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 ...

We propose a rapid, one-pot method to generate photoluminescent (PL) mesoporous silicon nanoparticles (PSiNPs). Typically, mesoporous silicon (meso-PSi) films, obtained by electrochemical etching of monocrystalline silicon substrates, do not display strong PL because the silicon nanocrystals (nc-Si) in the skeleton are generally too large to display quantum confinement effects. Here we describe an improved approach to form photoluminescent PSiNPs from meso-PSi by partial oxidation in aqueous sodium borate (borax) solutions. The borax solution acts to simultaneously oxidize the nc-Si surface and to partially dissolve the oxide product. This results in reduction of the size of the nc-Si core into the quantum confinement regime, and formation of an insulating silicon dioxide (SiO 2 ) shell. The shell serves to passivate the surface of the silicon nanocrystals more effectively localizing excitons and increasing PL intensity. We show that the oxidation/dissolution process can be terminated by addition of excess citric acid, which changes the pH of the solution from alkaline to acidic. The process is monitored in situ by measurement of the steady-state PL spectrum from the PSiNPs. The measured PL intensity increases by 1.5- to 2-fold upon addition of citric acid, which we attribute to passivation of non-radiative recombination centers in the oxide shell. The measured PL quantum yield of the final product is up to 20%, the PL activation procedure takes <20 min, and the resulting material remains stable in aqueous dispersion for at least 1 day. The proposed phenomenological model explaining the process takes into account both pH changes in the solution and the potential increase in solubility of silicic acid due to interaction with sodium cations.

The preparation of luminescent core–shell nanoparticles of porous silicon is reported by M. J. Sailor and co‐workers on page 5688. The “shell” in these nanoparticles is a passivating silicon oxide layer, synthesized by partial oxidation of the quantum‐confined crystalline silicon skeleton in an aqueous solution of sodium tetraborate (borax). Control of the chemistry of the passivation layer is found to be crucial to maximize the quantum yield and to control the rate of aqueous dissolution of the resulting nanoparticles.

Pediatric malignancies are rare compared to adult cancers, and cooperative groups such as the Children's Oncology Group (COG) serve critical roles in testing key question in clinical trials. We sought to characterize the prevalence of off-study treatment of pediatric patients per Children's Oncology Group (COG) trials, as this approach may offer improved clinical outcomes but may also subject children to treatment with suboptimal, unproven regimens. Materials/Methods: We conducted a 12-question REDCap survey that was sent to 358 radiation oncologists listed as members of COG. Radiation oncologists were queried regarding their practice patterns for recent and ongoing COG protocols for medulloblastoma (ACNS0331, ACNS1422), ependymoma (ACNS0121), neuroblastoma (ANBL0532), Ewing sarcoma (AEWS1221), rhabdomyosarcoma (ARST1431), and Hodgkin lymphoma (AHOD1331). Data were collected anonymously through January 2020. Results: We received 97 responses (27.1%). The most common factor affecting consideration of immediate adoption of COG trial paradigms was improvement of clinical outcomes (n Z 70, 77.8%). Nine radiation oncologists treated average-risk medulloblastoma with 18 Gy craniospinal irradiation (CSI) off-study prior to publication of the ACNS0331 results (abstract, 2016). Eight physicians consider 18 Gy CSI for WNT-driven average-risk medulloblastoma, per the open ACNS1422. Of the 21 respondents who omitted radiation for grade II supratentorial ependymomas after gross total resection (GTR), 9 still consider this approach off-study since publication of ACNS0121 that showing 5 out of 11 patients recurring in the observation arm. Of the 50 radiation oncologists who treated highrisk neuroblastoma with boost to 36 Gy if GTR was not achieved, per ANBL0532, 10 still consider boost since publication of the ANBL0532 abstract (2019) that showed no benefit to the boost. Thirty-two respondents treated metastatic Ewing sarcoma with SBRT per AEWS1221, off-study. Twenty chose SBRT doses other than the AEWS1221-recommended 40 Gy in 5 fractions. Forty-one treated group 3 rhabdomyosarcoma with radiation tailored to chemotherapy-response per the open ARST1431 study. Fifty-four who treat high-risk Hodgkin lymphoma considered radiation to bulky mediastinal disease or sites with poor response to chemotherapy and 74 used involved site radiotherapy (ISRT) as prescribed by the open AHOD1331 study. Conclusion: Many pediatric radiation oncologists adopt COG trial treatment regimens before data are available in either abstract or final peer-reviewed form. This approach has the potential to offer patients state-of-the-art treatments, early in their development. However, given that some trials find no benefit and/or disclose detriment of tested radiation treatment paradigms, it is increasingly important to enroll patients on trial rather than follow regimens of open clinical trials, off-study, prior to availability of the results.