Onur Parlak

Template-Directed Hierarchical Self-Assembly of Graphene Based Hybrid Structure for Electrochemical Biosensing

A template-directed self-assembly approach, using functionalised graphene as a fundamental building block to obtain a hierarchically ordered graphene-enzyme-nanoparticle bioelectrode for electrochemical biosensing, is reported. An anionic surfactant was used to prepare a responsive, functional interface and direct the assembly on the surface of the graphene template. The surfactant molecules altered the electrostatic charges of graphene, thereby providing a convenient template-directed assembly approach to a free-standing planar sheet of sp(2) carbons. Cholesterol oxidase and cholesterol esterase were assembled on the surface of graphene by intermolecular attractive forces while gold nanoparticles are incorporated into the hetero-assembly to enhance the electro-bio-catalytic activity. Hydrogen peroxide and cholesterol were used as two representative analytes to demonstrate the electrochemical sensing performance of the graphene-based hybrid structure. The bioelectrode exhibited a linear response to H2O2 from 0.01 to 14 mM, with a detection limit of 25 nM (S/N=3). The amperometric response with cholesterol had a linear range from 0.05 to 0.35 mM, sensitivity of 3.14 µA/µM/cm(2) and a detection limit of 0.05 µM. The apparent Michaelis-Menten constant (Km(app)) was calculated to be 1.22 mM. This promising approach provides a novel methodology for template-directed bio-self-assembly over planar sp(2) carbons of a graphene sheet and furnishes the basis for fabrication of ultra-sensitive and efficient electrochemical biosensors.

On/off-switchable zipper-like bioelectronics on a graphene interface.

An on/off-switchable graphene-based zipper-like interface is architectured for efficient bioelectrocatalysis. The graphene interface transduces a temperature input signal into structural changes of the membrane, resulting in the amplification of electrochemical signals and their transformation into the gated transport of molecules through the membrane.

Structuring Au nanoparticles on two-dimensional MoS2 nanosheets for electrochemical glucose biosensors.

Two-dimensional (2D) bioelectronics is an emerging field of research which fuses the advantages of 2D nanomaterials with those of nanobiotechnology. Due to the various physical and chemical properties present in layered counterparts of 2D materials, including high charge density, large surface area, remarkable electron mobility, ready electron transport, sizeable band gaps and ease of hybridisation, they are set to become a versatile tool to fabricate sensitive and selective novel biodevices, which might offer an unique advantages to tackle key energy, medical and environmental issues. Current 2D bioelectronics research is focused on the design of simple-to-use and cheaper biodevices, while improving their selectivity, sensitivity and stability. However, current designs generally suffer from a lack of efficiency, relatively low sensitivity, slow electron transfer kinetics, high background charging current and low current density arising from poor mass transport. Here, we report a nanoparticle-structured MoS2 nanosheet as an ideal semiconductor interface, which is able to form a homogenous layer on the electrode surface for the assembly of gold nanoparticles. This not only enhances electrocatalytic reactions, but also provides excellent electrochemical properties such as high faradic-to-capacitive current ratios, high current density and electron mobility, and faster mass transport, due to the dominance of radial diffusion. The MoS2/Au NPs/GOx bioelectrode exhibits a linear response to glucose from 0.25 to 13.2mM, with a detection limit of 0.042µM (S/N=3) and sensitivity of 13.80µA/µM/cm2.

pH-induced on/off-switchable graphene bioelectronics

Switchable interfaces can deliver functionally reversible reactivity with their corresponding analytes, which allows one to positively respond to the activity of biological elements, including enzymes and other biomolecules, through an encoded stimulus. We have realized this by the design of stimuli-responsive graphene interfaces for the pH-encoded operation of bioelectronics. Herein, we have demonstrated stimuli-responsive graphene interfaces for the pH-encoded operation of bioelectronics. The resulting switchable interfaces are capable of the highly specific, on-demand operation of biosensors, which has significant potential in a wide range of analytical applications.

Switchable Bioelectrocatalysis Controlled by Dual Stimuli-Responsive Polymeric Interface

The engineering of bionanointerfaces using stimuli-responsive polymers offers a new dimension in the design of novel bioelectronic interfaces. The integration of electrode surfaces with stimuli-responsive molecular cues provides a direct control and ability to switch and tune physical and chemical properties of bioelectronic interfaces in various biodevices. Here, we report a dual-responsive biointerface employing a positively responding dual-switchable polymer, poly(NIPAAm-co-DEAEMA)-b-HEAAm, to control and regulate enzyme-based bioelectrocatalysis. The design interface exhibits reversible activation-deactivation of bioelectrocatalytic reactions in response to change in temperature and in pH, which allows manipulation of biomolecular interactions to produce on/off switchable conditions. Using electrochemical measurements, we demonstrate that interfacial bioelectrochemical properties can be tuned over a modest range of temperature (i.e., 20-60 °C) and pH (i.e., pH 4-8) of the medium. The resulting dual-switchable interface may have important implications not only for the design of responsive biocatalysis and on-demand operation of biosensors, but also as an aid to elucidating electron-transport pathways and mechanisms in living organisms by mimicking the dynamic properties of complex biological environments and processes.

