Fluorescent Nanospheres Research Articles

Electrostatic layer-by-layer nanoassembly on biological microtemplates: platelets.

Platelets were coated with 78-nm silica nanoparticles, 45-nm fluorescent nanospheres, or bovine immunoglobulin G (IgG) through layer-by-layer assembly by alternate adsorption with oppositely charged linear polyions. Sequential deposition on platelet surfaces of cationic poly(dimethyldiallylammonium chloride) and anionic poly(styrene sulfonate) was followed by adsorption of nanoparticles or immunoglobulins. Nano-organized shells of platelets were demonstrated by transmission electron microscopy and fluorescence microscope images. Bovine IgG was assembled on platelets, as verified with anti-bovine IgG-FITC labeling. Localized targeting of anti-IgG shelled platelets was also demonstrated. An ability to coat blood cells with nano-organized shells can have applications in cardiovascular research and targeted drug delivery.

Simultaneous topographical and optical characterization of near-field optical aperture probes by way of imaging fluorescent nanospheres

We introduce a method for a simultaneous topographical and optical characterization of aperture probes for scanning near-field optical microscopy which is based on imaging of small sized fluorescent nanospheres (∼20 nm). The near-field optical fluorescence image of a nanosphere maps the intensity distribution of light at the end face of the probe whereas the simultaneously taken height image contains information about the aperture–sample distance. We used this method to control a mechanical modification of a near-field probe. By squeezing a probe repeatedly against a smooth glass substrate and thereby removing obstructing protrusions the aperture was brought as close as possible to the sample surface which resulted in a strongly improved optical resolution.

Nanoscale Clustering of RGD Peptides at Surfaces Using Comb Polymers. 2. Surface Segregation of Comb Polymers in Polylactide

Part 1 of these studies described poly(methyl methacrylate-r-polyoxyethylene methacrylate) P(MMA-r-POEM) comb polymers that present Arg-Gly-Asp (RGD) peptides at a surface in nanoscale clusters on a protein-resistant background for control of cell adhesion. Here in part 2, we examine surface segregation of these peptide-modified and unmodified comb polymers blended with polylactide (PLA) as a self-assembly approach suitable for surface modification of porous tissue engineering scaffolds. Multiple thermodynamic driving forces for surface enrichment of the comb polymer are exploited by annealing PLA/P(MMA-r-POEM) blends above the glass transition of the blend components but below the melting point of PLA, while in contact with water. Predictions of the interfacial composition profiles of annealed blends were made using a self-consistent field (SCF) lattice model. The calculations predict strong enrichment of the comb in the top approximately 50 A of blends, and organization of comb molecules in quasi-2D conformations at the interface, similar to the apparent structure of pure comb surfaces in contact with water described in part 1. Experimentally, PLA/comb blend surfaces were characterized by contact angle measurements, XPS, quantification of ligand-cluster surface density and stability by AFM and fluorescent nanosphere labeling, and cell attachment assays. These data were consistent with SCF predictions, showing significant enrichment of the comb at water-annealed surfaces and RGD cluster densities consistent with 2D conformations for comb molecules in the surface layer. Bulk miscibility of the blends was verified by dynamic rheometry, small-angle neutron scattering, DSC and X-ray diffraction studies. Surface segregation of combs provided tunable cell adhesion on PLA through surface-localized nanoclusters of RGD atop a cell-resistant background.

Spatially correlated fluorescence/AFM of individual nanosized particles and biomolecules.

