Visual Observation and Characterization of Fluorescent ...imaelab.jpn.org/wp-content/uploads/2019/06/Visual... · The G4 and G4.5 PAMAM dendrimer lms on well-cleaned quartz and silicon

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Copyright copy 2011 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 11 4838ndash4845 2011

Visual Observation and Characterization of FluorescentPoly(amido amine) Dendrimer in Film State

Govindachetty Saravanan1 and Toyoko Imae12lowast1Graduate School of Science and Technology Keio University Hiyoshi Yokohama 223-8522 Japan

2Graduate Institute of Engineering National Taiwan University of Science and TechnologyKeelung Road Taipei 10607 Taiwan

The fluorescent property of PAMAM dendrimers were examined at film state rather than in solu-tion The O2-treated PAMAM dendrimer displayed strong blue fluorescence due to its conservationof luminance in the film state and diminished its intensity with degas The fluorescent property ofPAMAM dendrimers was utilized as a fluorescent probe on functional patterned substrates for visualobservation by a fluorescence microscope G4 and G45 PAMAM dendrimers having peripheralgroups of functional amine and carboxylate respectively were adsorbed selectively by electro-static interactions on patterned carboxylic acid and amine terminated surfaces respectively result-ing in strong fluorescent patterns This suggests the possible application of fluorescent PAMAMdendrimers as a fluorophor for the visualizable reactions It was confirmed from an X-ray photo-electron spectroscopy that O2 molecules interact with tertiary amine moiety in PAMAM dendrimersbut not amide group These results give us an important support for the principle of fluorescencephenomenon

Keywords Patterned Poly(amido amine) Dendrimer Film Fluorescence Microscope X-rayPhotoelectron Spectroscopy

1 INTRODUCTION

The family of poly(amido amine) (PAMAM) dendrimercan be used to monitor the properties of biomate-rials owing to its well-characterized architecture bio-compatibility nonimmunogenicity and water-solubility1

Number of studies about molecular assemblies of PAMAMdendrimers on various solid substrates are carried out byadsorption self-assembled monolayer (SAM) and pattern-ing techniques where the various peripheral groups (ndashOHndashCOOH ndashNH2 of PAMAM dendrimers having highreactivity selectively bind to the functional substrates2ndash9

The SAM of dendrimers has been used as a DNA (orpolyelectrolyte) detector and a biochemical sensor basedon polyelectrolyte-ligand interaction10ndash13 The molecularassemblies of PAMAM dendrimers have also been pat-terned by techniques of microcontact printing14ndash17 scan-ning probe lithography18 and photolithography19 whichwere examined by atomic force microscopy scanning elec-tron microscopy etc However there are no reports ofvisual observation on selective adsorption of PAMAMdendrimers on solid substrates

lowastAuthor to whom correspondence should be addressed

It has been found that the family of aged or O2-treatedPAMAM dendrimer emits blue photoluminescence underexcitation around 360 nm The fluorescence of PAMAMdendrimers and their derivatives or analogs has been stud-ied by some research groups20ndash33 Therefore it is expectedthat when the target materials are selectively labeled byfluorescent PAMAM dendrimer as a fluorescent probe oneis allowed to investigate properties and assembling of theobjective materials by simple fluorescence technique Inci-dentally the visualization by a fluorescence microscopyhas been carried out on PAMAM dendrimer-dyed fibersand dendritic nanohydrogels of PAMAM Dendron28ndash29

Additionally it can be noticed that the current investiga-tion of photoluminescence for the family of PAMAM den-drimer has been carried out only in solutionIn the present work the selective adsorption of fluores-

cent G4 and G45 (G generation) PAMAM dendrimers onpatterned SAM substrates with different affinities to den-drimers is visually detected by a fluorescence microscopySAM preparation and photolithography are used to createthe functional substrates with carboxylic acid- or amine-terminated pattern along with methyl-terminated patternSubsequently the fluorescent property of dendrimers in asolid state on the substrates is successfully investigated

4838 J Nanosci Nanotechnol 2011 Vol 11 No 6 1533-48802011114838008 doi101166jnn20114107


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Saravanan and Imae Visual Observation and Characterization of Fluorescent Poly(amido amine) Dendrimer in Film State

under gasdegas process of oxygen The present workindicates the extensive possibility for family of PAMAMdendrimer to be utilized even at the solid film as a fluo-rescence probe on the microscopic observation Moreoverfacile and highly sensitive detection of fluorescent den-drimer probe on a fluorescence microscope is the strongadvantage on the various biomedical applications sensingtechnology and molecular recognition

