Porous Silicon for Photosensitized Formation of Singlet Oxygen in Water and in Simulated Body Fluid: Two Methods of Modification by Undecylenic Acid

Abstract

Initially H-terminated and therefore hydrophobic surface of electrochemically prepared luminescent porous silicon (PSi) powder was transformed to the hydrophilic one by means of surface modification by undecylenic acid. Physical adsorption of undecylenic acid as a non-ionic surfactant and its chemical binding through C[triple bond]C bond opening and Si-C bond formation were applied as two different methods of PSi surface modification, physical and chemical modification, respectively. Luminescence of aqueous suspensions of the both types of modified PSi powders in merely water and in simulated body fluid physiological electrolyte was measured as a function of time. Many-fold (up to 20 times) building-up of the luminescence intensity was observed for PSi aqueous suspensions during the first few days, the growth was followed by a slower (a week and more) luminescence intensity decay. As it is evidenced by FTIR spectra and SEM images, the effect of the luminescence growth and decay of PSi suspension in water can be in part attributed to the PSi surface oxidation accompanied by its dissolution and de-aggregation of large PSi particles. It is concluded also from the experiments on PSi luminescence reversible quenching by O2 that SiO-related surface states with the excitation energy about 2.2 eV are formed during water-assisted oxidation of Si nanocrystal surface. An appearance of a large number of such surface states can be also responsible for the observed PSi luminescence building-up.

Peptides for the Biofunctionalization of Silicon for Use in Optical Sensing with Porous Silicon Microcavities

“…Biomolecules can also be sensed by optical reflectivity to reveal refraction index changes within a photonic PSi structure such as a microcavity resonator (PSM), as any slight change in the effective optical thickness (product of refractive index and physical thickness) causes a spectral shift in the interference peaks 23–25. It was also recognized that to obtain reliable optical and photosensitizing properties, PSi materials need to be conveniently stabilized 26. To avoid unwanted protein denaturation when in contact with SC surfaces, proteins must first be functionalized with linkers 27.…”

Protein delivery based on uncoated and chitosan-coated mesoporous silicon microparticles

“…The use of composite nanostructured materials in pharmaceutical technology is a powerful approach that opens new possibilities for the development of highly functional drug delivery devices. Better known in microelectronics, nanostructured semiconductors have been recently recognized to bear great promise for biomedical purposes such as tissue engineering [1], medical diagnosis [2], and drug delivery [3,4]. One of the most interesting features of porous silicon is its longterm stability at low pH (<6.0) [5] and the high hydrophobic nature of its native surface that can be extremely advantageous for the adsorption and delivery of small hydrophobic molecules such as doxorubicin [6], dexamethasone [7] or porphyrins [8].…”

3D porous silicon (nanorods array, nanosheets, and nanoclusters) production

“…Plus, its pore sizes and the surface chemistry are controllable [2]. NPS powder can be obtained using several techniques [3][4][5]; as electrochemical [6], vapor phase etching [7] and stain etching of Si-wafers [8]. The production of bulk (PS) in large dimensions shape that is synthesized using ball milling process and pressing, simultaneously, and sintering of Siparticles.…”