Article pubs.acs.org/acssensors
Wireless Oxygen Sensors Enabled by Fe(II)-Polymer Wrapped Carbon Nanotubes Rong Zhu, Maude Desroches,† Bora Yoon, and Timothy M. Swager* Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States S Supporting Information *
ABSTRACT: Oxygen causes food spoilage and drug degradation, which is addressed commercially by modified atmosphere packaging. We report herein a wireless oxygen sensor, O2-pCARD, from solution processed FeII-poly(4-vinylpyridine)single-walled carbon nanotube composites on commercial passive near-field communication tags. A large irreversible attenuation in the reflection signal of an O2-p-CARD was observed in response to oxygen at relevant concentrations, enabling non-line-of-sight monitoring of modified atmosphere packaging. These devices allow for cumulative oxygen exposure inside a package to be read with a conventional smartphone. We have demonstrated that an O2-p-CARD can detect air ingress into a nitrogen-filled vegetable package at ambient conditions. This technology provides an inexpensive, heavy-metal-free, and smartphone-readable method for in situ non-line-of-sight quality monitoring of oxygen-sensitive packaged products. KEYWORDS: carbon nanotubes, wireless sensing, radio frequency identification, oxygen sensing, dosimeter
I
levels, but rapid microbial growth can consume the oxygen, and a real-time oxygen sensor will thereby provide an inaccurate measurement of the damage to the content’s packaging. Current technologies for oxygen monitoring in packages rely on optical methods. Luminescence and colorimetric-based indicators have been developed based on oxygen induced redox reactions.6,7 Because of the underlined mechanism they are usually implemented with line-of-sight access and read in the presence of a light source. Many indicators involve precious metal complexes (Pd, Ru) and display reversible response. A number of recent efforts have been directed toward optical oxygen dosimeters.6a We envisioned a technology complementary to the known reversible optical sensors, which uses a chemiresistive wireless sensing platform we recently introduced that leverages commercial passive radio frequency identification (RFID) technology (Figure 1).8,9 This method can be implemented by simply placing a chemiresistive element into the resonant circuit of a commercially available near-field communication (NFC) tag, and the result is a chemically actuated resonant device (CARD) (Figure 2a). The chemical information on a CARD’s surrounding environment can be transduced by a simple RF reader, which is a standard feature in modern smartphones that have NFC capabilities. An important feature of the CARD is that it can be read through opaque nonconductive materials that are commonly used in food and
mproving food and drug safety is recognized as a global priority, and to comprehensively address this need will require new technologies. The implementation of new sensing technologies for monitoring the quality of food and drugs along the supply chain has the prospects to create improvements.1 This need is especially acute for perishable products such as fruit, meat, wine, as well as air- and/or moisture-sensitive pharmaceuticals. Most food spoilage is caused or enabled by oxygen. The presence of oxygen not only allows the growth of numerous aerobic microorganisms that pose a health threat, but also causes oxidative chemical reactions that degrade food quality, nutrition, and flavors.2 For drugs, both hydrolytic and aerobic degradation are common, and the latter usually has a larger irreversible effect.3 The most common solution to extending the lifetime of these products is to use modified atmosphere packaging (MAP), wherein packages are sealed in an inert gas (typically nitrogen, argon, or carbon dioxide) atmosphere.4 In this context, the oxygen level within the package can be used as an indicator for the package integrity and quality of the contents during the production, storage, distribution, and retail processes. Sensors for packaging must be readily interrogated and, above all, inexpensive. A viable sensor for oxygen monitoring of individual packaging requires low-cost, battery-free sensors that can be easily integrated into the enclosure.5 Additionally, sensors exhibiting irreversible responses, properly called dosimeters, are generally most useful as they will report on the cumulative oxygen exposure.4,6a In particular, small leaks developed in a package can often temporally elevate the oxygen © XXXX American Chemical Society
