Highly sensitive Membrane-based Pressure Sensors (MePS) for real

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Highly sensitive Membrane-based Pressure Sensors (MePS) for real-time monitoring of catalytic reactions Alessandra Zizzari, Monica Bianco, Loretta L. del Mercato, Antonio Sorarù, Mauro Carraro, Paolo Pellegrino, Elisabetta Perrone, Anna Grazia Monteduro, Marcella Bonchio, Rosaria Rinaldi, Ilenia Viola, and Valentina Arima Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b01531 • Publication Date (Web): 16 May 2018 Downloaded from http://pubs.acs.org on May 16, 2018

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Analytical Chemistry

Highly sensitive Membrane-based Pressure Sensors (MePS) for realtime monitoring of catalytic reactions Alessandra Zizzaria,b, Monica Biancoa, Loretta L. del Mercatoa, Antonio Sorarùc, Mauro Carraroc, Paolo Pellegrinob, Elisabetta Perronea, Anna G. Montedurod, Marcella Bonchioc, Rosaria Rinaldib, Ilenia Violae*, Valentina Arimaa* a

CNR NANOTEC - Institute of Nanotechnology c/o Campus Ecotekne, via Monteroni, 73100, Lecce, Italy Department of Mathematics and Physics E. De Giorgi, University of Salento, 73100, Lecce, Italy c ITM-CNR and Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131, Padova, Italy d National Institute of Gastroenterology “S. De Bellis” Research Hospital, via Turi 27, 70013, Castellana Grotte (Bari), Italy e CNR NANOTEC - Institute of Nanotechnology, S.Li.M Lab, c/o Department of Physics, Sapienza University, P.le A. Moro 5, 00185, Rome, Italy

b

Corresponding Authors: * [email protected];* [email protected]

ABSTRACT: Functional, flexible and integrated lab-on-chips, based on elastic membranes, are capable of fine response to external stimuli, so to pave the way for many applications as multiplexed sensors for a wide range of chemical, physical and biomedical processes. Here, we report on the use of elastic thin membranes (TMs), integrated with a reaction chamber, to fabricate a Membrane-based Pressure Sensor (MePS) for reaction monitoring. In particular, the TM becomes the key-element in the design of a highly sensitive MePS capable to monitor gaseous species production in dynamic and temporally fast processes with high resolution and reproducibility. Indeed, we demonstrate the use of a functional MePS integrating a 2 µm thick polydimethylsiloxane TM by monitoring the dioxygen evolution resulting from catalytic hydrogen peroxide dismutation. The operation of the membrane, explained using a diffusion-dominated model, is demonstrated on two similar catalytic systems with catalase-like activity, assembled into polyelectrolyte multilayers capsules. The MePS, tested in a range between 2-50 Pa, allows detecting a dioxygen variation of the µmol L-1s-1 order. Due to their structural features, flexibility of integration and biocompatibility, the MePSs are amenable of future development within advanced lab-on-chips.

Microreactors for (bio)chemical applications represent an important frontier of current research, being a family of lab-onchips in which several synthetic or analytical steps can be performed 1-4. In order to achieve the precise control of the working conditions required within microscale devices, there is the need to develop novel sensing tools that can be easily integrated within the microreactors, as valid alternative to off-line detection methods 5,6. Among the variety of parameters, pressure is the most critical one to evaluate in real time the outcome of reactions generating gaseous products 7. Indeed, although standard pressure gauge can be interfaced with microreactors through interconnections, the large dead volume of the last ones may negatively affect the final response of the sensor in term of sensitivity and response time. A more accurate estimation of pressure values may come from the use of in situ pressure microsensors based on piezoresistive 8,9, capacitive 10-12, optical 12 and interferometric 13 effects. Particularly, optical sensors have been demonstrated to be easily miniaturized within low cost microfluidic chips 14-16. However, these methods require sophisticated optical read-out set up for signal transduction. Thin membranes (TMs) represent an interesting tool for monitoring pressure changes occurring within the microchannels 17-20, being their stimuli-responsive sensitivity

tunable depending on the elastic properties of the material and on its thickness. Among several materials available to produce TMs with a technology compatible with microfluidic reactors, polydimethylsiloxane (PDMS) is the most appealing one, thanks to its elastic properties and its easy microstructuring via soft lithography 21,22. Moreover, due to its well-known biocompatibility, PDMS TMs have been already proposed as an ideal substrate for cell proliferation 23, for estimation of cell monolayer elasticity, and for sensing of antigen-antibody interactions 24. In this study, we report on a low-cost and easy-to-read pressure sensing chip, based on a PDMS TM, whose response is dependent on the TM deflection. The Membrane-based Pressure Sensor (MePS) consists of a TM mounted on the back side of a reaction chamber, and the pressure changes due to gas production can be addressed by imaging the membrane deflection with a high-resolution camera and estimating such a value through an image analysis software. The range of pressure that can be detected depends on the chamber internal diameter as well as on the membrane thickness 23. To give an estimation, a MePS consisting of chambers of 8 mm diameter with a 2 µm TM, has been tested in a range between 2-50 Pa without observing any TM rupture. The MePS has been then

