Global Perspective of Plant-Based Cosmetic Industry and Possible Contribution of Sri Lanka to the Development of Herbal Cosmetics.

The global consumption of plant-based cosmetics has shown spectacular growth in recent years because of rising consumer awareness regarding the long-term health benefits of natural ingredients. As the global demand for herbal cosmetics increases, there are ample opportunities for Sri Lanka as a tropical Asian country to expand its productions and global exports along with its unique biodiversity and inherited traditional knowledge. Therefore, the present review attempts to give an overview of the widely used medicinal plants in the global herbal cosmetic industry and strengths, challenges, and possible solutions for the development of the herbal cosmetic industry of Sri Lanka. Information was collected using electronic search (using Pub Med, Science Direct, Web of Science, Google Scholar, TEEAL, and Scopus) for articles published in peer-reviewed journals, industrial reports, market surveys, and library search for local books on ethnobotany. Important plant-derived ingredients used in the global herbal cosmetic industry are essential oils, colorants, oils, fats, and waxes. The traditional usage of 108 medicinal plant species (belonging to 58 families) in cosmetic treatments was identified from the local books of Sri Lanka. Of these, 49 plant species were reported as new ingredients for the herbal cosmetic industry. However, the lack of ethnobotanical and ethnopharmacological surveys to identify the cosmetic potential plants, insufficient or absence of continuous supply of raw materials for production in line with the existing demand, the lack of quality control of raw materials and finished cosmetic products, improper systematic cultivation systems for medicinal plants, poor postharvest practices, and the lack of innovations are major challenges encountered in Sri Lanka for the development of the herbal cosmetic industry. In conclusion, addressing these vital knowledge gaps is a timely requirement of the country for the sustainable development of the herbal cosmetic industry in Sri Lanka. Furthermore, assembling of the multidisciplinary cooperation of botanists, chemists, toxicologists, researchers, and biologists is crucial to analyze the interesting functional properties, efficacy, and effectiveness of documented medicinal plants with cosmetic potential.

Ethnopharmacological Survey on Medicinal Plants Used for Cosmetic Treatments in Traditional and Ayurveda Systems of Medicine in Sri Lanka.

Medicinal plants have been used for therapeutic and beauty applications in Sri Lanka with documented history of over 2,500 years. This inherited knowledge, which has been handed down from generation to generation, provides a largely unexplored source for the potential development of active ingredients for cosmetic formulations. Therefore, the present comprehensive survey was conducted to identify cosmetic potential medicinal plants species in Sri Lanka. Personal interviews were conducted via a semistructured questionnaire with randomly selected 30 traditional practitioners and 90 Ayurveda physicians in Sri Lanka. Data were collected on plants and specific plant parts used for the treatment of skin care, hair care, and oral care topically. The acquired data were verified using the Ayurveda authentic books and quantitatively analyzed using relative frequency of citation (RFC), use value (UV), relative importance (RI), and factor informant consensus (FIC). Results revealed about the usage of 133 different plant species belonging to 64 families in cosmetic treatments under the categories of skin care, hair care, and oral care. Majority of medicinal plants were used in skin care treatments (39%) followed by hair care (20%) and oral care (17%). Aloe vera (L.) Burm.f. reported the highest RFC value (0.83) and UV (3.66). The highest RI value was reported from Asparagus racemosus Willd. and Hibiscus rosa-sinensis L. (1.67). The dominant plant family was reported as family Fabaceae. The most utilized plant part was stated as leaves (34%) followed by bark (14%). The survey further revealed about treatments for 17 skin-related, 9 hair-related, and 2 oral-related beauty issues. All RFC values were comparatively high for identified different beauty issues. Many herbal preparations were prepared using water as the medium whilst most common mode of application was reported as paste (37%). In conclusion, acquired information could ultimately be utilized for the development of the herbal cosmetic industry through the isolation and characterization of bioactive compounds from the documented plants while preserving the traditional knowledge.

Emerging Herbal Cosmetic Production in Sri Lanka: Identifying Possible Interventions for the Development of the Herbal Cosmetic Industry.

