Ppm detection of alcohol vapors via metal organic framework functionalized surface plasmon resonance sensors

Transcription

1 Supporting Information Ppm detection of alcohol vapors via metal organic framework functionalized surface plasmon resonance sensors Wouter Vandezande a, Filip Delport c, Kris P.F. Janssen b, Rob Ameloot a, Dirk E. De Vos a, Jeroen Lammertyn c, and Maarten B.J. Roeffaers a a Centre for Surface Chemistry and Catalysis, Department of Microbial and Molecular Systems, University of Leuven, Celestijnenlaan 200F, Post Box 2461, 3001 Heverlee, Belgium b Molecular Imaging and Photonics, Department of Chemistry, University of Leuven, Celestijnenlaan 200F, Post Box 2404, 3001 Heverlee, Belgium c Division of Mechatronics, Biostatistics and Sensors, Department of Biosystems, University of Leuven, Willem de Croylaan 42, Post Box 2428, 3001 Heverlee, Belgium CONTENTS Experimental section Preparation of sensor probes. Spectral data acquisition. Vapor flow control. Scanning Electron Microscopy. Gold SPR layer thickness. Crystallographic characterization. Results Table S1. Statistical information and parameters of the fitted calibration curves. Table S2. LODs for the detection of n-buoh and MeOH with the ZIF-8 and ZIF-93-FO-SPR sensors. Table S3. The averages and standard deviations of the 80 randomly measured n-buoh vapors Figure S1. SEM images of the surface of an SPR probe after applying a nucleation step of ZIF-8 and ZIF-93, the nucleation step followed by a growth step of ZIF-8 and ZIF-93, and only the growth step of ZIF-8. Figure S2. SEM images were taken at the border of a scratch made in ZIF-8 and ZIF-93 layers deposited on the surface of two FO-SPR probes. Figure S3. The calibration curve obtained by measuring the SPR-wavelength of five different solvents Figure S4. An AFM image was taken at the border of a scratch in the gold layer on an SPR probe. Figure S5. the calibration curves for the ZIF-8 and ZIF-93-SPR sensors for MeOH and n-buoh vapors. Figure S6. The RI and the low-pass filtered, first derivative of the RI signal of 80 random n-buoh vapors. Figure S7. Schematic of VOC mixing setup. Figure S8. The powder X-ray diffractograms of ZIF-8 and ZIF-93 1

2 EXPERIMENTAL SECTION Preparation of sensor probes. In short, part of the outer cladding of a multimode TECS optical fiber (FT400EMT, Thorlabs, Germany) with a 400 µm core diameter was removed. The remaining TECS cladding was removed using acetone and an optical cleaning tissue. The optical fiber was then cut so that at one end 6 mm was free of cladding and 1 mm at the other end. The longer claddingfree end was first coated with a thin gold layer (39 nm) using a sputter coater and serves for the later deposition of the MOF sensing layer. The resulting SPR wavelength of the FO-SPR probe without MOF coating was close to 600 nm when immersed in water (n 589nm = ). The short cladding-free end ensures a good connection with the bifurcated optical fiber, which was on one end connected to a spectrometer (USB4000-UV-NIR-ES, nm, Ocean Optics, USA) and on the other end connected to a white-light light source (HL-2000-FSHA, nm, Ocean Optics, USA). All components were interconnected using SMA-type connectors. Spectral data acquisition. Spectra were recorded by integrating the detector signal for 100 ms (10 Hz). At the start of a measurement, the light intensity was adjusted to counts by adjusting the attenuation screw of the light source. The reflectance spectrum was calculated as the ratio of the current spectrum and a reference spectrum. The latter was recorded with the FO-SPR probe in air. Both the current and reference spectrum were corrected by subtraction of a dark spectrum which was recorded also with the FO-SPR probe in air, but with the light source turned off. If measurements were done with an MOF coated FO- SPR probe, reference spectrum was recorded before any surface deposition had taken place. The SPR absorption should be visible in the reflectance spectrum if the refractive index around the FO-SPR probe was in the measurable range (± 1.30 to 1.40). The wavelength with the lowest intensity of the reflectance spectrum was determined. A window was taken around this minimum, with 165 nm on either side of it. By fitting the spectrum in this window with a parabola, the absolute minimum of the reflectance spectrum was analytically determined. This minimum was the SPR wavelength. All calculations were done real-time with LabVIEW 12 (National Instruments, USA). Low pass filter To reduce the noise level on the measured SPR wavelength, a low pass filter was applied with MATLAB version 2015b (The MathWorks, Inc., USA). The filter existed out of an equiripple filter with a transition band between 0.2 and 0.5 Hz and an attenuation intensity of 75 db. This filter was only used when indicated. Vapor flow control. To test the MOF-SPR sensors for the detection of VOCs a flow setup was built using tubing, tube fittings, and adapters and, Swagelok valves, a custom bubbler and three mass flow controllers (MFCs) (5850S, Brooks Instruments, USA). Nitrogen gas was used as a carrier which was produced by a nitrogen gas generator (MIDIGAS, Parker, USA) and dried by a desiccant air dryer (ZANDER ecodry KMT, Parker, USA). As seen in Figure S7, one MFC, MFC1 (0-72 L/h flow range), was directly connected to the sample chamber for flushing and diluting purposes. The other MFCs, MFC2 (0-72 L/h flow range) and MFC3 (0-4 L/h flow range), were connected to the bubbler followed by the sample chamber. MFC2 and MFC3 were thus used to control the VOC flow rate to the sample chamber. MFC3 had a smaller flow range due to its higher flow resolution control which was necessary to accurately produce small VOC flows. Thus, MFC2 was used for the higher VOC flows and MFC3 for the lower VOC flows. The flows of all MFCs come together before the sample the chamber to allow for proper mixing. By adjusting the flows of the MFC and keeping the total flow in the sample chamber always at 72 L/h a range of a range of different VOC concentrations could be generated. The VOCs used for vapor generation were methanol, ethanol, isopropanol (Sigma-Aldrich, 99.5 %) and n-butanol (Sigma-Aldrich, 99.4 %). Scanning Electron Microscopy. For scanning electron microscope (SEM) measurements the samples were first attached to a SEM sample holder with carbon tape and a thin nanolayer of gold is deposited with a JFC-1300 sputter coater (Jeol, Japan) using argon gas Alphagaz 1 (Air Liquide, %). The actual SEM study was done with a JSM-6010LV (Jeol, Japan). The obtained images were taken with secondary electron imaging at 5 kv and with a spot size of 20 unit. Gold SPR layer thickness. The FO-SPR probe was scratched to create a transition between the gold coating and the underlying fiber core. The probe was subsequently fixed to a glass plate with double-sided tape and imaged using an Atomic Force Microscope AFM (SmartSPMTM 1000, AIST-NT, USA). Crystallographic characterization. X-ray Diffraction (XRD) measurements were performed on a STOE STADI-MP (STOE, Germany) diffractometer in Bragg-Brentano mode with Cu Kα radiation. XRD simulations with Rietveld refinement were performed using the software Mercury 27. 2