Individual fluorescent polystyrene nanospheres (<10-100-nm diameter) and individual fluorescently labeled DNA molecules were dispersed on mica and analyzed using time-resolved fluorescence spectroscopy and atomic force microscopy (AFM). Spatial correlation of the fluorescence and AFM measurements was accomplished by (1) positioning a single fluorescent particle into the near diffraction-limited confocal excitation region of the optical microscope, (2) recording the time-resolved fluorescence emission, and (3) measuring the intensity of the excitation laser light scattered from the apex of an AFM probe tip and the AFM topography as a function of the lateral position of the tip relative to the sample substrate. The latter measurements resulted in concurrent high-resolution (approximately 10-20 nm laterally) images of the laser excitation profile of the confocal microscope and the topography of the sample. Superposition of these optical and topographical images enabled unambiguous identification of the sample topography residing within the excitation region of the optical microscope, facilitating the identification and structural characterization of the nanoparticle(s) or biomolecule(s) responsible for the fluorescence signal observed in step 2. These measurements also provided the lateral position of the particles relative to the laser excitation profile and the surrounding topography with nanometer-scale precision and the relationship between the spectroscopic and structural properties of the particles. Extension of these methods to the study of other types of nanostructured materials is discussed.

Nanoscale clustering of RGD peptides at surfaces using Comb polymers. 1. Synthesis and characterization of Comb thin films.

Theoretical and experimental studies were conducted to elucidate the structure and properties of amphiphilic comb polymer thin films presenting nanoscale clusters of Arg-Gly-Asp (RGD) peptides for control of cell adhesion on biomaterials. Combs comprised of a poly(methyl methacrylate) backbone and short poly(ethylene oxide) side chains were synthesized, and peptides were tethered to the side chain ends to create nanoscale peptide clusters. In thin films, comb polymers containing >or = 30 wt % six to nine unit PEO side chains completely resisted adhesion of a model fibroblast cell line in the presence of 7.5% serum over 24 h. These same polymers modified with RGD peptides elicited tunable cell adhesion when mixed with unmodified combs in varying proportion. A self-consistent field lattice model of the interface between comb polymer films and water predicts an organization of the top molecular layer of comb polymer with the backbone oriented parallel to the interface in quasi-two-dimensional confinement and hydrophilic side chains extended in a brushlike layer into solution. This picture of a quasi-2D configuration is consistent with the observed surface properties of comb films in water as well as measurements of the RGD cluster density on mixed comb surfaces using fluorescent nanosphere labeling of ligand clusters.

Photon-burst analysis in two-photon fluorescence excitation flow cytometry.

We studied the use of a dramatically reduced testing zone in combination with two-photon excitation and photon-burst analysis in high-throughput rare-event detection simulation using a modified flow cytometer. Two-photon excitation measurements were performed with a mode-locked titanium:sapphire laser. Fluorescence emission was measured with a photon-counting avalanche photodiode. Measured signal was analysed offline by autocorrelation and burst detection methods. Test samples were composed of full blood and orange fluorescent polystyrene nanospheres mixed in full blood. Results show that two-photon fluorescence excitation and time-correlation analysis provide a good signal-to-noise ratio for rare-event particle detection in a turbid sample environment.

Cholinergic And Non-Cholinergic Afferents Of The Caudolateral Parabrachial Nucleus: A Role In The Long-Term Enhancement Of Rapid Eye Movement Sleep

