Unveiling the therapeutic potential of thymol from Nigella sativa L. seed: selective anticancer action against human breast cancer cells (MCF-7) through down-regulation of Cyclin D1 and proliferative cell nuclear antigen (PCNA) expressions.

BACKGROUND: Breast adenocarcinoma cells (MCF-7) are characterized by the overexpression of apoptotic marker genes and proliferative cell nuclear antigen (PCNA), which promote cancer cell proliferation. Thymol, derived from Nigella sativa (NS), has been investigated for its potential anti-proliferative and anticancer properties, especially its ability to suppress Cyclin D1 and PCNA expression, which are crucial in the proliferation of cancer cells. METHODS: The cytotoxicity of thymol on MCF-7 cells was assessed using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) and lactate dehydrogenase (LDH) release methods. Thymol was tested at increasing concentrations (0-1000 µM) to evaluate its impact on MCF-7 cell growth. Additionally, Cyclin D1 and PCNA gene expression in thymol-treated and vehicle control groups of MCF-7 were quantified using real-time Polymerase Chain Reaction (RT-qPCR). Protein-ligand interactions were also investigated using the CB-Dock2 server. RESULTS: Thymol significantly inhibited MCF-7 cell growth, with a 50% inhibition observed at 200 µM. The gene expression of Cyclin D1 and PCNA was down-regulated in the thymol-treated group relative to the vehicle control. The experimental results were verified through protein-ligand interaction investigations. CONCLUSIONS: Thymol, extracted from NS, demonstrated specific cytotoxic effects on MCF-7 cells by suppressing the expression of Cyclin D1 and PCNA, suggesting its potential as an effective drug for MCF-7. However, additional in vivo research is required to ascertain its efficacy and safety in medical applications.

Fabrication of novel AgVO3/BiOI nanocomposite photocatalyst with photoelectrochemical activity towards the degradation of Rhodamine B under visible light irradiation.

In the present work, a visible light driven AgVO3/BiOI nanocomposite photocatalyst with different wt % (1, 2, 3) of AgVO3 was fabricated by using facile hydrothermal method. Further, the nanocomposite was characterized by FT-IR, XRD, SEM, TEM, EDS, UV-vis DRS, photoluminescence and photoelectrochemical studies. The structural characterization showed nanorods on nanosheet surface. Among different AgVO3 loaded samples, the photocatalytic efficiency of 1 wt % AgVO3/BiOI nanocomposite was found to be comparatively higher than the pure BiOI and AgVO3. The photodegradation rate constant values of pure BiOI, AgVO3 and 1, 2, 3 wt % AgVO3/BiOI nanocomposites are 0.006, 0.0033, 0.0255, 0.01575, 0.0116 min-1 respectively. This enhanced photocatalytic activity was due to the increasing visible light absorption ability and efficient separation of the charge carriers. Thereby, the 1 wt % AgVO3/BiOI nanocomposite photocatalyst exhibited increased photodegradation activity, photostability and recyclability characteristics. The radical trapping experiment confirmed the role of OH and h+ in the photocatalytic degradation of RhB. Based on this, the probable mechanism of degradation of RhB under visible light irradiation has also been proposed. Hence, we believe it could be a promising material that can be employed for the photodegradation of organic pollutants present in wastewater.

Investigation of the Optical Properties of a Novel Class of Quinoline Derivatives and Their Random Laser Properties Using ZnO Nanoparticles.

Quinoline Schiff bases display potential applications in optoelectronics and laser fields because of their unique optical properties that arise from extensive delocalization of the electron cloud, and a high order of non-linearity. In this context, a new class of conjugated quinoline-derivative viz. N-(quinolin-3-ylmethylene)anilines were synthesized from 2-hydroxyquinoline-3-carbaldehyde in two good yielding steps. The ability of these imines to accept an electron from a donor is denoted by their electron acceptor number and sites, which is calculated using density functional theory (DFT). The optical properties such as FT-IR, Raman, UV-VIS, and EDS spectra were calculated using TD-DFT, which also provided the energy gap, HOMO-LUMO structure. The optical properties of the synthesized imino quinolines were experimentally studied using photoluminescence and absorption spectroscopy. The properties such as Stokes shift and quantum yield were calculated using experimental data. Furthermore, the compound bearing a methyl group on the aryl ring and ZnO nanoparticles (hydrothermally synthesized) were dissolved in toluene, and optically excited with a 355 nm nanosecond laser, which produced a random laser.

