Metal oxide QD based ultrasensitive microsphere fluorescent sensor for copper, chromium and iron ions in water

Zinc nitride quantum dots as an efficient probe for simultaneous fluorescence detection of Cu2+ and Mn2+ ions in water samples

The exceptional ascending heights of graphene (carbon) and boron nitride nanostructures have invited scientists to explore metal nitride nanomaterials. Herein, Zn3N2 quantum dots (QDs) were prepared via a simple hydrothermal route from the reaction between zinc nitrate hexahydrate and ammonia solution that possess efficient strength towards sensing applications of metal ions (Cu2+ and Mn2+). The as-prepared Zn3N2 QDs show bright fluorescence, displaying an emission peak at 408 nm upon excitation at 320 nm, with a quantum yield (QY) of 29.56%. It was noticed that the fluorescence intensity of Zn3N2 QDs linearly decreases with the independent addition of Cu2+ and Mn2+ ions, displaying good linearity in the ranges 2.5-50 µM and 0.05-5 µM with detection limits of 21.77 nM and of 63.82 nM for Cu2+ and Mn2+ ions, respectively. The probe was successfully tested for quantifying Cu2+ and Mn2+ in real samples including river, canal, and tap water, providing good recoveries with a relative standard deviation  < 2%. Furthermore, the masking proposition can successfully eliminate the interference if the two metal ions exist together. It was found that thiourea is efficiently able to mask Cu2+ and selectively quenches Mn2+, and L-cysteine is able to halt the quenching potential of Mn2+ and is selectively able to sense Cu2+. The Zn3N2 QDs provide a simple way for the simultaneous detection of both Cu2+ and Mn2+ ions in environmental samples at low sample preparations requirements.

Stimuli-directed selective detection of Cu2+ and Cr2O72- ions using a pH-responsive chitosan-poly(aminoamide) fluorescent microgel in aqueous media

In this work, the preparation of a pH-responsive fluorescent microgel, (NANO-PAMAM-CHT), is presented for the selective detection of Cu2+ and Cr2O72- ions. The NANO-PAMAM-CHT (nanosized polyaminoamide-chitosan microgel) is synthesized via aza-Michael addition reactions in a controlled and stepwise manner in water, using easily affordable starting materials like 1,4-diaminobutane, N,N'-methylene-bis-acrylamide, NIPAM and chitosan. NANO-PAMAM-CHT shows pH-responsive fluorescent properties, whereas the fluorescence intensity shows a pH-responsive change. Due to the selective fluorescence quenching, the microgel can detect both Cu2+ ions and Cr2O72- ions selectively at ambient pH in aqueous medium. Moreover, it can selectively differentiate between Cu2+ ion and Cr2O72- ions at pH ∼3 in water. The limits of detection for Cu2+ ions and Cr2O72- ions are reported as 16.9 μM and 2.62 μM, respectively (lower than the minimum allowed level in drinking water) at pH ∼7. Mechanistic study further reveals the dynamic quenching phenomenon in the presence of Cu2+ ions and static quenching in the presence of Cr2O72- ions.

Recent Breakthroughs in Using Quantum Dots for Cancer Imaging and Drug Delivery Purposes

Cancer is one of the leading causes of death worldwide. Because each person's cancer may be unique, diagnosing and treating cancer is challenging. Advances in nanomedicine have made it possible to detect tumors and quickly investigate tumor cells at a cellular level in contrast to prior diagnostic techniques. Quantum dots (QDs) are functional nanoparticles reported to be useful for diagnosis. QDs are semiconducting tiny nanocrystals, 2-10 nm in diameter, with exceptional and useful optoelectronic properties that can be tailored to sensitively report on their environment. This review highlights these exceptional semiconducting QDs and their properties and synthesis methods when used in cancer diagnostics. The conjugation of reporting or binding molecules to the QD surface is discussed. This review summarizes the most recent advances in using QDs for in vitro imaging, in vivo imaging, and targeted drug delivery platforms in cancer applications.

