A Simple Colloidal Synthesis for Gram-Quantity Production of Water-Soluble ZnS Nanocrystal Powders

Thermally assisted optical processes in InP/ZnS quantum dots

The utilization of InP-based biocompatible quantum dots (QDs) necessitates a comprehensive understanding of the structure-dependent characteristics influencing their optical behavior. The optimization of core/shell QDs for practical applications is of particular interest due to their reduced toxicity, enhanced photostability, and improved luminescence efficiency. This optimization involves analyzing thermally activated processes involving exciton and defect-related energy levels. This study investigates water-soluble colloidal InP/ZnS QDs with varying shell thicknesses and stabilizing coatings using temperature-dependent optical absorption (OA) and photoluminescence (PL). Our results indicate that all samples experience temperature-induced shifts in exciton absorption and luminescence peaks due to interactions with acoustic phonons. Despite the wide size distribution of nanocrystals, the halfwidth of the bands remains constant. We observe a temperature-dependent Stokes shift in InP/ZnS QDs, revealing the fine structure of exciton states across different configurations. Furthermore, our findings demonstrate common mechanisms underlying PL thermal quenching in these QDs, regardless of the shell thickness or coating type. Specifically, defect-related emissions arise from localized energy levels at the core/shell interface. At the same time, exciton PL quenching primarily occurs through thermally activated electron migration from the InP core to the ZnS shell. Overall, our study highlights the potential for tailoring the temperature response of InP/ZnS QDs by adjusting shell thickness, offering opportunities to optimize their performance for specific applications.

Prospects of ZnS and ZnO as smart semiconductor materials in light-activated antimicrobial coatings for mitigation of severe acute respiratory syndrome coronavirus-2 infection

We carried out theoretical and experimental analyses of ZnO and ZnS nanoparticles as smart semiconductor materials in light-activated antimicrobial coating for application in masks. We used low-cost hydrothermally processable precursors to direct the growth of the coatings on cotton fabric. Both ZnO and ZnS coatings had high reactivities as disinfection agents in photocatalysis reactions for the degradation of a methylene blue dye solution. Also, these coatings showed excellent UV protection properties. For understanding at the molecular level, the broad-spectrum biological activities of the ZnO and ZnS coatings against Fusarium Oxysporum fungi, Escherichia coli bacteria, and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus and their variants, were investigated computationally. Hexagonal Zn6O6 and Zn6S6 clusters were used as models for the simulations through excited- and ground-state calculations. The theoretical findings show that changes in the local chemical environment in these excited systems have a profound impact on their physical and chemical properties and thus, can provide a better understanding to engineer new functional materials in light-activated antimicrobial coatings for the mitigation of SARS-CoV-2 infection.

Highly-sensitive aptasensor based on fluorescence resonance energy transfer between l-cysteine capped ZnS quantum dots and graphene oxide sheets for the determination of edifenphos fungicide

With the advantages of excellent optical properties and biocompatibility, single-strand DNA-functionalized quantum dots have been widely applied in biosensing and bioimaging. A new aptasensor with easy operation, high sensitivity, and high selectivity was developed by immobilizing the aptamer on water soluble l-cysteine capped ZnS quantum dots (QDs). Graphene oxide (GO) sheets are mixed with the aptamer-QDs. Consequently, the aptamer-conjugated QDs bind to the GO sheets to form a GO/aptamer-QDs ensemble. This aptasensor enables the energy transfer based on a fluorescence resonance energy transfer (FRET) from the QDs to the GO sheets, quenching the fluorescence of QDs. The GO/aptamer-QDs ensemble assay acts as a "turn-on'' fluorescent sensor for edifenphos (EDI) detection. When GO was replaced by EDI, the fluorescence of QDs was restored and its intensity was proportional to the EDI concentration. This GO-based aptasensor under the optimum conditions exhibited excellent analytical performance for EDI determination, ranging from 5×10^-4 to 6×10^-3mg L^-1 with the detection limit of 1.3×10^-4mgL^-1. Furthermore, the designed aptasensor exhibited excellent selectivity toward EDI compared to other pesticides and herbicides with similar structures such as diazinon, heptachlor, endrin, dieldrin, butachlor and chlordane. Good reproducibility and precision (RSD =3.9%, n =10) of the assay indicates the high potential of the aptasensor for quantitative trace analysis of EDI. Moreover, the results demonstrate the applicability of the aptasensor for monitoring EDI fungicide in spiked real samples.

