CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe− ions in aqueous solution

Quantum dots based sensitive nanosensors for detection of antibiotics in natural products: A review

Residual antibiotics in food products originated from administration of the antibiotics to animals may be accumulated through food metabolism in the human body and endanger safety and health. Thus, developing a prompt and accurate way for detection of antibiotics is a crucial issue. The zero-dimensional fluorescent probes including metals based, carbon and graphene quantum dots (QDs), are highly sensitive materials to use for the detection of a wide range of antibiotics in natural products. These QDs demonstrate unique optical properties like tunable photoluminescence (PL) and excitation-wavelength dependent emission. This study investigates the trends related to carbon and metal based QDs preparation and modification, and their diverse detection application. We discuss the performance of QDs based sensors application in various detection systems such as photoluminescence, photoelectrochemical, chemiluminescence, electrochemiluminescence, colorimetric, as well as describing their working principles in several samples. The detecting mechanism of a QDs-based sensor is dependent on its properties and specific interactions with particular antibiotics. This review also tries to describe environmental application and future perspective of QDs for antibiotics detection.

Visual detection of S2- with a paper-based fluorescence sensor coated with CdTe quantum dots via headspace sampling

A simple method was developed in this work for facile and visual detection of S^2- using a paper-based fluorescence (FL) sensor coated with CdTe quantum dots (QDs) by headspace sampling. With the addition of hydrochloric acid, the target S^2- in the liquid phase would transform to H₂ S, which was released to headspace and quenched the FL of CdTe QDs in a linear manner through a gas-solid reaction, with any possible liquid-phase interference avoided. The regular quenching caused by S^2- in analyte solution with increased concentration could be easily observed by the naked eye, and the limit of detection (LOD) for this method was 0.13 μM and 0.93 μM for FL and visual sensing, respectively, comparable or not to that by other sensing probes. A relative standard deviation of 1.2% was accomplished from seven replicated measurements, implying the high reproducibility, and the recovery for the spiked water samples ranging from 94 to 103%, and illustrating the satisfactory reliability of this method. Moreover, the preparation of this paper sensor was facile and did not require any complicated or time-consuming procedures for additional modification or functionalization as for other probes previously reported.

A review on nanostructure-based mercury (II) detection and monitoring focusing on aptamer and oligonucleotide biosensors

Heavy metal ion pollution is a severe problem in environmental protection and especially in human health due to their bioaccumulation in organisms. Mercury (II) (Hg²⁺), even at low concentrations, can lead to DNA damage and give permanent harm to the central nervous system by easily passing through biological membranes. Therefore, sensitive detection and monitoring of Hg²⁺ is of particular interest with significant specificity. In this review, aptamer-based strategies in combination with nanostructures as well as several other strategies to solve addressed problems in sensor development for Hg²⁺ are discussed in detail. In particular, the analytical performance of different aptamer and oligonucleotide-based strategies using different signal improvement approaches based on nanoparticles were compared within each strategy and in between. Although quite a number of the suggested methodologies analyzed in this review fulfills the standard requirements, further development is still needed on real sample analysis and analytical performance parameters.

A review of bioselenol-specific fluorescent probes: Synthesis, properties, and imaging applications

Bioselenols are important substances for the maintenance of physiological balance and offer anticancer properties; however, their causal mechanisms and effectiveness have not been assessed. One way to explore their physiological functions is the in vivo detection of bioselenols at the molecular level, and one of the most efficient ways to do so is to use fluorescent probes. Various types of bioselenol-specific fluorescent probes have been synthesized and optimized using chemical simulations and by improving biothiol fluorescent probes. Here, we review recent advances in bioselenol-specific fluorescent probes for selenocysteine (Sec), thioredoxin reductase (TrxR), and hydrogen selenide (H₂Se). In particular, the molecular design principles of different types of bioselenols, their corresponding sensing mechanisms, and imaging applications are summarized.