Received: May 16, 2017 Accepted: June 28, 2017
A
DOI: 10.1021/acssensors.7b00327 ACS Sens. XXXX, XXX, XXX−XXX
Article
ACS Sensors
metal ions deplete the hole carrier concentrations in SWCNTs, and with oxidation the higher-valent electrophilic metal ions reverse this process to increase the hole carrier density.10 This scheme is ideally paired with the poly(4-vinylpyridine)SWCNT (P4VP-SWCNT) composites we recently reported.11 Specifically, this method gives persistent dispersion of SWCNTs that can be used to deposit conductive networks by spray coating that display enhanced sensitivity and minimal baseline drift.12 An additional and critical feature is that the pyridine moieties in P4VP bind and stabilize a broad spectrum of metal ions in intimate contact with the SWCNTs. The ability to position metal ions in close proximity to the SWCNT walls ensures a strong response (high sensitivity) from oxygen induced changes, which in the present system involves changes in the ratio of FeII to FeIII. Herein we report a battery-free wireless device that affords a tunable dosimetric response to oxygen exposure via the aerobic oxidation of FeII (Figure 2b) that can be readily implemented in a modified atmosphere package. We initially demonstrated oxygen sensing by immobilization of the P4VP-SWCNT-FeII chemiresistor on a glass surface. However, we show that the method is readily extended to wireless NFC devices (O2-pCARDs) that are smartphone compatible and detect oxygen at concentrations relevant to modified atmosphere packaging. Finally, the performance of this device to ambient air ingress was assessed in a vegetable package.
Figure 1. Design concept of a small and battery-free near-field communication (NFC) sensor that measures oxygen exposure from inside a sealed package. An RF reader, in this case, a smartphone, can remotely read the sensor’s state, and access the quality of the package contents without a line of sight.
■
EXPERIMENTAL SECTION
General Materials. All chemicals and reagents were purchased from Sigma-Aldrich and used without additional purification, unless otherwise noted. 3-Bromopropyltrichlorosilane was purchased from Oakwood and used as is. Fe(MeCN)6(BF4)2, Co(MeCN)6(BF4)2, and Mn(MeCN)4(BF4)2 were synthesized according to a previously reported method.13 Acetonitrile was dried and distilled from calcium hydride under argon and stored with 4 Å molecular sieves in a nitrogen glovebox. Single-walled carbon nanotubes (0.7 to 1.3 nm diameter) were purchased from Sigma-Aldrich (Lot #MKBP3333 V). P4VPSWCNT (P4VP: 50 mg, SWCNT: 5.0 mg) dispersion in N,Ndimethylformamide (DMF, 10 mL) was prepared following the previously described method.11 This dispersion is referred to as “dispersion I” throughout the following text. Sylgard 184 (base and curing agent) was purchased from Dow Corning. This study uses commercially available Texas Instruments HF-I Tag-It Plus Transponder Inlays (TI-Tag). Characterization. UV−vis-NIR absorption spectra were obtained using an Agilent Cary 5000 spectrophotometer. ATR-FTIR spectra were obtained using a Thermo Scientific Nicolet 6700 FTIR with a Ge crystal for ATR. X-ray photoelectron spectroscopy (XPS) was performed with a PHI Versaprobe II XPS spectrometer. Scanning electron microscope (SEM) images were obtained using a JEOL JSM6700F FESEM at an accelerating voltage of 3 and 10 kV. All gassensing experiments were performed at ambient conditions unless otherwise indicated. Surface-Immobilized Sensors on Glass Substrates. Following literature procedures, a P4VP-SWCNT chemiresistor platform immobilized on a glass substrate was prepared from dispersion I using 3-bromopropyltrichlorosilane as the surface anchoring agent.11 General Procedure A: Fabrication of Surface-Immobilized Oxygen Sensors. A P4VP-SWCNT chemiresistor device immobilized on a glass substrate was transferred into a nitrogen-filled glovebox. The device was soaked in a solution of Fe(MeCN)6(BF4)2 (5 mg/mL in acetonitrile) for 4 h followed by drying under vacuum overnight. Other metal ion composites were produced following General Procedure A with slight modifications. Surface-immobilized P4VPSWCNT-CoII, P4VP-SWCNT-MnII, and metal-free P4VP-SWCNT sensors were fabricated from Co(MeCN)6(BF4)2, Mn(MeCN)4(BF4)2 (5 mg/mL in acetonitrile), respectively.
