Fluorescence Emission Of Quantum Dots Research Articles

Quantum Dots‐Functionalized Encryption Camera for Text Image Security Protection

With the wide utilization of mobile devices with a camera as online communication tools, there is a great need to develop image encryption technology for protecting confidential and sensitive information. Herein, quantum dots‐functionalized encryption (QDE) camera is proposed by integrating the fluorescence emission of quantum dots (QDs) with charge coupled device or complementary metal oxide semiconductor detector arrays during the imaging process. The variation of the photoluminescence emission from QDs controlled by UV365 nm illumination provides a convenient way to scramble the spatial distribution of RGB values in the captured image, which expands the information entropy of the captured image to realize in situ image encryption. The encrypted text images can be decrypted by a convolutional neural network‐based algorithm, resulting in high‐quality decrypted images with peak signal‐to‐noise ratio up to 45 dB. Compared with the previous reported image encryption techniques of chaotic cryptosystem, fluorescent material‐based encryption, and optical encryption, the proposed QDE camera shows advantages of high execution speed and easy miniaturization. It provides a promising in situ image encryption technique to guarantee information security in digitization process.

Highly luminescent water-dispersed silicon quantum dots for fluorometric determination of oxytetracycline in milk samples.

A fluorescent probe based on silicon quantum dots (SiQDs) was developed for the selective and sensitive detection of oxytetracycline (OTC) via the inner filter effect (IFE). The water-soluble fluorescent SiQD was synthesized based on the reaction of 3-Aminopropyltriethoxysilane (APTES) and sodium citrate as precursors by the one-pot hydrothermal process. The strong fluorescence emission of quantum dots (QDs) was obtained at 440 nm when excited at 350 nm and OTC had a broad absorption band between 200 and 400 nm. The excitation spectrum of SiQDs was completely overlapped with the absorption spectrum of OTC. The light at an excitation wavelength of QDs absorbed by OTC caused a decrease in fluorescence intensity with an increase in the concentration of OTC. Under optimal conditions, the linear concentration range was 0.92–9.2 µg mL1 with a detection limit (LOD; S/N = 3) of 0.19 µg mL -1 . The proposed method was applied to the determination of OTC in milk samples and satisfactory recoveries (98.8–100.5%) with low RSD % values (0.93–2.31%) were achieved. This simple, selective, sensitive, rapid, and cheap method can be used as a promising tool for OTC analysis in food safety.

S-doped carbon dots capped ZnCdTe quantum dots for ratiometric fluorescence sensing of guanine

Quantum dots (QDs)-based ratiometric fluorescence probe have drawn extensive attention in recent years. However, intrinsic dual-emitting QDs were rarely reported, and most of them were based on the metal doped-QDs. Herein, an intrinsic dual-emitting ZnCdTe QDs were synthesized by using fluorescence S doped-carbon dots (CDs) as capping ligands for the first time in this work, two emission peaks (derived from CDs and QDs respectively) were observed in CDs-ZnCdTe QDs and the probe showed excellent stability and optical properties. Moreover, we found that the fluorescence emission of QDs could be quenched by guanine via excited state electron transfer or the aggregation of QDs, but the emission of CDs remained stable, thus we successfully developed a ratiometric probe for the determination of guanine. Under optimized conditions, the detection limit of guanine was 0.076 μmol⋅L−1 (3σ/k), with a linear range from 0.25 to 40.0 μmol⋅L−1. The smart ratiometric fluorescence probe was demonstrated for the detection of guanine in DNA samples with satisfactory recoveries ranging from 96.95 to 102.50%, indicating it was a promising biosensor for highly selectively and sensitively determination of guanine.

Sensitive fluorescence and chemiluminescence procedures for methamphetamine detection based on CdS quantum dots

Two novel, simple and sensitive fluorescence (FL) and chemiluminescence (CL) procedures were established for methamphetamine (MA) determination. l-Cysteine capped CdS quantum dots (QDs) were synthesized by a simple one-step hydrothermal procedure and characterized by their specific absorption and emission spectra. The structure and morphology of QDs were investigated using X-ray diffraction (XRD) pattern, transmission electron microscopy (TEM) and scanning electron microscope (SEM). It is found that the prepared CdS QDs have a remarkable promoting effect on rhodamine B (RhoB)-cetyltrimethylammonium bromide (CTAB)-KMnO4 CL reaction. Based on this influence, a new efficient CL system was introduced. On the other hand, the FL and CL emission intensities of QDs undergo a remarkable alteration in the presence of low quantities of MA. The optimization of the effective parameters was performed and the high sensitivity was obtained in 0.013molL−1 Tris buffer at pH=6.5 with 0.2mmolL−1 CdS QDs. In this condition, MA had a notable linear quenching effect on the FL emission of QDs which formed the basis of simple FL probe for sensitive determination of MA in the range of 6.7–400ngmL−1. Also, MA can remarkably enhance the intensity of developed CL system. Under the optimized conditions (0.15molL−1 H2SO4, 0.15mmolL−1 RhoB, 0.13mmolL−1 QDs, 0.3mmolL−1 CTAB and 0.4mmolL−1 KMnO4), the improved CL intensity was proportional to the concentration of MA in the range of 0.25–125ngmL−1 with limit of detection (3s) of 0.086ngmL−1, which is over 20 times better than the introduced FL method. The developed FL and CL methods were exploited for accurate determination of MA in human urine samples.

Spectroscopic investigation of alloyed quantum dot-based FRET to cresyl violet dye.

