Detecting Mercury (II) and Thiocyanate Using "Turn-on" Fluorescence of Graphene Quantum Dots

Role of silver nanoparticles and silver nanoclusters for the detection and removal of Hg(ii)

Silver metal, being a 3d transition metal in group 11 in the periodic table, is widely used in material science for its distinguished plasmonic properties. Nanoparticles (NPs) and nanoclusters (NCs) are widely used in sensing applications having a surface plasmon band and emissive properties, respectively. Mercury is one of the detrimental toxins and threats to various ecosystems. The distinction between nanoparticles and nanoclusters, the utility and toxicity of heavy metal mercury, fluorometric and colorimetric approaches to the recognition of mercury ions with NPs and NCs, the mechanism of detection, spot detection, and natural water sample analyses were illustrated in detail in this review article. Moreover, the sensing platform and analyte (Hg2+) fate were described for substantiating the mechanism. It was observed that NCs are mostly utilized for fluorometric approaches, while NPs are mostly employed for colorimetric approaches. Fluorometric detection is mainly quenching-based. However, sensing with enhancement was found in a few reports. Adulteration of other metals with silver particles often modifies the sensing platform.

Highly efficient and selective Hg(II) adsorbent: ZnS grown on the surface of 4A zeolite and supported on starch aerogels

In this study, ZnS nanoparticles were loaded on the surface of zeolite NaA and embedded in a carbon aerogel to prepare C@zeolite-ZnS, where zeolite NaA was used in order to adsorb Zn²⁺ ions released during ion exchange, and the carbon aerogel had good dispersion as a carrier for ZnS to solve the ZnS agglomeration problem. The morphology and structure of C@zeolite-ZnS were characterized by FT-IR, XRD, SEM, BET, and XPS. C@zeolite-ZnS showed excellent selectivity and high removal rate for Hg(II) ions with a maximum adsorption capacity of 795.83 mg/g. When the pH, adsorption time, and Hg(II) ion concentration were 6, 30 min, and 25 mg/L at 298 K, the corresponding adsorption and removal rates reached 99.90% and 124.88 mg/g, respectively. Thermodynamic studies have shown that the adsorption process is a spontaneous heat absorption process. Furthermore, after up to 10 cycles of adsorption, the adsorbent still exhibited outstanding stability and high adsorption capacity with removal rates exceeding 99%. In conclusion, C@zeolite-ZnS, which is stable and reusable and has the ability to meet industrial emission standards after adsorption of Hg(II) ions, is very promising for industrial applications.

A review of graphene quantum dots and their potential biomedical applications

Today, nanobiotechnology is a pioneering technology in biomedicine. Every day, new nanomaterials are synthesized with elevated physiochemical properties for better diagnosis and treatment of diseases. One advancing class of materials is the Graphene family. Among different kinds of graphene derivatives, graphene quantum dots (GQDs) show fantastic optical, electrical, and electrochemical features originating from their unique quantum confinement effect. Due to the distinct properties of GQD, including large surface-to-volume ratio, low cytotoxicity, and easy functionalization, this nanomaterial has gone popular in biomedical field. Herein, a short overview of different strategies developed for GQD synthesis and functionalization is discussed. In the following, the most recent progress of GQD based nanomaterials in different biomedical fields, including bio-imaging, drug/gene delivery, antimicrobial, tissue engineering, and biosensors, are reviewed.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.

Carbon dots-based nanomaterials for fluorescent sensing of toxic elements in environmental samples: Strategies for enhanced performance

Rapid industrialization and manufacturing expansion have caused heavy metal pollution, which is a critical environmental issue faced by global population. In addition, the disadvantages presented by conventional detection methods such as the requirement of sophisticated instruments and qualified personnel have led to the development of novel nanosensors. Recently, carbon dots (CDs) have been presented as a multifunctional nanomaterial alternative for the accurate detection of heavy metal ions in water systems. The capacity of CDs to detect contaminants in wastewater -including heavy metals- can be found in the literature; however, to the best of our knowledge, none of them discusses the most recent strategies to enhance their performance. Therefore, in this review, beyond presenting successful examples of the use of CDs for the detection of metal ions, we further discuss the strategies to enhance their photoluminescence properties and their performance for environmental monitoring. In this manner, strategies such as heteroatom-doping and surface passivation are reviewed in detail, as well as describing the mechanisms and the effect of precursors and synthesis methods. Finally, the current challenges are described in detail to propose some recommendations for further research.

