Redox Active Binary Logic Gate Circuit for Homeland Security

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A Redox Active Binary Logic Gate Circuit for Homeland Security Pramod Gaikwad, Kavita Kadlag, Manasa Nambiar, Mruthyunjayachari Chattanahalli Devendrachari, Shambhulinga Aralekallu, Alagar Raja Kottaichamy, Zahid Manzoor Bhat, Ravikumar Thimmappa, Shahid Pottachola Shafi, and Musthafa Ottakam Thotiyl Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b00823 • Publication Date (Web): 03 Jul 2017 Downloaded from http://pubs.acs.org on July 6, 2017

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Analytical Chemistry

A Redox Active Binary Logic Gate Circuit for Homeland Security Pramod Gaikwad, Kavita Kadlag, Manasa Nambiar, Mruthyunjayachari Chattanahalli Devendrachari, Shambhulinga Aralekallu, Alagar Raja Kottaichamy, Zahid Manzoor Bhat, Ravikumar Thimmappa, Shahid Pottachola Shafi, Musthafa Ottakam Thotiyl* Department of Chemistry and Center for Energy Science, Indian Institute of Science Education and Research (IISER) Pune, Dr. Homi Bhabha Road, Pashan, Pune 411008, India ABSTRACT: Bipolar junction transistors are at the frontiers of modern electronics owing to their discrete voltage regulated operational levels. Here we report a redox active binary logic gate (RLG) which can store a ‘0’ and ‘1’ with distinct operational levels, albeit without an external voltage stimuli. In the RLG a shorted configuration of half-cell electrodes provided the logic low level and decoupled configuration relaxed the system to the logic high level due to self-charge injection into the redox active polymeric system. Galvanostatic intermittent titration and electrochemical quartz crystal microbalance studies indicate the kinetics of selfcharge injection are quite faster and sustainable in polypyrrole based RLG recovering more than 70% signal in just 14 seconds with minor signal reduction at the end of 10000 cycles. These remarkable properties of RLGs are extended to design a security sensor which can detect and count intruders in a locality with decent precision and switching speed.

Bipolar junction transistors (BJT) are ubiquitous in modern electronic devices because of their ability to function either as a switch or an amplifier.1-3These basic transistor functions are derived from their ability to act either as an insulator or a conductor tunable by an input voltage. Transistor can function as an amplifier in the common emitter configuration, where the input is applied between the base and emitter terminals and the amplified output is collected at the emitter-collector terminals.4-5 When it is used as a switch in the common base configuration, transistor will be in the OFF state (cut off mode) if the applied bias is below the barrier potential of the diode, as opposed to the ON state at voltages > barrier potentials (saturation mode).6-8 This remarkable ability of transistors to control large amounts of power with relatively small input signals brought them to the frontiers of modern electronics. Further the two distinct levels available with bipolar junction transistors transform them in to simple memory devices that store a ‘0’ when it is off and a ‘1’ when it is on. Such circuits are called binary logic gates and transistor based fundamental logic gates are AND, OR and NOT.9-14 Here for the first time we mimic these properties of transistors using simple electrochemical systems and report a redox active binary logic gate (RLG) circuit that can store a ‘0’ and ‘1’ with two distinct voltage levels of operation. We further demonstrate the applicability of RLG as an electrochemical security sensor because of their importance in homeland security. Since the redox active binary logic gate (RLG) based security sensor proposed here is battery type and self regenerable, the sensor readouts are inherently voltage levels and sensing probes as such do not require external power supply for its functioning unlike the state of the art security sensors like IR sensors, PIR sensors, ultrasonic motion sensors, magnetic sensors etc. EXPERIMENTAL SECTION

