Spectrally selective fluorescence imaging of Chlorobaculum tepidum reaction centers conjugated to chelator-modified silver nanowires

Dorota Kowalska,Justyna Grzelak,Khuram Ashraf,Joanna Niedziolka-Jonsson,Heiko Lokstein,Richard Cogdell,Marcin Szalkowski,Sebastian Mackowski

doi:10.1007/s11120-017-0455-y

Abstract

A polyhistidine tag (His-tag) present on Chlorobaculum tepidum reaction centers (RCs) was used to immobilize photosynthetic complexes on a silver nanowire (AgNW) modified with nickel-chelating nitrilo-triacetic acid (Ni-NTA). The optical properties of conjugated nanostructures were studied using wide-field and confocal fluorescence microscopy. Plasmonic enhancement of RCs conjugated to AgNWs was observed as their fluorescence intensity dependence on the excitation wavelength does not follow the excitation spectrum of RC complexes in solution. The strongest effect of plasmonic interactions on the emission intensity of RCs coincides with the absorption spectrum of AgNWs and is observed for excitation into the carotenoid absorption. From the absence of fluorescence decay shortening, we attribute the emission enhancement to increase of absorption in RC complexes.

Highlights

Photosynthetic organisms, including bacteria, algae, and plants, can efficiently capture sunlight and convert it into biologically useful forms of chemical energy
Contribution of bacteriochlorophylls a (BChl a) to the absorption spectrum of the reaction centers (RCs) is shown in two spectral regions from 300 to 430 nm, and between 540 and 850 nm
The FMO protein attached to the RCs contains BChl a, and absorbs light in the spectral region from 550 to 645 nm (Olson 2004)

Summary

Introduction

Photosynthetic organisms, including bacteria, algae, and plants, can efficiently capture sunlight and convert it into biologically useful forms of chemical energy. RCs are responsible for separating electric charges across the photosynthetic membrane Nature has optimized this process for high quantum efficiency, where the number of charges separated per absorbed photon is close to unity. There are several types of photosynthetic reaction centers, including bacterial RCs and reaction centers of higher plants, photosystem I (PSI) and photosystem II (PSII) (Nagy et al 2014). Their unique properties have stimulated intense research focused on employing these photochemically active biomolecules as potential building-blocks for photosensors (Govorov and Carmeli 2007; Terasaki et al 2007; Terasaki 2016), biosensors for detection of, e.g., herbicides

Methods

Results

Conclusion