Facile Assembly Enhanced Spontaneous Fluorescence Response of Ag + Ion Containing Polyelectrolyte Multilayer Films

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1 Supporting Information Facile Assembly Enhanced Spontaneous Fluorescence Response of Ag + Ion Containing Polyelectrolyte Multilayer Films Xiayun Huang and Nicole S. Zacharia*,, Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843, United States Department of Polymer Engineering, The University of Akron, Akron, Ohio 44325, United States * nzacharia@uakron.edu 1. Experimental Section 1.1 Materials Poly(acrylic acid) (PAA, MW=50,000, 25 wt% in H 2 O), linear poly(ethylene imine) and poly(allylamine hydrochloride) were purchased from Polysciences Inc. Poly(acrylic acid) (PAA, MW=100,000, 35 wt% in H 2 O), poly(dimethyldiallyl ammonium chloride), and branched poly(ethylene imine) (BPEI, Mw=25,000) was obtained from Sigma-Aldrich. Poly(amido amine) (PAMAM) G3-NH2 ethylene diamino core dendrimers were obtained from Dendritech. Silver nitrate was purchased from Alfa Aesar. Deionized water (18.2 MΩ) was obtained from a Milli-Q water purification system and used for all experiments. All materials used were of at least analytical reagent grade and used as received without further purification. 1.2 Characterization Surface composition was characterized by X-ray photoelectron spectrometer (XPS, Kratos Axis Ultra Imaging, Chestnut Ridge, NY). FTIR spectra were obtained using an IR Prestige 21 system (Shimadzu Corp., Japan) and analyzed by IRsolution V.1.40 software. The thickness of the PEM films was measured using profilometer (KLA Tencor Instruments P6), and values reported represent an average of 5 different positions on the film. Fluorescence spectra of BPEI-Ag + /PAA PEM and fluorescence quenching studies after exposure to various vapors and solutions were measured by

2 spectrofluorometry (PTI QuantaMaster Series, Photon Technology International, Inc, NJ) using an excitation at 450 nm. The slit width was 3 nm for both the excitation and emission mode using 30 o solid sample holder. The BPEI-Ag + /PAA PEM and PEM after formaldehyde treatments were measured by UV-2250 system (Shimadzu Corp., Japan). Elemental analysis was performed employing inductively coupled plasma mass spectrometry (ICP-MS) (Perkin-Elmer DRCII) using a commercial ICP standard for silver ions. 1.3 PEM Assembly PEMs were assembled onto glass slides, quartz glass and silicon wafers. Before use, they were treated in a freshly prepared piranha solution (mixture of H 2 SO 4 (98%) and H 2 O 2 (30%) with the volume ration v/v=7/3) at room temperature for 4 h and rinsed with water of neutral ph. All the substrates were dried by a stream of filtered nitrogen gas before use. Polycationic BPEI solution (40 mmol/l with respect to the amine groups) was mixed with AgNO 3 to form a stable complex. These complexes were used for assembly of PEMs with negatively charged weak polyelectrolyte (PAA, 20 mmol/l with respect to the carboxylic acid groups). The ph of these solutions was adjusted with 1 mol/l NaOH or 1 mol/l HNO 3 solution to 9.5 for BPEI-Ag + ion complex solution and 4.5 for PAA solution. All multilayer assembly was carried out in a dark environment at room temperature using a StratoSeqiemce VI dipper (NanoStrata Inc.) and a Zeiss HMS series programmable slide stainer. Cleaned and dried substrates were first exposed to BPEI-Ag + ion complex solution for 10 min followed by three separate DI water rinse baths. Then, the substrates are exposed to PAA solution for 10 min and then again to three DI water rinse baths. This cycle was repeated until the desired number of bilayers was reached. The multilayer films are dried and stored in dark environment at room temperature (~25 o C and relative humidity at ~55%) for 24 h before any test. Analogous procedures were used to multilayer BPEI with PAA-Ag + ion complex as well as complexes with both polyelectrolytes. 1.4 Formaldehyde gas detection All films used for formaldehyde gas detection were assembled using 30 bilayers BPEI-Ag + /PAA PEMs with Ag + ion concentration of 3 mmol/l in the assembly complex

