Hongyun Liu

Multiple-Stimuli Responsive Bioelectrocatalysis Based on Reduced Graphene Oxide/Poly(N-isopropylacrylamide) Composite Films and Its Application in the Fabrication of Logic Gates

In the present work, reduced graphene oxide (rGO)/poly(N-isopropylacrylamide) (PNIPAA) composite films were electrodeposited onto the surface of Au electrodes in a fast and one-step manner from an aqueous mixture of a graphene oxide (GO) dispersion and N-isopropylacrylamide (NIPAA) monomer solutions. Reflection-absorption infrared (IR) and Raman spectroscopies were employed to characterize the successful construction of the rGO/PNIPAA composite films. The rGO/PNIPAA composite films exhibited reversible potential-, pH-, temperature-, and sulfate-sensitive cyclic voltammetric (CV) on-off behavior to the electroactive probe ferrocenedicarboxylic acid (Fc(COOH)2). For instance, after the composite films were treated at -0.7 V for 7 min, the CV responses of Fc(COOH)2 at the rGO/PNIPAA electrodes were quite large at pH 8.0, exhibiting the on state. However, after the films were treated at 0 V for 30 min, the CV peak currents became much smaller, demonstrating the off state. The mechanism of the multiple-stimuli switchable behaviors for the system was investigated not only by electrochemical methods but also by scanning electron microscopy and X-ray photoelectron spectroscopy. The potential-responsive behavior for this system was mainly attributed to the transformation between rGO and GO in the films at different potentials. The film system was further used to realize multiple-stimuli responsive bioelectrocatalysis of glucose catalyzed by the enzyme of glucose oxidase and mediated by the electroactive probe of Fc(COOH)2 in solution. On the basis of this, a four-input enabled OR (EnOR) logic gate network was established.

Logic Gate System with Three Outputs and Three Inputs Based on Switchable Electrocatalysis of Glucose by Glucose Oxidase Entrapped in Chitosan Films

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.

A novel strategy to improve the sensitivity of antibiotics determination based on bioelectrocatalysis at molecularly imprinted polymer film electrodes

A new strategy for the sensitive detection of kanamycin (KA) and other antibiotics based on molecularly imprinted polymer (MIP) and bioelectrocatalysis was developed in the present study. The KA-polypyrrole MIP films were electropolymerized on the surface of pyrolytic graphite (PG) electrodes, with pyrrole (PY) serving as the monomer and KA as the template. Because KA is electro-inactive, electroactive K3[Fe(CN)6] was used as the probe in the cyclic voltammetric (CV) measurements. The difference of the CV reduction peaks of K3[Fe(CN)6] at electrodes between the MIP films after KA removal and KA-rebinding MIP films could thus be used to determine KA quantitatively. When horseradish peroxidase (HRP) and H2O2 were added into the testing solution, the detection sensitivity of the system was greatly amplified because the electrochemical reduction of H2O2 could be catalyzed by HRP and mediated by K3[Fe(CN)6]. With the bioelectrocatalysis amplification, the limit of detection (LOD) for KA fell as low as 28 nM, approximately two orders of magnitude lower than that for the MIP films in the absence of enzymatic catalysis. The strategy demonstrated the generality. Not only KA but also other antibiotics, such as oxytetracycline (OTC), could be determined by this method. More significantly, in addition to the K3[Fe(CN)6]-HRP-H2O2 system, other bioelectrocatalysis systems, such as Fc(COOH)2-GOD-glucose (Fc(COOH)2=ferrocenedicarboxylic acid, GOD=glucose oxidase), could also be used to amplify the CV signal and realize the sensitive detection of KA for the MIP film system, thereby illustrating the great potential and prospects of the strategy.

Enzymatic logic calculation systems based on solid-state electrochemiluminescence and molecularly imprinted polymer film electrodes

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 0.7V 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.

A resettable and reprogrammable keypad lock based on electrochromic Prussian blue films and biocatalysis of immobilized glucose oxidase in a bipolar electrode system

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 (Vtot) 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 Vtot 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 Vtot between +2.5 and -1.5V. Based on these, a keypad lock was developed with AA, glucose and Vtot 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.

A resettable and reprogrammable biomolecular keypad lock with dual outputs based on glucose oxidase–Au nanoclusters–Prussian blue nanocomposite films on an electrode surface

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 H2O2 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 Resettable Keypad Lock with Visible Readout Based on Closed Bipolar Electrochemistry and Electrochromic Poly(3-methylthiophene) Films

A closed bipolar electrode (BPE) system was developed with electrochromic poly(3-methylthiophene) (PMT) films electropolymerized on the ITO/rGO electrode as one pole of BPE in the reporting reservoir and the bare ITO electrode as another pole of BPE in the analyte reservoir, in which rGO represents reduced graphene oxide. Under a suitable driving voltage (Vtot), the electrochemical reduction/oxidation of electroactive probes, such as H2O2/glutathione (Glu), in the analyte reservoir could induce the reversible color change of PMT films in the reporting reservoir between blue and red. Based on this, a keypad lock with H2O2 , Glu, and Vtot =-3.0 V as the three inputs and the color change of PMT films as the visible output was established. This system was easily operated and did not need to synthesize the complex compounds or DNA molecules. The security system was easy to reset and could be used repeatedly.

An enzymatic calculation system based on electrochemiluminescence and fluorescence of luminol and cyclic voltammetry of ferrocene methanol

In this work, a biomolecular calculation system was developed based on electrochemiluminescence (ECL) and fluorescence emission (FL) of luminol and cyclic voltammetry (CV) of ferrocene methanol (FMA). When triethylamine (TEA) was added in luminol solution as a coreactant, a great ECL peak at 1.1 V was observed. While the further addition of enzymatic system, esterase/ethyl butyrate (EB), would significantly lower the ECL response. On the other hand, TEA could quench the FL signal of luminol at 430 nm, while the injection of esterase/EB in the luminol solution could enhance the FL signal. Furthermore, FMA exhibited a CV peak pair at 0.2 V and could decrease the ECL signal greatly in the luminol/TEA solution. Based on these interesting results, a 3-input and 5-output biomolecular logic gate was established with TEA, FMA and esterase/EB as inputs and the ECL, CV and FL signals as outputs. Moreover, some nonarithmetic logic devices, such as an encoder, a decoder, a 3-input keypad lock and two dual transfer gates were elaborately designed on the same platform. This work presented a new example of how the complexity of biocomputing system could be enhanced either by increasing the number of outputs of traditional logic gates or by fabricating some nonarithmetic logic devices based on the same simple electrochemical system.