Au nanoparticle concentration study in hybrid plasmonic microlasers.

In this paper, the concentration effects of Au nanoparticles placed in dye-doped polymeric spherical microlasers are investigated. The microlasers (average diameter of ∼293µm) are made with a mixture of UV curable polymer named Norland Blocking Adhesive (NBA) and Rhodamine 6 G. Four different ratios (between the Au nanoparticles and the NBA solutions) are investigated here, namely, 1000, 2000, 3000, and 4000 ratios. The Au nanoparticles (size of ∼5nm) are randomly scattered within the microlaser. The light is collected via a multimode optical fiber, ending to a spectrometer/CCD camera. It is found that the 3000 ratio case exhibited the lowest energy threshold value and the highest photonic emission slope. The 4000 ratio (lowest concentration) exhibited a behavior that was very similar to a microlasers with no Au particles. In terms of longevity of the laser modes, the 3000 ratio case exhibited the most stable emission, although the laser mode disappeared at an earlier time. The emission of the 2000 ratio case dropped drastically after a few seconds but increased after that before dropping again; in this case, the TE and TM laser modes were found to be in competition with each other due to the partial overlapping of the plasmonic emission with some of the resonant cavity modes and due to the thermal expansion effect. The quality factor was found to be of the same order of magnitude for all cases (∼104). Ultimately, this work allows us to select the optimum microlaser's configuration in terms of Au nanoparticle concentration as well as laser mode emission and longevity for different mechanical and biomedical sensing applications.

Untethered photonic sensor for wall pressure measurement.

In this Letter, we study a novel untethered photonic wall pressure sensor that uses as sensing element a dome-shaped micro-scale laser. Since the sensor does not require any optical or electrical cabling, it allows measurements where cabling tends to be problematic. The micro-laser is made by a mixture of Trimethylolpropane Tri(3-mercaptopropionate), commercial name THIOCURE and Polyethylene (glycol) Diacrylate (PEGDA) mixed with a solution of rhodamine 6G. Two different volume ratios between the THIOCURE and the PEGDA are studied, since different ratios lead to different mechanical properties. In addition, two different sensor configurations are presented: (i) sensor coupled to a membrane, that allows differential wall pressure measurement and (ii) sensor without membrane that allows absolute wall pressure measurement. The sensitivity plots are presented in the paper for both sensor configurations and polymer ratios.

Dome-shaped whispering gallery mode laser for remote wall temperature sensing.

In this paper, we carried out experiments to investigate dome-shaped microlaser based on the whispering gallery modes for remote wall temperature sensing. The dome-shaped resonator was made of Norland blocking adhesive (NBA 107) doped with a solution of rhodamine 6G and ethanol. Two different configurations are considered: (i) resonator placed on top of a thin layer of 10:1 polydimethylsiloxane (10:1 PDMS), and (ii) resonator encapsulated in a thin layer of 10:1 PDMS. The microlaser was remotely pumped using a Q switch Nd:YAG laser with pulse repetition rate of 10 Hz, pulse linewidth of 10 ns, and pulse energy of 100 µJ/cm². The excited optical modes showed an average optical quality factor of 104 for both configurations. In addition, the measurements showed sensitivity to temperature of ~0.06 nm/°C and a resolution of 1°C for both configurations. This sensitivity was limited by the resolution of the experimental setup used in these studies.

Bio-based composites fabricated from wood fibers through self-bonding technology.

Green composite processing technology of wood fibers is an inevitable choice for global sustainable development. In this research, waste poplar powder with different particle sizes was used to prepare glue-free biocomposites with good mechanical and waterproof properties by hot-molding. The biocomposites made of larger size wood powder had better tensile strength (40.3 MPa) and the biocomposites made of smaller size wood powder had the greater bending strength (50.5 MPa). The thickness swelling rate of the biocomposites was only 4.26% after soaking in water for 24 h. The cross-section morphology of the biocomposites showed that the cell wall collapses enhanced the interfacial bonding. Chemical analysis showed that lignin repolymerized with cellulose and hemicellulose for the vitrification transition. In addition, the biocomposites with excellent mechanical properties had no formaldehyde release, which can replace the traditional density boards made of adhesives and applied as furniture materials and in line with the concept of cleaner production.

Plasmonic and Hybrid Whispering Gallery Mode-Based Biosensors: Literature Review.

