Supporting Information. Plasmonic Biofoam: A versatile Optically-active Material

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1 Supporting Information Plasmonic Biofoam: A versatile Optically-active Material Limei Tian 1, Jingyi Luan 1, Keng-Ku Liu 1, Qisheng Jiang 1, Sirimuvva Tadepalli 1, Maneesh Gupta 2, Rajesh R. Naik 2,3*, and Srikanth Singamaneni 1* 1 Department of Mechanical Engineering and Materials Science, and Institute of Materials Science and Engineering, Washington University in St. Louis, St. Louis, MO 2 Soft Matter Materials Branch, Materials and Manufacturing Directorate, and Human Performance Wing, Wright-Patterson, Air Force Base, Dayton, OH *To whom correspondence should be addressed: singamaneni@wustl.edu (SS) and rajesh.naik@us.af.mil (RRN) Materials: Cetyltrimethylammonium bromide (CTAB), chloroauric acid, ascorbic acid, sodium hydroxide, citric acid, disodium phosphate, horseradish peroxidase, sodium azide, 1-tetradecanol, hydrogen peroxide, 2,2'-azino-bis(3-ethylbenzothiazoline-6- sulphonic acid) (ABTS), 2-naphthalenethiol (2-NT), and sodium borohydride were purchased from Sigma-Aldrich. Silver nitrate and filter paper (Whatman #1) were purchased from VWR International. Glucose, yeast extract, and peptone were purchased from Fisher Scientific. Gluconacetobacter hansenii (ATCC 53582) and Escherichia coli (E.coli, ATCC 35218) were purchased from ATCC. All chemicals have been used as received with no further purification. Synthesis of gold nanorods (AuNRs): Gold nanorods were synthesized using a seedmediated approach. 1, 2 Seed solution was prepared by adding 0.6 ml of an ice-cold sodium borohydride (NaBH 4 ) aqueous solution (10mM) into a mixture of 9.75 ml of cetyltrimethylammonium bromide (CTAB, 0.1 M) and 0.25 ml of chloroauric acid (HAuCl 4, 10 mm) solution under vigorous stirring at room temperature (1000 rpm). The color of the seed solution changed immediately from yellow to brown after NaBH 4 addition. Growth solution was prepared by mixing 95 ml of CTAB (0.1 M), 1.0 ml of silver nitrate (10 mm), 5.0 ml of HAuCl 4 (10 mm), 0.8 ml of ascorbic acid (0.1 M) and 2.0 ml of HCl (1 M) in order, followed by gentle shaking. To the resulting colorless growth solution, 0.24 ml of freshly prepared seed solution was added. After 24 h of aging, AuNR solution was centrifuged at 10,000 rpm for 30 min to remove excess reactants and dispersed in nanopure water (18.2 MΩ-cm). Most of free CTAB was removed by

2 two centrifugation/redispersion cycles, which facilitates the adsorption of AuNRs through electrostatic interaction on cellulose nanofibrils. Bacterial nanocellulose (BNC) hydrogel preparation: Gluconacetobacter hansenii was grown in test tubes containing 6 ml of media at 30 C under shaking at 250 rpm. The media used for the bacterial culture is composed of aqueous solution of 2% (w/v) glucose, 0.5% (w/v) yeast extract, 0.5% (w/v) peptone, 0.27% (w/v) disodium phosphate, and 0.5% (w/v) citric acid. After 3 days of growth, 1.0 ml of the above solution was inoculated to 9 ml of media in a 6 cm petridish followed by gentle mixing. Subsequently, the Petri dish was kept static and covered at room temperature. After 3 days, a thin film of bacterial nanocellulose (~1.0 mm in thickness) formed at the liquidair interface. The nanocellulose film is washed in 500 ml of 0.1 M NaOH aqueous solution at boiling temperature for 1 hour, followed by washing in nanopure water for 2 days under gentle agitation to remove the impurities. Microscopy characterization: Scanning electron microscope (SEM) images were obtained using FEI Nova 2300 Field Emission and Hitachi S4800 High Resolution SEM at an accelerating voltage of 10 kv. Plasmonic aerogel and plasmonic paper was gold sputtered for 120 sec before SEM imaging. Transmission electron microscope (TEM) images were obtained using a field emission TEM (JEM-2100F, JEOL) operating at an accelerating voltage of 200 kv. Spectroscopy: UV vis extinction spectra were collected using a Shimadzu 1800 spectrophotometer. Extinction spectra from plasmonic aerogel were collected using a CRAIC microspectrophotometer (QDI 302) coupled to a Leica optical microscope (DM 4000M) with 20x objective in the range of nm with 10 accumulations and 0.1 sec exposure time in reflection mode. The spectral resolution of the spectrophotometer is 0.2 nm. Raman spectra were collected using a Renishaw invia confocal Raman spectrometer mounted on a Leica microscope with a 20x objective (NA = 0.4) and 785 nm wavelength diode laser with a laser spot size of ~1.2 µm and power of 0.7 mw at the sample surface. The thickness of the aerogel used for the SERS measurements was around 1 mm, which is much higher than the laser beam waist diameter (~1.2 µm) and focal depth (~11.5 µm). Thermal conductivity measurements of hydrated plasmonic aerogel and pristine BNC aerogel: The thermal conductivity of BNC-based plasmonic aerogel and BNC aerogel in hydrated state was measured by sandwiching the material between two glass microscope slides. The sample was slightly compressed to maintain good contact with glass slides, and then placed on a hot plate with an ice cube on the top slide. The

3 cross-sectional temperature distribution of the sandwiched material was monitored by an IR camera (ICI 7320 USB camera). Fourier equation was used to calculate the thermal conductivity of each sample using the following formula: = The heat flux, normalized by area, was calculated with the known thermal conductivity (K) of glass slides to be ~1.05. The thermal conductivity was calculated based on the assumptions that the same heat flux was experienced by contacting sample and the glass slide and the emissivity of glass slides and samples is 0.9.

