λ/12 Super Resolution Achieved in Maskless Optical Projection Nanolithography for Efficient Cross-Scale Patterning.

The emerging demand for device miniaturization and integration prompts the patterning technique of micronano-cross-scale structures as an urgent desire. Lithography, as a sufficient patterning technique, has been playing an important role in achieving functional micronanoscale structures for decades. As a promising alternative, we have proposed and demonstrated the maskless optical projection nanolithography (MLOP-NL) technique for efficient cross-scale patterning. A minimum feature size of 32 nm, which is λ/12 super resolution breaking the optical diffraction limit, has been achieved by a single exposure. Furthermore, multiscale two-dimensional micronano-hybrid structures with the size over hundreds of micrometers and the precision at tens of nanometers have been fabricated by simply controlling the exposure conditions. The proposed MLOP-NL technique provides a powerful tool for achieving cross-scale patterning with both large-scale and precise configuration with high efficiency, which can be potentially used in the fabrication of multiscale integrated microsystems.

Cucurbit[7]uril-Carbazole Two-Photon Photoinitiators for the Fabrication of Biocompatible Three-Dimensional Hydrogel Scaffolds by Laser Direct Writing in Aqueous Solutions.

We have introduced a novel water-soluble two-photon photoinitiator based on the host-guest interaction between 3,6-bis[2-(1-methyl-pyridinium)vinyl]-9-pentyl-carbazole diiodide (BMVPC) and cucurbit[7]uril (CB7) because most of the commercial photoinitiators have poor two-photon initiating efficiency in aqueous solutions. The binding ratio of BMVPC and CB7 was determined as 1:1 by isothermal titration calorimetry and quantum chemical calculation. The formation of the host-guest complex increases the two-photon absorption cross-section about five times, and improves the water solubility required as the photoinitiator for hydrogel fabrication. The BMVPC-CB7 inclusion complex was used as the one-component photoinitiator, and the polyethylene glycol diacrylate with promising biocompatibility was used as the hydrogel monomer to form the aqueous-phase photoresist system applied to two-photon polymerization microfabrication. A relatively low laser threshold of 4.5 mW, a high fabricating resolution of 180 nm, and the true three-dimensional (3D) fabricating capability in the aqueous solution have been obtained by using the as-prepared photoresist system. Finally, 3D engineering hydrogel scaffold microstructures with low toxicity and good biocompatibility have been fabricated and cocultured with living HeLa cells, which demonstrates the potential for further application in tissue engineering.

Biocompatible Three-Dimensional Hydrogel Cell Scaffold Fabricated by Sodium Hyaluronate and Chitosan Assisted Two-Photon Polymerization.

The biocompatibility of the three-dimensional (3D) hydrogel cell scaffolds that sodium hyaluronate (SH) and carboxymethyl chitosan (Chitosan) has been investigated. The minimum processing threshold of 2.94 mW and the feature line width of 80 nm have been obtained by the two-photon polymerization (TPP) technology using the as-prepared biocompatible photoresist. Through tuning the contents of the cross-linker in the hydrogel, the mechanical property of 3D hydrogel scaffold can be optimized to ensure the stability and affinity of scaffold. Furthermore, we have fabricated the SH and Chitosan assisted 3D hydrogel cell scaffolds and investigated the biocompatibility. This study provides a facile method to develop 3D biocompatible hydrogel cell scaffold, which would open up new avenues for the potential application in tissue engineering.

Electrical and thermal properties of silver nanowire fabricated on a flexible substrate by two-beam laser direct writing for designing a thermometer.

Accurate knowledge of electrical conductivity and thermal conductivity temperature dependence plays a crucial role in the design of a thermometer. Here, by using a two-beam laser direct writing system, an individual silver nanowire (AgNW) with well-defined dimensions is fabricated on a polyethylene terephthalate (PET) substrate. The temperature dependence of the resistivity of the fabricated AgNW is measured ranging from 10 to 300 K, and fitted with the Bloch-Grüneisen formula. The residual resistivity ((1.62 ± 0.20) × 10-7 Ω m) of the AgNW is larger than that of the bulk material (1 × 10-11 Ω m). The electron-phonon coupling constant of the AgNW is (1.08 ± 0.13) × 10-7 Ω m, which is larger than that of the bulk silver (5.24 × 10-8 Ω m). Moreover, the Debye temperature of the AgNW is 199.30 K and is lower than that of the bulk silver (235 K). The Lorenz number of the fabricated AgNW is found to decrease as the temperature increases. Besides, the Lorenz number (2.66 × 10-7 W Ω K-2) is larger than the Sommerfeld value (2.44 × 10-8 W Ω K-2) at room temperature. The measurement results allow one to design a thermometer in the temperature range 40-300 K. The flexibility of the AgNW is also excellent, and the resistance increase of the AgNW is only 2.58% when the AgNW bending about 1000 times with a bending radius of 1 mm.

