration in the 3D multicellular spheroids. This enzyme-responsive modular peptide can lead to specific tumor targeting and deeper tumor penetration, holding great promise to enhance the treatment efficacy of QD-based theranostics.

Doxorubicin Conjugated γ-Globulin Functionalised Gold Nanoparticles: A pH-Responsive Bioinspired Nanoconjugate Approach for Advanced Chemotherapeutics

Developing successful nanomedicine hinges on regulating nanoparticle surface interactions within biological systems, particularly in intravenous nanotherapeutics. We harnessed the surface interactions of gold nanoparticles (AuNPs) with serum proteins, incorporating a γ-globulin (γG) hard surface corona and chemically conjugating Doxorubicin to create an innovative hybrid anticancer nanobioconjugate, Dox-γG-AuNPs. γG (with an isoelectric point of ~7.2) enhances cellular uptake and exhibits pH-sensitive behaviour, favouring targeted cancer cell drug delivery. In cell line studies, Dox-γG-AuNPs demonstrated a 10-fold higher cytotoxic potency compared to equivalent doxorubicin concentrations, with drug release favoured at pH 5.5 due to the γ-globulin corona's inherent pH sensitivity. This bioinspired approach presents a novel strategy for designing hybrid anticancer therapeutics. Our study also explored the intricacies of the p53-mediated ROS pathway's role in regulating cell fate, including apoptosis and necrosis, in response to these treatments. The pathway's delicate balance of ROS emerged as a critical determinant, warranting further investigation to elucidate its mechanisms and implications. Overall, leveraging the robust γ-globulin protein corona on AuNPs enhances biostability in harsh serum conditions, augments anticancer potential within pH-sensitive environments, and opens promising avenues for bioinspired drug delivery and the design of novel anticancer hybrids with precise targeting capabilities.

Recent Advances in Chemistry, Mechanism, and Applications of Quantum Dots in Photodynamic and Photothermal Therapy

Semiconductor quantum dots (QD) are a kind of nanoparticle with unique optical properties that have attracted a lot of attention in recent years. In this paper, the characteristics of these nanoparticles and their applications in nanophototherapy have been reviewed. Phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT), has gained special importance because of its high accuracy and local treatment due to the activation of the drug at the tumor site. PDT is a new way of cancer treatment that is performed by activating light-sensitive compounds named photosensitizers (PS) by light. PSs cause the destruction of diseased tissue through the production of singlet oxygen. PTT is another non-invasive method that induces cell death through the conversion of near-infrared light (NIR) into heat in the tumor situation by the photothermal agent (PA). Through using energy transfer via the FRET (Förster resonance energy transfer) process, QDs provide light absorption wavelength for both methods and cover the optical weaknesses of phototherapy agents.

Recent Breakthroughs in Using Quantum Dots for Cancer Imaging and Drug Delivery Purposes

Cancer is one of the leading causes of death worldwide. Because each person's cancer may be unique, diagnosing and treating cancer is challenging. Advances in nanomedicine have made it possible to detect tumors and quickly investigate tumor cells at a cellular level in contrast to prior diagnostic techniques. Quantum dots (QDs) are functional nanoparticles reported to be useful for diagnosis. QDs are semiconducting tiny nanocrystals, 2-10 nm in diameter, with exceptional and useful optoelectronic properties that can be tailored to sensitively report on their environment. This review highlights these exceptional semiconducting QDs and their properties and synthesis methods when used in cancer diagnostics. The conjugation of reporting or binding molecules to the QD surface is discussed. This review summarizes the most recent advances in using QDs for in vitro imaging, in vivo imaging, and targeted drug delivery platforms in cancer applications.

Novel Förster Resonance Energy Transfer probe with quantum dot for a long-time imaging of active caspases inside individual cells

With the goal to investigate biological phenomena at a single-cell level, we designed, synthesized and tested a molecular probe based on Förster resonance energy transfer (FRET) between a highly luminescent quantum dot (QD) as a donor and a fluorophore or fluorescence quencher as an acceptor linked by a specific peptide. In principle, QD luminescence, effectively dissipated in the probe, is switched on after the cleavage of the peptide by a protease and the release of the quencher. We proposed a novel synthesis strategy of a probe. A two-step synthesis consists of: (i) Conjugation of CdTe QDs functionalized by -COOH groups of succinic acid on the nanoparticle surface with the designed specific peptide (GTADVEDTSC) using a ligand-exchange approach; (ii) A fast, high-yield reaction of amine-reactive succinimidyl group on the BHQ-2 quencher with N-terminal of the peptide. This way, any crosslinking between individual nanoparticles and any nonspecific conjugation bonds are excluded. The analysis of the product after the first step proved a high reaction yield and nearly no occurrence of unreacted QDs, a prerequisite of the specificity of our luminescent probe. Its parameters evaluated as Michaelis-Menten description of enzymatic kinetics are similar to products published by other groups. Our research is focused on the fluorescence microscopy analyses of biologically active molecules, such as proteolytic active caspases, playing important roles in cell signaling regulations in normal and diseased states. Consequently, they are attractive targets for clinical diagnosis and medical therapy. The ultimate goal of our work was to synthesize a new QD luminescent probe for a long-time quantitative monitoring of active caspase-3/7 distribution in apoptotic osteoblastic MC3T3-E1 cells treated with camptothecin. As a result of comparison, our synthetized luminescent probe provides longer imaging times of caspases than commercial products. The probe proved the stability of the luminescence signal inside cells for more than 14 days.