2 EXPERIMENTAL DETAILS

21 Materials

Methanol solutions of G4 and G45 PAMAM den-drimers (PAMAM-NH2 PAMAM-COOminus) were pur-chased from Aldrich Co Ltd These dendrimerscontain 64 (amine) and 128 (carboxylate) terminalgroups respectively n-octadecyltrimethoxysilane (ODS)3-aminopropyltriethoxysilane (APS) and ammoniumper-sulfate ((NH42S2O8 were obtained from Tokyo ChemicalIndustries Co Ltd Acros Organics Co Ltd and WakoChemicals Co Ltd respectively Ethanol and toluene wereproducts from Junsei Chemical Co Ltd Purified waterwas prepared by a Millipore milli-Q system

22 Preparation

Silicon and glass substrates (Matsunami micro cover glass18times 18 mm) were patterned by SAM procedure andphotolithography1934 Prior to the patterning on silicon orglass substrate the substrates were carefully cleaned byultrasonication for 5 min each in piranha solution wateracetone and ethanol followed by drying in an oven Thesubstrates were further cleaned photochemically by irradi-ation of UV light in vacuum which is generated from anexcimer lamp (Ushio Electric UER20-172V = 172 nmwith a power density of 10 mWcmminus2 in order to removeany organic contaminants The UV irradiation was carriedout at a pressure of 15times102 pa with a proximate gap oflt10 nm between the substrate and photomask The radi-ation at short wavelength produces the oxygen atoms andozone molecules from atmospheric oxygen molecules byphotoexcitation which decompose the carbonndashcarbon andcarbonndashhydrogen bonds of organic molecules35

Two different types of precursors ODS and APSwere employed for the preparation of carboxylic acidand amine terminated patterns respectively The car-boxylic acid (ODS-COOH) and amine (ODS-NH2terminated patterns were immersed in a 05 mM solu-tion of G4 or G45 PAMAM dendrimer for 24 h andthus the dendrimer-treated substrates were denotedby PAMAM-NH2ODS-COOH PAMAM-COOminusODS-COOH PAMAM-NH2ODS-NH2 and PAMAM-COOminusODS-NH2 Prior to the immersion of thesesubstrates solutions of PAMAM dendrimers were agedfor 7 days under the addition of an aqueous 01 M solution

of ammoniumpersulfate The dendrimer-treated substrateswere dried by N2 gas and then examined by optical andfluorescence microscopyThe G4 and G45 PAMAM dendrimer films on well-

cleaned quartz and silicon (n type (100) wafer NilacoCo) substrates were prepared from 50 mm3 of a 5 wtPAMAM dendrimer solution by a spin coating methodwhere the substrates were rotated at 100 rpm for 5 minThis process was repeated for four times and then the filmswere dried overnight at room temperature under vacuumPAMAM dendrimer films on substrates were aged in thepresence of O2 gas and degassed Then the films were ana-lyzed by UV-visible absorption spectroscopy fluorescencespectroscopy and X-ray photoelectron spectroscopy (XPS)

23 Measurements

UV-visible absorption spectra on quartz substrates werecollected on a Shimadzu Bio Spec-1600 spectrometer Flu-orescence spectra were recorded on a Hitachi F-3010 flu-orescence spectrophotometer where the excitation sourcewas Xenon lamp operated at 150 W The optical (Halogenlamp LHS-H100P-1 12 V 100 W) and fluorescence(super high pressure mercury lamp Model C-SHG1100 W) microscopic images were taken on a Nikon-Eclipse TE 2000-U microscope For fluorescence micro-scopic images the silicon substrates were irradiated at 365nm excitation wavelength by using DM 400 and RA 400filters XPS studies on quartz substrates were performed ona JPS-9000 MX JEOL photoelectron spectrometer usingMgK monochromatized X-ray beam at a constant dwelltime of 100 ms X-ray scans were performed by using passenergies of 50 eV for wide scan and of 10 eV for nar-row scan The anode voltage and current were 10 kV and10 mA respectively All core level spectra were obtainedat a photoelectron takeoff angle of 90 with respect to thePAMAM dendrimer films

3 RESULTS AND DISCUSSION

31 Visual Observation of G4 and G45 PAMAMDendrimers on ODS-COOH and ODS-NH2

Patterned Substrates

The functional patterned substrates allow us to investi-gate the properties and assembling of materials and canbe used for various applications like sensing technologiesorganic light-emitting diodes organic thin-film transistorsetc36ndash41 Moreover they can be model surfaces of bio-materials which are prepared readily by a large varietyof available techniques4243 The substrates with ndashNH2 orndashCOOH surface pattern along with methyl surface patternare ones of model surfaces of biomaterials The fluorescentG4 and G45 PAMAM dendrimers possessing ndashNH2 andndashCOOminus functional groups respectively on their peripherycan be expected to be adsorbed selectively on these model

