Subdiffraction fluorescence imaging of biomolecular structure and distributions with quantum dots

We introduce semiconductor quantum dot-based fluorescence imaging with approximately 2-fold increased optical resolution in three dimensions as a method that allows both studying cellular structures and spatial organization of biomolecules in membranes and subcellular organelles. Target biomolecules are labelled with quantum dots via immunocytochemistry. The resolution enhancement is achieved by three-photon absorption of quantum dots and subsequent fluorescence emission from a higher-order excitonic state. Different from conventional multiphoton microscopy, this approach can be realized on any confocal microscope without the need for pulsed excitation light. We demonstrate quantum dot triexciton imaging (QDTI) of the microtubule network of U373 cells, 3D imaging of TNF receptor 2 on the plasma membrane of HeLa cells, and multicolor 3D imaging of mitochondrial cytochrome c oxidase and actin in COS-7 cells.

Agonist-dependent internalization of D2 receptors: imaging quantification by confocal microscopy

In positron emission tomography and single photon emission computed tomography studies using D2 dopamine (DA) receptor radiotracers, a decrease in radiotracer binding potential (BP) is usually interpreted in terms of increased competition with synaptic DA. However, some data suggest that this signal may also reflect agonist (DA)-induced increases in D2 receptor (D2R) internalization, a process which would presumably also decrease the population of receptors available for binding to hydrophilic radioligands. To advance interpretation of alterations in D2 radiotracer BP, direct methods of assessment of D2R internalization are required. Here, we describe a confocal microscopy-based approach for the quantification of agonist-dependent receptor internalization. The method relies upon double-labeling of the receptors with antibodies directed against intracellular as well as extracellular epitopes. Following agonist stimulation, DA D2R internalization was quantified by differentiating, in optical cell sections, the signal due to the staining of the extracellular from intracellular epitopes of D2Rs. Receptor internalization was increased in the presence of the D2 agonists DA and bromocriptine, but not the D1 agonist SKF38393. Pretreatment with either the D2 antagonist sulpiride, or inhibitors of internalization (phenylarsine oxide and high molarity sucrose), blocked D2-agonist induced receptor internalization, thus validating this method in vitro. This approach therefore provides a direct and streamlined methodology for investigating the pharmacological and mechanistic aspects of D2R internalization, and should inform the interpretation of results from in vivo receptor imaging studies.

Host-symbiont interactions of the primary endosymbiont of human head and body lice

The first mycetome was discovered more than 340 yr ago in the human louse. Despite the remarkable biology and medical and social importance of human lice, its primary endosymbiont has eluded identification and characterization. Here, we report the host-symbiont interaction of the mycetomic bacterium of the head louse Pediculus humanus capitis and the body louse P. h. humanus. The endosymbiont represents a new bacterial lineage in the -Proteobacteria. Its closest sequenced relative is Arsenophonus nasoniae, from which it differs by more than 10%. A. nasoniae is a male-killing endosymbiont of jewel wasps. Using microdissection and multiphoton confocal microscopy, we show the remarkable interaction of this bacterium with its host. This endosymbiont is unique because it occupies sequentially four different mycetomes during the development of its host, undergoes three cycles of proliferation, changes in length from 2–4 µm to more than 100 µm, and has two extracellular migrations, during one of which the endosymbionts have to outrun its host’s immune cells. The host and its symbiont have evolved one of the most complex interactions: two provisional or transitory mycetomes, a main mycetome and a paired filial mycetome. Despite the close relatedness of body and head lice, differences are present in the mycetomic provisioning and the immunological response.—Perotti, M. A., Allen, J. M., Reed, D. L., Braig, H. R. Host-symbiont interactions of the primary endosymbiont of human head and body lice.

Time course of gag protein assembly in HIV-1-infected cells: a study by immunoelectron microscopy

Recent biochemical studies have identified high molecular complexes of the HIV Gag precursor in the cytosol of infected cells. Using immunoelectron microscopy we studied the time course of the synthesis and assembly of a HIV Gag precursor protein (pr55gag) in Sf9 cells infected with recombinant baculovirus expressing the HIV gag gene. We also immunolabeled for pr55gag human T4 cells acutely or chronically infected with HIV-1. In Sf9 cells, the time course study showed that the first Gag protein appeared in the cytoplasm at 28-30 h p.i. and that budding started 6-8 h later. Colloidal gold particles, used to visualize the Gag protein, were first scattered randomly throughout the cytoplasm, but soon clusters representing 100 to 1000 copies of pr55gag were also observed. By contrast, in cells with budding or released virus-like particles the cytoplasm was virtually free of gold particles while the released virus-like particles were heavily labeled. Statistical analysis showed that between 80 and 90% of the gold particles in the cytoplasm were seen as singles, as doublets, or in small groups of up to five particles probably representing small oligomers. Clusters of gold particles were also observed in acutely infected lymphocytes as well as in multinuclear cells of chronically infected cultures of T4 cells. In a few cases small aggregates of gold particles were found in the nuclei of T4 lymphocytes. These observations suggest that the Gag polyprotein forms small oligomers in the cytoplasm of expressing cells but that assembly into multimeric complexes takes place predominantly at the plasma membrane. Large accumulations of Gag protein in the cytoplasm may represent misfolded molecules destined for degradation.

