Fluorescence Resonance Energy Transfer Phenomenon Research Articles

Detection of SARS-CoV-2 S protein based on FRET between carbon quantum dots and gold nanoparticles

The COVID-19 pandemic caused by SARS-CoV-2 virus brings nasty crisis for public health in the world. Until now, the virus has caused multiple infections in many people. Detecting antigen to SARS-CoV-2 is a powerful method for the diagnosis of COVID-19 and is helpful for controlling and stopping the pandemic. Herein, a rapid and quantitative detection method of SARS-CoV-2 spike(S) protein was built based on the fluorescence resonance energy transfer (FRET) phenomenon without complicated steps. In the process of detecting, the carbon quantum dots (CQDs) and gold nanoparticles (AuNPs) act as donor and acceptor. By modifying the SARS-CoV-2 antibodies on the surface of CQDs and AuNPs, we achieved S protein specific detection using the distance-based FRET phenomenon. Through the electric charge regulation, the limit of detection (LOD) is 0.05 ng/mL, the linear range is 0.1–100 ng/mL, and the detection process only takes 12 min. The proposed method exhibits several advantages such as be available for variants (B.1.1.529 and B.1.617.2) and be suitable for human serum, which is of significance for detecting viral in time and prevention the viral transmission.

A Dual-Mode Method Based on Aptamer Recognition and Time-Resolved Fluorescence Resonance Energy Transfer for Histamine Detection in Fish.

Histamine produced via the secretion of histidine decarboxylase by the bacteria in fish muscles is a toxic biogenic amine and of significant concern in food hygiene, since a high intake can cause poisoning in humans. This study proposed a fluorometric and colorimetric dual-mode specific method for the detection of histamine in fish, based on the fluorescence labeling of a histamine specific aptamer via the quenching and optical properties of gold nanoparticles (AuNPs). Due to the fluorescence resonance energy transfer phenomenon caused by the proximity of AuNPs and NaYF4:Ce/Tb, resulting in the quenching of the fluorescence signal in the detection system, the presence of histamine will compete with AuNPs to capture the aptamer and release it from the AuNP surface, inducing fluorescence recovery. Meanwhile, the combined detection of the two modes showed good linearity with histamine concentration, the linear detection range of the dual-mode synthesis was 0.2-1.0 μmol/L, with a detection limit of 4.57 nmol/L. Thus, this method has good selectivity and was successfully applied to the detection of histamine in fish foodstuffs with the recoveries of 83.39~102.027% and 82.19~105.94% for Trichiurus haumela and Thamnaconus septentrionalis, respectively. In addition, this method was shown to be simple, rapid, and easy to conduct. Through the mutual verification and combined use of the two modes, a highly sensitive, rapid, and accurate dual-mode detection method for the analysis of histamine content in food was established, thereby providing a reference for the monitoring of food freshness.

Coupling of hydrophobic graphene quantum dots with photochromic molecule for fabrication of transparent photo-responsive polymeric films manifesting FRET functioning

