Monitoring the Surface Chemistry of Functionalized Nanomaterials with a Microfluidic Electronic Tongue

Transcription

1 Supporting Information Monitoring the Surface Chemistry of Functionalized Nanomaterials with a Microfluidic Electronic Tongue Flavio M. Shimizu, Anielli M. Pasqualeti, Fagner R. Todão, Jessica F. A. de Oliveira,,, Luis C. S. Vieira, Suely P. C. Gonçalves, Gabriela H. da Silva,, Mateus B. Cardoso,,, Angelo L. Gobbi, Diego S. T. Martinez,, Osvaldo N. Oliveira, Jr., and Renato S. Lima*,, Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, São Paulo , Brasil Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, São Paulo , Brasil Laboratório Nacional de Luz Síncrotron, Centro Nacional de Pesquisa em Energia e Materiais, Campinas, São Paulo , Brasil Instituto de Química, Universidade Estadual de Campinas, Campinas, São Paulo , Brasil Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Piracicaba, São Paulo , Brasil *Corresponding author: Renato Sousa Lima, renato.lima@lnnano.cnpem.br. This supplementary material contemplates information on: 1. Preparation of the nanomaterials 2. Circuit diagram of the electrodes 3. Number of sensing units 4. Characterization of the electrodes 5. Characterization and classification of the nanoparticles 6. Characterization and classification of the nanotubes 7. Effects of the sample concentration and dielectric thickness S1

2 1. Preparation of the nanomaterials Functionalized silica nanoparticles About 13 ml of tetraethyl orthosilicate (TEOS) were mixed with 425 ml of ethanol under magnetic stirring for 30 min. Afterward, 17 ml of NH 4OH were added and left under stirring overnight at room temperature. The formed nanoparticles were chemically modified with different molar ratios of TEOS to 1-[3-(trimethoxysilyl)propyl]urea (TMSPU), namely, 1.0:0.5, 1.0:1.0, 1.0:1.5, and 1.0:2.0. For this purpose, the silica nanoparticles (SiO 2NPs) were successively stirred overnight, centrifuged at rpm for 10 min, washed three times with both ethanol and deionized water, lyophilized at room temperature, and dispersed in water using ultrasound bath for 30 min. The bare SiO 2NPs were synthesized following the routine described above in the absence of TMSPU. Oxidized multi-walled carbon nanotubes First, the multi-walled carbon nanotubes (MWCNTs) were dispersed in HNO mmol L 1 at 5:1 ratio (mg of MWCNT to ml of HNO 3) using ultrasound bath during 5 min. Following, the dispersion was magnetically stirred at 150 C in a conventional reflux system for MWCNT oxidation. Distinct samples were produced changing the oxidation time as 6, 12, 24, and 48 h. Next, the nanotubes were washed with deionized water until ph 6 using Millipore filtration and polytetrafluoroethylene membrane (0.2 µm). Finally, the CNTs were lyophilized, dispersed in water ultrasound bath for 1 h, and stored at room temperature. 2. Circuit diagram of the electrodes Figure S1. Association of capacitors in the e-tongue. Circuit diagram (A) and stereoscopy image (the same presented in Figure 1 of main text) of the lateral view of the sample channel with the cross section of the two channels (both filled with red dye) where electrodes are inserted above (E A) and below (E B) the sample, forming the capacitor (B). The dielectrics consisted of the sample fluid and dielectric film on the electrodes. I n and C n mean current and capacitance, respectively. 3. Number of sensing units There is no a definite rule for the number of sensing units since it is tightly tied to the electrodes material and similarity between the samples. Anyway, the e-tongue performance is generally improved with the number of sensing units as a function of the increase in the volume information to be correlated in the multivariate statistical analyses. According to Suslick, 1 an optimal e-tongue should contain as much chemical diversity as possible. For instance, we previously showed that an e-tongue with distinct film-based resistors ensures classifications stronger than a microchip with only one type of film thin-based resistor. 2 Herein, the use of four sensing units allowed us for reaching strong classifications. S2

3 4. Characterization of the electrodes Figure S2. Surface characterization of the electrodes. Images and size distributions by FE-SEM (A) and 3D surface topographies recorded by AFM of the oxide-coated microwires (B). In (A), all the scale bars represent 200 nm. The oxide thin films associated with each data are identified above the results (SiO 2, NiO 2, Al 2O 3, and Fe 2O 3 films). Figure S3. FE-SEM image (A) and AFM data (B) of the bare microwire. In (A), the scale bar means 200 nm. S3

4 Figure S4. EDS data of the bare and oxide-coated surfaces of the microwires as identified in each graphic. 5. Characterization and classification of the nanoparticles A Figure S5. Bare nanoparticles and evaluation of the functionalization with TMSPU. SEM image of the bare SiO 2NPs (A) and FTIR spectra of the bare and functionalized SiO 2NPs (B). B Transmittance (%) SiO 2 NPs Bare TMSPU (0.5X) TMSPU (1X) TMSPU (1.5X) TMSPU (2X) Wavenumber (10 2 cm -1 ) S4