Effects of Graphene Oxide (GO) and Reduced Graphene Oxide (rGO) on Green-Emitting Conjugated Copolymer's Optical and Laser Properties Using Simulation and Experimental Studies.

The properties of a conjugated copolymer (CP), poly[(9,9-Dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene) (PDVF-co-MEH-PV), were investigated in the presence of graphene oxide (GO) and reduced graphene oxide (rGO) using absorption, fluorescence, laser, and time-resolved spectroscopy. CPs are usually dissolved in low-polar solvents. Although GO does not dissolve well, rGO and PDVF-co-MEH-PV dissolve in chloroform due to their oxygen acceptor sites. Hence, we studied rGO/PDVF-co-MEH-PV (CP/rGO), performing all experiments and simulations in chloroform. We performed simulations on PDVF-co-MEH-PV, approximate GO, and rGO using time-dependent density-functional theory calculations to comprehend the molecular dynamics and interactions at the molecular level. The simulation polymer used a tail-truncated oligomer model with up to three monomer units. The simulation and experimental results were in agreement. Further, the PDVF-co-MEH-PV exhibited fluorescence, laser quenching, rGO-mediated laser blinking, and spectral broadening effects when GO and rGO concentrations increased. The experimental and simulation results were compared to provide a plausible mechanism of interaction between PDVF-co-MEH-PV and rGO. We observed that for lower concentrations of rGO, the interaction did not considerably decrease the amplified spontaneous emissions of PDVF-co-MEH-PV. However, the fluorescence of PDVF-co-MEH-PV was considerably quenched at higher concentrations of rGO. These results could be helpful for future applications, such as in sensors, solar cells, and optoelectronic device design. To demonstrate the sensor capability of these composites, a paper-based sensor was designed to detect ethanol and nitrotoluene. An instrumentation setup was proposed that is cheap, reusable, and multifunctional.

A straightforward synthesis of visible light driven BiFeO3/AgVO3 nanocomposites with improved photocatalytic activity.

Herein, an efficient visible-light-driven BiFeO3/AgVO3 nanocomposite was effectively fabricated via a facile co-precipitation procedure. The physicochemical properties of BiFeO3/AgVO3 nanocomposites were investigated via Fourier transform-infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), UV visible diffuse reflectance spectroscopy (DRS) and photoelectrochemical studies (PEC). The photocatalytic activity (PCA) of BiFeO3/AgVO3 nanocomposites was assessed with regard to the photocatalytic degradation of Rhodamine-B (RhB) when subjected to visible light irradiation (VLI). Upon 90 min of illumination, the optimal 3%-BiFeO3/AgVO3 nanocomposite showed a greater photocatalytic degradation, which was ∼3 times higher than the bare AgVO3. The lower PL intensity of 3%-BiFeO3/AgVO3 nanocomposite exposed the low recombination rate, which improved the photo-excited charge carriers separation efficiency. The experimental outcomes showed that the BiFeO3/AgVO3 nanocomposite might be an encouraging material for treatment of industrial and metropolitan wastewater. Moreover, a plausible RhB degradation mechanism was proposed proving the participation of the generated OH and O2- radicals in the degradation over BiFeO3/AgVO3 nanocomposite.

Antifungal activity of nanoemulsion from Cleome viscosa essential oil against food-borne pathogenic Candida albicans.