Recent Advances in Colorimetric Tests for the Detection of Infectious Diseases and Antimicrobial Resistance

Diagnosis of infection-causing microorganisms with sensitive, rapid, selective and economical diagnostic tests is critical to start the right treatment. With these tests, the spread of infections can be prevented. In addition to that, the detection of antimicrobial resistance also makes a significant contribution to public health. In recent years, different types of diagnostic tests have been developed as alternatives to traditional diagnostic tests used in clinics. In particular, colorimetric tests, which minimize the need for an instrument, have advantages owing to their cost effectiveness, rapid response and naked-eye detection and practical use. In this review, we especially focused on pH indicators and nanomaterial-based colorimetric tests in detection of infection-causing microorganisms and antimicrobial resistance.

Aflatoxin detection technologies: recent advances and future prospects

Aflatoxins have posed serious threat to food safety and human health. Therefore, it is important to detect aflatoxins in samples rapidly and accurately. In this review, various technologies to detect aflatoxins in food are discussed, including conventional ones such as thin-layer chromatography (TLC), high performance liquid chromatography (HPLC), enzyme linked immunosorbent assay (ELISA), colloidal gold immunochromatographic assay (GICA), radioimmunoassay (RIA), fluorescence spectroscopy (FS), as well as emerging ones (e.g., biosensors, molecular imprinting technology, surface plasmon resonance). Critical challenges of these technologies include high cost, complex processing procedures and long processing time, low stability, low repeatability, low accuracy, poor portability, and so on. Critical discussion is provided on the trade-off relationship between detection speed and detection accuracy, as well as the application scenario and sustainability of different technologies. Especially, the prospect of combining different technologies is discussed. Future research is necessary to develop more convenient, more accurate, faster, and cost-effective technologies to detect aflatoxins.

MicroLED biosensor with colloidal quantum dots and smartphone detection

A fluorescence sensor with the capability for spatially multiplexed measurements utilizing smartphone detection is presented. Bioconjugated quantum dots are used as the fluorescent tag and are excited using a blue-emitting microLED (µLED). The 1-dimensional GaN µLED array is butt-coupled to one edge of the glass slide to take advantage of total internal reflection fluorescence (TIRF) principles. The bioassays on the top surface of the glass waveguide are excited and the resultant fluorescence is detected with the smartphone. The red, green, and blue channels of the digital image are utilized to spectrally separate the excitation light from the fluorescence for analysis. Using a biotin-functionalized glass slide as proof of principle, we have shown that streptavidin conjugated quantum dots can be detected down to a concentration of 8 nM.

Surface decorated quantum dots: Synthesis, properties and role in herbal therapy

Quantum dots are the serendipitous outcome of materials research. It is the tiny carbonaceous nanoparticles with diameters ranging from 1 to 10 nm. This review is a brief discussion of the synthesis, properties, and biomedical applicability of quantum dots, especially in herbal therapy. As quantum dots are highly polar, they can be surface decorated with several kinds of polar functionalities, such as polymeric molecules, small functional molecules, and so on. The review also consists of the basic physical and optical properties of quantum dots and their excitation-dependent properties in the application section. We focus on therapeutics, where quantum dots are used as drugs or imaging probes. Nanoprobes for several diagnostics are quite new in the biomedical research domain. Quantum dot-based nanoprobes are in high demand due to their excellent fluorescence, non-bleaching nature, biocompatibility, anchoring feasibility for several analytes, and fast point-of-care sensibility. Lastly, we also included a discussion on quantum dot-based drug delivery as phytomedicine.

Bioanalytical Applications of Graphene Quantum Dots for Circulating Cell-Free Nucleic Acids: A Review

Graphene quantum dots (GQDs) are carbonaceous nanodots that are natural crystalline semiconductors and range from 1 to 20 nm. The broad range of applications for GQDs is based on their unique physical and chemical properties. Compared to inorganic quantum dots, GQDs possess numerous advantages, including formidable biocompatibility, low intrinsic toxicity, excellent dispensability, hydrophilicity, and surface grating, thus making them promising materials for nanophotonic applications. Owing to their unique photonic compliant properties, such as superb solubility, robust chemical inertness, large specific surface area, superabundant surface conjugation sites, superior photostability, resistance to photobleaching, and nonblinking, GQDs have emerged as a novel class of probes for the detection of biomolecules and study of their molecular interactions. Here, we present a brief overview of GQDs, their advantages over quantum dots (QDs), various synthesis procedures, and different surface conjugation chemistries for detecting cell-free circulating nucleic acids (CNAs). With the prominent rise of liquid biopsy-based approaches for real-time detection of CNAs, GQDs-based strategies might be a step toward early diagnosis, prognosis, treatment monitoring, and outcome prediction of various non-communicable diseases, including cancers.