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validated by monitoring over time the dioxygen (O2) produced during catalytic hydrogen peroxide (H2O2) dismutation. This reaction is typical of catalase enzymes, and can be employed for the detection of H2O2 in different kinds of biochemical and environmental samples. For example, it has been exploited to monitor the glucose-driven cellular respiration (combining catalyzed oxidation of glucose by glucose oxidase with catalase-mediated breakdown of H2O2) 25. Moreover, the evolution of O2 is a simple method to compare different biomimetic systems with applications as catalytic antioxidants 26,27. Within this scenario, we have used the MePS to monitor the efficiency of H2O2 dismutation to O2 and H2O by a tetrarutheniumsubstituted polyoxometalate (Na10[Ru4O4(OH)2(H2O)4(γSiW10O36)2], Ru4POM), integrated into the shell of polyelectrolyte multilayer (PEM) capsules with different layer organization. These PEM capsules were previously used for mixing a H2O2-enriched aqueous fluid within microchannels, and the pressure of the evolved O2, measured off-line, was correlated with the effects on fluid displacement 28. In this work, we aim at a direct in situ monitoring of the small pressure variations due to O2 production occurring in a reaction chamber under catalytic conditions. Although PDMS TMs have already been demonstrated to blow up in response to gas volume variations 29,30 , the approach with blowing down TMs presented herein guarantees the sensitivity (in the range of few Pa or even lower) and the fast response time (< 100s) needed to monitor the behavior of catalytic reactions since the first instances. As further innovative aspect, a model taking into account gas diffusion towards the membrane was developed to estimate the amount of oxygen produced during the reaction using the MePS. This attributes a higher versatility of applications to TM-based microsystems and makes them more sensitive and quickly responsive to chemical and biological processes occurring at the membrane interface 23,24. EXPERIMENTAL SECTION Chemicals and materials. Soda–lime microscopic glass slides were provided by Pearl, CLEVIOS PH 500 (poly(3,4ethylenedioxythiophene)polycation (PEDOT) and a poly(styrenesulfonate) polyanion (PSS) PEDOT-PSS 1:6) were purchased from Heraeus Clevios GmbH (Germany), toluene was purchased from J. T. Baker (USA). Sylgard-184, a two-part poly(dimethylsiloxane) (PDMS) elastomer, was purchased from Dow Corning (USA). Milli-Q water with a resistivity of 18.2 MΩ cm was used. Poly(sodium 4styrenesulfonate) (PSS, Mw ≈ 70,000 Da), poly(allylamine hydrochloride) (PAH, Mw ≈56,000 Da), calcium chloride dehydrate (CaCl2), sodium carbonate (Na2CO3), ethylenediaminetetraacetic acid disodium salt dehydrate (EDTA), sulfuric acid (H2SO4, 98%) and hydrogen peroxide (H2O2, 30%) were purchased from Sigma-Aldrich (Milan, Italy). PES syringe filters (0.45 µm) were purchased from Sartorius Stedim (Germany). The synthesis of Na10[Ru4O4(OH)2(H2O)4(γ-SiW10O36)2] (Ru4POM) was performed following a previously reported procedure 31. MePS assembly. The MePS consists of a reaction chamber of 8 mm diameter, bonded to a PDMS TM that was prepared and characterized as described in ESI (sections S1-S2). To allow multiple analysis, three MePSs have been integrated on a single chip (see Figure 1a). To fabricate the chambers, PDMS pre-polymer and curing agent, mixed in a weight ratio of 10:1, were deposited over a glass petri dish and degassed. Hence, the mixture was cured at 140 °C for 15 min in oven and a