Pathogenic and spoilage fungi cause enormous challenges to food related fatal infections. Plant essential oil based classical emulsions can functions as antifungal agents. To investigate the antifungal spectrum, that is the scope of the nanoemulsion composed of Cleome viscosa essential oil and Triton-x-100 fabricated by ultrasonication method. Minimum inhibitory and fungicidal concentration of essential oil nanoemulsion (EONE) was tested against food borne pathogenic C. albicans. The MIC and MFC values ranged from 16.5 to 33 µl/ml with significant reduction on biofilm of C. albicans isolates. The alteration of molecular fingerprints was confirmed by Fourier transformed infrared spectroscopy and subsequent reduction of chitin levels in cell walls was noted by spectroscopic analysis. The EONE and their bioactive compounds cause collateral damage on C. albicans cells.

TD-DFT Simulation and Experimental Studies of a Mirrorless Lasing of Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)].

In this work, we investigate the TD-DFT simulation, optical, and mirrorless laser properties of conjugated polymer (CP) Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)], also known as (PFO-co-PPV-MEHB) or ADS125GE. TD-DFT calculations were performed for three monomer units with truncated tails using time-dependent density functional theory (TD-DFT) calculations. The calculations showed a highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) structure and a very high oscillator strength of 6.434 for the singlet-singlet transition at 374.43 nm. Experimentally, the absorption and fluorescence spectra were examined at various concentrations in verity of solvents, such as benzene, toluene, and hexane. The experimental results obtained in hexane were comparable with theoretical UV-VIS spectra calculated under vacuum. Amplified spontaneous emission (ASE) spectra peaked at approximately 509 nm for CO PFO-co-PPV-MEHB in solution and were obtained at suitable concentrations and pump energies. Additionally, the photochemical stability of this CP and coumarin (C510) were compared. Time-resolved spectroscopy (TRS) studies with a sub-nanosecond resolution were performed for the CO under various pump energies. These results showed the excited state dynamics and single-pass optical gain of CO PFO-co-PPV-MEHB.

Time-resolved spectroscopy of radiative energy transfer between a conjugated oligomer and polymer in solution.

We report a short investigation of the energy transfer process between the conjugated oligomer 1,4-bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF) and the conjugated polymer poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene-vinylene] - end capped with DMP (MDMO-PPV). The radiative energy transfer (RET) process shows a time delay, and the formation of the excimer causes a further delay. All these processes were studied using time-resolved spectroscopy (TRS), which has three-dimensional (3D) features with wavelength, intensity and time (picosecond) as the X, Y and Z-axis, respectively. We observed a definitive delay (1 ns) in the fluorescence from MEDMO-PPV concerning the fluorescence of the oligomer, indicating the RET. The TRS of different relative concentrations and temperature effects on the energy transfer process was also studied. The quantum yield, critical distance, polarizability and change of MEDMO-PPV were calculated. The excimer of the MEDMO-PPV produces Amplified Spontaneous Emission (ASE) after a time delay of at least 0.5 ns, which was also observed in this study.

Narrowband Spontaneous Emission Amplification from a Conjugated Oligomer Thin Film.

In this paper, we studied the laser and optical properties of conjugated oligomer (CO) 1,4-bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF) thin films, which were cast onto a quartz substrate using a spin coating technique. BECV-DHF was dissolved in chloroform at different concentrations to produce thin films with various thicknesses. The obtained results from the absorption spectrum revealed one sharp peak at 403 nm and two broads at 375 and 428 nm. The photoluminescence (PL) spectra were recorded for different thin films made from different concentrations of the oligomer solution. The threshold, laser-induced fluorescence (LIF), and amplified spontaneous emission (ASE) properties of the CO BECV-DHF thin films were studied in detail. The ASE spectrum was achieved at approximately 482.5 nm at a suitable concentration and sufficient pump energy. The time-resolved spectroscopy of the BECV-DHF films was demonstrated at different pump energies.

Mesoporous Tungsten Trioxide Photoanodes Modified with Nitrogen-Doped Carbon Quantum Dots for Enhanced Oxygen Evolution Photo-Reaction.