3 Relative Intensity ratio (%) solution. Formaldehyde gas detection was carried out by vaporizing formaldehyde solution in a close-capped 30 ml bottle. 100 L of formaldehyde (37% in H 2 O) was drop to the bottom of the bottle and PEM was clip to the cap of the close-capped bottle. The corresponding formaldehyde concentration was 0.13%. The formaldehyde in aqueous solution vaporizes to gas at 25 o C and reduces the Ag + in the PEM to Ag particles. PEMs were kept in this formaldehyde gas environment for varying amounts of time in a dark environment and the fluorescent intensity of each specimen was detected by the spectrofluorometer with an excitation of 450 nm and UV-Vis spectrometry. 2. Fluorescence quenching through Ag + ion reduction Time (min) Figure S1. Relative fluorescence emission intensity at 615 nm of 30 bilayer BPEI-Ag + ion/paa film after exposure to 365 nm UV radiation for a certain time duration (from 0 min to 420 min). The excitation wavelength was fixed at 450 nm. Concentration of BPEI and PAA were 40 mmol/l and 20 mmol/l with respect to the repeating group. And the concentration of Ag + in the BPEI-Ag + ion complex solution was 3 mmol/l.

4 Figure S2. (A) Fluorescent excitation (dash line) and emission (solid line) spectra of 10 bilayer BPEI-Ag + /PAA film with 1, 3, 6 mmol/l Ag + in BPEI-Ag + complex solution. After thermal reduction, the 615 nm emission quenching and new band around 480 nm was formed due to the formation of nanocluster. Concentration of BPEI and PAA were 40 mmol/l and 20 mmol/l with respect to the repeating group.

5 A 30 bilayer BPEI-Ag + ion/paa film was cut as 1 cm 1 cm for 365 nm UV radiation for specified times (from 0 min to 420 min). The UV lamp was 8 watt and the distance from the lamp to film surface was kept as 7 cm. Ag + in the BPEI-Ag + ion/paa film was photochemically reduced to Ag nanoparticles. Different than other Ag nanocluster film systems reported elsewhere fabricated by the photochemical reduction of Ag + ion, [1] the BPEI-Ag + /PAA film does not increase in fluorescence intensity or form new band (data not shown here) till 420 min when exposure to UV radiation. Instead, the fluorescence intensity decreases due to the Ag + ion reduction (Figure S1). A new band (~480 nm emission band) appears when Ag nanoclusters were formed via thermal reduction (Figure S2). At the same time, the emission band at 615 nm is observed to decrease. NaBH 4 immersion then reduces the Ag + ion in BPEI-Ag + ion/paa film to Ag nanoparticle instead of nanoclusters and quenches the fluorescent emission (Figure S3).

6 Figure S3. 30 bilayer BPEI-Ag + ion/paa film and BPEI-Ag NP/PAA film under visible light and UV radiation. The BPEI-Ag NP/PAA film was prepared via 30 min 10 mmol/l NaBH 4 reduction of BPEI-Ag + ion/paa film. Concentration of BPEI and PAA were 80 mmol/l and 60 mmol/l with respect to the repeating group. The concentration of Ag + ion in the BPEI-Ag + ion complex solution was 1 mmol/l. 3. Assembly with variations in Ag + ion concentration Table S1. Various concentrations of Ag + ion were assembled in 30 bilayer BPEI-Ag + ion/paa films by varying the Ag + concentration in BPEI-Ag + ion assembly complex solution during assembly. The concentration of BPEI and PAA were 40 mmol/l and 20 mmol/l with respect to the repeating group. The concentration of Ag + ion in the BPEI-Ag + ion complex solution was 1 mmol/l, 3 mmol/l and 6 mmol/l. Polyelectrolyte-ion complex multilayer Amount of Ag + (x10-4, mmol/mm 3 ) BPEI-Ag + /PAA BPEI-Ag + /PAA BPEI-Ag + /PAA

7 Figure S4 Fluorescence spectra of 30 bilayer BPEI-Ag + /PAA, BPEI/PAA-Ag + ion, and BPEI-Ag + /PAA Ag + film with different molecular weight of PAA as assemble solution. The emission spectra were obtained by excited at 450 nm. The concentration of BPEI and PAA were 40 mmol/l and 20 mmol/l with respect to the repeating group. The concentrations of Ag + ion in the BPEI-Ag + ion complex solution or PAA-Ag + ion complex solution were fixed as 1 mmol/l. The fluorescence intensity varies when change Ag + ion in BPEI and PAA solution and also varies with PAA in different molecular weight.

