Hymenopteran parasitoid complex and fall armyworm: a case study in eastern India.

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) has significantly affected maize crop yields, production efficiency, and farmers' incomes in the Indian Eastern Gangetic Plains region since it was first observed in India in 2018. A lack of awareness by maize growers of the appropriate selection, method, and timing of insecticide application not only creates a barrier to sustainable FAW control but also contributes to increased environmental pollution, reduced human health and increased production costs. We demonstrated that FAW inflicted the most damage in early whorl growth stage of maize, regardless of whether chemical insecticides were applied. FAW egg masses and larvae collected from maize fields in which no insecticides had been sprayed showed high parasitism rates by parasitoid wasps; in contrast fields that had been sprayed had much lower rates of parasitism on FAW. Ten hymenopteran parasitoids were observed in maize fields across the study region, suggesting a diversity of natural methods to suppress FAW in maize at different growth stages. These included two FAW egg parasitoids and eight FAW larval parasitoids. Microplitis manilae Ashmead was the most abundant FAW larval parasitoid species, and Telenomus cf. remus was the dominant FAW egg parasitoid species. Endemic FAW parasitoids such as those observed in this study have great potential as part of a sustainable, cost-effective agroecological management strategy, which can be integrated with other methods to achieve effective control of FAW.

Light-to-Heat Conversion of Optically Trapped Hot Brownian Particles.

Anisotropic hybrid nanostructures stand out as promising therapeutic agents in photothermal conversion-based treatments. Accordingly, understanding local heat generation mediated by light-to-heat conversion of absorbing multicomponent nanoparticles at the single-particle level has forthwith become a subject of broad and current interest. Nonetheless, evaluating reliable temperature profiles around a single trapped nanoparticle is challenging from all of the experimental, computational, and fundamental viewpoints. Committed to filling this gap, the heat generation of an anisotropic hybrid nanostructure is explored by means of two different experimental approaches from which the local temperature is measured in a direct or indirect way, all in the context of hot Brownian motion theory. The results were compared with analytical results supported by the numerical computation of the wavelength-dependent absorption efficiencies in the discrete dipole approximation for scattering calculations, which has been extended to inhomogeneous nanostructures. Overall, we provide a consistent and comprehensive view of the heat generation in optical traps of highly absorbing particles from the viewpoint of the hot Brownian motion theory.

Angle-resolved plasmonic photocapacitance of gold nanorod dimers.

The assembly of nanostructures with plausible statistical orientations has provided the opportunity to correlate physical observables to develop a diverse range of niche applications. The dimeric configurations of gold nanorods have been chosen as atypical model systems to correlate optoelectronic with mechanical properties at a number of combinations of angular orientations. Metals are considered as conductors in electronics and reflectors in optics - therefore, metallic particles at the nanoscale exhibit unique optoelectronic characteristics that enable the design of materials to meet the demand of the modern world. Gold nanorods have often been adopted as prototypical anisotropic nanostructures owing to their excellent shape-selective plasmonic tunability in the vis-NIR region. When a pair of metallic nanostructures is sufficiently close to exhibit electromagnetic interaction, the evolution of collective plasmon modes, substantial enhancement of the near-field and strong squeezing of the electromagnetic energy at the interparticle spatial region of the dimeric nanostructures occur. The localised surface plasmon resonance energies of the nanostructured dimers strongly depend on the geometry as well as the relative configurations of the neighbouring particle pairs. Recent advances in the 'tips and tricks' guide have even made it possible to assemble anisotropic nanostructures in a colloidal dispersion. The optoelectronic characteristics of gold nanorod homodimers at different mutual orientations with statistical variation of the angle between 0 and 90° at particular interparticle distances have been elucidated from both theoretical and experimental perspectives. It has been observed that the optoelectronic properties are governed by mechanical aspects of the nanorods at different angular orientations of the dimers. Therefore, we have approached the design of an optoelectronic landscape through the correlation of the plasmonics and photocapacitance through the optical torque of gold nanorod dimers.

Photothermal Reshaping of One-Dimensional Plasmonic Polymers: From Colloidal Dispersion to Living Cells.

Cellular internalization of plasmonic metal nanostructured materials has recently become a requisite for biomedical engineering of several intracellular processes that could foster an extensive paradigm to perform desired functions in the living cells. While numerous anisotropic metal nanostructures can be employed to pursue the specific functions, their incorporation becomes restricted due to morphological specificity to be engulfed in the cells. Due to recent advent in the self-assembly strategies, individual gold nanospheres could be interdigitated to one-dimensional plasmonic polymers and undergo subsequent laser-induced photothermal reshaping to rod-like nanostructures. The salient feature of biological significance is merely the variation of particle size within the polymers that engenders a dramatic impact on the radiative and nonradiative properties expressed in the scale of Faraday number (F a) and Joule number (J 0), respectively, as a function of the aspect ratio (α) of the nanorods. The effect on the nonradiative properties augments designing of nanoscale thermometry essential for photothermal applications in living cells. The conception of the colloidal dispersion has been extended to the cellular environment in a mice model; the selective accumulation of the nanostructures in the cells could provide an invading relationship between plasmonic characteristics, temperature distribution, and the biological issues. The critical correlation between optical and thermal characteristics toward biomedical manipulation from both theoretical and experimental perspectives could augment a milestone toward the progress of modern medical sciences.

Plasmonic Sensing: Connecting the Dots.

Plasmonic sensitivity of noble metals has often been attributed to the morphology of the nanostructures and dielectric effects of both the materials and the surrounding medium. The measurable plasmonic shift with respect to the change in local dielectric as a function of analyte concentrations within nanoscale volume forms the basis of plasmonic sensing. However, the situation of the surrounding medium in the presence of multicomponent systems and, moreover, inhomogeneous adsorption around the anisotropic nanostructures become seemingly complicated as the precise description of several individual components becomes nearly impossible. Therefore, we have designed a retrospective formalism through a critical condensation of the electromagnetic scattering theories, macroscopic mixing rules, and micromechanics at the metal-analyte interface that can be adopted as generalized model irrespective of morphology of the nanostructures and the nature of analytes to account for the response of all the individual (microscopic) components to the observed (macroscopic) plasmonic sensing.

Manipulating the confinement of electromagnetic field in size-specific gold nanoparticles dimers and trimers.

The intriguing light-matter interactions can be governed by controlling the particle size and shape, electromagnetic interactions and dielectric properties and local environment of the metal nanostructures. Amongst the different approaches that have been engendered to manipulate light at the nanoscale, the self-assembly of metallic nanostructures with controllable interparticle distances and angular orientations, which strongly impact their optical attributes, is one of the viable avenues to exploit their utility in a diverse range of niche applications. The simplest geometrical architectures that enable such modulations are dimers with changeable interparticle distances and trimers with an additional degree of angular orientation to correlate the plasmonic observables with the observed spectral characteristics. Wet chemical approaches have been adopted in this study for the synthesis of size-selective gold nanoparticles, and appropriate organic linkers have judiciously been employed to induce plasmonic interactions amongst the gold nanoparticles in close proximity to each other. The combination of experimental observations and electromagnetic simulations adopted to probe the plasmonic interactions revealed that the electrodynamic coupling effect was very sensitive to particle size, interparticle distances and angular orientations in these simple nanoassemblies. The capability to precisely manipulate the electric field at the junctions between these plasmon-coupled nanoparticles could pave the way for the application of these nanoassemblies in surface-enhanced spectroscopies and sensing applications.