Nanostructured photoanodes are attractive materials for hydrogen production via water photo-electrolysis process. This study focused on the incorporation of carbon quantum dots doped with nitrogen as a photosensitizer into mesoporous tungsten trioxide photoanodes (N-CQD/meso-WO3) using a surfactant self-assembly template approach. The crystal structure, composition, and morphology of pure and N-CQD- modified mesoporous WO3 photoanodes were investigated using scanning electron and transmission microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Due to their high surface area, enhanced optical absorption, and charge-carrier separation and transfer, the resulting N-CQD/meso-WO3 photoanodes exhibited a significantly enhanced photocurrent density of 1.45 mA cm-2 at 1.23 V vs. RHE under AM 1.5 G illumination in 0.5 M Na2SO4 without any co-catalysts or sacrificial reagent, which was about 2.23 times greater than its corresponding pure meso-WO3. Moreover, the oxygen evolution onset potential of the N-CQD/meso-WO3 photoanodes exhibited a negative shift of 95 mV, signifying that both the charge-carrier separation and transfer processes were promoted.

Optically Pumped Intensive Light Amplification from a Blue Oligomer.

We demonstrated the time-resolved dynamics of laser action from the conductive oligomer (CO) 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF). Absorption and fluorescence spectra were studied for BECV-DHF in different solvents under a wide range of concentrations. The Fourier-transform infrared spectroscopy (FTIR) spectrum was measured using simulation and experiments. The Ultraviolet-Visible (UV-VIS) spectra of the BECV-DHF were simulated in two different solutions. This CO formed a dimer and had two vibration bands in nonpolar solvents, partially dissolved in polar protic solvents, and created an H-type aggregate in polar aprotic solvents. BECV-DHF produced amplified spontaneous emission (ASE) at 464 nm in many solvents. The high efficiency of ASE is due to the waveguiding and self-assembly nature of the oligomer, which is very rare for optically pumped systems. However, BECV-DHF did not produce ASE in polar protic solvents. BECV-DHF produced ASE in both longitudinal and transverse pumping, and the full-width half maximum (FWHM) was 4 nm and 8 nm respectively for different solvents, such as toluene and acetone. The CO had a very low threshold pump energy (~0.5 mJ). The ASE efficiency was approximately 20%. The time-resolved spectroscopy (TRS) studies showed a temporal Gaussian-shaped ASE output from this CO. BECV-DHF shows remarkably high stability compare to the conjugated polymer (CP) PFO-co-pX.

A Temperature-Tunable Thiophene Polymer Laser.

This paper reports a temperature-tunable conjugated polymer poly[3-(2-ethyl-isocyanato-octadecanyl)-thiophene] (TCP) laser working in superradiant (SR)-or amplified spontaneous emission (ASE)-mode. The absorption spectra indicated the aggregate (mostly dimer) formation upon increasing concentration and/or decreasing temperature. Amplified spontaneous emission (ASE) was observed at suitable concentration, temperature, and pump energy values. The efficiency of the ASE from the TCP polymer was improved by energy transfer from an oligomer 9,9,9',9',9″,9″-hexakis(octyl)-2,7',2',7″-trifluorene (HOTF). Moreover, the ASE wavelength can be tuned between 550 and 610 nm by changing the temperature of the solution from 60 to 10 °C. To the best of our knowledge, this is the first report of a high-power, temperature-tunable, and conjugated polymer laser.

3D nanorhombus nickel nitride as stable and cost-effective counter electrodes for dye-sensitized solar cells and supercapacitor applications.