J Nanosci Nanotechnol 11 4838ndash4845 2011 4839



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Visual Observation and Characterization of Fluorescent Poly(amido amine) Dendrimer in Film State Saravanan and Imae

surfaces The fluorescent PAMAM dendrimers were pre-treated by adding an aqueous 01 M (NH42S2O8 solutionand used throughout the patterning experiments becausethis treatment enhances the fluorescence of PAMAM den-drimers even at very short time process25 Figure 1 showsthe comparison of fluorescence intensity of persulfate-treated and untreated G4 PAMAM dendrimer on siliconsubstrate which was prepared by spin-coating dendrimer inwater (05 mM) at 100 rpm for five times The persulfate-treated dendrimer displayed a strong blue fluorescenceemission band at 452 nm at excitation wavelength of360 nm and an excitation band at 370 nm at emis-sion wavelength of 452 nm The fairly strong fluores-cence intensity of persulfate-treated dendrimer superior tountreated one indicates the conservation of luminescenceeven at the film stateFigure 2 denotes the procedure for the selective adsorp-

tion of PAMAM dendrimer on methylcarboxylic acid-terminated patterned silicon substrates For this purposethe well-cleaned silicon substrates were put together witha few drops (02 cm3 of ODS liquid in a Teflon con-tainer which was covered tight with a lip and then retainedin an oven at 150 C for 3 h The formation of ODSSAMs on substrates was examined by contact angle ofpure water the silicon substrate terminated with methylgroups brought about a highly hydrophobic contact angleat 86plusmn 2 The carboxylic acid pattern was prepared asrectangular closed area by exposing an ODS SAM sub-strate to UV light for 100 s under photo mask in the pres-ence of oxygen gas Then alkyl groups of ODS out of thephoto mask underwent partial oxidation on the exposureprocess through UV light and were decomposed into car-boxylic acid-terminated pattern194445 which resulted in

Fig 1 Fluorescence spectra of pristine (black) and persulfate-treated(blue) G4 PAMAM dendrimer films on a silicon substrate Insets arephotos of 05 mM G4 PAMAM dendrimer solutions before preparingfilms

Fig 2 A scheme of the pattern preparation on ODS SAM on a siliconsubstrate and the adsorption of PAMAM dendrimers on it Photographsindicate fluorescence microscopic images after the adsorption procedureof G4 and G45 PAMAM (PAMAM-NH2 PAMAM-COOminus) dendrimers(top) Carboxylic acid pattern on an ODS SAM (ODS-COOH) (bottom)Amine pattern on an ODS SAM (ODS-NH2

the ODS-COOH patterned substrate with ODS frame Thewater contact angle of the resultant substrate was 64plusmn2

After the adsorption of G4 PAMAM dendrimer asshown in Figure 2 the fluorescence microscopic imageof the substrate at excitation wavelength of 365 nm dis-played strong fluorescent pattern with two distinct regionsthat is the dark frame and the bright fluorescent rectan-gles The dark frame is indicative of the ODS SAM with-out adsorption of dendrimer because amine-terminated G4PAMAM dendrimer does not adsorb on methyl-terminatedpattern Whereas the clear and well-defined fluorescentregion suggests the adsorption of fluorescent G4 PAMAMdendrimer since the peripheral amine groups of G4

4840 J Nanosci Nanotechnol 11 4838ndash4845 2011



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PAMAM dendrimer bind on carboxylic acid-terminatedsubstrate Then the binding interaction should be electro-static because the adsorption process was carried out inwater at neutral pH where amine and carboxylic acid areprotonated and deprotonated respectivelyThe reverse effect is also expected ie G45 PAMAM

dendrimer (with ndashCOOH peripheral groups) will interactwith amine-terminated substrate Figure 2 shows the pro-cedure for preparation of APS SAM pattern on ODS SAMsubstrate The ODS SAM substrate loaded photo maskwas irradiated by UV light for 20 min in the presenceof oxygen so as to remove completely ODS SAM fromthe unmasked area45 The APS SAM was introduced onthe ODS-removed pattern by immersion of patterned ODSsubstrates for 24 h in a 4 mM toluene solution of APSThus the resultant patterned substrate of ODS and APS(ODS-NH2 was washed with toluene and ethanol driedunder N2 atmosphere and maintained for 1 h at 120 Cin oven Then G45 PAMAM dendrimers were adsorbedon the ODS-NH2 patterned substrate As expected strongfluorescent pattern was displayed as shown in Figure 2The bright rectangular region is an outcome of an effec-tive interaction between ndashCOOH peripheral groups ofG45 PAMAM dendrimers and NH2 terminated pattern onthe substrate However the dark frame region suggests thatno such interaction was observed between G45 PAMAMdendrimer and methyl-terminated group of ODS SAM onthe substrateThe results described above indicate that the electro-

static interaction is a main driving force of the selectiveadsorption of dendrimers on the patterned substrates