5 Figure S6. Parallel coordinate plots using the capacitors of different dielectrics for the functionalized SiO 2NPs. Table S1. Silhouette coefficients from IDMAP, Sammon, and PCA using the capacitors of different dielectrics for SiO 2NPs Projection Technique Silhouette Coefficient (S) IDMAP 0.95 SAMMON 0.91 PCA 0.92 Figure S7. Classification of the bare and functionalized SiO 2NPs using association of oxide-coated resistors. The classification of the clusters was very poor, with S of 0.05 only. The lack of reproducibility for the water-related clusters is not associated with the passivation of the microwires, but to the high similarity between the spectra of the distinct samples that indicates the poor sensitivity of this e-tongue. Such unsatisfactory sensitivity damages the classification for analyses made in different moments. S5

6 Figure S8. Multiplex classification with capacitors of different dielectrics employing channels of approximately 700 and 800 µm. While W;W means the pumping of only water in the two devices, the other sample sets are identified in accordance with the pumping of 0.5, 1.0, and 1.5 (represent TEOS:TMSPU molar ratios of 1.0:0.5, 1.0:1.0, and 1.0:1.5, respectively) in C 1 and C 2 (see main text), respectively. The pairs of clusters with the same samples but pumped in the channels in an inverted order are highlighted by asterisks. S was calculated as Characterization and classification of the nanotubes A B C h 12h 24h 48h Oxidation time (hours) h 12h h h Figure S9. Colloidal stability studies of the nanotubes. Photos of the MWCNTs in different times from the dispersion of these materials in water ultrasound bath for 20 min (A), zeta potential of the oxidized MWCNTs (B), and measurements of absorbance that were recorded in a UV visible spectrophotometer (Libra S70, Biochrom, Cambridge, UK) (C). No sedimentation was observed in (A), all of the negative potentials were higher than 30 mv in (B), and the absorbance values presented very low deviations after 120 min in (C). All these data indicate a satisfactory colloidal stability of the MWCNTs. Absorbance (a.u.) Zeta potential (mv) Time (min) S6

7 Figure S10. Parallel coordinate plots using the capacitors of different dielectrics for the oxidized MWCNTs. Table S2. Silhouette coefficients from IDMAP, Sammon, and PCA using the capacitors of different dielectrics for MWCNTs Projection Technique Silhouette Coefficient (S) IDMAP 0.93 SAMMON 0.92 PCA h 12h 6h 24h NaCl Figure S11. Classification of the MWCNTs using the capacitors of different metals insulated by SiO 2. The distinction of the clusters was satisfactory, with S of Aqueous solution of ppm NaCl was used as control sample, indicating the absence of electrode contamination as well. S7

8 7. Effects of the sample concentration and dielectric thickness We assessed the effects of the sample concentration and dielectric film thickness on the e-tongue performance using the capacitors with stainless steel microwires insulated by the different dielectric films as described in the main text. First, experiments for MWCNTs at 10.0 ppm revealed a decrease in capacitances and classification ability (0.67 S) as shown in Figure S12 (A,B), where the capacitance spectra and IDMAP plot are illustrated. Conversely, the data for ppm MWCNTs with 400 nm dielectric films led to a raise in the capacitance values and enhanced sensitivity between the samples oxidized during 6 and 24 h. For instance, the maximum capacitances (at 1 Hz) recorded with 800 and 400 nm films for the sample oxidized for 24 h were and nf, respectively. The resulting capacitance spectra and IDMAP library are shown in Figure S12 (C,D). Strong distinction of the nanotubes was achieved with S of The clusters in IDMAP plot showed similar behavior to those for 800 nm films and the changes in capacitances ranged especially from 1 to 10 3 Hz. In contrast to data obtained with 800 nm dielectrics, sample-related alterations in capacitance were not noted at 10 4 Hz frequency. In addition, the low dispersion of the triplicates of the samples and water once again indicated good precision and absence of nonspecific adsorptions on electrodes. Concerning the increase in capacitance by reducing the thickness of the dielectrics from 800 to 400 nm, it is relevant to underline that the distance between the electrodes was kept the same, whereas the thickness of the sample was increased. Indeed, for each capacitor, the dielectric is composed of the solid dielectric film and sample. In these cases, the formation of the dielectric electric field is related to the mechanisms of dipolar polarization (dipoles of the solid film) and ionic conduction (e.g., π electrons of the nanotube), respectively. The increase in capacitance with the decrease in thickness of the oxide films suggests the ionic conduction mechanism on nanotube is more effective for polarization, leading to a higher dielectric electric field and, then dielectric constant. This phenomenon raises the capacitance according to Gauss law. 3 Figure S12. Classification of the modified MWCNTs. Spectra of real capacitance (C) (A) and IDMAP plot for MWCNTs at 10.0 ppm (B). Spectra (C) and distinction of MWCNTs at ppm with 400 nm dielectrics (D). Insets in (A,C) depict the ratios of the capacitance spectra of the MWCNTs in relation to water (W). The identification of the samples in (A) is also valid for (C). S8

9 8. References 1. Askim, J. R.; Mahmoudi, M.; Suslick, K. S. Optical Sensor Arrays for Chemical Sensing: The Optoelectronic Nose. Chem. Soc. Rev. 2013, 42, Shimizu, F. M.; Todão, F. R.; Gobbi, A. L.; Oliveira Jr., O. N.; Garcia, C. D.; Lima, R. S. Functionalization-Free Microfluidic Electronic Tongue Based on a Single Response. ACS Sens. 2017, 2, Halliday, D.; Resnick, R.; Walker, J. Fundamentals of Physics, New York: Ed. John Wiley & Sons, 6th ed., S9