Radiative decay engineering 6: Fluorescence on one-dimensional photonic crystals

During the past decade the interactions of fluorophores with metallic particles and surfaces has become an active area of research. These near-field interactions of fluorophores with surface plasmons have resulted in increased brightness and directional emission. However, using metals has some disadvantages such as quenching at short fluorophore–metal distances and increased rates of energy dissipation due to lossy metals. These unfavorable effects are not expected in dielectrics. In this article, we describe the interactions of fluorophores with one-dimensional (1D) photonic crystals (PCs), which have alternating layers of dielectrics with dimensions that create a photonic band gap (PBG). Freely propagating light at the PBG wavelength will be reflected. However, similar to metals, we show that fluorophores within near-field distances of the 1DPC interacts with the structure. Our results demonstrate that these fluorophores can interact with both internal modes and Bloch surface waves (BSWs) of the 1DPC. For fluorophores on the surface of the 1DPC, the emission dominantly occurs through the 1DPC and into the substrate. We refer to these two phenomena together as Bragg grating-coupled emission (BGCE). Here we describe our preliminary results on BGCE. 1DPCs are simple to fabricate and can be handled and reused without damage. We believe that BGCE provides opportunities for new formats for fluorescence detection and sensing.     

Brilliant camouflage: photonic crystals in the diamond weevil, Entimus imperialis

The neotropical diamond weevil, Entimus imperialis, is marked by rows of brilliant spots on the overall black elytra. The spots are concave pits with intricate patterns of structural-coloured scales, consisting of large domains of three-dimensional photonic crystals that have a diamond-type structure. Reflectance spectra measured from individual scale domains perfectly match model spectra, calculated with anatomical data and finite-difference time-domain methods. The reflections of single domains are extremely directional (observed with a point source less than 5°), but the special arrangement of the scales in the concave pits significantly broadens the angular distribution of the reflections. The resulting virtually angle-independent green coloration of the weevil closely approximates the colour of a foliaceous background. While the close-distance colourful shininess of E. imperialis may facilitate intersexual recognition, the diffuse green reflectance of the elytra when seen at long-distance provides cryptic camouflage.     

Statoliths in Phycomyces: characterization of octahedral protein crystals

To identify the molecular mechanisms of gravitropism in the fungus Phycomyces blakesleeanus we determined several biochemical and physical parameters of paracrystalline protein bodies, so-called octahedral crystals. The crystals, which are present throughout the central vacuoles of the sporangiophore, function as statoliths (Schimek et al., 1999a,b). They possess an average volume of 9.96 microm(3) and a specific mass of 1.26 g cm(-3). SDS-PAGE of purified crystals shows three major proteins with relative molecular masses of 16, 46.5, and 55 kDa. These proteins are absent in gravitropism mutants which lack the crystals. Phototropism mutants (genotype mad) which are graviresponsive (class 1) and those which are defective in gravitropism (class 2) contain the crystals and the three associated proteins. Absorption spectra of isolated crystals and in situ absorption spectra of growing zones indicate the presence of chromophores, probably oxidized and reduced flavins. The flavin nature of the chromophores is also indicated by their fluorescence properties. It appears likely that the chromophores represent an essential part of the statoliths and thus the gravitropic transduction chain.     

Spontaneous emission of semiconductor quantum dots in inverse opal SiO2 photonic crystals at different temperatures

The photoluminescence (PL) characteristics of CdSe quantum dots (QDs) infiltrated into inverse opal SiO₂ photonic crystals (PCs) are systemically studied. The special porous structure of inverse opal PCs enhanced the thermal exchange rate between the CdSe QDs and their surrounding environment. Finally, inverse opal SiO₂ PCs suppressed the nonlinear PL enhancement of CdSe QDs in PCs excited by a continuum laser and effectively modulated the PL characteristics of CdSe QDs in PCs at high temperatures in comparison with that of CdSe QDs out of PCs. The final results are of benefit in further understanding the role of inverse opal PCs on the PL characteristics of QDs. Copyright © 2015 John Wiley & Sons, Ltd.     

Highly effective protein detection for avidin-biotin system based on colloidal photonic crystals enhanced fluoroimmunoassay

There has been immense interest in both instruments and methods to enhance fluorescence signal and achieve highly sensitive fluoroimmunoassay (FIA). In this paper, we present a facile, low-cost and general method of biotinylated colloidal photonic crystal (PC) to improve the FIA of avidin (avidin FIA). The fluorescence signal intensity of the avidin FIA on the colloidal PC can be enhanced over two orders of magnitude relative to the control sample, attributed to the large surface area, resonance field and coherent scattering effect of the colloidal PC. The detection limit is shrunk to 1/69 of that of the control sample. Furthermore, the signal to interference ratio (S/I ratio) is increased because the band-edge induced fluorescence enhancement is wavelength-selective. The interference fluorescence does not go up proportionally while the signal is significantly enhanced by the colloidal PCs. It is believed that the colloidal PC modified with biotin can act as an effective material for a general and sensitive fluoroimmunoassay.     