The Conductive Silver Nanowires Fabricated by Two-beam Laser Direct Writing on the Flexible Sheet.

Flexible electrically conductive nanowires are now a key component in the fields of flexible devices. The achievement of metal nanowire with good flexibility, conductivity, compact and smooth morphology is recognized as one critical milestone for the flexible devices. In this study, a two-beam laser direct writing system is designed to fabricate AgNW on PET sheet. The minimum width of the AgNW fabricated by this method is 187 ± 34 nm with the height of 84 ± 4 nm. We have investigated the electrical resistance under different voltages and the applicable voltage per meter range is determined to be less than 7.5 × 103 V/m for the fabricated AgNW. The flexibility of the AgNW is very excellent, since the resistance only increases 6.63% even after the stretched bending of 2000 times at such a small bending radius of 1.0 mm. The proposed two-beam laser direct writing is an efficient method to fabricate AgNW on the flexible sheet, which could be applied in flexible micro/nano devices.

Transition of lasing modes in polymeric opal photonic crystal resonating cavity.

We demonstrate the transition of lasing modes in the resonating cavity constructed by polystyrene opal photonic crystals and 7 wt. % tert-butyl Rhodamine B doped polymer film. Both single mode and multiple mode lasing emission are observed from the resonating cavity. The lasing threshold is determined to be 0.81 µJ/pulse for single mode lasing emission and 2.25 µJ/pulse for multiple mode lasing emission. The single mode lasing emission is attributed to photonic lasing resulting from the photonic bandgap effect of the opal photonic crystals, while the multiple mode lasing emission is assigned to random lasing due to the defects in the photonic crystals. The result would benefit the development of low threshold polymeric solid state photonic crystal lasers.

Carboxylated Nanodiamond: Aggregation Properties in Aqueous Dispersion System and Application in Living Cell Fluorescence Imaging.

Nanodiamond, which has a lattice defect, the energy band gap and good biocompatibility, is an ideal inorganic fluorescent imaging material for cells. However, the nanodiamond aggregation is not exactly suitable for cells' endocytosis if the size is too small or too big. Therefore, it has a profound meaning to modify the surface of nanodiamond and control the dispersion of nanodiamond aggregate. In this study, the surface of the detonated nanodiamond is modified into carboxylated nanodiamond by using the method of mixed acid oxidation. Then, the nanodiamond aggregates' dispersion in water is regulated by adjusting the pH, which is first discussed as a factor influencing the size of nanodiamond aggregation. This process further induces the corresponding change of the electrostatic force between nanoparticles, improves its applicability in the field of living cell fluorescence imaging.

Low threshold photonic crystal laser based on a Rhodamine dye doped high gain polymer.

We demonstrate low threshold lasing oscillation in a photonic crystal (PhC) laser by using tert-butyl Rhodamine B (t-Bu-RhB) doped gain media. Lactonic t-Bu-RhB is synthesized to improve doping concentration in polymethylmethacrylate (PMMA) films, and then isomerized to the zwitterion form to achieve highly fluorescent gain medium. The t-Bu-RhB doped PMMA film is sandwiched by a pair of polystyrene colloidal crystals to construct a PhC resonating cavity. Single-mode laser oscillation at 592 nm is observed when the PhC resonating cavity is pumped by a Nd:YAG laser. The lasing threshold is 0.12 MW cm(-2) utilizing 6.9 wt% t-Bu-RhB doped PMMA films, which is only 1/60 of that with 3 wt% t-Bu-RhB doped PMMA films. The concentration-dependent lasing action is attributed to different gain factors of the t-Bu-RhB doped PMMA films. Furthermore, a spatially and spectrally coherent laser beam from the PhC resonating cavity is verified by exploring the far-field image and angular dependence of the lasing emission. The approach provides a facile and efficient strategy to reduce the lasing threshold for fabricating low threshold PhC lasers.

Steering electromagnetic beams with conical curvature singularities.