Figure 2. (a) Conversion of a commercially available NFC tag into a wireless sensor (p-CARD) via deposition of chemiresistive material (Rs) at the indicated locations. The circuit diagram of p-CARD is shown. C, tuning capacitor; L, inductor (antenna); RIC, resistance of integrated circuit (IC); CIC, capacitance of IC; Rs, chemiresistor. (b) Poly(4-vinylpyridine) disperses single-walled carbon nanotubes and coordinates to Fe(II) ions. This hybrid system is a sensitive chemiresistor that displays irreversible (dosimetric) response to oxygen exposure to enable an O2-p-CARD.
especially drug containers. The CARD’s sensing data is naturally coupled with the ID information programmed into the integrated circuit of the NFC tag. Hence, CARDs serve as intelligent labels that allow manufacturers, retailers, or customers to simultaneously track the quality and historical data of the product using the existing RFID systems. Our chemiresistor designs achieve selective irreversible O2 responses by merging a single-walled carbon nanotube (SWCNT) network with an earth-abundant reducing metal ion that undergoes irreversible aerobic oxidation. The reducing B
DOI: 10.1021/acssensors.7b00327 ACS Sens. XXXX, XXX, XXX−XXX
Article
ACS Sensors Wireless Sensor (O2-p-CARD). General Procedure B: Fabrication of O2-p-CARD (Figure 5a). Dispersion I (2 μL) was dropcast at the locations indicated in Figure 2, followed immediately by subjecting the device to a high vacuum environment in a desiccator for 10 min. This sequence was repeated so that 4 μL dispersion I was deposited in total. The resulting P4VP-SWCNT thin film obtained was washed with 0.2 mL dichloromethane dropwise to remove excess P4VP and air-dried. The device was transferred into a nitrogen-filled glovebox. Under nitrogen atmosphere, 20 μL Fe(MeCN)6·(BF4)2 solution (5 mg/mL in acetonitrile) was dropcast on top of the P4VP-SWCNT thin film. The device was allowed to sit for 15 min before subjecting it to high vacuum for 30 min in the vacuum chamber. This device was then inserted into a plastic sensing enclosure, which was sealed with electrical tape and taken out from the glovebox. The enclosure was immediately purged with 1 L/min N2 for 10 min before used for oxygen sensing. The gas flow delivery system used for wireless sensing was identical to that described in the previous section (Figure S7). Device RF Response Characterization. We monitored the RF signal response of O2-p-CARDs from 10−20 MHz with a custommade loop probe connected via a BNC cable to a vector network analyzer (VNA) (Agilent E5061B) by measuring reflection coefficient (S11) at 50 Ω port impedance and 0 dBm input power. The distance between the probe and the device in the sensing enclosure was fixed throughout an experiment (typically in the range of 0.5−1 cm). The S11-determined resonant frequency ( f 0) minimum gain value (noted as “Gain” in short, in dB) was measured and acquired using a custombuilt LabView program that executed a minimum-search algorithm at specified time intervals and tabulated the data into an exportable file. Demonstration of Smartphone Readability Switch. An O2-pCARD was fabricated following General Procedure B with slight modifications. A total amount of 12 μL of dispersion I was deposited, instead of 4 μL; and 3 mL dichloromethane was used to wash off the excess P4VP. The initial gain was around −1.2 dB (close to the readability cutoff) and the readability switch could be observed within a few exposure cycles. We utilized the Samsung Galaxy S4 (SGS4) to demonstrate the device readability switch upon oxygen exposure. The “NFC Reader (Adam Nybäck)” was used to read the tags.14 For the purposes of this study, the tag is considered “on” or “readable” if the unique identification number can be retrieved within 5 s or less of holding the smartphone at ∼2.5 cm distance away from the tag. Conversely, the tag is considered “off” or “unreadable” if the unique identification number cannot be retrieved under the same conditions. Device Modification for Oxygen-Detection at Elevated Humidity. Following General