4.5±0.5 mm thick PDMS slide was obtained. After removal from the glass dish, reaction chambers of 8.0±0.2 mm diameter were produced using suitable punchers. The punched slide (Figure 1a, part I) and the PDMS TMs deposited on the glass substrate (Figure 1a, part II) were both plasma oxidized at 100 W, 240 sccm, 4 mbar for 60s and put in conformal contact (Figure 1a, step 1). After sealing with further prepolymer/curing agent and polymerization at 140°C for 15 min (using additional PDMS as glue, Figure 1a, step 2), the slidemembrane assembly was put into water for 5 min while stirring, to transfer the TM on the chambers and remove the glass substrate (Figure 1a, step 3). Then, washing by pure water was performed to remove PEDOT-PSS residues on the membrane side that was in contact with the glass substrate. Finally, the entire assembly (Figure 1a, step 4) was placed onto PDMS support bases (Figure 1a, part IV), loaded with the solutions to be tested and closed with a clean glass cover (Figure 1a, part III), ready for the experiments. Scanning Electron Microscopy (SEM) characterizations have been performed to show the appearance in cross section of the membrane to confirm the 2 µm thickness (Fig.2b) as described in ESI (section S1.4). Bulge test. To test the flexibility properties of the 2 µm TM, water was dropped into the chamber of the chip with steps of 50 µL droplets that locally deformed the membrane. As the volume of water increased, the membrane underlying the droplet extended isotropically under the gravity force. The membrane deflection (w) was monitored by CAM 200 (KSV Instruments Ltd., Finland) instrument, measured by using ImageJ software analysis (see Fig. S3) and plotted versus water volume (Fig. 3a). The error on the w estimation was of ± 12 µm. Reaction monitoring experiments. To evaluate the effect of the catalytic reaction, the MePSs were loaded with 200 µL of aqueous mixture containing the catalytic or non-catalytic capsules batches (1.9 x 103 cps/mL, corresponding to a final concentration of 7.7 µM Ru4POM), mixed with H2O2 (100 µL H2O2 30%, yielding a final concentration of 4.89 M). The preparation of the capsules using the layer-by-layer assembly 32,33 is described in ESI (section S1.5 28,34). CAM 200 and ImageJ software analysis were used to monitor and measure the evolution of membrane deflection for 25 min acquiring one image per minute. Then the deflection values were reported as function of time (Fig. 4). Control O2 monitoring was performed at the same experimental conditions, with 2 mL of B1 or B2 suspension and H2O2, by using a conventional reactor equipped with a differential pressure transducer connected to a measurement module (National Instruments, see Fig. S4). RESULTS AND DISCUSSION The chip shown in Fig. 1 consists of three MePSs for multiple analyses. After loading of the liquid to be tested in the reaction chambers, the response due to the membrane vertical deflection (w) is acquired with a camera and quantitatively calculated by ImageJ software (see Fig. S3). Since the PDMS TM is the key-element for chemical sensing, in the fabrication of a MePS we primarily focused the attention on membranes production, characterization, and transfer. Then we performed a bulge test for the TM calibration and we monitored the catalytic reactions in the assembled MePSs. A complete discussion on membrane production and integration to the reaction chamber is reported in ESI (section S2).


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Analytical Chemistry

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Figure 1. a) Scheme of the fabrication process. The PDMS slide with three 8 mm punched chambers (part I) is assembled via plasma treatment to the glass substrate (step 1) on which PEDOT-PSS (yellow layer) and a PDMS thin layer (red layer) (part II) are deposited. Then the glass substrate and the PEDOT-PSS layer are removed by further sealing (using PDMS as glue) and water immersion (steps 2-3). Finally the resulting system is assembled to support bases (IV) and a glass cover (III) (step 4). b) Picture of the chip on the contact angle instrument to test the membrane deflection during loading with well-defined volumes of water (bulge test).

_________________________________________________________________________________________________________ able to preserve its hydrophilicity better than bulk PDMS. The Membranes characterization. A full characterization of the 2 observed behavior is related to the mobility of PDMS oligoµm TMs was performed after oxygen plasma treatment, which mers that diffuse during the time towards the silica surface is needed to make them hydrophilic and to bond the chamber generated by the plasma treatment35,36. The higher percentage slide in the final chip configuration. The study reported in Fig. 2a represents a comparison between the wettability of a 2 µm of oligomers in the bulk compared to that in the membranes is TM and a bulk PDMS slide. The Water Contact Angle (WCA) probably the main reason of the fast and complete recovery of evolution was followed during 14 days. Both samples at the bulk PDMS 37. beginning, before the plasma treatment, exhibited the same The presence of a silica layer on the membrane surface is evivalue (119-120°). After plasma treatment, the values dropped dent from the SEM studies performed to observe the morpholto 0, becoming the surfaces strongly hydrophilic. Then, after 8 ogy of the membrane. As shown in Fig. S5b, the membrane days from the treatment, bulk PDMS recovered its hydrophosurface appears full of cracks after plasma treatment (see Fig. bicity almost completely, while the membranes displayed a S5a for comparison). different behavior. The TM hydrophobic recovery was slower In the areas far from the cracks some AFM images as the one than the bulk and the reached WCA plateau value was smaller. shown in Fig. S5c have been acquired. The surface at a few We calculated that after 14 days from oxygen plasma treatmicron scale appears flat with round-shaped nanostructures. ment, the recovery of bulk PDMS was complete (100%), An average roughness of 0.32 ± 0.02 nm was measured on the while a recovery of 53% was estimated for the TM, being thus TMs. _________________________________________________________________________________________________________

Figure 2. a) Study of the wettability properties of the 2 µm PDMS TM compared with bulk PDMS. Water Contact angle (WCA) evolution at 0, 2, 4, 6, 8, 10 and 14 days from oxygen plasma treatment. Values of pristine bulk PDMS and TM (soon after preparation) are reported as stars. b) SEM image of a 2 µm TM transferred onto a PDMS microstructured slide to calculate the real thickness.