A novel water-soluble quantum dot–neutral red fluorescence resonance energy transfer probe for the selective detection of megestrol acetate

Megestrol acetate can specifically quench the fluorescence intensity of the β-CD-QD–NR FRET probe at low concentration levels.

Kinetic fluorescence quenching of CdS quantum dots in the presence of Cu(II): chemometrics-assisted resolving of the kinetic data and quantitative analysis of Cu(II)

In this work, the kinetic fluorescence behavior of CdS quantum dots (QDs) in the presence of Cu(II) was investigated. In contrast to some other transition metal ions such as Ag(I), Ni(II), and Hg(II), a gradual red-shift in the emission spectrum of CdS QDs was observed for Cu(II) during the reaction course. More investigations revealed the existence of two chemical components in the recorded kinetic data in the presence of Cu(II). Multivariate curve resolution-alternating least squares (MCR-ALS) method was applied in order to extract pure emission spectra and time-dependent profiles of these two components at different concentrations of Cu(II). The results obtained from resolving the data by MCR-ALS got some information about the mechanism of the interaction between CdS QDs and Cu(II) ions which were in good agreement with those reported in the literature. Moreover, the multivariate method of analysis, partial least-squares (PLS) method, was used to develop a multivariate calibration model for quantitative analysis of Cu(II) using the entire kinetic data sets. The calibration and validation sets were created ranging from 0.02 to 1μM of Cu(II) and were successfully calibrated and predicted by the PLS model. This method allowed a sensitive determination of Cu(II) ions with a detection limit of 13nM based on three times of the standard deviation corresponding to PLS regression.

Biosynthesis and Antimicrobial Activity of Semiconductor Nanoparticles against Oral Pathogens

Dental care is an essential phenomenon in human health. Oral pathogens can cause severe break which may show the way to serious issues in human disease like blood circulation and coronary disease. In the current study, we demonstrated the synthesis and antimicrobial activity of cadmium sulphide and zinc sulphide nanoparticles against oral pathogens. The process for the synthesis of cadmium sulphide (CdS) and zinc sulphide (ZnS) nanoparticles is fast, novel, and ecofriendly. Formation of cadmium sulphide (CdS) and zinc sulphide (ZnS) nanoparticles was confirmed by surface plasmon spectra using UV-Vis spectrophotometer. The morphology of crystalline phase of nanoparticles was determined from transmission electron microscopy (TEM) and X-ray diffraction (XRD) spectra. The average size of cadmium sulphide (CdS) and zinc sulphide (ZnS) nanoparticles was in the range of 10 nm to 25 nm and 65 nm, respectively, and the observed morphology was spherical. The results indicated that the proteins, which contain amine groups, played a reducing and controlling responsibility during the formation of cadmium sulphide (CdS) and zinc sulphide (ZnS) nanoparticles in the colloidal solution. The antimicrobial activity was assessed against oral pathogens such as Streptococcus sp. Staphylococcus sp. Lactobacillus sp., and Candida albicans and these results confirmed that the sulphide nanoparticles are exhibiting good bactericidal activity.

Retracted Article: Red luminescent manganese-doped zinc sulphide nanocrystals and their antibacterial study

The red luminescence of ZnS:Mn²⁺ nanocrystals at ∼612 nm and the broad spectrum antibacterial activity of biotin capped ZnS:Mn²⁺ nanocrystals.

Applications of quantum dots as probes in immunosensing of small-sized analytes

Quantum dots (QDs) are semiconductor nanoparticles with very interesting optical properties, like high quantum yield or narrow and size-tuneable fluorescence spectra. Current applications of QDs are widespread, their use as fluorescence labels in bioassays being one of the most promising. These nanoparticles are usually conjugated to highly specific biomolecules like antibodies, oligonucleotides, enzymes or aptamers to improve assay selectivity. In this review, QD surface passivation, conjugation to biomolecules, and purification strategies are discussed with special emphasis to the development of QD-based immunoassays for the detection of low molecular weight compounds given the relevance of this sort of analytes in health, food safety, pharmaceutical, or environmental monitoring areas. The aim of this review is to summarise the main achievements attained so far and to initialise researchers in the field of antibody-based assays employing QDs as labels, such as fluorescence-linked immunosorbent assay (FLISA), fluorescence (or Förster) resonance energy transfer (FRET), immunochromatographic methods, and immunosensors.