In this study, a novel sensor on the basis of polymeric film comprising hydrophobic graphene quantum dots (GQDs-Amine) as fluorescent donor and spiropyran (SP) as photochromic acceptor was developed. The polymeric fluorescence sensor was synthesized through a four-step approach, beginning with the synthesize of photochromic component (SP) having hydroxyl functional group. Then, the amine-functionalized GQDs denoted as GQDs-Amine were synthesized through direct carbonization of citric acid in the presence of benzyl amine. GQDs-Amine was then decorated with SP to achieve GQDs-Amine-SP. In the final step, by using either polylactic acid (PLA) or polymethyl meta acrylate (PMMA) as polymeric precursors and via a simple solvent casting methodology, the related polymeric films comprising photoactive elements were prepared. All synthesized compounds were characterized using various methods such as nuclearmagnetic resonance (NMR) spectroscopy, elemental analysis (CHN), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, and field-emission scanning electron microscopy (FE-SEM). According to the related experiments, 0.582 mmol SP was successfully immobilized per gram of GQDs-Amine-SP. Also, after grafting of SP onto the surface of GQDs-Amine, the contact angle remarkably increased from 19° to 64° due to the difference hydrophobic nature between SP and its merocyanine (MC) form. The fluorescence resonance energy transfer (FRET) phenomenon occurred via exposure of GQDs-Amine-SP to alternating cycles of UV–vis irradiations. To confirm the FRET phenomenon and existing a good matching between the UV–vis absorption region of SP and the fluorescence emission spectra of GQDs-Amine, the photoluminescence activity of material was also performed in different mediums as well as in solid state. These solutions were exposed to UV light(365 nm) at various time intervals and their fluorescence properties were investigated under excitation at 400 nm. With increasing the time of UV light exposure up to 220 s, the fluorescence intensity increased at 620 nm, and inversely, the fluorescence intensity decreased at 471 nm. A similar pattern but with higher intensity were also observed for the polymeric films fabricated using phase inversion method. According to the UV–vis and fluorometric analyses, the GQDs-Amine-SP and the corresponding films showed excellent photoreversibility, photostability, and prominentfatigue resistance.

A highly sensitive strategy for glypican-3 detection based on aptamer/gold carbon dots/magnetic graphene oxide nanosheets as fluorescent biosensor

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in China. Glypican-3 (GPC3) is a specific antigen related to HCC, which is widely used in clinical detection as a reliable marker of HCC. In this paper, a highly sensitive homogeneous apatasensor was designed for GPC3 detection based on fluorescence resonance energy transfer (FRET) where the GPC3 aptamer labelled gold carbon dots (AuCDs-GPC3Apt) are used as a donor and magnetic graphene oxide (Fe3O4/GO) nanosheets are used as an acceptor. A one-step hydrothermal method was used to synthesize AuCDs to provide sufficient fluorescence. The FRET phenomenon exists between AuCDs-GPC3Apt and Fe3O4/GO, which weakens the fluorescence intensity of the whole system. When the target GPC3 is added to the FRET system, the fluorescent AuCDs-GPC3Apt binds to the GPC3 and forms a folded structure, which leads to AuCDs-GPC3Apt separation from Fe3O4/GO nanosheets. The Fe3O4/GO is then magnetically separated so that the fluorescence of free labelled AuCDs-GPC3Apt is restored. Under the optimum conditions, the fluorescence recovery rate is linearly correlated with the concentration of GPC3 (5-100ng·mL-1) and the detection limit is 3.01ng·mL-1 (S/N = 3). This strategy shows recoveries from 98.76 to 101.29% in real human serum samples and provides an immediate and effective detection method for the quantification of GPC3 with great potential applications for early diagnosis of HCC. A sensitive homogeneous FRET-based apatasensor was designed for GPC3 detection where the AuCDs-GPC3Apt is a donor and Fe3O4/GO nanosheets are an acceptor. The GPC3 fluorescent aptasensor combines wider output range with low cost, high specificity, and good anti-interference.

Rapid and Highly Sensitive Detection of Target DNA Related to COVID-19 Virus With a Fluorescent Bio-conjugated Probe via a FRET Mechanism

A novel cyanine 3 (Cy3)-based bio-conjugated sensor has been developed to detect target DNA or extracted RNA from COVID -19 samples using the fluorescence resonance energy transfer (FRET) experiment. A special sequence of the COVID -19 genome was selected as a complementary DNA (target DNA) part. The opposite chain of this target sequence was designed in 2 parts; one part was attached to the Cy3 organic dye (capture DNA or Cy3- DNA), and the other part was attached to the BHQ2 molecule (quencher DNA or BHQ2- DNA). The Cy3 molecule acts as a donor pair, and BHQ2 acts as an acceptor pair in the FRET experiment. The capture DNA and quencher DNA can form a sandwiched complex in the presence of target DNA. The formation of the entitled sandwiched hybrid causes the decrement of emission intensity of the Cy3 donor in bio-conjugated Cy3-DNA via energy transfer from Cy3 (as a donor) to BHQ2 (as an acceptor). Indeed, in the presence of non-complementary DNA, the pairing of DNA strands does not occur, the FRET phenomenon does not exist, and therefore fluorescence intensity of Cy3 does not decrease. Moreover, this biosensor was successfully applied to analyze real samples containing extracted RNA of COVID -19 prepared for the reverse transcriptase-polymerase chain reaction (RT-PCR) test, and the results were promising.

