Diatom frustules decorated with zinc oxide nanoparticles for enhanced optical properties

Enhancement of hemostatic properties of Cyclotella cryptica frustule through genetic manipulation

BACKGROUND

The silicified cell wall of diatoms, also known as frustule, shows huge potential as an outstanding bio-nanomaterial for hemostatic applications due to its high hemostatic efficiency, good biocompatibility, and ready availability. As the architectural features of the frustule determine its hemostatic performance, it is of great interest to develop an effective method to modify the frustule morphology into desired patterns to further improve hemostatic efficiency.

RESULTS

In this study, the gene encoding Silicalemma Associated Protein 2 (a silicalemma-spanning protein) of Cyclotella cryptica (CcSAP2) was identified as a key gene in frustule morphogenesis. Thus, it was overexpressed and knocked down, respectively. The frustule of the overexpress lines showed no obvious alteration in morphology compared to the wild type (WT), while the size, specific surface area (BET), pore volume, and pore diameter of the knockdown strains changed greatly. Particularly, the knockdown frustules achieved a more pronounced coagulation effect and in vivo hemostatic performance than the WT strains. Such observations suggested that silicalemma proteins are ideal genetic encoding targets for manipulating frustule morphology associated hemostatic properties. Furthermore, the Mantel test was adopted to identify the key morphologies associated with C. cryptica bleeding control. Finally, based on our results and recent advances, the mechanism of frustule morphogenesis was discussed.

CONCLUSION

This study explores a new strategy for enhancing the hemostatic efficiency of the frustule based on genetic morphology modification and may provide insights into a better understanding of the frustule morphogenesis mechanism.

Surprising Eutectics: Enhanced Properties of ZnO-ZnWO4 from Visible to MIR

Zinc oxide-zinc tungstate (ZnO-ZnWO4 ) is a self-organized eutectic composite consisting of parallel ZnO thin layers (lamellae) embedded in a dielectric ZnWO4 matrix. The electromagnetic behavior of composite materials is affected not only by the properties of single constituent materials but also by their reciprocal geometrical micro-/nano-structurization, as in the case of ZnO-ZnWO4 . The light interacting with microscopic structural features in the composite material provides new optical properties, which overcome the possibilities offered by the constituent materials. Here remarkable active and passive polarization control of this composite over various wavelength ranges are shown; these properties are based on the crystal orientation of ZnO with respect to the biaxiality of the ZnWO4 matrix. In the visible range, polarization-dependent polarized luminescence occurs for blue light emitted by ZnO. Moreover, it is reported on the enhancement of the second harmonic generation of the composite with respect to its constituents, due to the phase matching condition. Finally, in the medium infrared spectral region, the composite behaves as a metamaterial with strong polarization dependence.

Domes and semi-capsules as model systems for infrared microspectroscopy of biological cells

It is well known that infrared microscopy of micrometer sized samples suffers from strong scattering distortions, attributed to Mie scattering. The state-of-the-art preprocessing technique for modelling and removing Mie scattering features from infrared absorbance spectra of biological samples is built on a meta model for perfect spheres. However, non-spherical cell shapes are the norm rather than the exception, and it is therefore highly relevant to evaluate the validity of this preprocessing technique for deformed spherical systems. Addressing these cases, we investigate both numerically and experimentally the absorbance spectra of 3D-printed individual domes, rows of up to five domes, two domes with varying distance, and semi-capsules of varying lengths as model systems of deformed individual cells and small cell clusters. We find that coupling effects between individual domes are small, corroborating previous related literature results for spheres. Further, we point out and illustrate with examples that, while optical reciprocity guarantees the same extinction efficiency for top vs. bottom illumination, a scatterer's internal field may be vastly different in these two situations. Finally, we demonstrate that the ME-EMSC model for preprocessing infrared spectra from spherical biological systems is valid also for deformed spherical systems.

Exogenous Contrast Agents in Photoacoustic Imaging: An In Vivo Review for Tumor Imaging

The field of cancer theranostics has grown rapidly in the past decade and innovative ‘biosmart’ theranostic materials are being synthesized and studied to combat the fast growth of cancer metastases. While current state-of-the-art oncology imaging techniques have decreased mortality rates, patients still face a diminished quality of life due to treatment. Therefore, improved diagnostics are needed to define in vivo tumor growths on a molecular level to achieve image-guided therapies and tailored dosage needs. This review summarizes in vivo studies that utilize contrast agents within the field of photoacoustic imaging—a relatively new imaging modality—for tumor detection, with a special focus on imaging and transducer parameters. This paper also details the different types of contrast agents used in this novel diagnostic field, i.e., organic-based, metal/inorganic-based, and dye-based contrast agents. We conclude this review by discussing the challenges and future direction of photoacoustic imaging.