3 RESULTS Table S1. Statistical information and parameters of the fitted calibration curves indicated with their respective analyte and MOF used on the MOF-FO-SPR sensor. MeOH, ZIF-8 MeOH, ZIF-93 n-buoh, ZIF-8 n-buoh, ZIF-93 dri dt, value 3.1E E E E-04 standard error 1.2E E E E-05 HWCI* 3.4E E E E-04 k value 2.35E-01 5E E E-01 standard error 5.5E E E E-02 HWCI* 1.5E E E E-02 n value 4.4E E E E+00 standard error 2.2E E E E-01 HWCI* 6.0E E E E+00 A value 4.2E-01 n/a n/a n/a standard error 3.5E-02 n/a n/a n/a HWCI* 9. 8E-02 n/a n/a n/a adjusted R² * HWCI: half-width of the confidence interval Table S2. LODs for the detection of n-buoh and MeOH with the ZIF-8 and ZIF-93-FO-SPR sensors. For convenience, the LODs are also provided in ppm and Pa, as these units are usually used in literature and by lawmakers. n-buoh, ZIF-8 n-buoh, ZIF-93 MeOH, ZIF-8 MeOH, ZIF-93 LOD p/p 0 (x 10-3 ) LOD (Pa) LOD (ppm) Table S3. The averages and standard deviations of the subdivided 80 randomly measured n-buoh vapors with their corresponding applied p/p 0 set center. center of applied p/p 0 set window average ± standard deviation ± ± ± ± ± ± ± ± ± ±

4 Figure S1. SEM images of the surface of an SPR probe after applying a nucleation step of ZIF-8 (A) and ZIF-93 (D), the nucleation step followed by a growth step of ZIF-8 (B) and ZIF-93 (E), and only the growth step of ZIF-8 (C) each with a scale bar of 1 µm. Figure S2. SEM images were taken at the border of a scratch made in ZIF-8 (A) and ZIF-93 (B) layers deposited on the surface of two FO-SPR probes. The measured thickness was 0.19 ± 0.04 µm for ZIF-8 and 0.2 ± 0.1 µm for ZIF-93. The scale bar indicates 0.5 µm. 4

5 Figure S3. The calibration curve obtained by measuring the SPR-wavelength of five different solvents: MeOH, water, EtOH, n- PrOH, and n-buoh. The error bars indicate one standard deviation. These data were fitted with a light reflection model of isotropic multilayered media by variating the gold thickness and NA of the FO-SPR sensor. Figure S4. Left, an AFM image was taken at the border of a scratch in the gold layer on an SPR probe. Right, a profile was taken in the middle of this AFM image. The gold thickness near the scratch border averages out to 39 nm. 5

6 Figure S5. the calibration curves for the ZIF-8 and ZIF-93-SPR sensors for MeOH and n-buoh vapors. The error bars indicate the standard deviation. Figure S6. The RI signal of 80 random p/p 0 of n-buoh consecutively measured (A). The low-pass filtered, first derivative of the RI of the same measurements. Note that the positive peaks are associated to VOC adsorption and the negative RI changes are linked to the desorption step. 6

7 Figure S7. Schematic of VOC mixing setup with MFCs 1-3, bubbler with liquid VOC, measuring cell MC, light source LS and spectrometer SM. MFC 1 and 2 are the same while MFC 3 has a lower minimal flow capacity. The LS and SM are connected to the MC with a bifurcated optical fiber. Figure S8. The powder X-ray diffractograms of ZIF-8 and ZIF-93 match the corresponding simulated diffractograms (sim). 7