Recyclable fluorescence sensing based on copper clusters for simultaneous determination of copper ions and ammonia

A one-step strategy for synthesizing fluorescent copper clusters stabilized by L-cysteine has been successfully established in aqueous solutions. The direct determination of copper ions was realized by the fluorescence enhancement phenomenon caused by the preparation and aggregation process. At the same time, ammonia treatment can lead to rapid fluorescence quenching, resulting from the influence on the aggregation behavior of Cu clusters, while the fluorescence can be recovered by the continuous addition of copper ions. Therefore, a recyclable fluorescence sensing system is constructed for the simultaneous determination of copper ions and ammonia. This method is simple, anti-interference and has been successfully applied to the determination of environmental samples.

Chemiluminescence of doped carbon dots with H2O2-KMnO4 system for the detection of Cu2+ and tannin

The carbon dots doped with chlorine and phosphorus (CDs-Cl,P) were used as chemiluminescence (CL) reagent for the sensitive detection of copper ions (Cu²⁺) and tannin (TA). The CDs-Cl,P was found to strongly enhance the reaction of H₂O₂ and KMnO₄ in alkaline medium. The enhanced CL behavior of CDs-Cl,P was investigated and it was found that some radicals such as ^•OH, ^•O₂^- and ¹O₂ appeared in the CL reaction process. The participation of Cu²⁺ could result in an enhanced CL intensity of the CDs-Cl,P-H₂O₂-KMnO₄ system due to the Cu²⁺-catalyzed decomposition of H₂O₂ resulting in more ^•OH generation. Therefore, the CDs-Cl,P-H₂O₂-KMnO₄ system was used to selectively quantify Cu²⁺ in solution by CL emission. A linear increase was observed between CL intensity and Cu²⁺ concentration. The CDs-Cl,P-H₂O₂-KMnO₄ system allowed the detection of Cu²⁺ down to lower concentration of 0.1 μM with a linear range of 0.2-60.0 μM. Moreover, TA as a common polyphenolic compound, could selectively decrease the CL signal of the CDs-Cl,P-H₂O₂-KMnO₄-Cu²⁺ system due to its complexation with Cu²⁺. On this basis, the CL assay for TA was also developed. The detection limit was 0.14 μM and the linear range was from 5.0 μM to 100.0 μM. The proposed method was successfully applied to the determination of Cu²⁺ and TA in water, rice dumplings leaves, sodium copper chlorophyllin and wine samples with satisfactory results.

Pb2+ Responsive Cu-In-Zn-S Quantum Dots With Low Cytotoxicity

Water-soluble Cu-In-Zn-S quantum dots (CIZS QDs) with orange fluorescence have been synthesized with a glutathione (GSH) as stabilizer via facile a one-step hydrothermal method. The optimal reaction conditions of CIZS QDs including temperature, time, pH, and the molar ratios of precursors were studied. TEM results indicate that the aqueous-dispersible CIZS QDs are quasi-spherical, and the average diameters are 3.76 nm with excellent fluorescent stability. Furthermore, the cytotoxicity of CIZS QDs was investigated by the microcalorimetry combining with TEM and the IC50 was 10.2 μM. CIZS QDs showed a promising perspective in applications such as a fluorescent probe for bioimaging and biolabeling due to the low cytotoxicity and good biocompatibility. Moreover, the CIZS QDs can distinguish Pb2+ ion from other ions, offering great potentials in lead ion determination in drinking water. According to the results of UV, XRD, FL, PL, and ITC methods, the mechanism of CIZS QDs-Pb2+ assay is due to hydrogen bonding or van der Waals forces in the formation of Pb2+ and CIZS QDs.

A Simple Colorimetric Assay for Sensitive Cu2+ Detection Based on the Glutathione-Mediated Etching of MnO2 Nanosheets

In this paper, we developed a quick, economical and sensitive colorimetric strategy for copper ions (Cu²⁺) quantification via the redox response of MnO₂ nanosheets with glutathione (GSH). This reaction consumed MnO₂ nanosheets, which acted as a catalyst for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product (oxTMB). In the presence of Cu²⁺, the GSH was catalyzed to GSSG (oxidized glutathione), and the solution changed from colorless to deep blue. Under the optimum conditions, the absorption signal of the oxidized product (oxTMB) became proportional to Cu²⁺ concentration in the range from 10 to 300 nM with a detection limit of 6.9 nM. This detection system showed high specificity for Cu²⁺. Moreover, the system has been efficaciously implemented for Cu²⁺ detection in actual tap water samples. The layered-nanostructures of MnO₂ nanosheets make it possess high chemical and thermal stability. TMB can be quickly oxidized within 10 min by the catalyzing of MnO₂ nanosheets with high oxidase-like activity. There is no need of expensive reagents, additional H₂O₂ and complicated modification processes during the colorimetric assay. Therefore, the strategy primarily based on MnO₂ nanosheets is promising for real-time, rapid and highly sensitive detection of Cu²⁺ under practical conditions.