Fig 3 Fluorescence (top) and optical (bottom) microscopic images of PAMAM-NH2ODS-COOH PAMAM-COOminusODS-COOH PAMAM-NH2ODS-NH2 PAMAM-COOminusODS-NH2

In order to make sure this conclusion the adsorptionbehavior of G45 PAMAM dendrimer on ODS-COOH orG4 PAMAM dendrimer on ODSndashNH2 was examined Asseen in Figure 2 distinct bright regions were not observedfor both combinations suggesting no considerable attrac-tion between dendrimer and patterned substrate in thiscombination Additionally it can be insisted that the flu-orescence microscopic observation is the highly excellenttechnique to detect the existence of PAMAM dendrimerson the selected area since the distinction by the opticalmicroscopic images is not easy for the dendrimers on glasssubstrates which are prepared by the procedure same asthat on silicon substrates as shown in Figure 3

32 Effect of O2 Gas on G4 and G45 PAMAMDendrimer in Film State

Different from previous works which were done insolutions131924ndash2646 dendrimers in the film state provideus the solvent-free fluorescence behavior and the outrightevaluation on the structural aspect of PAMAM dendrimersduring aging under O2 gas Figure 4 shows emission flu-orescence spectra for G45 PAMAM dendrimer film ona silicon substrate which was aged under O2 gas at var-ious time intervals When the substrate was irradiated at360 nm a strong emission band was observed at 435 nmand its intensity increased with increasing aging time Thesame trend was also found in excitation fluorescence spec-tra The strong excitation band was observed at 370 nmand intensified with increasing aging time at the emissionof 460 nm as shown in Figure 4 These results support




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Fig 4 Fluorescence spectra of a G45 PAMAM dendrimer film on asilicon substrate at different aging time under O2 gas atmosphere

that O2 molecules are doped within PAMAM dendrimerin the film and participate in the enhancement of the fluo-rescence intensityO2-treated PAMAM dendrimer films were overnight

subject to vacuum condition in order to ensurethe enhanced fluorescence property through dopingO2 The emission fluorescence intensity of O2-treatedG45 PAMAM dendrimer films decreased after vacuumtreatment as shown in Figure 5(top) As with the emissionfluorescence intensity the excitation fluorescence inten-sity also decreased after vacuum treatment The simi-lar trends on fluorescence variation were found again forG4 PAMAM dendrimer films as seen in Figure 5(bot-tom) It should be noticed that the successive gasdegasprocess on G4 PAMAM dendrimer films reproduced theincreasedecrease behavior of emission and excitationintensities (see Fig 5(bottom inset)) These results clearlyindicate that O2 molecules are doped within PAMAM den-drimer films by noncovalent binding to enhance the fluo-rescence property of PAMAM dendrimersAccording to the successive UV-visible absorption spec-

tra for a G45 PAMAM dendrimer film on quartz substratewhich was aged in the presence of O2 gas at various timeintervals as sown in Figure 6 an absorption band (maybeassigned to nndashlowast transition) was observed at 286 nmand intensified systematically with increasing aging timeSince the present experiments were carried out at solvent-free this variation in the absorption band is the intrinsicbehavior of PAMAM dendrimer Therefore it should benoticed that the local configuration of PAMAM dendrimerin the film may be changed during aging process under O2

atmosphere However it must also be recognized that theposition of the absorption band is lower than that of theexcitation bandThe pristine and O2-treated PAMAM dendrimer films

on quartz substrate were examined further by high resolu-tion XPS in order to investigate the influence of O2 gas onthe enhancement of fluorescence High resolution spectrawere recorded for the main core level peaks of C N and

Fig 5 Fluorescence spectra of PAMAM dendrimer films on a siliconsubstrate Dotted line pristine solid line O2-treated (3 d) dashed linedegas-treated (overnight in vacuum) (top) G45 (bottom) G4 An insetis a plot of fluorescence intensity variation during two cycles of the O2-and degas-treatments

O and exemplified in Figure 7 The XPS was deconvolutedinto component peaks and resultant data are summarizedin Table I The C1s region of a G4 PAMAM dendrimerfilm revealed clearly the different chemical states of carbon

Fig 6 UV-visible absorption spectra of a G45 PAMAM dendrimerfilm on a quartz substrate at different aging time under O2 gasatmosphere




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Fig 7 Observed XPS of G4 PAMAM dendrimer films on a quartz substrate and deconvolution of C1s N1s and O1s peaks (a) Pristine (b) O2-treated (8 d)

