Red Emissive Quantum Dots Research Articles

Bright Red Luminescence from Ag–In–Ga–S-Based Quantum Dots with the Introduction of Copper

Abstract This study presents cadmium-free, red-emission quantum dots (QDs) synthesized by incorporating Cu into silver indium gallium sulfide/gallium sulfide (Ag–In–Ga–S/Ga–S) core/shell QDs. By using a previous technique, in which the original Ag–In–Ga–S/Ga–S core/shell QDs exhibiting band-edge photoluminescence (PL) were improved to achieve a narrower emission and facile synthesis, we injected a mixture of Cu and Ag sources into a heated solution containing In, Ga, and S sources. This resulted in the formation of Ag–Cu–In–Ga–S quinary QDs without any precipitation. After being coated with a Ga–S shell, these QDs exhibit a red PL with a spectral full-width at half maximum of 55–60 nm. Although the PL wavelength was responsive to changes in In/Ga ratios, it was unaffected by variations in Cu/Ag ratios due to the transition between conduction band electrons and holes localized at Cu cites. Notably, the electroluminescence device exhibited high-purity red light that satisfies the recommendation ITU-R BT.2020 standard.

A smartphone-based fluorospectrophotometer and ratiometric fluorescence nanoprobe for on-site quantitation of pesticide residue

Cost-effective and user-friendly quantitation at points-of-need plays an important role in food safety inspection, environmental monitoring, and biomedical analysis. This study reports a stand-alone smartphone-based fluorospectrophotometer (the SBS) installed with a custom-designed application (the SBS-App) for on-site quantitation of pesticide using a ratiometric sensing scheme. The SBS can collect fluorescence emission spectra in the wavelength range of 380-760nm within 5s. A ratiometric fluorescence probe is facilely prepared by directly mixing the blue-emissive carbon nanodots (the Fe3+-specific fluorometric indicator) and red-emissive quantum dots (the internal standard) at a ratio of 11.6 (w/w). Based on the acetylcholinesterase/choline oxidase dual enzyme-mediated cascade catalytic reactions of Fe2+/Fe3+ transformation, a ratiometric fluorescence sensing scheme is developed. The practicability of the SBS is validated by on-site quantitation of chlorpyrifos in apple and cabbage with a comparable accuracy to the GC-MS method, offering a scalable solution to establish a cost-effective surveillance system for pesticide pollution.

Point-of-need quantitation of 2,4-dichlorophenoxyacetic acid using a ratiometric fluorescent nanoprobe and a smartphone-based sensing system

This study reports a new ratiometric fluorescence probe (referred to as rQD@PS@bCDs) and a smartphone-based sensing system for on-site quantitation of Fe3+, ascorbic acid (AA), alkaline phosphatase (ALP) and 2,4-dichlorophenoxyacetic acid (2,4-D). rQD@PS@bCDs with well-resolved dual emissions is facilely synthesized by covalent conjugation of red-emissive quantum dots (rQDs), the internal standard, with blue-emissive carbon dots (bCDs), the Fe3+-specific fluorescent indicator. 2,4-D can specifically inhibit the enzymatic activity of ALP, leading to suppress the production of AA which can reduce Fe3+ to Fe2+ and thereafter trigger the fluorescence response of rQD@PS@bCDs. Taking advantages of these highly specific cascade catalytic reactions, ratiometric fluorescence schemes are established for sensing Fe3+, AA, ALP and 2,4-D both in aqueous solution and on paper-based microarray. The smartphone-based fluorescence detector integrated with the rQD@PS@bCDs-based microarray demonstrated good sensing performance with a wide linear range and low detection limit, and is successfully applied to quantitate 2,4-D in cabbage and tap water samples. The reported method which enables point-of-need quantitation in a sample-in-result-out manner and highlights its features of cost-effectiveness and ease-of-use, is ideally for food safety inspection, environment surveillance, health monitoring at point-of-need, especially in low resource settings.

Determination of tuberculosis-related volatile organic biomarker methyl nicotinate in vapor using fluorescent assay based on quantum dots and cobalt-containing porphyrin nanosheets.