Shedding Light on Graphene Quantum Dots: Key Synthetic Strategies, Characterization Tools, and Cutting-Edge Applications

During the last 20 years, the scientific community has shown growing interest towards carbonaceous nanomaterials due to their appealing mechanical, thermal, and optical features, depending on the specific nanoforms. Among these, graphene quantum dots (GQDs) recently emerged as one of the most promising nanomaterials due to their outstanding electrical properties, chemical stability, and intense and tunable photoluminescence, as it is witnessed by a booming number of reported applications, ranging from the biological field to the photovoltaic market. To date, a plethora of synthetic protocols have been investigated to modulate the portfolio of features that GQDs possess and to facilitate the use of these materials for target applications. Considering the number of publications and the rapid evolution of this flourishing field of research, this review aims at providing a broad overview of the most widely established synthetic protocols and offering a detailed review of some specific applications that are attracting researchers’ interest.

Quantum Dots Based Fluorescent Probe for the Selective Detection of Heavy Metal Ions

Heavy metal ions are one of the primary causes of environmental pollution. A marshal effect of heavy metal ions is a paramount ultimatum to humans, aquatic animals and other organisms present in nature. Multitude arrays of materials have been proclaimed for sensing of heavy metal ions and also many methodologies are applied for heavy metal ion sensing. Due to their toxicity and non-biodegradability, it is required to be perceived immediately prior to its manifestation of harmful effects. Quantum Dots (QDs) are zero-dimensional nanomaterial particles and owing to their distinctive optical and electronic properties, they are utilized as nanosensors. QDs have enriched fluorescence properties which includes broad excitation spectrum, narrow emission spectrum and photostability. QDs offer eclectic and sensitive detection of heavy metal ions due to presence of discrete capping agents and different functional groups present on the surface of the QDs. These capping layers and functional groups attune the sensing capability of the QDs, which leverages the interactions of QDs with various analytes by different mechanisms. This review, comprising of papers from 2011 to 2020,focuses on heavy metal ions sensing potential of various quantum dots and its applicability as a nanosensor for on field heavy metal ions detection in water. Quantum Dots (QDs) based Heavy Metal Detection.

Formation of Mercury Droplets at Ambient Conditions through the Interaction of Hg(II) with Graphene Quantum Dots

Unlike other metals, Hg forms droplets at ambient conditions when a Hg(II) salt interacts with hydroxyl-enriched graphene quantum dots (HEGQDs). The hydroxylation of GQD surface is evident from FT-IR, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The scanning electron microscopy images of Hg(II)-HEGQDs incubated for 0, 1, 24, and 168 h show Hg droplets with the size of 0.1, 0.3, 0.8, and 2 μm, respectively. The XPS studies confirm the presence of Hg(0) and also reveal a noticeable decline in the composition percentage of C-O, whereas a marked increase is observed in the C═O composition percentage. The pathway for the formation of droplets induces immediate reduction of Hg(II) to Hg(0) by both hydroxyl groups and π electron cloud present on the surface of HEGQDs, followed by coalescence. The formed Hg(0) is then strongly adsorbed on the hollow sites of graphene and acts as a nucleation site for the growth of droplets. The kinetics of the reaction obeys LaMer Burst nucleation followed by coalescent growth in addition to autocatalytic reduction and finally follows the Oswald ripening mechanism. The internal pressure of Hg droplets gradually decreases as the radius of the drop increases over the incubation time and liquid-rhombohedral transformation is likely to take place at a radius of 0.8 nm.

Red-fluorescent graphene quantum dots from guava leaf as a turn-off probe for sensing aqueous Hg(ii)

In this work, we have prepared red-fluorescent graphene quantum dots and utilized as a highly selective and sensitive fluorescence turn-off probe for detection of the toxic metal ion Hg²⁺ from guava leaf extract.