Monte Carlo Simulation of the Efficiency of Fluorescence Resonance Energy Transfer, FRET Phenomenon.

The article aimed to outline a statistical model based on nonlinear regressions for the efficiency of the Fluorescence Resonance Energy Transfer (FRET) phenomenon and to select a general simulation method of the FRET phenomenon, independent of the nature of the active substance used as a donor. For this purpose, several statistical models of Polynoal and nonlinear Gaussiene regressions were first tested, which would fit as well as possible the variation in time efficiency and its dependence on the concentrations of active substances. The regression models used were implemented and tested in the R language. In the second part of the study we aprooached the problem of simulating the efficiency of FRET by adapting a Monte Carlo method, using as a starting point the previously determined regressive models.

FRET-Based In-Cell Detection of Highly Selective Supramolecular Complexes of meso-Tetraarylporphyrin with Peptide/BODIPY-Modified Per-O-Methyl-β-Cyclodextrins.

Artificial supramolecular systems capable of self-assembly and that precisely function in biological media are in high demand. Herein, we demonstrate a highly specific host-guest-pair system that functions in living cells. A per-O-methyl-β-cyclodextrin derivative (R8-B-CDMe ) bearing both an octaarginine peptide chain and a BODIPY dye was synthesized as a fluorescent intracellular delivery tool. R8-B-CDMe was efficiently taken up by HeLa cells through both endocytosis and direct transmembrane pathways. R8-B-CDMe formed a 2 : 1 inclusion complex with tetrakis(4-sulfonatophenyl)porphyrin (TPPS) as a guest molecule in water, from which fluorescence resonance energy transfer (FRET) from R8-B-CDMe to TPPS was observed. The FRET phenomenon was clearly detected in living cells using confocal microscopy techniques, which revealed that the formed supramolecular R8-B-CDMe /TPPS complex was maintained within the cells. The R8-B-CDMe cytotoxicity assay revealed that the addition of TPPS counteracts the strong cytotoxicity (IC50 =16 μM) of the CD cavity due to complexation within the cells. A series of experiments demonstrated the bio-orthogonality of the supramolecular per-O-methyl-β-CD/tetraarylporphyrin host-guest pair in living cells.

Preparation of Curcubit[6]uril functionalized CuO Nanoparticles: A New Nanosensing Scheme Based on Fluorescence recovery after FRET for the Label Free Determination of Dopamine

AbstractIn this manuscript, the aim is to functionalize CuO nanoparticles with the supramolecular host molecule, in this case curcubit[6]uril to have a host guest interaction between the CuO nanoparticles and probe (guest) molecules. Acridine Orange (AO) is applied as a guest molecule. Acridine orange binds with curcubit[6]uril via its carbonyl rims. In the presence of curcubit[6]uril conjugated CuO nanoparticles, the fluorescence intensity of AO is quenched by the CuO NPs through fluorescence resonance energy transfer phenomenon. However, dopamine adsorbs on the surface of CuO nanoparticles by getting incorporated into CB[6] host molecules and kicks out AO from curcubit[6]uril pocket, thus, discouraging fluorescence resonance energy transfer phenomenon and thus enhancing fluorescence intensity of AO by a factor of 3. This fluorescence recovery has been utilized to design a new detection system for dopamine. The assay, measured at fluorescence excitation and emission wavelengths of 480 nm and 520 nm respectively, works in the 0–40 μM concentration range of dopamine with 40 nM limit of detection. This method is not interfered by ascorbic acid, uric acid, glucose, tryptophan and acetaminophen. The proposed method provides a good recovery from synthetic samples and shows good stability.

