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We studied optical properties and photocurrent characteristics of PbS nanowires grown by chemical vapor deposition. Distinct bandedge photoluminescence (PL) emission was observed in the mid-infrared spectral range and the quantum confinement effect estimated from the PL peak energy was within 40 meV, consistent with the average diameter of the nanowire (∼70 nm) being significantly larger than the exciton Bohr radius (∼18 nm). We also demonstrated interdigit photo detectors making use of these PbS nanowires suspended between two pre-patterned Ti electrodes, where Ti also acted as metal catalyst for the nanowire growth. The threshold wavelength of the photocurrent was found to be ∼3 μm at room temperature.

Since oxygenic photosynthesis evolved in the common ancestor of cyanobacteria during the Archean, a range of sensing and response strategies evolved to allow efficient acclimation to the fluctuating light conditions experienced in the diverse environments they inhabit. However, how these regulatory mechanisms are assimilated at the molecular level to coordinate individual gene expression is still being elucidated. Here, we demonstrate that integration of a series of three distinct light signals generate an unexpectedly complex network regulating expression of the sole DEAD-box RNA helicase, CrhR, encoded in Synechocystis sp. PCC 6803. The mechanisms function at the transcriptional, translational and post-translation levels, fine-tuning CrhR abundance to permit rapid acclimation to fluctuating light and temperature regimes. CrhR abundance is enhanced 15-fold by low temperature stress. We initially confirmed that the primary mechanism controlling crhR transcript accumulation at 20 °C requires a light quantity-driven reduction of the redox poise in the vicinity of the plastoquinone pool. Once transcribed, a specific light quality cue, a red light signal, was required for crhR translation, far-red reversal of which indicates a phytochrome-mediated mechanism. Examination of CrhR repression at 30 °C revealed that a redox- and light quality-independent light signal was required to initiate CrhR degradation. The crucial role of light was further revealed by the observation that dark conditions superseded the light signals required to initiate each of these regulatory processes. The findings reveal an unexpected complexity of light-dark sensing and signaling that regulate expression of an individual gene in cyanobacteria, an integrated mechanism of environmental perception not previously reported.

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