Aqueous synthesis of tunable fluorescent, semiconductor CuInS2 quantum dots for bioimaging

Recent Advances in NIR or X-ray Excited Persistent Luminescent Materials for Deep Bioimaging

Due to their persistent luminescence, persistent luminescent (PersL) materials have attracted great interest. In the biomedical field, the use of persistent luminescent nanoparticles (PLNPs) eliminates the need for continuous in situ excitation, thereby avoiding interference from tissue autofluorescence and significantly improving the signal-to-noise ratio (SNR). Although persistent luminescence materials can emit light continuously, the luminescence intensity of small-sized nanoparticles in vivo decays quickly. Early persistent luminescent nanoparticles were mostly excited by ultraviolet (UV) or visible light and were administered for imaging purposes through ex vivo charging followed by injection into the body. Limited by the low in vivo penetration depth, UV light cannot secondary charge PLNPs that have decayed in vivo, and visible light does not penetrate deep enough to reach deep tissues, which greatly limits the imaging time of persistent luminescent materials. In order to address this issue, the development of PLNPs that can be activated by light sources with superior tissue penetration capabilities is essential. Near-infrared (NIR) light and X-rays are widely recognized as ideal excitation sources, making persistent luminescent materials stimulated by these two sources a prominent area of research in recent years. This review describes NIR and X-ray excitable persistent luminescence materials and their recent advances in bioimaging.

Luminescent Quantum Dots: Synthesis, Optical Properties, Bioimaging and Toxicity

Luminescent nanomaterials such as semiconductor nanocrystals (NCs) and quantum dots (QDs) attract much attention to optical detectors, LEDs, photovoltaics, displays, biosensing, and bioimaging. These materials include metal chalcogenide QDs and metal halide perovskite NCs. Since the introduction of cadmium chalcogenide QDs to biolabeling and bioimaging, various metal nanoparticles (NPs), atomically precise metal nanoclusters, carbon QDs, graphene QDs, silicon QDs, and other chalcogenide QDs have been infiltrating the nano-bio interface as imaging and therapeutic agents. Nanobioconjugates prepared from luminescent QDs form a new class of imaging probes for cellular and in vivo imaging with single-molecule, super-resolution, and 3D resolutions. Surface modified and bioconjugated core-only and core-shell QDs of metal chalcogenides (MX; M = Cd/Pb/Hg/Ag, and X = S/Se/Te,), binary metal chalcogenides (MInX₂; M = Cu/Ag, and X = S/Se/Te), indium compounds (InAs and InP), metal NPs (Ag, Au, and Pt), pure or mixed precision nanoclusters (Ag, Au, Pt), carbon nanomaterials (graphene QDs, graphene nanosheets, carbon NPs, and nanodiamond), silica NPs, silicon QDs, etc. have become prevalent in biosensing, bioimaging, and phototherapy. While heavy metal-based QDs are limited to in vitro bioanalysis or clinical testing due to their potential metal ion-induced toxicity, carbon (nanodiamond and graphene) and silicon QDs, gold and silica nanoparticles, and metal nanoclusters continue their in vivo voyage towards clinical imaging and therapeutic applications. This review summarizes the synthesis, chemical modifications, optical properties, and bioimaging applications of semiconductor QDs with particular references to metal chalcogenide QDs and bimetallic chalcogenide QDs. Also, this review highlights the toxicity and pharmacokinetics of QD bioconjugates.