A single microinjection of the cholinergic agonist carbachol into the feline caudolateral parabrachial nucleus produces an immediate increase in state-independent ipsilateral ponto-geniculo-occipital waves, followed by a long-term rapid eye movement sleep enhancement lasting 7–10 days. Using retrogradely-transported fluorescent carbachol-conjugated nanospheres and choline acetyltransferase immunohistochemistry, afferent projections to this injection site for long-term rapid eye movement sleep enhancement were mapped and quantified. Six regions in the brain stem contained retrogradely-labelled cells: the raphe nuclei, locus coeruleus, laterodorsal tegmental nucleus, pedunculopontine tegmental nucleus, parabrachial nucleus, and the pontine reticular formation. The retrogradely-labelled (rhodamine+) cells in the pontine reticular formation and pedunculopontine tegmental nucleus contributed the predominant input to the parabrachial nucleus injection site (34.3 ± 5.3% and 28.4 ± 5.6%, respectively), compared to the laterodorsal tegmental nucleus (5.8 ± 3.8%), parabrachial nucleus (13.5 ± 3.1%), raphe nuclei (12.9 ± 2.7%), and locus coeruleus (5.1 ± 2.4%). By comparison with findings of afferent input to the induction site for short-latency rapid eye movement sleep in the anterodorsal pontine reticular formation, the parabrachial nucleus injection site is characterized by a similar proportion of afferents, except that the raphe nuclei were found to provide more than a two-fold greater input. Retrogradely-labelled neurons quantified in these nuclear regions consisted of 21.5% double-labelled (rhodamine+/choline acetyltransferase+) cholinergic and 78.5% noncholinergic (rhodamine+/choline acetyltransferase ) cells. The pedunculopontine tegmental nucleus contributed the predominant (51.7 ± 8.2%) cholinergic input, compared to laterodorsal tegmental nucleus (20.7 ± 10.2%), parabrachial nucleus (23.1 ± 7.5%), and pontine reticular formation (4.4± 2.1%). A comparative analysis of the total retrogradely-labelled cells within each nuclear region which were also double-labelled showed the highest proportion in the laterodorsal tegmental nucleus (76.2 ± 7.5%) compared to pedunculopontine tegmental nucleus (39.4 ± 3.6%), parabrachial nucleus (37.3 ± 2.8%), and pont±he reticular formation (3.2 ± 2.1%). These data indicate that while pedunculopontine tegmental nucleus and laterodorsal tegmental nucleus neurons exert a powerful cholinergic influence on the injection site for long-term rapid eye movement enhancement, a major component of the afferent circuitry is non-cholinergic. Since the non-cholinergic input includes contributions from the locus coeruleus and raphe nuclei, it is probable that the caudolateral parabrachial nucleus contains cholinergic and aminergic afferent systems that participate in the long-term enhancement of rapid eye movement sleep.

Embryonic Neurons Transplanted to Regions of Targeted Photolytic Cell Death in Adult Mouse Somatosensory Cortex Re-form Specific Callosal Projections

In the neocortex, the effectiveness of potential transplantation therapy for diseases involving neuronal loss may depend upon whether donor neurons can reestablish the precise long-distance projections that form the basis of sensory, motor, and cognitive function. During corticogenesis, the formation of these connections is affected by tropic factors, extracellular matrix, structural pathways, and developmental cell death. Previous studies demonstrated that embryonic neurons and multipotent neural precursors transplanted into neocortex of mice undergoing photolytically induced, synchronous, apoptotic neuronal degeneration selectively migrate into these regions, where they differentiate into pyramidal neurons and accept afferent synaptic input. The experiments presented here assess whether embryonic neurons transplanted into regions of somatosensory cortex undergoing targeted cell death differentiate further and develop long-distance axons and whether this outgrowth is target specific. Neocortical neurons from Gestational Day 17 mouse embryos were dissociated, prelabeled with fluorescent nanospheres and a lipophilic dye (DiI or PKH), and transplanted into adult mouse primary somatosensory cortex (S1) undergoing apoptotic degeneration of callosal projection neurons. Donor neurons selectively migrated into and differentiated within regions of targeted neuronal death in lamina II/III over a 2-week period, in agreement with our prior studies. To detect possible projections made by donor neurons 2, 4, 6, 8, or 10 weeks following transplantation, the retrogradely transported dye fluorogold (FG) was stereotaxically injected into contralateral S1, ipsilateral secondary somatosensory cortex (S2), or ipsilateral thalamus. Ten weeks following transplantation, 21 ± 5% of the labeled donor neurons were labeled by FG injections into contralateral S1, demonstrating that donor neurons sent projections to this distant area, the original target of host neurons undergoing photolytically induced cell death. No donor neurons were labeled with FG injections into ipsilateral S2 or thalamus, nearby targets of other subpopulations of neurons in S1. These data indicate that in the adult neocortex: (1) transplanted immature neurons are capable of extending long-distance projections between hemispheres through the mature white matter of the corpus callosum and (2) these projections are formed with specificity to replace projections by neurons undergoing synchronous degeneration. These experiments provide an experimental system with which to test factors affecting such outgrowth and connectivity. Taken together, these results suggest that the reconstruction and repair of cortical circuitry responsible for sensory, motor, or cognitive function may be possible in the mature neocortex, if donor neurons or precursor cells are provided with the correct combination of local and distant signals within an appropriately permissive host environment.