Biochemical characterization of endogenously formed eosinophilic crystals in the lungs of mice

Crystals seldom form spontaneously within tissues of mammals, except in the urinary tract or in association with eosinophil-rich diseases in humans (Charcot-Leyden crystals). Endogenously formed eosinophilic crystals have been reported in respiratory tract and other tissues of several strains of mice, but the biochemical characterization of these crystals has not been reported. In this study, eosinophilic crystal formation was examined in homozygous C57BL/6J viable motheaten mice, lung-specific surfactant apoprotein C promoter/soluble human tumor necrosis factor p75 receptor type II fusion protein transgenic mice (C57BL/6NTac x Sv/129), and CD40L-deficient mice with spontaneous Pneumocystis carinii infection. In viable motheaten but not wild type mice, rapidly developing crystals represented a major feature of the fatal lung injury induced by macrophage dysregulation. Conversely, eosinophilic crystals did not form until 4-8 months of age in transgenic and CD40L-deficient mice and were present in 10-30% of age-matched wild type controls. Mass spectrometry analysis of proteins from bronchoalveolar lavage fluid identified the crystals as Ym1, sometimes referred to as T-lymphocyte-derived eosinophil chemotactic factor. The Ym1 sequence was homologous to chitinase, and enzymatic assays indicated a 3-5-fold increase in chitinase activity compared with control mice. Intracellular and extracellular crystals associated with epithelial damage suggested that the crystals may contribute to lung inflammation through mechanical damage and enzymatic degradation.     

Beta-bungarotoxin. Preparation and characterization of crystals suitable for structural analysis

Phospholipases in some snake venoms are potent neurotoxins that target their enzymatic action to the synaptic membrane. One of these is the heterodimeric neurotoxin, beta-bungarotoxin, which binds with a protease inhibitor-like subunit to a presynaptic potassium channel and then blocks neurotransmission with a second subunit that has phospholipase A2 activity. We have prepared and characterized well ordered crystals of the most toxic beta-bungarotoxin isoform, beta 1-bungarotoxin. The crystals are monoclinic, space group C2, with unit cell parameters: a = 176.5 A, b = 39.3 A, c = 92.7 A, and beta = 114.8 degrees. Rotation-function analysis of the Patterson function, as calculated from a 2.3-A data set, reveals an asymmetric unit composed of four heterodimers. These heterodimers appear to be associated as two crystallographically distinct (AB)4 tetramers, each having dihedral D2 symmetry. The two are positioned with equivalent molecular 2-fold axes coincident with crystallographic dyads, but rotated by 55 degrees relative to one another. X-ray analysis of these crystals will permit direct visualization of the specific structural motifs and chemical features that underlie phospholipase neurotoxicity.     

Light and myopic refraction in children.

Studies over many years, carried out in different climatic zones of the country, were focussed on the investigation of the role of light in the prophylaxis of development of near-sightedness. It has been found that not only the accommodation reflex but also the pupillary reflex play a role in the enhancement of the optic power of the eye. A scheme of interaction of the mentioned reflexes depending on the level of visible radiation was presented. Provision of optimum illumination is one of the basic conditions for the prevention of eye fatigue and development of myopia.     

Detection and characterization of merohedral twinning in crystals of oxalyl-coenzyme A decarboxylase from Oxalobacter formigenes

Oxalyl-coenzyme A decarboxylase is a thiamin diphosphate dependent enzyme active in the catabolism of the highly toxic compound oxalate. The enzyme from Oxalobacter formigenes has been expressed as a recombinant protein in Escherichia coli, purified to homogeneity and crystallized. Two crystal forms were obtained, one showing poor diffraction and the other merohedral twinning. Crystals in the former category belong to the tetragonal space group P4(2)2(1)2. Data to 4.1 A resolution were collected from these crystals and an incomplete low resolution structure was initially determined by molecular replacement. Crystals in the latter category were obtained by co-crystallizing the protein with coenzyme A, thiamin diphosphate and Mg(2+)-ions. Data to 1.73 A were collected from one of these crystals with apparent point group 622. The crystal was found to be heavily twinned, and a twin ratio of 0.43 was estimated consistently by different established methods. The true space group P3(1)21 was deduced, and a molecular replacement solution was obtained using the low resolution structure as template when searching in detwinned data.     

Capillary isoelectric focusing coupled with dynamic imaging detection: A one-dimensional separation for two-dimensional protein characterization

Here, we devised a novel approach for two-dimensional (2D) protein characterization using a single one-dimensional separation followed by a second characterization in the same instrument. The approach combines capillary isoelectric focusing (CIEF), which separates proteins according to pI, with dynamic imaging detection, which permits monitoring of protein diffusion in real time and thereby allows estimation of molecular weight from diffusion coefficient. Compared with classical 2D gel electrophoresis, the approach provided several significant advantages including speed and ease in operation and automation, while yielding comparable accuracy. The approach was applicable for protein samples of low to moderate complexity.     

Preparation and initial characterization of crystals of the photoprotein aequorin from Aequorea victoria

Crystals of recombinant aequorin, the photoprotein from the jellyfish Aequorea victoria, have been grown from solutions containing sodium phosphate. The crystals grow as thin plates which diffract to beyond 2.2 Å resolution. The crystals are orthorhombic, space group P2₁2₁2 ₁; the axes are a = 89.1(1), b = 88.4(1), and c = 52.7(1) Å. The asymmetric unit contains two molecules. Crystals exposed to calcium ion solutions emit a steady glow and slowly deteriorate, confirming that the crystals consist of a charged, competent photoprotein. This represents the first successful preparation of single crystals of a photoprotein suitable for diffraction analysis. © 1993 Wiley-Liss, Inc.     

Biochemical characterization of crystals from the dermal iridophores of a chameleon Anolis carolinensis

The biochemical characteristics of dermal iridophore crystals from Anolis carolinensis have been investigated. Iridophores isolated by collangenase-hyaluronidase treatment were sonicated and their contents fractionated through sucrose. Pure iridophore crystals so obtained were examined by chromatography and electron diffraction. They were found to be pure hydrated crystalline form. The suggestion is made that the subcrystalline structure of this guanine does not play a role in color production by the iridophore.