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_________________________________________________________________________________________________________ in Fig. S3). Fig. 3a shows the membrane deflection w when Bulge Tests. A characterization of the elastic properties of the some microliters of water are added into the reaction chamber. TM was performed via bulge tests 23 by measuring the maxiThis measure represents the calibration of a MePS for the remum deflection at the center of the membrane (w) (red arrows action monitoring experiments. _________________________________________________________________________________________________________

Figure 3. a) Bulge test for MePS calibration. Inset: a photograph of the deflected membrane. b) Plot and cubic fit of the red curve reported in Fig. 3a according to equation 1. The coefficients A and B obtained from the fitting procedure are reported in the inset. _________________________________________________________________________________________________________ The weight of the water droplets added induce a deformation of the membrane. Being 38:

where P is the uniform pressure applied to the membrane, w is the maximum deflection measured at the center of the membrane, r is the membrane radius, d its thickness, σ0 its residual stress, E its Young’s modulus, and ν its Poisson’s ratio. The geometrical coefficients C1, C2, and f(v) for circular membranes are 4, 2.67 and 1 respectively 39. In addition, the equation 1, written in a synthetic form with coefficients A and B, has been used as fitting function. Considering that P in this specific situation is essentially due to the weight of liquid volume, it can be calculated by applying the fundamental law of the hydrostatic pressure of a liquid by the action of gravity and the forces acting on the liquid surface (Stevino’s law):

Reaction monitoring experiments. The reaction monitoring experiments have been performed by loading the MePSs with 200 µL of solutions of the Ru4POM-functionalized PEM capsules (corresponding to 7.7 µM POM) and H2O2 (4.89 M). We have recently shown the use of these functionalized capsules to produce elastic turbulence within microchannels, thus providing alternative systems for mixing and pumping fluids, thanks to the propulsion generated by the release of O2 bubbles 30. Here, two different batches of Ru4POM-functionalized PEM capsules (see scheme in Fig. 4a) were used and produced by embedding equimolar amounts of catalyst between the polymer layers (sample B1), or in the most external layer of the capsules (sample B2). As control sample, PEM capsules without the Ru4POM were produced (sample B3, see scheme in Fig. 4a) and mixed with H2O2. The reaction consists in H2O2 dismutation into O2 and water by the confined oxygenic Ru4POM:

2H2O2

P

(Equation 1)

(Equation 2)

with ρ, representing the water density, g the gravity acceleration and h the height of water level in the chamber. With the equation (2) we can calculate the pressure exerted by the volume of liquid on the elastic membrane, P, in Fig. 3b, by using experimental deflections, w (shown in Fig. 3a). We observed that a regression fitting of the calculated P data satisfies a cubic polynomial model, P = Aw + Bw3, with coefficients A and B described by the elastic response of a TM (shown in eq. 1). The coefficients A and B obtained from the fitting procedure are reported in the inset of Fig. 3b. Knowing the dependence of the B coefficient from the TM’s Young modulus (see eq. 1), we obtain a value of E=5.95 ± 0.54 MPa which is in agreement with previous works on plasma-treated PDMS TMs 40-44.

2H2O +O2

and it has been monitored by measuring w at different time points, as shown in Fig. 4b. As observed, wt = w0 for B3 (blue curve, control sample, not loaded with Ru4POM) and H2O2. Red and black curves represent the behavior of Ru4POMfunctionalized PEM capsules, B1 and B2, during the reaction with H2O2. In both cases, the w steadily increases because of O2 generation during the reaction. In the picture of Fig. S6 some bubbles are visible in the chip when the experiments are carried on with reactive batches. The linear behavior of the two reactive batches was fitted and it was calculated a ∆w (deflection rate) of (120±2) nm/s and (100±4) nm/s for B1 and B2 respectively.


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Analytical Chemistry ________________________________________________________________________________________________________

Figure 4. a) Reaction scheme showing H2O2 decomposition catalyzed by Ru4POM embodied within PEM capsules (B1), or electrostatically adsorbed on the external shell of PEM capsules (B2). The study is carried on in comparison with Ru4POM-free microcapsules (B3). b) Membrane deflection w versus time for B1, B2 and B3. The curves reported are an average of two different experiments acquired by using the same pressure sensors (different reaction chambers of the same MePS assembly) but using freshly mixed H2O2 and capsules aliquots. _________________________________________________________________________________________________________ In order to quantify the amount of O2 generated in the MePSs, we first consider that at constant temperature and volume, the pressure exerted by an ideal gas depends only on the total number of gaseous moles as it occurs in a traditional set up. However, for a MePS (Fig.1) we have a high-confinement condition both for liquid and gas phase, so the evolved O2 is mainly confined within the liquid 45. In addition, within the MePS the dismutation process reaches the equilibrium in a much longer time than that of the O2 diffusion. For all these reasons we have calculated the number of O2 moles accounting for: i) the ideal gas law, , with the pressure P related to the TM deformation (eq. 1) observed during the catalytic reaction; ii) the second Fick's law of diffusion 46, !