Characterization of Chirality in Diffractive Metasurfaces by Photothermal Deflection Technique

Chirality, a lack of mirror symmetry, is present in nature at all scales; at the nanoscale, it governs the biochemical reactions of many molecules, influencing their pharmacology and toxicity. Chiral substances interact with left and right circularly polarized light differently, but this difference is very minor in natural materials. Specially engineered, nanostructured, periodic materials can enhance the chiro-optical effects if the symmetry in their interactions with circular polarization is broken. In the diffraction range of such metasurfaces, the intensity of diffracted orders depends on the chirality of the input beam. In this work, we combine a photothermal deflection experiment with a novel theoretical framework to reconstruct both the thermal and optical behavior of chiro-optical behavior in diffracted beams.

FTIR Photoacoustic and ATR Spectroscopies of Soils with Aggregate Size Fractionation by Dry Sieving

Granulometric fractionation as a source of additional information on organic-matter and inorganic matrix components of soils using FTIR-photoacoustic spectroscopy (FTIR-PAS) supported by attenuated-total reflection FTIR spectroscopy (ATR-FTIR) for a wide range of aggregate fractions (10-5000 μm) was used to compare the sensitivity, reproducibility, information contents, and representativity of fractionated samples. For chernozem and sod-podzolic soils and different agricultural-use chernozem samples, differences in the composition were found, manifested in normalized spectra of microaggregate fractions, with the range of 10-100 μm bearing the complete information. Most changes are observed in the soil organic matter range (1900-1340 cm-1), although these changes are slight, and in the soil-matrix region (550-300 cm-1). The latter region increases the intensity of bands corresponding to amorphous silica and clay minerals in fine fractions, while the intensity of bands attributed to quartz lattice vibrations decreases. FTIR-PAS spectra do not differ considerably at high interferometer modulation frequencies as the signal-penetration depth is comparable with particle sizes. The soil fractions below 20 μm result in the maximum sensitivity, reproducibility, and signal-to-noise ratio, showing no changes from coarser fractions by the information content and, thus, providing representative samples for analysis. The fractionation shows more differences in the sod-podzolic and chernozem soil fractions than the whole soil spectra. FTIR-PAS provides better sensitivity and reproducibility in the 4000-2000 cm-1 region and ATR-FTIR in the 2000-100 cm-1 region.

Photoacoustics for listening to metal nanoparticle super-aggregates

Photoacoustic signal detection has been used to build a new strategy to determine the mesoscale self-assembly of metal nanoparticles in terms of size distribution and aggregate packing density (metal nanoparticle filling factor). A synergistic approach integrating photoacoustic signal and theoretical studies, validated by conventional light scattering and electron microscopy techniques, allows us to obtain a well-defined morphological interpretation of nanoparticle-based super-aggregates. By pumping light in a complex system, the acousto-thermal effect was listened to, providing information on the aggregation phenomena. Super-aggregates of covalently interconnected silver nanoparticles (AgNPs) functionalized with an organometallic dithiol are identified in solution, as a proof of concept for the versatility of the photoacoustic approach. According to our results, tiny AgNPs (size less than 10 nm) assembled into a 3D-network of super-aggregates (SA-AgNPs) with sizes in the range 100-200 nm and a filling factor in the range of 30-50%. Low-cost, rapid, and easy photoacoustic measurement in the low frequency range (less than 100 Hz) was revealed to be an innovative method to characterize the fundamental structure/property correlation of metal nanoparticle super-aggregates. This morpho-optical approach, which uses the absorption and scattering properties of nanoparticles in the liquid phase, opens new perspectives for advanced biomedical and structural applications.

Carbon Nanodots as a Potential Transport Layer for Boosting Performance of All-Inorganic Perovskite Nanocrystals-Based Photodetector