Tunable Optical Molecular Thermometers Based on Metallacrowns

The effect of ligands' energy levels on thermal dependence of lanthanide emission was examined to create new molecular nanothermometers. A series of Ln₂Ga₈L₈^'L₈^″ metallacrowns (shorthand Ln₂L₈^'), where Ln = Gd³⁺, Tb³⁺, or Sm³⁺ (H₃L' = salicylhydroxamic acid (H₃shi), 5-methylsalicylhydroxamic acid (H₃mshi), 5-methoxysalicylhydroxamic acid (H₃moshi), and 3-hydroxy-2-naphthohydroxamic acid (H₃nha)) and H₂L″ = isophthalic acid (H₂iph), was synthesized and characterized. Within the series, ligand-centered singlet state (S₁) energy levels ranged from 23,300 to 27,800 cm^-1, while triplet (T₁) energy levels ranged from 18,150 to 21,980 cm^-1. We demonstrated that the difference between T₁ levels and relevant energies of the excited ⁴G_5/2 level of Sm³⁺ (17,800 cm^-1) and ⁵D₄ level of Tb³⁺ (20,400 cm^-1) is the major parameter controlling thermal dependence of the emission intensity via the back energy transfer mechanism. However, when the energy difference between S₁ and T₁ levels is small (below 3760 cm^-1), the S₁ → T₁ intersystem crossing (and its reverse, S₁ ← T₁) mechanism contributes to the thermal behavior of metallacrowns. Both mechanisms affect Ln³⁺-centered room-temperature quantum yields with values ranging from 2.07(6)% to 31.2(2)% for Tb₂L₈^' and from 0.0267(7)% to 2.27(5)% for Sm₂L₈^'. The maximal thermal dependence varies over a wide thermal range (ca. 150-350 K) based on energy gaps between relevant ligand-based and lanthanide-based electronic states. By mixing Tb₂moshi₈^' with Sm₂moshi₈^' in a 1:1 ratio, an optical thermometer with a relative thermal sensitivity larger than 3%/K at 225 K was created. Other temperature ranges are also accessible with this approach.

Semiconductor quantum dots for photodynamic therapy: Recent advances

Photodynamic therapy is a promising cancer treatment that induces apoptosis as a result of the interactions between light and a photosensitizing drug. Lately, the emergence of biocompatible nanoparticles has revolutionized the prospects of photodynamic therapy (PDT) in clinical trials. Consequently, a lot of research is now being focused on developing non-toxic, biocompatible nanoparticle-based photosensitizers for effective cancer treatments using PDT. In this regard, semiconducting quantum dots have shown encouraging results. Quantum dots are artificial semiconducting nanocrystals with distinct chemical and physical properties. Their optical properties can be fine-tuned by varying their size, which usually ranges from 1 to 10 nm. They present many advantages over conventional photosensitizers, mainly their emission properties can be manipulated within the near IR region as opposed to the visible region by the former. Consequently, low intensity light can be used to penetrate deeper tissues owing to low scattering in the near IR region. Recently, successful reports on imaging and PDT of cancer using carbon (carbon, graphene based) and metallic (Cd based) based quantum dots are promising. This review aims to summarize the development and the status quo of quantum dots for cancer treatment.

Construction and Evaluation of Traceable rhES-QDs-M-MS Protein Delivery System: Sustained-Release Properties, Targeted Effect, and Antitumor Activity

Recombinant human endostatin (rhES) is a protein drug with poor stability and short in vivo circulation time. The present study was therefore aimed at developing sustained-release lung targeted microspheres drug delivery system and evaluating its targeting efficiency using in vivo imaging techniques with quantum dots (QDs) as the imaging material. The oil-soluble QDs were coated with amphiphilic polymers to obtain a polymer-quantum dots micelle (QDs-M) with the potential to stably disperse in water. The rhES and QDs-M were combined using covalent bonds. The rhES-QDs-M microspheres (rhES-QDs-M-MS) were prepared using electrostatic spray technology and also evaluated via in vivo imaging techniques. The pharmacodynamics was further studied in mice. The rhES-QDs-M-MS (4-8 μm) were stable in an aqueous medium with good optical properties. The in vitro studies showed that the rhES-QDs-M-MS had sustained release which was maintained for at least 15 days (cumulative release >80%) without any burst release. The rhES-QDs-M-MS had a very high safety profile and also effectively inhibited the in vitro proliferation of human umbilical vein endothelial cells by about 70%. The pharmacokinetic results showed that the rhES could still be detected at 72 h in the experimental group which meant that the rhES-QDs-M-MS had a significant sustained-release effect. The rhES-QDs-M-MS had a better lung targeting effect and higher antitumor activity compared with the rhES. The traceable rhES-QDs-M-MS served as a promising drug delivery system for the poorly stable rhES proteins and significantly increased its lung-targeted effect, sustained-release properties, and antitumor activities.

Development of quantum dot-phthalocyanine integrated G-quadruplex /double-stranded DNA biosensor

In the present study, the phthalocyanine (Pc) integrated mercaptopropionic acid capped quantum dot (mpa@QD) biosensor has been developed for the quantitative determination of G-quadruplex and double-stranded DNA. The working principle of the developed biosensor platform is based on the quenching of the emission signal of the mpa@QD in the presence of Pc (closed position) and the recovery of the fluorescence signal in the presence of DNA (open position). The parameters affecting biosensor performance, such as Pc type and concentration, were optimized. Since the developed biosensor aimed to determine G-quadruplex and double-stranded DNA in biological samples, the effect of common ions (such as Na⁺, Mg²⁺) and serum albumin found in many biological matrices on the biosensor performance were examined. The effect of common ions on biosensor signal was negligible, except Zn²⁺. The analytical properties of the biosensor, such as linear range, calibration sensitivity, relative standard deviation %, the limit of detection, and quantification, were determined. The limit of detection and quantification values were found 0.055 μM and 0.18 μM for AS1411, 0.061 μM and 0.20 μM for Tel21, 0.038 μM and 0.13 μM for Tel45 and 0.091 μM and 0.30 μM for ctDNA. Several different synthetic samples were prepared. The spiked synthetic samples such as mammalian cell medium were used to evaluate the analytical performance of Pc-mpa@QD. All synthetic samples were prepared with polyethylene glycol, which resembles biological samples' crowded environment.