Targetable Mesoporous Silica Nanoprobes for Mapping the Subcellular Distribution of H2Se in Cancer Cells

Hydrogen selenide, a highly active reductant, is believed as a key molecule in the cytotoxicity of inorganic selenium compounds. However, the detail mechanism has hardly been studied because the distribution of H₂Se in the subcellular organelles remains unclear. Herein, we exploited a series of novel targetable mesoporous silica nanoplatforms to map the distribution of H₂Se in cytoplasm, lysosome, and mitochondria of cancer cells. The subcellular targeting moiety-conjugated mesoporous silica nanoparticles were assembled with a near-infrared fluorescent probe (NIR-H₂Se) for detecting endogenous H₂Se in the corresponding organelles. The confocal fluorescence imaging of cancer cells induced by Na₂SeO₃ found out a higher concentration of H₂Se accumulated only in mitochondria. Consequently, the H₂Se burst in mitochondria-triggered mitochondrial collapse that led to cell apoptosis. Hence, the selenite-induced cytotoxicity in cancer cells associates with the alteration in mitochondrial function caused by high level of H₂Se. These findings provide a new way to explore the tumor cell apoptosis signaling pathways induced by Na₂SeO₃, meanwhile, we propose a research strategy for tracking the biomolecules in the subcellular organelles and the correlative cellular function and related disease diagnosis.

Biological Chemistry of Hydrogen Selenide

There are no two main-group elements that exhibit more similar physical and chemical properties than sulfur and selenium. Nonetheless, Nature has deemed both essential for life and has found a way to exploit the subtle unique properties of selenium to include it in biochemistry despite its congener sulfur being 10,000 times more abundant. Selenium is more easily oxidized and it is kinetically more labile, so all selenium compounds could be considered to be "Reactive Selenium Compounds" relative to their sulfur analogues. What is furthermore remarkable is that one of the most reactive forms of selenium, hydrogen selenide (HSe- at physiologic pH), is proposed to be the starting point for the biosynthesis of selenium-containing molecules. This review contrasts the chemical properties of sulfur and selenium and critically assesses the role of hydrogen selenide in biological chemistry.

Ultrasensitive optical detection of anions by quantum dots

Quantum dots (QDs) have received great interest for diverse applications over the past few decades due to their unique photophysical properties like their tunable band gap, facile solution processability and versatile surface functionalization with different ligands. Quantum dot based optical analysis techniques with high sensitivity and selectivity have been developed to detect anions in aqueous solution for environmental monitoring, medicinal diagnostics, and the analysis of biological samples and industrial processes. Here we review the latest research progress of semiconductor QDs for sensing of anions in aqueous solution or in vivo, and discuss the photophysical mechanisms and outlook for the potential development in QD based optical sensing for anions.

A highly selective near-infrared fluorescent probe for imaging H2Se in living cells and in vivo

Hydrogen selenide (H2Se), a highly reactive Se species, is an important selenium metabolism intermediate involved in many physiological and pathological processes. This compound is of scientific interest with regard to the real-time monitoring of H2Se in living cells and in vivo to understand the anti-cancer mechanism of selenium. However, monitoring H2Se in living cells is still challenging due to the lack of straight forward, highly selective and rapid methods. Here, we developed a novel small-molecule fluorescent probe, NIR-H2Se, for imaging endogenous H2Se. NIR-H2Se exhibited high selectivity toward H2Se over selenocysteine (Sec), H2S and small molecule thiols and was successfully used to image the H2Se content in HepG2 cells during Na2SeO3-induced apoptosis. Increased H2Se content and reduced ROS levels were observed under hypoxic conditions compared to normoxic conditions, which indicated that the cell apoptosis induced by Na2SeO3 under a hypoxic environment is via a non-oxidative stress mechanism. Thus, this probe should serve as a powerful tool for exploring the physiological function of H2Se and Se anticancer mechanisms in a variety of physiological and pathological contexts.

A review on fluorescent inorganic nanoparticles for optical sensing applications

Fluorescent inorganic nanoparticles are immerging novel materials that can be adopted for a large number of optical bioassays and chemical sensing probes.

Room-temperature phosphorescence probe based on Mn-doped ZnS quantum dots for the sensitive and selective detection of selenite

Selenite was selectively and sensitively detected based on the room-temperature phosphorescence quenching of Mn–ZnS QDs caused by HSe⁻ from the reaction of selenite and glutathione.

