SupportingInformation

Differentialfunctionalisationoftheinternalandexternal

surfacesofcarbon-stabilisednanoporoussilicon

MariaAlba,MorganeRobin,DonnaMenzies,ThomasR.Gengenbach,BeatrizPrieto-Simon*,NicolasH.Voelcker*

Correspondence:CorrespondingAuthor:Nicolas.Voelcker@monash.edu;Beatriz.Prieto-Simon@monash.edu

Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2019

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1 Materialsandmethods

1.1 Reagents,materialsandsolutions

P-type,borondoped,0.55-1.00mWcmresistivity,(100)-orientedcrystallinesiliconwaferswerepurchasedfromSiltronix,France.Hydrofluoricacid(HF,48%w/w)waspurchasedfromScharlau(Australia),10-undecanoicacidwaspurchasedfromAlfaAesar(Australia).N-hydroxysuccinimide(NHS),N-(3-dimethylaminopropyl)Nʹ-ethylcarbodiimidehydrochloride(EDC),ethanolamine,phosphatebufferedsaline(PBS)and2-(N-morpholino)-ethanesulfonicacid(MES)tablets,poly(ethyleneglycol)bis(amine)(Mw=3000,PEG-bis(amine)),fluoresceinisothiocyanate(FITC),pentafluorophenol(PFP),andN,N-diisopropylethylamine(DIEA)werepurchasedfromSigma-Aldrich(Australia).Sodiumhydroxide(NaOH,ARgrade)waspurchasedfromMerck(Australia).Cyanine5amine(Cy5-amine)waspurchasedfromLumiprobe(USA).

1.2 FabricationofpSifilms

pSifilmswereproducedfromp-typesiliconbyelectrochemicaletchinginHF-basedsolution.First,theparasiticlayerwasremoved(Chamardetal.,1998;Sciaccaetal.,2011)byapplyingacurrentdensityof68mAcm-2for30sinasolutionof3:1ofHFtoethanol.Then,thisparasiticlayerwasdissolvedin0.1MNaOHaqueoussolutionandthoroughlyrinsedwithMilliQwaterandethanol,thendriedunderaN2flow.ThepSifilmwasgeneratedbyelectrochemicaletchingundergalvanostaticconditionsina3:1solutionofHFtoethanol,applyingaconstantcurrentdensityof54mAcm-2for22min.Next,theHF-basedelectrolytewasremoved,andthesamplewasthoroughlywashedwithMilliQwaterandethanol,thendriedunderaN2flow.Immediatelyafteretching,thepreparedpSifilmwasfunctionalised.

1.3 ChemicalmodificationofpSifilms

FreshlyetchedpSisampleswerethermallyhydrocarbonisedfollowingapreviouslyreportedprocedure(Jalkanenetal.,2014).Briefly,thefreshlyetchedpSisampleswereplacedinaquartztubeandpurgedwithN2for45minataflowrateof2Lmin-1.Then,acetylenegaswasintroducedtogetherwithN2intothetubeataratioof1:1acetylene/N2for15min.Afterthistime,thequartztubewasintroducedintoatubularfurnacepreheatedat525°C.After14min30s,theacetyleneflowwasinterrupted,andafter15minthequartztubewasremovedfromthefurnace.ThetubewasthenallowedtocooldowntoroomtemperatureunderaN2flowbeforethepSisampleswereremoved.Then,carboxylicacidfunctionalitywasintroducedbythermalhydrosilylationwith10-undecanoicacidat150°Cfor12hinaN2environment.Then,thefunctionalisedsampleswerethoroughlyrinsedwithethanolanddriedunderaN2stream.

1.3.1 ExternalfunctionalisationofpSifilms

Afterfunctionalisationwith10-undecanoicacid,theesteractivationofthecarboxylicacidgroupsontheexternalpSisurfacewasperformedinaqueousphasebyincubationfor20minwith20mMEDCand65mMNHSin0.1MESbuffer,pH5.5,atroomtemperature.Subsequently,thesamplewasincubatedin100µgmL-1PEG-bis(amine)inPBSfor1h,thenthoroughlywashedwithPBSanddriedunderaN2stream.Tofluorescentlylabeltheaminefunctionality,thesamplewasincubatedina10µgmL-1FITCsolutioninPBSfor15min,protectedfromlight,andsubsequentlythoroughlywashedwithPBSanddriedwithaN2stream.

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1.3.2 InternalfunctionalisationofpSifilms

TheexternallymodifiedpSisamplewasincubatedintoa0.2MEDC,0.2MPFPand0.2MDIEAmixtureinabsoluteethanol(30min,atroomtemperature).Afterwards,thepSisamplewasrinsedwithabsoluteethanol,anddriedunderaN2stream.Fluorescentlabellingwasperformedbyincubatingthesamplewith10µgmL-1Cy5-aminesolutioninPBSfor30min.Finally,thesamplewaswashedwithPBS,driedunderN2andstoredinthedark.

1.4 CharacterisationofpSifilmsaftersurfacemodification

1.4.1 ScanningElectronMicroscopy(SEM)

ForSEMimagingofthepSisurfaces,samplesweremountedonanaluminiumstubwithdouble-sidedcarbontape.SampleswereimagedwithaFEINovafieldemissiongunscanningelectronmicroscopeusinganInLensdetectorinhigh-resolutionmodeandanacceleratingvoltageof10kV.

