Agglomeration of Luminescent Porous Silicon Nanoparticles in Colloidal Solutions

Abstract

We have prepared colloidal solutions of clusters composed from porous silicon nanoparticles in methanol, water and phosphate-buffered saline (PBS). Even if the size of the nanoclusters is between 60 and 500 nm, due to their highly porous “cauliflower”-like structure, the porous silicon nanoparticles are composed of interconnected nanocrystals having around 2.5 nm in size and showing strong visible luminescence in the orange-red spectral region (centred at 600–700 nm). Hydrophilic behaviour and good solubility of the nanoclusters in water and water-based solutions were obtained by adding hydrogen peroxide into the etching solution during preparation and 16 min long after-bath in hydrogen peroxide. By simple filtration of the solutions with syringe filters, we have extracted smaller nanoclusters with sizes of approx. 60–70 nm; however, these nanoclusters in water and PBS solution (pH neutral) are prone to agglomeration, as was confirmed by zeta potential measurements. When the samples were left at ambient conditions for several weeks, the typical nanocluster size increased to approx. 330–400 nm and then remained stable. However, both freshly filtered and aged samples (with agglomerated porous silicon nanoparticles) of porous silicon in water and PBS solutions can be further used for biological studies or as luminescent markers in living cells.

In Situ Growth of ZnO inside a Porous Silicon Matrix Obtained by Electrochemical Etching with a Hydrofluoric Acid-Formaldehyde Solution

“…We noted the presence of two well-determined luminescence bands: a band of luminescence centered at 700 nm and another band of luminescence centered at 727 nm. As discussed above, the origin of these bands is due to quantum confinement in PS [22]. Similarly, for the ZnO/PS shown in Figure 2(c), the presence of three well-determined luminescence bands was observed: two at 698 nm and 712 nm corresponding to the quantum confinement of electrons in the nanocrystals of silicon in PS [22] and another centered at 774 nm that has been related to oxygen defects such as O i and O Zn [25][26][27].…”

“…The band of luminescence centered at 548 nm may be associated with the complex nature of the surface states present on the large internal surface of the PS [21]. The PL emission band from 620-800 nm originates from the quantum confinement of electrons in the nanocrystals of silicon in PS [22].…”

Structural and luminescence properties of silicon nanocrystals in colloidal solutions for bio applications

“…Hydrophylic behavior of the Si‐ncs can be achieved through deeper oxidation of the silicon nanoparticles by slight modification of the etching conditions: “oxidized” porous silicon was etched with addition of a small amount of 30% hydrogen peroxide to the electrolyte, then having an after‐etching hydrogen peroxide bath for 16 min (for more details on preparation conditions, see Ref. ).…”

“…Surface modification of Si‐ncs in colloidal solutions by methyl groups was carried out in plasma‐synthesized Si‐ncs, too, and the attempt to avoid agglomeration by steric stabilization of the Si‐ncs by simple organic compounds is presented (see also Ref. ).…”

Si nanocrystal solution with stability for one year

“…hydrocarbons, 40,52 and stable optical properties over a period of months were observed aer long-alkyl passivation. 33,44 Because Si is a bioinert, abundant, and cost-effective material, [59][60][61][62] colloidal SiNPs have been used to develop solar cells, 63 light emitters, 64 on-skin sensors, 65 and Li-ion batteries 66 via solution processes. [67][68][69][70][71][72][73][74][75][76] In a previous study, we synthesized SiNCs using the two different methods of PLA 30,35,42,44,46,47,54 and ball milling, 77 both of which are mechano-synthesis methods.…”