Metal ion (silver, cadmium and zinc ions) modified CdS quantum dots for ultrasensitive copper ion sensing

Metal ion (Ag(+), Cd(2+), Zn(2+)) modified CdS quantum dots (QDs) were synthesized and used for Cu(2+) sensing. Modification by these metal ions could enhance the PL intensity of CdS QDs with the extent of the PL enhancement being related to the concentration of the metal ions. Different metal ion (Ag(+), Cd(2+), Zn(2+)) modified CdS QDs also showed different analytical characteristics for Cu(2+) sensing. In particular, Ag( + ) modified CdS QDs showed greatly enhanced sensitivity for Cu(2+) determination than did the unmodified CdS QDs. A limit of detection (LOD) of 2.0 × 10(-10) M was obtained for Ag(+) modified CdS QDs, which is the lowest LOD obtained using QDs as fluorescence probes for Cu(2+) sensing. This study demonstrates the important role of surface state of QDs in fluorescence sensing.

Semiconductor quantum dots: synthesis and water-solubilization for biomedical applications

BACKGROUND

Quantum dots (QDs) are generally nanosized inorganic particles. They have distinctive size-dependent optical properties due to their very small size (mostly < 10 nm). QDs are regarded as promising new fluorescent materials for biological labeling and imaging because of their superior properties compared with traditional organic molecular dyes. These properties include high quantum efficiency, long-term photostability and very narrow emission but broad absorption spectra.

OBJECTIVE/METHODS

Recent developments in synthesizing high quality semiconductor QDs (mainly metal-chalcogenide compounds) and forming biocompatible structures for biomedical applications are discussed in this paper.

RESULTS/CONCLUSIONS

This information may facilitate the research to create new materials/technologies for future clinical applications.

Precipitation and growth of zinc sulfide nanoparticles in the presence of thiol-containing natural organic ligands

In sulfidic aquatic systems, metal sulfides can control the mobility and bioavailability of trace metal pollutants such as zinc, mercury, and silver. Nanoparticles of ZnS and other metal sulfides are known to exist in oxic and anoxic waters. However, the processes that lead to their persistence in the aquatic environment are relatively unknown. The objective of this study was to evaluate the importance of dissolved natural organics in stabilizing nanoparticulate ZnS that precipitates under environmentally relevant conditions. Precipitation and growth of ZnS particles were investigated in the presence of dissolved humic acid and low-molecular weight organic acids that are prevalent in sediment porewater. Dynamic light scattering was used to monitor the hydrodynamic diameter of particles precipitating in laboratory solutions. Zn speciation was also measured by filtering the ZnS solutions (< 0.2 microm) and using anodic stripping voltammetry to confirm that Zn was coordinated to sulfide during the precipitation experiments and not to the dissolved organic ligands. X-ray photoelectron spectroscopy and electron microscopy were used to confirm that amorphous particles containing Zn and S were precipitating in the suspensions. Observed growth rates of ZnS particles varied by orders of magnitude, depending on the type and concentration of organic ligand in solution. In the presence of humic acid and thiol-containing ligands (cysteine, glutathione, and thioglycolate), observed growth rates decreased by 1-3 orders of magnitude relative to controls without the ligands. In contrast, growth rates of the particles were consistently within 1 order of magnitude of the ligand-free control when oxygen- and amine-containing ligands (oxalate, serine, and glycolate) were present Furthermore, particle growth rates decreased with an increase in thiol concentration and increased with NaNO3 electrolyte concentration. These studies suggest that specific surface interactions with thiol-containing organics may be one factor that contributes to the persistence of naturally occurring and anthropogenic nanoparticles of ZnS and other metal sulfides in the aquatic environment.

Temperature-induced aggregation of poly(N-isopropylacrylamide)-stabilized CdS quantum dots in water

Water-soluble nanosized semiconductor CdS particles (quantum dots, QDs) were synthesized with a protective layer of covalently grafting linear thermally sensitive poly(N-isopropylacrylamide) chains. Reversible association and dissociation of these CdS particles can be induced via an alteration of the solution temperature. The formation and fragmentation of the QD aggregates of the CdS particles were systematically investigated by laser light scattering (LLS) and confirmed by transmission electron microscopy (TEM). There exists a hysteresis during one heating-and-cooling cycle. The CdS particles stabilized with shorter PNIPAM chains (Mn=15,000 g/mol) can associate to form larger and denser spherical aggregates with a much higher aggregation number than those grafted with longer PNIPAM chains (Mn=31,000 g/mol) in the heating process. The dissociation (fragmentation) in the cooling process has two stages: initially, the aggregates dissociate as the temperature decreases, and then, the fragmentation stops over a wider temperature range before complete dissociation. We attribute such a two-stage fragmentation to a balanced effect of inter- and intrachain hydrogen bonding as well as the hydrophobic interaction between PNIPAM chains and CdS particles.