A highly sensitive aptasensor for vascular endothelial growth factor based on fluorescence resonance energy transfer from upconversion nanoparticles to MoS2 nanosheets.

A novel sensitive aptasensor for vascular endothelial growth factor-165 (VEGF165) was constructed based on fluorescence resonance energy transfer (FRET) by employing upconversion nanoparticles (UCNPs) and MoS2 nanosheets as the energy donor and acceptor, respectively. The upconversion fluorescence resonance energy transfer (UC-FRET) was triggered by the physical adsorption interaction between the aptamer and MoS2 nanosheets, leading to a remarkable quenching of UCNP fluorescence up to 95%. Upon addition of VEGF165 to the UCNP-aptamer system before MoS2 nanosheets were added, the aptamer preferentially bound to VEGF165 with the change of spatial conformation, which weakened the van der Waals' force between the MoS2 nanosheets and the aptamer, thus leading to the separation of the donor and the acceptor. Consequently, the FRET phenomenon was inhibited and the luminescence of UCNPs was regained, which was linearly related to the concentration of VEGF165 in the range of 0.1 ng mL-1 to 16 ng mL-1. By taking advantage of the extreme fluorescence quenching ability of MoS2 nanosheets and the optical merits of UCNPs, the aptasensor based on UC-FRET exhibited favorable performance for the homogeneous assay of VEGF165 in human serum, which is of great value for clinical diagnosis of tumors and related biological studies.

Ratiometric enhanced fluorometric determination and imaging of intracellular microRNA-155 by using carbon dots, gold nanoparticles and rhodamine B for signal amplification

An ultrasensitive and highly reliable ratiometric assay is described for the determination of microRNA-155. It works at the attomolar concentration level and hashigh selectivity which warrants its potential application in cancer biomarker tracking. The excellent performance of this method results from (a) the use of a hybrid conjugate prepared from Rhodamine B (RhB), carbon dots (CDs) and probe-microRNA, and (b) from the measurement of fluorescence resonance energy transfer (FRET) that is observed in the AuNP/target-microRNA system as a result of RNA hybridization. The dye RhB (emission peak at 580nm) serves as an internal reference. The sensitivity of this assay is increased by about 30% because of the broad emissions of CDs (489nm and 665nm) through a sequential FRET phenomenon. RhB-CDs were covalently bio-conjugated to probe microRNA. In the presence of AuNPs, the fluorescence of the CDs is quenched, while in the presence of microRNA-155, the ratio of fluorescences at 489 and 665nm (I489/I665) is enhanced again. A linear relationship exists between the ratio of fluorescence and the concentration of microRNA-155 in the range from 1 aM to 0.1μM, and the detection limit is 0.3 aM. The assay was applied to quantitative studies of target microRNA-155 in multiple pathways associated with cancer progression in biological fluids include human serum samples and cancer cells. The nanoprobe also deliver clear signal to microRNA target in fixed and lived MDA-MB-231 cells. Graphical abstract A ratiometric FRET sensing method used for microRNA-155 detection at aM concentration level using CDs and AuNPs as donor-acceptor respectively and Rhodamine B as amplification reagent. The application of assay for imaging of microRNA-155 in fixed and live MDA-MB-231 cells is demonstrated.

Covalently Linked Perylene Diimide-Polydiacetylene Nanofibers Display Enhanced Stability and Photocurrent with Reversible FRET Phenomenon.