Silver chalcogenide nanoparticles: a review of their biomedical applications

Silver chalcogenide (Ag2X, where X = S, Se, or Te) nanoparticles have been extensively investigated for their applications in electronics but have only recently been explored for biomedical applications. In the past 10 years, Ag2X, primarily silver sulfides at first, have become of great importance as quantum dots, since they not only possess excellent deep tissue imaging properties in the near-infrared regions I and II, but also have low toxicities. Their appealing properties have led to numerous recent developments of Ag2X for biomedical applications. Furthermore, Ag2X have been discovered in the past 2-3 years to be potent X-ray contrast agents, adding to the numerous biomedical uses of these nanoparticles. In this review, we discuss the most recent advances in silver chalcogenide nanoparticle use in areas such as bio-imaging, theranostics, and biosensors. Moreover, we examine the advances in synthetic approaches for these nanoparticles, which include aqueous and organic syntheses routes. Finally, we discuss the advantages and current limitations in the use of silver chalcogenides for different biomedical applications and their potential for advancement and expansions in use.

Synthesis and Bioapplications of Ag2 S Quantum Dots with Near-Infrared Fluorescence

Quantum dots (QDs) with near-infrared fluorescence (NIR) are an emerging class of QDs with unique capabilities owing to the deeper tissue penetrability of NIR light compared with visible light. NIR light also effectively overcomes organism autofluorescence, making NIR QDs particularly attractive in biological imaging applications for disease diagnosis. Considering latest developments, Ag₂ S QDs are a rising star among NIR QDs due to their excellent NIR fluorescence properties and biocompatibility. This review presents the various methods to synthesize NIR Ag₂ S QDs, and systematically discusses their applications in biosensing, bioimaging, and theranostics. Major challenges and future perspectives concerning the synthesis and bioapplications of NIR Ag₂ S QDs are discussed.

Photoluminescent Nanoparticles for Chemical and Biological Analysis and Imaging

Research related to the development and application of luminescent nanoparticles (LNPs) for chemical and biological analysis and imaging is flourishing. Novel materials and new applications continue to be reported after two decades of research. This review provides a comprehensive and heuristic overview of this field. It is targeted to both newcomers and experts who are interested in a critical assessment of LNP materials, their properties, strengths and weaknesses, and prospective applications. Numerous LNP materials are cataloged by fundamental descriptions of their chemical identities and physical morphology, quantitative photoluminescence (PL) properties, PL mechanisms, and surface chemistry. These materials include various semiconductor quantum dots, carbon nanotubes, graphene derivatives, carbon dots, nanodiamonds, luminescent metal nanoclusters, lanthanide-doped upconversion nanoparticles and downshifting nanoparticles, triplet-triplet annihilation nanoparticles, persistent-luminescence nanoparticles, conjugated polymer nanoparticles and semiconducting polymer dots, multi-nanoparticle assemblies, and doped and labeled nanoparticles, including but not limited to those based on polymers and silica. As an exercise in the critical assessment of LNP properties, these materials are ranked by several application-related functional criteria. Additional sections highlight recent examples of advances in chemical and biological analysis, point-of-care diagnostics, and cellular, tissue, and in vivo imaging and theranostics. These examples are drawn from the recent literature and organized by both LNP material and the particular properties that are leveraged to an advantage. Finally, a perspective on what comes next for the field is offered.

