Universal emission intermittency in quantum dots, nanorods, and nanowires

Virtually all known fluorophores, including semiconductor nanoparticles, nanorods and nanowires exhibit unexplainable episodes of intermittent emission blinking. A most remarkable feature of the fluorescence intermittency is a universal power law distribution of on- and off-times. For nanoparticles the resulting power law extends over an extraordinarily wide dynamic range: nine orders of magnitude in probability density and five to six orders of magnitude in time. The exponents hover about the ubiquitous value of -3/2. Dark states routinely last for tens of seconds, which are practically forever on quantum mechanical time scales. Despite such infinite states of darkness, the dots miraculously recover and start emitting again. Although the underlying mechanism responsible for this phenomenon remains an enduring mystery and many questions remain, we argue that substantial theoretical progress has been made.Comment: 9 pages, 2 figures, Accepted versio

Probing and controlling fluorescence blinking of single semiconductor nanoparticles

In this review we present an overview of the experimental and theoretical development on fluorescence intermittency (blinking) and the roles of electron transfer in semiconductor crystalline nanoparticles. Blinking is a very interesting phenomenon commonly observed in single molecule/particle experiments. Under continuous laser illumination, the fluorescence time trace of these single nanoparticles exhibit random light and dark periods. Since its first observation in the mid-1990s, this intriguing phenomenon has attracted wide attention among researchers from many disciplines. We will first present the historical background of the discovery and the observation of unusual inverse power-law dependence for the waiting time distributions of light and dark periods. Then, we will describe our theoretical modeling efforts to elucidate the causes for the power-law behavior, to probe the roles of electron transfer in blinking, and eventually to control blinking and to achieve complete suppression of the blinking, which is an annoying feature in many applications of quantum dots as light sources and fluorescence labels for biomedical imaging

Atomic Force Microscopy Study of Protein–Protein Interactions in the Cytochrome CYP11A1 (P450scc)-Containing Steroid Hydroxylase System

<p>Abstract</p> <p>Atomic force microscopy (AFM) and photon correlation spectroscopy (PCS) were used for monitoring of the procedure for cytochrome CYP11A1 monomerization in solution without phospholipids. It was shown that the incubation of 100 &#956;M CYP11A1 with 12% Emulgen 913 in 50 mM KP, pH 7.4, for 10 min at <it>T</it> = 22&#176;C leads to dissociation of hemoprotein aggregates to monomers with the monomerization degree of (82 &#177; 4)%. Following the monomerization procedure, CYP11A1 remained functionally active. AFM was employed to detect and visualize the isolated proteins as well as complexes formed between the components of the cytochrome CYP11A1-dependent steroid hydroxylase system. Both Ad and AdR were present in solution as monomers. The typical heights of the monomeric AdR, Ad and CYP11A1 images were measured by AFM and were found to correspond to the sizes 1.6 &#177; 0.2 nm, 1.0 &#177; 0.2 nm and 1.8 &#177; 0.2 nm, respectively. The binary Ad/AdR and AdR/CYP11A1_mon complexes with the heights 2.2 &#177; 0.2 nm and 2.8 &#177; 0.2 nm, respectively, were registered by use of AFM. The Ad/CYP11A1_mon complex formation reaction was kinetically characterized based on optical biosensor data. In addition, the ternary AdR/Ad/CYP11A1 complexes with a typical height of 4 &#177; 1 nm were AFM registered.</p

Detection of hepatitis C virus core protein in serum by atomic force microscopy combined with&nbsp;mass spectrometry

Yuri D Ivanov,1 Anna L Kaysheva,1,2 Pavel A Frantsuzov,1 Tatyana O Pleshakova,1 Nikolay V Krohin,1 Alexander A Izotov,1 Ivan D Shumov,1 Vasiliy F Uchaikin,1 Vladimir A Konev,1 Vadim S Ziborov,1 Alexander I Archakov11Institute of Biomedical Chemistry, 2PostgenTech Ltd, Moscow, RussiaAbstract: A method for detection and identification of core antigen of hepatitis C virus (HCVcoreAg)-containing particles in the serum was proposed, with due account taken of the interactions of proteotypic peptides with Na+, K+, and Cl- ions. The method is based on a combination of reversible biospecific atomic force microscopy (AFM)-fishing and mass spectrometry (MS). AFM-fishing enables concentration, detection, and counting of protein complexes captured on the AFM chip surface, with their subsequent MS identification. Biospecific AFM-fishing of HCVcoreAg-containing particles from serum samples was carried out using AFM chips with immobilized antibodies against HCVcoreAg (HCVcoreAgim). Formation of complexes between anti-HCVcoreAgim and HCVcoreAg-containing particles on the AFM chip surface during the fishing process was demonstrated. These complexes were registered and counted by AFM. Further MS analysis allowed reliable identification of HCVcoreAg within the complexes formed on the AFM chip surface. It was shown that MS data processing, with account taken of the interactions between HCVcoreAg peptides and Na+, K+ cations, and Cl- anions, allows an increase in the number of peptides identified.Keywords: hepatitis C virus, molecular detector, biospecific fishin

Correlated fluorescence blinking in two-dimensional semiconductor heterostructures

‘Blinking’, or ‘fluorescence intermittency’, refers to a random switching between ‘ON’ (bright) and ‘OFF’ (dark) states of an emitter; it has been studied widely in zero-dimensional quantum dots1 and molecules2, 3, and scarcely in one-dimensional systems4, 5. A generally accepted mechanism for blinking in quantum dots involves random switching between neutral and charged states6, 7 (or is accompanied by fluctuations in charge-carrier traps8), which substantially alters the dynamics of radiative and non-radiative decay. Here, we uncover a new type of blinking effect in vertically stacked, two-dimensional semiconductor heterostructures9, which consist of two distinct monolayers of transition metal dichalcogenides (TMDs) that are weakly coupled by van der Waals forces. Unlike zero-dimensional or one-dimensional systems, two-dimensional TMD heterostructures show a correlated blinking effect, comprising randomly switching bright, neutral and dark states. Fluorescence cross-correlation spectroscopy analyses show that a bright state occurring in one monolayer will simultaneously lead to a dark state in the other monolayer, owing to an intermittent interlayer carrier-transfer process. Our findings suggest that bilayer van der Waals heterostructures provide unique platforms for the study of charge-transfer dynamics and non-equilibrium-state physics, and could see application as correlated light emitters in quantum technology.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore