Supporting Information

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1 Supporting Information Amperometric Detection of Sub-ppm Formaldehyde using SWCNTs and Hydroxylamines: A Referenced Chemiresistive System Shinsuke Ishihara, *,, Jan Labuta, Takashi Nakanishi, Takeshi Tanaka, and Hiromichi Kataura World Premier International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Tsukuba, Ibaraki , Japan Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki , Japan *Corresponding author: ISHIHARA.Shinsuke@nims.go.jp S1

2 1. Materials All reagent grade solvents and materials were purchased from Sigma-Aldrich, Tokyo Chemical Industry or Alfa Aesar, and used without further purification. SWCNTs prepared by high-pressure catalytic CO decomposition (HiPco, NanoIntegris, USA) were used as starting material, and isolation of SWCNTs were performed as we reported previously. S1 Synthesis of metallo-supramolecular polymer MSP was described in the previous report. S2. 2. Methods 2.1 Dispersion of SWCNTs and device fabrication In a typical device, 0.02 mg of SWCNTs and 0.1 mg of anthracene-based ligand (Figure S1) were suspended in 0.2 ml of o dichlorobenzene (o DCB) and toluene mixture (1:4 in vol.). Copper acetate monohydrate dissolved in methanol (10.6 mm, 16.4 μl) was added to form metallo-supramolecular polymer (MSP). The suspension was treated in an ultrasonic bath for 30 min at room temperature. The suspension was centrifuged (6238 g, rpm, 15 min, Rev Spin 102 from Revolutionary Science), and supernatant solution (top 50 %) was collected. The dispersion (ca. 0.5μl) was drop-cast on interdigitated electrode. Interdigitated gold electrode with electrode gap of 200 μm was purchased from BVT Technologies (No. CC1.W1). The solvent was removed in air. The drop-casting of the dispersion was repeated until the resistance of SWCNTs network (measured by a ohmmeter) reached desired values. Sensors were kept in glass vial with screw cap under air atmosphere, and the sensors were stable at least over several months. In case of preparing sensors without MSP, 0.02 mg of SWCNTs were suspended in 0.2 ml of o dichlorobenzene (o DCB) and toluene mixture (4:1 in vol.). The suspension was treated in an ultrasonic bath for 30 min at room temperature. Centrifuge was not performed since most of SWCNTs precipitate. The suspension (ca. 0.5μl) was drop-cast on interdigitated electrode immediately after sonication. Figure S1. Chemical structure of MSP. S2

3 2.2 Functionalization of SWCNTs sensors with hydroxylamine derivatives Typical procedure of functionalizing SWCNTs sensors with hydroxylamine derivatives is shown in Figure S2. Hydroxylamine hydrochloride (1) was added into methanol until saturate (ca. 100 mg/ml). Then, the solution of 1 was drop-casted on SWCNTs sensor, filter paper (qualitative filter paper, Whatman), or PVDF membrane filter (0.2 μm, Millipore, Ominipore membrane filter, JGWP). Then, methanol was dried in air. Loading amount of 1 is approximately 0.5 mg for each type of sensor (compared with sub-ppm level in air, amount of 1 is in largely excess). Filter paper and PVDF membrane filter were cut to adjust size, and SWCNTs sensors were covered with them. Note that thin spacer (0.4 mm) was inserted between SWCNTs sensor and filter paper (or PVDF membrane) for promoting diffusion of analyte gases. Filter paper and PVDF membrane filter were fixed by tape. Figure S2. (a-d) Typical procedure of functionalizing SWCNTs sensors with hydroxylamine derivatives. (e) Side view of resulting sensor, S-SWCNTs/MSP/1/PVDF. 2.3 Gas detection measurements Gas detection measurements were acquired using a test clip fitted with a glass chamber to connect the interdigitated microelectrodes to a PalmSens EmStat potentiostat with a MUX16 multiplexer. S2 A constant potential of 0.10 V was applied across the electrodes, and the current was recorded using PSTrace software (v. 4.8) as the device was exposed to analyte gas. S3

