PALAZZO ET AL . VOL. 8 ’ NO. 8 ’ 7834–7845 ’ 2014 www.acsnano.org 7834 July 31, 2014 C 2014 American Chemical Society Electronic Transduction of Proton Translocations in Nanoassembled Lamellae of Bacteriorhodopsin Gerardo Palazzo, †,‡, * Maria Magliulo, † Antonia Mallardi, § Maria Daniela Angione, †, ) Danka Gobeljic, ^,4 Gaetano Scamarcio, ^ Emiliano Fratini, ‡,X Francesca Ridi, ‡,X and Luisa Torsi †,‡, * † Dipartimento di Chimica, Università degli Studi di Bari “A. Moro”, Via Orabona, 4, 70126 Bari, Italy, ‡ CSGI (Center for Colloid and Surface Science), Units of Bari and Florence, Italy, § CNR-IPCF, Istituto per i Processi Chimico-Fisici, Via Orabona, 4, 70126 Bari, Italy, ^ CNR-IFN and Dipartimento Interateneo di Fisica, Università degli Studi di Bari “A. Moro”, Via Orabona, 4, 70126 Bari, Italy, and X Dipartimento di Chimica “Ugo Schiff”, Università degli Studi di Firenze, Via della Lastruccia, 3, 50019 Sesto Fiorentino, Italy. M.M. and M.D.A. fabricated the devices and carried out the electrical, optical, and sensing measurements. A.M. prepared and characterized the PM suspensions and discussed the relevant data. E.F. and F.R. performed the GISAXS and AFM experiments. G.S. and D.G. performed the Raman measurements. L.T. and G.P. conceived and wrote the manuscript. ) Present address: (M. Daniela) Angione School of Chemistry and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), University of Dublin Trinity College, College Green, Dublin, Dublin D2, Ireland. 4 Present address: (D. Gobeljic) Institute for Material Science and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Universitätsstraße 15, 45141 Essen, Germany. B acteriorhodopsin (bR) is a small (∼26 kDa) transmembrane protein that transduces light energy into the chemical free energy of a proton gradient occurring across the cell membrane that sustains, in vivo, the cell life through ATP synthesis. 1 bR has a rather simple structure consisting of a single polypeptidic chain folded into seven-membrane-spanning R-helices in which a single molecule of retinylidene chromophore (retinal) is cova- lently bound to a lysine residue of the poly- peptide through an imine known as a Schiff base. This is the light-absorbing moiety responsible for initiating a photoinduced proton translocation process. The overall cycle is initiated as the retinal chromophore absorbs a green-yellow photon (hν), triggering a rather complicated photo- cycle. 2 The primary photochemical event involves the isomerization of the retinal from all-trans to 13-cis, producing the first trap- pable intermediate state, and it proceeds through several states characterized by dif- ferent absorbance maxima. 3 The longest living M 412 intermediate, also characterized by the most blue-shifted absorbance, is the deprotonated Schiff base. When bR proteins are kept dry, the photocycle stops at the M-state, before the Schiff base can be repro- tonated, due to the shortage of protons. Ultrafast photoinduced charge separation * Address correspondence to luisa.torsi@uniba.it; gerardo.palazzo@uniba.it. Received for review March 10, 2014 and accepted July 31, 2014. Published online 10.1021/nn503135y ABSTRACT An organic field-effect transistor (OFET) integrating bacteriorhodop- sin (bR) nanoassembled lamellae is proposed for an in-depth study of the proton translocation processes occurring as the bioelectronic device is exposed either to light or to low concentrations of general anesthetic vapors. The study involves the morphological, structural, electrical, and spectroscopic characterizations necessary to assess the functional properties of the device as well as the bR biological activity once integrated into the functional biointerlayer (FBI)-OFET structure. The electronic transduction of the protons phototranslocation is shown as a current increase in the p-type channel only when the device is irradiated with photons known to trigger the bR photocycle, while Raman spectroscopy reveals an associated CdC isomer switch. Notably, higher energy photons bring the cis isomer back to its trans form, switching the proton pumping process off. The investigation is extended also to the study of a PM FBI-OFET exposed to volatile general anesthetics such as halothane. In this case an electronic current increase is seen upon exposure to low, clinically relevant, concentrations of anesthetics, while no evidence of isomer-switching is observed. The study of the direct electronic detection of the two different externally triggered proton translocation effects allows gathering insights into the underpinning of different bR molecular switching processes. KEYWORDS: organic field-effect transistors . conformational changes . bioelectronic device . bacteriorhodopsin . electronic sensing . self-assembly . proton-pumping mechanism ARTICLE