Acetylene-sourced CVD-synthesised catalytically active graphene for electrochemical biosensing.

In this study, we have demonstrated the use of chemical vapour deposition (CVD) grown-graphene to develop a highly-ordered graphene-enzyme electrode for electrochemical biosensing. The graphene sheets were deposited on 1.00mm thick copper sheet at 850°C using acetylene (C2H2) as carbon source in an argon (Ar) and nitrogen (N2) atmosphere. An anionic surfactant was used to increase wettability and hydrophilicity of graphene; thereby facilitating the assembly of biomolecules on the electrode surface. Meanwhile, the theoretical calculations confirmed the successful modification of hydrophobic nature of graphene through the anionic surface assembly, which allowed high-ordered immobilisation of glucose oxidase (GOx) on the graphene. The electrochemical sensing activities of the graphene-electrode was explored as a model for bioelectrocatalysis. The bioelectrode exhibited a linear response to glucose concentration ranging from 0.2 to 9.8mM, with sensitivity of 0.087µA/µM/cm2 and a detection limit of 0.12µM (S/N=3). This work sets the stage for the use of acetylene-sourced CVD-grown graphene as a fundamental building block in the fabrication of electrochemical biosensors and other bioelectronic devices.

Organic Electronics for Point-of-Care Metabolite Monitoring

In this review we focus on demonstrating how organic electronic materials can solve key problems in biosensing thanks to their unique material properties and implementation in innovative device configurations. We highlight specific examples where these materials solve multiple issues related to complex sensing environments, and we benchmark these examples by comparing them to state-of-the-art commercially available sensing using alternative technologies. We have categorized our examples by sample type, focusing on sensing from body fluids in vitro and on wearable sensors, which have attracted significant interest owing to their integration with everyday life activities. We finish by describing a future trend for in vivo, implantable sensors, which aims to build on current progress from sensing in biological fluids ex vivo.

Molecularly selective nanoporous membrane-based wearable organic electrochemical device for noninvasive cortisol sensing

A new wearable nanoporous organic electrochemical device used as a medical diagnostics tool for noninvasive hormone sensing. Wearable biosensors have emerged as an alternative evolutionary development in the field of healthcare technology due to their potential to change conventional medical diagnostics and health monitoring. However, a number of critical technological challenges including selectivity, stability of (bio)recognition, efficient sample handling, invasiveness, and mechanical compliance to increase user comfort must still be overcome to successfully bring devices closer to commercial applications. We introduce the integration of an electrochemical transistor and a tailor-made synthetic and biomimetic polymeric membrane, which acts as a molecular memory layer facilitating the stable and selective molecular recognition of the human stress hormone cortisol. The sensor and a laser-patterned microcapillary channel array are integrated in a wearable sweat diagnostics platform, providing accurate sweat acquisition and precise sample delivery to the sensor interface. The integrated devices were successfully used with both ex situ methods using skin-like microfluidics and on human subjects with on-body real-sample analysis using a wearable sensor assembly.

Interfacing Graphene for Electrochemical Biosensing

The integration of carbon-based materials to bridge the biological and electronic worlds has fundamentally changed the understanding of how to generate functional bioelectronic devices, including biosensors, biofuel cells and bioactuators, and also opened up a new window for the future of bioelectronics.

Switchable bioelectronics on graphene interface (Presentation Recording)

Smart and flexible bioelectronics on graphene have emerged as a new frontier in the field of biosensors and bioelectronics. Graphene has begun to be seen as an ideal signal transducer and a promising alternative for the production of low-cost bioelectronic devices.1-2 However, biological systems used in these devices suffer from a lack of control and regulation. There is an obvious need to develop “switchable” and “smart” interfaces for both fundamental and applied studies. Here, we report the fabrication of a stimuli-responsive graphene interface, which is used to regulate biomolecular reactions. The present study aims to address the design and development of a novel auto-switchable graphene bio-interface that is capable of positively responding, by creating smart nanoarchitectures. By changing the external conditions such as temperature, light and pH of the medium, we acheived control of the biochemical interactions. In the negative mode, access of an associated enzyme to its substrate is largely restricted, resulting in a decrease in the diffusion of reactants and the consequent activity of the system. In contrast, the biosubstrate could freely access the enzyme facilitating bioelectrocatalysis in a positive response. Using electrochemical techniques, we demonstrated that interfacial bio-electrochemical properties can be tuned by modest changes in conditions. Such an ability to independently regulate the behaviour of the interface has important implications for the design of novel bioreactors, biofuel cells and biosensors with inbuilt self-control features.