A low-cost and simple drop-casting method was used to fabricate a carbon nanodot (C-dot)/all-inorganic perovskite (CsPbBr3) nanosheet bilayer heterojunction photodetector on a SiO2/Si substrate. The C-dot/perovskite bilayer heterojunction photodetector shows a high performance with a responsivity (R) of 1.09 A/W, almost five times higher than that of a CsPbBr3-based photodetector (0.21 A/W). In addition, the hybrid photodetector exhibits a fast response speed of 1.318/1.342 µs and a highly stable photocurrent of 6.97 µA at 10 V bias voltage. These figures of merits are comparable with, or much better than, most reported perovskite heterojunction photodetectors. UV–Vis absorption and photoluminescent spectra measurements reveal that the C-dot/perovskite bilayer heterojunction has a band gap similar to the pure perovskite layer, confirming that the absorption and emission in the bilayer heterojunction is dominated by the top layer of the perovskite. Moreover, the emission intensity of the C-dot/perovskite bilayer heterojunction is less than that of the pure perovskite layer, indicating that a significant number of charges were extracted by the C-dot layer. The studied band alignment of the C-dots and perovskites in the dark and under emission reveals that the photodetector has a highly efficient charge separation mechanism at the C-dot/perovskite interface, where the recombination rate between photogenerated electrons and holes is significantly reduced. This highly efficient charge separation mechanism is the main reason behind the enhanced performance of the C-dot/perovskite bilayer heterojunction photodetector.

Photoacoustic and fluorescence lifetime imaging of diatoms

Photoacoustic and fluorescent methods are used intensely in biology and medicine. These approaches can also be used to investigate unicellular diatom algae that are extremely important for Earth's ecology. They are enveloped within silica frustules (exoskeletons), which can be used in drug delivery systems. Here, we report for the first time the successful application of photoacoustic (PA) and fluorescent visualization of diatoms. Chlorophyll a and c and fucoxanthin were found likely to be responsible for the photoacoustic effect in diatoms. The PA signal was obtained from gel drops containing diatoms and was found to increase with the diatom concentration. The fluorescence lifetime of the diatom chromophores ranged from 0.5 to 2 ns. The dynamic light scattering, absorbance, and SEM characterization techniques were also applied. The results were considered in combination to elucidate the nature of the photoacoustic signal. Possible biotechnological applications are proposed for the remote photoacoustic monitoring of algae.

High-Performance Ultraviolet Photodetector Based on a Zinc Oxide Nanoparticle@Single-Walled Carbon Nanotube Heterojunction Hybrid Film

A hybrid film consisting of zinc oxide nanoparticles (ZnO NPs) and carbon nanotubes (CNTs) is formed on a glass substrate using a simple and swift spin coating process for the use in ultraviolet photodetectors (UV PDs). The incorporation of various types of CNTs into ZnO NPs (ZnO@CNT) enhances the performance of UV PDs with respect to sensitivity, photoresponse, and long-term operation stability when compared with pristine ZnO NP films. In particular, the introduction of single-walled CNTs (SWNTs) exhibits a superior performance when compared with the multiwalled CNTs (MWNTs) because SWNTs can not only facilitate the stability of free electrons generated by the O₂ desorption on ZnO under UV irradiation owing to the built-in potential between ZnO and SWNT heterojunctions, but also allow facile and efficient transport pathways for electrons through SWNTs with high aspect ratio and low defect density. Furthermore, among the various SWNTs (arc-discharged (A-SWNT), Hipco (H-SWNT), and CoMoCat (C-SWNT) SWNTs), we demonstrate the ZnO@A-SWNT hybrid film exhibits the best performance because of higher conductivity and aspect ratio in A-SWNTs when compared with those of other types of SWNTs. At the optimized conditions for the ZnO@A-SWNT film (ratio of A-SWNTs and ZnO NPs and electrode distance), ZnO@A-SWNT displays a sensitivity of 4.9 × 10³ % with an on/off current ratio of ~10⁴ at the bias of 2 V under the UV wavelength of 365 nm (0.47 mW/cm²). In addition, the stability in long-term operation and photoresponse time are significantly improved by the introduction of A-SWNTs into the ZnO NP film when compared with the bare ZnO NPs film.

Nondestructive Characterization at Nanoscopic Scale by Photoacoustic and Photothermal Techniques -INVITED

Photoacoustic and Photothermal Spectroscopy are excellent techniques for studying the optical absorption spectra of opaque and highly light-scattering substances such as nanomaterials. In this paper we review recent advances in the methodology and its novel applications at the nanoscopic scale.

Size and Shape-Dependent Solubility of CuO Nanostructures

In our theoretical study, the enhanced solubility of CuO nanoparticles in water saturated by air is predicted based on a simple thermodynamic model. CuO is considered in the form of nanoparticles with various shapes. The interfacial energy of a solid CuO/dilute aqueous solution interface was assessed by applying the average CuO surface energy and contact angle of a sessile drop of water. The equilibrium CuO solubility was calculated using Gibbs energy minimization technique. For the smallest spherical nanoparticles considered in this work (r = 2 nm), the solubility is significantly higher than the solubility of bulk material. In the case of cylindrical nanoparticles, the solubility increase is even more considerable. The CuO spherical nanoparticles solubility was also calculated using the Ostwald–Freundlich equation which is known to overestimate the solubility as discussed in this contribution.