Green synthesis of glyco-CuInS2 QDs with visible/NIR dual emission for 3D multicellular tumor spheroid and in vivo imaging

Glyco-quantum dots (glyco-QDs) have attracted significant interest in bioimaging applications, notably in cancer imaging, because they effectively combine the glycocluster effect with the exceptional optical properties of QDs. The key challenge now lies in how to eliminate the high heavy metal toxicity originating from traditional toxic Cd-based QDs for in vivo bioimaging. Herein, we report an eco-friendly pathway to prepare nontoxic Cd-free glyco-QDs in water by the "direct" reaction of thiol-ending monosaccharides with metal salts precursors. The formation of glyco-CuInS₂ QDs could be explained by a nucleation-growth mechanism following the LaMer model. As-prepared four glyco-CuInS₂ QDs were water-soluble, monodispersed, spherical in shape and exhibited size range of 3.0-4.0 nm. They exhibited well-separated dual emission in the visible region (500-590 nm) and near-infrared range (~ 827 nm), which may be attributable to visible excitonic emission and near-infrared surface defect emission. Meanwhile, the cell imaging displayed the reversibly distinct dual-color (green and red) fluorescence in tumor cells (HeLa, A549, MKN-45) and excellent membrane-targeting properties of glyco-CuInS₂ QDs based on their good biorecognition ability. Importantly, these QDs succeed in penetrating uniformly into the interior (the necrotic zone) of 3D multicellular tumor spheroids (MCTS) due to their high negative charge (zeta potential values ranging from - 23.9 to - 30.1 mV), which overcame the problem of poor penetration depth of existing QDs in in vitro spheroid models. So, confocal analysis confirmed their excellent ability to penetrate and label tumors. Thus, the successful application in in vivo bioimaging of these glyco-QDs verified that this design strategy is an effective, low cost and simple procedure for developing green nanoparticles as cheap and promising fluorescent bioprobes.

Biomedical Applications of Quantum Dots: Overview, Challenges, and Clinical Potential

Despite the massive advancements in the nanomedicines and their associated research, their translation into clinically-applicable products is still below promises. The latter fact necessitates an in-depth evaluation of the current nanomedicines from a clinical perspective to cope with the challenges hampering their clinical potential. Quantum dots (QDs) are semiconductors-based nanomaterials with numerous biomedical applications such as drug delivery, live imaging, and medical diagnosis, in addition to other applications beyond medicine such as in solar cells. Nevertheless, the power of QDs is still underestimated in clinics. In the current article, we review the status of QDs in literature, their preparation, characterization, and biomedical applications. In addition, the market status and the ongoing clinical trials recruiting QDs are highlighted, with a special focus on the challenges limiting the clinical translation of QDs. Moreover, QDs are technically compared to other commercially-available substitutes. Eventually, we inspire the technical aspects that should be considered to improve the clinical fate of QDs.

Multifunctional MnCuInSe/ZnS quantum dots for bioimaging and photodynamic therapy

In this work, manganese (Mn)-doped CuInSe quantum dots (QDs) with a ZnS passivation layer (MnCuInSe/ZnS) have been synthesized via a one-pot microwave-assisted hydrothermal reaction using glutathione (GSH) as a stabilizer. The MnCuInSe/ZnS core-shell QDs combine magnetic resonance imaging (MRI), excitation-dependent red emission, and reactive oxygen radical generation functions, in which regulation of Mn2+ incorporation leads to synergistic imaging and therapeutic modalities. The MnCuInSe/ZnS QDs exhibit high colloidal and photochemical stability in simulated media and at different pH values. An r2/r1 ratio of 9.99 was calculated from MRI studies suggesting their potential application as dual-modal imaging agents. Based on in vitro tests on Hela, B16, and HepG2 cell lines, it is apparent that MnCuInSe/ZnS QDs impose no significant cytotoxicity in the dark, while they can efficiently generate singlet oxygen radicals for photodynamic therapy of cancers, killing more than 80% of B16 cells within 5 min of laser irradiation (671 nm, 1 W cm−2). Furthermore, in vitro fluorescence imaging and cellular internalization of QDs are examined to visualize cellular uptake and in situ ROS generation. Therefore, this research exemplifies a new set of multifunctional chalcogenide QDs for theranostic applications.