Near-infrared Zn-doped Cu2S quantum dots: an ultrasmall theranostic agent for tumor cell imaging and chemodynamic therapy

Theranostic agents that integrated chemodynamic therapy (CDT) and imaging functions have great potential application in personalized cancer therapy. However, most theranostic agents were fabricated by chemically coupling two or more independent functional units with diagnostic or therapeutic capabilities, and therefore have a large size. To date, one-step synthesis of unmodified ultrasmall quantum dots (QDs) integrating CDT and fluorescence imaging capabilities remains a challenge. Herein, we reported a simple one-step synthesis method of ultrasmall (2.46 nm) Zn-doped Cu₂S (Zn:Cu₂S) QDs with inherent properties of both high CDT activity and near-infrared fluorescence imaging capability. The fluorescence of Cu₂S QDs was significantly enhanced approximately tenfold after Zn doping due to the compensation of defects. In vitro and in vivo experiments demonstrated that the Zn:Cu₂S QDs could specifically and significantly inhibit the cancer cell growth (inhibition rate exceeded 65%) without damaging the normal cells. Furthermore, the CDT mechanism study suggested that a Fenton-like reaction occurred after the Zn:Cu₂S QDs entered the tumor cells, inducing apoptosis via the mitochondrial signaling pathway, and activating the production of reactive oxygen species (ROS) and autophagy to selectively eliminate tumor cells to achieve CDT. This work proposed a simple one-step synthesis of unmodified ultrasmall QDs with fluorescence imaging and CDT, which provides a promising strategy for QDs to act as multi-functional theranostic agents.

Toxicity of different types of quantum dots to mammalian cells in vitro: An update review

Currently, there are a great quantity type of quantum dots (QDs) that has been developed by researchers. Depending on the core material, they can be roughly divided into cadmium, silver, indium, carbon and silicon QDs. And studies on the toxicity of QDs are also increasing rapidly, but in vivo tests in model animals fail to reach a consistent conclusion. Therefore, we review the literatures dealing with the cytotoxicity of QDs in mammalian cells in vitro. After a short summary of the application characteristics of five types of QDs, the fate of QDs in cells will be discussed, ranging from the uptake, transportation, sublocation and excretion. A substantial part of the review will be focused on in vitro toxicity, in which the type of QDs is combined with their adverse effect and toxic mechanism. Because of their different luminescent properties, different subcellular fate, and different degree of cytotoxicity, we provide an overview on the balance of optical stability and biocompatibility of QDs and give a short outlook on future direction of cytotoxicology of QDs.

Efficient detection doxorubicin hydrochloride using CuInSe2@ZnS quantum dots and Ag nanoparticles

Doxorubicin hydrochloride (DOX) is an effective anthracycline anticancer drug. However, the exceeded taken up could induce several side-effects such as cardiotoxicity, alopecia. Therefore, the level of DOX needs to be closely monitored to avoid the occurrence of its side-effects. Herein, we report a novel core CuInSe₂ - shell ZnS quantum dots (CuInSe₂@ZnS, QDs) and Ag nanoparticles (NPs) fluorescence sensor based on the surface plasmon resonance effect (SPR) of Ag NPs. The CuInSe₂@ZnS QDs were prepared by water phase reflux method with the 3-mercaptopropionic acid (MPA) as stabilizer and ligand. The fluorescence intensity of CuInSe₂@ZnS QDs/Ag NPs significantly reduced by DOX, which is mainly based on the electrostatic interaction between the DOX and fluorescence sensors. The inhibition of photoluminescence (ln F₀/F) was linearly relationship to the concentration of DOX in the range of 2-100 μM with the detection limit as low as 0.05 μM. The as-prepared sensor has a high selectivity and sensitivity to DOX. Furthermore, the new sensor has been successfully applied to the determination of DOX in human serum samples with satisfactory results. Our work provides a clue for developing a novel CuInSe₂@ZnS QDs/Ag NPs based fluorescence sensor for DOX detection.

One-step preparation of red-emitting carbon dots for visual and quantitative detection of copper ions

A one-step solvothermal method for the preparation of carbon dots with red fluorescence (R-CDs) was put forward, in which sodium citrate and formamide were chosen as precursors, while formamide was adopted as the solvent. The fluorescence emission peak of the as-prepared R-CDs remained the same (600 nm) when the excitation wavelength increased from 490 nm to 560 nm, and the fluorescence quantum yield is 35.3%. Furthermore, the fluorescence intensity of the as-prepared R-CDs could be selectively quenched by copper ions, and the mechanism of Cu²⁺ quenching R-CDs is the combination of static and dynamic quenching. As a result, the R-CDs were applied for the construction of a fluorescent sensor without any modification for the quantitative and visual detection of copper ions, which is a typical contaminant in water. The limit of detection for the fluorescent sensor was as low as 5 nmol/L, and it can be used to fast and directly confirm whether the content of copper ions in drinking water meets the criteria of the United States Environmental Protection Agency and the World Health Organization.