1.4.2 Infrared(IR)spectroscopy

ThesurfacefunctionalisationwascharacterisedaftereachchemicalmodificationstepusingattenuatedtotalreflectanceFouriertransforminfraredspectroscopy(ATR-FTIR).AThermoScientificNicolet6700FTIRinstrumentcoupledtoadiamonddetectorwasusedtocollectspectrawitharesolutionof4cm-1,afteraveraging64scans.Backgroundspectrawereblankedusingair.ThedatawereprocessedusingOMINCsoftware.

1.4.3 X-rayphotoelectronspectroscopy(XPS)

X-rayphotoelectronspectroscopy(XPS)analysiswasperformedusingeitheranAXISUltraDLDoranAXISNovaspectrometer(KratosAnalyticalInc.,Manchester,UK)withamonochromatedAlKαsourceatapowerof180W(15kV×12mA),ahemisphericalanalyseroperatinginthefixedanalysertransmissionmode,andthestandardaperture(analysisarea:0.3mm×0.7mm).Thetotalpressureinthemainvacuumchamberduringanalysiswastypicallybetween10-9and10−8mbar.

1.4.4 Time-of-flightsecondaryionmassspectrometry(ToF-SIMS)

ToF-SIMSmeasurementswereperformedusingaPhysicalElectronicsInc.PHITRIFTVnanoToFinstrument(Chanhassen,MN,USA)equippedwithapulsedliquidmetalAu+primaryiongun(LMIG),operatingat30kV.Theextractorcurrentoftheionsourcewasmaintainedat3μA.Surfaceanalyseswereperformedusing“bunched”Au1beamsettingsforsurfaceimagingandspectroscopy.MasscalibrationofthespectrawasdonewithCH3

+,C2H5+,andC3H7

+ions.Experimentswereperformedathighvacuum(<10-8mbar)andinthestaticmode(i.e.below1012ionscm-2)tominimisesampledamage.

1.4.5 Watercontactanglemeasurements

Watercontactanglemeasurementswereconductedusingacustom-builtgoniometer,withaPanasonicCCTVcamera(WV-BP550/G)tocapturethedrop-surfaceimages.A3μldropofMilliQwaterwasdepositedontoeachsurfaceusinga10μLsyringe.AphotographwasimmediatelycapturedandcontactanglesweredeterminedusingImageJ(v1.50i,NIH,USA).

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2.5.6Confocalmicroscopy

ConfocalfluorescencemicroscopyimageswereobtainedusinganinvertedCarlZeissLSM710confocalmicroscopewithanECPlan-Neofluar20x/0.30M27objective.ThepSisurfaceswereexcitedatwavelengthsof485and640nmandemissionwascollectedina576–701nmrange.

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2 SupplementaryFigures

Fig.S1.SEMmicrographsoffreshly-etchedpSiin(A)cross-sectionaland(B)topviews.

A B

10 µm 100 nm

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Fig.S2.XPShighresolutionC1sspectraforTHCpSi(black);thermallyhydrosilylatedTHCpSi(blue),andexternallyfunctionalisedTHCpSiwithPEG-(bis)amine(red).Thepositionofspectralfeaturesdiscussedinthemaintextaremarkedwithdashedlines.

280282284286288290292294296Binding energy (eV)

Nor

mal

ised

uni

ts

THCpSi

UnCOOH

PEG

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Fig.S3.Representativestaticdeionisedwater(pH5.5)contactanglesof(A)freshly-etchedpSi;(B)THC-treatedpSi;and(C)THCpSiafterthermalhydrosilylationwith10-undecanoicacid.

A B C

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Fig.S4.ATR-FTIRspectrumofA)aTHCpSifilmexclusivelyinternallyfunctionalisedwithPFP;B)showsazoom-ininthespectralrangeof1850-1325cm-1.ThesignaturepeakofPFParisesat1520cm-1.

3500 3000 2500 2000 1500 1000

Abso

rban

ce

Wavenumber (cm-1)

1800 1700 1600 1500 1400

Abso

rban

ce

Wavenumber (cm-1)

C-F

A B

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FigS5.XPShighresolutionXPSF1sspectraforthermallyhydrosilylatedTHCpSi(blackline)andinternallyfunctionalisedTHCpSiwithPFP.Theadditionalpeakobservedatbindingenergyof 689.5 eV after PFP functionalisation corresponds to C-F, whereas the peak at 687 eVcorrespondstoionicF.ThelatterisdetectedonallHF-etchedpSisurfaces.

680682684686688690692694696698700

Binding energy (eV)

Nor

mal

ised

uni

ts

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Fig.S6.Cross-sectionalimagesofpSifilms.(A)SEMimage,showingananoporouslayeroffreshly-etchedpSiwithathicknessofapproximately35µm.Cross-sectionalviewsbyfluorescenceconfocalmicroscopyofadifferentiallyfunctionalisedTHCpSilayercollectedinthe(B)greenandfar-redchannels(simultaneouslaserexcitationat485and640nm);(C)greenchannel(excitationat485nm);and(D)far-redchannel(excitationat640nm).

A

50 µm 50 µm 50 µm 50 µm

B C D