!

# describing the time-dependence of concentration c $ of dissolved O2 due to the diffusion D through the elastic TM; iii) the O2 concentration, which is directly proportional to its partial pressure within the liquid as results from the Henry's law, % &' . All in all, we have evaluated the concentration c of dissolved O2 in a MePS as: "

%∝

* +,

-./0 *

∆2

(equation 3)

with P the pressure acting on elastic membrane during reaction; D the diffusion coefficient of O2, S and d the membrane surface area and thickness; KO2 is the Henry’s coefficient for O2 and ∆t is the time interval analyzed. With these considerations and by using eq. 3, the molar concentrations of O2 produced during the catalytic reaction for both samples, B1 and B2, are shown in Fig. 5a as calculated from the MePSs. The results of MePSs are compared with O2 concentration as estimated by conventional off-line methods (Fig. 5b) using the ideal gas law and normalized considering the liquid volume (2mL). The rates of growth with time calculated using a linear regression fit on the experimental pressure data (between 200-1800 s, see Figure S7 and S8) by the MePS and by the traditional method are reported in Tab. 1. The results of Tab. 1 are inter-

esting considering the remarkable difference between the two approaches. In general, we note that the growth rates of the molar concentration measured with MePS are higher than the conventional measures. In both cases, B1 seems to be more efficient than B2. However, for sample B2, a greater deviation is observed between the two approaches even if the trends appear similar, considering that a certain time (t ≈ 900s for MePS and t ≈ 1400 s for the conventional set up) B2, which initially produces a larger amount of O2, starts generating O2 more slowly than B1 (see Figure 5). In order to compare the efficiency of detection we have used a linear model to determine the rate of O2 evolution in the initial timeframe. After an initial gap probably due to instrumental inertia, all kinetics display a regular trend up to > 30 min. In the fit range (200-1800 s) the linear trend keeps valid for MePS, while it does not fully take into account the response of the differential pressure transducer (see Fig. S7-S8). The coefficients of determination, R2, were also calculated in the fitting procedure (Tab.1). R2, that is indicative of the adherence of experimental data to the linear model, shows more convergence for MePS. More discrepancy is noted with the conventional technique, especially for B2. We suppose that this result is due to a different sensitivity of the measurement techniques. Thus, to evaluate the sensitivity of MePS, we calculated the membrane deflection, w, versus the reaction pressure, Preact, namely the pressure component detected during the catalytic process for B1 and B2, and shown in Figure S9. Since sensitivity is characteristic of the measuring instrument, we observe that for MePS the behavior is similar for both samples B1 and B2. Thanks to the high permeability of the multilayers, indeed, the embedded and the surface POM display a similar behavior. The linear fitting of these data gives an estimated sensitivity for MePS of about (0.400±0.039) Pa/µm. For the conventional set-up we have a fixed pressure sensitivity that depends only on the characteristic value of the pressure gauge used, which is of about 100 Pa.



________________________________________________________________________________________________________

Figure 5. Molar concentration of O2 ([O2], µmol/L) produced during the catalytic reaction for B1 and B2 capsules and obtained a) by measuring the deformation of the TM during the reaction in the MePS and b) by a conventional method. A scheme of the MePS is reported as inset in Fig. 5a. A picture of the conventional set up is reported as inset in Fig. 5b. _________________________________________________________________________________________________________ Table 1. Rate of growth with time of molar concentration of O2 (µmol L-1s-1) produced during the catalytic reaction for sample B1 and B2 and carried out by the two different techniques (MePS and conventional set-up). The above values have been determined by a linear fit of the [O2] experimental data (between 200-1800 s, see Figures S7-8). Coefficient of determination R2 is reported for all the results as a measure of the accuracy of the model. Sample

MePS (µmol L-1s-1)

R2 (MePS)

Conventional set-up (µmol L-1s-1)

R2 (Conv)