Crystallization in poly(L-lactide)-b-poly(epsilon-caprolactone) double crystalline diblock copolymers: a study using X-ray scattering, differential scanning calorimetry, and polarized optical microscopy

The crystallization of well-defined poly(L-lactide)-b-poly(epsilon-caprolactone) diblock copolymers, PLLA-b-PCL, was investigated by time-resolved X-ray techniques, polarized optical microscopy (POM), and differential scanning calorimetry (DSC). Two compositions were studied that contained 44 and 60 wt % poly(L-lactide), PLLA (they are referred to as (L44C5614)-C-11 and (L60C409)-C-12, respectively, with the molecular weight of each block in kg/mol as superscript). The copolymers were found to be initially miscible in the melt according to small-angle X-ray scattering measurements (SAXS). Their thermal behavior was also indicative of samples whose crystallization proceeds from a mixed melt. Sequential isothermal crystallization from the melt at 100 degreesC (for 30 min) and then at 30 degreesC (for 15 min) was measured. At 100 degreesC only the PLLA block is capable of crystallization, and its crystallization kinetics was followed by both WAXS and DSC; comparable results were obtained that indicated an instantaneous nucleation with three-dimensional superstructures (Avrami index of approximately 3). The spherulitic nature of the superstructure was confirmed by POM. When the temperature was decreased to 30 degreesC, the PCL block was able to crystallize within the PLLA negative spherulites (with an Avrami index of 2, as opposed to 3 in homo-PCL), and its crystallization rate was much slower than an equivalent homo-PCL. Time-resolved SAXS experiments in (L60C409)-C-12 revealed an initial melt mixed morphology at 165 degreesC that upon cooling transformed into a transient microphase-separated lamellar structure prior to crystallization at 100 degreesC.

Comparative characterisation by atomic force microscopy and ellipsometry of soft and solid thin films

Ellipsometry and atomic force microscopy (AFM) were used to study the film thickness and the surface roughness of both 'soft' and solid thin films. 'Soft' polymer thin films of polystyrene and poly(styrene-ethylene/butylene-styrene) block copolymer were prepared by spin-coating onto planar silicon wafers. Ellipsometric parameters were fitted by the Cauchy approach using a two-layer model with planar boundaries between the layers. The smooth surfaces of the prepared polymer films were confirmed by AFM. There is good agreement between AFM and ellipsometry in the 80-130 nm thickness range. Semiconductor surfaces (Si) obtained by anisotropic chemical etching were investigated as an example of a randomly rough surface. To define roughness parameters by ellipsometry, the top rough layers were treated as thin films according to the Bruggeman effective medium approximation (BEMA). Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased etching time, although AFM results depend on the used window size. The combined use of both methods appears to offer the most comprehensive route to quantitative surface roughness characterisation of solid films. Copyright (c) 2007 John Wiley & Sons, Ltd.

Use of thermography and fibre optics microscopy for the evaluation of railway structures in the Athens Metro in Greece (Invited Paper)

Rolling Contact Fatigue (RCF) is one of the main issues that concern, at least initially, the head of the railway; progressively they can be of very high importance as they can propagate inside the material with the risk of damaging the railway. In this work, two different non-destructive techniques, infrared thermography (IRT) and fibre optics microscopy (FOM), were used in the inspection of railways for the tracing of defects and deterioration signs. In the first instance, two different approaches (dynamic and pulsed thermography) were used, whilst in the case of FOM, microscopic characterisation of the railway heads and classification of the deterioration -- damage on the railways according to the UIC (International Union of Railways) code, took place. Results from both techniques are presented and discussed.

Surface properties and locations of gluten proteins and lipids revealed using confocal scanning laser microscopy in bread dough

Surface properties of gluten proteins were measured in a dilation test and in compression and expansion tests. The results showed that monomeric gliadin was highly surface active, but polymer glutenin had almost no surface activity. The locations of those proteins in bread dough were investigated using confocal scanning laser microscopy and compared with polar and nonpolar lipids. Added gluten proteins participated in the formation of the film or the matrix, surrounding and separating individual gas cells in bread dough. Gliadin was found in the bulk of dough and gas 'cell walls'. Glutenin was found only in the bulk dough. Polar lipids were present in the protein matrix and in gas 'cell walls', as well as at the surface of some particles, which appeared to be starch granules. However, nonpolar lipid mainly occur-red on the surface of particles, which may be starch granules and small lipid droplets. It is suggested that the locations of gluten proteins in bread dough depends on their surface properties. Polar lipid participates the formation of gluten protein matrix and gas 'cell walls'. Nonpolar lipids may have an effect on the rheological properties by associating with starch granule surfaces and may form lipid droplets. (C) 2004 Published by Elsevier Ltd.