A ratiometric fluorescent probe for pH detection based on Ag2S quantum dots-carbon dots nanohybrids

In this study, a novel ratiometric fluorescent nanoprobe for pH monitoring has been developed by synthesizing red fluorescent Ag₂S quantum dots (Ag₂S QDs) and green fluorescent carbon dots (CDs) nanohybrids (Ag₂S CDs) in one pot using CDs as templates. The nanoprobe exhibits dual-emission peaks at 500 and 670 nm under a single-excitation wavelength of 450 nm. The red fluorescence can be selectively quenched by increasing pH, while the green fluorescence is an internal reference. Therefore, the change of the relative fluorescence intensity (I₅₀₀/I₆₇₀) in the ratiometric Ag₂S CDs probes can be used for pH sensing. The results revealed that I₅₀₀/I₆₇₀ of Ag₂S CDs probes was linearly related to pH variation between pH 5.4 and 6.8. Meanwhile, the Ag₂S CDs probes possessed a good reversibility along with pH changing between 5.0 and 7.0 without any interruption from common metal ions, proteins and other interferences.

Facile one-step synthesis of quaternary AgInZnS quantum dots and their applications for causing bioeffects and detecting Cu2

Water-soluble AgInZnS quantum dots (AIZS QDs) were synthesized with glutathione (GSH) as a stabilizer by a facile one-step method based on a hydrothermal reaction between the nitrate salts of the corresponding metals and sodium sulfide as a sulfide precursor at 110 °C. The optimal reaction conditions (temperature, time, pH, and the molar ratios of the precursors) were studied. According to the data from TEM, XPS, and XRD, AIZS QDs were characterized with excellent optical properties. The results showed that the aqueous-dispersible AIZS QDs were quasi-spherical and their average diameter was 3.51 nm. Furthermore, the cytotoxicity of AIZS QDs was investigated by microcalorimetry and microscopy techniques (confocal microscopy and TEM). The data revealed that AIZS QDs exhibited low toxicity, biocompatibility, and good water stability, due to which they could be used as a fluorescent probe for bioimaging and labeling. In addition, AIZS QDs could be used as a sensor to detect Cu²⁺ because the fluorescence of AIZS QDs was quenched by Cu²⁺.

Water-soluble AgInZnS quantum dots were synthesized with glutathione as a stabilizer by a facile one-step method based on a hydrothermal reaction at 110 °C. It exhibited excellent optical properties, which can be used as sensor to detect Cu²⁺.

An ultrasensitive and selective fluorescent nanosensor based on porphyrinic metal–organic framework nanoparticles for Cu2+ detection

A fluorescent nanosensor based on ultrasmall MOF-525 NPs was proposed for the monitoring of Cu²⁺ in aqueous solution and living cells.

A novel “on–off–on” fluorescence assay for the discriminative detection of Cu(ii) and l-cysteine based on red-emissive Si-CDs and cellular imaging applications

Copper ions (Cu²⁺) and l-cysteine (l-Cys) in the human body always play critical roles in various physiological processes, while abnormal Cu²⁺ and l-Cys concentrations in the biological system lead to many diseases.

Silver sulfide nanoparticles for photodynamic therapy of human lymphoma cells via disruption of energy metabolism

Recently, studies on the application of light-responsive semiconductor nanomaterials for photodynamic therapy (PDT) of non-solid tumors have attracted tremendous attention. Herein, 6.98 nm Ag₂S nanoparticles (Ag₂S NPs) with excellent aqueous dispersibility, stability, and biocompatibility were synthesized by a facile strategy without any post-modification. In vitro studies indicated that Ag₂S NPs could significantly inhibit the growth of human lymphoma cells (Raji cells) compared with hepatoma carcinoma cells (Hep G2 cells) under light irradiation. Further studies revealed that Ag₂S NPs could specifically induce the accumulation of intracellular reactive oxidative species in Raji cells under light irradiation, and induce significant disruption of energy metabolism. This finding provides inspiration for the potential application of Ag₂S semiconductor nanoparticles as a photosensitizer to significantly and specifically treat human lymphoma through PDT.

Ag₂S/BSA hybrid nanoparticles were prepared and studied for their ability to inhibit the growth of human lymphoma cells under light irradiation, via inducing the accumulation of intracellular reactive oxidative species to disrupt energy metabolism.