Sharif Digital Repository

Simply obtained by the oxidation of levodopa in alkaline media, polylevodopa nanoparticles are able to quench the fluorescence emission of CdTe quantum dots (QDs) via energy transfer mechanism. The extent of this quenching can be exploited for the quantification of levodopa, as an important therapeutic agent in the treatment of Parkinson's disease. However, to effectively improve the detection performance, in this study, we have designed a ratiometric probe by making use of variations in both the emission of QDs and the intrinsic emission of polylevodopa nanoparticles. The enhanced sensitivity, in particular, arose from the measurement of the ratio of fluorescence intensities at two... 

The giant Kerr nonlinearity with reduced linear and nonlinear absorption in a four-level quantum dot by employing the tunnel coupling is investigated. It is shown that by enhancement of tunnel coupling value the Kerr nonlinearity increases and at the same time linear and nonlinear absorption reduces at the long wavelength which is very important for communicational applications. Enhanced of Kerr nonlinearity in a double quantum dots is investigated. It is found that the electron tunneling has an essential role to reducing the linear absorption and increasing the Kerr nonlinearity at long wavelength  

Highly fluorescent and water-soluble cadmium selenide quantum dots (QDs) functionalised by thio-cyclodextrin (HS-CD) and mercaptoacetic acid (MAA) as surface coating agents (QDs-CD-MAA) were synthesised successfully. The synthesised hybrid nanomaterials, QDs-CD-MAA, were able to form water-soluble complexes with paclitaxel and folic acid. QDs and their complexes were characterised by usual spectroscopy and microscopy methods. Size and morphology of functionalised QDs were dependent on their capping agents and guest molecules. Short-term in vitro cytotoxicity tests on mouse tissue connective fibroblast adhesive cells (L929) showed that conjugation of CD molecules onto the surface of QDs... 

Cationic polymers such as poly-L-lysine (PLL) are able to interact electrostatically with DNA to produce polymeric systems with nanometric diameters due to the neutralization and accumulation of DNA. This study integrates the outstanding properties of carbon quantum dots (CQDs) with PLL to develop a novel gene delivery vehicle with a core-shell hybrid nanostructure. The CQD/PLL core-shell nanoparticles (NPs) were, therefore, synthesized in such a way that they had narrow size distribution and an average diameter under 10 nm, both of which were confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectroscopy exhibited that... 

The importance of tracing dopaminergic agents in the progression assessment of Parkinson's disease has boosted the demand for fast, sensitive, and real-time multi-analyte detection. Herein, visual and fingerprint fluorimetric patterns have been created by an optical sensor array to simultaneously detect and discriminate among levodopa, carbidopa, benserazide, and entacapone, as important dopaminergic agents. A dual emissive nanoprobe consisting of red quantum dots and blue carbon dots with an overall pink emission has been fabricated to provide unique emission patterns in the presence of the target analytes. The sensor elements in the array come from it's differential response in the absence... 

Carbon-based quantum dots (CDs) are mainly divided into two sub-groups; carbon quantum dots (CQDs) and graphene quantum dots (GQDs), which exhibit outstanding photoluminescence (PL) properties, low toxicity, superior biocompatibility and facile functionalization. Regarding these features, they have been promising candidates for biomedical science and engineering applications. In this work, we reviewed the efforts made to modify these zero-dimensional nano-materials to obtain the best properties for bio-imaging, drug and gene delivery, cancer therapy, and bio-sensor applications. Five main surface modification techniques with outstanding results are investigated, including doping, surface... 

Carbon-based quantum dots (CDs) are mainly divided into two sub-groups; carbon quantum dots (CQDs) and graphene quantum dots (GQDs), which exhibit outstanding photoluminescence (PL) properties, low toxicity, superior biocompatibility and facile functionalization. Regarding these features, they have been promising candidates for biomedical science and engineering applications. In this work, we reviewed the efforts made to modify these zero-dimensional nano-materials to obtain the best properties for bio-imaging, drug and gene delivery, cancer therapy, and bio-sensor applications. Five main surface modification techniques with outstanding results are investigated, including doping, surface... 

The type of passivating ligands and the ligand exchange method influence the quality of lead sulfide quantum dot films. This imparts on the efficiency of optoelectronic devices. To get a compact arrangement of the nanocrystals in a thin film (⁓100 nm) via self-assembling, we used organic-inorganic perovskites with mixed halides for the solid-state exchange of oleic acid ligands on PbS QDs (⁓ 4 nm). Formamidinium lead halides FAPbIxBr3-x (x= 3,2,1,0) were used. X-ray spectroscopy shows that successful replacement of oleic acid with FA happens by short immersion of the films (2 min) in the solution. Transmission electron microscopy shows that nano-scale cracks, short-range ordering, and fusion... 

