Metal Nanostructures for Environmental Pollutant Detection Based on Fluorescence

Heavy metal ions and pesticides are extremely dangerous for human health and environment and an accurate detection is an essential step to monitor their levels in water. The standard and most used methods for detecting these pollutants are sophisticated and expensive analytical techniques. However, recent technological advancements have allowed the development of alternative techniques based on optical properties of noble metal nanomaterials, which provide many advantages such as ultrasensitive detection, fast turnover, simple protocols, in situ sampling, on-site capability and reduced cost. This paper provides a review of the most common photo-physical effects impact on the fluorescence of metal nanomaterials and how these processes can be exploited for the detection of pollutant species. The final aim is to provide readers with an updated guide on fluorescent metallic nano-systems used as optical sensors of heavy metal ions and pesticides in water

Supramolecular Luminescent Sensors

There is great need for stand-alone luminescence-based chemosensors that exemplify selectivity, sensitivity, and applicability and that overcome the challenges that arise from complex, real-world media. Discussed herein are recent developments toward these goals in the field of supramolecular luminescent chemosensors, including macrocycles, polymers, and nanomaterials. Specific focus is placed on the development of new macrocycle hosts since 2010, coupled with considerations of the underlying principles of supramolecular chemistry as well as analytes of interest and common luminophores. State-of-the-art developments in the fields of polymer and nanomaterial sensors are also examined, and some remaining unsolved challenges in the area of chemosensors are discussed

Development Of Metal-Containing Nanoparticles For Chemical Analysis And Bioanalysis

Metal-containing nanoparticles (MCPs) have been applied in fields ranging from environmental monitoring to biomedicine. This breadth is due to the outstanding behavior of MCPs as catalysts and imaging agents, and the ease with which nanoparticle morphology, composition, and reactivity (such as agglomeration) can be controlled. The work described in this dissertation will have two fundamentally different foci that are both essential for further development of MCPs as tools for chemical and bioanalysis. The first focus is on particle-by-particle characterization MCPs and the second focus is on creation of new composite MCPs. A total of four projects are included in this dissertation as follows. The first project shows how to optimize a relatively new analysis method, single-particle inductively-coupled plasma mass spectrometry (spICP-MS), for the particle-by-particle characterization of MCPs. Bulk analysis methods such conventional ICP-MS produce an aggregate signal derived from many particles at once, whereas spICP-MS produces a discrete per-particle signal that is monitored over time to produce an ensemble of per-particle signals. Bulk analysis is very reliable for obtaining accurate average metal content per particle because the signal is inherently an average for many particles. However, all per-particle information is lost with bulk analysis methods. Conversely, spICP-MS provides a very rare window into the per-particle composition of MCPs; however, its method parameters such as particle concentration, ICP ionization efficiency, and dwell time must be carefully optimized for accurate per-particle analysis. This work demonstrates how to optimize spICP-MSfor large MCPs—a particularly challenging size range—by using standard samples of gold nanoparticles ranging from 30 nm to 150 nm. The second project uses properly optimized spICP-MS conditions to measure per-particle metal concentration of large-sized (\u3e 100 nm) silica nanoparticles prepared by the water-in-oil microemulsion method and doped with tris(2,2’-bipyridyl)ruthenium(II). This is a well-studied MCP model that provides numerous avenues for bulk analysis (e.g., absorption spectrophotometry) and comparison with spICP-MS findings. Despite excellent correspondence of all methods for average Ru content over a wide range in doping levels, the per-particle doping level provided by spICP-MS does not—remarkably—adhere to a simple Gaussian-like distribution but shows a highly unusual geometric distribution. This result means, contrary to common assumption, the per-particle concentration of metal-dopant in silica nanoparticles prepared by the water-in-oil microemulsion method varies significantly per particle. These findings demonstrate that spICP-MS provides an essential per-particle window into MCP composition that is entirely missing with conventional bulk analysis methods. They also show that spICP-MS screening should become a routine characterization for new MCPs. The third project shows how to prepare and apply a ratiometric and fluorescent MCP for the sensitive and selective in vitro imaging of copper ions (Cu2+). This MCP contains conjugated polymer dots prepared from polydioctylfluorene (PFO), doped with a silica nanoparticle (PFO@SiO2), and assembled with red emissive gold nanoclusters (AuNCs) at the PFO@SiO2 surface to form a sandwich nanostructure, PFO@SiO2@AuNCs. This nanostructure exhibits two fluorescence emission peaks associated with the PFO polymers (438 nm) and AuNCs (630 nm). When Cu2+ coordinates with carboxyl groups on the AuNCs, the AuNC emission decreases in contrast to the constant PFO emission. This behavior provides a highly sensitive and selective ratiometric signal that can be applied for in vitro imaging and determination of Cu2+ in biological samples. The fourth project develops a turn-off type fluorescence resonance energy transfer (FRET) method based on a MCP composite that is sensitive to cysteine. The composite consists of AuNCs conjugated with polyvinylcarbazole polymer nanoparticles (PVK PNs) that demonstrate a strong FRET between two distinct fluorescence emission peaks under excitation of 342 nm. The MCP composite is highly sensitive to cysteine concentration though a quenching process at 630 nm due to the decomposition of aurophilic bonds consisting of Au(I)-thiolate ligands under high pH value and the etching ability of cysteine toward gold atoms. The MCP composite shows potential for determination of other biomolecules

