Molecularly Designed Layer-by-Layer (LbL) Films to Detect Catechol Using Information Visualization Methods Pedro H. B. Aoki, † Priscila Alessio, † Leonardo N. Furini, † Carlos J. L. Constantino, † Ta ́ cito T. A. T. Neves, ‡ Fernando V. Paulovich, ‡ Maria Cristina F. de Oliveira, ‡ and Osvaldo N. Oliveira, Jr.* ,§ † Faculdade de Ciê ncias e Tecnologia, UNESP, Presidente Prudente, SP, 19060-900, Brazil ‡ Instituto de Ciê ncias Matema ́ ticas e de Computaç ã o, USP, CP 668, 13560-970 Sã o Carlos, SP, Brazil § Instituto de Física de Sã o Carlos, SP, USP, CP 369, 13560-970 Sã o Carlos, Brazil * S Supporting Information ABSTRACT: The control of molecular architectures has been exploited in layer-by-layer (LbL) films deposited on Au interdigitated electrodes, thus forming an electronic tongue (e-tongue) system that reached an unprecedented high sensitivity (down to 10 -12 M) in detecting catechol. Such high sensitivity was made possible upon using units containing the enzyme tyrosinase, which interacted specifically with catechol, and by processing impedance spectroscopy data with information visualization methods. These latter methods, including the parallel coordinates technique, were also useful for identifying the major contributors to the high distinguish- ing ability toward catechol. Among several film architectures tested, the most efficient had a tyrosinase layer deposited atop LbL films of alternating layers of dioctadecyldimethylammonium bromide (DODAB) and 1,2-dipalmitoyl-sn-3-glycero-fosfo-rac-(1-glycerol) (DPPG), viz., (DODAB/DPPG) 5 /DODAB/Tyr. The latter represents a more suitable medium for immobilizing tyrosinase when compared to conventional polyelectrolytes. Furthermore, the distinction was more effective at low frequencies where double-layer effects on the film/liquid sample dominate the electrical response. Because the optimization of film architectures based on information visualization is completely generic, the approach presented here may be extended to designing architectures for other types of applications in addition to sensing and biosensing. ■ INTRODUCTION The design of new supramolecular materials has been at the forefront of materials science, especially in nanotechnology efforts. There are many methods of producing such materials, but there has been an emphasis on fabrication techniques that allow for control of molecular architectures, including the Langmuir-Blodgett (LB) 1,2 and the electrostatic layer-by-layer (LbL) 3,4 methods. In some cases, the final properties of the fabricated materials can mimic the highest-performance natural materials, as in the LbL films made with carbon nanotube composites 5 and clay nanosheets 6 that reached record strength. Efficient polymer light-emitting diodes were obtained with LbL films where molecular-scale engineering of charge-injection layers was exploited to generate graded electronic profiles. 7 In fact, for organic electronics devices the LbL method has been proven suitable to control exciton diffusion 8 and energy transfer. 9 Other examples of controlled architectures include film coatings with antireflection, antifogging, and self-cleaning properties, produced with all-nanoparticle LbL films, 10 and the hollow spheres with controlled size and shape that can be used in drug delivery. 11 Indeed, the search for new biological applications has driven developments in novel architectures, in various instances incorporating proteins 12 or serving to control cell interactions. 13 LbL assembly was also exploited to produce functional electrically conducting networks starting with 1D nanostructures with such a degree of control that cross points in the networks could be addressed individually. 14 A common feature in the work mentioned above is the combination of distinct materials in a single film architecture, normally found when seeking synergy among the film components. The importance of controlling architecture has led to the coinage of the term nanoarchitectonics, 15,16 which is defined as “a technology system to be used for arranging nanoscale structural units, i.e., the nanostructure unit as a group of atoms or molecules in a predesignated configuration”. 17 Numerous materials can indeed be explored within the nanoarchitectonics paradigm, from the obvious organic Special Issue: Interfacial Nanoarchitectonics Received: November 14, 2012 Revised: January 1, 2013 Published: January 28, 2013 Article pubs.acs.org/Langmuir © 2013 American Chemical Society 7542 dx.doi.org/10.1021/la304544d | Langmuir 2013, 29, 7542-7550