Bioelectrocatalysis DOI: 10.1002/anie.200604082 Adaptive Orientation of Multifunctional Nanowires for Magnetic Control of Bioelectrocatalytic Processes** Óscar A. Loaiza, Rawiwan Laocharoensuk, Jared Burdick, MarcellaC. Rodríguez, JoseM. Pingarron, Maria Pedrero, and Joseph Wang* Bioelectronics, the coupling of biomaterials and electronic devices, is a major interdisciplinary research area. [1,2] In one rapidly growing area of bioelectronics, magneto-bioelec- tronics, external magnetic fields are used to control bioelec- trochemical processes. [2] Hirsch et al. [3] were the first to report on magnetoswitchable bioelectrocatalysis in connection to relay-modified magnetic spheres. Recent developments in the use of functionalized microparticles for switching bioelectro- catalytic reactions (in the presence of soluble enzymes) have been reviewed. [2] New adaptive nanomaterials capable of providing semi-analogue control of bioelectrochemical pro- cesses (in addition to “on/off” switching) should greatly enhance the power and capabilities of magneto-bioelec- tronics. Here we wish to report on the use of enzyme-function- alized nanowires for the magnetic control of bioelectrocata- lytic transformations, without removal of the biocatalyst from the surface. Nanowires have recently received considerable attention as potential components for functional nanoelec- tronic devices. [4] We describe here how nanowires can add a unique dimension to magneto-bioelectronics, as they facili- tate reversible modulation and fine-tuning of bioelectrocat- alytic processes, in addition to the “on/off” switching common to functionalized magnetic spheres. [2,3] Recently we demon- strated that catalytic nickel nanowires can be used for magnetic control of the electrochemical reaction of methanol through reversible changes in the nanowire orientation. [5] In the present work we used two-segment gold/nickel nano- wires—prepared by a template-guided synthesis and func- tionalized with glucose oxidase (GOx)—for controlling the biocatalytic oxidation of glucose, in connection to a surface- bound ferrocene (Fc) electron-transfer mediator. Spatially selective functionalization with the enzyme was accomplished by application of a self-assembled monolayer (SAM) of mercaptoacetic acid (MAA) onto the gold segment, followed by electrostatic attraction of the polyethyleneimine (PEI) polycation and of the negatively charged enzyme. Figure 1 depicts the new setup for nanowire-based magnetoswitchable tuning of bioelectrocatalytic processes. Positioning the func- tionalized nanowire in the horizontal orientation ensures effective contact of the enzyme and the surface-bound mediator, and leads to a mediated activation of GOx (Figure 1A). Switching the nanowires to the vertical position greatly hinders the communication between the nanowire- confined GOx and the surface Fc relay (Figure 1B), while retracting the nanowires from the surface (by moving the magnetic field) totally blocks the mediated activation of GOx (Figure 1C). Such magnetically modulated bioelectrocatalyt- ic transformations can be repeated multiple times when the surface orientation of the GOx-functionalized nanowires is switched between the vertical and horizontal positions. To the best of our knowledge, this is the first example illustrating the reorientation of a surface-confined enzyme for tuning bio- electrocatalytic transformations. This adaptive orientation of biocatalytic nanowires holds great promise for the external control of devices ranging from biosensors to biofuel cells, in response to specific needs. Multisegment nanowires offer the Figure 1. Nanowire-based magnetoswitchable bioelectrocatalytic pro- cesses. In the experimental setup with the GOx–gold/nickel nanowires and the Fc-modified surface, the magnetic field can be oriented in the horizontal (A), vertical (B), and “off” (C) positions, for activating (A), hindering (B), and blocking (C) the communication between the nanowire-confined GOx and the surface Fc relay. The corresponding cyclic voltammograms are also shown. [*] Ó. A. Loaiza, R. Laocharoensuk, J. Burdick, Dr. M. C. Rodríguez, Prof. Dr. J. Wang Departments of Chemical Engineering and Chemistry and Biochemistry Biodesign Institute Arizona State University Tempe, AZ 85287 (USA) Fax: (+ 1)480-727-0412 E-mail: joseph.wang@asu.edu Dr. J. M. Pingarron, Dr. M. Pedrero Universidad Complutense Madrid Facultad de Ciencias Químicas 28040 Madrid (Spain) [**] This research was supported by grants from the National Science Foundation (grant number CHE 0506529) and the US EPA (STAR Program). Communications 1508 # 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2007, 46, 1508 –1511