Photoluminescent Porous Si/SiO₂ Core/Shell Nanoparticles Prepared by Borate Oxidation

Abstract

5688 wileyonlinelibrary.com emission. [ 5 ] The emission from nanocrystalline silicon is much more effi cient than the corresponding process in bulk silicon due to a combination of two effects: 1) electron and hole wave functions overlap more effectively in quantum-confi ned silicon, [ 6 ] and 2) nonradiative impurities and lattice defects are not as accessible when the bulk silicon material is divided into nanocrystalline domains. [ 5,7 ] It is widely accepted that the green to near infrared PL from PSi originates from band-toband recombination of quantum-confi ned excitons, [ 8 ] and that the emissive centers responsible for PL are strongly infl uenced by oxides and other species at the Si surface. [ 9 ] This also appears to be the case for nanoparticles derived from PSi.Micron-scale and nanoscale particles of luminescent PSi have been employed for biological applications due to their biocompatibility, biodegradability and large specifi c capacity for therapeutic reagents. [10][11][12][13][14][15][16][17] For in vivo imaging, luminescent PSi nanoparticles (LPSiNPs) are an attractive alternative to conventional heavy-metal-containing quantum dots, which have been shown to be toxic in biological environments. [18][19][20][21] In addition, the long-lived excited state of LPSiNPs allows high fi delity, low background imaging when employed in time gated experiments. [ 22 ] A limitation of LPSiNPs has been that the quantum yield is typically <10%, [ 10 ] signifi cantly lower than direct band-gap semiconductor quantum dots or many of the common organic imaging fl uorophores. For instance, with the proper surface passivation, CdSe and CdS quantum dots can achieve PL quantum yields of ≈80-90%. [23][24][25][26] A number of reports have demonstrated quantum yields for individual silicon nanocrystals as large as 60%, [27][28][29][30][31][32] however these are dense Si nanocrystals and not porous nanostructures. The relatively low quantum yield of LPSiNPs is assumed to be due to the existence of nonradiative defects at the surface of the high surface area silicon skeleton. A method for overcoming this specifi c limitation is needed.Here we present a systematic study of the activation of photoluminescence in PSi derived nanoparticles by controlled chemical oxidation of the surface. A number of reports have demonstrated LPSiNPs as biological imaging agents, [ 4,10,22,33,34 ] and the material used in all of these can be considered to be a core-shell nanoparticle in which a shell of SiO 2 encases the active porous Si skeleton. However, the growth of oxide used to activate PL in these LPSiNPs has not been investigated in Photoluminescent Porous Si/SiO 2 Core/Shell Nanoparticles Prepared by Borate OxidationJinmyoung Joo , Jose F. Cruz , Sanahan Vijayakumar , Joel Grondek , and Michael J. Sailor * A systematic study on the activation of photoluminescence from luminescent porous silicon nanoparticles (LPSiNPs) by oxidation in aqueous media containing sodium tetraborate (borax) is presented. The treatment promotes surface oxidation ...

Gated Luminescence Imaging of Silicon Nanoparticles

“…Luminescent PSiNPs were prepared with a Si-SiO 2 core—shell structure as described previously 50,51 and polyethylene glycol (PEG) was grafted to the outer shell to improve colloidal stability and biocompatibility. We chose a mouse brain for this set of experiments (Figure 1c) due to the typically high levels of autofluorescence seen from these tissues.…”

“…The freestanding porous silicon film was fractured by ultrasonication for 16 h, and the resulting nanoparticles were mildly oxidized by immersion in aqueous solution of sodium tetraborate (0.8 mM) to activate photo-luminescence. 51 To conjugate peptides to the PSiNPs, a 500 μ L aliquot of PSiNPs (2 mg mL −1 in ethanol) was mixed with 10 μ L of 3-(ethoxydimethyl)-propylamine silane by vortex overnight. The nanoparticles were rinsed three times with ethanol and then further reacted with 500 μ L of succinimidyl carboxy methyl ester–polyethylene glycol–maleimide (SCM-PEG-MAL, MW 5000, Laysan Bio, 10 mg mL −1 in ethanol) for 2 h, followed by rinsing with ethanol and deionized water.…”

Antibiotic-loaded nanoparticles targeted to the site of infection enhance antibacterial efficacy

“…58, 59 In brief, the silicon wafer was anodized in an electrolyte composed of 3:1 ( v:v ) of 48 % aqueous HF:ethanol. The etching waveform consisted of a square wave in which a lower current density of 50 mA/cm 2 was applied for 1.8 sec, followed by a higher current density pulse of 400 mA/cm 2 for 0.36 sec.…”

Tunable and white light emitting AlPO4 mesoporous glass by design of inorganic/organic luminescent species

“…22,23 We note that our result is, in general, higher than the room temperature quantum yield reported for porous silicon. 24 The inset of Fig. 3(c) gives pink, white, and green luminescent photos taken under 395 nm excitation in dark, respectively, further indicating that Eu-coumarin 535 co-doped AlPO 4 mesoporous glasses could be used as converting phosphors for UV LED chips to generate W-LEDs.…”