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Herein, a resettable and reprogrammable biomolecular keypad lock on the basis of a closed bipolar electrode (BPE) system was established. In this system, one ITO electrode with immobilized chitosan (CS) and glucose oxidase (GOD), designated as CS-GOD, acted as one pole of BPE in the sensing cell; another ITO with electrodeposited Prussian blue (PB) films as the other pole in the reporting cell. The addition of ascorbic acid (AA) in the sensing cell with driving voltage (V tot ) at +2.5V would make the PB films become Prussian white (PW) in the reporting cell, accompanied by the color change from blue to nearly transparent. On the other hand, with the help of oxygen, the addition of glucose in the sensing cell with V tot at -1.5V would induce PW back to PB. The change of color and the corresponding UV-vis absorbance at 700nm for the PB/PW films in the reporting cell could be reversibly switched by changing the solute in the sensing cell between AA and glucose and then switching V tot between +2.5 and -1.5V. Based on these, a keypad lock was developed with AA, glucose and V tot as 3 inputs, and the color change of the PB/PW films as the output. This keypad lock system combined enzymatic catalysis with bipolar electrochemistry, demonstrating some unique advantages such as good reprogrammability, easy resettability and visual readout by naked eye., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this work, electrochromic Prussian blue (PB) films were electrodeposited on the surface of indium tin oxide (ITO) electrodes, and a dispersion mixture of glucose oxidase (GOD), chitosan (CS) and gold nanoclusters (AuNCs) was then cast on the PB surface to form CS-AuNC-GOD/PB nanocomposite film electrodes. The blue PB component in the films could be changed into its colourless reduced form of Prussian white (PW) upon application of -0.2 V. The addition of glucose to the solution would produce H 2 O 2 with the help of GOD in the films and oxygen in the solution, which could oxidize PW back to PB. In the meantime, the fluorescence emission signal of the AuNCs in the films was greatly influenced by the form of PB/PW. Based on these properties, the amperometric current, fluorescence intensity and UV-vis absorbance of the film electrodes demonstrated potential- and glucose-sensitive ON-OFF behaviors. Thus, a 2-input/3-output biomolecular logic gate system with 3 different types of output signals and a 2-to-1 encoder were developed. Furthermore, a resettable and reprogrammable 3-input biomolecular keypad lock was established with fluorescence intensity and UV-vis absorbance as dual outputs, which greatly enhanced the security level of the keypad lock. This work reported for the first time an enzyme-based keypad lock with dual outputs, which might open a new avenue to design more complicated biomolecular keypad lock systems.

A logic-gate system with three outputs and three inputs was developed based on the bioelectrocatalysis of glucose by glucose oxidase (GOx) entrapped in chitosan films on the electrode surface by means of ferrocenedicarboxylic acid (Fc(COOH)2 ). Cyclic voltammetric (CV) signals of Fc(COOH)2 exhibited pH-triggered on/off behavior owing to electrostatic interactions between the film and the probe at different pH levels. The addition of glucose greatly increased the oxidation peak current (Ipa ) through the electrocatalytic reaction. pH and glucose were selected as two inputs. As a reversible inhibitor of GOx, Cu(2+) was chosen as the third input. The combination of three inputs led to Ipa with different values according to different mechanisms, which were defined as three outputs with two thresholds. The logic gate with three outputs by using one type of enzyme provided a novel model to build logic circuits based on biomacromolecules, which might be applied to the intelligent medical diagnostics as smart biosensors in the future., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Dual-responsive poly(N,N-diethylacrylamide) (PDEA) hydrogel films with entrapped horseradish peroxidase (HRP) and glucose oxidase (GOD) were successfully prepared on electrode surface with a simple one-step polymerization procedure under mild conditions, designated as PDEA-HRP-GOD. Cyclic voltammetric (CV) response of electroactive probe K3Fe(CN)6 at the film electrodes displayed reversible thermo- and sulfate-responsive switching behavior. For example, at 25 °C, the K3Fe(CN)6 demonstrated a well-defined CV peak pair with large peak currents for the films, showing the on state, while at 40 °C, the CV response was greatly suppressed and the system was at the off state. The influence of temperature and Na2SO4 concentration on the switching behavior of the film system was not independent or separated, but was synergetic. The responsive mechanism of the system was ascribed to the structure change of PDEA component in the films with temperature and sulfate concentration. This switching property of the PDEA-HRP-GOD films could be further used to realize dual-responsive catalytic oxidation of glucose sequentially by HRP and GOD entrapped in the films with Fe(CN)6 (3-) as the mediator through changing the surrounding temperature and Na2SO4 concentration. This system may establish a foundation for fabricating a new type of multi-switchable electrochemical biosensors based on bienzyme electrocatalysis.