Procedure B, an O2-p-CARD was fabricated. Sylgard 184 base was mixed with the curing agent at a 10:2 weight ratio under ambient conditions and then degassed in vacuo. In a nitrogen-filled glovebox, 0.5 mL of this resulting mixture was deposited on the O2-pCARD to obtain a film of 1.2 cm × 1.4 cm (Figure S9c), followed by curing on an aluminum foil-covered hot plate at 110 °C for 2 d under nitrogen atmosphere. The resulting barrier coating thickness was determined to be ∼0.2 mm. Similarly, a coating of ∼1.2 mm thick was obtained using 1.5 mL Sylgard 184 base/curing agent mixture, with an extended curing time of 4 d. A humid mixed gas flow was generated by actively bubbling through water and used for sensing experiments (Figure S9a). A digital house humidity sensor (Extech 445715) was connected to the outlet of the gas flow system for monitoring. The relative humidity of the gas flow could be adjusted between 40% and 80% by varying the amount of water in the bubbler and kept constant (±5%) throughout an individual sensing experiment. Detection of Air Ingress in a Compromised Package Setting. An O2-p-CARD was fabricated following General Procedure B with modifications: A total amount of 12 μL of dispersion I was deposited, instead of 4 μL; and 3 mL dichloromethane was used to wash off the excess P4VP. A 1.2-mm-thick cross-linked PDMS barrier coating was applied following the procedure described above, affording a modified O2-p-CARD. Under nitrogen gas purging (3 L/min), this device was inserted into a 20 cm × 15 cm polyethylene resealable zipper storage bag (McMaster-Carr) containing fresh vegetables. The bag was further
purged with N2 for 5 min before resealed. The bag was placed on the probe of VNA with the O2-p-CARD facing down. The device gain was monitored over time. At t = 55 min, the bag was fully unzipped to open to air (25% RH).
■
RESULTS AND DISCUSSION The chemiresistor development leverages our recently reported P4VP-SWCNT platform that allows for covalent anchoring on glass substrates.11 The immobilized films are modified by complexation of reduced metal ions for reaction with oxygen. An attractive feature of this platform is that it enables the incorporation of metal ions proximate to the graphene sidewalls without covalently modifying the SWCNTs. Although covalent methods may also be effective, the present process is in principle less perturbative to the nanotube’s transport properties. In the choice of metal component, we identified the rich aerobic oxidation chemistry of FeII species as a more environmentally benign and cost-efficient option than existing heavy metal-based methods. In fact, iron compounds are widely used as oxygen scavengers for packaging.15 We thus targeted Fe(MeCN)6(BF4)2 as the precursor for introducing FeII into the P4VP-SWCNT network, with the expectation that the labile acetonitrile ligand will allow fast irreversible ligand exchange with the stronger pyridyl ligands or P4VP.16 Following the outlined strategy, we treated the surfaceanchored P4VP-SWCNT composite with Fe(MeCN)6(BF4)2 for 4 h under nitrogen atmosphere before rinsing with solvents to remove the unbound Fe species (Figure S1). Scanning electron microscopy imaging of the Fe-composite on glass confirmed the presence of a robust nanotube network after multistep manipulations (Figure S2). FTIR spectrum of the Fecomposite revealed a small and reproducible shift to higher frequency of the P4VP pyridine centered stretching vibration bands (1604 cm−1) as compared to that of the pristine P4VPSWCNT composite (1598 cm−1), which is consistent with bands observed in known FeII-pyridine complexes (1603 cm−1) (Figure 3a).16 The incorporation of iron after treatment was further confirmed by X-ray photoelectron spectroscopy (Figure 3b).
Figure 3. (a) ATR-FTIR spectra of P4VP-SWCNT composites on a glass substrate before (black plot) and after (blue plot) Fe incorporation. (b) XPS spectra of the pristine P4VP-SWCNT composite and Fe-incorporated P4VP-SWCNT composite immobilized on a glass substrate. Red dots display characteristic peaks for Fe.