Theranostic Gelatin Nanoparticles for Antigen Delivery and Combined Strategies for Transcutaneous Application

Transcutaneous application of vaccines is a promising strategy to enhance the effectiveness of vaccination using a reachable route of administration. Additionally, replacing the conventional needles with skin mechanical penetration techniques as microneedles or skin laser microporation will offer great advantages. This transcutaneous delivery techniques are pain-free and will help to avoid the hazards of needles. For the delivery of antigens, nanocarriers are so promising to enhance and modulate their immune response. The nanocarriers offer merits such as antigen protection from degradation, and controlling the release rate of the antigen. Additionally, due to the particulate nature of the nanocarriers, they can potentially display the antigen in a way that better mimics pathogens. For this aim, ovalbumin as a model antigen has been delivered using functionalized theranostic gelatin nanoparticles to bone marrow-derived dendritic cells (BMDCs). The nanoparticles were rendered fluorescent by using a novel imaging agent (gold and silver alloy nanoclusters) that emits near-infra red light. This was beneficial to study the nanoparticles uptake by BMDCs and also to image the nanoparticles within the skin tissue. Finally, the developed theranostic nanocarriers induced the maturation of the BMDCs and enhanced the proliferation of both helper T cells (CD4+) and cytotoxic T cells (CD8+). This indicates the potential efficacy of the delivery system for vaccination either against allergy or viruses and tumors

Gold and silver nanoparticle-based colorimetric sensors: New trends and applications

Gold and Silver nanoparticles (AuNPs and AgNPs) are perfect platforms for developing sensing colorimetric devices thanks to their high surface to volume ratio and distinctive optical properties, particularly sensitive to changes in the surrounding environment. These characteristics ensure high sensitivity in colorimetric devices. Au and Ag nanoparticles can be capped with suitable molecules that can act as specific analyte receptors, so highly selective sensors can be obtained. This review aims to highlight the principal strategies developed during the last decade concerning the preparation of Au and Ag nanoparticle-based colorimetric sensors, with particular attention to environmental and health monitoring applications

Maximizing analytical precision: exploring the advantages of ratiometric strategy in fluorescence, Raman, electrochemical, and mass spectrometry detection

Ratiometric strategy are an invaluable method that helps to detect and quantify analytes. This approach relies on measuring changes in the ratio of two or more signals to improve the accuracy and sensitivity of the results. Ratiometric strategies are widely used in a variety of fields including biomedical, environmental monitoring and food safety. It is particularly popular when traditional single-signal based detection methods are not feasible, especially when interfering substances severely affect the detection. In addition, ratiometric methods have the potential to improve the accuracy and reliability of analyte detection, leading to better results in a variety of complex environments. The article provides a comprehensive review of ratiometric strategy, focusing on ratiometric fluorescent nanoprobes for the visual detection of analytes. This paper also discusses the design of ratiometric two-photon fluorescent probes for biomedical imaging, the synthesis of ratiometric surface-enhanced Raman scattering nanoprobes for the imaging of intracellular analytes, the development of ratiometric molecularly imprinted electrochemical sensors for detection of electroactive species, and the use of isotopically-labeled internal standards in matrix-assisted laser desorption/ionization for ratiometric analysis. The article not only discusses each technique in detail, including its principles, advantages, potential applications, and limitations, but also highlights recent advances in each method and possible future directions