In the present work, N,N-diethylacrylamide (DEA) and methyl acrylic acid (MAA) monomers were copolymerized into P(DEA-co-MAA) thin films on the electrode surface with a simple one-step polymerization method at ambient temperature and pressure, and the enzyme glucose oxidase (GOD) was entrapped in the films, designed as P(DEA-co-MAA)-GOD. The cyclic voltammetric (CV) response of ferrocene dicarboxylic acid (Fc(COOH)2) at the film electrodes was very sensitive to environmental stimuli, such as temperature, pH, the identity and concentration of anions, and the concentration of CO2 in solution. This multiresponsive CV behavior of the system could be further employed to switch the electrochemical oxidation of glucose catalyzed by GOD entrapped in the films with Fc(COOH)2 as the mediator in solution, demonstrating the amplification effect. The SEM and stereomicroscopy results showed that the multisensitive behaviors of the system were attributed to the structure change of the copolymer films with the stimuli. Specifically, the synergistic effect of temperature and pH was observed, and the hydrogen bonding between PDEA and PMAA components in the copolymer played a key role for this. The present system could be performed under physiological conditions at 37 °C and pH 7.4, which may offer numerous possibilities not only to design new multiswitchable biosensors based on bioelectrocatalysis but also to establish foundations for controlled drug delivery and other medical applications.

The molecularly imprinted polymer (MIP) films were electropolymerized on the surface of Au electrodes with luminol and pyrrole (PY) as the two monomers and ampicillin (AM) as the template molecule. The electrochemiluminescence (ECL) intensity peak of polyluminol (PL) of the AM-free MIP films at 0.7 V vs Ag/AgCl could be greatly enhanced by AM rebinding. In addition, the ECL signals of the MIP films could also be enhanced by the addition of glucose oxidase (GOD)/glucose and/or ferrocenedicarboxylic acid (Fc(COOH) 2 ) in the testing solution. Moreover, Fc(COOH) 2 exhibited cyclic voltammetric (CV) response at the AM-free MIP film electrodes. Based on these results, a binary 3-input/6-output biomolecular logic gate system was established with AM, GOD and Fc(COOH) 2 as inputs and the ECL responses at different levels and CV signal as outputs. Some functional non-Boolean logic devices such as an encoder, a decoder and a demultiplexer were also constructed on the same platform. Particularly, on the basis of the same system, a ternary AND logic gate was established. The present work combined MIP film electrodes, the solid-state ECL, and the enzymatic reaction together, and various types of biomolecular logic circuits and devices were developed, which opened a novel avenue to construct more complicated bio-logic gate systems. [ABSTRACT FROM AUTHOR]

A logic-gate system with three outputs and three inputs was developed based on the bioelectrocatalysis of glucose by glucose oxidase (GOx) entrapped in chitosan films on the electrode surface by means of ferrocenedicarboxylic acid (Fc(COOH)2). Cyclic voltammetric (CV) signals of Fc(COOH)2 exhibited pH-triggered on/off behavior owing to electrostatic interactions between the film and the probe at different pH levels. The addition of glucose greatly increased the oxidation peak current (Ipa) through the electrocatalytic reaction. pH and glucose were selected as two inputs. As a reversible inhibitor of GOx, Cu2+ was chosen as the third input. The combination of three inputs led to Ipa with different values according to different mechanisms, which were defined as three outputs with two thresholds. The logic gate with three outputs by using one type of enzyme provided a novel model to build logic circuits based on biomacromolecules, which might be applied to the intelligent medical diagnostics as smart biosensors in the future. [ABSTRACT FROM AUTHOR]

Dual-responsive poly( N, N-diethylacrylamide) (PDEA) hydrogel films with entrapped horseradish peroxidase (HRP) and glucose oxidase (GOD) were successfully prepared on electrode surface with a simple one-step polymerization procedure under mild conditions, designated as PDEA-HRP-GOD. Cyclic voltammetric (CV) response of electroactive probe KFe(CN) at the film electrodes displayed reversible thermo- and sulfate-responsive switching behavior. For example, at 25 °C, the KFe(CN) demonstrated a well-defined CV peak pair with large peak currents for the films, showing the on state, while at 40 °C, the CV response was greatly suppressed and the system was at the off state. The influence of temperature and NaSO concentration on the switching behavior of the film system was not independent or separated, but was synergetic. The responsive mechanism of the system was ascribed to the structure change of PDEA component in the films with temperature and sulfate concentration. This switching property of the PDEA-HRP-GOD films could be further used to realize dual-responsive catalytic oxidation of glucose sequentially by HRP and GOD entrapped in the films with Fe(CN) as the mediator through changing the surrounding temperature and NaSO concentration. This system may establish a foundation for fabricating a new type of multi-switchable electrochemical biosensors based on bienzyme electrocatalysis. [ABSTRACT FROM AUTHOR]