With the FeII incorporation confirmed, we set out to test the response of our chemiresistor to oxygen exposure (Figure 4a). It was observed that the conductance of the surface-anchored P4VP-SWCNT-FeII chemiresistor increased substantially (∼30%) upon the first 50 s exposure to 18% oxygen diluted by nitrogen. In addition, this response was found to be largely irreversible (dosimetric).17 These observations are consistent C
DOI: 10.1021/acssensors.7b00327 ACS Sens. XXXX, XXX, XXX−XXX
Article
ACS Sensors
they are integrated into the resonant RF circuit. This scheme ensures a monotonic decrease in RF signal reflection across the NFC frequency band in response to decreasing Rs. This method also allows unambiguous determination of exposure and facile tuning for smartphone readability. Additionally, the linear RF gain response region for Rs in this device is reasonably large (0.1 kΩ to 1 MΩ). For comparison, strategies involving antenna modification typically require an Rs < 1 kΩ.9d,e The pCARD’s working window encompasses the typical dynamic ranges of carbon nanotube-based chemiresistors, thereby making it a suitable platform. Finally, the simplicity of the pCARD fabrication process is also highly desired from a practical perspective, as devices can be readily produced by printing functional SWCNTs on commercial passive NFC tags. The device fabrication begins with dropcasting of a DMF P4VP-SWCNT dispersion, I, onto the indicated locations of an NFC tag (Figure 5a).11 After vacuum removal of the solvent,
Figure 4. (a) Chemiresistive traces of quadruplicate surfaceimmobilized SWCNT-P4VP-FeII sensor devices in response to 18% O2 in N2 (v/v). Shaded areas indicate individual exposures. Flow rate = 2 L/min. (b) Average conductance change of (≥3) devices fabricated from varying metal species in response to 50 s O2 or CO2 exposure diluted in N2 . Fe II : Fe(MeCN) 6(BF 4) 2 ; CoII : Co(MeCN)6(BF4)2; MnII: Mn(MeCN)4(BF4)2. FeII[a]: The devices were fabricated under ambient atmosphere instead of nitrogen.
with our hypothesis that P4VP bound FeII species are quickly oxidized by oxygen irreversibly, generating FeIII species that withdraw charge from the SWCNTs and increase the hole carrier density and conductivity. We also noticed that the response was attenuated after multiple exposures, which we attribute to the consumption of active FeII species and/or the creation of stable mixed valence clusters. The irreversible nature of the response provides a good estimation of cumulative oxygen exposure as long as the initial conductance is known. We have also confirmed that the presence of FeII is essential for the response as a control sensor consisted of pristine P4VPSWCNT afforded no response (Figure 4b). Sensors fabricated from similar acetonitrile complexes derived from CoII or MnII displayed minimal response, which was expected because these species are less prone to oxidation.13 We further tested our P4VP-SWCNT-FeII chemiresistors for responses to carbon dioxide, which is a component of air (ca. 0.04% by volume) and is also generated from metabolic processes. It was found that the system displays only a minor response to an elevated concentration of carbon dioxide (1%) with the detection of a slight conductance decrease. To ensure a maximum response, the FeII-incorporation was performed under nitrogen atmosphere. However, this process can also be carried out at ambient conditions and without using degassed or anhydrous solvent, albeit at an expense of the ultimate response (Figure 4b). Having identified an oxygen responsive chemiresistor, we have integrated it into the circuit of an NFC tag for wireless sensing. This was accomplished using our recently developed protocol, which involves a single-step dropcasting deposition of the chemiresistive material to create a device we refer to as a pCARD (Figure 2a).8b The “p” signifies a parallel relationship between the chemiresistor (Rs) and the integrated circuit as
Figure 5. (a) Schematic description of the fabrication of an O2-pCARD. (b) Reflection spectra (S11) of O2-p-CARDs fabricated with varying amount of P4VP-SWCNT dispersion I or the dichloromethane used for rinsing show tunable initial gains. Removal of excess P4VP with rinsing decreases the signal as a result of the conductive increase of the SWCNTs wired in parallel to the integrated circuit shown in red.
