Silicon Nanoparticle based Fluorescent Biological Label via Low Temperature Thermal Degradation of Chloroalkylsilane

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1 Supporting Informations Silicon Nanoparticle based Fluorescent Biological Label via Low Temperature Thermal Degradation of Chloroalkylsilane By Pradip Das, a Arindam Saha, a Amit Ranjan Maity, a Sekhar C. Ray b and Nikhil R. Jana a, * Experimental Section Materials: Chloro(dimethyl)octadecylsilane (95%), octadecylamine (ODA, 9%), folic acid (FA, 97%), triethylamine (Et 3 N, 99%), poly(maleic anhydride-alt--octadecene) (M n 3,-5,), O,O -Bis(2- aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol (M r 5), dimethyl sulfoxide (DMSO), N,N -dicyclohexylcarbodiimide (DCC, 99%), N-hydroxy succinimide (NHS, 98%) were purchased from Sigma-Aldrich.,3,5-trimethylbenzene (TMB, 98%) was purchased from Spectrochem. Synthesis of silicon nanoparticles: Silicon nanoparticles were synthesized by low temperature thermal decomposition of chloro(dimethyl)octadecylsilane as a precursor in presence of octadecylamine as capping agent at normal atmospheric environment. Briefly, chloro(dimethyl)octadecylsilane (69.4 mg) and octadecylamine (6.7 mg) were added into 2 ml of TMB taken in three naked round bottom flask. This solution was then heated to 4 ºC for different times from 6 to 72 hours. Depending on heating time, the produced silicon nanoparticles were named as Si-6, Si-8, Si-36, Si-48 and. Silicon nanoparticles were isolated from free reagents by conventional precipitation-redispersion method. Typically, TMB solution of silicon nanoparticle is mixed with equal volume of hexane to precipitate the particles and precipitated particle were then isolated and dissolved in chloroform. This chloroform solution was then mixed with minimum volume of hexane to precipitate the particles. This precipitate is again isolated and dissolves in chloroform. This hexane based precipitation and chloroform based dissolution is repeated 2-3 times and finally particles were dissolved in chloroform.

2 Synthesis of polymer coated nanoparticles: Polymer coated nanoparticles were prepared using the previously described method with minor modification. 52,53 In brief, 2 mg poly(maleic anhydride-alt--octadecene) polymer was dissolved in ml chloroform and mixed with 5 µl chloroform solution of nanoparticles (2 mg/ml) followed by sonication for minutes. Subsequently chloroform solution of 25 µl of O, O -bis(2-aminopropyl) polypropylene glycol-blockpolyethylene glycol-block-polypropylene glycol (PEG-diamine) (prepared by mixing 3:25 volume ratio of PEG-diamine and chloroform) was added and sonicated for minutes. After that additional 25 µl PEG-diamine solution was added and sonicated for further minutes. The resultant solution was allowed to stand overnight at room temperature and then chloroform was evaporated. The residue was dispersed in 2 ml of aqueous Na 2 CO 3 solution. The polymer coated aqueous nanoparticles was mixed with twice volume of acetone and precipitated particles were isolated from supernatant containing free polymer by high speed centrifuge and dissolved in water. Finally particle solution was dialyzed to remove any excess reagents. Synthesis of folate-nhs: Folate-NHS was prepared following our reported method. 58 Briefly, folic acid (5 mg) and Et 3 N (75 µl) were added into ml of distilled DMSO and subsequently DCC (7 mg) was added. The solution was stirred for one hour in absence of light and then NHS (6 mg) was added to the solution followed by stirring for overnight under nitrogen atmosphere. The resultant folate-nhs was separated from solution by the addition of diethyl ether and purified by dry THF. Folate functionalization of nanoparticles: Polymer coated nanoparticles were reacted with folate-nhs to prepare the folate functionalized nanoparticles. The primary amine groups present on the surface of polymer coated particle reacted with NHS group with the resultant covalent linkage. In a typical process,.5 ml polymer coated nanoparticles solution was prepared in bicarbonate buffer solution of ph 9. Next, freshly prepared folate-nhs ( mm) solution was prepared in DMF and 2 µl of this solution was added to it. The solution was stirred for overnight and then excesses reagents and free folic acid were removed by dialyzing against basic water and then normal using dialysis membrane (MWCO ~2-4 Da).