Quantum dots (QDs), bright luminescent semiconductor nanoparticles, have found numerous applications ranging from optoelectronics to bioimaging. Here, we present a systematic investigation of fluorescence resonance energy transfer (FRET) from hydrophilic ternary alloyed quantum dots (CdSeS/ZnS) to cresyl violet dye with a view to explore the effect of composition of QD donors on FRET efficiency. Fluorescence emission of QD is controlled by varying the composition of QD without altering the particle size. The results show that quantum yield of the QDs increases with increase in the emission wavelength. The FRET parameters such as spectral overlap J(λ), Förster distance R0, intermolecular distance (r), rate of energy transfer k(T)(r), and transfer efficiency (E) are determined by employing both steady-state and time-resolved fluorescence spectroscopy. Additionally, dynamic quenching is noticed to occur in the present FRET system. Stern-Volmer (K(D)) and bimolecular quenching constants (k(q)) are determined from the Stern-Volmer plot. It is observed that the transfer efficiency follows a linear dependence on the spectral overlap and the quantum yield of the donor as predicted by the Förster theory upon changing the composition of the QD.

Conjugation of nano and quantum materials with bovine serum albumin (BSA) to study their biological potential

Conjugates of gold nanoparticles (AuNPs) and semiconductor quantum dots (CdS/T) have been synthesized with bovine serum albumin (BSA) using wet chemistry. The optical properties of nano and quantum materials and their BSA conjugate have been studied using UV–Visible and Fluorescence spectroscopy. UV–Visible spectrum of pure BSA showed an absorption maximum at 278nm, which showed blue shift after its conjugation with nano and quantum materials. Increased concentration of AuNPs during conjugation resulted in broadening of BSA peak (278nm), which can be related to the formation of ground state complex formation, caused by the partial adsorption of BSA on the surface of NPs. However, increased concentrations of BSA resulted in decrease in SPR intensity of gold nanoparticles (528nm) and absorbance peak of BSA started diminishing. AuNPs acted as quencher for BSA fluorescence intensity, when excited at 280nm. The binding constant (K) and the number of binding sites (n) between AuNPs and BSA have been found to be 1.97×102 LM−1 and 0.6 respectively. With quantum dots, conjugation resulted in enhancement of fluorescence emission of quantum dots when excited at 300nm, which might be due to the stabilizing effect of BSA on QDs or due to energy transfer from tryptophan moieties of albumin to quantum dots.

Nanoconjugates of CdTe@ZnS quantum dots with cobalt tetraamino-phthalocyanine: Characterization and implications for the fluorescence recognition of superoxide anion

The covalent linking of thiol-capped CdTe@ZnS QDs with cobalt tetraamino-phthalocyanine results in the fluorescence quenching of the former, the resulting conjugates can detect superoxide anion (O 2 − ) with detection limits of about 2 nM. ► Cobalt tetraamino-phthalocyanine was coordinated to CdTe@ZnS quantum dots. ► The fluorescence emission of quantum dots was quenched by the phthalocyanine. ► The conjugates could detect superoxide anion. The covalent linking of thiol-capped CdTe@ZnS QDs with cobalt tetraamino-phthalocyanine (CoTAPc) has been successfully carried out. Several techniques such as time-resolved fluorescence measurements, thermal gravimetric analysis, transmission electron microscopy and spectrophotometric techniques were employed to characterize the nanoconjugates. Covalent binding of the QDs with CoTAPc resulted in the fluorescence quenching of the former. In the presence of varying concentrations of superoxide anion (O 2 − ), the fluorescence of the QDs in the conjugate was gradually enhanced and the detection limits obtained were 2.1 and 2.4 nM for the smaller and larger QDs, respectively. Based on the excellent selectivity displayed by the nanoconjugates towards O 2 − over other biologically active species, a potential nanosensor was developed.

A Single Molecule Investigation of the Photostability of Quantum Dots

Quantum dots (QDs) are very attractive probes for multi-color fluorescence imaging in biological applications because of their immense brightness and reported extended photostability. We report here however that single QDs, suitable for biological applications, that are subject to continuous blue excitation from a conventional 100 W mercury arc lamp will undergo a continuous blue-switching of the emission wavelength eventually reaching a permanent dark, photobleached state. We further show that β-mercaptoethanol has a dual stabilizing effect on the fluorescence emission of QDs: 1) by increasing the frequency of time that a QD is in its fluorescent state, and 2) by decreasing the photobleaching rate. The observed QD color spectral switching is especially detrimental for multi-color single molecule applications, as we regularly observe spectral blue-shifts of 50 nm, or more even after only ten seconds of illumination. However, of significant importance for biological applications, we find that even small, biologically compatible, concentrations (25 µM) of β-mercaptoethanol has a significant stabilizing effect on the emission color of QDs, but that greater amounts are required to completely abolish the spectral blue shifting or to minimize the emission intermittency of QDs.

Modification of Blinking Statistics in Solid State Quantum Dot/Conjugated Organic Polymer Composite Nanostructures

ABSTRACTFluorescence intermittency, or “blinking” in quantum dot systems has been the subject of great interest since the first observation of this phenomenon nearly 10 years ago. The stability of quantum dot fluorescence emission is especially important in the context of photovoltaic, optoelectronic, and biological applications, where device performance, or the ability to track labeled particles, is affected adversely by fluorescence intermittency. Single-molecule spectroscopy combined with atomic force microscopy measurements reveal that CdSe quantum dots functionalized with oligo(phenylene vinylene), OPV, ligands exhibit modified optical properties such as suppression of blinking when compared to conventional TOPO covered or ZnS-capped CdSe quantum dots. The blinking suppression is shown to be highly sensitive to the degree of ligand coverage on the quantum dot surface and this effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. This direct surface derivatization of quantum dots with organic ligands also enables a “tunable” quantum dot surface that allows dispersion of quantum dots in a variety of polymer supported thin films without phase segregation. This facilitates straightforward inclusion of these new hybrid materials into solid state formats and suggests exciting new applications of composite quantum dot/organic systems in optoelectronic systems.