4 A B C Figure S1. Photographs of (A) pristine silica aerogel, (B) silica-based plasmonic aerogel, and (C) corresponding shattered pieces (B) upon gentle compression, which depicts the brittle nature of the silica aerogel.

5 A B Figure S2. SEM images of (A) top surface of bacterial nanocellulose (BNC) aerogel showing non-woven 3D network of cellulose nanofibrils with a highly open microporous structure (Inset: photograph of BNC aerogel after freeze-drying) and (B) top surface of plasmonic aerogel reveals dense and uniform adsorption of AuNRs on the nanofibers of the aerogel (Inset: photograph of the aerogel densely loaded with AuNRs exhibiting deep green color).

6 A Figure S3. (A) Transmission electron microscopy (TEM) image of gold nanorods (AuNRs) employed in this work. The dimension of AuNRs is approximately 52 nm in length, and 13 nm in diameter.

7 A Weight loss (%) C Plasmonic aerogel BNC aerogel Temperature ( o C) B Weight loss (%) Silk aerogel Plasmonic aerogel Temperature ( o C) D Figure S4. (A) Thermogravimetric analysis (TGA) of BNC aerogel and BNC-based plasmonic aerogels. The weight fraction of AuNR in the plasmonic BNC-foam was determined to be ~57%. (B) Thermogravimetric analysis of silk aerogel and silk-based plasmonic aerogels. The weight fraction of AuNR in the plasmonic silk-foam was determined to be ~20%. (C) Photograph and (D) optical microgragh of gold residue of 5.4 mg left after TGA of BNC-based plasmonic aerogel.

8 500nm Figure S5. Scanning electron microscopy (SEM) image showing gold nanorods adsorbed on a common laboratory filter paper, called plasmonic paper. The plasmonic paper was employed as a 2D reference for comparing the SERS activity and photothermal steam generation efficiency of the plasmonic aerogel.

9 A B C Temperature ( o C) W/cm W/cm No laser Weight loss(g/cm 2 ) Time (s) 5.1 W/cm W/cm 2 No laser Time (s) Evaporation rate (mg/cm 2 s) W/cm W/cm 2 No laser Time (s) Figure S6. (A) Temperature increase of plasmonic aerogel suspended on the water surface as a function of irradiation time with 808 nm laser at different laser powers indicated in the plot, (B) corresponding cumulative weight loss of water, and (C) corresponding instantaneous water evaporation rates.

10 q'' (kw m -2 ) A K= W m -1 K Measurements 1.0 Linear fit dt/dx (10 3 Km -1 ) q'' (kw m -2 ) B K=0.525 W m -1 K -1 Measurements Linear fit dt/dx (10 3 K m -1 ) Figure S7. Thermal conductivities of (A) BNC aerogel and (B) plasmonic aerogel in wet state were measured to be W m -1 K -1 and W m -1 K -1, respectively (inset shows the cross-section IR images of the sandwich architecture employed in the measurement.

11 Figure S8. IR images depicting the increase in temperature of plasmonic aerogel loaded with 1-tetradecanol to around 41⁰С (slightly higher than the melting point of 1- tetradecanol) after 15 min of laser irradiation.

12 A B Figure S9. (A) Scanning electron microscopy (SEM) image showing the cross section of plasmonic aerogel loaded with 1-tetradecanol. The cross-section shows the brittle fracture of the crystalline 1-tetradecanol (fractured below the melting temperature of 1- tetradecanol). (B) High resolution SEM image showing the micropores of plasmonic aerogel filled with 1-tetradecanol.

13 A B Figure S10. (A) Cross-sectional SEM image showing the plasmonic aerogel loaded with 1-tetradecanol after 15 min of laser irradiation. (B) High resolution SEM image shows distinct fibrous morphology and microcavities, resulting from the successful release of 1- tetradecanol.

14 Absorbance (a.u.) A B C min Absorbance (a.u.) Wavelength (nm) min Absorbance (a.u.) Wavelength (nm) Triggered release of NaN Wavelength (nm) Figure S11. (A) Absorption spectra of green color product produced by the oxidation of azinobis [3-ethylbenzothiazoline-6-sulfonic acid]-diammonium salt (ABTS). A linear increase in the absorption intensity with time suggests the preserved activity of horseradish peroxidase (HRP) released from plasmonic aerogel after 2 min of laser irradiation. (B) Absorption spectra of green color product monitored after 1 min of laser irradiation depicting the slower enzyme kinetics, corresponding to the smaller amount of released HRP. (C) Absorption spectra of green color product collected after triggered release of NaN 3 (a known inhibitor of HRP) by laser irradiation for 1 min, which resulted in immediate inhibition of the enzyme activity as evidenced by the freezing of the absorption intensity of the enzymatic reaction product.

15 References 1. Orendorff, C. J.; Murphy, C. J., Quantitation of Metal Content in the Silver-Assisted Growth of Gold Nanorods. J. Phys. Chem. B 2006, 110, Huang, X.; Neretina, S.; El-Sayed, M. A., Gold Nanorods: From Synthesis and Properties to Biological and Biomedical Applications. Adv. Mater. 2009, 21,