3 Cell and tissue labeling: HeLa cells were cultured in cell culture flask and then subcultured in cell culture plate with.5 ml folate free RPMI-64 media having % fetal bovine serum (FBS) and % penicillin/streptomycin. After overnight, cells which were attached to the tissue culture plate were washed with phosphate buffer solution and then 5 µl fresh media was added. After overnight -5 µl of nanoparticles solution (2 mg/ml) was added and incubated for 4 hours. After that µl of nuclear straining dye (Hoechst 33342) was added and incubated for minutes. Next, unbound nanoparticles and excesses dye were removed by repeated washing with PBS buffer solution. The washed cells were fixed by using of 4 % paraformaldehyde followed by mounting with 5 % glycerol. The cells were then used for imaging. Human dissected cervical cancer positive tissue was frozen and sectioned following the standard procedure. 58 The conventional histopathological assay was used to detect cancer of the biopsy tissue samples. For labeling study, 5 μm thick sectioned tissue sample was incubated with nanoparticle solution for 4 hours and then extensively washed with PBS buffer solution to remove any unbound nanoparticles. Next, sample was incubated with solution of hoechst dye for 5 minutes for staining of cell nucleus. Finally, washed sample was imaged under bright field and fluorescence mode. MTT assay: HeLa cells were seeded into 24-well plate in 5 µl folate free RPMI-64 media. After 24 hours, cell were treated with various amounts of nanoparticles having different final concentration ( mg/ml) and incubated for 24 hours. After that cells were washed with PBS buffer solution. Next, 5 µl of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT, 5 mg /ml in PBS buffer) was added to every well and incubated for 4 hours. Next, the supernatant was removed carefully, leaving the violet formazan in the plate. The precipitate was mixed with 5 µl of : water-dmf mixture and then absorbance was measured at 57 nm using microplate reader. The relative cell viability was calculated assuming % cell viability for sample having no nanoparticle. Instrumentation: UV-Visible absorption spectra were measured using Shimadzu UV-255 UV-Visible spectrophotometer and photoluminescence emission, excitation spectra were obtained using BioTek

4 SynergyMx microplate reader. Transmission electron microscopy (TEM) imaging and energy dispersive X-ray (EDS) spectroscopy was performed using FEI Technai G2 F2 electron microscope. X-ray photoelectron spectroscopy (XPS) was performed using a Omicron (Serial No-57) X-ray photoelectron spectrometer. Time correlated single photon counting (TCSPC) spectra was obtained through exciting the sample with picoseconds diode laser (IBH Nanoled) using Horiba Jobin Yvon IBH Fluorocube apparatus. Temperature dependent photoluminescence (PL) of solid nanoparticles was performed by Triax 3 monochromator and a multichannel photomultiplier detector under UV excitation with 325 nm line of He- Cd laser. Fourier transform infrared (FTIR) spectroscopy was performed on Perkin Elmer Spectrum FTIR spectrometer. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed using TA SDT Q6 and TA DSC Q2 instrument, respectively. Electron paramagnetic resonance (EPR) was measured using JEOL JES-FA 2 ESR spectrometer using purified solid samples at 77 K. Dynamic light scattering (DLS) and Zeta potential study were performed using a NanoZS (Malvern) instrument, after dialyzing the samples. Fluorescence images and photostability of different silicon nanoparticles were performed by drop casting of sample solution on glass slide and images were taken using Olympus IX 8 microscope attached with digital camera. The fluorescence images of the cell/tissue were captured by Carl Zeiss Apotome Imager.Z fluorescence microscope.