the film showed negligible conductivity (>10 MΩ); however the conductivity increased (80% RH (1.2 mm film). Inset: schematic illustration of the barrier coating.
component widely used in food, cosmetics, and medical devices. The elasticity of the cross-linked PDMS film also provides additional mechanical robustness to the device. We initially applied a ∼0.2-mm-thick PDMS coating on an O2-p-CARD. The cross-linking was performed by heating the device at 110 °C for an extended time period and the sensor demonstrated good thermal stability by remaining active after this process. The resulting device was found to produce a flat E
DOI: 10.1021/acssensors.7b00327 ACS Sens. XXXX, XXX, XXX−XXX
Article
ACS Sensors
current RFID systems for the tracking and quality monitoring of food and pharmaceuticals.
baseline and desired monotonic response toward oxygen exposures at 40 and 60% RH (Figure 8, traces (a) and (b)). A delay in the response was observed, which is attributable to oxygen diffusing through the barrier coating. For >80% RH, a thicker coating was found necessary. As shown in Figure 8, trace (c), an O2-p-CARD coated with ∼1.2-mm-thick PDMS provided the desired response at this humidity with a longer delay that is consistent with the increased coating thickness. It should be noted that the overall gain change remains consistent across different humidity levels. In a final demonstration, we implemented a device in an N2filled package to test its performance in a simulated real-world use case. To this end, a PDMS-modified O2-p-CARD was placed in a nitrogen-flushed ziplock polyethylene storage bag containing fresh vegetables and sealed (Figure 9a). The device
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssensors.7b00327. Additional experimental procedures and characterizations, photos of the experimental setups, gas sensing traces for Figures 4 and 6, an additional example showing the monitoring of air ingress in a compromised green tea package, data for stability, and low temperature tests (PDF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Timothy M. Swager: 0000-0002-3577-0510 Present Address †
Department of Chemistry, Université Laval, Québec, Canada.
Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
Figure 9. O2-p-CARD as a smart label implemented in an N2-filled package containing fresh vegetables. (a) Photos of the package. (b) The device’s gain plot over time. Inset: reflection spectra at different times.
Notes
The authors declare the following competing financial interest(s): A patent has been filed on this technology.
■
ACKNOWLEDGMENTS The authors would like to acknowledge the financial support of the Chemical and Biological Technologies Department at the Defense Threat Reduction Agency (DTRA-CB) via Grant BA12PHM123 in the “Dynamic Multifunctional Materials for a Second Skin D[MS]2” program and the Army Research Office through the MIT Institute for Soldier Nanotechnology. The authors would like to thank I. Jeon and M. He (MIT) for conducting XPS spectroscopy experiments.
gain was continuously monitored and remained mostly unchanged during the first 55 min, indicating minimal oxygen exposure (Figure 9b).18 At t = 55 min, the package was unzipped to open to air (∼25% RH). After a short delay period, the device gain underwent a sharp increase followed by a steady saturated state, reflecting the air ingress that could have compromised the content quality. We also conducted similar experiments for monitoring green tea packaging as detailed in the Supporting Information (SI Section 4). Green tea is known to be air sensitive and the low humidity in this