Design of protein-nanomaterial hybrids as tools for sensing, imaging and bioelectronics

217 p.El diseño de proteínas permite construir herramientas nanotecnológicas adaptadas para su uso en campos como la biomedicina o la industria. Las proteínas de repetición CTPR son una buena opción para desarrollar nano-herramientas dada su estructura modular y tolerancia a mutaciones, lo que permite combinar módulos funcionalizados sin comprometer la estabilidad de la proteína. Además, las proteínas CTPR pueden modificarse para desarrollar módulos que coordinan metales, lo que permite la unión de nanomateriales metálicos con propiedades interesantes como las nanopartículas de oro, o la síntesis de nanocristales metálicos in situ. En la presente tesis doctoral se propone un sistema modular de proteínas CTPR funcionalizadas con nanomateriales metálicos para su aplicación como herramientas nanotecnológicas en sensórica, imagen y bioelectrónica. Para ello, primero se establece un diseño de CTPR con residuos de coordinación de metales y se estudia en profundidad las propiedades fotoluminiscentes que emergen de nanocristales de oro coordinados a dichas CTPR. A continuación, se elaboran diseños de CTPR coordinando nanomateriales metálicos y se aplican como sensores de parámetros ambientales, como la temperatura o la presencia de iones metálicos; como sondas fluorescentes para detección correlativa de orgánulos celulares usando microscopía de fluorescencia y fluorescencia de rayos-X; y como bloques de construcción para elaborar biomateriales conductores

Enzymatic activation of a peptide functionalised gold nanoparticle system for prodrug delivery.

M. Sc. University of KwaZulu-Natal, Westville 2009.Traditional chemotherapeutic drugs are often restricted by severe side effects and a lack of specificity. An approach aimed at improving the selectivity of cancer drugs includes the use of prodrugs that can be selectively activated in tumour tissue (tumour-activated prodrugs). Peptide prodrugs cleavable by proteases in the tumour environment have been widely explored to improve the therapeutic index of cytotoxic drugs. In this study we demonstrate that the cell surface proteases over expressed in tumour cells are capable of cleaving the peptide CKAFKRK attached to gold nanoparticles (GNPs). This proteolic cleavage exposes the potential cytotoxic “agent” to the tumour cell. As these proteases are not over expressed in healthy cells, the prodrug will take much longer to be activated. A simple system is developed in this study as a proof of concept by replacing the cytotoxic agent with a fluorophore. An enhanced fluorescence emission is expected on exposure of the peptide functionalised GNP to the tumour cells, whereas a constant level of emission is anticipated on exposure to the healthy cell line

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host–guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems

Synthesis and Characterization of Ag Doped TiO2, CdS, ZnS Nanoparticles for Photocatalytic, Toxic Ions Detection, and Antimicrobial Applications

