Nonresonant CARS Imaging of Porous and Solid Silicon Nanoparticles in Human Cells

Coherent anti-Stokes Raman scattering (CARS), a nonlinear optical method for rapid visualization of biological objects, represents a progressive tool in biology and medicine to explore cells and tissue structures in living systems and biopsies. In this study, we report efficient nonresonant CARS imaging of silicon nanoparticles (SiNPs) in human cells as a proof of concept. As both bulk and porous silicon exhibit a high third-order nonlinear susceptibility, χ⁽³⁾, which is responsible for the CARS intensity, it is possible to visualize the SiNPs without specific labels. Porous and solid SiNPs were obtained from layers of porous and nonporous silicon nanowires and mesoporous silicon. Electron microscopy and Raman spectroscopy showed that porous SiNPs consisted of ∼3 nm silicon nanocrystals (nc-Si) and pores, whereas solid nanoparticles comprised ∼30 nm nc-Si. All types of SiNPs were nontoxic at concentrations up to 500 μg/mL after 24 h of incubation with cells. We demonstrated that although nc-Si possesses a distinguished narrow Raman band of about 520 cm^-1, it is possible to detect a high CARS signal from SiNPs in the epi-direction even in a nonresonant regime. 3D CARS images showed that all types of studied SiNPs were visualized as bright spots inside the cytoplasm of cells after 3-6 h of incubation because of the contrast provided by the high third-order nonlinear susceptibility of SiNPs, which is 1 × 10⁴ to 1 × 10⁵ times higher than that of water and typical biological media. Overall, CARS microscopy can provide localization of SiNPs within biological structures at the cellular level and can be a powerful tool for in vitro monitoring of silicon-based drug delivery systems or use SiNPs as labels to monitor various bioprocesses inside living cells.

Multifunctional hydrophobin: toward functional coatings for drug nanoparticles

Efficient delivery of nanosized drug formulations to the desired body sites is not always reached despite the rapid development of pharmaceutical nanotechnologies. In spite of the undoubted effect of the size for increased bioavailability and controlled drug delivery, submicrometer formulations also require a deeper level of design. The surface properties of the particles determine the stability of the particles, interactions with the body, and targeting potentials of drugs. Thus, the efficacy of the drug can be increased utilizing the surface layer of the nanoparticles. Influencing the surface characters of the drug is the main focus of the present work, which introduces a method for preparing nanoparticles with functional sites from low-solubility drugs using hydrophobin (HFB) proteins. Particles were prepared by precipitating a lipophilic drug (beclomethasone dipropionate) in water in the presence of the HFB proteins. Particle size below 200 nm could easily be reached with increasing HFB concentration. The particles were shown to be stable for at least 5 h in suspension, and they could be stored for longer periods of time after freeze-drying. Labeling studies using green fluorescent protein (GFP) genetically fused to a HFB clearly demonstrated that the surface of the nanoparticles was covered with the hydrophobins and that the surface could be further modified by utilizing fusion proteins. This provides a template for a variety of different functional surface-bound groups that could be tailored by modifying the hydrophilic side of the HFB via protein bioengineering. In this study, the combination of proteins and traditional pharmaceutical technology was used to synthesize functionalized protein-coated nanoparticles for drug delivery purposes.

Surface Pressure, Hysteresis, Interfacial Tension, and CMC of Four Sorbitan Monoesters at Water-Air, Water-Hexane, and Hexane-Air Interfaces

The purpose of this study was to investigate the interfacial properties of sorbitan monoesters (Span 20, 40, 60, and 80). The surface pressure was investigated at the water-air interface using a Langmuir-Blodgett apparatus. Interfacial tensions at n-hexane-air and water-n-hexane interfaces were measured by a du Nouy tensiometer. The effects of different surface-active agents and their concentrations on the interfacial properties of surfactant films were determined. With saturated sorbitan monoesters the lengthening of the hydrocarbon chain increases the collapse pressure and molecular area at the water-air interface. Unsaturated Span 80 had a lower collapse pressure and a larger molecular area than its saturated counterpart Span 60. Under compression-expansion cycles, all sorbitan monoesters showed hysteresis effects. At the n-hexane-air interface there were no differences in the interfacial tension between different sorbitan monoesters. At the water-n-hexane interface, differences in CMCs were small, but the surface excess of Span 80 was markedly smaller and the molecular area larger than the corresponding values of other sorbitan monoesters. Copyright 2000 Academic Press.