case allowed for the monitoring with tags that did not require a moisture barrier coating. In conclusion, a chemiresistor that displays a dosimetric response to oxygen has been developed based on a FeII-P4VPSWCNT composite. A ∼30% increase in the conductance of this chemiresistor was observed with a 50 s exposure to 18% O2. We incorporated this chemiresistor into an NFC resonant RF circuit via simple dropcasting and produced a wireless oxygen sensor, O2-p-CARD. It was shown that the reflection signal of an O2-p-CARD decreased irreversibly in response to oxygen at concentrations that are relevant for modified atmosphere packaging. A binary (on → off) smartphone detection can be set to trigger at different cumulative oxygen exposures by adjusting the formulation and amount of material applied to the tag. We demonstrated that an O2-p-CARD could be inserted in a nitrogen-filled vegetable package for monitoring air ingress at ambient conditions. The O2-pCARD provides an inexpensive, heavy-metal-free, and smartphone-addressable alternative for in situ non-line-of-sight quality monitoring of oxygen-sensitive content in a modified atmosphere package. Our devices can be readily integrated into
■
REFERENCES
(1) (a) Yam, K. L.; Lee, D. S. Emerging Food Packaging Technologies: Principles and Practice; Woodhead Publishing: 2012. (b) Akala, E. O. Effect of Packaging on Stability of Drugs and Drug Products, in Pharmaceutical Manufacturing Handbook: Regulations and Quality (ed Gad, S. C.); John Wiley & Sons, Inc.: 2008. (2) Brody, A. L.; Strupinsky, B. R.; Kline, L. R. Active Packaging for Food Applications; Technomic Publishing Co.: 2001. (3) Li, M. Organic Chemistry of Drug Degradation (No. 29); Royal Society of Chemistry: 2012. (4) (a) Ahvenainen, R. Novel Food Packaging Techniques; Woodhead Publishing: 2003. (b) Brown, M.; Leeson, L. J. Protection of OxygenSensitive Pharmaceuticals with Nitrogen. J. Pharm. Sci. 1969, 58, 242− 245. (c) Mahajan, R.; Templeton, A.; Harman, A.; Reed, R. A.; Chern, R. T. The Effect of Inert Atmospheric Packaging on Oxidative Degradation in Formulated Granules. Pharm. Res. 2005, 22, 128−140. (5) (a) Han, J. H. Innovations in food packaging; Academic Press: 2005. (b) Yam, K. L.; Takhistov, P. T.; Miltz, J. Intelligent Packaging: Concepts and Applications. J. Food Sci. 2005, 70, R1−R10. (6) (a) Mills, A. Oxygen Indicators and Intelligent Inks for Packaging Food. Chem. Soc. Rev. 2005, 34, 1003−1011. (b) Wang, X.-D.; Wolfbeis, O. S. Optical Methods for Sensing and Imaging Oxygen: Materials, Spectroscopies and Applications. Chem. Soc. Rev. 2014, 43, F
DOI: 10.1021/acssensors.7b00327 ACS Sens. XXXX, XXX, XXX−XXX
Article
ACS Sensors 3666−3761. (c) Quaranta, M.; Borisov, S. M.; Klimant, I. Indicators for Optical Oxygen Sensors. Bioanal. Rev. 2012, 4, 115−157. (7) Elegant study on the integration of optical oxygen indicators, a digital color reporting system, and a LED light in an RFID tag has been reported: (a) Martínez-Olmos, A.; Fernández-Salmerón, J.; Lopez-Ruiz, N.; Rivadeneyra Torres, A.; Capitan-Vallvey, L. F.; Palma, A. J. Screen Printed Flexible Radiofrequency Identification Tag for Oxygen Monitoring. Anal. Chem. 2013, 85, 11098−11105. (b) Escobedo, P.; Erenas, M. M.; Lopez Ruiz, N.; Carvajal, M. A.; González Chocano, S.; de Orbe-Payá, I.; Capitan-Vallvey, L. F.; Palma, A. J.; Martínez Olmos, A. Flexible Passive near Field Communication Tag for Multigas Sensing. Anal. Chem. 2017, 89, 1697−1703. (8) (a) Azzarelli, J. M.; Mirica, K. A.; Ravnsbæk, J. B.; Swager, T. M. Wireless Gas Detection with a Smartphone via RF Communication. Proc. Natl. Acad. Sci. U. S. A. 