Fluorescent Colloids Research Articles

DNA and DNAzyme-Mediated 2D Colloidal Assembly

DNA-mediated interactions present a significant opportunity for controlling colloidal self-assembly. Using microcontact printing to achieve spatial control of DNA-surface patterning and DNA-functionalized polystyrene colloids, we report that DNA hybridization can be utilized for sequence-specific reversible self-assembly of well-ordered 2D colloidal arrays. Two essential indicators of DNA-hybridization mediated assembly were confirmed: thermal reversibility and sequence specificity. The arrays melted at 50 degrees C and reassembled when introduced to fresh colloid suspension, and sequence specificity with <1% nonspecific binding was confirmed using fluorescent polystyrene colloids. The real-time assembly of the colloids onto the periodically patterned substrate was monitored by simple laser diffraction to obtain assembly kinetics. Maximum surface coverage of DNA-mediated assembly was determined to be 0.593 for DNA-functionalized 100 nm polystyrene colloids, and 90% of the assembly was complete after 6.25 h of hybridization in 50 mM NaCl Tris buffer. We also demonstrate that DNAzymes, catalytic DNA molecules, can be incorporated into the design, and in the presence of 10 microM Pb(2+), the hybridization-induced array assembly can be disrupted via DNAzyme activity.

Site-Specific Anchoring of a Flavonol Dye into Zeolite β Nanoparticles

Microporous zeolite nanoparticles have been used as a host for the confinement of 3-hydroxyflavone (3-OHF), leading to stable fluorescent colloids that may constitute a first step in the development of future biomarkers. Prior to the dye inclusion, the host physicochemical properties (porosity and crystalline structure) have been extensively studied. In particular, conditions for obtaining a template-free host have been established. It has been shown that standard calcination procedures, required to reveal the micropores, cannot be straighforward applied since they leave a non-negligible concentration of template residues in the host. Afterward, structural and chemical characterization, as well as simulation of 3-OHF-loaded zeolite β colloids enabled to determine the presence and location of [(3-OHF)Al] chelates in the zeolite micropores. Characterization of the dye loading by independent techniques involving elemental analysis, pore volume, and crystalline structure investigations highlighted the determi...

DNA-Mediated Phase Behavior of Microsphere Suspensions

We have constructed a phase diagram for DNA-modified microsphere suspensions based on experimental and theoretical studies. The system is comprised of 1 microm red fluorescent colloids functionalized with strands of an identical oligonucleotide sequence and 1 microm green fluorescent colloids functionalized with the complementary sequence. Keeping the suspension composition and temperature fixed, the phase behavior of colloidal mixtures was studied as a function of salt and oligonucleotide concentration. We observed a colloidal fluid phase of dispersed, single particles at low salt concentrations and low DNA densities. We attribute this colloidal fluid phase to unfavorable hybridization conditions. With increasing salt or hybridizing oligonucleotide concentrations, we observed phase transitions of fluid --> fluid + aggregates --> aggregates due to an increase in duplex affinity, duplex number, or both. Computational analysis assigns a 4 kBT attraction between pairs of complementary microspheres at the destabilizing fluid --> fluid + aggregates transition.

Single-Particle Colloid Tracking in Four Dimensions

Coating a close-packed fluorescent colloid monolayer with a nanometer-thick metal film followed by sonication in liquid produces modulated optical nanoprobes. The metal coating modulates the fluorescence as these structures rotate in suspension, enabling the use of these particles as probes to monitor both rotational and center-of-mass (translational) dynamics in complex environments. Here, we demonstrate methods to simultaneously measure two translational and two rotational degrees of freedom, with excellent agreement to theory. The capability to determine two angles of rotation opens several new avenues of future research.