B1

0.3500±0.0076

0.987

0.273±0.009

0.970

B2

0.2890±0.0040

0.994

0.149±0.010

0.891

This higher sensitivity on the imprinted deformation allows to more accurately detect the O2 production over time as shown by the values of R2 in Table 1. More importantly, in the case of MePS, sensitivity can also be modulated by modifying the diameter and thickness of the membrane, thus making MePS suitable for monitoring kinetics of different gas evolving reactions. Another aspect, to increase the overall sensitivity of a MePS, is to use a more accurate and precise method to detect the membrane deflection. To this aim, interferometric optical techniques could be implemented 47 . Besides, in MePS, given the high surface/volume ratio (which could be even increased by changing the reaction chamber height/diameter ratio) and the high-confinement of liquid volume with catalytic capsules acting on TM, it is possible to appreciate even smaller amounts of the evolved O2, with greater sensitivity and already from the first instants of reaction. On the contrary, although the conventional off-line method allows to monitor dynamics of the catalytic reaction over a longer period of time (see Fig. S10), it requires larger volumes of suspension (2 mL) and gives less reproducible measurements in the first moments of reaction owing to larger dead volume (> 20 mL) as well as to the lower and fixed instrumental sensitivity. As further experiment, with the aim of comparing the MePS with TM-based “blowing up” set up for oxygen monitoring 17-

20,24,29,47-49

, a 2 µm TM was bonded to the upper side of a reaction microchamber (bottom-TM configuration 30). Its response was compared with the MePS one for B1 capsules. As Fig. S.11 shows, the response of the membrane to gas production is faster in the MePS (red scheme, red curve) than in the top-TM configuration (blue scheme, blue curve). It seems that for the catalytic reaction we investigate, the configuration with the membrane at the top of the reaction chamber is not convenient. There is a certain time (of roughly 25 min) in which the top-TM chip shows an inertia towards blowing; on the contrary, a linear response from the first moments of the reaction process occur in the MePS (bottom-TM configuration). This was attributed to the gravity force and the component of diffusion acting on the TM in MePS that allow overcoming the limit of the TM elastic response and immediately deform the membrane. Moreover, the use of a chamber with a capacity of a few hundred of microliters allows to work in a confined regime and exploit the interactions at the liquid-membrane interface to increase the sensitivity. Hence, the comparison of MePSs with standard methods and with similar “blowing-up” systems discussed in literature, confirms the superior suitability of MePSs to monitor pressures of few Pa in terms of sensitivity and response time. Nevertheless, the application here shown is the first example of a MePS able to monitor gas evolving reaction over the time and measure the absolute concentration of the gaseous species in-


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Analytical Chemistry volved, as O2 molecules in our case. The MePS allows to demonstrate the potentiality of the method proposed to perform studies of gas production in simple chips. Concerning the process under investigation, the MePS has been validated for monitoring the catalytic oxygen evolution produced by two differently functionalized smart capsules, being thus suitable for monitoring both enzymatic and biomimetic catalase-like activity. It has been, even, possible to estimate the efficiency difference of the two capsules. In the considered time-scale (200-1800s), the results obtained with the MePS attest that the configuration with a more confined Ru4POM catalyst, named sample B1, is slightly more efficient than sample B2 (with external Ru4POM). This difference is also confirmed by the conventional method and speaks in favour of a higher stability for the first assembly.

Author Contributions

CONCLUSIONS A MePS based on flexible PDMS TMs has been fabricated and used for chemical sensing to monitor the production of oxygen over the time in catalytic reactions. Such an integrated micro-sensor consists of a millimeter reaction chamber with a 2 µm thick elastic membrane. The MePS detects microdeformations produced during the catalytic reaction and correlates them to pressure variations exerted on the membrane in the range between 2 and 50 Pa with a sensitivity of (0.400±0.039) Pa/µm. Finally, studying the flow dynamics within the reaction chamber, we can correlate the pressure to the molar concentration of O2 produced during the catalytic reactions. The MePS allows to detect, in real-time, a concentration variation of O2 in the range of µmol L-1 s-1 with a linear dependence of the pressure response since the first instants of the reaction. This is not trivial considering that standard differential pressure transducers do not always show a linear dependence of pressure during the time, given their fixed and low sensitivity. As further advantage, thanks to its bottom-TM configuration, MePS appears more sensitive and fast responding to chemical reactions than conventional “blowing up” systems. Instead, due to its structure, the MePS is amenable of further improvements to increase sensitivity by modulating membrane thickness, reaction chamber diameter (to increase the surface/volume ratio) and by developing a set up to finely detect membrane deflection during the time. Furthermore, its easy fabrication via replica molding allows easy integration within advanced LOCs and easy interfacing to GC-Mass detectors to measure the total pressure as well identify gases in mixtures. This would expand the applications of MePSs with interesting perspectives for the monitoring of gaseous species in processes of flow chemistry, biosensing and cell biology.

REFERENCES

ASSOCIATED CONTENT Supporting Information Details on membrane preparation and characterization, on the synthesis of polyelectrolytes multilayer capsules, discussion on MePS assembly, as well as additional figures which support some results of the main paper are reported in a separate file (PDF).