Although the herbal cosmetic industry has exponentially increased globally, manufacturing of herbal cosmetic products in Sri Lanka is still very limited. Therefore, objectives of the study were to recognize plants used in commercialized herbal cosmetic products and major constraints faced by herbal cosmetic manufacturers and to identify possible interventions for the development of herbal cosmetic industry of Sri Lanka. Information was gathered via a semistructured questionnaire by personal interviews with 11 large-scale multiple herbal cosmetic products manufacturers. Collected data were analyzed via frequency index for usage and descriptive statistics. A total of 115 plant species belonging to 56 families were identified. Extensive usage of Aloe vera (L.) Burm.f., Coscinium fenestratum (Goetgh.) Colebr., and Santalum album L. (90.91%) was reported among herbal cosmetic manufacturers. The highest number of plants or plant materials was used for manufacturing skin care products (54.78%) followed by hair care (19.13%) and oral care (6.96%). The majority of plants were reported from the plant family Fabaceae (16 species). Leaves (20.87%) were the widely used plant part, whereas 10 plant species were used as whole plants. Inadequacy of 7 plants/plant materials and importation of 8 plant materials for the production were also recognized. As major constraints faced by herbal cosmetic manufacturers, inadequate availability and poor quality of raw materials were emphasized. In conclusion, establishing proper cultivation system, implementing strategies for quality control of raw materials, and conducting ethnobotany, ethnopharmacological surveys to identify cosmetic potential of medicinal plants and partnerships with universities to transfer technology for product development to industries are possible interventions for the development of herbal cosmetic industry of Sri Lanka.

Deterministic Nanoassembly of Quasi-Three-Dimensional Plasmonic Nanoarrays with Arbitrary Substrate Materials and Structures.

Guided manipulation of light through periodic nanoarrays of three-dimensional (3D) metal-dielectric patterns provides remarkable opportunities to harness light in a way that cannot be obtained with conventional optics yet its practical implementation remains hindered by a lack of effective methodology. Here we report a novel 3D nanoassembly method that enables deterministic integration of quasi-3D plasmonic nanoarrays with a foreign substrate composed of arbitrary materials and structures. This method is versatile to arrange a variety of types of metal-dielectric composite nanoarrays in lateral and vertical configurations, providing a route to generate heterogeneous material compositions, complex device layouts, and tailored functionalities. Experimental, computational, and theoretical studies reveal the essential design features of this approach and, taken together with implementation of automated equipment, provide a technical guidance for large-scale manufacturability. Pilot assembly of specifically engineered quasi-3D plasmonic nanoarrays with a model hybrid pixel detector for deterministic enhancement of the detection performances demonstrates the utility of this method.

Generation of vectorial optical fields with slot-antenna-based metasurface.

A transmission-type metasurface composed of carefully designed rectangular slot antennas for the generation of vectorial optical fields is proposed and demonstrated. Acting as local linear polarizers, these slot antennas enable the spatial modulation of optical fields in amplitude, phase, and polarization for the cross-polarized component of the scattered field. As an illustration, a metasurface capable of forming a radially polarized scattered field with specific vectorial beam patterns with appropriate excitation at normal incidence is designed, fabricated, and tested. The radially polarized scattered field is designed to be further tightly focused by a high numerical aperture objective lens in order to obtain a uniform longitudinally polarized optical needle field along the propagation direction. Characterization experiments demonstrate that its overall extinction ratio satisfies the amplitude modulation requirement, and a corresponding π phase modulation is realized as proposed.

Demonstration of beam steering via dipole-coupled plasmonic spiral antenna.

