Supporting Information

Transcription

1 Supporting Information Wiley-VCH Weinheim, Germany Spatial and Directional Control over Self-Assembly Using Catalytic Micropatterned Surfaces** Alexandre G. L. Olive, Nor Hakimin Abdullah, Iwona Ziemecka, Eduardo Mendes, Rienk Eelkema,* and Jan H. van Esch* anie_ _sm_miscellaneous_information.pdf anie_ _sm_si_movie.avi

2 A- General Remarks All reagents were purchased from commercial sources and were used as provided unless otherwise stated. Tri-acylhydrazide cyclohexane and the benzaldehyde were prepared according to previously published procedures. AFM experiments were performed on an Ntegra P8 from NT-MDT using NSG01 series cantilever (reson. Freq. 150 KHz, force const. 5.5 N/m) mounted with Diamond Like Carbon (DLC) tips also purchased from NT-MDT. Fluorescence Confocal Microscopy experiments were realized on a Zeiss LSM 700 microscope. XPS measurements were recorded with a Thermo scientific instrument (K-alpha surfaces analysis). B- Microcontact Printing Preparation of glass substrates Prior to use, glass substrates (cover slides from VWR) were treated in H 2 SO 4 at 60 o C for 12 hours and then rinsed extensively with H 2 O and ethanol before drying under a nitrogen stream. They were then treated in plasma oven for 2 minutes to oxidize the outer SiO 2 layer producing hydroxysilanes groups on the surface. Preparation of the stamps PDMS stamps (Sylgard 184 silicon elastomer, with 10 % of curing agent) were prepared against a silicon wafer master displaying the negative image of the desired patterns. An inking solution containing the appropriate amount of MPTS (20 % v/v) was prepared. 50 µl of the inking solution were placed on a glass substrate then the PDMS stamp was gently disposed on top of and left for incubation for 15 s. The stamp was then removed and dried for 1 min in air until no solvent was visible with naked eye. Transfer of pattern via stamping The prepared PDMS stamp is then dropped on top of the treated glass for 2 minutes at 60 o C after which the stamp is carefully removed with tweezers. The glass substrate was then baked with a heat gun set at 150 o C for 1 min, cleaned with H 2 O, EtOH and finally dried over a N 2 stream. Binding of fluorescent probe to thiol patterns To characterize the thiol pattern obtained by micro-contact printing, a fluorescence probe, fluorescein diacetate 5-maleimide (Sigma-Aldrich) was used. This compound covalently and selectively binds to 6

3 thiol functions under basic conditions. A micro-molar solution of the probe in H 2 O (buffer ph 10) / DMSO 1/1 was prepared. The previously prepared glass substrates were immersed overnight in this solution. They were then removed, washed with water, ethanol and dried over a stream of N 2. Patterns were then imaged with the help of a fluorescent confocal microscope or AFM. Oxidation of thiol pattern into sulfonic acid groups Glass substrates carrying patterned thiols were dipped into hydrogen peroxide overnight at 65 o C. They were then taken out, cleaned with water and ethanol, and then dried over a stream of N 2. Chemical characterization of the surfaces by XPS Glass substrate were prepared as mentioned previously and directly inserted in the instrument. 400 μm beam spot was used. C- Characterization of micropatterns A solution of (3-mercaptopropyl)trimethoxysilane (MPTS) 20 % v/v in toluene was used as ink, on PDMS stamps with micrometer-sized regular patterns (See part B. SI). [1] Verification of MPTS grafting was performed by confocal microscopy, using a fluorescent probe (fluorescein-5-maleimide) that reacts selectively to thiol functions. [2] The confocal microscopy images revealed fluorescent patterns corresponding to those previously stamped, confirming that thiol groups had been transferred to the surface (Figure S2). Further evidence of the thiol pattern was obtained by atomic force microscopy (AFM) images and X-ray photoelectron microscopy (XPS) measurements (Figure S3). AFM images revealed the presence of a monolayer of MPTS of 0.8 ± 0.2 nm height matching the size of the MPTS molecules (0.7 ± 0.05 nm). XPS spectra displayed a band with a doublet structure in the S 2p region characteristic of the splitting into S 2p3/2 and S 2p1/2 levels of the S energy levels. These two peaks at respectively and ev with a peak area ratio of 2:1 confirm that thiol groups are present on the surface [3] and that they are covalently bound to the glass substrate. [4] Next, the desired sulfonic acid patterns were obtained by oxidation of the thiol groups using hydrogen peroxide. Transformation of the SH patterns into SO 3 H patterns was verified by AFM and XPS (SI: Figure S3). The presence of a single peak ( ev) in the sulphur atom region of the XPS spectrum confirmed that all thiol functions had been converted to sulfonic acid groups. 7