AUTHOR INFORMATION Corresponding Author * [email protected] * [email protected]

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

ACKNOWLEDGMENT We thank the “Cluster in Bioimaging” (cod. QZYCUM0, “Aiuti a sostegno dei cluster tecnologici regionali 2014”, Bando Regione Puglia n. 399 del 28/07/2014) and Safe&Smart (PON R&C 20072013 “Cluster Tecnologici Nazionali”, CTN01_00230_248064) and University of Padova (PRAT 2015 prot. CPDA158234) for funding. We gratefully acknowledge prof. G. Scoles for fruitful discussions.

(1) Arima, V.; Pascali, G.; Lade, O.; Kretschmer, H. R.; Bernsdorf, I.; Hammond, V.; Watts, P.; De Leonardis, F.; Tarn, M. D.; Pamme, N.; Cvetkovic, B. Z.; Dittrich, P. S.; Vasovic, N.; Duane, R.; Jaksic, A.; Zacheo, A.; Zizzari, A.; Marra, L.; Perrone, E.; Salvadori, P. A., et al. Lab Chip 2013, 13, 2328-2336. (2) Gutmann, B.; Cantillo, D.; Kappe, C. O. Angewandte Chemie International Edition 2015, 54, 6688-6728. (3) Pastre, J. C.; Browne, D. L.; Ley, S. V. Chemical Society Reviews 2013, 42, 8849-8869. (4) Wegner, J.; Ceylan, S.; Kirschning, A. Advanced Synthesis & Catalysis 2012, 354, 17-57. (5) Kraus, T.; Günther, A.; de Mas, N.; Schmidt, M. A.; Jensen, K. F. Experiments in Fluids 2004, 36, 819-832. (6) McMullen, J. P.; Jensen, K. F. Annu Rev Anal Chem (Palo Alto Calif) 2010, 3, 19-42. (7) Knapkiewicz, P. Journal of Micromechanics and Microengineering 2013, 23, 035014. (8) Eaton, W. P.; Smith, J. H. Smart Materials and Structures 1997, 6, 530. (9) Kanda, Y.; Yasukawa, A. Sensors and Actuators A: Physical 1997, 62, 539-542. (10) Bakhoum, E. G.; Cheng, M. H. M. IEEE Transactions on Components and Packaging Technologies 2010, 33, 79-83. (11) Zhang, Y.; Howver, R.; Gogoi, B.; Yazdi, N. In 2011 16th International Solid-State Sensors, Actuators and Microsystems Conference, 2011, pp 112-115. (12) Roriz, P.; Carvalho, L.; Frazão, O.; Santos, J. L.; Simões, J. A. Journal of Biomechanics 2014, 47, 1251-1261. (13) Aref, S. H.; Latifi, H.; Zibaii, M. I.; Afshari, M. Optics Communications 2007, 269, 322-330. (14) Taffoni, F.; Formica, D.; Saccomandi, P.; Pino, G.; Schena, E. Sensors 2013, 13, 14105. (15) Mignani, A. G.; Baldini, F. Reports on Progress in Physics 1996, 59, 1. (16) Hill, G. C.; Melamud, R.; Declercq, F. E.; Davenport, A. A.; Chan, I. H.; Hartwell, P. G.; Pruitt, B. L. Sensors and Actuators A: Physical 2007, 138, 52-62. (17) Song, W.; Psaltis, D. Biomicrofluidics 2011, 5, 441104411011. (18) Chung, K.; Lee, H.; Lu, H. Lab on a Chip 2009, 9, 33453353. (19) Hardy, B. S.; Uechi, K.; Zhen, J.; Pirouz Kavehpour, H. Lab on a Chip 2009, 9, 935-938. (20) Gervais, T.; El-Ali, J.; Gunther, A.; Jensen, K. F. Lab on a Chip 2006, 6, 500-507. (21) de Jong, J.; Lammertink, R. G. H.; Wessling, M. Lab on a Chip 2006, 6, 1125-1139. (22) Ng, J. M.; Gitlin, I.; Stroock, A. D.; Whitesides, G. M. Electrophoresis 2002, 23, 3461-3473.