4 2.4 General procedure of creating vapors For measuring device response to volatile organic compounds and to water, a handmade gas generator system (Figure S3) was used to produce analyte gas with known concentration. Under constant flow rate and temperature, mass of analyte liquid in test tube was measured every 1 hr for three times, and averaged evaporation rate of analyte was calibrated based on the decrease of mass. Typically, flow rate of air was 300 ml/min, and temperature of thermostatic bath was 40 ºC. gas was supplied from gas cylinder with compressed air. Humidity was controlled using water chamber. It is confirmed (by thermometer) that temperature of gas supplied to sensor is unchanged by thermostatic bath. Humidity sensor Flow meter 0.3 L/min Vent Water chamber Flow meter 0.3 L/min Flow meter 0.3 L/min Sensor Compressed (dry) Thermostatic bath Figure S3. Experimental setup of hand-made gas generator. 2.5 Procedure of creating vapor vapor with controlled concentration was produced using the apparatus shown in Figure S4. Formalin solution (37%) was diluted with water, and 1 ml of formalin solution (37%, 7.4%, 1.85%, 0.37%, 0.123%, or 0%) in glass test tube was located in two-necked flask (200 ml) kept at 40±1 ºC. gas (1000 ml/min) with controlled humidity was injected into the flask as a carrier gas. Concentration of was determined by commercially-available gas detector (RIKEN KEIKI Co., Ltd., FP-31) and detector tube (GASTEC, 91L). Thus, we obtained 6.7, 3.0, 0.9, 0.19, and 0.05 ppm of vapor by using 37%, 7.4%, 1.85%, 0.37%, and 0.123% formalin solutions, respectively. The concentration of was stable over 1 day. gas was supplied from gas cylinder with compressed air. Humidity was controlled using water chamber. When pure water is located and kept in the two-necked flask at 40 o C, concentration of water vapor increased by 420 ppm, which is only +1.4 % relative humidity at 25 ºC. S4

5 Humidity sensor Flow meter 0.3 L/min Vent Water chamber Flow meter 1 L/min Vent Flow meter 0.3 L/min Sensor Compressed (dry) Thermostatic bath Figure S4. Experimental setup for creating vapor. 3. Additional sensing data I(t) ppm 3 ppm 0 S/M-SWCNT -20 M-SWCNT ppm S-SWCNT Figure S5. Normalized electric current trace of S-SWCNTs/1/PVDF, M- SWCNTs/1/PVDF, and S/M-SWCNTs/1/PVDF sensors to 3.0 ppm vapor (in air, flow rate = 300 ml/min, 22.3 ºC, RH = 39.2%). S/M-SWCNTs denote mixture of S- SWCNTs and M-SWCNTs in 2:1 ratio. S5

6 80 I(t) ppm 0.9 ppm 0.9 ppm 0 S-SWCNT/MSP S-SWCNT Figure S6. Normalized electric current trace of S-SWCNTs/MSP/1/PVDF and S- SWCNTs/1/PVDF sensors to 0.9 ppm vapor (in air, flow rate = 300 ml/min, 22.0 ºC, RH = 34.5%). S6

7 Figure S7. (a) Normalized electric current trace of S-SWCNTs/MSP/1/PVDF and S- SWCNTs/MSP sensors to 0.9 ppm (in air, flow rate = 300 ml/min, 22.2±1 ºC, RH = 36.2±1.3%), revealing good reversibility. (b) Normalized electric current trace of S-SWCNTs/MSP/1/PVDF sensor to 6.7 ppm for a long time (in air, flow rate = 300 ml/min, 20.5±1 ºC, RH = 36.5±1%), revealing long lifetime. S7

8 I(t) %RH 0.9 ppm 37%RH 68%RH 0.9 ppm 68%RH 68%RH 1.5%RH 12.5%RH 1.5%RH 0.9 ppm 1.5%RH 0.9 ppm 12.5%RH 12.5%RH 35%RH Figure S8. Normalized electric current trace of S-SWCNTs/MSP/1/PVDF sensors to 0.9 ppm under various relative humidity (RH)(in air, flow rate = 300 ml/min, 22.2 ºC) I(t) H 2 O H 2 O H 2 O Figure S9. Normalized electric current trace of S-SWCNTs/MSP/1/PVDF sensor to 420 ppm water vapor (in air, flow rate = 300 ml/min, 22±0.5 ºC, RH = 38.8 ±1%). Water vapor was created at identical condition to that of vapors, and these responses were used as blank response of Figure 3b in the main manuscript. S8

9 15 10 I(t) H 2 O H 2 O H 2 O Figure S10. Normalized electric current trace of S-SWCNTs/MSP/1/PVDF sensors to 3200 ppm water vapor (in air, flow rate = 300 ml/min, 22±0.5 ºC, RH = 38.8 ±1%) I(t) MeOH MeOH MeOH Figure S11. Normalized electric current trace of S-SWCNTs/MSP/1/PVDF sensors to 1200 ppm methanol vapor (in air, flow rate = 300 ml/min, 22±0.5 ºC, RH = 38.8 ±1%). S9

10 I(t) 05 EtOH EtOH EtOH Figure S12. Normalized electric current trace of S-SWCNTs/MSP/1/PVDF sensors to 440 ppm ethanol vapor (in air, flow rate = 300 ml/min, 22±0.5 ºC, RH = 38.8 ±1%). 10 I(t) 5 0 THF THF THF Figure S13. Normalized electric current trace of S-SWCNTs/MSP/1/PVDF sensors to 860 ppm tetrahydrofuran (THF) vapor (in air, flow rate = 300 ml/min, 22±0.5 ºC, RH = 38.8 ±1%). S10