We describe how the transformation-optics technique can be used to design an effective medium mimicking the conical curvature singularity. Anholonomic coordinate transformation gives rise to linear topological defects that break the rotational symmetry. The bending and splitting of the optical beams are found analytically and numerically, depending on the incident direction and the topological charge. Beyond their practical applications to omnidirectional beam steering for photonics, our findings set forth an attractive realm to simulate the relevant physical phenomena in the optical laboratory.

Biscarbazolylmethane-based cyanine: a two-photon excited fluorescent probe for DNA and selective cell imaging.

Here, we have introduced a novel biscarbazolylmethane-based cyanine as a two-photon excited fluorescent probe, 6,6'-bis[2-(1-methylpyridinium)vinyl]-bis(9-methyl-carbazol-3-yl)methane diiodide, which has two vinylpyridinium carbazole moieties connected by a non-rigid methylene bridge. This molecule possesses a larger Stokes shift and enhanced two-photon absorption cross-section than the previously reported vinylpyridinium carbazole monocyanine, which is mainly attributed to the "through-space" type intramolecular charge transfer. The low fluorescence quantum yield and 30-fold fluorescence enhancement once binding with calf thymus DNA highlight this molecule as a promising fluorescence light-up probe for DNA. The obvious induced circular dichroism signals have proved that the molecule with soft-connected bis-cationic centers can specifically interact with various DNA structures. Cell viability study shows that the probe has very low cytotoxicity. The probe exhibits high staining selectivity for mitochondria in living HeLa cells. Its capability to stain nuclear DNA has been confirmed by fixed cell staining. Furthermore, the application for two-photon excited fluorescence imaging demonstrates high potential of the probe for nonlinear bioimaging with 3D resolution.

Two-photon induced photopolymerization using photoinitiator with an intramolecular radical quenching moiety for nanolithography.

We have investigated the photoinitiating properties of the photoinitiator 3,6-bis[2-(4-nitrophenyl)-ethynyl]-9-(4-methoxy-benzyl)-carbazole (BNMBC), which has an intramolecular radical quenching group "p-methoxybenzyl," in the substrate lines fabrication of two-photon induced photopolymerization (TPIP). Another photoinitiator 3,6-bis[2-(4-nitrophenyl)-ethynyl]-9-benzyl-carbazole (BNBC) with similar chemical structure but not radical quenching group was studied for comparison. Their photopolymerization properties were studied with resins in which BNBC and BNMBC were used as photoinitiators with a molar ratio of 0.02%, respectively. The linewidth of polymer lines fabricated by TPIP of the photoresist that contained BNMBC could be decreased to 65% of those using BNBC. Besides, we introduced a radical quencher, phenyl methyl ether (PhOCH3), to BNBC and further studied the photopolymerization properties by using BNBC, BNBC/PhOCH3 and BNMBC as photoinitiators with a molar ratio of 0.1%. The results further indicated that BNMBC was effective to confine the radical diffusion in polymerization due to the radical quenching effect of moiety. This intramolecular radical quenching moiety exhibited more effective confining effect of radical diffusion compared to the intermolecular radical quencher PhOCH3. Furthermore, arbitrary complex three-dimensional (3D) microstructure was achieved using the photoresist with photoinitiator BNMBC. The approach could open up broad prospect for improving the resolution in TPIP.

A novel serine/threonine protein phosphatase type 5 from second-generation merozoite of Eimeria tenella is associated with diclazuril-induced apoptosis.

Screening the anticoccidial drug targets is very important for developing novel drugs and revealing the molecular basis of drug resistance in coccidia. Due to high effectivity and safety, diclazuril was used widely in the poultry industry. To assess the roles of the serine/threonine protein phosphatase type 5 of second-generation merozoites in Eimeria tenella (EtPP5) in the anticoccidial activity of diclazuril against chicken coccidiosis, EtPP5 was cloned using reverse transcriptase polymerase chain reaction and rapid amplification of cDNA ends. Ultrastructural changes in second-generation merozoites and mRNA expression level of EtPP5 were monitored by transmission electron microscopy (TEM) and quantitative real-time PCR, respectively. The results showed that the full length of the cloned EtPP5 cDNA (2,495 bp) encompassed a 1,647-bp open reading frame encoding a polypeptide of 548 residues with an estimated molecular mass of 60.82 kDa and a theoretical isoelectric point of 5.89. Molecular analysis of EtPP5 reveals the presence of a C-terminal phosphatase domain and an extended N-terminal tetratricopeptide repeat motif, a typical feature of protein phosphatases. The cDNA sequence has been submitted to the GenBank database with accession number JX987508. EtPP5 shared 89% homology with the published sequence of a PP5 ortholog of Toxoplasma gondii at the amino acid level (GenBank XP_002364442.1). TEM observed that diclazuril induced ultrastructural changes in second-generation merozoites. Quantitative real-time PCR analysis showed that compared with the control group, the level of EtPP5 mRNA expression was significantly downregulated by 51.4% by diclazuril treatment. The high similarity of EtPP5 to previously described PP5 of other organisms, as well as its downregulated expression and connection with apoptosis in the second-generation merozoites induced by diclazuril, suggests that it could act an important role in understanding the signaling mechanism underlining the diclazuril-induced merozoites apoptosis.