5 Table S. Summary of different synthetic methods for fluorescent silicon nanoparticles. Silicon precursor Method Emission (QY) Size Functionalization/ application Ref. SiCl 4 reduction with sodium blue (-) 2- nm naphthalenide SiCl 4 reduction with LiAlH 4 blue ( %).4 nm bioimaging 29 Si(OMe) 4 reduction with LiAlH 4 blue (-3 %).6 nm bioimaging 3 SiCl 4 reduction with LiAlH 4 blue (3-23 %) -2 nm SiCl 4 reduction with NaPh 2 blue (2 %) -4 nm SiCl 4, reduction with LiAlH 4 blue (25 %) 3 nm hexyltrichloros ilane, diphenylsilane thermal degradation at 5 blue-green (23 %) -4 nm and 345 bar Diphenylsilane thermal degradation at 5 and 83 bar tetramethylsila ne/ tetraethylsilane SiBr 4 silane silane silane trichlorosilane octyltrichlorosi lane Si wafer thermal degradation at 68 C plasma assisted decomposition laser pyrolysis followed by HF-HNO 3 etching laser pyrolysis followed by HF-HNO 3 etching blue to red (---) 2-6 nm nm blue-green(24 %) 2-3 nm polymer coating (hydrodynamic size 5 nm), cell imaging blue to red 5 nm (---) red (7 % in 4 nm micelle incorporated ( CHCl 3, 2 % in nm), transferin functionalized water) and cell imaging blue-nir (---) 2-8 nm micelle encapsulated, in vivo 27 imaging red-nir (5-4 % in -5 nm toluene) laser pyrolysis followed by HF-HNO 3 etching pyrolysis followed by HF etching electrochemical reduction blue (6 %) 5 nm electrochemical etching in presence of HF, H 2 O 2, polyoxometalate silicon wafer electrochemical etching red to NIR ( %) 5 nm(porou s) hydrogen silsesquioxane thermal degradation at 5- C followed by HF etching blue-nir (---) -4 nm in vivo application 36 green-red (4 %) 3.4 nm hydrogen thermal degradation at NIR (26 %) 4 nm lipid capping, bioimaging 2 silsesquioxane -2 C hydrogen thermal degradation at red-nir (.4-8 %) 3-9 nm, silsesquioxane -4 C --- NaSi reaction with NH 4 Br blue (---) 4-5 nm Mg 2 Si reaction with Br 2 green (7 %) 2.4 nm functionalized with DNA 4 NaSi heating with NH 4 Br and green (3 %) 4 nm Gluteric acid functionalized, 38 glutaric acid at 2 o C bioimaging Na 4 Si 4 microwave heating with blue (23 %) 3.4 nm NH 4 Br Si nanowire microwave heating with red (5 %) 4 nm antibody conjugated, cell 4 glutaric acid imaging Si nanowire microwave heating with red (8 %) 3.2 nm 4 nm hydrodynamic size, 42 immunoglobulin bioimaging Silicon pieces ball milling blue (6 %) < nm

6 Table S2. Properties of various silicon nanoparticle prepared by present approach. Sample Excitation/ Emission Wavelength (nm) Fluorescence quantum yield ( ) Lifetime (ns) Si-6 37 nm/43 nm % a.8 Si-8 43 nm /5 nm 3 % b., 3.3, 9.2 Si nm/57 nm 6 % c.4, 4.6 Si nm/57 nm 6 % c.8, 2.7, nm/6 nm 8 % d.5, 4.6 Polymer 55 nm/6 nm 5 % d.5,.9, 5.9 coated 2 Quantum yield was measured using different standards such as quinine sulfate a, fluorescein b, rhodamine 6G c and rhodamine B d. Fluorescence quantum yield for each type of silicon nanoparticle is measured at the excitation wavelength that produces maximum emission intensity. 2 The quantum yield of polymer coated Si-6, Si-8, Si-36 and Si-48 nanoparticles are %, %, 3 % and 3 %, respectively.

7 Si-6 Si-6 Si-48 Si-6 Si-48 Polymer coated Figure S. TEM images of different size silicon nanoparticles under low and high magnifications. Size distributions of these nanoparticles are shown in Figure.

8 Figure S2. Energy dispersive X-ray (EDS) spectrum of Si-48 nanoparticles after complete separation of free reagents. The spectrum demonstrates the presence of silicon and oxygen suggesting that silicon nanoparticles surface has some oxides.

9 % Transmittance % Transmittance a) b) ODA Polymer coated Polymer CDOS Wavenumber (cm - ) Wavenumber (cm - ) Figure S3. a) FTIR spectra of chloro(dimethyl)octadecylsilane(cdos), octadecylamine(ods) and nanoparticle. The strong peaks around 3 cm - is due to C-H stretching of long chain hydrocarbons and strong peaks around 34 cm - is due to N-H/O-H stretching of octadecylamines/silanols. Si-C stretching frequency present at 245 cm - for CDOS is substantially decreased in, suggesting that Si-C bond in chloro(dimethyl)octadecylsilane precursor is broken in nanoparticle formation condition. (b) FTIR spectra of nanoparticle, polymer and polymer coated nanoparticle. The peaks at 2 cm - and 55 cm - in polymer coated samples indicates the presence of C-O and NH 2 groups, respectively, which proves effective polymer coating on the samples.

