Controlling bacterial growth using artificial nanostructures inspired
from natural species is of immense importance in biomedical applications.
In the present work, a low cost, fast processing, and scalable anisotropic
wet etching technique is developed to fabricate the densely packed
disordered silicon nanopyramids (SiNPs) with nanosized sharp tips.
The bactericidal characteristics of SiNPs are assessed against strains
implicated in nosocomial and biomaterial-related infections. Compared
to the bare silicon with no antibacterial activities, SiNPs of 1.85 ±
0.28 μm height show 55 and 75% inhibition of Escherichia coli (Gram-negative) and Bacillus subtilis (Gram-positive) bacteria, whereas
the silicon nanowires (SiNWs) fabricated using a metal-assisted chemical
etching method show 50 and 58% inhibition of E. coli and B. subtilis. The mechanistic
studies using a scanning electron microscope and live/dead bacterial
cell assay reveal cell rupture and predominance of dead cells on contact
with SiNPs and SiNWs, which confirms their bactericidal effects. Chemical
stability and cell viability studies demonstrate the biocompatible
nature of SiNP and SiNW surfaces. Owing to their capability to kill
both Gram-negative and positive bacteria and minimal toxicity to murine
fibroblast cells, SiNPs can be used as an antibacterial coating on
medical devices to prevent nosocomial and biomaterial-related infections.
Controlling the light reflection using vertically-aligned nanowires has great importance in fundamental research with interesting applications in photonic devices. Here, we discuss the spatial- and polarization-dependent reflectivity measurements from the cross-sectional as well as from the top surface of vertically-aligned disordered silicon nanowires. The gradient variation in an effective refractive index along the nanowire length is estimated using the cross-sectional reflectivity measurements. We have studied the gradient variation of an effective refractive index profile and its tunability with the nanowire length. The reflectivity is measured to be as low as 5% irrespective of spatial directions and the polarization of incident light in a broad wavelength range. This constitutes the signature of a broadband omnidirectional anti-reflector that is scalable with the nanowire length. The reflectivity measurements are in good agreement with theoretical calculations. Such omnidirectional anti-reflection in a broad wavelength range is useful for applications such as photon management in photovoltaic devices and disorder-induced light scattering.
The spatial- and spectral-dependent optical reflectivity measurements are essential to characterize various natural as well as artificial micron-scale photonic nanostructures. However, it is onerous to measure spatially and spectrally resolved reflectivity values from such photonic nanostructures due to their size limitations. Here, we discuss the development of a versatile micro-reflectivity setup with an in situ optical microscope combined with high-resolution actuators to measure the reflectivity from areas as small as 25 × 25 µm2. We illustrate the reflectivity measurements from natural as well as artificially prepared ordered and disordered photonic nanostructures. The optical features that are hidden in the conventional reflectivity measurements are clearly resolved using the micro-reflectivity measurements. The proposed setup is also capable of measuring the polarization-dependent reflectivity and transmission of light.
The sparkling colors on the wing scales of butterflies are one of the most fascinating light–matter interactions in nature and have been an intense area of research in recent times. Controlling the light diffusion and absorption due to multiple scattering induced by the inherent disorder in the wing scales is required for applications in imaging, light trapping, and localization using such bio-inspired photonic structures. Here, we study the selective anisotropic light diffusion and absorption in the nanoarchitectures of Pieris rapae and Graphium sarpedon butterfly wing scales in the visible range. We have measured broadband spatially independent low values of specular reflectivity and ballistic transmission from the ventral and the dorsal sides of the wing scales, which are supported with finite-difference time-domain simulations. The specular reflectivity value as small as 3% indicates strong diffuse scattering within the scales, probed using total transmission and reflection measurements. We have found finite wavelength-dependent absorption
<2024 scite LLC. All rights reserved.