4 Electrostatic potential (mv) ph D- Modelling of surface charges and ph The electrostatic potential of the negatively charged surface in presence of electrolytes (buffer) can be determined using the Grahame equation combined with the surface dissociation constant of the acidic sulfonic groups (1). ( [ ] ) ( ) [ ] [ ] (1) where σ is the surface charge density (-0.2 C/m 2 ), α the fraction of sites dissociated, K d the constant of dissociation of the acids (10 -pka ), ψ 0 the electrostatic potential, ε permittivity of the medium (80 C 2 J -1 m -1 ), ε 0 permittivity of vacuum ( C 2 J -1 m -1 ), k the Boltzmann constant, T the temperature, e the charge of an electron. The concentrations represents the concentration in bulk and are given in M. [Na + ] is the concentration of the buffer, [H + ] is equal to 10 -ph. The pka of sulfonic acid on glass surface is 2.8. For the system considered, we found from simulation that the electrostatic potential on the surface is 122 mv for ph 7 and -106 mv for ph 5, and tends to 0 in bulk (see Graph S1), almost all the sulfonic acid functions are dissociated at ph 7 (α=0.98) against 72 % at ph 5. Silanol groups are present in the non-stamped area, they have a pka of 8.4 and a surface charge density of -10 mc / m 2 which is independent from the ionic strength and the ph for glass substrate immersed into solution with a ph < 7. We found that only 7 % of the SiOH groups are dissociated and that the ph near the surface in between stamped area is the same as in bulk (Table S1) distance from surface (nm) Graph S1: Electrostatic potential (red line, filled markers) and ph (blue line, empty markers) as a function of the distance from surface, for a glass substrate functionalized with sulfonic acid functions immersed in a 0.1 M sodium phosphate buffer ph 7 (circles) and ph 5 (squares). 8

5 Table S1: data obtained from simulations Bulk ph Surface ph ψ 0 (mv) α Length ph gradient (nm) -SO 3 H -SiOH n/a n/a E- Fiber s growth on pattern surface A cuvette made of PDMS (10 x 10 x 3 mm) was treated in plasma oven for 5 min in order to render the surface hydrophilic and promote adhesion with glass substrates. It was then filled with a solution of the gelator precursors (1 and 2) at the desired concentration and ph. Glass substrates were then carefully placed on it, the sulfonic acid pattern facing the solution. The 2 elements were then flipped up-side down and placed on a confocal microscope (Fig. S2a). In order to characterize and visualize the fibers by confocal microscopy, a fluorescent dye (fluorescein carrying an aldehyde and a PEG tail) was used in a ratio of 0.01 % mol. F- Confocal microscopy Imaging of nanofibers were carried out on a Zeiss LSM 700 equipped with a Zeiss Axio Observer inverted microscope, 40x PlanFluor oil immersion objective lens (NA 1.3) using incident wavelengths of 458 nm and 488 nm. A z-step size of 0.53 µm was used to optically section the samples and the z- stacks were performed with confocal pinhole set to 1.0 airy unit. Time lapse movies were made from z-stacks acquired every 15 minutes for 2 hours. The images at the same focal point were arranged from time zero until the end to show the process of fibers growth. Data files were processed by using ZEN 2011 (Carl Zeiss) and ImageJ software (National Institutes of Health). G- Orientation experiment To obtain images with the resolution needed to calculate the Texture Direction Index (S) by 2D Fourier transform, analyses were carried out on samples grown in the xy direction. Being limited by the resolution of the confocal microscope in the xz plane, the catalytic pattern was not placed on the bottom wall of the cuvette, but on a side wall such that the fibers would grow parallel to the substrate allowing imaging in the xy plane (Figure S7). Using this setup, S was calculated 9