Because of their unique structural and optical properties, 1D perylene diimide (PDI) derivatives have gained attention for use in optoelectronic devices. However, PDI-containing self-assembled supramolecular systems often are of limited use because they have supramolecular architectures that are held together by weak noncovalent π-π stacking, hydrogen bonding, and hydrophobic interactions. As a result, they are intrinsically unstable under solution-processing conditions. To overcome this limitation, a polydiacetylene (PDA)-based strategy is developed to construct a solvent-resistant and stable PDI assembly. For this purpose, first the monomer PDI-BisDA is generated, in which two polymerizable diacetylene (DA) units are covalently linked to a PDI core. Importantly, 254 nm UV irradiation of self-assembled PDI-BisDA nanofibers forms solvent-resistant and stable PDI-PDA fibers. Owing to the presence of PDA, the generated polymer fibers display an increased photocurrent. In addition, the existence of PDA and PDI moieties in the fiber leads to the occurrence of switchable on-off fluorescence resonance energy transfer (FRET) between the PDI and reversibly thermochromic PDA chromophores.

Fluorescence Resonance Energy Transfer, Small-Angle Neutron Scattering, and Dynamic Light Scattering Study on Interactions of Gemini Surfactants Having Different Spacer Groups with Protein at Various Regions of Binding Isotherms.

The binding interactions of three gemini surfactants having different spacer groups (12-4-12, 12-8-12, and 12-4(OH)-12) with a high concentration (150 μM) of bovine serum albumin (BSA) at various regions of binding isotherms have been studied by means of steady-state fluorescence and fluorescence anisotropy, time-correlated single-photon counting fluorescence of trans-2-[4-(dimethylamino)styryl]benzothiazole, small-angle neutron scattering (SANS), and dynamic light scattering (DLS) measurements. The fluorescence resonance energy transfer phenomenon between the twisted intramolecular charge transfer fluorescent molecule, trans-2-[4-(dimethylamino)styryl]benzothiazole as an acceptor, and tryptophan 213 (Trp-213) of BSA as a donor has been successfully used to probe the binding interactions of gemini surfactants with protein at all regions of binding isotherms. The increasing order of energy transfer efficiency at a higher concentration range of surfactants is 12-8-12 > 12-4-12 > 12-4(OH)-12. Stronger binding of micelles of gemini surfactant molecules having a comparatively more hydrophobic spacer group with the hydrophobic segments of the protein results in closer approach of trans-2-[4-(dimethylamino)styryl]benzothiazole molecules solubilized in micelles to Trp-213. The average excited-state lifetimes become shorter with a trend of increase in contribution from the fast component and decrease in contribution from the slow component to the decay with increasing concentration of a surfactant. The nonradiative rate constant of trans-2-[4-(dimethylamino)styryl]benzothiazole increases with increasing concentration of a surfactant because the average microenvironment around it in protein–surfactant aggregates is more polar as compared to that in native protein. SANS and DLS measurements were carried out for the study of the structural deformations in the protein, on enhancement of the concentration of the gemini surfactants. The necklace and bead model has been used for the analysis of SANS data for the protein–surfactant complexes. At a higher concentration range, 12-8-12 and 12-4-12 have a slightly smaller fractal dimension and a larger correlation length as compared to 12-4(OH)-12. DLS data show that the increasing order of hydrodynamic diameter for the complexes of protein with three gemini surfactants in their high concentration range is 12-4(OH)-12 < 12-4-12 < 12-8-12.

Fluorescence Resonance Energy Transfer Visualization of Molecular Delivery from Polymeric Micelles.

Polymeric micelles are important carriers for anticancer drug delivery. However, rare papers focused on the dynamic of drug in the core of micelles. In this paper, we used fluorescence resonance energy transfer (FRET) technique to investigate the dynamic diffusion of drug from polymeric micelles. mPEG-PCL diblock copolymers were used as carriers. A pair of fluorescence molecules Cy3 and Cy5 was selected to evoke the FRET phenomenon. Cy5 was immobilized on the terminal group of PCL segments, Cy3 was encapsulated in the Cy5 modified polymeric micelles as the model drug. The drug loaded polymeric micelles were incubated with 4T1 breast cancer cells. The FRET was observed to explore the dynamic of Cy3 in the micelles. The results showed that the Cy3 loaded micelles were stable in aqueous solution as the energy-transfer efficiency (ETE, I660/I565) rarely decreased even when the time was as long as 120 h. The ETE increased with the content of encapsulated Cy3. The FRET spectra showed that the ETE of the Cy3 loaded polymeric micelles lowered with the release of Cy3 in PBS. The intracellular tracking of the Cy3 loaded micelles found more than 60% loaded drug was release within 12 h with the calculation of ETE in FRET spectra and it was same to confocal laser scanning and flow cytometry results.