(see Fig 7 and Table I)4748 The component peaks wereobtained at binding energies of 2861 (CndashC O) 2869(CndashN) and 2896 (C O) eV for the pristine G4 PAMAMdendrimer film The binding energy of CndashN peak was con-siderably lowered to 2856 eV after aged at O2 atmospherewhile the binding energies of CndashC O and C O peaksremained in the almost same energy Changes were alsoobserved in the N1s region for G4 PAMAM dendrimerfilm The N1s spectra can be deconvoluted into threecomponent peaks at the binding energies of 4004 (NndashH2 4010 (NndashC) and 4015 (NHndashC O) eV The amidenitrogen exists at higher binding energy than primary andtertiary amine nitrogen since amide nitrogen bears thepartial positive charge because of its resonance struc-ture Although the binding energies of the primary amineand amide nitrogen were not changed by O2-treatmentthe energy of the tertiary amine nitrogen shifted 12 eVand observed at 3998 eV In the broad O1s spectra forPAMAM dendrimer films the O1s peak of the amide oxy-gen was observed at 5333 eV and did not vary even afterO2-treatment However the peak of pristine dendrimer filmat 5350 eV lowered down to 5344 eV after O2-treatmentThe third peak was observed at the binding energy of5326 eV although the energy is scarcely susceptible forO2-treatment While both peaks at 5350 and 5326 eV arenot assigned to oxygen in PAMAM dendrimer the O1s

Table I XPS peaks of pristine and O2-treated G4 and G45 PAMAM dendrimer films (number binding energy in eV)

C1s N1s O1sPAMAMdendrimer film CndashC O CndashN C O NH2 ndashNlt O CndashNH OH C O

Pristine G4 2861 2869 2896 4004 4010 4015 5326 5333 5350O2-treated G4 2862 2856 2895 4004 3998 4014 5325 5332 5344Pristine G45 2869 2873 2896 mdash 4011 4013 5325 5331 5350O2-treated G45 2870 2862 2896 mdash 4005 4011 5324 5331 5341

peaks of surface oxide and hydroxyl of quartz substrateappear in this region Then it is difficult to distinguish thepeaks of surface oxide or hydroxyl groups on quartz andthose of other chemical states of oxygen such as free O2

or H2O as previously reported4849 Figure 8 displays XPSof a G4 PAMAM dendrimer film on a silicon substrate atdifferent aging time under O2 gas atmosphere It is consis-tent with the results in Figure 7 that the C N and O peaksvaried to lower binding energies with aging However itshould be noticed that the remarkable variation of bindingenergy occurred after aging for three days although thedetectable change in fluorescence intensity was observedeven after aging for one day under O2 gas

The XPS of G45 PAMAM dendrimer films behavedlike that of G4 PAMAM dendrimer films on the effectof O2-treatment (see Table I) Differently from invariableC1s peaks of CndashC O (2869 eV) and C O (2896 eV)a CndashN (2873 eV) peak shifted to 2862 eV In the N1sregion while the peaks for tertiary amine and amide nitro-gen were observed at the binding energy of 4011 and4013 eV respectively the binding energy of tertiary aminenitrogen shifted to 4005 eV but there was no consid-erable shift for amide nitrogen after the O2-treatmentFor the O1s region the peaks at the binding energies of5325 eV (CndashOH) and 5331 eV (C O) were invariablefor both pristine and aged G45 PAMAM dendrimer film




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Fig 8 Observed XPS of a G4 PAMAM dendrimer film on a siliconsubstrate at different aging time under O2 gas atmosphere Aging timepristine (red) 3 d (black) 6 d (green) 20 d (blue)

The binding energy at 5350 eV of the pristine film low-ered into 5341 eV after O2-treatmentThe PAMAM dendrimer consists of three different

components such as amide spacer tertiary amine andperipheral ndashCOOminus or ndashNH2 (in the case of G45 andG4 PAMAM dendrimers respectively) functional groupsin their chemical structure Then the XPS examinationallows us to estimate the effect of O2 treatment at atomiclevel The XPS results for G4 and G45 PAMAM den-drimers are summarized in common as follows(1) The binding energies of carbon nitrogen and oxygenin amide and primary amine are not affected by the O2-treatment(2) The binding energies of carbon and nitrogen in tertiaryamine are lowered on the process of the O2-treatment(3) Besides peaks from PAMAM dendrimer the addi-tional component peak of O1s is observed at 5350 eVand it is lowered after the O2-treatment suggesting theexistence of other chemical states of oxygen eg O2