Transition metal nitride based materials have attracted significant interest owing to their excellent properties and multiple applications in the field of electrochemical energy conversion and storage devices. Herein we synthesize 3D nanorhombus nickel nitride (Ni3N) thin films by adopting a reactive radio frequency magnetron sputtering process. The as-deposited 3D nano rhombus Ni3N thin films were utilized as cost-effective electrodes in the fabrication of supercapacitors (SCs) and dye-sensitized solar cells (DSSCs). The structure, phase formation, surface morphology and elemental composition of the as-deposited Ni3N thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM). The electrochemical supercapacitive performance of the Ni3N thin films was examined by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques, in 3 M KOH supporting electrolyte. The areal capacitance of the Ni3N thin film electrode obtained from CV analysis was 319.5 mF cm-2 at a lower scan rate of 10 mV s-1. Meanwhile, the Ni3N thin film showed an excellent cyclic stability and retained 93.7% efficiency of its initial capacitance after 2000 cycles at 100 mV s-1. Interestingly, the DSSCs fabricated with a Ni3N CE showed a notable power energy conversion efficiency of 2.88% and remarkable stability. The prominent performance of the Ni3N thin film was ascribed mainly due to good conductivity, high electrochemically active sites with excellent 3D nano rhombus structures and high electrocatalytic activity. Overall, these results demonstrate that the Ni3N electrode is capable of being considered for efficient SCs and DSSCs. This investigation also offers an essential directive for the advancement of energy storage and conversion devices.

Time Evolution of the Excimer State of a Conjugated Polymer Laser.

An excited dimer is an important complex formed in nano- or pico-second time scales in many photophysics and photochemistry applications. The spectral and temporal profile of the excimer state of a laser from a new conjugated polymer, namely, poly (9,9-dioctylfluorenyl-2,7-diyl) (PFO), under several concentrations in benzene were investigated. These solutions were optically pumped by intense pulsed third-harmonic Nd:YAG laser (355-nm) to obtain the amplified spontaneous emission (ASE) spectra of a monomer and an excimer with bandwidths of 6 and 7 nm, respectively. The monomer and excimer ASEs were dependent on the PFO concentration, pump power, and temperature. Employing a sophisticated picosecond spectrometer, the time evolution of the excimer state of this polymer, which is over 400 ps, can be monitored.

A High Power, Frequency Tunable Colloidal Quantum Dot (CdSe/ZnS) Laser.

Tunable lasers are essential for medical, engineering and basic science research studies. Most conventional solid-state lasers are capable of producing a few million laser shots, but limited to specific wavelengths, which are bulky and very expensive. Dye lasers are continuously tunable, but exhibit very poor chemical stability. As new tunable, efficient lasers are always in demand, one such laser is designed with various sized CdSe/ZnS quantum dots. They were used as a colloid in tetrahydrofuran to produce a fluorescent broadband emission from 520 nm to 630 nm. The second (532 nm) and/or third harmonic (355 nm) of the Nd:YAG laser (10 ns, 10 Hz) were used together as the pump source. In this study, different sized quantum dots were independently optically pumped to produce amplified spontaneous emission (ASE) with 4 nm to 7 nm of full width at half-maximum (FWHM), when the pump power and focusing were carefully optimized. The beam was directional with a 7 mrad divergence. Subsequently, these quantum dots were combined together, and the solution was placed in a resonator cavity to obtain a laser with a spectral width of 1 nm and tunable from 510 to 630 nm, with a conversion efficiency of about 0.1%.

Gamma-Irradiation Effects on the Spectral and Amplified Spontaneous Emission (ASE) Properties of Conjugated Polymers in Solution.

In this paper, we investigate the effects of gamma (γ) radiation on the spectral and mplified spontaneous emission (ASE) properties of two conjugated polymers (CPs) viz., poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH⁻PPV) (CPM) and poly{[2-[2',5'-bis(2″-ethylhexyloxy)phenyl]-1,4-phenylenevinylene]-co-[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene]} (BEHP-co-MEH⁻PPV) (BMP) in tetrahydrofuran (THF). Gamma irradiation strongly affected the photophysical properties of these CPs. To explore these changes, gamma radiation, in the range of 2⁻50 kGy, was used to maintain the temperature at 5 °C constant for all doses at a dose rate of 12.67 kGy/h, using a 60Co gamma ray. The ASE profiles of the CPs in THF were obtained under the high power excitation of a Nd:YAG laser (355 nm), pre- and post-radiation. The result revealed a dramatic blue shift of the fluorescence and the ASE spectra after gamma irradiation. This shift in the luminescence and ASE spectra could be a response to the conformational disorders such as gamma irradiation-induced polymer crosslinking, which was verified using Raman spectra, FTIR, and swelling experiments. This could be the first report on the effect of gamma radiation on the ASE properties of conjugated polymers.

