The interface between plant organelles and non-biological nanostructures has the potential to impart organelles with new and enhanced functions. Here, we show that single-walled carbon nanotubes (SWNT) passively transport and irreversibly localize within the lipid envelope of extracted plant chloroplasts, promote over three times higher photosynthetic activity than that of controls, and enhance maximum electron transport rates. The SWNT–chloroplast assemblies also enable higher rates of leaf electron transport in vivo through a mechanism consistent with augmented photoabsorption. Concentrations of reactive oxygen species inside extracted chloroplasts are significantly suppressed by delivering poly(acrylic acid)–nanoceria or SWNT–nanoceria complexes. Moreover, we show that SWNT enable near-infrared fluorescence monitoring of nitric oxide both ex vivo and in vivo, thus demonstrating that a plant can be augmented to function as a photonic chemical sensor. Nanobionics engineering of plant function may contribute to the development of biomimetic materials for light-harvesting and biochemical detection with regenerative properties and enhanced efficiency.
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Figure 1. Enhanced photosynthetic activity of isolated chloroplasts with SWNT–NC was shown by electron transfer to DCPIP. b, Higher maximum electron-transport rates in extracted chloroplasts and leaves were quantified by the yield of chlorophyll fluorescence (P <0.05, t-test, n=3–8). c, Electron-transport-rate light curves indicated enhanced photosynthesis above 100 μmol m−2 s−1 for5 mg l−1 SWNT leaves (P < 0.05, t-test, n=5–8). d, SWNTs modified chloroplast ultraviolet, visible and near-infrared absorption spectrum. e, A suspension made mostly of semiconducting SWNTs increased chloroplast reduction of DCPIP whereas a solution enriched with metallic SWNTs (m-SWNTs) had lower effect in photosynthetic activity. f, Increased ROS scavenging by SWNT–NC and PAA–NC inside chloroplasts was quantified by the oxidation of H2DCFDA to DCF. g, Reduction in superoxide concentration was facilitated by nanoparticles localized at chloroplast sites of ROS generation. h,i, NO sensing by ss(AT)15–SWNTs delivered into extracted chloroplasts (h) and in vivoin leaves of A. thaliana (i) was evidenced by a strong quenching in fluorescence for all chiralities. j, In vivo plant sensing set-up whereby a leaf infiltrated with ss(AT)15–SWNTs was excited by a 785 nm epifluorescence microscope. k, ×20 view of ss(AT)15–SWNTs inside a leaf before (left) and after (right) addition of 20 μl dissolved NO solution with three SWNT regions of interest circled. l, Peak intensity–time traces of three ss(AT)15–SWNT regions showed stepwise quenching of SWNT by NO, ranging from 40 to 60% intensity decrease. Error bars represent s.d.