Materials and methods. Ferric chloride, HCl, H2SO4, 3, 4ethylenedioxythione (EDOT), pyrrole, ammonium per sulphate, aniline and Al foils were procured from Sigma Aldrich, India. Aniline, Pyrrole and EDOT were distilled prior to the synthesis of corresponding polymers. Synthesis of polymers and fabrication of RLG system. For the synthesis of polypyrrole (PPy), 1.0 g of pyrrole was dissolved in 80 ml of 1 M HCl solution.15 To the solution of pyrrole added 3.0 g of ferric chloride pinch by pinch and the reaction mixture color turned to dark blue. The stirring of the reaction mass was continued for 24 hrs for the completion of reaction. Polyaniline (PANI) was synthesized as follows. 1.0 g of aniline was added in to a beaker containing 50 ml of 1 M HCl solution.16 To the beaker containing aniline, 3.8 g of ammonium persulfate was added slowly with constant stirring. After the complete addition of ammonium persulfate the reaction mass turned to dark green. The stirring was continued for 24 hrs for the completion of reaction. To synthesize poly 3, 4ethylenedioxythione (PEDOT) about 1.0 g of alcoholic solution of 3, 4-ethylenedioxythione (EDOT) was dissolved in 1 M HCl solution by sonication.17 To the above reaction mass added 3.0 g of ammonium per sulphate slowly with constant stirring. The stirring was continued for about 24 hrs for the completion of the reaction. In all the cases after 24 hrs the obtained product was collected by filtration, and washed thoroughly with acid to remove unreacted monomer and finally washed with water and kept for drying for about 10-15 hrs in a vacuum oven. The purified polymer was made as slurry with 5 wt% PTFE and coated on titanium nitride (TiN) current collector for half-cell studies, characterizations and RLG fabrications. TiN was chosen as the current collector because of its decent hardness, conductivity, mechanical and chemical stabilities.18,19 Al anode (5 X 1 cm) and conducting polymer

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Scheme 1. Schematic illustration of the operation of redox active binary logic gate (RLG). (a) Logic HIGH level and (b) logic LOW level of operation. E1 is Al anode and E2 is polypyrrole cathode immersed in 1M H2SO4 solution.

cathodes (5 X 1cm) were coupled in H2SO4 to make the battery type redox active polymeric logic gate (RLG) circuit with distinct operational levels as shown in Scheme 1. Characterization. Percentage transmittance of PANI, PPy and PEDOT before and after use in RLG was measured in the UV-vis region using a Perkin Elmer Lambda 950 machine. Morphology of the conducting polymers was investigated by a JSM-5300LV (Japan) scanning electron microscope (SEM). Galvanostatic discharge measurements were carried out in a two-electrode configuration at a specific discharge current of 200 µA/cm2 in 1 M H2SO4 medium using a VMP-300 Biologic electrochemical workstation. Impedance spectra were acquired in the range 100 kHz to 10 mHz at 0 V vs. open circuit voltage (OCV) with 10 mV AC excitation signal. Galvanostatic intermittent titration technique (GITT) measurements were carried out in a two-electrode RLG system by applying a discharge current of 200 µA/cm2 for 5 minutes and a relaxation period (at zero current) of 1 hour and the process was repeated for several cycles while measuring the quasi open circuit voltage. Electrochemical Quartz Crystal Microbalance (EQCM) measurements were carried out in two-electrode RLG systems using Au coated quartz resonator (8.95 MHz) with SEIKOEG&G QCM922A. Polymers were electrodeposited on to Au coated quartz crystal by applying a potential of 900 mV for 100 seconds. Frequency change was monitored during the discharge period at 200 µA/cm2 for 5 minutes and the relaxation period (at zero current) for 1 hour. Frequency shift was converted to mass change by the Sauerbrey equation. The cyclic voltammograms of PANI, PPy and PEDOT supported on a glassy carbon electrodes were acquired using a threeelectrode configuration with a Pt counter electrode and an Ag/AgCl (3M KCl) reference electrode. Device fabrication and operation of RLG. RLG was fabricated by using aluminum anode and conducting polymer cathode. RLG generates two distinct voltage levels (HIGH/LOW)