N

O

N

HOndash

Scheme 1 Schematic representation of O2-encapsulated branched ele-ment of PAMAM dendrimer unit O2 molecules attack the tertiary aminemoiety rather than the amide spacer moiety

in the PAMAM dendrimer film Then it is assumed thatthe tertiary amine moiety in the PAMAM dendrimer isattacked by O2 as illustrated in Scheme 1 and as aresult that the binding energies of tertiary amine moi-ety and O2 are lowered that is the binding are stabi-lized These results seem to be consistent with previousreports that tertiary amine should be a common moiety ofPAMAM and related dendrimers with blue photolumines-cence phenomenon46 that is the family of PAMAM den-drimers with different terminal moieties (ndashOH ndashCOOHndashNH2 etc)252629 poly(alkyleneimine) dendrimers3132

poly(amino ester) dendrimers27 poly(propyl ether imine)dendrimer33 polyethyleneimine30 and triethylamine46

4 CONCLUSIONS

Fluorescent G4 and G45 PAMAM dendrimers were char-acterized at film state O2-treated PAMAM dendrimer filmsdisplayed the luminescence which was detected by exci-tation and emission spectra Selective adsorption of fluo-rescent PAMAM dendrimers on hydrophilichydrophobicpatterned substrates was determined by means of a fluores-cence microscope It was conformed from strong lumines-cence on corresponding pattern that the peripheral ndashNH2

and ndashCOOH functional groups of G4 and G45 PAMAMdendrimers respectively were selectively adsorbed on car-boxylic acid and amine terminated patterns respectivelyby strong electrostatic interaction However no such flu-orescence patterns were observed if there were no stronginteractions between PAMAM dendrimers and functional-ized substrates Luminescence intensity changed with O2

filling and degas indicating the nonchemical binding ofO2 with dendrimer It could be newly mentioned from XPSthat O2-treatment affected tertiary amine moiety but notamide group in the PAMAM dendrimersObviously the present results suggest that the lumines-

cent behavior occurs not only in solution but also evenat film state Moreover the direct discovery of the affectof O2 on tertiary amine in PAMAM dendrimer allowsus to confirm previous assumption46 for the luminescencemechanism of PAMAM dendrimers The attractive fea-tures of the present technique are the simplicity repro-ducibility and sensitivity on the detection of the selective




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adsorption of PAMAM dendrimers on functionalized sub-strates Further the fluorescent property of PAMAM den-drimers utilized through the present procedure is highlyeffective suggesting that family of PAMAM dendrimerscan be used to label and monitor the target systems as flu-orophor Especially the fluorescent PAMAM dendrimerswhich are nontoxic can be selectively labeled to thefunctionalized systems such as biomaterials and valuablyutilized as a sensor of selective molecular recognition inmedical therapy and testing

Acknowledgment This work was financially supportedin part by Japan-Taiwan Joint Research Program of Inter-change Association Japan

References and Notes

1 A K J Patri U J Majoros and J Baker J Curr Opin Chem Biol6 466 (2002)

2 S Rubin G Bar T N Taylor R W Cutts J Zawodzinski andA Thomos J Vac Sci Technol A 14 1870 (1996)

3 G Bar S Rubin R W Cutts T N Taylor J Zawodzinski andA Thomos Langmuir 12 1172 (1996)

4 S A Evenson and J P S Badyal Adv Mater 9 1097 (1997)5 H Tokuhisa M Zhao L A Baker V T Phan D L Dermody

M E Garcia R F Peez R M Crooks and T T Mayer J AmChem Soc 120 4492 (1998)

6 L A Baker F P Zamborini L Sun and R M Crooks Anal Chem71 4403 (1999)

7 K M A Rahman C J Durning N J Turro and D A TomaliaLangmuir 16 10154 (2000)

8 J Li D Qin J J R Baker and D A Tomalia Polym Prepr41 1446 (2000)

9 M Ito T Imae K Aoi K Tsutsumiuchi H Noda and M OkadaLangmuir 18 9754 (2002)

10 H C Yoon M-Y Hong and H-S Kim Langmuir 17 1234 (2001)11 M-Y Hong H C Yoon M-Y Hong and H-S Kim Langmuir

19 416 (2003)12 E Kim K Kim H Yang Y T Kim and J Kwak Anal Chem

75 5665 (2003)13 T Yamazaki and T Imae J Nanosci Nanotech 5 1066 (2005)14 D Arrington M Curry and S C Street Langmuir 18 7788 (2002)15 H Li D J Kang M J Blamire and E T S Huck Nano Lett

2 347 (2002)16 X C Wu A M Bittner and K Kern Langmuir 18 4984

(2002)17 A M Bittner X C Wu and K Kern Adv Funct Mater 12 432

(2002)18 R Mckendry W T S Huck B Weeks M Fiorini C Abell and

T Rayment Nano Lett 2 713 (2002)19 T Yamazaki T Imae H Sugimura N Saito K Hayashi and