Functionalized CdS quantum dots-based luminescence probe for detection of heavy and transition metal ions in aqueous solution

Strong luminescence CdS quantum dots (QDs) have been prepared and modified with l-cysteine by a facile seeds-assistant technique in water. They are water-soluble and highly stable in aqueous solution. CdS QDs evaluated as a luminescence probe for heavy and transition metal (HTM) ions in aqueous solution was systematically studied. Five HTM ions such as silver(I) ion, copper(II) ion, mercury(II) ion, cobalt(II) ion, and nickel(II) ion significantly influence the photophysics of the emission from the functionalized CdS QDs. Experiment results showed that the fluorescence emission from CdS QDs was enhanced significantly by silver ion without any spectral shift, while several other bivalent HTM ions, such as Hg(2+), Cu(2+), Co(2+), and Ni(2+), exhibited effective optical quenching effect on QDs. Moreover, an obvious red-shift of emission band was observed in the quenching of CdS QDs for Hg(2+) and Cu(2+) ions. Under the optimal conditions, the response was linearly proportional to the concentration of Ag(+) ion ranging from 1.25 x 10(-7) to 5.0 x 10(-6)molL(-1) with a detection limit of 2.0 x 10(-8)molL(-1). The concentration dependence of the quenching effect on functionalized QDs for the other four HTM ions could be well described by typical Stern-Volmer equation, with the linear response of CdS QDs emission proportional to the concentration ranging from 1.50 x 10(-8) to 7.50 x 10(-7)molL(-1) for Hg(2+) ion, 3.0 x 10(-7) to 1.0 x 10(-5)molL(-1) for Ni(2+) ion, 4.59 x 10(-8) to 2.295 x 10(-6)molL(-1) for Cu(2+) ion, and 1.20 x 10(-7) to 6.0 x 10(-6)molL(-1) Co(2+) ion, respectively. Based on the distinct optical properties of CdS QDs system with the five HTM ions, and the relatively wide linear range and rapid response to HTM ions, CdS QDs can be developed as a potential identified luminescence probe for familiar HTM ions detection in aqueous solution.

Facile synthesis of water-soluble and size-homogeneous cadmium selenide nanoparticles and their application as a long-wavelength fluorescent probe for detection of Hg(II) in aqueous solution

Highly luminescent uncoated water-soluble and mono-disperse CdSe nanoparticles (NPs) have been prepared facilely. Uncoated CdSe core NPs possessing a good size distribution was accompanied with long wavelength of fluorescence emission. It is interesting to note that these functionalized NPs are soluble in water medium stably for more than 1 month, and no significant changes were found in the optical characteristics in comparison with fresh CdSe NPs prepared. The functionalized CdSe NPs exhibited strong specific affinity for mercury(II) through their surface functional groups. Based on the significant quenching of fluorescence emission of functionalized CdSe NPs with a long-wavelength 630nm, a simple, rapid and specific detection for Hg(II) was proposed. Under optimum conditions, the response of linearly proportional to the concentration of Hg(II) is between 0mol/L and 1.25x10(-6)mol/L, and the limit of detection is 4.50x10(-9)mol/L. The relative standard deviation (R.S.D.) of six replicate measurements is 2.0% for 2.0x10(-7)mol/L of Hg(II). In terms of fluorescence quenching at 630nm of CdSe NPs, no obvious wavelength shift or no new emission band in presence of Hg(II) at pH 7.50 of phosphate buffer solution were found; furthermore, a significant reduction in absorbance at 230nm of CdSe NPs was first observed in our work. We could speculate that Hg(II) as an effective quencher (even at low concentration) for functionalized CdSe NPs emission suggests that it is capable of directly intercepting one of the charge carriers, thus disrupting the recombination process.