Development of fluorescent carbon nanoparticles from Madhuca longifolia flower for the sensitive and selective detection of Cr6+: a collective experimental-computational approach

Herein, blue-emitting carbon nanoparticles (CNPs) were synthesized using the Madhuca longifolia flower for the highly selective and sensitive detection of Cr6+ ions in aqueous media using a simple, green, and cost-effective approach, and computational experiments were also performed. The prepared CNPs were well-dispersed in water with an average diameter of 12 nm and functionalized with carbonyl, hydroxyl and carboxylic acid groups. The decrease in the fluorescence intensity of the CNPs with an increase in the content of Cr6+ provided an important signal for the sensitive and selective detection of Cr6+ in aqueous media. The limit of detection for Cr6+ in an aqueous medium was found to be 103 ppb, which is more sensitive in comparison with the previously reported study. Furthermore, the validation of the proposed higher sensing feature and more selective nature of the CNPs towards Cr6+ was also explained using an in silico approach. The results from the theoretical calculations based on the DFT approach demonstrated that the binding energy (BE) of the CNPs with three transition metal (TM) cations (Cr6+, Fe3+, and Hg2+) follows the order of Cr6+ > Fe3+ > Hg2+, where the Cr6+ TM cation associated with the CNPs possesses the highest valence state, showing the highest sensing feature and highest selectivity among the investigated ions, as expected. The metal ions associated with the CNPs having a higher charge and a smaller radius indicated a higher BE and larger degree of deformation of the CNPs. Moreover, to achieve new insights into the structural, stability/energetics, and electronic features, some useful tools, such as NCI-plot, HOMO-LUMO gap, MESP, and QTAIM analysis were employed, which facilitated noteworthy outcomes.

Capped ZnO quantum dots with a tunable photoluminescence for acetone detection

Acetone is a dangerous material that poses a major risk to human health. To protect against its harmful impacts, a fluorescent biosensor 3-aminopropyl triethoxysilane capped ZnO quantum dots (APTES/ZnO QDs) was investigated to detect low concentrations of acetone. Numerous techniques, including Fourier transform infrared (FTIR), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), zeta potential, UV-vis absorption, and photoluminescence (PL), are used to thoroughly verify the successful synthesis of pristine ZnO QDs and APTES/ZnO QDs. The HRTEM micrograph showed that the average size distributions of ZnO QDs and APTES/ZnO QDs were spherical forms of 2.6 and 1.2 nm, respectively. This fluorescent probe dramatically increased its sensitivity toward acetone with a wide linear response range of 0.1-18 mM and a correlation coefficient (R²) of 0.9987. The detection limit of this sensing system for acetone is as low as 42 μM. The superior selectivity of acetone across numerous interfering bioanalytics is confirmed. Reproducibility and repeatability experiments presented relative standard deviations (RSD) of 2.2% and 2.4%, respectively. Finally, this developed sensor was applied successfully for detecting acetone in a diabetic patient's urine samples with a recovery percentage ranging from 97 to 102.7%.

Fluorescence Properties of ZnOQDs-GO-g-C3N4 Nanocomposites

In this paper, the fluorescence properties of ZnOQD-GO-g-C₃N₄ composite materials (ZCGQDs) were studied. Firstly, the addition of a silane coupling agent (APTES) in the synthesis process was explored, and it was found that the addition of 0.04 g·mL^-1 APTES had the largest relative fluorescence intensity and the highest quenching efficiency. The selectivity of ZCGQDs for metal ions was also investigated, and it was found that ZCGQDs showed good selectivity for Cu²⁺. ZCGQDs were optimally mixed with Cu²⁺ for 15 min. ZCGQDs also had good anti-interference capability toward Cu²⁺. There was a linear relationship between the concentration of Cu²⁺ and the fluorescence intensity of ZCGQDs in the range of 1~100 µM. The regression equation was found to be F₀/F = 0.9687 + 0.12343C. The detection limit of Cu²⁺ was about 1.74 μM. The quenching mechanism was also analyzed.