O Takai J Nanosci Nanotechnol 5 1792 (2005)20 D M Watkins Y Sayed-Sweet J W Kilmash N J Turro and

D A Tomalia Langmuir 13 3136 (1997)21 M H Kleinman J H Flory D A Tomalia and N J Turro J Phys

Chem B 104 11472 (2000)

22 W Chen D A Tomalia and J L Thomas Macromolecules33 9169 (2000)

23 P M R Paulo R Gronheid F C De Schryver and S M B CostaMacromolecules 36 9135 (2003)

24 J Zhang J T Petty and R M Dickson J Am Chem Soc125 7780 (2003)

25 I W Lee Y Bae and A J Bard J Am Chem Soc 126 8358(2004)

26 D Wang and T Imae J Am Chem Soc 126 13204 (2004)27 D Wu Y Liu C He and S H Goh Macromolecules 38 9906

(2005)28 D Onoshima and T Imae Soft Matter 2 141 (2006)29 D Wang T Imae and M Miki J colloid Interface Sci 306 222

(2007)30 L Pastor-Peacuterez Y Chen Z Shen A Lahoz and S-E Stiriba

Macromol Rapid Commun 28 1404 (2007)31 O Yemul and T Imae Colloid Polym Sci 286 747 (2008)32 K Tamano and T Imae J Nanosci Nanotechnol 8 4329 (2008)33 G Jayamurugan C P Umesh and N Jayaraman Org Lett 10 9

(2008)34 H Sugimura A Hozumi T Kameyama and O Takai Surf Inter-

face Anal 34 550 (2002)35 K Inoue M Michimori M Okuyama and Y Hamakawa Jpn J

Appl Phys 26 805 (1987)36 A Bernard E Delamarche H Schmid B Michel H R Bosshard

and H Biebuyck Langmuir 14 2225 (1998)37 N L Jeon I S Choi G M Whitesides N Y Kim P E Laibinis

Y Harada K R Finnie G S Girolami and R G Nuzzo ApplPhys Lett 76 4201 (1999)

38 H X He Q G Li Z Y Zhou H Zhang S F Y Li and Z F LiuLangmuir 16 9683 (2000)

39 Y Koide Q Wang J Cui D D Benson and T J Marks J AmChem Soc 122 11266 (2000)

40 C R Kagen T L Breen and L L Kosbar Appl Phys Lett79 3536 (2001)

41 T L Breen P M Fryer R W Nunes and M E Rothwell Lang-muir 18 194 (2002)

42 H Seidel L Csepregi A Heuberger and H BaumgaertelJ Electrochem Soc 137 3612 (1990) H Seidel L CsepregiA Heuberger and H Baumgaertel J Electrochem Soc 137 3626(1990)

43 H Sugimura and N Nakagiri Appl Phys A 66 S427 (1998)H Sugimura K Ushiyama A Hozumi and O Takai Langmuir16 885 (2000)

44 L Hong H Sugimura T Furukawa and O Takai Langmuir19 1966 (2003) L Hong K Hayashi H Sugimura O TakaiN Nakagiri and M Okada Surf Coat Technol 169 211 (2003)

45 The oxidation of methyl groups of ODS on Si substrates by UV lightwas strongly depended on the proximate gap between the substrateand photomask and the pressure of oxygen

46 C-C Chu and T Imae Macromol Rapid Commun 30 89 (2009)47 G Beamson and D Briggs High Resolution XPS of Organic Poly-

mers The Scienta ESCA300 database John Wiley and Sons NewYork (1992)

48 R Schlapak D Armitage S-N Zeni G Latini J H GruberP Mesquida Y Samotskaya M Hohage F Cacialli andS Howorka Langmuir 23 8916 (2007)

49 S E Koh K D McDonald D H Holt C S Dulcey J A Chaneyand P E Pehrsson Langmuir 22 6249 (2006)

Received 26 September 2010 Accepted 21 October 2010




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under gasdegas process of oxygen The present workindicates the extensive possibility for family of PAMAMdendrimer to be utilized even at the solid film as a fluo-rescence probe on the microscopic observation Moreoverfacile and highly sensitive detection of fluorescent den-drimer probe on a fluorescence microscope is the strongadvantage on the various biomedical applications sensingtechnology and molecular recognition

2 EXPERIMENTAL DETAILS

21 Materials

Methanol solutions of G4 and G45 PAMAM den-drimers (PAMAM-NH2 PAMAM-COOminus) were pur-chased from Aldrich Co Ltd These dendrimerscontain 64 (amine) and 128 (carboxylate) terminalgroups respectively n-octadecyltrimethoxysilane (ODS)3-aminopropyltriethoxysilane (APS) and ammoniumper-sulfate ((NH42S2O8 were obtained from Tokyo ChemicalIndustries Co Ltd Acros Organics Co Ltd and WakoChemicals Co Ltd respectively Ethanol and toluene wereproducts from Junsei Chemical Co Ltd Purified waterwas prepared by a Millipore milli-Q system