Alteration of embryonic AT(2)-R and inflammatory cytokines gene expression induced by prenatal exposure to lipopolysaccharide affects renal development.

UNLABELLED: Prenatal exposure to LPS(lipopolysaccharide) results in renal damage in offspring rats, but the mechanism is unknown. The present study was to explore the role of angiotensin II and inflammation in the development of renal damage induced by prenatal exposure to LPS. The pregnant rats were randomly divided into two groups, i.e., control group, LPS group. The rats in the two groups were administered intraperitoneally with vehicle or 0.79 mg/kg LPS on 8th, 10th and 12th day during gestation. The mRNA expression of angiotensinogen, renin, AT(1)-R, AT(2)-R, TNF-α and IL-6 in embryos were assessed. Renal Ang II-positive cells, monocytes/macrophages, lymphocytes, collagen I and TUNEL-positive cells were identified by immunohistochemical staining in newborn and 7-week-old offspring rats. The number of glomeruli and creatinine clearance rate were determined in offspring at 7 weeks of age. The results showed that prenatal LPS decreased AT(2)-R mRNA expression but increased TNF-α and IL-6 mRNA expression in embryos. Prenatal LPS decreased renal angiotensin II-positive cells in newborn offspring rats, while these increased in 7-week-old offspring rats. Prenatal LPS decreased glomerular number and creatinine clearance rate but increased renal infiltrating monocytes/macrophages and lymphocytes at 7 weeks of age. Prenatal LPS also increased TUNEL-positive cells and collagen I expressions in newborn rats and 7-week-old offspring rats. CONCLUSION: Alteration of embryonic AT(2)-R and inflammatory cytokines gene expression induced by prenatal exposure to lipopolysaccharide affects renal development.

C2v symmetrical two-photon polymerization initiators with anthracene core: synthesis, optical and initiating properties.

A series of C(2v) symmetrical two-photon absorption compounds with anthracene core, 2,7-bis[2-(4-substituted phenyl)-vinyl]-9,10-dipentyloxyanthracenes designated as I, II and III (the substituted groups at the 4-position of phenyl of I, II and III were dimethylamino, methyl and cyano, respectively) were designed and synthesized as initiators in two-photon induced polymerization (TPIP). The anthracene ring was modified by linking vinylphenyl groups to the 2,7-position to extend conjugation system length and two pentyloxy groups to the 9,10-position to serve as electronic donors. Two-photon absorption cross section of I was around 300 GM, which was much larger than the 10 GM of II and 29 GM of III at 800 nm. I of 0.18% molar ratio in resin composed of methacrylic acid and dipentaerythritol hexaacrylate exhibited a dramatically low threshold of 0.64 mW compared with commercial photoinitiator benzil at a scanning speed 10 µm s(-1). Moreover, the threshold of photoinitiator I was only increased to 2.53 mW at a scanning speed of 1000 µm s(-1). The dependency of threshold on the concentration and exposure time was in accordance with theoretical calculation. Finally, a reasonable mechanism of the two-photon initiating process was proposed. This study provides good prospects for developing low threshold photoinitiator in TPIP.

Gold nanoparticles prepared by glycinate ionic liquid assisted multi-photon photoreduction.

We have successfully prepared gold nanoparticles (AuNPs) with flower-like and spherical morphology through multi-photon photoreduction (MPR) of an aqueous solution of HAuCl(4) and (2-hydroxyethyl) trimethylammonium glycinate ([HETMA][Gly]) ionic liquid (IL) through the use of a femtosecond laser. The results of (1)H NMR and UV-Vis absorption indicated that AuNPs were produced from the photoreduction of the [Gly]-Au(iii) complex. Spherical AuNPs of about 2.5 nm were obtained on the solution when irradiated for 2 h, then aggregated into flower-like AuNPs of several tens of nanometers assisted by the IL with an increase in the irradiation time. Furthermore, precipitates of spherical AuNPs with the size of around 15 nm were formed after being irradiated for 6 h. The mechanisms of the MPR reaction and controlled growth of AuNPs have also been discussed.