Simultaneous biosensing of CA125 and CA15-3 tumor markers and imaging of OVCAR-3 and MCF-7 cells lines via bi-color FRET phenomenon using dual blue-green luminescent carbon dots with single excitation wavelength

Here, we developed a facile route to synthesize two CDs with the maximum emission locates at 326 nm and 443 nm under 230 nm excitation. The absolute photoluminescence quantum yield (QY) is as high as 29% and 52% for CD-1 and CD-2 with strong blue-green fluorescence, respectively. The functionalized CDs (CDs-NH2, CDs-COOH) conjugated with antibodies used for simultaneous detection of two tumor-markers using fluorescence resonance energy transfer (FRET) strategy, when MoS2 nanosheets functionalized with ssDNA related aptamers applied as quencher. The response of sensor enhanced gradually with increasing of targets at range 0.05–8 pg/mL with detection limit (DL) 5.0 fg/mL for CA125, while for CA15-3 concentration range was 1.0–35 pg/mL and DL was 0.5 pg/mL. This strategy revealed a stable analytical performance for the detection of OVCAR-3 and MCF-7 cells lines ranging from 1000 to 10,000 cells/mL with DL 2–3 cells in 10 μL of injected sample. When the CDs-Ab was used in selective imaging of MCF-7 and OVCAR-3 cancer cells, a strong PL emission was observed. After incubation times, both the cells size and shape clearly remained without any change. The results demonstrate that the CDs are a potentially excellent bioimaging component in pathological diagnosis, biomedicine research and management of cancer diseases.

Multiple Dye Doped Core-Shell Silica Nanoparticles: Outstanding Stability and Signal Intensity Exploiting FRET Phenomenon for Biomedical Applications

We present a one-pot synthesis of core-shell silica nanoparticles (SiNPs) as a novel fluorescent probe for biological applications. SiNPs were doped with a different number of dyes to ensure high efficiency Fluorescence Resonance Energy Transfer (FRET). Dyes are individually entrapped in the silica core without a covalent bonding between them. The strong interconnection achieved inside the core, a FRET with efficiency up to 86% was obtained. Nanoparticles called NTB530, NTB575 and NTB660 contain two, three and four different dyes respectively. Nanoparticles can be excited with a common blue laser and characterized by a long Stokes Shift up to the near-IR emission. Photostability, tested under continuous irradiation with a mercury lamp, showed higher stability of our Nanoparticles compared to commercial dyes like Fluorescein and R-Phycoerythrin. To prove the potential application of our Nanoparticle in flow-cytometry, they were conjugated with Anti-Human CD8 antibody and tested in comparison with commercial ones.

Competition-derived FRET-switching cationic conjugated polymer-Ir(III) complex probe for thrombin detection

A novel, label-free and convenient strategy for thrombin assay has been developed based on the fluorescence resonance energy transfer (FRET) from a cationic conjugated polymer (CCP) to Ir(III) complex. The energy donor (CCP) and acceptor (Ir(III) complex) were taken into close proximity through π-π stacking interaction and electrostatic interaction, leading to the occurrence of FRET. However, the introduction of the thrombin aptamer upset the status and blocked the FRET process, but afterwards the reappearance of FRET phenomenon was confirmed by the special binding interaction between aptamer and thrombin, thus achieving the quantitative detection of thrombin. This assay could detect thrombin as low concentration as about 0.05pM and provided a highly specific selectivity among other nonspecific proteins. Moreover, the strategy may allow our platform to provide similar sensitivity toward different targets in an aptamer-structure-independent manner. Furthermore, the assay can be used to detect thrombin in diluted real urine or serum samples with a satisfactory recovery, implying its great potential for rapid detection of thrombin in the clinic.