at the output, and these levels depend upon circuit shorting and opening between the electrodes of RLG (Scheme 1). Firstly the half-cell electrodes were immersed in 1M H2SO4 electrolyte which in turn was introduced through the inlet in the RLG assembly. Potential differences were generated between the electrodes due to the distinct redox potentials of the halfcells. Initially the redox active conducting polymer is in the conducting form and the voltage will be at the maximum (1.2 V) as shown in (Scheme 1a). This is taken as the logic ‘HIGH’ level. A spring mechanism is used to connect both the electrodes, thus short circuiting the cell. This short circuit causes the reduction of redox active conducting polymer from conducting to non-conducting form and the voltage decreases to 0 V (Scheme 1b). This is taken as the logic ‘LOW’ level of operation. Figure S1, Supporting Information shows the block diagram and hardware system of object counting and security system which are based on this simple concept. In block diagram first block is RLG. RLG generates ‘HIGH ‘or ‘LOW’ voltage levels at the output depending on the pressure applied on the substrate platform to short the electrodes. The analogue output obtained from the RLG is given to Arduino Uno board (Microcontroller Atmega328). The programs used to display the output of the RLG were written in ‘C’ language and it was uploaded into the microcontroller. According to the program, microcontroller controlled the electronic circuitry and compared those voltage levels. This way RLG can count and sense the number of objects in that locality. In the program, we set a reference voltage and when the potential value decreases below the set reference value, the RLG becomes closed and the count value will be incremented by one which will be displayed on 20x4 Alphanumeric Liquid Crystal Display. These simultaneously switch on the LED and the buzzer to indicate the presence of objects on the substrate platform of RLG. On the other hand if the potential value is above the set reference voltage then the RLG will be in the open state and the value of the counter remains in the previous count and LED, buzzer will be in the

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Figure 1. (a), (b) and (c) are voltage and current vs. load resistance plots for Al-PPy, Al-PANI and Al-PEDOT RLGs respectively and (d) power vs. load resistance curves for Al-redox active conducting polymeric RLGs.

OFF state to indicate the absence of any object on RLG substrate. RESULTS AND DISCUSSION

The sensor consists of two half-cells, an Al anode half-cell with high standard negative reduction potential (-1.66 V vs. SHE) and a range of conducting polymer cathode half-cells with positive formal potentials (~0.22 V vs. Ag/AgCl), cyclic voltammograms (Figure S2, Supporting Information). 20-21 Al was chosen as the anode half-cell electrode because of its high abundance, light weight, high negative standard reduction potential and good stability in sulphate containing acidic electrolytes and conducting polymers were chosen as the cathode half-cell because of its ease of synthesis, processability and ability to undergo fast and reversible pseudo capacitive charge injections/ejections tunable by the surrounding media.22-25 For example it is known that when conducting polymers are immersed in alkaline media it can undergo dedoping to nonconducting form and a sufficiently acidic pH can cause the conducting form to recover.26-28 Nevertheless for the proposed electrochemical device to function as a logic gate akin to transistors, it should have two distinct operational levels, say a conducting ON state and a non- conducting OFF state controllabel by an external modulation. This will dictate its ability to function as a switch. In such a case, the device can communicate a great deal of data and control various other appliances. As explained earlier these states in binary logics are 1 (ON)

and 0 (OFF). Binary 1 is typically considered as logic high and 0 as logic low. In the redox active binary logic gate (RLG) fabricated here the redox energies of Al and psuedocapacitive redox transitions in conducting polymers are coupled, to make a battery type system with an open circuit voltage >1 V (Figure 1a-1c) and a real power in the range 150-400 µW/cm2 (Figure 1d). The output voltage, current and power measured as a function of load resistance for a range of conducting polymeric cathode half-cells with Al anode half-cell are shown in (Figure 1a-1c). At the open circuit voltage (OCV), (Figure 1a-1c) the cell delivered least current and maximum resistance as opposed to maximum current and least resistance at the short circuit, which is typical of any battery. The current and voltage profiles intersected at a particular load resistance which is proportionate to the internal resistance of the cell. The maximum power obtained with PANI, PEDOT and PPy were 164, 374 and 377 μW/cm2 respectively suggesting that the polymer cathodes do change the device chemistry noticeably. The lower power density observed on Al-PANI RLG could be due to higher electronic resistance of the polymer electrode, four probe I-V curves, (Figure S3 and Table S1, Supporting Information). The operating region of the proposed RLG is marked in (Figure 1a-1c) and it is at the open circuit (OCV) and short circuit (SC) conditions, making it as device possessing two distinct voltage levels akin to binary logics in transistor circuits. Therefore the OCV and SC can function as logic high (1) and logic low (0) respectively in the proposed RLG simi-