Biocompatible CuInS2 Nanoparticles as Potential Antimicrobial, Antioxidant, and Cytotoxic Agents

A simple hydrothermal route is employed to synthesize pure copper indium disulfide (CIS) and CIS nanoparticles (NPs) mediated by various natural plant extracts. The plant extracts used to mediate are Azadirachta indica (neem), Ocimum sanctum (basil), Cocos nucifera (coconut), Aloe vera (aloe), and Curcuma longa (turmeric). The tetragonal unit cell structure of as-synthesized NPs is confirmed by X-ray diffraction. The analysis by energy-dispersive X-rays shows that all the samples are near-stoichiometric. The morphologies of the NPs are confirmed by high-resolution scanning and transmission modes of electron microscopy. The thermal stability of the synthesized NPs is determined by thermogravimetric analysis. The optical energy band gap is determined from the absorption spectra using Tauc's equation. The antimicrobial activity analysis and the estimation of the minimum inhibitory concentration (MIC) value of the samples are performed for Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Enterobacter aerogenes, and Staphylococcus aureus pathogens. It shows that the aloe-mediated CIS NPs possess a broad inhibitory spectrum. The best inhibitory effect is observed against S. aureus, whereas the least effect was exhibited against P. vulgaris. The least MIC value is found for aloe-mediated CIS NPs (0.300 mg/mL) against S. aureus, P. aeruginosa, and E. aerogenes, along with basil-mediated NPs against E. coli. The antioxidant activity study showed that the IC₅₀ value to inhibit the scavenging activity is maximum for the control (vitamin C) and minimum for pure CIS NPs. The in vivo cytotoxicity study using brine shrimp eggs shows that the pure CIS NPs are more lethal to brine shrimp than the natural extract-mediated CIS NPs. The in vitro cytotoxicity study using the human lung carcinoma cell line (A549) shows that the IC₅₀ value of turmeric extract-mediated CIS NPs is minimum (15.62 ± 1.58 μg/mL). This observation reveals that turmeric extract-mediated CIS NPs are the most potent in terms of cytotoxicity toward the A549 cell line.

Facile aqueous synthesis of ZnInS quantum dots and its application for selective detection of Co2+Ions

The synthesis of ZnInS (ZIS) quantum dots (QDs) in aqueous medium using thioglycolic acid (TGA) and sodium citrate as dual capping agents has been reported. The as-synthesized ZIS QDs were water soluble, emitting at 512 nm and nearly spherical in shape with average particle size of 8.9 ± 1.4 nm. The as-synthesized ZIS QDs were tested for its fluorescence response against different metal ions and the results revealed that ZIS QDs were selectively quenched by Co²⁺ions compared to other ions. The fluorescence sensing experiment showed that ZIS QDs has a linear response against the concentration of Co²⁺ions (0.1-100μM ) with the detection limit of 0.099μM. Based on the transmission electron microscope and absorption spectroscopy analyzes, the fluorescence quenching is attributed to the formation of surface ligand-metal complex (TGA-Co²⁺ions) which caused aggregation of the QDs. The present method explores the synthesis of zero-dimentional ZIS QDs and its potential in the selective detection of Co²⁺ions in aqueous solution.

The Photoluminescence and Biocompatibility of CuInS2-Based Ternary Quantum Dots and Their Biological Applications

Semiconductor quantum dots (QDs) have become a unique class of materials with great potential for applications in biomedical and optoelectronic devices. However, conventional QDs contains toxic heavy metals such as Pb, Cd and Hg. Hence, it is imperative to find an alternative material with similar optical properties and low cytotoxicity. Among these materials, CuInS2 (CIS) QDs have attracted a lot of interest due to their direct band gap in the infrared region, large optical absorption coefficient and low toxic composition. These factors make them a good material for biomedical application. This review starts with the origin and photophysical characteristics of CIS QDs. This is followed by various synthetic strategies, including synthesis in organic and aqueous solvents, and the tuning of their optical properties. Lastly, their significance in various biological applications is presented with their prospects in clinical applications.