Abstract: N,N-diethylacrylamide (DEA) and 4-vinylpyridine (4VP) were polymerized into P(DEA-co-4VP) copolymer hydrogel films with immobilized glucose oxidase (GOD) on electrode surface with the simple one-step procedure under mild conditions, designed as P(DEA-co-4VP)-GOD. Cyclic voltammetric (CV) response of ferrocenedicarboxylic acid (Fc(COOH)2) probe at P(DEA-co-4VP)-GOD film electrodes was very sensitive to environmental pH, temperature, and sulfate concentration. For example, in pH 5.0 buffers, the CV response of Fc(COOH)2 was quasi-reversible with quite large peak heights at 25°C for the films, showing the on state; while at pH 9.0, the peaks were greatly suppressed and the system was at the off state. This pH-sensitive on-off switching behavior of the films toward the probe was reversible and could be repeated for many times between pH 5.0 and 9.0. Similarly, the film system could be switched on-off reversibly when the temperature was changed between 25 and 39°C, or when the concentration of Na2SO4 was changed between 0 and 0.50M. This triply responsive property could be further used to realize triply switchable electrochemical oxidation of glucose catalyzed by GOD immobilized in the films and mediated by Fc(COOH)2 in solution. The responsive mechanism of the system was also explored and discussed. The pH-sensitive property was attributed to the electrostatic interaction between the P4VP component of the films and the probe at different pH, while the thermo- and sulfate-sensitive behavior was ascribed to the structure change of PDEA constituent of the films with temperature and Na2SO4 concentration, respectively. These “smart” films combine the unique stimuli-responsive properties of both P4VP and PDEA with enzymatic reactions and may be used to fabricate a novel type of multi-controllable electrochemical biosensors based on bioelectrocatalysis. [Copyright &y& Elsevier]

Abstract: Oppositely charged poly(allylamine hydrochloride) (PAH) and hyaluronic acid (HA) were assembled into {PAH/HA} n layer-by-layer (LBL) films on pyrolytic graphite (PG) electrodes. Glucose oxidase (GOD) in solution was then loaded into the films, designated as {PAH/HA} n –GOD. When the {PAH/HA} n –GOD film electrodes were placed in pH 5.0 buffers containing ferrocenedicarboxylic acid (Fc(COOH)2) and glucose, a well-defined and large cyclic voltammetric (CV) oxidation wave of glucose catalyzed by GOD immobilized in the films and mediated by Fc(COOH)2 in solution was observed. However, when the films were placed in pH 9.0 buffers containing the same amount of Fc(COOH)2 and glucose, the electrocatalytic response was quite small. The bioelectrocatalysis for the film system was at the “on” state at pH 5.0 and at the “off” state at pH 9.0. This pH-sensitive “on–off” behavior was reversible and could be repeated for several times. The possible mechanism of the pH-switchable bioelectrocatalysis was explored and discussed, and should be mainly attributed to the different electrostatic interaction between Fc(COOH)2 and the films at different pH. This work provides a novel model to realize pH-controllable bioelectrocatalysis based on the enzyme-loaded LBL assembly films, and may guide us to develop the tunable electrochemical biosensors based on electrocatalysis with immobilized enzymes. [ABSTRACT FROM AUTHOR]

Abstract: Natural double-stranded DNA and the enzyme glucose oxidase (GOD) were assembled into layer-by-layer films on electrode surface. In the presence of glucose and Fe2+ in incubation solutions, GOD in the films could catalyze the reaction of glucose and O2, and the produced H2O2 would further react with Fe2+, generating hydroxyl radical ( the Fenton reaction, which could severely damage DNA in the films. The electrocatalytic oxidation of DNA guanines by (bpy=2,2′-bipyridine) produced by electrooxidation of at the electrodes was used to detect DNA damage induced by the in situ Fenton reaction. The additional catalase (Cat) layers assembled into the films could effectively protect the DNA from damage by decomposing the H2O2 produced in situ, and only when the Cat layers were located in close proximity to the GOD layers, the protection of DNA in the inner layers was most effective. The present work provides an in vitro model system to mimic the real bioprocess in DNA damage and protection through a simple electrochemical approach combined with layer-by-layer assembly. [Copyright &y& Elsevier]

