Graphene has emerged as a promising material for photonic applications fuelled by its superior electronic and optical properties. However, the photoresponsivity is limited by the low absorption cross-section and ultrafast recombination rates of photoexcited carriers. Here we demonstrate a photoconductive gain of ∼105 electrons per photon in a carbon nanotube–graphene hybrid due to efficient photocarriers generation and transport within the nanostructure. A broadband photodetector (covering 400–1,550 nm) based on such hybrid films is fabricated with a high photoresponsivity of >100 A W−1 and a fast response time of ∼100 μs. The combination of ultra-broad bandwidth, high responsivities and fast operating speeds affords new opportunities for facile and scalable fabrication of all-carbon optoelectronic devices.

The LYR family consists of proteins of diverse functions that contain the conserved tripeptide 'LYR' near the N-terminus, and it includes Isd11, which was previously observed to have an important role in iron-sulfur (Fe-S) cluster biogenesis in Saccharomyces cerevisiae. Here, we have cloned and characterized human ISD11 and shown that human ISD11 forms a stable complex in vivo with the human cysteine desulfurase (ISCS), which generates the inorganic sulfur needed for Fe-S protein biogenesis. Similar to ISCS, we have found that ISD11 localizes to the mitochondrial compartment, as expected, but also to the nucleus of mammalian cells. Using RNA-interference techniques, we have shown that suppression of human ISD11 inactivated mitochondrial and cytosolic aconitases. In addition, ISD11 suppression activated iron-responsive element-binding activity of iron regulatory protein 1, increased protein levels of iron regulatory protein 2, and resulted in abnormal punctate ferric iron accumulations in cells. These results indicate that ISD11 is important in the biogenesis of Fe-S clusters in mammalian cells, and its loss disrupts normal mitochondrial and cytosolic iron homeostasis.

Ferredoxins are iron–sulfur proteins that have been studied for decades because of their role in facilitating the monooxygenase reactions catalyzed by p450 enzymes. More recently, studies in bacteria and yeast have demonstrated important roles for ferredoxin and ferredoxin reductase in iron–sulfur cluster assembly. The human genome contains two homologous ferredoxins, ferredoxin 1 (FDX1) and ferredoxin 2 (FDX2 — formerly known as ferredoxin 1L). More recently, the roles of these two human ferredoxins in iron–sulfur cluster assembly were assessed, and it was concluded that FDX1 was important solely for its interaction with p450 enzymes to synthesize mitochondrial steroid precursors, whereas FDX2 was used for synthesis of iron–sulfur clusters, but not steroidogenesis. To further assess the role of the FDX–FDXR system in mammalian iron–sulfur cluster biogenesis, we performed siRNA studies on FDX1 and FDX2, on several human cell lines, using oligonucleotides identical to those previously used, along with new oligonucleotides that specifically targeted each gene. We concluded that both FDX1 and FDX2 were important in iron–sulfur cluster biogenesis. Loss of FDX1 activity disrupted activity of iron–sulfur cluster enzymes and cellular iron homeostasis, causing mitochondrial iron overload and cytosolic iron depletion. Moreover, knockdown of the sole human ferredoxin reductase, FDXR, diminished iron–sulfur cluster assembly and caused mitochondrial iron overload in conjunction with cytosolic depletion. Our studies suggest that interference with any of the three related genes, FDX1, FDX2 or FDXR, disrupts iron–sulfur cluster assembly and maintenance of normal cytosolic and mitochondrial iron homeostasis.

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