22 Preparation

Silicon and glass substrates (Matsunami micro cover glass18times 18 mm) were patterned by SAM procedure andphotolithography1934 Prior to the patterning on silicon orglass substrate the substrates were carefully cleaned byultrasonication for 5 min each in piranha solution wateracetone and ethanol followed by drying in an oven Thesubstrates were further cleaned photochemically by irradi-ation of UV light in vacuum which is generated from anexcimer lamp (Ushio Electric UER20-172V = 172 nmwith a power density of 10 mWcmminus2 in order to removeany organic contaminants The UV irradiation was carriedout at a pressure of 15times102 pa with a proximate gap oflt10 nm between the substrate and photomask The radi-ation at short wavelength produces the oxygen atoms andozone molecules from atmospheric oxygen molecules byphotoexcitation which decompose the carbonndashcarbon andcarbonndashhydrogen bonds of organic molecules35

Two different types of precursors ODS and APSwere employed for the preparation of carboxylic acidand amine terminated patterns respectively The car-boxylic acid (ODS-COOH) and amine (ODS-NH2terminated patterns were immersed in a 05 mM solu-tion of G4 or G45 PAMAM dendrimer for 24 h andthus the dendrimer-treated substrates were denotedby PAMAM-NH2ODS-COOH PAMAM-COOminusODS-COOH PAMAM-NH2ODS-NH2 and PAMAM-COOminusODS-NH2 Prior to the immersion of thesesubstrates solutions of PAMAM dendrimers were agedfor 7 days under the addition of an aqueous 01 M solution

of ammoniumpersulfate The dendrimer-treated substrateswere dried by N2 gas and then examined by optical andfluorescence microscopyThe G4 and G45 PAMAM dendrimer films on well-

cleaned quartz and silicon (n type (100) wafer NilacoCo) substrates were prepared from 50 mm3 of a 5 wtPAMAM dendrimer solution by a spin coating methodwhere the substrates were rotated at 100 rpm for 5 minThis process was repeated for four times and then the filmswere dried overnight at room temperature under vacuumPAMAM dendrimer films on substrates were aged in thepresence of O2 gas and degassed Then the films were ana-lyzed by UV-visible absorption spectroscopy fluorescencespectroscopy and X-ray photoelectron spectroscopy (XPS)

23 Measurements

UV-visible absorption spectra on quartz substrates werecollected on a Shimadzu Bio Spec-1600 spectrometer Flu-orescence spectra were recorded on a Hitachi F-3010 flu-orescence spectrophotometer where the excitation sourcewas Xenon lamp operated at 150 W The optical (Halogenlamp LHS-H100P-1 12 V 100 W) and fluorescence(super high pressure mercury lamp Model C-SHG1100 W) microscopic images were taken on a Nikon-Eclipse TE 2000-U microscope For fluorescence micro-scopic images the silicon substrates were irradiated at 365nm excitation wavelength by using DM 400 and RA 400filters XPS studies on quartz substrates were performed ona JPS-9000 MX JEOL photoelectron spectrometer usingMgK monochromatized X-ray beam at a constant dwelltime of 100 ms X-ray scans were performed by using passenergies of 50 eV for wide scan and of 10 eV for nar-row scan The anode voltage and current were 10 kV and10 mA respectively All core level spectra were obtainedat a photoelectron takeoff angle of 90 with respect to thePAMAM dendrimer films

3 RESULTS AND DISCUSSION

31 Visual Observation of G4 and G45 PAMAMDendrimers on ODS-COOH and ODS-NH2

Patterned Substrates

The functional patterned substrates allow us to investi-gate the properties and assembling of materials and canbe used for various applications like sensing technologiesorganic light-emitting diodes organic thin-film transistorsetc36ndash41 Moreover they can be model surfaces of bio-materials which are prepared readily by a large varietyof available techniques4243 The substrates with ndashNH2 orndashCOOH surface pattern along with methyl surface patternare ones of model surfaces of biomaterials The fluorescentG4 and G45 PAMAM dendrimers possessing ndashNH2 andndashCOOminus functional groups respectively on their peripherycan be expected to be adsorbed selectively on these model




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Documents

Visual Observation and Characterization of Fluorescent ...imaelab.jpn.org/wp-content/uploads/2019/06/Visual... · The G4 and G4.5 PAMAM dendrimer lms on well-cleaned quartz and silicon