Synthesis of ligand-selective ZnS nanocrystals exhibiting ligand-tunable fluorescence

High-quality ZnS nanocrystals (NCs) of nearly identical size are synthesized using isomeric ligands, o-, m-, p-phenylenediamines (PDAs) that bind to the NC cores. The fluorescence emission from the NC is tunable according to the structure of the isomer. The measured fluorescence quantum yields (QYs) are 2-3 times higher for NCs that are passivated with isomeric PDA ligands than the fluorescence QY of NCs prepared at the absence of PDAs. The NC morphologies were studied by low-angle and wide-angle X-ray diffraction (XRD), and by transmission electron microscopy (TEM). The average correlating sizes were found to be 3.0+/-0.3, 3.7+/-0.30, and 3.0+/-0.5 nm for the NCs that were passivated with o-PDA, m-PDA, and p-PDA, respectively. The Fourier-transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) studies were carried out to investigate the shell structure and the interaction between the core and the shell. The adsorbed ligands were quantitatively analyzed by TGA. The structure, morphology, and optical properties of these PDA passivated NCs were compared with the NCs prepared in the absence of PDA.

Synthesis of glutathione-capped CdS quantum dots and preliminary studies on protein detection and cell fluorescence image

A series of glutathione (GSH)-capped aqueous CdS quantum dots (QDs) with strong photoluminescence (PL) were prepared by changing the reaction temperatures and times on the basis of optimization of the mole ratio of S to Cd. The reaction time was shortened to about 1/10 compared with that reported previously by increasing the reaction temperature. The absorption and fluorescence spectra indicated good optical properties with PL full width of half-maximum (FWHM) of about 100 nm. The excitation spectrum was broad and continuous in the range 200-480 nm. The PL quantum efficiency (QE) of the prepared QDs was about 36% compared with rhodamine 6G (95%). The shape and size of the CdS QDs were characterized using high-resolution transmission electron microscopy (HRTEM). The prepared QDs were conjugated with bovine serum albumin (BSA) and onion inner pellicle cells and used as fluorescence probes for the first time. The results demonstrated that the fluorescence of CdS can be enhanced by BSA and the enhanced fluorescence intensity is proportional to the concentration of BSA in the range 1.0-10 mg/L. The aggregation of CdS in onion inner pellicle cells and its fluorescence images indicated that the QDs can aggregate around cells soaked for 8 h in CdS solution but enter the interior of cells and become aggregated to the nucleus when they are soaked in CdS solution for longer, e.g. 98 h.

A novel fluorescent array for mercury (II) ion in aqueous solution with functionalized cadmium selenide nanoclusters

Mono-disperse CdSe nanoclusters have been prepared facilely and functionalized with l-cysteine through two steps by using safe and low cost substances. They are water-soluble and biocompatible. Especially these functionalized quantum dots can be stably soluble in water more than for 30 days, and the intensity of fluorescence and absorbance was decreased less than 15% of fresh prepared CdSe colloids. These functionalized CdSe QDs exhibited strong specific affinity for mercury (II) through QDs interface functional groups. Based on the quenching of fluorescence signals of functionalized CdSe QDs at 530 nm and no obvious wavelength shift or no new emission band in present of Hg (II) at pH 7.75 of phosphate buffer solution, a simple, rapid and specific array for Hg (II) was proposed. In comparison with conventional organic fluorophores, these nanoparticles are brighter, more stable against photobleaching, and do not suffer from blinking. Under optimum conditions, the response of linearly proportional to the concentration of Hg (II) between 0 and 2.0 x10(-6) mol L(-1), and the limit of detection is 6.0 x 10(-9) mol L(-1). The relative standard deviation of six replicate measurements is 1.8% for 1.0 x 10(-7) mol L(-1) Hg (II). The mechanism of reaction is also discussed. The proposed method was successfully applied for Hg (II) detection in four real samples with a satisfactory result that was obtained by cold vapor atomic fluorescence spectrometry (CV-AFS).

Water-soluble quantum dots for biomedical applications

Semiconductor nanocrystals are 1-10nm inorganic particles with unique size-dependent optical and electrical properties due to quantum confinement (so they are also called quantum dots). Quantum dots are new types of fluorescent materials for biological labeling with high quantum efficiency, long-term photostability, narrow emission, and continuous absorption spectra. Here, we discuss the recent development in making water-soluble quantum dots and related cytotoxicity for biomedical applications.