Optical antennas have been utilized to tailor the emission properties of nanoscale emitters in terms of the intensity, directivity and polarization. In this letter, we further explore the capability of beam steering via the use a spiral plasmonic structure as a transmitting antenna. According to both numerical simulation and experimental observations, the beaming direction can be steered through introducing a displacement of the feeding point to the spiral antenna from the geometrical center. For a 3-turn Archimedes' spiral antenna, experimental results show that steering angles of 3° and 7° are obtainable when the excitation location is transversally shifted from the center by a displacement of 200 nm and 500 nm, respectively. Furthermore, the emitted photons carry spin angular momentum determined by the chirality of the spiral optical antenna. A steerable nanoscale spin photon source may find important applications in single molecule sensing, quantum optical information processing and integrated photonic circuits.

Hybrid spiral plasmonic lens: towards an efficient miniature circular polarization analyzer.

A hybrid spiral plasmonic lens that consists of alternating spiral slot and spiral triangular sub-aperture array can differentiate circular polarization of different handedness and enable a miniature circular polarization analyzer design with high efficiency. The improved performance compared to pure spiral slot lens comes from the fact that the hybrid lens is capable of focusing both the radial and the azimuthal polarization components of a circular polarization, doubling the coupling efficiency. In this paper, the spin-dependent plasmonic focusing properties of a spatially arranged triangular sub-aperture array and a hybrid spiral plasmonic lens are demonstrated using a collection mode near field scanning optical microscope. The coupling efficiency could be further improved through optimizing the geometry of the hybrid lens.

Beaming circularly polarized photons from quantum dots coupled with plasmonic spiral antenna.

Coupling nanoscale emitters via optical antennas enables comprehensive control of photon emission in terms of intensity, directivity and polarization. In this work we report highly directional emission of circularly polarized photons from quantum dots coupled to a spiral optical antenna. The structural chirality of the spiral antenna imprints spin state to the emitted photons. Experimental results reveal that a circular polarization extinction ratio of 10 is obtainable. Furthermore, increasing the number of turns of the spiral gives rise to higher antenna gain and directivity, leading to higher field intensity and narrower angular width of emission pattern in the far field. For a five-turn Archimedes' spiral antenna, field intensity increase up to 70-fold simultaneously with antenna directivity of 11.7 dB has been measured in the experiment. The highly directional circularly polarized photon emission from such optically coupled spiral antenna may find important applications in single molecule sensing, quantum optics information processing and integrated photonic circuits as a nanoscale spin photon source.

Reduction of scattering loss of silicon slot waveguides by RCA smoothing.

Because of stronger optical confinement density, silicon slot waveguides tend to have higher scattering loss than normal ridge waveguides with same sidewall roughness. A wet chemical process is found to be highly effective in reducing the surface roughness and scattering loss. A reduction in scattering loss by 10.2 dB/cm for TE and 8.5 dB/cm for TM polarizations has been achieved.

Two-photon fluorescence characterization of spiral plasmonic lenses as circular polarization analyzers.

The spiral plasmonic lens is capable of focusing the left-hand and right-hand circular polarizations into spatially separated plasmonic fields caused by the geometric phase effect. Its function as a circular polarization analyzer has been studied analytically and numerically in a previous Letter [Opt. Lett.34, 3047 (2009)OPLEDP0146-959210.1364/OL.34.003047]. Single Archimedes' spiral grooves with lateral sizes of approximately 4lambda(spp) (approximately 2.8 microm) were milled into a gold thin film by using a focused ion beam. The function of such a simple spiral plasmonic lens serving as a circular polarization analyzer was experimentally characterized with two-photon fluorescence microscopy. The circular polarization extinction ratio of the two-photon fluorescent signal is estimated to be larger than 200 for a detector diameter up to 0.3lambda(spp).

Experimental confirmation of miniature spiral plasmonic lens as a circular polarization analyzer.

A spiral plasmonic lens can focus circular polarization of a given handedness while simultaneously defocus the circular polarization of the opposite chirality, which may be used as a miniature circular polarization analyzer. In this letter, we experimentally investigated the plasmonic focusing properties of the spiral lens using a collection mode near-field scanning optical microscope. A single Archimedes' spiral slot with a single turn was etched through gold thin film as a spiral plasmonic lens. The plasmonic field at the focus of a spiral lens strongly depends on the spin of the incident photon. Circular polarization extinction ratio better than 50 is obtainable with a device size as small as only 4 times of surface plasmon wavelength.