Combining metal nanoclusters and carbon nanomaterials: Opportunities and challenges in advanced nanohybrids

The development of functional materials with uniquely advanced properties lies at the core of nanoscience and nanotechnology. From the myriad possible combinations of organic and/or inorganic blocks, hybrids combining metal nanoclusters and carbon nanomaterials have emerged as highly attractive colloidal materials for imaging, sensing (optical and electrochemical) and catalysis, among other applications. While the metal nanoclusters provide extraordinary luminescent and electronic properties, the carbon nanomaterials (of zero, one or two dimensions) convey versatility, as well as unique interfacial, electronic, thermal, optical, and mechanical properties, which altogether can be put to use for the desired application. Herein, we present an overview of the field, for experts and non-experts, encompassing the basic properties of the building blocks, a systematic view of the chemical preparation routes and physicochemical properties of the hybrids, and a critical analysis of their ongoing and emerging applications. Challenges and opportunities, including directions towards green chemistry approaches, are also discussed.

Quantum Dots for Cancer-Related miRNA Monitoring

Quantum dots (QDs) possess exceptional optoelectronic properties that enable their use in the most diverse applications, namely, in the medical field. The prevalence of cancer has increased and has been considered the major cause of death worldwide. Thus, there has been a great demand for new methodologies for diagnosing and monitoring cancer in cells to provide an earlier prognosis of the disease and contribute to the effectiveness of treatment. Several molecules in the human body can be considered relevant as cancer markers. Studies published over recent years have revealed that micro ribonucleic acids (miRNAs) play a crucial role in this pathology, since they are responsible for some physiological processes of the cell cycle and, most important, they are overexpressed in cancer cells. Thus, the analytical sensing of miRNA has gained importance to provide monitoring during cancer treatment, allowing the evaluation of the disease's evolution. Recent methodologies based on nanochemistry use fluorescent quantum dots for sensing of the miRNA. Combining the unique characteristics of QDs, namely, their fluorescence capacity, and the fact that miRNA presents an aberrant expression in cancer cells, the researchers created diverse strategies for miRNA monitoring. This review aims to present an overview of the recent use of QDs as biosensors in miRNA detection, also highlighting some tutorial descriptions of the synthesis methods of QDs, possible surface modification, and functionalization approaches.

Comparative Studies of Blue-Emitting Zinc Selenide Nanocrystals Doped with Ag, Cu, and Mg towards Medical Applications

Blue-emitting Ag(+)-, Cu(2+)-, and Mg(2+)-doped ZnSe nanoparticles (NPs) were successfully synthesized at 80 °C by the precipitation method by using mercaptopropionic acid (MPA) as a stabilizer. UV–visible and photoluminescence (PL) studies were applied to investigate their physicochemical properties. Their structural properties were confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and transmission electron microscopy (TEM). The size of the ZnSe: X-capped MPA showed a strong relationship with dopant metals. The diameters of the Mg-doped ZnSe and the Cu-doped ZnSe were 22–24 nm, while the Ag-doped ZnSe was halved, at about 13 nm. The photoluminescence was within a wavelength range of 400–550 nm. In addition, the PL intensities, as well as the photoluminescence quantum yields, were in the order of the decreasing ionic radii of the dopant metals (ZnSe:Ag < ZnSe:Mg < ZnSe:Cu). Furthermore, through the interaction with lysine, the PL intensity of the ZnSe:X was changed. Interestingly, the capacity of the ZnSe:Mg for lysine was significantly higher than that of other dopant metals. Moreover, the toxicity of the ZnSe:Mg was relatively insignificant toward the hMSCs (about 80% cell viability at 320 ppm), compared to the transition-metal dopant. Therefore, the ZnSe:Mg material could have great potential for bioapplications.

Functionalized Nanostructured Bioactive Carriers: Nanoliposomes, Quantum Dots, Tocosome and Theranostic Approach

BACKGROUND

Lipidic nanocarriers have great potential for the encapsulation and delivery of numerous bioactive compounds. They have demonstrated significant benefits over traditional disease management and conventional therapy. The benefits associated with the particular properties of lipidic nanocarriers include site-specific drug deposition, improved pharmacokinetics and pharmacodynamics, enhanced internalization and intracellular transport, biodegradability, and decreased biodistribution. These properties result in the alleviation of the harmful consequences of conventional treatment protocols. Scope and approach: The administration of various bioactive molecules has been extensively investigated using nanostructured lipid carriers. In this article, theranostic applications of novel formulations of lipidic nanocarriers combined or complexed with quantum dots, certain polymers such as chitosan, and metallic nanoparticles (particularly gold) are reviewed. These formulations have demonstrated better controlled release features, improved drug loading capability, as well as a lower burst release rate. As a recent innovation in the field of drug delivery, tocosomes and their unique advantages are also explained in the final section of this entry.

