& Gold Nanoparticles

Effect of Gold Nanoparticles on the Structure and Electron-Transfer Characteristics of Glucose Oxidase Redox Polyelectrolyte-Surfactant Complexes

M. Lorena Cortez,[a, b] Waldemar Marmisoll�,[a] Diego Pallarola,[b] L�a I. Pietrasanta,[c]

Daniel H. Murgida,[a] Marcelo Ceol�n,[b] Omar Azzaroni,*[b] and Fernando Battaglini*[a]

Abstract: Efficient electrical communication between redoxproteins and electrodes is a critical issue in the operationand development of amperometric biosensors. The presentstudy explores the advantages of a nanostructured redox-active polyelectrolyte–surfactant complex containing [Os-(bpy)2Clpy]

2 + (bpy = 2,2’-bipyridine, py = pyridine) as theredox centers and gold nanoparticles (AuNPs) as nanodo-mains for boosting the electron-transfer propagationthroughout the assembled film in the presence of glucoseoxidase (GOx). Film structure was characterized by grazing-incidence small-angle X-ray scattering (GISAXS) and atomicforce microscopy (AFM), GOx incorporation was followed bysurface plasmon resonance (SPR) and quartz-crystal microba-

lance with dissipation (QCM-D), whereas Raman spectroelec-trochemistry and electrochemical studies confirmed the abil-ity of the entrapped gold nanoparticles to enhance the elec-tron-transfer processes between the enzyme and the elec-trode surface. Our results show that nanocomposite films ex-hibit five-fold increase in current response to glucosecompared with analogous supramolecular AuNP-free films.The introduction of colloidal gold promotes drastic meso-structural changes in the film, which in turn leads to a rigid,amorphous interfacial architecture where nanoparticles,redox centers, and GOx remain in close proximity, thusimproving the electron-transfer process.

Introduction

The development of novel materials and methods aiming toimprove the sensitivity, selectivity, reliability, and time responseof biosensors has placed these devices in the center of the an-alytical scene. Within this context, amperometric sensors arequite appealing as they can fulfill those requirements[1] withthe additional potential to enable miniaturization, a fundamen-tal requisite for implantable medical devices.[2] A key issue inthe development of any biosensor is its sensitivity, which inthe case of amperometric biosensors is controlled by several

factors, such as substrate diffusion, redox mediator features,and the electrical communication between the recognition ele-ment and the other device components. The most studied ex-ample is the glucose biosensor, where the efficient electricalcommunication between the biological recognition element(GOx) and the transducer (the mediator/working electrode in-terface) is often challenged by the enzyme’s insulating shell ofamino acids. To overcome this limitation, a wide variety of sur-face-functionalization strategies, such as self-assembled mono-layers,[3] polymers,[4] proteic coatings,[5] and hydrogels,[6] havebeen explored to preserve the native structure and function ofthe incorporated enzyme.[7]

In the past several years, carbon nanotubes[8] (CNTs) andgold nanoparticles[9] (AuNPs) have shown excellent electrocata-lytic properties, which were immediately applied to the devel-opment of biosensors.[10] Particularly, the inclusion of AuNPswas intended to allow direct electron transfer, in which theelectrons can directly tunnel from the catalytic center of theenzyme to the surface of the current collector,[11] even thoughthis strategy presents some limitations.[12] Another approach isto use them as catalytic domains in the layer-by-layer (LbL) as-sembly of polyelectrolyte multilayers to create composite filmsat electrode interfaces.[13] As an alternative,[14] polyelectrolyte–surfactant complexes[15] display similar characteristics regardingsurface functionalization while, at the same time, exhibitingcertain benefits concerning the initial modification of the elec-trode surface.[16] In recent years, we have begun a systematic

[a] Dr. M. L. Cortez, Dr. W. Marmisoll�, Dr. D. H. Murgida, Dr. F. BattagliniINQUIMAE - Departamento de Qu�mica Inorg�nica Anal�tica yQu�mica F�sica, Facultad de Ciencias Exactas y NaturalesUniversidad de Buenos Aires, CONICETCiudad Universitaria, Pabell�n 2C1428EHA Buenos Aires (Argentina)E-mail : battagli@qi.fcen.uba.ar

[b] Dr. M. L. Cortez, Dr. D. Pallarola, Dr. M. Ceol�n, Dr. O. AzzaroniInstituto de Investigaciones Fisicoqu�micas Tas y Aplicadas (INIFTA)Departamento de Qu�mica, Facultad de Ciencias ExactasUniversidad Nacional de La Plata, CONICETCC 16 Suc. 4 (1900) La Plata (Argentina)E-mail : azzaroni@inifta.unlp.edu.ar

[c] Dr. L. I. PietrasantaCentro de Microscop�as Avanzadas and Departamento de F�sicaFacultad de Ciencias Exactas y Naturales, Universidad de Buenos AiresCiudad Universitaria, Pabell�n 1C1428EHA Buenos Aires (Argentina)

Chem. Eur. J. 2014, 20, 13366 – 13374 � 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim13366

Full PaperDOI: 10.1002/chem.201402707