Herein, poly(N-isopropylacrylamide- co -N,N′-dimethylaminoethylmethacrylate) copolymer films were polymerized on electrode surface with a simple one-step method, and the enzyme horseradish peroxidase (HRP) was embedded in the films simultaneously, which were designated as P(NiPAAm- co -DMEM)-HRP. The films exhibited a reversible structure change with the external stimuli, such as pH, CO 2 , temperature and SO 4 2 - , causing the cyclic voltammetric (CV) response of electroactive K 3 Fe(CN) 6 at the film electrodes to display the corresponding multi-stimuli sensitive ON–OFF behavior. Based on the switchable CV property of the system and the electrochemical reduction of H 2 O 2 catalyzed by HRP in the films and mediated by Fe(CN) 6 3− in solution, a 5-input/3-output logic gate was established. To further increase the complexity of the logic system, another enzyme glucose oxidase (GOD) was added into the films, designated as P(NiPAAm- co -DMEM)-HRP-GOD. In the presence of oxygen, the oxidation of glucose in the solution was catalyzed by GOD in the films, and the produced H 2 O 2 in situ was recognized and electrocatalytically reduced by HRP and mediated by Fe(CN) 6 3− . Based on the bienzyme films, a cascaded or concatenated 4-input/3-output logic gate system was proposed. The present work combined the multi-responsive interface with bioelectrocatalysis to construct cascaded logic circuits, which might open a new avenue to develop biocomputing elements with more sophisticated functions and design novel glucose biosensors. [ABSTRACT FROM AUTHOR]

Stable molybdenum disulfide quantum dots (MoS 2 QDs) were synthesized using a simple method and embedded into chitosan (Chit) films with glucose oxidase (GOD) on the surface of a polyaniline (PANI) pre-electrodeposited ITO electrode, designated as Chit-MoS 2 -GOD/PANI. At the prepared film electrode, the fluorescence property of MoS 2 QDs as well as the catalytic properties of MoS 2 QDs and GOD were well maintained and could be reversibly regulated by external stimuli, such as pH, potential, and the concentrations of glucose and ascorbic acid (AA) in the solution. By controlling the redox state of PANI with an externally applied voltage, the color of the film electrode switched between violet blue and nearly transparent, simultaneously quenching/dequenching the fluorescence signals from MoS 2 QDs through Fӧster resonance energy transfer (FRET). The electrocatalytic signals toward hydrogen peroxide (H 2 O 2), a product formed by biocatalysis between glucose and GOD, could be tuned through the catalytic capacity of MoS 2 QDs in the films. Thus, an intelligent platform was built based on the film electrode with pH, potential, glucose and AA as inputs and UV – vis extinction (E), photoluminescent intensity (PL), and amperometric current (I) as outputs. Combinational logic operations such as a 4-input/5-output logic network and sequential logic operations such as a keypad lock and a reprogrammable delay/data (D) flip flop was first simulated in a biocomputing system with the film-modified electrode. This work demonstrated the construction of a multiple stimulus-responsive system with dual-functional nanomaterials and provided a new approach for sequential logic operations for further applications in the information storage. Several combinational and sequential logic devices were preliminary built through a stimulus-responsive biointerface with immobilized MoS 2 quantum dots (MoS 2 QDs) and glucose oxidase (GOD) in chitosan (Chit) hydrogel films on the surface of polyaniline (PANI) pre-deposited ITO electrode. [Display omitted] • Dual-functional MoS 2 QDs were utilized as a "bridge" to design a biocomputing platform. • Both the electrocatalysis and biocatalysis of the film electrode were controllable. • Switchable electrochemical, fluorescence and UV–vis signals were used as outputs. • Preliminary simulation of a D flip flop at a film electrode was first implemented. [ABSTRACT FROM AUTHOR]

Abstract: The films with binary architecture combining electropolymerized poly(4-vinylpyridine) (P4VP) as the inner layers and chemically polymerized poly(N,N′-diethylacrylamide) (PDEA) hydrogels containing glucose oxidase (GOD) as the outer layers were successfully prepared on electrode surface, designated as P4VP/PDEA-GOD. Cyclic voltammetric response of ferrocenedicarboxylic acid (Fc(COOH)2) at P4VP/PDEA-GOD film electrodes showed reversible on–off behaviors to environmental pH, temperature, ClO4 −, and SO4 2− concentration. In particular, the films exhibited a very sensitive ClO4 −-responsive behavior toward Fc(COOH)2 with the critical concentration as low as 0.01M. The responsive mechanism of the films to different stimuli was discussed and explored by comparative experiments. The pH- and ClO4 −-sensitive properties were mainly attributed to the electrostatic interaction between P4VP inner layers and Fc(COOH)2 under different conditions, and the thermo- and SO4 2−-responsive behaviors should be ascribed to the structure change of PDEA hydrogels in PDEA-GOD outermost layers under different conditions. The multiple stimuli-responsive films could be further used to realize multiply switchable electrochemical oxidization of glucose catalyzed by GOD immobilized in the films with Fc(COOH)2 in solution as the mediator. The films with the unique binary architecture may open a new way to establish a foundation for fabricating a novel type of multi-controllable biosensors based on bioelectrocatalysis with immobilized enzymes. [Copyright &y& Elsevier]