KEY FINDINGS AND CONCLUSIONS

Theranostic medicine requires nanocarriers with improved target-specific accumulation and bio-distribution. Towards this end, lipid-based nanocarrier systems and tocosomes combined with unique properties of quantum dots, biocompatible polymers, and metallic nanoparticles seem to be ideal candidates to be considered for safe and efficient drug delivery.

Nanoparticles for Diagnosis and Target Therapy in Pediatric Brain Cancers

Pediatric brain tumors represent the most common types of childhood cancer and novel diagnostic and therapeutic solutions are urgently needed. The gold standard treatment option for brain cancers in children, as in adults, is tumor resection followed by radio- and chemotherapy, but with discouraging therapeutic results. In particular, the last two treatments are often associated to significant neurotoxicity in the developing brain of a child, with resulting disabilities such as cognitive problems, neuroendocrine, and neurosensory dysfunctions/deficits. Nanoparticles have been increasingly and thoroughly investigated as they show great promises as diagnostic tools and vectors for gene/drug therapy for pediatric brain cancer due to their ability to cross the blood–brain barrier. In this review we will discuss the developments of nanoparticle-based strategies as novel precision nanomedicine tools for diagnosis and therapy in pediatric brain cancers, with a particular focus on targeting strategies to overcome the main physiological obstacles that are represented by blood–brain barrier.

Cell membrane-engineered nanoparticles for cancer therapy

Cell-membrane-coated nanotechnology involves dressing the synthetic nanoparticles (NPs) with membrane derived from different types of cells to endow the NPs with the properties of a specific cell type and to further...

Synthetic Approaches, Modification Strategies and the Application of Quantum Dots in the Sensing of Priority Pollutants

Polycyclic aromatic hydrocarbons (PAHs) and nitro-aromatic compounds (NACs) are two classifications of environmental pollutants that have become a source of health concerns. As a result, there have been several efforts towards the development of analytical methods that are efficient and affordable that can sense these pollutants. In recent decades, a wide range of techniques has been developed for the detection of pollutants present in the environment. Among these different techniques, the use of semiconductor nanomaterials, also known as quantum dots, has continued to gain more attention in sensing because of the optical properties that make them useful in the identification and differentiation of pollutants in water bodies. Reported studies have shown great improvement in the sensing of these pollutants. This review article starts with an introduction on two types of organic pollutants, namely polycyclic aromatic hydrocarbons and nitro-aromatic explosives. This is then followed by different quantum dots used in sensing applications. Then, a detailed discussion on different groups of quantum dots, such as carbon-based quantum dots, binary and ternary quantum dots and quantum dot composites, and their application in the sensing of organic pollutants is presented. Different studies on the comparison of water-soluble quantum dots and organic-soluble quantum dots of a fluorescence sensing mechanism are reviewed. Then, different approaches on the improvement of their sensitivity and selectivity in addition to challenges associated with some of these approaches are also discussed. The review is concluded by looking at different mechanisms in the sensing of polycyclic aromatic hydrocarbons and nitro-aromatic compounds.

Design and Application of Near-Infrared Nanomaterial-Liposome Hybrid Nanocarriers for Cancer Photothermal Therapy

Liposomes are attractive carriers for targeted and controlled drug delivery receiving increasing attention in cancer photothermal therapy. However, the field of creating near-infrared nanomaterial-liposome hybrid nanocarriers (NIRN-Lips) is relatively little understood. The hybrid nanocarriers combine the dual superiority of nanomaterials and liposomes, with more stable particles, enhanced photoluminescence, higher tumor permeability, better tumor-targeted drug delivery, stimulus-responsive drug release, and thus exhibiting better anti-tumor efficacy. Herein, this review covers the liposomes supported various types of near-infrared nanomaterials, including gold-based nanomaterials, carbon-based nanomaterials, and semiconductor quantum dots. Specifically, the NIRN-Lips are described in terms of their feature, synthesis, and drug-release mechanism. The design considerations of NIRN-Lips are highlighted. Further, we briefly introduced the photothermal conversion mechanism of NIRNs and the cell death mechanism induced by photothermal therapy. Subsequently, we provided a brief conclusion of NIRNs-Lips applied in cancer photothermal therapy. Finally, we discussed a synopsis of associated challenges and future perspectives for the applications of NIRN-Lips in cancer photothermal therapy.

Sulfur-doped carbon dots synthesis under microwave irradiation as turn-off fluorescent sensor for Cr(III)

This study synthesized a facile and high sensitive fluorescent probe based on sulfur-doped carbon dots (S-CDs) using a one-step microwave irradiation method. The probe exhibited a strong blue emission and a high quantum yield (QY) of 36.40%. In the detection, the presence of trivalent chromium (Cr(III)) strongly quenched the PL intensity of S-CDs by the inner filter effect (IFE) quenching mechanism of Cr(III) on the S-CDs. The S-CDs exhibited good sensitivity to turn-off Cr(III) detection with a linear range concentration of 0–45 μM and a detection limit of 0.17 μM. Furthermore, the proposed method has been successfully applied for Cr(III) detection in natural water samples with the 93.68–106.20% recoveries.