10 Weight loss (%) Heat Flow (W/g) Heat Flow (W/g) Intensity (CPS) Intensity (CPS) a C s b O s Binding Energy (ev) Binding Energy (ev) Figure S4. XPS spectra of (a) C s and (b) O s of purified nanoparticles showing that silicon nanoparticles consist of oxidized SiO x H y layer and passivating long chain octadecyl groups. Deconvoluted C s has been fitted with two components and assigned as C-C/C-H bond ( ev) and carbon atoms bonded to electronegative element such as nitrogen or oxygen ( 286.8). Deconvoluted O s spectrum fitted with three components with peaks at 53.7 ev, 53.7 ev and ev. The first two peaks are due to presence of Si-O and Si=O groups and third component comes from the surface hydroxyl groups. 8 6 CDOS ODA CDOS & ODA Temperature ( C) -.6 a) b) c) Temperature ( C) Temperature ( C) Figure S5. a) Thermogravimetric analysis of chloro(dimethyl)octadecylsilane(cdos), octadecylamine(oda), mixture of CDOS and ODA and nanoparticle, b) differential scanning calorimetry of CDOS and c) differential scanning calorimetry of mixture of CDOS and ODA.

11 Absorbance Emission Intensity (a.u.) a) b) Si-48 Si-36 Si-8 Si Wavelength (nm) Figure S6. a) Absorption ( ), photoluminescence excitation (.. ) and emission spectra of chloroform solution of silicon nanoparticle produced in the reaction condition after heating for 6 hours (Si-6), 8 hours (Si-8), 36 hours (Si-36), 48 hours (Si-48) and 72 hours (). Emission has been measured by exciting at 37 nm for Si-6, 43 nm for Si-8, 48 nm and 55 nm for Si-36, Si-48 and. (Yellow and red line indicates the emission spectra at 48 nm and 55 nm excitation, respectively.) b) Solid sample prepared after purification, showing that method can be adapted for milligram to gram scale synthesis.

12 Figure S7. Microscopic image of films of Si-6 (a, b, c), Si-8 (d, e, f) and (g, h, i) which are captured by depositing their respective chloroform solutions on the glass slide. The images are acquired under bright field (a, d, g) or fluorescence modes under UV excitation (b), blue excitation (c, e, h) and green excitation (f, i).

13 Figure S8. Emission spectra of Si-6 (a), Si-8 (b), Si-36 (c), Si-48 (d), (e) and polymer coated Si- 72 (f) under different excitation wavelengths.

14 BF Si-6 F (UV) Si-6 min F (UV) Si-6 min 5 m 5 m 5 m BF Si-8 F (blue) Si-8 min F (blue) Si-8 min 5 m 5 m 5 m BF F (blue) min F (blue) min 5 m 5 m 5 m BF F (green) min F (green) min 5 m 5 m 5 m BF -polymer F (blue) -polymer min F (blue) -polymer min 5 m 5 m 5 m BF -polymer F (green) -polymer min F (green) -polymer min 5 m 5 m 5 ms8 Figure S9. Photostability studies of different silicon nanoparticles. Films of Si-6, Si-8, and polymer coated were prepared by depositing respective chloroforms solutions on the glass slides and then imaged under bright field (BF) or under fluorescence mode (F) with UV, blue and green excitation.

15 Figure S. Emission spectra of solid nanoparticle at different temperatures, showing that emission decreases with the increasing temperature.

16 Figure S. Fluorescence lifetime decay spectra of solutions of Si-6 (a), Si-8 (b), Si-36 (c), Si-48 (d), (e) and polymer coated (f). Blue and red lines correspond to experimental and fitted data, respectively.

17 Absorbance Emission Intensity (a.u.) Emission Intensity (a.u.) Figure S2. Photoluminescence (PL) spectra of polymer coated nanoparticles before (blue) and after reaction with fluorescamine (green), indicating the presence of primary amine groups on the surface of polymer coated nanoparticles. Emission of silicon is masked by high emission of fluorescamineamine complex a) control b) control c) Si-folate Si-folate control Si-folate Wavelength (nm) Wavelength (nm) Wavelength (nm) Figure S3. (a) Absorption spectra of polymer coated before and after conjugation with folic acid, showing the appearance of 375 nm band due to folate. (b, c) Fluorescence spectra of polymer coated under 48 nm excitation (b) and 55 nm excitation (c), before and after conjugated with folate.

18 Cell Viability (%) Figure S4. Fluorescence images of HeLa cells after labeling with polymer coated nanoparticle showing that it does not label cells as nanoparticle is not functionalized with folic acid. Cells were labeled with nanoparticle and hoechst dye and imaged under differential interference contrast (DIC) mode (a) or fluorescence mode with UV excitation (b), blue excitation (c) and green excitation (d). Blue emission under UV excitation is due to nucleus staining by hoechst dye. control Si-folate Concentration (mg/ml) Figure S5. Viability of HeLa cells after 24 hours incubation with different concentrations of polymer coated (control) and folic acid conjugated functionalized nanoparticle (Si-folate).