Methyl nicotinate (MN) is a representative and typical volatile organic marker of Mycobacterium tuberculosis, and the specific detection of MN in human breath facilitates non-invasive, rapid, and accurate epidemic screening of tuberculosis infection. Herein, we constructed a fluorescent assay consisted of CdTe quantum dots (QD) and cobalt-metalized tetrakis(4-carboxyphenyl) porphyrin (CoTCPP) nanosheets to determine methyl nicotinate (MN) in vapor samples. Red-emission QD (λex=370 nm, λem=658 nm) acts as signal switches whose fluorescence signals can be effectively quenched by CoTCPP nanosheets but restored in the presence of MN. The strategy relied on the distinct binding affinity of cobalt ion and MN. MN restored the fluorescence of QD quenched by CoTCPP in a concentration-dependent manner, which exhibited a well-linear relationship in the range 1-100 μM, anda limit of detection of0.59 μM. The proposed platform showed sensitivity and selectivity to detect MN in vapor samples with satisfactory RSD below 3.33%. The method ischeap, simple, and relatively rapid (detected within 4 min), which suggestsa potential in tuberculosis diagnosis in resource- and professional-lacked areas.

A cascade-triggered ratiometric fluorescent sensor based on nanocomposite for lactate determination

For this study, a cascade-triggered ratiometric fluorescent sensor based on nanocomposites was designed to detect lactate. This sensor was established by breaking the inner-filter effect (IFE) between blue emission carbon dots (bCDs) and silver nanoparticles (AgNPs) and activating the dynamic quenching process of red emission quantum dots (rQDs) and Ag+. In this sensor (bCDs/AgNPs-rQDs), the fluorescence of bCDs was quenched by the formation of CDs/AgNPs, and recovered by adding lactate. Subsequently, the quenching of rQDs was triggered by Ag+, which originated from the disintegration of AgNPs. This cascade-triggered ratiometric fluorescent sensor for lactate detection was established with the LOD (limit of detection) of 0.12 μM. The developed probe was applied to lactate detection in human serum with satisfactory results, indicating that the probe has enormous potential in clinical practice.

Liposomal Spherical Nucleic Acid Scaffolded Site-Selective Hybridization of Nanoparticles for Visual Detection of MicroRNAs.

In this study, the advanced liposomal spherical nucleic acid (L-SNA) is exploited for the first time to establish a spherical, three-dimensional biosensing platform by hybridizing with a set of nanoparticles. By hydrophilic and hydrophobic interactions as well as programmable base-pairing, red-emission quantum dots (QDs), green-emission QDs, and gold nanoparticles (AuNPs) are encapsulated into the internal aqueous core, the intermediate lipid bilayer, and the outer SNA shell, respectively, producing an L-SNA-nanoparticle hybrid. As a result of the site-selective encapsulation, the hybrid constitutes a liposomal fluorescent "core-resonance energy transfer" system surrounded by a SNA shell, as is imaged at the single-particle resolution by confocal microscopy. With the outer SNA shell as three-dimensional substrate for duplex-specific nuclease target recycling reaction, the hybrid is capable of amplified detection of microRNAs, featuring one target to many AuNP-manipulated, dual-emission QD-based ratiometric fluorescence. More importantly, the ratiometric fluorescence facilitates the hybrid to visualize microRNAs with remarkably high resolution, which is exemplified by traffic light-type transition in fluorescence color for diagnosing circulating microRNAs in clinical serum samples. Substantially, the controllable hybridization with functional nanoparticles opens an avenue for the exciting biomedical applications of liposomal spherical nucleic acids.