UV Sensitivity of MOS Structures with Silicon Nanoclusters

Selective UV sensitivity was observed in Metal-Oxide-Semiconductor structures with Si nanoclusters. Si nanocrystals and amorphous Si nanoparticles (a-Si NPs) were obtained by furnace annealing of SiO_x films with x = 1.15 for 60 min in N₂ at 1000 and 700 °C, respectively. XPS and TEM analysis prove phase separation and formation of Si nanocrystals in SiO₂, while the a-Si NPs are formed in SiO_1.7 matrix. Both types of structures show selective sensitivity to UV light; the effect is more pronounced in the structure with nanocrystals. The responsivity of the nanocrystal structure to 365 nm UV light is ~ 4 times higher than that to green light at 4 V applied to the top contact. The observed effect is explained by assuming that only short wavelength radiation generates photocarriers in the amorphous and crystalline nanoclusters.

Absorption spectra of nanodiamond aqueous dispersions by optical absorption and optoacoustic spectroscopies

The multispectral modality and technique for optically dense samples of optoacoustic spectroscopy were applied to measure spectra and high absorbances of concentrated aqueous dispersions of undoped nanodiamonds. The data from optoacoustic and optical transmission measurements and DSC data of the mean particle size by the Gibbs-Kelvin equation are compared to estimate the difference in composition of various nanodiamond trademarks. Optoacoustic spectra confirm the contribution of surface dimer chains into the absorption of nanodiamonds in the long wavelength range. Optoacoustic and conventional absorption spectra of aqueous solutions of nanodiamond fractions after centrifugation (15300g) and ultracentrifugation (130000g) revealed a separation of a highly absorbing non-diamond sp² phase. The two-step separation by ultracentrifugation followed by extra centrifugation made it possible to isolate a highly absorbing and soluble nanodiamond phase with the particle size of 3.6 nm, showing a change in spectra compared to the starting nanodiamond material.

Photoacoustic Sensing of Trapped Fluids in Nanoporous Thin Films: Device Engineering and Sensing Scheme

Accessing fluid infiltration in nanogranular coatings is an outstanding challenge, of relevance for applications ranging from nanomedicine to catalysis. A sensing platform, allowing quantifying the amount of fluid infiltrated in a nanogranular ultrathin coating, with thickness in the 10-40 nm range, is here proposed and theoretically investigated by multiscale modeling. The scheme relies on impulsive photoacoustic excitation of hypersonic mechanical breathing modes in engineered gas-phase-synthesized nanogranular metallic ultrathin films and time-resolved acousto-optical read-out of the breathing modes frequency shift upon liquid infiltration. A superior sensitivity, exceeding 26 × 10³ cm²/g, is predicted upon equivalent areal mass loading of a few ng/mm². The capability of the present scheme to discriminate among different infiltration patterns is discussed. The platform is an ideal tool to investigate nanofluidics in granular materials and naturally serves as a distributed nanogetter coating, integrating fluid sensing capabilities. The proposed scheme is readily extendable to other nanoscale and mesoscale porous materials.

Eco-sustainable systems based on poly(lactic acid), diatomite and coffee grounds extract for food packaging

In the food packaging sector many efforts have been (and are) devoted to the development of new materials in order to reply to an urgent market demand for green and eco-sustainable products. Particularly a lot of attention is currently devoted both to the use of compostable and biobased polymers as innovative and promising alternative to the currently used petrochemical derived polymers, and to the re-use of waste materials coming from agriculture and food industry. In this work, multifunctional eco-sustainable systems, based on poly(lactic acid) (PLA) as biopolymeric matrix, diatomaceous earth as reinforcing filler and spent coffee grounds extract as oxygen scavenger, were produced for the first time, in order to provide a simultaneous improvement of mechanical and gas barrier properties. The influence of the diatomite and the spent coffee grounds extract on the microstructural, mechanical and oxygen barrier properties of the produced films was deeply investigated by means of X-Ray diffraction (XRD), infrared spectroscopy (FT-IR, ATR), scanning electron microscopy (SEM), uniaxial tensile tests, O₂ permeabilimetry measurements. An improvement of both mechanical and oxygen barrier properties was recorded for systems characterised by the co-presence of diatomite and coffee grounds extract, suggesting a possible synergic effect of the two additives.