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Ravi Pamu1 Venkatanarayana Prasad Sandireddy2 Ramki Kalyanaraman2 3 Bamin Khomami1 2 Dibyendu Mukherjee1 2

1, The University of Tennessee, Knoxville, Tennessee, United States
2, The University of Tennessee, Knoxville, Tennessee, United States
3, The University of Tennessee, Knoxville, Tennessee, United States

Photosystem I (PS I), the photosynthetic membrane protein, undergoes light activated (λ=680 nm) charge separation and unidirectional electron transfer with near-unity quantum efficiency. The robust photoelectrochemical (PEC) activities of PSI make it an ideal biomaterial for bio-hybrid photovoltaic and/or, optoelectronic devices.1,2 But, the first step towards rational design of such devices requires systematic electrochemical characterizations of PSI assembly in tailored biotic-abiotic interfaces.3 In the past, such interfaces have been created using plasmonic metal nanostructures to tune optoelectronic properties of molecular fluorophores. Herein, we investigate plasmon-enhanced photocurrents from PSI assembled with plasmonic Ag and Au nanopatterned structures. Based on our recent works, we present the first-ever experimental verification of plasmon-induced photocurrent enhancements from PSI attached to Fischer patterns of Ag nano-pyramids (Ag-NP) whose resonance peaks are tuned to match the PSI absorption peaks at ~450 and ~680 nm. Detailed atomic force microscopy (AFM) characterizations reveal both the background Fischer patterns and the PSI immobilization on them. The plasmon enhanced photocurrents indicate enhancement factors of ~6.5 and ~5.8 as compared to PSI assembly on planar Ag substrates for nominal excitation wavelengths of 660 and 470 nm respectively.4 The comparable enhancement factors from both 470 nm and 660 nm excitations, in spite of a significantly weaker plasmon absorption peak at ~450 nm for the Ag-NP structures, can be explained by previously reported observations of excessive plasmon-induced fluorescence emission losses from PSI in red region of the excitation wavelengths. Based on these results, our on-going efforts are directed towards the systematic investigation of the effect of varying plasmon peak positions tuned with designer nanopatterns on the plasmon-enhanced photocurrents from PSI assembly on these structures. We aim to carry out systematic studies on the role of tailored Ag and Au nanopatterned substrates designed with E-beam lithography for specific peak plasmonic resonance peaks and the distance of separation between PSI to the plasmonic surfaces on plasmon-induced photocurrents from PSI complexes. Aforementioned work will shine light on the fundamental biophysics behind the alterations in excitation energy transfer mechanism among chlorophylls in PSI under plasmon-induced localized electric field.<!--![endif]---->
References:
(1) D.Mukherjee, M. May, B. Khomami; J. Coll. Interf. Sci., 2011, 358, 477..
(2) D. Mukherjee, M. May, M. Vaughn, B. D. Bruce, B. Khomami; Langmuir, 2010, 26, 16048.
(3) T. Bennett, H. Nirooman, R. Pamu, I. Ivanov, D. Mukherjee, B. Khomami; PCCP, 2016, 18, 8512.
(4) R. Pamu, B. Lawrie, R. Kalyanaraman, D. Mukherjee, B. Khomami;Nature Comm., 2016, Submitted.

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