Relaxation Oscillation with Picosecond Spikes in a Conjugated Polymer Laser.

Optically pumped conjugated polymer lasers are good competitors for dye lasers, often complementing and occasionally replacing them. This new type of laser material has broad bandwidths and high optical gains comparable to conventional laser dyes. Since the Stokes' shift is unusually large, the conjugated polymer has a potential for high power laser action, facilitated by high concentration. This paper reports the results of a new conjugated polymer, the poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}](PFO-co-MEH-PPV) material, working in the green region. Also discussed are the spectral and temporal features of the amplified spontaneous emissions (ASE) from the conjugated polymer PFO-co-MEH-PPV in a few solvents. When pumped by the third harmonic of the Nd:YAG laser of 10 ns pulse width, the time-resolved spectra of the ASE show relaxation oscillations and spikes of 600 ps pulses. To the best of our knowledge, this is the first report on relaxation oscillations in conjugated-polymer lasers.

Laser from Optically Pumped Quantum Dot CdSe/ZnS in a Colloidal Liquid.

In this study, we had investigated the amplified spontaneous emission (ASE) characteristics of CdSe/ZnS quantum dot (QDs) in a colloidal liquid. A third harmonic of Nd:YAG laser (355 nm) was used to produce laser-induced fluorescence (LIF) at 605 nm with a spectral width of 0 nm [full width at half maximum (FWHM)]. When the pump power and focusing were carefully optimized, an ASE at 610 nm with a spectral width of Δλ = 8 nm (FWHM) could be obtained. The beam was directional with a divergence of 10 milli radians (mrad); but the conversion efficiency was about 0.05%.

Fluorescence spectral diagnosis of malaria: a preliminary study.

BACKGROUND: Malaria is the most common disease transmitted by the bite by an infected female anopheles mosquito and caused by the plasmodium parasite. It is mostly prevalent in subtropical regions receiving abundant rain and supporting copious mosquito breeding. This disease is generally detected by the microscopic examination of blood films or antigen based rapid diagnostic test. Only occasionally the parasite DNA is detected using polymerase chain reaction in certain advanced, expensive laboratories. METHODS: An innovative spectral detection method based on the fluorescence spectra of a set of blood plasma biomolecules [tyrosine, tryptophan, nicotinamide adenine dinucleotide (NAD), and flavin adenine dinucleotide (FAD)] and red blood cell (RBC)-associated porphyrin is being evolved by our group. RESULTS: The research so far has exhibited sensitivity and specificity values exceeding 90% based on the spectral features of blood components of 14 malaria patients and 20 numbers of age adjusted normal controls. The fluorescent biomolecules go out of proportion when the malarial parasite breaks down the hemoglobin of blood. CONCLUSION: This technique has the potential to be used as an alternative diagnostic procedure for malaria since the instrumentation involved is portable and inexpensive. VIRTUAL SLIDES: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_182.

Photoluminescence spectra of CdSe/ZnS quantum dots in solution.

The spectral properties of CdSe/ZnS core-shell quantum dots (QDs) of 3 nm size have been studied under different organic solvents, concentrations and temperatures. Our results showed that the absorption spectra of CdSe/ZnS in benzene have two humps; one around 420 nm and another at 525 nm, with a steady increase in absorption along UV region, and the absorption spectral profile under a wide range of concentrations did not change. On the other hand, the photoluminescence (PL) spectra of CdSe/ZnS in benzene showed two bands one around 375 nm and the other around 550 nm. It could be seen that the band at 375 nm is due to the interaction between the shell (ZnS) with the solvent species in high excited state, and the band at 550 nm is due to core alone (CdSe).