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Figure 2. Rise and fall time measurements of RLGs in 1M H2SO4 electrolyte. (a) Al-PPy, (b) Al-PANI and (c) Al-PEDOT.

lar to transistor circuits and therefore the proposed RLG possesses the qualities of a switch. Importantly for practical applications the switch should be self regenerable and should possess fast switching speed. This was analyzed in the present investigation by short circuiting the electrodes and allowing it to relax to its open circuit voltage level. Since Al electrode is in large excess the performance will be limited by the cathode material and the regaining of the OCV will be mainly dictated by the ability of the cathode to self-recover. It should be read with the well- known ability of conducting polymers to modulate their redox energy by surrounding environment.26-28 The self-recovery of the cathode was investigated for different conducting polymers (Figure 2), by short circuiting the electrodes and allowing it to relax to its open circuit voltage level. The turn-on time (ton) is defined as the sum of delay time (td) and rise time (tr). tr is defined as the time required by the output signal to rise from 10% to 90% w.r.t OCV (logic 1). td is defined as the time taken by the output signal to reach 10% of its logic 1 value. Similarly turn-off time (toff) is defined as the sum of the storage time (ts) and fall time (tf). tf means the time required by the output signal to fall from 90% to 10% of its logic high value and ts is the time required for the output to fall to 90% of its logic 1 value. As shown in (Figure 2 and Table 1) the rise time for the recovery of 90% signal for AlPPy logic gate was 400 and >1000 seconds respectively. When the ON time was fixed to 200 seconds and analyzed the evolution of voltage levels after short circuiting the Al anode to different conducting polymers, the signal of PPy electrode was regained to its more than 90% level whereas the

signals of PEDOT and PANI were recovered only to 76% and 72% respectively, making the PPy possessing better qualities to function as a switch (better sensitivity and faster self regenerability). To further screen the polymeric half-cells in order to identify the one with better sensitivity, response time, self regenerability and cyclability we carried out cycling studies by repeatedly short circuiting the half-cell electrodes and allowing them to relax to their OCV at fixed ton (200 seconds) and toff (20 seconds). When PPy demonstrated a stable and steady response regaining more than 90% voltage levels throughout the cycling studies, PANI and PEDOT demonstrated either poor self regenerability or cyclability, (Figure S4, Supporting Information). Therefore the stability of PPy half-cell under repeated cycling was found to be impressive as opposed to other two conducting polymeric half-cells. Table 1. Rise time measurement with different RLGs

Sr. No.

RLG

Rise time tr (s)

1 2 3

Al- PPy Al- PANI Al- PEDOT

160 >1000 460

Retention rate (%) at 160s 90 72 76

OCV (V) 1.18 1.10 1.30

It should be noted that as synthesized polymers were in the conducting state with chloride dopant, scanning electron micrographs with energy dispersive X-ray (Figure S5, Supporting Information) and UV-vis spectroscopy studies (Figure S6, Supporting Information). SEM reveals a near granular morphology for all the conducting polymers and EDS demonstrate


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Figure 3. Galvanostatic discharge curves for Al-PPy, Al-PANI and Al-PEDOT RLGs in 1M H2SO4 at a rate of 200 μA/cm2. (a) At ton = 1000 seconds and (b) at ton = 200 seconds.