Hierarchical CdSe-gold hybrid nanocrystals: synthesis and optical properties.

The synthesis of hybrid nanostructures with controlled size, shape, composition and morphology has attracted increasing attention due to the fundamental and applicable interest. Here, we demonstrate the synthesis and optical properties of hierarchical CdSe-Au hybrid nanostructures with zinc blende (ZB) CdSe nanocrystals (NCs). For 3.5 nm ZB CdSe NCs, one Au cluster was deposited on each CdSe NC. Nevertheless, several Au clusters were selectively deposited on the apexes of 5 nm and 8 nm ZB CdSe NCs, resulting from the different reactivity of crystal facets. Furthermore, hierarchical CdSe-Au nanostructures with complex morphology were organized with the isolated CdSe-Au hybrid NCs by the coalescence of Au domains on the CdSe-Au hybrid NCs. UV-Vis spectra revealed a red tail upon the deposition of Au clusters. The chemical joint of Au on CdSe NCs was further confirmed by fluorescence quenching. The optical limiting performance of CdSe-Au hybrid NCs dispersed in toluene was investigated at 532 nm using a Nd:YAG laser with the pulse width of 8 ns.

Asymmetric fishnet metamaterials with strong optical activity.

We investigate the optical properties of mono- and double-layer asymmetric fishnet metamaterials with orientated elliptical holes, which exhibit exotic spectral and polarization rotating characteristics in the visible spectral range. Our results show that nontrivial orientations of the holes with respect to the reciprocal lattice vectors of the periodic lattice in both systems produce strong polarization rotation as well as additional enhanced optical transmission peaks. Analysis of the electromagnetic field distribution shows the unusual effect is produced by the spinning localized surface plasmon resonances due to the asymmetric geometry. High sensitivity of the hybridized mode on the dielectric spacing, the aspect ratio of the holes and the embedding media in double-layer structure is also observed. The dependence of spectral and polarization response on the orientation of the holes and the embedding media is useful for design of chiral metamaterials at optical frequencies and tailoring the polarization behavior of the metallic nano-structures.

Optimization and characterization of a highly-efficient diffraction nanograting for MHz XUV pulses.

We designed, fabricated and characterized a nano-periodical highly-efficient blazed grating for extreme-ultraviolet (XUV) radiation. The grating was optimized by the rigorous coupled-wave analysis method (RCWA) and milled into the top layer of a highly-reflective mirror for IR light. The XUV diffraction efficiency was determined to be around 20% in the range from 35.5 to 79.2 nm. The effects of the nanograting on the reflectivity of the IR light and non-linear effects introduced by the nanograting have been measured and are discussed.

Microscale golden Candock leaves self-aggregated on a polymer surface: Raman scattering enhancement and superhydrophobicity.

Gold nanoparticles (AuNP's) prepared through a controllable synthesis and aggregation process are attractive for their unique properties that arise from their surface plasmon resonances (SPRs). However, aggregation-controlled AuNP's on amorphous surfaces have not been well explored. In this study, we present a simple in situ synthesis method for preparing AuNP's in which the AuNP's self-aggregate into microscale Candock-leaf-like structures on a polyelectrolyte film (PEF) surface. In this approach, the PEF plays an important role in adsorbing and storing AuCl(4)(-) as well as in controlling the release speed of AuCl(4)(-) in the preparation process. The mechanism for forming these Candock-leaf-like structures has been illustrated by both the growth process of gold nanoparticles and the Ostwald ripenning of the aggregations. AuNP's with a unique structure exhibited significantly enhanced surface Raman scattering and strong superhydrophobicity.

Morphology modification of silver microstructures fabricated by multiphoton photoreduction.

We have investigated the morphology modification of silver microstructures fabricated by the multiphoton photoreduction process. The microstructures have been fabricated by a femtosecond laser under different irradiation time and repeated scanning numbers. Trans-4-[4-(dimethylamino)-N-methylstilbazolium] p-tosylate (DAST) was used as photosensitizer and effectively reduced the laser power to 0.66 mW. The increase of the irradiation time and repeated scanning induced more reduction in the multiphoton photoreduction microfabrication process, resulting in the optimization of the linewidth. The fusion of silver nanoparticles was confirmed, which led to the morphology change of silver microstructures for achieving the compact metallic microstructures. The result would provide an important protocol to fabricate the metallic microstructures for the electronic and photonic applications.