Transmembrane photosynthetic proteins, Photosystem I (PSI) are nano-scale biological photodiodes that enable light-activated unidirectional electron flow. The robust photochemical properties make PSI a promising candidate for harnessing solar energy.1-3 However, the role of natural membrane confinements of PSI in orchestrating this photoactivated charge separation with near unity quantum efficiency is ill-understood yet, imperative for the rational design of PSI-based energy conversion devices. Motivated by this lack of fundamental understanding, herein we investigate the photoactivity of biomimetic constructs of cyanobacterial PSI encapsulated within solid-supported lipid bilayers (SLB) assembled on electrodes. PSI-confined SLBs are assembled from PSI-proteoliposomes that are synthesized from our recently developed facile routes for engineering negatively charged phospholipid (DPhPG) bilayer membranes.4 Absorption/fluorescence spectroscopy and direct visualization using atomic force microscopy (AFM) have already demonstrated the formation of biomimetic PSI-proteoliposomes that indicate alterations in photo responses as evident from their unique emission signatures.5 In this talk, we present detailed chronoamperometry measurements to investigate the corresponding photocurrent variations arising from the aforementioned PSI confinements in SLBs supported on self-assembled monolayer (SAM) substrates. These measurements, in conjunction with cryo-transmission electron microscopy (cryo-TEM), AFM imaging and force spectroscopy, allow for direct visualizations and detection of SLBs of PSI-proteoliposomes on the substrates. Our results indicate the role of microenvironment alterations heretofore not considered in triggering ~ 4-5 fold enhancements in photocurrents generated from PSI complexes under SLB confinements as compared to those from a dense monolayer of equivalent concentrations of PSI on SAM substrates.6 Such studies provide deeper insight into the functional roles of membrane scaffoldings in optimizing charge transport efficiencies in photosynthetic proteins.
(1) T. Bennett, H. Nirooman, R. Pamu, I. Ivanov, D. Mukherjee, B. Khomami; PCCP, 2016, 18, 8512.
(2) D. Mukherjee, M. May, B. Khomami; J. Coll. Interf. Sci., 2011, 358, 477.
(3) D. Mukherjee, M. May, M. Vaughn, B. D. Bruce, B. Khomami; Langmuir, 2010, 26, 16048.
(4) H. Niroomand, G. A. Venkatesan, S. A. Sarles, D. Mukherjee, B. Khomami; J. Membr. Biol., 2016, 249, 523.
(5) H. Niroomand, D. Mukherjee, B. Khomami; Scientific Rep., 2017, 7.
(6) H. Niroomand, R. Pamu, D. Mukherjee, B. Khomami; Nature Nanotech., 2017, Submitted.