the presence of chloride dopants in its matrix (Figure S5, Supporting Information).UV-vis spectroscopy of as synthesized polymer indicates the signature peaks at longer wavelengths corresponding to its conducting states, (Figure S6, Supporting Information).29-33 When the Al electrode is short circuited to polymeric cathode half-cells, the polaronic band at longer wavelength is blue shifted for PPy (483 nm to 465 nm), PANI (836 nm to 609 nm), and PEDOT (686 nm to 612 nm) electrodes, spectroelectrochemistry data, (Figure S6, Supporting Information) indicating the formation of non-conducting state of respective polymers. After 1000 seconds of the removal of short circuiting, the recorded spectra of conducting polymers demonstrate their recovery almost to respective conducting states. However at shorter time scales (< 200 seconds), UVVis spectroelectrochemistry studies (Figure S6, Supporting Information) indicate the charge injection is efficient only in PPy and the spectra for PEDOT and PANI could not completely regain to its parent state. Therefore when short circuiting is removed, the self-recovery of conducting polymers demonstrated in Figure 2 and Figure S4, Supporting Information is actually the self-doping of the non-conducting state to the conducting state tuned by the surrounding media and the kinetics of this self-doping is faster in PPy as further revealed below for Figures 3 and 4. This is proved by consecutive galvanostatic discharge after a waiting period of 1000 seconds without applying any external power supply to charge the Al-conducting polymeric battery. As shown in (Figure 3), during the second discharge Al-PPy cell regained almost ~90% of its first discharge capacity without any external power supply while Al-PANI cell furnished only 60% its first discharge capacity, confirming that PPy can self-recover rapidly and therefore possesses better switch relevant parameters. Even though the Al-PEDOT system regained to ~90% of its first discharge capacity in the second cycle, its cyclic stability is found to be inferior as shown in (Figure S4c, Supporting Information). When the waiting period for the second discharge is reduced to 200 seconds from 1000 seconds, only PPy delivered >80% capacity retention and PEDOT and PANI responses were inferior, (Figure 3b). It should be noted that the behavior outlined in Figure 3 is typical of any battery or supercapacitor.34-36 Self-recovery is a redox transition back to conducting state as the probes are immersed in acidic pH, therefore the present observation confirms that PPy

possess better self-recovery and switching speed compared to PANI and PEDOT half-cells. The discharge plateau at the discharge rate of 200 μA/cm2 for all redox active polymers in the first discharge were almost identical because all the conducting polymers were initially in the conducting state, Figure 1, Figures S5-S7 (Supporting Information). However the discharge plateaus were very different for PANI and PEDOT in the second discharge especially at shorter relaxing ton time interval which is attributed to the difference in charge injection kinetics in the polymeric system (Figure 2 and Figure S6, Supporting Information). In essence at the short circuit a redox transition occurred from the conducting to non-conducting state at the polymer electrode and guided by the surrounding media it will be reversed on relaxing to the open circuit. This redox transition is further investigated by electrochemical impedance spectroscopy as explained below. The Nyquist plot (Figure S7, Supporting Information) reveals PPy and PEDOT possessing lower equivalent series resistance and charge transfer resistance compared to PANI, in line with battery charge discharge measurements, (Figure 3). The Nyquist plots (Figure S7, Supporting Information) indicate an increase of charge transfer resistance on discharging and a corresponding decrease on relaxing (after 1000 seconds of discharging) in all polymeric half cells suggesting the polymers can self-recover. However at shorter time scales (~200 seconds) only PPy could self-recover and not PANI. Even though impedance spectroscopy demonstrates somewhat a faster self-recovery in PEDOT half cells (Figure S7c, Supporting Information), it possessed poor cyclability as demonstrated in (Figure S4c, Supporting Information). The faster selfdoping kinetics of PPy could be due to its higher electronic and ionic conductivity over other polymers, four probe conductivity plots (Figure S3 and Table S1, Supporting Information), however the electronic conductivity of PEDOT is only slightly different from PPy. Since electronic transport in conducting polymers are accompanied by anion transport, the fast switching speed in PPy compared to other polymers are due to extremely fast surface governed anion transport. Since injecting anions are identical (sulphate) in all the three cases (PPy, PEDOT and PANI) a difference in their charge injection kinetics should stem from polymer’s inherent structure. This is investigated by galvanostatic intermittent titration technique (GITT) and electrochemical quartz crystal microbalance



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Figure 4. (a) GITT of different RLGs. During repeated cycling a discharge pulse of 200 μA/cm2 was applied for 5 minutes and the system was allowed to relax for 1 hour (at zero current). (b) Frequency shift vs. time plots during relaxation normalized to that during discharge and corresponding (c) mass change vs. time plots acquired from EQCM.