Room temperature synthesis of manganese oxide quantum dots and their application as a fluorescent probe for the detection of metal ions in aqueous media

A rapid and facile route to access fluorescent manganese oxide quantum dots (MOQDs) has been developed at room temperature; the as-prepared MOQDs can serve as a fluorescent probe for the detection of metal ions in aqueous media.

Quantum dot based turn-on fluorescent probes for anion sensing

The design of fluorescent probes for turn-on sensing of anions has been especially significant because it can effectively enhance sensing sensitivity by decreasing the background interference. In the present work, we have systematically studied the potential applications of fluorescent quantum dots (QDs) in turn-on anion sensing. The fluorescence of QDs are firstly quenched by three different mechanisms, i.e. fluorescence resonance energy transfer, electron transfer and surface states modulated fluorescence. The fluorescence of the pre-quenched QDs can then be recovered by various anions due to the modulating effects of added anions on the interaction between QDs and QDs, the interaction between QDs and quenchers, and the surface chemistry of the quenched QDs, respectively. The results described here indicate that turn-on sensing of various anions by QDs-based systems can be achieved by rationally choosing fluorescence modulating strategies, demonstrating the versatility of QDs in the corresponding applications.

Synthesis of positively charged CdTe quantum dots and detection for uric acid

The CdTe dots (QDs) coated with 2-Mercaptoethylamine was prepared in aqueous solution and characterized with fluorescence spectroscopy, UV-Vis absorption spectra, high-resolution transmission electron microscopy and infrared spectroscopy. When the λex=350 nm, the fluorescence peak of positively charged CdTe quantum dots is at 592 nm. The uric acid is able to quench their fluorescence. Under optimum conditions, the change of fluorescence intensity is linearly proportional to the concentration of uric acid in the range 0.4000-3.600 μmol L(-1), and the limit of detection calculated according to IUPAC definitions is 0.1030 μmol L(-1). Compared with routine method, the present method determines uric acid in human serum with satisfactory results. The mechanism of this strategy is due to the interaction of the tautomeric keto/hydroxyl group of uric acid and the amino group coated at the CdTe QDs.

Clinical potential of quantum dots

Advances in nanotechnology have led to the development of novel fluorescent probes called quantum dots. Quantum dots have revolutionalized the processes of tagging molecules within research settings and are improving sentinel lymph node mapping and identification in vivo studies. As the unique physical and chemical properties of these fluorescent probes are being unraveled, new potential methods of early cancer detection, rapid spread and therapeutic management, that is, photodynamic therapy are being explored. Encouraging results of optical and real time identification of sentinel lymph nodes and lymph flow using quantum dots in vivo models are emerging. Quantum dots have also superseded many of the limitations of organic fluorophores and are a promising alternative as a research tool. In this review, we examine the promising clinical potential of quantum dots, their hindrances for clinical use and the current progress in abrogating their inherent toxicity.

Fluorescent method for the determination of sulfide anion with ZnS:Mn quantum dots

Water-soluble Mn(2+)-doped ZnS quantum dots (QDs) were prepared using mercaptoacetic acid as the stabilizer. The optical properties and structure features were characterized by X-Ray, absorption spectrum, IR spectrum and fluorescence spectrum. In pH 7.8 Tris-HCl buffer, the QDs emitted strong fluorescence peaked at 590 nm with excitation wavelength at 300 nm. The presence of sulfide anion resulted in the quenching of fluorescence and the intensity decrease was proportional to the S(2-) concentration. The linear range was from 2.5 x 10(-6) to 3.8 x 10(-5) mol L(-1) with detection limit as 1.5 x 10(-7) mol L(-1). Most anions such as F(-), Cl(-), Br(-), I(-), CH(3)CO(2) (-), ClO(4) (-), CO(3) (2-), NO(2) (-), NO(3) (-), S(2)O(3) (2-), SO(3) (2-) and SO(4) (2-) did not interfere with the determination. Thus a highly selective assay was proposed and applied to the determination of S(2-) in discharged water with the recovery of ca. 103%.