Syntheses of APTMS-Coated ZnO: An Investigation towards Penconazole Detection

Extrinsic chemiluminescence can be an efficient tool for determining pesticides and fungicides, which do not possess any intrinsic fluorescent signal. On this basis, (3-aminopropyl) trimethoxysilane (APTMS)-coated ZnO (APTMS@ZnO) was synthesized and tested as an extrinsic probe for the fungicide penconazole. Several synthetic routes were probed using either a one-pot or two-steps method, in order to ensure both a green synthetic pathway and a good signal variation for the penconazole concentration. The synthesized samples were characterized using X-ray diffraction (XRD), infrared (IR), Raman and ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM) imaging and associated energy-dispersive X-ray (EDX) analysis. The average size of the synthesized ZnO nanoparticles (NPs) is 54 ± 10 nm, in line with previous preparations. Of all the samples, those synthesized in two steps, at temperatures ranging from room temperature (RT) to a maximum of 40 °C, using water solvent (G-APTMG@ZnO), appeared to be composed of nanoparticles, homogeneously coated with APTMS. Chemiluminescence tests of G-APTMG@ZnO, in the penconazole concentration range 0.7-1.7 ppm resulted in a quenching of the native signal between 6% and 19% with a good linear response, thus indicating a green pathway for detecting the contaminant. The estimated detection limit (LOD) is 0.1 ± 0.01 ppm.

Enhanced fluorescent iron oxide quantum dots for rapid and interference free recognizing lysine in dairy products

In this work, a simple, easy and selective method for sensing lysine in an acidic medium was developed based on fluorescent iron oxide quantum dots (IO QDs). IO QDs using the hydrothermal method were prepared with different conditions (concentration of NPs, amount of citric acid, heating time, heating temperature, and total volume in the hydrothermal reactor) where iron oxide nanoparticles (IO NPs) were used as the starting materials. TEM, FTIR, UV-Vis Spectrometry, fluorescence spectrometry, Powder XRD, VSM were used to characterize the as-prepared IO QDs. The surface of the IO QDs contained -OH, -COO^-, and other functional groups that acted as a bridge to bind the IO QDs nanoprobe with the surrounding analytes. Under acidic conditions (pH 3.0), IO QDs exhibited a rapid and interference-free fluorescence enhancement behavior after adding lysine within 2 min at room temperature, whereas other amino acids had no effect on IO QDs fluorescence. Therefore, the IO QDs prepared in this study have shown potential in lysine sensing applications. The results showed that the relative FL intensity was linear with lysine concentration in the range of 1-100 μM and had a detection limit of 0.66 μM. This proposed method has high selectivity for lysine over other amino acids, and the developed methods were used in real sample with good recoveries. Under relatively acidic conditions, a specific and fast lysine interaction was observed, resulting in the successful of IO QDs as the fluorescent probe for rapid and interference-free lysine assessment in dairy products.

RAFT Hydroxylated Polymers as Templates and Ligands for the Synthesis of Fluorescent ZnO Quantum Dots

The remarkable photoluminescent properties, biocompatibility, biodegradability, and antibacterial properties of zinc oxide quantum dots (ZnO QDs) coupled with their low cost and nanoscale size guarantee bio-related and technological applications. However, the effect of the polymeric ligand during synthesis has hardly been investigated compared to other less environmentally friendly QDs. Thus, the objective of this work was to focus on the synthesis of fluorescent hybrid ZnO QDs by the sol-gel method using different polymers with hydroxyl groups as templates and ligands to obtain stable particles in different media. For this purpose, well-defined hydroxylated statistical polymers and block copolymers were synthesized using reversible-addition fragmentation chain transfer (RAFT) polymerization to establish the influence of molecular weight, hydrophobic/hydrophilic balance, and polymer architecture on the colloidal and photophysical properties of the synthesized hybrid ZnO QDs. Dynamic light scattering (DLS), TEM, and X-ray diffraction measurements indicated the formation of stable nanoparticles of a few nanometers. A remarkable enhancement in terms of fluorescence was observed when ZnO QDs were synthesized in the presence of the hydroxylated homopolymers and even more so with block copolymers architecture. Organosilanes combined with the hydroxylated polymers were used to improve the colloidal stability of ZnO QDs in aqueous media. These samples exhibited uniform and stable enhanced photoluminescence for nearly five months of being investigated. Among other applications, the hybrid ZnO QDs synthesized in this work exhibit high selectivity to detect Cr⁶⁺, Fe²⁺, or Cu²⁺ in water.

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.