(EQCM).37-39 GITT data for the three different RLGs suggest the relaxation signal (at zero current) after iR drop regains to higher OCV value in the case of PPy RLG compared to PANI and PEDOT RLGs indicating a faster charge injection kinetics in the former compared to the latter, (Figure 4a). The sustainability of charge injection/ejection during cycling is evident in Al-PPy compared to Al-PANI and Al-PEDOT RLGs, Figure 4a. During cycling in PANI and PEDOT based RLGs the relaxation signal demonstrated either a lower value or declined drastically. It is known that PEDOT is unstable in its reduced state especially under acidic conditions, catalyzing the chemical evolution of H2.40, 41 As shown in Figure 4a PEDOT undergoes reduction during the discharge pulse and relaxes to the open circuit voltage during the relaxation pulse. Repeated discharge may cause excessive H2 evolution causing unwanted swelling and this may degrade the polymeric backbone with disruption of the polymer repeat chains. This may obstruct the fundamental charge transport mechanism thereby declining the performance of PEDOT gradually. EQCM is further used to understand the charge injection kinetics in RLGs and as demonstrated Al-PPy RLG during the relaxation pulse exhibited the highest frequency shift and mass change throughout the measured time scale compared to other RLGs (Figure 4b, c), clearly indicating the kinetics of charge injection is superior in PPy compared to PANI and PEDOT half-cells. Overall GITT and EQCM demonstrate that kinetics of charge injection during relaxation is superior in PPy half-cell compared to PANI and PEDOT cells leading to a self regenerable Al-PPy

RLG. EQCM further suggest that PANI film possesses higher resistance during relaxing compared to PPy and PEDOT polymeric half-cells. Based on the better switch relevant parameters of PPy, Al-PPy RLG was selected for further analysis. Based on the theoretical half-cell voltages the logic gate constructed using polypyrrole is expected to have a high voltage level of 1.8 V at the open circuit condition, yet it demonstrated an OCV close to 1.2 V. The single electrode potentials of Al electrode vs. a non-polarizable interface suggested a voltage of -0.98 V vs. SHE indicating major voltage loss occurred on Al anode possibly due to Al surface passivation in sulphuric acid media.42,43 Though this surface passivation is a disadvantage as it may be the responsible factor for the reduction in cell voltage, it is reported that the oxide layer provide excellent stability for Al electrodes in sulphate containing acidic electrolytes making it a suitable anode material under acidic conditions.42,43 Nevertheless PPy based RLG possesses fast switching speed, decent stability and reproducibility in its voltage levels on repeated cycling, (Figure 5). The data for 10000 cycles can be seen in Figure 5a and 5b for Al-PPy logic gate and at the end of 10000 cycles the logic high level maintained 80% of its initial signal output indicating decent cycle stability. Since Al-PPy RLG possesses decent qualities to function as a switch, we have investigated this system as a security sensor. The operation of the switch is shown in (Figure 5c and 5d and Figure S8, supporting information). When the working electrodes are apart the system will be at the open circuit voltage (logic high)


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Figure 5. (a) Cycling studies of Al-PPy based RLG for 10,000 cycles at constant ton = 200s and toff = 20s, (b) relaxation voltage vs. no. of cycles, (c) assembly of RLG and (d) architecture demonstrating object counting operation by Al-PPy RLG.

and if they are made to contact by applying a force, the voltage dropped to zero (logic low). However this short circuiting depends upon the spring constant of the spring used to hold the sensor platform. In the present investigation we have used a spring having a spring constant (k) of 346.5 N/m , and for a displacement of 3 mm a minimum weight of 0.106 kg is required on the substrate platform of the switch (using the formula F= -kx). Based on this, the battery switch can be extended to design a security sensor as shown in (Figure 5d). If a force is applied on the substrate platform (for example by an intruder) in such a way that the electrodes get short circuited, the low logic level will be immediately attained triggering an alarm. Based on the frequency of the lower and higher voltage level in principle it can be used to count the number of intruders in that locality. As explained earlier an Al-PPy based RLG can be used for sensing and counting the presence of intruders in a locality with fast switching speed and better sensitivity compared to other conducting polymer based RLGs. The sensing mechanism is the psuedocapacitive redox transition from conducting to non-conducting state of the polymer when the electrodes are pressed against each other with concomitant Al dissolution and self-doping of polymeric half-cell to its conducting form when the electrodes are allowed to relax to their original positions, since the polymer probes are immersed acidic solution having low pH. The amount of Al consumed for 100 cycles was calculated to be 0.085 mg based on the mass change measured after 10000 cycles (8.5 mg). This suggests that with