TiO2 nanorod layers are synthesized by simple chemical oxidation of Ti substrates. Diffuse reflectance spectroscopy measurements show effective light scattering properties originating from nanorods with length scales on the order of one micron. The films are sensitized with CdSe quantum dots (QDs) by successive ionic layer adsorption and reaction (SILAR) and integrated as a photoanode in quantum dot sensitized solar cells (QDSCs). Incorporating nanorods in photoanode structures provided 4- to 8-fold enhancement in light scattering, which leads to a high power conversion efficiency, 3.03% (Voc = 497 mV, Jsc = 11.32 mA/cm2, FF = 0.54), in optimized structures. High efficiency can be obtained... 

In this paper, for the first time, we present a semiclassical noise model for InAs/GaAs quantum dot (QD) laser considering two photon modes, i.e., ground and first excited states lasing. This model is based on the five level rate equations. By using this model, the effect of temperature variations on relative intensity noise (RIN) of QD laser is investigated. We find that the RIN significantly degrades when excited state (ES) lasing emerges at high temperature. Furthermore, we investigate the influence of the quantum dot numbers on the RIN properties  

Herein, a simple and novel method was used to synthesize a new structure of graphene which can be called hollow graphene. First, the ZnO-Graphene QDs synthesized by solution method and then ZnO QDs were dissolved from this structure using an acidic solution to obtain hollow structure of graphene. Afterward, this structure was used in PbS QDs solar cell in order to improve the transport of electron and decrease the recombination of the carriers. A power conversion efficiency of 5.3% was obtained using hollow graphene as a fast electron extraction layer due to the enhancement of EQE and current density. The improvement of PCE in this device was corresponded to efficient photosensitized... 

A structure is suggested for spasing. The presented surface plasmon amplification by stimulated emission of Radiation (SPASER) is made up of a graphene nanosphere, which supports localized surface plasmon modes, and a quantum dot array, acting as a gain medium. The gain medium is pumped by an external light source. Since all the plasmons are carried on a graphene platform, the structure features coherent surface plasmons with high confinement and large life time. All the structures are analyzed theoretically using full quantum mechanical description. The main advantage of the proposed SPASER is its simple tuning capability of changing graphene's Fermi level, which is performed by either... 

Chiral discrimination has always been a hot topic in chemical, food and pharmaceutical industries, especially when dealing with chiral drugs. Enantiomeric recognition not only leads to better understanding of the mechanism of molecular recognition in biological systems, but may further assist in developing useful molecular devices in biochemical and pharmaceutical studies. By emerging nanotechnology and exploiting nanomaterials in sensing applications, a great deal of attention has been given to the design of optical nanoprobes that are able to discriminate enantiomers of chiral analytes. This review explains how engineering nanoparticles (NPs) with desired physicochemical properties allows... 

In this work, we study the conductance of a general periodic quantum dot (QD) attached to ideal semi-infinite uniform metallic leads (nanocrystals), fully analytically. We propose a new general formula which relates conductance to transfer matrix (TM) for an isolated cell in the periodic dot. The equation describes exactly the dependence of the transmission coefficient (TC) on Fermi energy, dot-size, dot-lead coupling, and gate voltage for an arbitrary periodic dot. Then, we derive a nonlinear equation which gives the resonance, bound, and surface state energies. Finally, the TC has been calculated for gapless, single, and double gap models exactly. Moreover, we have also calculated the... 

Field-effect transistors have been widely used to study electronic transport and doping in colloidal quantum dot solids to great effect. However, the full power of these devices to elucidate the electronic structure of materials has yet to be harnessed. Here, we deploy nanodielectric field-effect transistors to map the energy landscape within the band gap of a colloidal quantum dot solid. We exploit the self-limiting nature of the potentiostatic anodization growth mode to produce the thinnest usable gate dielectric, subject to our voltage breakdown requirements defined by the Fermi sweep range of interest. Lead sulfide colloidal quantum dots are applied as the active region and are treated... 

A solution-processed, bottom-up nanowire network electrode is developed and employed in a bulk heterojunction colloidal quantum dot solar cell. The electrode features a ZnO template which is converted into locally connected, infi ltratable TiO2 nanowires. The new electrode allows the application of a thicker light absorbing fi lm without compromising the charge extraction, as reported by Edward H. Sargent, Ghassan Jabbour, and co-workers on page 1769. The frontispiece shows schematically the electrode shape and the resultant device architecture  

We derive the noise equivalent circuit model of semiconductor self-assembled quantum-dot (QD) lasers (SAQDL) from the rate equations including Langevin noise sources. This equivalent circuit allows a straightforward calculation of the noise of an SAQDL combined with electronic components. Using the presented model, we study how the carrier dynamics influences relative intensity noise (RIN) of QD lasers. We demonstrate that RIN is degraded with larger inhomogeneous broadening. Furthermore, we show that RIN is enhanced for lower quantum-dot coverage level