8 Absorbance (a.u.) Fluorescence emission occurs not only when Ag + ion is incorporated into the BPEI solution and is assembled into a film with PAA (BPEI-Ag + ion/paa film), but also when Ag + is first is complexed with PAA, and then assembled with BPEI. Figure S4 shows the fluorescence spectra of BPEI/PAA-Ag + film. Here, Ag + in the complex solution was fixed as 1 mmol/l. The two emission bands in the fluorescence spectra kept the same when excited at 450 nm. However, using different complexes (either BPEI-Ag + ion or PAA-Ag + ion) results in a different amount of Ag + being incorporated into the film and correspondingly a different fluorescence intensity. From ICP-MS results (data not shown here), it was found that a greater amount of Ag + ion incorporated in the film corresponds to a higher emission intensity. An increase in molecular weight of PAA chain also decreases the incorporation of Ag + ion into the film. Both the structure of PAA-Ag + ion complex changes in this case and causes a decrease in both the fluorescent intensity and the amount of Ag + ion incorporated into the film. Even in the case when Ag + is introduced in the BPEI-Ag + complex solution (and not the PAA solution), the resulting BPEI-Ag + ion/paa film still shows a decrease in both the fluorescent intensity and the amount of Ag + ion incorporated. 4. Interaction inside the BPEI-Ag + ion/paa film BPEI-Ag + 6 /PAA BPEI-Ag + 3 /PAA BPEI-Ag + 1 /PAA BPEI/PAA Wavenumber (cm -1 )

9 Figure S5. FTIR-ATR spectra of 30 bilayer BPEI-Ag + ion/paa films. The concentration of BPEI and PAA were 40 mmol/l and 20 mmol/l with respect to the repeating group. The concentration of Ag + ion in the BPEI-Ag + ion complex solution was 1 mmol/l, 3 mmol/l and 6 mmol/l in the BPEI-Ag + ion complex solution for LbL assembly. No distinguishable peak shifts can be seen in the spectra. The chelation of Ag + ion with the amine groups of the BPEI and the carboxylic acid groups of the PAA were studied by FTIR-ATR spectra of 30 bilayers BPEI-Ag + ion/paa film. BPEI-PAA film without any Ag + ion has a greater proportion of deprotonated carboxylic acid group (-COO - ) as evidenced by the peak at 1541 cm -1, compared to the peak of the protonated carboxyl group (-COOH) at 1710 cm -1, representing the degree of ionization of PAA in the film is very high and the deprotonated carboxyl group interacted with the protonated amine group of BPEI. The characteristic bands of BPEI are associated with the overlapped NH 2+ and NH bending vibrations at cm 1 and the CH bending vibrations at cm 1. When Ag + ion is assembled in the multilayer film, ATR-FTIR spectra do not show demonstrable peak shifts, meaning the amine group and carboxyl group keep the similar protonated/deprotonated ratio. Instead of interacted with each other, some of them were chelated with Ag + ion in the film.

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11 Figure S6. XPS spectra of 30 bilayer BPEI/PAA, BPEI-Ag + ion/paa film and BPEI-Ag NP/PAA film. The BPEI-Ag NP/PAA film was prepared via 30 min 10 mmol/l NaBH 4 reduction of BPEI-Ag + ion/paa film. Concentration of BPEI and PAA were 40 mmol/l and 20 mmol/l with respect to the repeating group. The concentration of Ag + ion in the BPEI-Ag + ion complex solution was 3 mmol/l. From the XPS spectra, the atomic ratio of silver on the surface is 1.3%, which was consisted with the ICP-MS resulting from the whole film. The N 1s photoelectron spectrum was superimposed with spectral features with peaks situated at and ev. The former is associated with N atoms in the deprotonated amine group and latter with protonated amine group. Both the protonated/deprotonated amine groups in BPEI were involved in chelation and electrostatic interactions. XPS peaks at 368 and 374 ev were assigned to the Ag 3d 5/2 and Ag 3d 3/2 peaks of Ag. Here, it is hard to determine the valence of Ag based on the XPS spectra. After Ag + ion reduction, the Ag NP film shows much higher intensity compared with Ag + ion film, showing that some of the silver in the film migrated to the surface after reduction.

12 I/I 0 (%) 5. Selective counterion detection * * * * 10 0 NaF NaCl NaBr NaI KCN Na2SO4Na2CO3 Nacit NaAc Figure S7. Relative fluorescent quenching of 30 bilayer BPEI-Ag + ion/paa film immersed in a 1 mmol/l salt solution for 10 min. After rinsed with water and dried with N 2. The fluorescent quenching is due to the local precipitation of silver salt. Concentrations of BPEI and PAA were 40 mmol/l and 20 mmol/l with respect to the repeating group. The Ag + ion concentration was fixed at 3 mmol/l. Figure S7 shows the change in intensity of the film s emission after 10 minutes of exposure to various salt solutions. Reaction with cyanide and various halide salts also quenches the fluorescence of the film. Reference [1] W. Zhang, J. Song, W. Liao, Y. Guan, Y. Zhang, X. X. Zhu, J. Mater. Chem. C 2013, 1,