Profuse color-evolution-based fluorescent test paper sensor for rapid and visual monitoring of endogenous Cu2+ in human urine

The fluorescent paper for colorimetric detection of metal ions has been widely fabricated using various sensing probes, but it still remains an elusive task to design a test paper with multicolor variation with target dosages for accurate determination. Herein, we report a profuse color-evolution-based fluorescent test paper sensor for rapid and visual monitoring of Cu2+ in human urine by printing tricolor probe onto filter paper. The tricolor probe consists of blue-emission carbon dots (bCDs), green-emission quantum dots (gQDs) and red-emission quantum dots (rQDs), which is based on the principle that the fluorescence of gQDs and rQDs are simultaneously quenched by Cu2+, whereas the bCDs as the photostable internal standard is insensitive to Cu2+. Upon the addition of different amounts of Cu2+, the ratiometric fluorescence intensity of the tricolor probe continuously varied, leading to color changes from shallow pink to blue with a detection limit of 1.3nM. When the tricolor probe solution was printed onto a sheet of filter paper, as-obtained test paper displayed a more profuse color evolution from shallow pink to light salmon to dark orange to olive drab to dark olive green to slate blue to royal blue and to final dark blue with the increase of Cu2+ concentration compared with dual-color probe-based test paper, and dosage scale as low as 6.0nM was clearly discriminated. The sensing test paper is simple, rapid and inexpensive, and serves as a visual platform for ultrasensitive monitoring of endogenous Cu2+ in human urine.

Sensitive and selective ratiometric nanosensors for visual detection of Cu2+ based on ions promoted oxidation reaction

Copper is a highly toxic environmental pollutant in the environmental, biological and chemical fields. Therefore, sensitive, selective and visual detection of Cu2+ is very important for human health and practical applications. Herein, a novel hybrid ratiometric fluorescent nanosensor was developed for rapid and on-site visualization of Cu2+ on the basis of integrating benzothiazole fluorophore (MDBT) and red-emissive quantum dots (QDs) embedded in silica nanospheres. Such hybrid ratiometric fluorescent nanosensor exhibits dual emissions at 420 and 640nm under a single excitation wavelength. Due to the ions promoted oxidation reaction of Cu2+ towards MDBT, the fluorescence of MDBT can be selectively enhanced. Although the embedded QDs are insensitive to the analyte, variations of the dual emission intensity ratios display continuous colour changes from red to blue. The ratiometric fluorescent approach shows high sensitivity and selectivity towards Cu2+ against other interfering metal ions. The detection limit of Cu2+ for the hybrid ratiometric fluorescent nanosensor is determined to be 41.71nM, which is much lower than the allowable level of Cu2+ (∼20μM) in drinking water set by U.S. Environmental Protection Agency. Furthermore, this kind of novel nanosensor can also be applied for Cu2+ detection in actual water samples and exhibits excellent detection ability. This hybrid ratiometric fluorescent nanosensor is simple, fully self-contained and thus potentially attractive for visual identification without the need of elaborate equipments.

Visual and fluorescent detection of mercury ions by using a dually emissive ratiometric nanohybrid containing carbon dots and CdTe quantum dots

The authors describe a carbon dot (CD) based dual-emission ratiometric optical probe for the on-site visual and fluorometric determination of mercury(II) ions. The nanoparticle (NP) probe was obtained by covalently linking the blue emissive carbon dots to the surface of silica nanoparticles containing red-emissive quantum dots (QDs). The red emitting QDs in the silica matrix are inert to Hg(II) and provide a reliable and constant reference signal. They also reduce their toxicity and improve the optical and chemical stabilities, while the blue emission CDs are very sensitive to Hg(II). With increasing concentration of Hg(II), a solution containing the NP probe undergoes a continuous color change from light purple to red. This can be seen with bare eyes or detected instrumentally by measurement of fluorescence intensity under excitation/emission wavelengths of 350/453 and 658 nm. The probe exhibits high sensitivity to Hg(II), with a detection limit of 0.47 nM (at an S/N ratio of 3). This is much lower than the allowable level of mercury (10 nM, ~10 ppb) in drinking water set by the U.S. Environmental Protection Agency. For practical use, the probe was used to quantify Hg(II) in (spiked) tap water where it gave recoveries between 95 and 106% and relative standard deviations between 1.9 and 3.2%. The probe can also be applied in filter paper-based assays, and this paves the way to point-of-care pollution control. This ratiometric probe is nontoxic and easily operated, and therefore shows potential applications for rapid and low-cost visual identification of Hg(II).

Visual and fluorescent detection of tyrosinase activity by using a dual-emission ratiometric fluorescence probe.