(23) Kang, E.; Ryoo, J.; Jeong, G. S.; Choi, Y. Y.; Jeong, S. M.; Ju, J.; Chung, S.; Takayama, S.; Lee, S. H. Adv Mater 2013, 25, 2167-2173. (24) Sang, S.; Feng, Q.; Tang, X.; Wang, T.; Huang, X.; Jian, A.; Ma, Z.; Zhang, W. Microelectronic Engineering 2015, 134, 33-37. (25) Tao, Z.; Raffel, R. A.; Souid, A.-K.; Goodisman, J. Biophysical Journal 2009, 96, 2977-2988. (26) Sartorel, A.; Truccolo, M.; Berardi, S.; Gardan, M.; Carraro, M.; Toma, F. M.; Scorrano, G.; Prato, M.; Bonchio, M. Chemical Communications 2011, 47, 1716-1718. (27) Grau, M.; Rigodanza, F.; White, A. J. P.; Soraru, A.; Carraro, M.; Bonchio, M.; Britovsek, G. J. P. Chemical Communications 2014, 50, 4607-4609. (28) del Mercato, L. L.; Carraro, M.; Zizzari, A.; Bianco, M.; Miglietta, R.; Arima, V.; Viola, I.; Nobile, C.; Sorarù, A.; Vilona, D.; Gigli, G.; Bonchio, M.; Rinaldi, R. Chemistry – A European Journal 2014, 20, 10910-10914. (29) Chaudhury, A. R.; Pantazis, A. K.; Chronis, N. Sensors and Actuators A: Physical 2016, 245, 63-67. (30) Zizzari, A.; Bianco, M.; del Mercato, L. L.; Carraro, M.; Bonchio, M.; Frigione, M.; Montagna, F.; Gigli, G.; Viola, I.; Arima, V. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2017, 532, 257-262. (31) Sartorel, A.; Carraro, M.; Scorrano, G.; Zorzi, R. D.; Geremia, S.; McDaniel, N. D.; Bernhard, S.; Bonchio, M. Journal of the American Chemical Society 2008, 130, 5006-5007. (32) del Mercato, L. L.; Ferraro, M. M.; Baldassarre, F.; Mancarella, S.; Greco, V.; Rinaldi, R.; Leporatti, S. Advances in colloid and interface science 2014, 207, 139-154. (33) del Mercato, L. L.; Guerra, F.; Lazzari, G.; Nobile, C.; Bucci, C.; Rinaldi, R. Nanoscale 2016, 8, 7501-7512. (34) Zizzari, A.; Bianco, M.; Miglietta, R.; del Mercato, L. L.; Carraro, M.; Soraru, A.; Bonchio, M.; Gigli, G.; Rinaldi, R.; Viola, I.; Arima, V. Lab on a Chip 2014, 14, 4391-4397. (35) Béfahy, S.; Lipnik, P.; Pardoen, T.; Nascimento, C.; Patris, B.; Bertrand, P.; Yunus, S. Langmuir 2010, 26, 3372-3375.

(36) Bowden, N.; Huck, W. T. S.; Paul, K. E.; Whitesides, G. M. Applied Physics Letters 1999, 75, 2557-2559. (37) Arima, V.; Bianco, M.; Zacheo, A.; Zizzari, A.; Perrone, E.; Marra, L.; Rinaldi, R. Thin Solid Films 2012, 520, 2293-2300. (38) Thangawng, A. L.; Ruoff, R. S.; Swartz, M. A.; Glucksberg, M. R. Biomed Microdevices 2007, 9, 587-595. (39) Pan, J. Y.; Lin, P.; Maseeh, F.; Senturia, S. D. In IEEE 4th Technical Digest on Solid-State Sensor and Actuator Workshop, 1990, pp 70-73. (40) Tan, J. L.; Tien, J.; Pirone, D. M.; Gray, D. S.; Bhadriraju, K.; Chen, C. S. Proceedings of the National Academy of Sciences 2003, 100, 1484-1489. (41) Brown, X. Q.; Ookawa, K.; Wong, J. Y. Biomaterials 2005, 26, 3123-3129. (42) Armani, D.; Liu, C.; Aluru, N. In Technical Digest. IEEE International MEMS 99 Conference. Twelfth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.99CH36291), 1999, pp 222-227. (43) Eddington D. T., C. W. C., Beebe, D. J. In 7th, International conference on miniaturized chemical and biochemical analysis systems: Squaw Valley, CA, 2003, pp 1089-1092. (44) Gray, D. S.; Tien, J.; Chen, C. S. J Biomed Mater Res A 2003, 66, 605-614. (45) Henry, W. Philosophical Transactions of the Royal Society of London 1803, 93, 29-276. (46) Lodish Harvey ; Berk Arnold ; Zipursky Lawrence S; Matsudaira Paul ; Baltimore David ; James, D. Molecular Cell Biology, 4th edition, 2000. (47) Augustyniak, I.; Knapkiewicz, P.; Sareło, K.; Dziuban, J. A.; Debourg, E.; Pons, P.; Olszacki, M. Sensors and Actuators A: Physical 2015, 232, 353-358. (48) Koley, G.; Liu, J.; Noman, M. W.; Yim, M.; Wen, X.; Hsia, T. Y. Materials Science and Engineering: C 2009, 29, 685-690. (49) Liu, X.; Zhu, Y.; Nomani, M. W.; Wen, X.; Hsia, T. Y.; Koley, G. Journal of Micromechanics and Microengineering 2013, 23, 025022.

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