Current advances in bio-fabricated quantum dots emphasising the study of mechanisms to diversify their catalytic and biomedical applications

Quantum dots (QDs), owing to their single atom-like electronic structure due to quantum confinement, are often referred to as artificial atoms. This unique physical property results in the diverse functions exhibited by QDs. A wide array of applications have been achieved by the surface functionalization of QDs, resulting in exceptional optical, antimicrobial, catalytic, cytotoxic and enzyme inhibition properties. Ordinarily, traditionally prepared QDs are subjected to post synthesis functionalization via a variety of methods, such as ligand exchange or covalent and non-covalent conjugation. Nevertheless, solvent toxicity, combined with the high temperature and pressure conditions during the preparation of QDs and the low product yield due to multiple steps in the functionalization, limit their overall use. This has driven scientists to investigate the development of greener, environmental friendly and cost-effective methods that can circumvent the complexity and strenuousness associated with traditional processes of bio-functionalization. In this review, a detailed analysis of the methods to bio-prepare pre-functionalized QDs, with elucidated mechanisms, and their application in the areas of catalysis and biomedical applications has been conducted. The environmental and health and safety aspects of the bio-derived QDs have been briefly discussed to unveil the future of nano-commercialization.

Harnessing selectivity in chemical sensing via supramolecular interactions: from functionalization of nanomaterials to device applications

Chemical sensing is a strategic field of science and technology ultimately aiming at improving the quality of our lives and the sustainability of our Planet. Sensors bear a direct societal impact on well-being, which includes the quality and composition of the air we breathe, the water we drink, and the food we eat. Pristine low-dimensional materials are widely exploited as highly sensitive elements in chemical sensors, although they suffer from lack of intrinsic selectivity towards specific analytes. Here, we showcase the most recent strategies on the use of (supra)molecular interactions to harness the selectivity of suitably functionalized 0D, 1D, and 2D low-dimensional materials for chemical sensing. We discuss how the design and selection of receptors via machine learning and artificial intelligence hold a disruptive potential in chemical sensing, where selectivity is achieved by the design and high-throughput screening of large libraries of molecules exhibiting a set of affinity parameters that dictates the analyte specificity. We also discuss the importance of achieving selectivity along with other relevant characteristics in chemical sensing, such as high sensitivity, response speed, and reversibility, as milestones for true practical applications. Finally, for each distinct class of low-dimensional material, we present the most suitable functionalization strategies for their incorporation into efficient transducers for chemical sensing.

Efficient and Versatile Application of Fluorescence DNA-Conjugated CdTe Quantum Dots Nanoprobe for Detection of a Specific Target DNA of SARS Cov-2 Virus

Regarding the outbreak of the SARS Cov-2 virus pandemic worldwide, it seems necessary to provide new diagnostic methods to combat the virus. A fluorescence CdTe quantum dots-DNA (QDs-DNA) nanosensor was prepared for efficient detection of a specific target complementary DNA or RNA from the SARS Cov-2 virus using FRET experiment via forming a classic "sandwich" structure. The sequence of the complementary DNA (target DNA) is planned based on a substantial part of the SARS Cov-2 virus genome, and oligonucleotides of QDs-DNA nanoprobe are designed to complement it. The water-soluble CdTe QDs-DNA was prepared by replacing the thioglycolic acid (TGA) on the surface of QDs with capture DNA (thiolated DNA) through a ligand-exchange method. Subsequently, with the addition of complementary (target DNA) and quencher DNA (BHQ₂-labeled DNA) into the QDs-DNA conjugates, sandwiched hybrids were formed. The resulting assembly brings the BHQ₂-labeled DNA (as the acceptor), and the QDs (as the donor) into proximity, leading to quenching of fluorescence emission from the donor QDs through the FRET mechanism. In other words, a simple, highly sensitive, selective, and rapid approach was introduced to detect complementary DNA sequence from a specific part of the SARS Cov-2 virus genome with a detection limit of 2.52 × 10^-9 mol L^-1. Furthermore, the planned nanosensor was well used for the detection of RNA from SARS Cov-2 viruses in real samples with satisfactory analytical results, and the outcomes were compared with RT-PCR (Reverse Transcription Polymerase Chain Reaction) as the well-known standard method.

Effect of Serum Albumin on Porphyrin-Quantum Dot Complex Formation, Characteristics and Spectroscopic Analysis

The effect of bovine serum albumin (BSA) upon interaction between CdTe QD functionalized by 3-Mercaptopropionic Acid (CdTe-3-MPA QD) and two water soluble porphyrins: positively charged meso-tetra methyl pyridyl porphyrin (TMPyP) and negatively charged meso-tetrakis(p-sulfonato-phenyl) porphyrin (TPPS₄), was studied in function of pH using the steady-state and time resolved optical absorption and fluorescence spectroscopies. It was shown that, depending on the charge state of the components, interaction with albumin could either prevent the formation of the QD…PPh complex, form a mixed QD…PPh…BSA complex or not affect PPh complexation with QD at all. The obtained results may be of interest for application in photomedicine.

Carbon Based Nanodots in Early Diagnosis of Cancer

Detection of cancer at an early stage is one of the principal factors associated with successful treatment outcome. However, current diagnostic methods are not capable of making sensitive and robust cancer diagnosis. Nanotechnology based products exhibit unique physical, optical and electrical properties that can be useful in diagnosis. These nanotech-enabled diagnostic representatives have proved to be generally more capable and consistent; as they selectively accumulated in the tumor site due to their miniscule size. This article rotates around the conventional imaging techniques, the use of carbon based nanodots viz Carbon Quantum Dots (CQDs), Graphene Quantum Dots (GQDs), Nanodiamonds, Fullerene, and Carbon Nanotubes that have been synthesized in recent years, along with the discovery of a wide range of biomarkers to identify cancer at early stage. Early detection of cancer using nanoconstructs is anticipated to be a distinct reality in the coming years.