Noninvasive Quantitative Measurement of Colloid Transport in Mesoscale Porous Media Using Time Lapse Fluorescence Imaging

We demonstrate noninvasive quantitative imaging of colloid and solute transport at millimeter to decimeter (meso-) scale. Ultraviolet (UV) excited fluorescent solute and colloid tracers were independently measured simultaneously during co-advection through saturated quartz sand. Pulse-input experiments were conducted at constant flow rates and ionic strengths 10(-3), 10(-2) and 10(-1) M NaCl. Tracers were 1.9 microm carboxylate latex microspheres and disodium fluorescein. Spatial moments analysis was used to quantify relative changes in mass distribution of the colloid and solute tracers over time. The solute advected through the sand at a constant velocity proportional to flow rate and was described well by a conservative transport model (CXTFIT). In unfavorable deposition conditions increasing ionic strength produced significant reduction in colloid center of mass transport velocity over time. Velocity trends correlated with the increasing fraction of colloid mass retained along the flowpath. Attachment efficiencies (defined by colloid filtration theory) calculated from nondestructive retained mass data were 0.013 +/- 0.03, 0.09 +/- 0.02, and 0.22 +/- 0.05 at 10(-3), 10(-2), and 10(-1) M ionic strength, respectively, which compared well with previously published data from breakthrough curves and destructive sampling. Mesoscale imaging of colloid mass dynamics can quantify key deposition and transport parameters based on noninvasive, nondestructive, spatially high-resolution data.

Rotational dynamics of colloidal spheres probed with fluorescence recovery after photobleaching.

We report a polarized fluorescence recovery after photobleaching (pFRAP) method to measure the rotational dynamics of fluorescent colloids over a wide dynamic range. The method is based on the polarization anisotropy in the fluorescence intensity, generated by bleaching of fluorescently labeled particles with an intense pulse of linearly polarized laser light. The rotational mobilities of the fluorescent particles can be extracted from the relaxation kinetics of the postbleach fluorescence polarization anisotropy. Our pFRAP setup has access to correlation times over a range of time scales from tens of microseconds to tens of seconds, and is highly sensitive, so very low concentrations of labeled particles can be probed. We present a detailed description of the theoretical background of pFRAP. The performance of the equipment is demonstrated for fluorescent colloidal silica spheres, dispersed in pure solvents as well as in fd-virus suspensions.

Novel fluorescent colloids as a DNA fluorescence probe.

Fluorescent perylene colloids in the 80-90 nm size range have been prepared by the reprecipitation method. These nanoparticles were modified by cetyltrimethylammonium bromide (CTAB) which inhibited their growth. The nanoparticles also readily interacted with DNA. The fluorescence emission was measured at lambda(ex)/ lambda(em)=400/565 nm. The fluorescence decrease of colloid-CTAB in aqueous solution was measured in the presence of nucleic acids. Under the optimum conditions, the ratio of fluorescence intensity in the absence and presence of nucleic acids was proportional to the concentration of nucleic acids over the range 0.02-5.1 micro g mL(-1) for FS (fish sperm) DNA or CT (calf thymus) DNA. The detection limits were 0.01 micro g mL(-1) for FS DNA and 0.012 micro g mL(-1) for CT DNA, respectively. Based on this approach, a new quantitative method for DNA assay is presented in this paper.

Light transmission technique for the evaluation of colloidal transport and dynamics in porous media.

Colloidal transport in porous media has been typically studied in column experiments from which data analysis was limited to the evaluation of effluent breakthrough curves and/or destructive sampling at the end of the experiments. The internal processes occur within a "black box", where direct observation is not possible and therefore are often poorly understood. In this paper, a nondestructive, noninvasive method is presented that allows for quantitative measurement of colloid distribution with unprecedented two-dimensional spatial and temporal resolution. This technique is well-suited to observing the effects of saturation transitions and physical heterogeneities on colloidal transport. The potential of this novel technique is explored by investigating the effect of particle size and concentration on flow dynamics under saturated and unsaturated conditions. In saturated-flow experiments, deviation from the classical advection-dispersion behavior is observed. In unsaturated systems, colloidal accumulation at the capillary fringe interface and a high deposition rate of microspheres to the unsaturated media are readily observed. The experimental system is limited to translucent porous media and fluorescent colloids and is only semiquantitative in variably saturated media; nevertheless, it holds great promise for elucidating many complex mechanisms that control or influence colloid transport in the subsurface.

