Structural and optical properties of nanoparticles formed by laser ablation of porous silicon in liquids: Perspectives in biophotonics

Abstract

The paper discusses the possibility of manufacturing silicon nanoparticles, which are suitable for contrasting biological tissues imaged by optical coherence tomography, by femtosecond laser ablation of porous silicon in various liquids. The manufactured nanoparticles are characterised by average sizes of 87, 112, and 102 nm for cases of ablation in water, ethanol, and liquid nitrogen, respectively, as well as a relatively narrow size distribution, which provides additional advantages for subsequent delivery into biological tissues. Electrochemical etching, which results in the formation of layers of porous silicon, allows the yield of ablation products to be increased several-fold by lowering the ablation threshold, thereby increasing the light scattering efficiency of the prepared suspensions compared with the case of using crystalline silicon as targets. The possibility of obtaining high-contrast images of a biotissue phantom based on an agar gel with embedded nanoparticles is shown. The magnitude of the contrast depends on the liquid used for ablation and correlates with the values of the reduced scattering coefficient of the studied suspensions.

Nanoparticles Produced via Laser Ablation of Porous Silicon and Silicon Nanowires for Optical Bioimaging

“…Additionally, the particles formed by ablation in water from microporous silicon demonstrate a pronounced bimodal size distribution. This phenomenon was earlier registered at pulsed laser ablation of crystalline silicon in water [18] and can be explained by the theory developed by Shih et al [42]. The appearance of smaller particles is due to the fast nucleation of atoms evaporated from Additionally, the particles formed by ablation in water from microporous silicon demonstrate a pronounced bimodal size distribution.…”

“…The appearance of smaller particles is due to the fast nucleation of atoms evaporated from Additionally, the particles formed by ablation in water from microporous silicon demonstrate a pronounced bimodal size distribution. This phenomenon was earlier registered at pulsed laser ablation of crystalline silicon in water [18] and can be explained by the theory developed by Shih et al [42]. The appearance of smaller particles is due to the fast nucleation of atoms evaporated from the target surface in the area of interaction with water molecules under continuous in time tendency towards thermodynamic equilibrium (cooling of ablation products) [39].…”

“…SiNPs are widely employed in fluorescence imaging either as contrasting agents [10,13,14] or sensors for quantitative measurements [15,16]. SiNPs-based contrast enhancement was demonstrated also in optical coherence tomography (OCT) [17,18] and magnetic resonance imaging [19]. Other SiNPs applications include tissue engineering [20], nonlinear-optical diagnostics [21], photo- [22] and ultrasound [23] hyperthermia.…”

“…Pulsed laser ablation in liquids (PLAL) technique allows to overcome this limitation and provides small mean sizes (5-100 nm) and chemical purity for biomedical applications of SiNPs simultaneously [14,17,18,[20][21][22]30]. However, to produce SiNPs with high concentration, this method requires either lasers with high pulse repetition rate and energy, or significant increase in exposure time.…”

“…Earlier we have demonstrated prospects of using SiNPs produced via PLAL of PSi as OCT [18] and fluorescence imaging [32] contrasting agents. The main aim of this work is a comprehensive study of structural, absorption, scattering, and fluorescence properties of SiNPs fabricated via PLAL of both target types: PSi films and SiNW arrays with different doping levels which defines the morphology of the targets [18,33,34].…”