Construction of new cross-linked supramolecular polymer with FRET phenomenon based on oligo(p-phenylenevinylene)-linked pillar[5]arene dimer

Cross-linked supramolecular polymers generally show distinct mechanical properties with intriguing functions, which have become one of the hot research topics in recent years. However, the cross-linked supramolecular polymers functionalised with fluorescence resonance energy transfer (FRET) properties have been rarely reported yet. Herein, a new cross-linked supramolecular polymer equipped with efficient FRET property was constructed successfully. The oligo(p-phenylenevinylene)-linked pillar[5]arene dimer (PA-OPV) functioned as a host and energy donor, while four pentanenitrile groups coupled porphyrin (CN-Por) acted as guest with energy acceptor. The supramolecular polymerisation and FRET properties were investigated by using NMR, viscosity, Fluorescence, UV–vis and SEM.

FRET-based acrylic nanoparticles with dual-color photoswitchable properties in DU145 human prostate cancer cell line labeling

Abstract Dual-color photoswitchable fluorescent polymer nanoparticles have emerged as an important type of cell detectors. Here, dual-color acrylic nanoparticles containing spiropyran and azo-carbazole derivatives with remarkable photostability and photoreversibility were employed. These prominent properties were attributed to the covalent bonding between the incorporated chromophores and the polymeric matrix and provided efficient fluorescence resonance energy transfer phenomenon. The obtained nanoparticles were purified after dialysis and delivered into DU145 cancer cells. Trypan blue dye exclusion assays showed that these nanoparticles were biocompatible with no toxicity to the cells. Fluorescence microscopy images demonstrated that the prostate cancer cells containing nanoparticles exhibited excellent cell uptake with green and red fluorescence emissions after primary excitation at 410 nm and subsequent irradiation at 365 nm, respectively, depicting their dual-color characteristics.

Photoluminescence: Dual Role of Blue Luminescent MoS2 Quantum Dots in Fluorescence Resonance Energy Transfer Phenomenon (Small 19/2014)

Photoluminescence: Dual Role of Blue Luminescent MoS₂ Quantum Dots in Fluorescence Resonance Energy Transfer Phenomenon (Small 19/2014)

Organic–Inorganic Interface‐Induced Multi‐Fluorescence of MgO Nanocrystal Clusters and Their Applications in Cellular Imaging

Surface functionalization of inorganic nanomaterials through chemical binding of organic ligands on the surface unsaturated atoms, forming unique organic-inorganic interfaces, is a powerful approach for creating special functions for inorganic nanomaterials. Herein, we report the synthesis of hierarchical MgO nanocrystal clusters (NCs) with an organic-inorganic interface induced multi-fluorescence and their application as new alternative labels for cellular imaging. The synthetic method was established by a dissolution and regrowth process with the assistance of carboxylic acid, in which the as-prepared MgO NCs were modified with carboxylic groups at the coordinatively unsaturated atoms of the surface. By introducing acetic acid to partially replace oleic acid in the reaction, the optical absorption of the produced MgO NCs was progressively engineered from the UV to the visible region. Importantly, with wider and continuous absorption profile, those MgO NCs presented bright and tunable multicolor emissions from blue-violet to green and yellow, with the highest absolute quantum yield up to (33±1) %. The overlap for the energy levels of the inorganic-organic interface and low-coordinated states stimulated a unique fluorescence resonance energy transfer phenomenon. Considering the potential application in cellular imaging, such multi-fluorescent MgO NCs were further encapsulated with a silica shell to improve the water solubility and stability. As expected, the as-formed MgO@SiO2 NCs possessed great biocompatibility and high performance in cellular imaging.