Toward Larger Chemical Libraries: Encoding with Fluorescent Colloids in Combinatorial Chemistry

Chemical library technology plays a central role in research areas such as drug discovery and gene screening.1 The most powerful combinatorial library synthesis method is the iterative “split and mix” synthesis on insoluble microscopic beads.2 This technique is an efficient method for accessing all combinations of chosen monomers such as nucleic acids, amino acids, or sugars in a small number of reactions. Compound identification from such large pools of compounds, be it bound to resin (one compound per bead) or in solution, is achieved through covalent attachment of molecular tags to the beads3 or through iterative deconvolution technologies.4 Herein we introduce an encoding method that involves physically attaching fluorescent colloidal particles (“reporters”) to the surface of solid support beads during split and mix syntheses, to produce an information-rich, colored barcode that can be easily, rapidly, and inexpensively decoded using fluorescence microscopy. This “colloidal barcoding” technique eliminates the need for compatible tagging chemistry in conventional molecular tagging3 or optical encoding5 procedures and permits unambiguous identification of compounds in libraries of any size and type.

Lichen planus pemphigoides: Combination therapy with tetracycline and nicotinamide

It has been speculated that lichen planus pemphigoides (LPP) represents the coexistence of lichen planus (LP) and bullous pemphigoid (BP), a variant of LP, a chance coexistence of LP and another autoimmune bullous dermatitis (i.e., dermatitis herpetiformis), or an independent disease. 1-4 Sobel, Miller, and Shatin 4 suggested that destruction of the basement membrane zone (BMZ) in LP may reveal previously unexposed antigens that result in the formation of circulating antibodies. Mora, Nesbitt, and Brantley 1 suggested that linear deposits of immunoglobins and complement (similar to those found in BP) in LPP may actually be an early immunopathologic change in LP, occurring before the appearance of fluorescent colloid bodies.

Surface Character and Adsorbability to Air Bubbles of a Hydrocarbon-grown Yeast

Hydrophobicity and amounts of polar groups on the cell surface were determined by the use of fluorescent probe, colloid titration, and acid titration. Surface hydrophobicity of hydrocarbon-grown cells was about 7 times greater than that of glucose-grown cells of the same strain, while amounts of polar groups did not differ so much. Adsorption of cells to air bubbles was maximum at pH 3. Langmuir’s adsorption isotherm held for the adsorption. Affinity to air bubbles of hydrocarbon-grown cells was 1.8 times greater than that of glucose-grown cells, while the theoretical maximum amounts of cells to adsorb per unit area of bubbles were equal for the both cells.

PHYSICAL AND PHOTOCHEMICAL PROPERTIES OF A FLUORESCENT CHLOROPHYLL COLLOID

Abstract— A fluorescent colloid of chlorophyll a, of which some qualitative properties were noted by Krasnovsky and Brin(11), has been quantitatively characterized. The colloid is formed in neutral PO4 buffer containing 0 1 to 8.0% Tween 20, and is stable in darkness. The extinction coefficient is 7.8 × 104 1. mole cm‐1 at the red absorption peak (668 mμ), the yield of fluorescence is ˜ 0.25, and the yield of photoautooxidative bleaching is ˜ 2 times 10‐4. The colloid sensitizes the autooxidation of paratoluenediamine with a yield of ˜0.01 to ˜0.3 depending on light intensity and substrate concentration. The yield is independent of detergent and chlorophyll concentrations. In all respects—except the dependence of yield on illumination—the colloid appears to be physically and photochemically equivalent to dissolved chlorophyll, as known in dilute solutions in organic solvents. The light dependence—the yield is inversely proportional to the cube root of absorbed intensity—could be due to a bimolecular back reaction of a chlorophyll or substrate derivative.