6 Experimental setup: A rectangular hole (35 x 20 mm) was cut into a piece of PDMS 17 mm thick and treated in plasma oven to provide adhesion with glass substrate constituting a pool. A pillar also made from PDMS was prepared (10 x 18 x 5 mm) in order to make the glass substrate stand perpendicular to the scanning plan of the confocal microscope. Glass substrates were then placed against the pillar with the sulfonic acid pattern (near the edge of substrate) facing the solution. Next, the pool with glass substrate was placed on a confocal microscope and the gelator precursors (aldehyde and hydrazide) were then pipetted into the cuvette. In order to determine whether the scanned images have a particular direction or not, the fibers texture were investigated with spatial parameter namely the Texture Direction Index, S. S is a measure of how dominant the dominating direction is, and is defined as the average amplitude sum divided by the amplitude sum of the dominating direction: where, A max, amplitude of the radial Fourier spectrum for each orientation in the plane, t, an index running through all angles on the surface With this definition values for S always run between 0 and 1. Surfaces with very dominant directions will have S values close to zero and if the amplitude sum of all direction are similar, S is close to 1. Scanned images were first sampled into smaller images (200 pixels x 200 pixels) representing image of fibers grown from the surface and fibers grown in bulk. Once images collected, the images were filtered by applying a Gaussian L Filter to eliminate noise and get correct representations of the images. The images were further processed by 2D Fourier Transform leading to information about value of dominant texture orientation of the fibers. Data files were processed by using SPIP software from Image Metrology A/S. 10

7 Count Count H- Figures Diameter (nm) height (nm) Figure S1: a- AFM image of fibers of 3 dispersed on a glass substrate b- & c- statistical analysis of fiber s size respectively diameter and height. 11

8 Figure S2: Fluorescence confocal microscopy of thiol pattern labelled with a fluorescent probe (fluorescein diacetate 5-maleimide). 12

9 a b c d e f Figure S3: AFM topography and phase images of monolayer of MPTS (a and b respectively); and equivalent oxidized MPTS (d & e) and their corresponding XPS spectra (c, f); AFM data recorded in tapping mode by using 1 nm tip (resonance frequency Hz) from NT-MDT Co, Moscow, Russia. 13

10 Figure S4: experimental setup, (i) microcontact printing using MPTS 20 % v/v in toluene as inking solution, stamping 2 min at 60 o C (ii) glass substrate immersed in H 2 O 2 at 65 o C for 12h (iii) glass substrate used as a wall of a cuvette containing 1 and 2 in phosphate buffer solutions (iv) spontaneous formation of fibers where the catalyst is located. 14

11 a b - Figure S5: a- picture of pattern of catalyst on glass substrate recovered by a PDMS cuvette containing gelator precursors, b- PDMS cuvette at the end of experiment entirely gelated evidenced by the air bubble remaining at the bottom. Figure S6: Fluorescent probe for fluorescence confocal microscopy imaging of the fibers. 15

12 Figure S7: Fluorescence confocal images from the orientation experiment (part F of this supporting information) a- before any structure is formed, b- at the end of the experiment, c- zoom on image b-, d- Count distribution of Stdi as a function of the fiber location. 16

13 Figure S8: Fluorescence confocal images (λex:458 nm, 464 nm < λem < 700 nm, pix, 1.3 µs / pix) of self-assembled fibers obtained from 10 µm bands spaced by 15 µm sulfonic acid pattern recovered by a solution (ph 7, 0.1 M phosphate buffer) of 20 mm solution of 1 and 120 mm solution of 2. Edge of the stamped area materialized with dashed red line. Figure S9: 3D fluorescence confocal images (λ ex :458 nm, 464 nm < λ em < 700 nm, pix, 1.3 µs / pix) of self-assembled fibers obtained from 10 µm bands spaced by 15 µm sulfonic acid pattern recovered by a solution (ph 7, 0.1 M phosphate buffer) of 20 mm solution of 1 and 120 mm solution of 2, scale for color code which stands for height at the bottom. 17

14 [1] P. Pallavicini, G. Dacarro, M. Galli, M. Patrini, J. Coll. Interf. Sci. 2009, 332, [2] a) D. J. Bigelow, G. Inesi, Biochem. 1991, 30, ; b) R. F. Chen, C. H. Scott, Anal. Lett. Part A. 1985, 18, [3] W. W. Zhang, C. S. Lu, Y. Zou, J. L. Xie, X. M. Ren, H. Z. Zhu, Q. J. Meng, J Coll. Interf. Sci. 2002, 249, [4] D. G. Castner, K. Hinds, D. W. Grainger, Langmuir 1996, 12,