2014, 111, 18162−18166. (b) Zhu, R.; Azzarelli, J. M.; Swager, T. M. Wireless Hazard Badges to Detect Nerve-Agent Simulants. Angew. Chem., Int. Ed. 2016, 55, 9662−9666. (9) For examples of RFID sensors in food-related applications: (a) Kumar, P.; Reinitz, H. W.; Simunovic, J.; Sandeep, K. P.; Franzon, P. D. Overview of RFID Technology and Its Applications in the Food Industry. J. Food Sci. 2009, 74, R101−R106. (b) Potyrailo, R. A.; Surman, C.; Nagraj, N.; Burns, A. Materials and Transducers Toward Selective Wireless Gas Sensing. Chem. Rev. 2011, 111, 7315−7354. (c) Potyrailo, R. A.; Nagraj, N.; Tang, Z.; Mondello, F. J.; Surman, C.; Morris, W. Battery-free Radio Frequency Identification (RFID) Sensors for Food Quality and Safety. J. Agric. Food Chem. 2012, 60, 8535−8543. (d) Jun, J.; Oh, J.; Shin, D. H.; Kim, S. G.; Lee, J. S.; Kim, W.; Jang, J. Wireless, Room Temperature Volatile Organic Compound Sensor Based on Polypyrrole Nanoparticle Immobilized Ultrahigh Frequency Radio Frequency Identification Tag. ACS Appl. Mater. Interfaces 2016, 8, 33139−33147. (e) Tanguy, N. R.; Fiddes, L. K.; Yan, N. Enhanced Radio Frequency Biosensor for Food Quality Detection Using Functionalized Carbon Nanofillers. ACS Appl. Mater. Interfaces 2015, 7, 11939−11947. (f) Smits, E.; Schram, J.; Nagelkerke, M.; Kusters, R.; van Heck, G.; van Acht, V.; Gerlinck, G. Development of Printed RFID Sensor Tags for Smart Food Packaging in Proceedings of the 14th International Meeting on Chemical Sensors, Nuremberg, Germany 2012, 403−406. (g) Smolander, M.; Seppa, H.; Hurme, E.; Varpuna, T.; Saari, J. M.; Suni, I.; Sammi, J.; Majander, P. Rfid Spoilage Sensor for Packaged Food and Drugs. U.S. Patent Appl. 10/495,927, 2002. (10) Forment-Aliaga, A.; Weitz, R. T.; Sagar, A. S.; Lee, E. J. H.; Konuma, M.; Burghard, M.; Kern, K. Strong p-Type Doping of Individual Carbon Nanotubes by Prussian Blue Functionalization. Small 2008, 4, 1671−1675. (11) Yoon, B.; Liu, S. F.; Swager, T. M. Surface-Anchored Poly(4vinylpyridine)−Single-Walled Carbon Nanotube−Metal Composites for Gas Detection. Chem. Mater. 2016, 28, 5916−5924. (12) Yang, L.; Zhang, R.; Staiculescu, D.; Wong, C. P.; Tentzeris, M. M. A Novel Conformal RFID-Enabled Module Utilizing Inkjet-Printed Antennas and Carbon Nanotubes for Gas-Detection Applications. IEEE Antenn. Wireless Propag. Lett. 2009, 8, 653−656. (13) Heintz, R. A.; Smith, J. A.; Szalay, P. S.; Weisgerber, A.; Dunbar, K. R. Inorganic Syntheses; Coucouvanis, D., Ed.; John Wiley and Sons, 2002; Vol 33, p 76. (14) This application is freely available from the Google Play Store at the time of this report. It was chosen because it displays the tag’s unique identification number without invoking other time- or energyintensive functions of the smartphone. (15) Miltz, J.; Perry, M. Evaluation of the Performance of Iron-based Oxygen Scavengers, with Comments on their Optimal Applications. Packag. Technol. Sci. 2005, 18, 21−27. (16) McGhee, L.; Siddique, R. M.; Winfield, J. M. Reactions of Hexakis(acetonitrile)iron(II) Hexafluorophosphate in Acetonitrile. Ligation of Ammonia, Pyridine, and Trimethylamine to Iron(II) and the Behaviour of Trimethyl Phosphite and Trimethylphosphine towards Iron(II), Nitrogen Donor Ligand Complex Cations. J. Chem. Soc., Dalton Trans. 1988, 1309−1314.
(17) The partial reversibility could be attributable to the direct oxygen doping of carbon nanotubes. (18) The slight initial increase in gain observed between 0 and 55 min could be attributable to a small amount of residual oxygen in the package.
G
DOI: 10.1021/acssensors.7b00327 ACS Sens. XXXX, XXX, XXX−XXX