11 Toluene Toluene Toluene I(t) Figure S14. Normalized electric current trace of S-SWCNTs/MSP/1/PVDF sensors to 720 ppm toluene vapor (in air, flow rate = 300 ml/min, 22±0.5 ºC, RH = 38.8 ±1%) Acetone Acetone I(t) Acetone Figure S15. Normalized electric current trace of S-SWCNTs/MSP/1/PVDF sensors to 1540 ppm acetone vapor (in air, flow rate = 300 ml/min, 22±0.5 ºC, RH = 38.8 ±1%). S11

12 8 6 Figure 3a ppm I(t) (μa) Figure S16. Electric current trace of S-SWCNTs/MSP/1/PVDF sensors showing increase of conductivity in air without ( sec.), implying degradation of MSP (through reaction of air impurity and 1). This behavior was not observed for S- SWCNTs/1/PVDF sensors. Previously we reported that S-SWCNTs/MSP sensor involves dosimetric and reversible responses. S3 In case of sensing we are observing only reversible part of response since dosimetric (i.e., irreversible) response is already occurred at the early stage ( sec.) in air. S12

13 4. Determination of limit of detection (LOD) Figure S17 is the magnified image of Figure 3b in the main manuscript. Limit of detection (LoD) of sensing response is described by equation (1). S4 LoD = meanblank σblank σlowest conc. (1) where meanblank, σblank and σlowest conc. are mean of response for blank, standard deviation of response for blank and the lowest gas concentration (in this case, = 0.05 ppm), respectively. LoD of response is estimated to be 0.92%, which corresponds to ppm of based on initial response (y = x ). 6 6 I(t) y = x σ blank = (ppm) σ lowest conc. = Figure S17. Response of S-SWCNTs/MSP/1/PVDF sensor upon exposure to blank and 0.05 ppm gases (magnified image of Figure 3b in the main manuscript.) for three times. Blank test is performed using pure water instead of formalin solution (see Figure S9). S13

14 5. Determination of fitted calibration curve for Figure 3b For construction of calibration curves we have chosen a combination of several elementary functions with free (fitted) parameters. The data were then fitted using following calibration curve F(x), which provides relationship between concentration (in ppm; denoted as x) and the sensor response (normalized change in electric current in %; denoted as y); see Figure S18a: F(x) = (2) Where the values of fitted parameters are a = , b = , c = , d = and e = Analogically the calibration curve G(y) which converts the sensor response (y) to concentration (x) has following form; see Figure S18b: G(y) = (3) Where the values of fitted parameters are a = , b = , c = , d = , e = and f = Figure S18. Fitted calibration curves for Figure 3b. (a) concentration to sensor response calibration curve y = F(x). (b) Sensor response to concentration calibration curve x = G(y). Note that concentration range for this calibration is 0 to 10 ppm, and response range is 0 to 100%. S14

15 6. A simple device to monitor Figure S19. (a) Photo image and electric circuit of a simple device to detect. As a typical example, Rsensor is a S-SWCNTs/MSP/1/PVDF sensor ( active) and Rref is a S-SWCNTs/MSP ( inactive). For clarity, fixed resistor is used as Rref in the image and circuit. (b) Photo image of the device when resistance of Rsensor and Rref are similar (Rsensor = ca. 20 kω, Rref = ca. 20kΩ). The right image was obtained by digital camera under out-of-focus condition in dark. (c) Photo image of the device when resistance of Rsensor and Rref are different (Rsensor = ca. 10 kω, Rref = ca. 20kΩ). Compared with observation by naked-eye under room light, difference of brightness in LED1 and LED2 looks more obvious when two LEDs are monitored by digital camera under outof-focus condition in dark. Camera on smartphone is also available to perform this observation. Although our present investigations are qualitative, we anticipate that quantitative analysis of will be possible by analyzing photo images. Also, more information will be obtained when more than two resistors are connected in parallel. S15

16 7. References S1. Yomogida, Y.; Tanaka, T.; Zhang, M.; Yudasaka, M.; Wei, X.; Kataura, H. Industrial- Scale Separation of High-purity Single-Chirality Single-wall Carbon Nanotubes for Biological Imaging. Nat. Commun. 2016, 7, S2. Ishihara, S.; Azzarelli, J. M.; Krikorian, M.; Swager, T. M. Ultratrace Detection of Toxic Chemicals: Triggered Disassembly of Supramolecular Nanotube Wrappers. J. Am. Chem. Soc. 2016, 138, S3. Ishihara, S.; O Kelly, C. J.; Tanaka, T.; Kataura, H.; Labuta, J.; Shingaya, Y.; Nakayama, T.; Ohsawa, T.; Nakanishi, T.; Swager, T. M. Metallic vs. Semiconducting SWCNT Chemiresistors: A Case for Separated SWCNTs Wrapped by Metallo- Supramolecular Polymer. ACS Appl. Mater. Interfaces, DOI: /acsami.7b S4. Armbruster, D. A.; Pry T. Limit of Blank, Limit of Detection and Limit of Quantitation. Clin. Biochem. Rev. 2008, 29, S49 S52. S16