In this work, we designed a dual-emission ratiometric fluorescence probe by hybridizing two differently colored quantum dots (QDs), which possess a built-in correction that eliminates the environmental effects and increases sensor accuracy. Red emissive QDs were embedded in the silica nanoparticle as reference while the green emissive QDs were covalently linked to the silica nanoparticle surface to form ratiometric fluorescence probes (RF-QDs). Dopamine (DA) was then conjugated to the surface of RF-QDs via covalent bonding. The ratiometric fluorescence probe functionalized with dopamine (DA) was highly reactive toward tyrosinase (TYR), which can catalyze the oxidization of DA to dopamine quinine and therefore quenched the fluorescence of the green QDs on the surface of ratiometric fluorescence probe. With the addition of different amounts of TYR, the ratiometric fluorescence intensity of the probe continually varied, leading to color changes from yellow-green to red. So the ratiometric fluorescence probe could be utilized for sensitive and selective detection of TYR activity. There was a good linear relationship between the ratiometric fluorescence intensity and TYR concentration in the range of 0.05-5.0 μg mL(-1), with the detection limit of 0.02 μg mL(-1). Significantly, the ratiometric fluorescence probe has been used to fabricate paper-based test strips for visual detection of TYR activity, which validates the potential on-site application.

A ratiometric fluorescence sensor for highly selective and sensitive detection of mercuric ion

Mercury is widely used in industry and easily leads to environmental pollution if discharged without proper waste control. On-site visual detection of mercuric ion is thus in demand and remains a great challenge. We herein demonstrate a detection method for rapid and on-site visualization of mercuric ion on the basis of integrating green-emissive imidazol fluorophore (PIPT) and red-emissive quantum dots (QDs) embedded in silica nanospheres. Such a nanohybrid fluorescent probe exhibits dual emissions at 500nm and 657nm under a single excitation wavelength. Due to the high chelating ability of PIPT toward mercuric ion, the fluorescence of PIPT could be selectively quenched while the fluorescence of the QDs is almost constant, leading to a distinct fluorescence color change from green to red, which can be applied for the rapid visualization of mercuric ion. This ratiometric fluorescent approach shows high sensitivity, high selectivity and anti-interference toward mercury against other metal ions. The detection limit of this method is determined to be 6.5nM. The probe has also been successfully demonstrated for the determination of mercuric ion in real water samples.

High color rendering index white LED based on nano-YAG:Ce3+ phosphor hybrid with CdSe/CdS/ZnS core/shell/shell quantum dots

To improve the poor color rendering index (CRI) of YAG:Ce-based white light-emitting diode (LED) due to the lack of red spectral component, core/shell/shell CdSe/CdS/ZnS quantum dots (QDs) were synthesized and blended into nano-YAG:Ce3+ phosphors. Prominent spectral evolution has been achieved by increasing the content of QDs. A white LED combining a blue LED with the blends of nano-YAG phosphors and orange- and red-emission QDs with a weight ratio of 1:1:1 was obtained. This kind of white LED showed excellent white light with luminescent efficiency, color coordinates, CRI and correlated color temperature (CCT) of 82.5 lm/W, (0.3264, 0.3255), 91 and 4580 K, respectively.

Luminescent CdSe Quantum Dot Doped Stabilized Micelles

A general method was developed to prepare siloxane surfactant C16H33−N+(Me)2−CH2CH2CH2−Si(OMe)3 Cl- micelles doped with highly luminescent lipophilic semiconductor CdSe quantum dots (QDs). Encapsulated green emission CdSe QDs with an emission maximum at 525 nm and red emission QDs with an emission maximum at 650 nm show absorption and emission spectra similar to free CdSe QDs capped by trioctylphosphine oxide (TOPO). Transmission electron microscopy images reveal that the luminescent micelles range from 50 nm to 130 nm in diameter. Each micelle contains over 100 QDs, which significantly increases the emission signal of the composite nanostructure compared to individual QDs. This signal increase enables quantitative luminescence measurements of the QDs using conventional fluorescence microscopes and nonintensified CCD imaging systems, thus making the QD-doped micelles valuable tools in cellular imaging applications. Hydrolysis of the organosilane headgroup of the surfactant forms a silica layer on the surf...