Targeted neocortical cell death in adult mice guides migration and differentiation of transplanted embryonic neurons

Local expression of cellular and molecular signals is required for normal neuronal migration and differentiation during neocortical development and during periods of plasticity in the adult brain. We have previously shown that neonatal and juvenile mice that induction of apoptotic degeneration in neocortical pyramidal neurons by targeted photolysis provides an altered environment that directs migration and differentiation of transplanted embryonic neurons. Here we employ the same paradigm in adult mice to test whether targeted photolysis induces the reexpression in the mature brain of developmental signals that control migration, differentiation and integration of embryonic neurons. We examined both the time course of migration and the morphologic and immunocytochemical differentiation of embryonic neurons transplanted into regions of targeted photolytic cell death. Pyramidal neurons in neocortical lamina II/III underwent photolytically induced apoptosis after retrograde incorporation of the photoactive chromophore chlorine e6 and transdural exposure to 674 nm near-infrared laser energy. Embryonic day 17 neocortical neurons were prelabeled with fluorescent nanospheres and the lipophilic dye PKH26, transplanted into regions of ongoing neuronal degeneration in adult mice, and examined histologically and immunocytochemically. Transplanted neurons began migration into regions of neuronal death within 3 d and differentiated into large pyramidal neurons similar to those degenerating. In contrast, neurons transplanted into intact cortex did not migrate, and they differentiate into small presumptive interneurons. Migration up to 430 microM in experimental mice was complete by 2 weeks; approximately 45% of the donor neurons migrated greater than 3 SDs beyond the mean for neurons transplanted into intact neocortex of age-matched adult hosts. Following migration, dendrites and axons of many donor neurons were properly oriented toward the pial surface and corpus callosum, indicating integration into the host parenchyma. Neurofilament and neuron-specific enolase staining further support appropriate differentiation and integration. These results indicate that signals guiding neuronal migration and differentiation in neocortex are reexpressed in adult mice well beyond the period of corticogenesis within regions of targeted photolytic cell death. Elucidating the molecular mechanisms underlying these events by comparison with adjacent unperturbed regions will contribute to efforts toward future therapeutic transplantation and control over endogenous plasticity.

Transplanted neocortical neurons migrate selectively into regions of neuronal degeneration produced by chromophore-targeted laser photolysis

Selective degeneration of neocortical callosal pyramidal neurons by noninvasive laser illumination was used for directed studies of neocortical transplantation, to test the hypothesis that transplanted embryonic neurons may seek to restore normal cytoarchitecture within an appropriately permissive local environment. At long wavelengths that penetrate through tissue without major absorption, photolysis can cause extremely selective degeneration to desired subpopulations of targeted neurons in vivo (Macklis and Madison, 1991; Madison and Macklis, 1993). Cell death is geographically defined and slowly progressive, allowing control over the anatomical substrate for transplantation. Targeting occurs by retrograde incorporation of cytolytic chromophores that are activated by specific-wavelength light. Intermixed neurons, glia, axons, blood vessels, and connective tissue remain intact. Degeneration was effected within neocortical lamina II/III of neonatal mouse pups following targeting in utero or early postnatally with photoactive nanospheres. Total neuron density was reduced typically by 25-30% within defined areas, with approximately 60% loss of large projection neurons and no change in the number of small, presumptive interneurons. Embryonic day 17 neocortical cell suspensions, which included recently postmitotic neurons destined to form lamina II/III, were transplanted lateral to these regions of ongoing neuron degeneration in juvenile mice. Cellular injections spanned laminae II-V, to provide donor neurons with both lateral and laminar choice for possible migration and integration. Donor cells were labeled in vitro with unique fluorescent and electron-dense nanospheres that allowed distinct identification of donor cells at both light and electron microscopic levels. Control experiments included neocortical transplants into intact age-matched hosts, into hosts with kainic acid lesions to neocortex, or distant to the region of photolytic neuronal degeneration; embryonic cerebellar transplants to the regions of selective photolytic degeneration; and grafts of hypoosmotically lysed neocortical cells to lesioned regions. After survival times of 1 hr to 12 weeks, labeled neurons were identified morphologically and positions were digitized for qualitative and quantitative analysis of position and specificity of migration and cellular integration; electron microscopy was used to confirm further the donor identities of migrated neurons. Neurons placed near host zones of photolytic neuron degeneration migrated up to 780 microns specifically within these zones; approximately 44% of donor neurons migrated significantly beyond the injection site to enter these regions. Migration and integration did not occur in normal, unaffected deeper layers IV-VI of these experimental mice, or in the normal lamina II/III bordering the transplantation site on the side opposite the neuron-deficient region. Control grafts of all five types revealed only minimal local spread without laminar preference.(ABSTRACT TRUNCATED AT 400 WORDS)