The progresses of nanoparticles (NPs) research have been passed through several advancements, such as simple spherical NPs to different shapes (anisotropic), hollow, core/shell, doped, movable core/shell or yolk shell, etc. These NPs have more advanced properties in several applications, such as catalysis, biomedical, electronics, solar cells, sensors, and so on because of high surface area to volume ratio, the presence of more loosely bound surface atoms, etc. When the particles are made of multimaterials it’s not only show improved property of the main material but also developed multifunctionality. Because of these reasons the multimaterials NPs are continuously drawing significant research attentions in the recent years. Under the multi-materials nanoparticles category, doped nanoparticles are also considered as an important class. This thesis is focused on synthesis, characterization, properties, and applications of Ag doped semiconductor nanoparticles. More specifically, TiO2, CdS, and ZnS were considered as the host materials and Ag as the dopant to form single, core/shell, hollow, and hollow bi-layer NPs for the applications in visible light induced photocatalytic degradation of organic compounds (nitrobenzene, metronidazole, methylene blue dye), antifungal agent (against Fusarium solani and Venturia inaquaelis), and sensor for the detection of arsenic and fluoride ions in aqueous media. The abstracts of the studied works are organized sequentially in the following paragraphs. Continuous increasing consumption of antibiotics in health care results to increase concentration of these compounds in surface water through wastewater treatment systems, which in turn, cause adverse effects on the aquatic ecosystems of the receiving water bodies, because of the intrinsic biological activity of these compounds. However, there are limited efforts on remediation of water pollution because of antibiotics using an effective and clean technology. In this study, photocatalytic activity of TiO2, CdS, and ZnS semiconductor nanoparticles were employed to degrade the metronidazole antibiotic in visible light irradiation. The particle size of pure TiO2, CdS, and ZnS was 33.39 ± 1.67, 4.06 ± 0.63, and 5.85 ± 0.5 nm, respectively. The particle size of Ag doped TiO2, CdS, and ZnS was 27.6 ± 2.08, 3.44 ± 0.76, and 4.91 ± 0.45 nm, respectively. The maximum degradation efficiencies of the pure TiO2, CdS and ZnS nanoparticles were 80.78, 82.46, and 81.66%, respectively. These particles were also modified by silver doping to improve its degradation efficiency. Doping of silver greatly enhanced the degradation efficiency of these nanoparticles. The particular concentrations of silver dopant were 1.00, 1.5, and 1.25% for TiO2, CdS, and ZnS nanoparticles for achieving the maximum degradation efficiency and the corresponding maximum degradation efficiencies were 94.39, 94.9%, and 95.11%. The basic mechanism of doping and the photocatalytic processes was explored in detail. A kinetic study of the degradation reaction shows first order kinetics fits well for all three cases. The reusability and stability of these photocatalyst were confirmed by the cyclic degradation test. In addition to the antibiotics, contamination of water because of other organic pollutants, especially synthetic dyes, causes severe environmental problems because of its toxic nature to microorganisms, aquatic life, and human beings. In this regard, an effective and clean remediation process for the remediation of dye contaminated effluent waters becomes more demanding to reduce the environmental impact. This section reports the photocatalytic behaviour of methylene blue using pure and silver doped semiconductor heterogeneous nanocatalysts (TiO2, CdS, and ZnS) under visible light. The photodegradation studies show there is a significant enhancement in degradation efficiency of all three nanoparticles after silver doping. For all nanoparticles, there is an optimum doping concentration to get the maximum degradation efficiency, which again depends on the material. The maximum degradation efficiencies for the three Ag doped TiO2, ZnS, and CdS nanoparticles were 95.9, 95.33, and 94.99% for 1.00, 1.25, and 1.50% Ag, respectively. The first order rate constant value of 1.00% Ag doped TiO2, 1.5% Ag doped CdS, and 1.25% Ag doped ZnS is 5.21, 5.72, and 7.71 times higher compared to their respective pure nanoparticles. The maximum degradation efficiency with minimum doping concentration among all three materials studied here was again found for TiO2. Further, silver doped hollow TiO2 (Ag-h-TiO2) nanoparticles were also synthesized by a sacrificial core (AgBr) method to enhance the surface area for higher photocatalytic activity. The Ag doping and the core removal was done simultaneously during the dissolution of the core in (NH4)OH solution. The mean particle size of synthesized Ag-h-TiO2 nanoparticles was 17.76 ± 2.85 nm with the wall thickness ~2.5 nm. The hollow structured nanoparticles have the specific surface area of 198.3 m2/g, where as solid TiO2 nanoparticles have the specific surface area of 95.1 m2/g. The suitability of this synthesized hollow