BACKGROUND: The term "plasmonic" describes the relationship between electromagnetic fields and metallic nanostructures. Plasmon-based sensors have been used innovatively to accomplish different biomedical tasks, including detection of cancer. Plasmonic sensors also have been used in biochip applications and biosensors and have the potential to be implemented as implantable point-of-care devices. Many devices and methods discussed in the literature are based on surface plasmon resonance (SPR) and localized SPR (LSPR). However, the mathematical background can be overwhelming for researchers at times. OBJECTIVE: This review article discusses the theory of SPR, simplifying the underlying physics and bypassing many equations of SPR and LSPR. Moreover, we introduce and discuss the hybrid whispering gallery mode (WGM) sensing theory and its applications. METHODS: A literature search in ScienceDirect was performed using keywords such as "surface plasmon resonance," "localized plasmon resonance," and "whispering gallery mode/plasmonic." The search results retrieved many articles, among which we selected only those that presented a simple explanation of the SPR phenomena with prominent biomedical examples. RESULTS: SPR, LSPR, tilted fiber Bragg grating, and hybrid WGM phenomena were explained and examples on biosensing applications were provided. CONCLUSIONS: This minireview presents an overview of biosensor applications in the field of biomedicine and is intended for researchers interested in starting to work in this field. The review presents the fundamental notions of plasmonic sensors and hybrid WGM sensors, thereby allowing one to get familiar with the terminology and underlying complex formulations of linear and nonlinear optics.

Photocatalytic degradation of surface-coated tourmaline-titanium dioxide for self-cleaning of formaldehyde emitted from furniture.

Formaldehyde emission is an intrinsic property derived from aldehyde-based resin that is used in wood-based composites. To reduce formaldehyde emission from plywood, the composite catalyst of tourmaline-titanium dioxide (T-TiO2) was fabricated by the sol-gel method. Furthermore, the impregnated paper loaded with the T-TiO2 composite catalyst was used to decorate the surface of 5-layer poplar plywood. The physicochemical structure, photocatalytic activity of T-TiO2 composite catalyst and its mechanism of degrading gaseous formaldehyde and generating air negative ions were assessed. The results discovered that the synergistic influence of the tourmaline and TiO2 anatase nanocrystals achieved good photodegradation of the gaseous formaldehyde. The neat T(20%)-TiO2 catalyst offered a higher formaldehyde removal efficiency (92.2%) than other catalysts, possessing 800 ions/cm3 of air negative ions concentration after 10-h visible light irradiation. The poplar plywood with a load of 3% T(20%)-TiO2 catalyst can stably induce the degradation formaldehyde into air negative ions with a concentration of 1200 ions/cm3 in visible light. The impregnation process of paper was feasible to be industrialized and the decorated wood-based composites can be widely applied in the furniture industry.

Novel Terahertz Spectroscopy Technology for Crystallinity and Crystal Structure Analysis of Cellulose.

Crystallinity is an essential indicator for evaluating the quality of fiber materials. Terahertz spectroscopy technology has excellent penetrability, no harmful substances, and commendable detection capability of absorption characteristics. The terahertz spectroscopy technology has great application potential in the field of fiber material research, especially for the characterization of the crystallinity of cellulose. In this work, the absorption peak of wood cellulose, microcrystalline cellulose, wood nano cellulose, and cotton nano cellulose were probed in the terahertz band to calculate the crystallinity, and the result compared with XRD and FT-IR analysis. The vibration model of cellulose molecular motion was obtained by density functional theory. The results showed that the average length of wood cellulose (WC) single fiber was 300 µm. The microcrystalline cellulose (MCC) was bar-like, and the average length was 20 µm. The cotton cellulose nanofiber (C-CNF) was a single fibrous substance with a length of 50 µm, while the wood cellulose nanofiber (W-CNF) was with a length of 250 µm. The crystallinity of cellulose samples in THz was calculated as follows: 73% for WC, 78% for MCC, 85% for W-CNF, and 90% for C-CNF. The crystallinity values were obtained by the three methods which were different to some extent. The absorption peak of the terahertz spectra was most obvious when the samples thickness was 1 mm and mixed mass ratio of the polyethylene and cellulose was 1:1. The degree of crystallinity was proportional to the terahertz absorption coefficients of cellulose, the five-movement models of cellulose molecules corresponded to the five absorption peak positions of cellulose.