Further histological evidence of the gastrointestinal absorption of polystyrene nanospheres in the rat

Further histological evidence of the oral absorption of fluorescent polystyrene nanospheres is presented. Fluorescent polystyrene microspheres of diameter ranging from 50 nm to 3 μm were administered daily for 10 days by oral gavage (2.5% w/v; 12.5 mg kg −1) to female Sprague Dawley rats. All except the 3 μm non-ionic fluorescent polystyrene nanospheres and microspheres were concentrated in the serosal layer of Peyer's patches and could be seen thereafter traversing the mesentery lymph vessels. The migrating particles were subsequently found in the lymph nodes and liver tissues. No particles were found in the lung or heart. We have previously shown that uptake and translocation is size dependent, increasing with decreasing size. Special emphasis is placed on the fate of the smallest particles investigated — 50 nm non-ionic polystyrene microspheres — which were seen in kidney and were also present in the villi and GI crypts.

The effect of increased intraocular pressure on the endothelium of Schlemm's canal

All aqueous humor draining through the conventional outflow pathway must cross the endothelium of Schlemm's canal (SC), likely by passing through micron-sized transendothelial pores. SC pores are non-uniformly distributed along the inner wall endothelium, but it is unclear how the distribution of pores relates to the non-uniform or segmental distribution of aqueous humor outflow through the trabecular meshwork. It is hypothesized that regions in the juxtacanalicular tissue (JCT) with higher local outflow should coincide with regions of greater inner wall pore density compared to JCT regions with lower outflow.Three pairs of non-glaucomatous human donor eyes were perfused at 8 mmHg with fluorescent tracer nanospheres to decorate local patterns of outflow segmentation through the JCT. The inner wall was stained for CD31 and/or vimentin and imaged en face using confocal and scanning electron microscopy (SEM). Confocal and SEM images were spatially registered to examine the spatial relationship between inner wall pore density and tracer intensity in the underlying JCT. For each eye, tracer intensity, pore density (n) and pore diameter (D) (for both transcellular “I” and paracellular “B” pores) were measured in 4–7 regions of interest (ROIs; 50 × 150 μm each). Analysis of covariance was used to examine the relationship between tracer intensity and pore density, as well as the relationship between tracer intensity and three pore metrics (nD, nD2 and nD3) that represent the local hydraulic conductivity of the outflow pathway as predicted by various hydrodynamic models.Tracer intensity in the JCT correlated positively with local pore density when considering total pores (p = 0.044) and paracellular B pores on their own (p = 0.016), but not transcellular I-pores on their own (p = 0.54). Local hydraulic conductivity as predicted by the three hydrodynamic models all showed a significant positive correlation with tracer intensity when considering total pores and B-pores (p < 0.0015 and p < 10−4) but not I-pores (p > 0.38).These data suggest that aqueous humor passes through micron-sized pores in the inner wall endothelium of SC. Paracellular B-pores appear to have a dominant contribution towards transendothelial filtration across the inner wall relative to transcellular I-pores. Impaired pore formation, as previously described in glaucomatous SC cells, may thereby contribute to greater outflow heterogeneity, outflow obstruction, and IOP elevation in glaucoma.