Synthesis of biocompatible, BSA capped fluorescent CaCO3 pre-nucleation nanoclusters for cell imaging applications

Novel, photostable, multicolour fluorescent, highly biocompatible, water soluble, BSA capped pre-nucleation CaCO3 nanoclusters (FCPN) (∼1.3 nm) are developed using a facile biomineralization process. M. oleifera leaf extract and BSA protein are used as sources of ascorbic acid and capping agent, respectively. The developed FCPN shows fluorescence in the blue, green, and yellow/red region with an average life time of 1.05, 6.23 and 30.60 ns, respectively. The MALDI-MS measurements reveal that these nanoclusters are 16, 50, 73, 222 and 936 molecules big. These FCPN, when incubated (up to 7 days) with MG-63 cells, demonstrate an increase in cell viability percentage with time period as compared to their control samples. Furthermore, these incubated cells were investigated using confocal microscopy to estimate the FCPN diffusion penetration depth using CTCF analysis. It has been observed that blue and green emitting FCPN penetrated 6 μm, whereas red emitting FCPN traversed only 4 μm. The relative quantum yield (Rhodamine 6G = 0.92) of FCPN for green emission was found to be 0.0175 in water. The prepared nanoclusters displayed four months shelf-life. These FCPN were prepared using an environmentally benign, inexpensive, green synthetic route without using toxic reducing agents. Furthermore, the current report discusses the detailed results, obtained from X-ray photoelectron spectroscopy, MALDI-MS, Fourier transform infrared spectroscopy, UV-visible, fluorescence spectroscopy, lifetime measurements, electron microscopy, fluorescence microscopy and confocal microscopy.

PSMA conjugated combinatorial liposomal formulation encapsulating genistein and plumbagin to induce apoptosis in prostate cancer cells

Although the biomedical sciences have achieved tremendous success in developing novel approaches to managing prostate cancer, this disease remains one of the major health concerns among men worldwide. Liposomal formulations of single drugs have shown promising results in cancer treatment; however, the use of multi drugs has shown a better therapeutic index than individual drugs. The identification of cancer-specific receptors has added value to design targeted drug delivering nanocarriers. We have developed genistein and plumbagin co-encapsulating liposomes (∼120 nm) with PSMA specific antibodies to target prostate cancer cells selectively in this work. These liposomes showed >90 % decrease in PSMA expressing prostate cancer cell proliferation without any appreciable toxicity to healthy cells and human red blood cells. Release of plumbagin and genistein was found to decrease the expression of PI3/AKT3 signaling proteins and Glut-1 receptors (inhibited glucose uptake and metabolism), respectively. The decrease in migration potential of cells and induced apoptosis established the observed anti-proliferative effect in prostate cancer cell lines. The discussed strategy of developing novel, non-toxic, and PSMA specific antibody conjugated liposomes carrying genistein and plumbagin drugs may also be used for encapsulating other drugs and inhibit the growth of different types of cancers.

Effect of alkali bases on the synthesis of ZnO quantum dots

The surface-modified zinc oxide quantum dots (ZnO QDs) have broad application prospects in the field of biomedicine because of their good water solubility, dispersibility, and high fluorescence stability. The alkali bases play important roles in controlling the morphology, size distribution, dispersity, and fluorescence intensity of the synthesized ZnO QDs. In this article, ZnO QDs were synthesized to induce hydrolysis–condensation reaction. The influences of alkali bases (LiOH, NaOH, and KOH) and the ratio of n(Zn2+):n(OH−) on the properties of synthesized ZnO QDs were investigated. The results show that the particle size of the ZnO QDs prepared using LiOH and NaOH as raw materials are smaller than that using KOH. ZnO QDs prepared at the ratio of n(Zn2+):n(LiOH) = 1:1 have the best fluorescence performance and dispersibility.

Phase Transfer and DNA Functionalization of Quantum Dots Using an Easy-to-Prepare, Low-Cost Zwitterionic Polymer

Small, stable, and bright quantum dots (QDs) are of interest in many biosensing and biomedical imaging applications, but current methodologies for obtaining these characteristics can be highly specialized or expensive. We describe a straightforward, low-cost protocol for functionalizing poly(isobutylene-alt-maleic anhydride) (PIMA) with moieties that anchor to the QD surface (histamine), impart hydrophilicity [(2-aminoethyl)trimethylammonium chloride (Me₃N⁺-NH₂)], and provide a platform for biofunctionalization via click chemistry (dibenzocyclooctyne (DBCO)). Guidelines to successfully use this polymer for QD ligand exchange are presented, and an example of biofunctionalization with DNA is shown. Stable QD-DNA conjugates are obtained with high yield and without requiring additional purification steps.

pH-dependent fluorescence of thiol-coated CdSe/CdS quantum dots in an aqueous phase