nanoparticles as photocatalyst were tested for the photocatalytic degradation of three important different classes of organic compounds such as nitrobenzene (NB), metronidazole (MTZ) antibiotic, and methylene blue dye (MBD) in aqueous solution under irradiation of visible light. The maximum NB degradation was obtained 95.5%, and the metronidazole degradation efficiency was found to be 96.55 and 94.77% under the irradiation of visible light for the initial MTZ concentration of 15 and 30 mg/L with catalyst dose of 0.5 g/L. Photodegradation studies show there is a significant enhancement of the degradation efficiency of the TiO2 after the hollow structure formation and silver doping. The recycling tests of the catalysts show only ~ 10% decrease in efficiency for NB and MTZ degradation after sixth cycle of reuse. The light emission capacity in terms of quantum yield (QY) is enhanced by 18.7% for Ag-h-TiO2 than that of pure TiO2 nanoparticles. The above mentioned hollow TiO2 NPs were also used as photoinduced antifungal agent. The chemical based pesticides are widely used in agricultural farming to protect crops from insect infestation and diseases. However, the excessive use of highly toxic pesticides causes several human health (neurological, tumour, cancer) and environmental problems. So, nanoparticles based green pesticides are of special importance in recent years. Antifungal activities of the pure and Ag doped (solid and hollow) TiO2 nanoparticles were studied against two potent phytopathogens, Fusarium solani (causing Fusarium wilt disease to potato, tomato etc.) and Venturia inaquaelis (causing apple scab disease) and found hollow nanoparticles are more effective than other two. The antifungal activities of the nanoparticles enhanced further under visible light exposure against these two phytopathogens. Fungicidal effect of the nanoparticles depends on different parameters, , such as particle concentration, and intensity of visible light. The minimum inhibitory dose of the nanoparticles for V.inaquaelis and F.solani are 0.75 and 0.43 mg/plate. Presence of Ag as a dopant helps to the formation of stable Ag-S and di-sulfide bond (R-S-S-R) in cellular protein, which leads to the cell damage. During photocatalysis generated OH radicals loosen the cell wall structure and finally lead to the cell death. The mechanisms of fungicidal effect of nanoparticles against these two phytopathogens are supported by biuret and triphenyl tetrazolium chloride analyses, and field emission electron microscopy. Apart from the fungicidal effect, at very low dose (0.015 mg/plate) the nanoparticles are successfully arrest production of toxic napthoquinone pigment for F.solani which is related to the fungal pathogenecity. The nanoparticles are found to be effective to protect spoiling of potato affected by F.solani or other fungus. The doped nanoparticles can also be used effectively for the easy detection of toxic ions in water. In this regard, fluoride ion detection has taken a considerable research interest in recent years because of its typical nature. It is an essential anion for biological and medical systems, as well as for some industrial applications. But, the fluoride ions above its permissible level can cause different diseases, such as fluorosis, urolithiasis, kidney failure, cancer, and even leading to death. Because of this reason a simple and low cost method is highly desirable for the detection of fluoride ion. In this study a fluorometric method based on Ag-CdS/Ag-ZnS nanoparticle is developed for the fluoride ion detection. The developed nanoparticles were of size range 5.92 ± 0.76 nm with shell layer of 0.75 nm and it showed the quantum yield of 77.57%. The method was tested in aqueous solution at different pH. The selectivity and sensitivity of the fluorescence probe was checked in the presence of other anions (Cl-, Br-, I-, OH-, NO3- SO42-, HCO3-, HPO42-, CH3COO-, H2PO4-). The fluoride ion concentration was varied in the rage 190 – 22,800 μg/L and the lower detection limit was obtained as 99.7 μg/L. Arsenic poisoning from drinking water is also an important global issue in recent years. Because of high level toxicity of arsenic to human health, an easy, inexpensive, and low level and highly selective detection technique is of great importance to take any early precautions. This study reports the synthesis of Ag doped hollow CdS/ZnS bi-layer (Ag-h-CdS/ZnS) nanoparticles for easy fluorometric determination of As(III) ions in aqueous phase. The hollow bi-layer structures are synthesized by a sacrificial core method using AgBr as the sacrificial core and the core is removed by dissolution in ammonium hydroxide solution. The synthesized nanoparticles were characterized by using different instrumental techniques. The particle size of Ag-h-CdS/ZnS nanoparticles is ~ 76.02 ± 2.47 nm with the shell thickness of CdS layer is 1.5 nm and ZnS layer is 1.8 nm. The QY of the Ag-h-CdS/ZnS nanoparticles is 88.14%. A good linear relationship is obtained between fluorescence quenching intensity and the As(III) concentration in the range of 750 – 22500 ng/L at neutral pH with a limit of detection as low as 226 ng/L