A novel technique for differentiation of proteins in the development of acid gel structure from control and heat treated milk using confocal scanning laser microscopy

The incorporation of caseins and whey proteins into acid gels produced from unheated and heat treated skimmed milk was studied by confocal scanning laser microscopy (CSLM) using fluorescent labelled proteins. Bovine casein micelles were labelled using Alexa Fluor 594, while whey proteins were labelled using Alexa Fluor 488. Samples of the labelled protein solutions were introduced into aliquots of pasteurised skim milk, and skim milk heated to 90 degrees C for 2 min and 95 degrees C for 8 min. The milk was acidified at 40 degrees C to a final pH of 4.4 using 20 g gluconodelta-lactone/l (GDL). The formation of gels was observed with CSLM at two wavelengths (488 nm and 594 nm), and also by visual and rheological methods. In the control milk, as pH decreased distinct casein aggregates appeared, and as further pH reduction occurred, the whey proteins could be seen to coat the casein aggregates. With the heated milks, the gel structure was formed of continuous strands consisting of both casein and whey protein. The formation of the gel network was correlated with an increase in the elastic modulus for all three treatments, in relation to the severity of heat treatment. This model system allows the separate observation of the caseins and whey proteins, and the study of the interactions between the two protein fractions during the formation of the acid gel structure, on a real-time basis. The system could therefore be a valuable tool in the study of structure formation in yoghurt and other dairy protein systems.

Agonist-dependent internalization of D2 receptors: Imaging quantification by confocal microscopy

In positron emission tomography and single photon emission computed tomography studies using D2 dopamine (DA) receptor radiotracers, a decrease in radiotracer binding potential (BP) is usually interpreted in terms of increased competition with synaptic DA. However, some data suggest that this signal may also reflect agonist (DA)-induced increases in D2 receptor (D2R) internalization, a process which would presumably also decrease the population of receptors available for binding to hydrophilic radioligands. To advance interpretation of alterations in D2 radiotracer BP, direct methods of assessment of D2R internalization are required. Here, we describe a confocal microscopy-based approach for the quantification of agonist-dependent receptor internalization. The method relies upon double-labeling of the receptors with antibodies directed against intracellular as well as extracellular epitopes. Following agonist stimulation, DA D2R internalization was quantified by differentiating, in optical cell sections, the signal due to the staining of the extracellular from intracellular epitopes of D2Rs. Receptor internalization was increased in the presence of the D2 agonists DA and bromocriptine, but not the D1 agonist SKF38393. Pretreatment with either the D2 antagonist sulpiride, or inhibitors of internalization (phenylarsine oxide and high molarity sucrose), blocked D2-agonist induced receptor internalization, thus validating this method in vitro. This approach therefore provides a direct and streamlined methodology for investigating the pharmacological and mechanistic aspects of D2R internalization, and should inform the interpretation of results from in vivo receptor imaging studies.

Surface structure of thin asymmetric PS-b-PMMA diblock copolymers investigated by atomic force microscopy

Asymmetric poly(styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymers of molecular weight M-n = 29,700g mol(-1) (M-PS = 9300 g mol(-1) M-PMMA = 20,100 g mol(-1), PD = 1.15, chi(PS) = 0.323, chi(PMMA) = 0.677) and M-n = 63,900 g mol(-1) (M-PS = 50,500 g mol(-1), M-PMMA = 13,400 g mol(-1), PD = 1.18, chi(PS) = 0.790, chi(PMMA) = 0.210) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Atomic force microscopy (AFM) was used to investigate the surface structure of thin films, prepared by spin-coating the diblock copolymers on a silicon substrate. We show that the nanostructure of the diblock copolymer depends on the molecular weight and volume fraction of the diblock copolymers. We observed a perpendicular lamellar structure for the high molar mass sample and a hexagonal-packed cylindrical patterning for the lower molar mass one. Small-angle X-ray scattering investigation of these samples without annealing did not reveal any ordered structure. Annealing of PS-b-PMMA samples at 160 degrees C for 24 h led to a change in surface structure.

Direct visualisation of lipid bilayer cubic phases using Atomic Force Microscopy

Inverse bicontinuous cubic (Q(II)) phases are nanostructured materials formed by lipid self-assembly. We have successfully imaged thin films of hydrated Q(II) phases from two different systems using AFM. The images show periodic arrays of water channels with spacing and symmetry consistent with published SAXS data on the bulk materials.

Coupling thin layer electrochemistry with epifluorescence microscopy: an expedient way of investigating electrofluorochromism of organic dyes

The first example of thin layer electrochemistry coupled to epifluorescence microscopy in the total internal reflectance mode is described and applied to the investigation of electrochemically modulated fluorescence of an organic dye (chloromethoxytetrazine) in solution. This technique allows to generate full redox switch of fluorescence when converting reversibly the dye into its anion radical, as well as to record the spectral features of the electrogenerated species. Recording simultaneously fluorescence intensity and lifetime along with coulombic charge as a function of the electrode potential will lead to a deep insight into the redox quenching mechanism.