The results presented in this paper show how the optical properties and colloidal stability of quantum dots (QDs) vary depending on pH conditions. For this investigation, as-synthesized hydrophobic CdSe/CdS QDs were transferred to an aqueous medium by surface modification with 3-mercaptopropionic acid. The ligand exchange procedure was applied under three different pH conditions: acidic, neutral and alkaline, to obtain three kinds of hydrophilic QDs dispersed in phosphate buffer. The efficiency of the functionalization of QDs was estimated based on the changes in ABS and the highest value was obtained under acidic conditions (45%). The efficiency of photoluminescence (PL) was also best preserved under these conditions, although it was 30 times less than the PL of hydrophobic QDs. Then, all three kinds of hydrophilic QDs were dispersed in solutions with a wide range of pH (2-12) and investigated by absorbance and PL measurements. The results show that QDs subjected to a ligand exchange procedure are characterized by intensive PL at the selected pH values, which correspond to pK_a of the ligand. This phenomenon is independent of the pH at which the ligand exchange procedure is conducted. Moreover, it was found that the PL intensity is preserved during the experiment for QDs functionalized under neutral conditions, whereas it decreases for acidic and increases for alkaline conditions.

Highly Sensitive Fluorescent Probe for Detection of Paraquat Based on Nanocrystals

Paraquat is one of the most toxic materials widely applied in agriculture in most countries. In the present study, a simple, innovative and inexpensive nano biosensor which is based on a thioglycolic acid (TGA) - CdTe@CdS core-shell nanocrystals (NCs) to detect paraquat, is suggested. The NCs based biosensor shows a linear working range of 10-100 nM, and limited detection of 3.5 nM. The proposed sensor that has been well used for the detection and determination of paraquat in natural water samples is collected from corn field and a canal located near to the corn field yielding recoveries as high as 98%. According to our findings, the developed biosensor shows reproducibility and high sensitivity to determine paraquat in natural water samples in which the amount of paraquat has low levels. The suggested method is efficiently applied to paraquat determination in the samples of natural water that are collected from a tap water and a canal located near to the cornfield.

Alendronate/cRGD-Decorated Ultrafine Hyaluronate Dot Targeting Bone Metastasis

In this study, we report the hyaluronate dot (dHA) with multiligand targeting ability and a photosensitizing antitumor model drug for treating metastatic bone tumors. Here, the dHA was chemically conjugated with alendronate (ALN, as a specific ligand to bone), cyclic arginine-glycine-aspartic acid (cRGD, as a specific ligand to tumor integrin αvβ3), and photosensitizing chlorin e6 (Ce6, for photodynamic tumor therapy), denoted as (ALN/cRGD)@dHA-Ce6. These dots thus prepared (≈10 nm in diameter) enabled extensive cellular interactions such as hyaluronate (HA)-mediated CD44 receptor binding, ALN-mediated bone targeting, and cRGD-mediated tumor integrin αvβ3 binding, thus improving their tumor targeting efficiency, especially for metastasized MDA-MB-231 tumors. As a result, these dots improved the tumor targeting efficiency and tumor cell permeability in a metastatic in vivo tumor model. Indeed, we demonstrated that (ALN/cRGD)@dHA-Ce6 considerably increased photodynamic tumor ablation, the extent of which is superior to that of the tumor ablation of dot systems with single or double ligands. These results indicate that dHA with multiligand can provide an effective treatment strategy for metastatic bone tumors.

Light-Induced Oxidase Activity of DNAzyme-Modified Quantum Dots

Here, we report the synthesis of a quantum dot (QD)-DNA covalent conjugate to be used as an H₂O₂-free DNAzyme system with oxidase activity. Amino-coupling conjugation was carried out between amino-modified oligonucleotides (CatG4-NH₂) and carboxylated quantum dots (CdTe@COOH QDs). The obtained products were characterized by spectroscopic methods (UV-Vis, fluorescence, circular dichroizm (CD), and IR) and the transmission electron microscopy (TEM) technique. A QD-DNA system with a low polydispersity and high stability in aqueous solutions was successfully obtained. The catalytic activity of the QD-DNA conjugate was examined with Amplex Red and ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate)) indicators using reactive oxygen species (ROS) generated by visible light irradiation. The synthesized QD-DNAzyme exhibited enhanced catalytic activity compared with the reference system (a mixture of QDs and DNAzyme). This proved the assumption that the covalent attachment of DNAzyme to the surface of QD resulted in a beneficial effect on its catalytic activity. The results proved that the QD-DNAzyme system can be used for generation of the signal by light irradiation. The light-induced oxidase activity of the conjugate was demonstrated, proving that the QD-DNAzyme system can be useful for the development of new cellular bioassays, e.g., for the determination of oxygen radical scavengers.

Emergence of sulfur quantum dots: Unfolding their synthesis, properties, and applications

Over the past few decades, the sphere of applied science has witnessed soaring demand in developing high performance, novel and sustainable materials due to ever-increasing population coupled with need for alternative-green-energy resources. Inevitably, sulfur research expands through the breadth of materials sciences including sustainable use of the by-products obtained from petroleum industry, preparation of biocompatible materials, and constructing energy harvesting devices, indispensable to our everyday lives. Congruous with popular heavy-metal free elemental quantum dots such as the carbon, silicon and phosphorus, emergence of sulfur quantum dots (SQDs) has drawn substantial attention due to their bright luminescence, infrequent to other sulfur allotropes. In this review article, we focus some of the pioneering advances on synthesis and characterizations of luminescent sulfur nanodots and their potential applications in bioimaging, fabrication of light emitting devices, sensing and catalysis. Finally, critical challenges along with future perspectives corresponding to this newly discovered research area have been discussed.