Plasmonic lens made of multiple concentric metallic rings under radially polarized illumination.

Optimal plasmonic focusing can be achieved through matching the rotational symmetry of the plasmonic lens to the polarization symmetry of a radially polarized illumination. In this letter, we report the experimental confirmation of the focusing properties and field enhancement effect of plasmonic lens made of multiple concentric annular rings using a collection mode near field scanning optical microscope. Surface plasmons excited at all azimuthal directions propagate toward the geometric center and constructively interfere at the focus to create a strongly enhanced evanescent optical "needle" field that is substantially polarized vertically to the plasmonic lens surface. The field enhancement factor can be improved through adding more rings while maintaining the plasmonic focal spot size. Strategy for optimizing the field enhancement factor is studied with both analytical and numerical methods.

Polymer underlayer assisted dewetting of a top metal nanofilm.

We demonstrated polymethylmethacrylate (PMMA) polymer underlayer assisted, focused-ion-beam (FIB)-induced dewetting of a top Au nanofilm where we found that the underlayer played a prominent and, in some cases, a useful role in the dewetting of the top layer. For an Au nanofilm deposited on a thick uniform PMMA underlayer, where the underlayer is stable and therefore does not dewet, irregularly spaced Au nanoparticles (AuNPs) were formed as expected by raster-scanning of a focused Ga-ion beam. On the other hand, topographically pre-patterned thin PMMA film provided heterogeneous nucleation sites for both the Au top layer and the PMMA underlayer to initiate dewetting at and guidance for forming regularly spaced AuNPs with much narrower size distribution at significantly lower ion dose levels when compared to the thick, uniform underlayer case. We also found that the underlayer assisted dewetting in this case relaxes the restriction on pre-pattern periodicity to obtain a single NP per pattern period, which is a noteworthy departure from the pre-patterned solid substrate case. FIB-induced AuNP areas can have sharp boundaries and can be positioned on a selected area of a substrate with high positional accuracy, which is important for the implementation of devices in sensing, nano-optics/photonics, and optoelectronic applications.

Microelectromechanical system pressure sensor integrated onto optical fiber by anodic bonding.

Optical microelectromechanical system pressure sensors based on the principle of Fabry-Perot interferometry have been developed and fabricated using the technique of silicon-to-silicon anodic bonding. The pressure sensor is then integrated onto an optical fiber by a novel technique of anodic bonding without use of any adhesives. In this anodic bonding technique we use ultrathin silicon of thickness 10 microm to bond the optical fiber to the sensor head. The ultrathin silicon plays the role of a stress-reducing layer, which helps the bonding of an optical fiber to silicon having conventional wafer thickness. The pressure-sensing membrane is formed by 8 microm thick ultrathin silicon acting as a membrane, thus eliminating the need for bulk silicon etching. The pressure sensor integrated onto an optical fiber is tested for static response, and experimental results indicate degradation in the fringe visibility of the Fabry-Perot interferometer. This effect was mainly due to divergent light rays from the fiber degrading the fringe visibility. This effect is demonstrated in brief by an analytical model.

Agile wide-angle beam steering with electrowetting microprisms.

A novel basis for beam steering with electrowetting microprisms (EMPs) is reported. EMPs utilize electrowetting modulation of liquid contact angle in order to mimic the refractive behavior for various classical prism geometries. Continuous beam steering through an angle of 14 degrees (+/-7 degrees ) has been demonstrated with a liquid index of n=1.359. Experimental results are well-matched to theoretical behavior up to the point of electrowetting contact-angle saturation. Projections show that use of higher index liquids (n~1.6) will result in steering through ~30 degrees (+/-15 degrees ). Fundamental factors defining achievable deflection range, and issues for Ladar use, are reviewed. This approach is capable of good switching speed (~ms), polarization independent operation, modulation of beam field-of-view (lensing), and high steering efficiency that is independent of deflection angle.