a1mg/cm2 PPy cathode, if the initial mass of Al electrode is ~100 mg it can last for more than 117000 cycles. Since the read out is voltage which is an intensive property the sensor is independent of the size and shape of the sensing probes which is an added advantage. The PPy based security sensor fabricated can tell the end user about the presence of suspicious movements when it is installed in a locality (Video 1, Supporting Information). Further in the proposed sensor as the signal readouts are inherently voltage levels, high and low logic levels are easily tunable providing extra handles to control response time of the sensor (Figure S9, Figure S10 and Table S2, Supporting Information). CONCLUSION We have demonstrated a redox active binary logic gate circuit with two distinct levels of operation akin to transistor based logic gate circuits, by coupling the redox energy of Al and conducting polymeric half-cells, however the switching does not require an external voltage. A short circuited configuration of half-cell electrodes favored the logic low level while decoupled configuration relaxed the system to its logic high level. UV-vis spectroelectrochemistry, EIS, GITT and EQCM studies demonstrated faster charge injection kinetics in PPy based RLG due to self-doping of polymeric half-cells when the electrodes are decoupled. This led to a sustainable RLG which could be cycled several times with little hysteresis in the output signal. The concept is further extended to a security



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sensor which could detect and count intruders in a locality with decent response time and switching speed. The potentiometric features of the overall sensor provide flexibility in the design of sensor as the areal and geometric features of the probes do not affect sensing signals. AUTHOR INFORMATION Corresponding Author *Email: [email protected]. Tel: +91(020)25908261. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT MOT acknowledges financial assistance from DST-SERB, MHRD and DST-Nanomission, India ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Supporting information contains block diagram and details of hardware system for object counting, electrochemistry of conducting polymers and tuning of logic levels in redox active logic gates. REFERENCES (1) Schwierz, F. Nat. Nanotechnol. 2010, 5, 487-496. (2) Yajima, T.; Hikita, Y.; Hwang, H. Y. Nat. Mater. 2011, 10, 198-201. (3) Colinge, J. P.; Lee, C. W.; Afzalian, A.; Akhavan, N. D.; Yan, R.; Ferain, I.; Razavi, P.; O’Neill, B.; Blake, A.; White, M.; Kelleher, A. M.; Mccarthy, B.; Murphy, R. Nat. Nanotechnol. 2010, 5, 225-229. (4) Kim, D. K.; Lai, Y.; Diroll, B. T.; Murray, C. B.; Kagan, C. R. Nat. Commun. 2012, 3, 1216-1222. (5) Yang, X.; Liu, G.; Balandin, A. A.; Mohanram, K. ACS Nano 2010, 4, 5532-5538. (6) Barman, S.; Saha, S.; Mondal, S.; Kumar, D.; Barman, A. Sci. Rep. 2016, 6, 33360-33370. (7) Tybrandt, K.; Gabrielsson, E.O.; Berggren, M. J. Am. Chem. Soc. 2011, 133, 10141-10145. (8) Lent, C. S. Science 2000, 288, 1597-1599. (9) Veldhorst, M.; Yang, C. H.; Hwang, J. C. C.; Huang, W.; Dehollain, J. P.; Muhonen, J. T.; Simmons, S.; Laucht, A.; Hudson, F. E; Itoh, K. M.; Morello, A.; Dzurak, A. S. Nature 2015, 526, 410-414. (10) Tamsir, A.; Tabor, J. J.; Voigt, C. A. Nature 2011, 469, 212-215. (11) Javey, A.; Kim, H.; Brink, M.; Wang, Q.; Ural, A.; Guo, J.; Mcintyre, P.; Mceuen, P.; Lundstrom, M.; Dai, H. Nat. Mater. 2002, 1, 241-246. (12) De Silva, A. P.; McClenaghan, N. D. Chem. Eur. J. 2004, 10, 574-586. (13) Wang, L.; Li, B. Phys. Rev. Lett. 2007, 99, 17-26. (14) Stojanovic, M. N.; Mitchell, T. E.; Stefanovic , D. J. Am. Chem. Soc. 2002, 124, 3555-3561. (15) Goel, S.; Mazumdar, N. A.; Gupta, A. Polym. Adv. Technol. 2010, 21, 205-210.

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Redox Active Binary Logic Gate Circuit for Homeland Security

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