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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.11.026 Byline: J.L. France (a), M.D. King (a), A. MacArthur (b) Keywords: Exobiology; Ices; Mars, Polar caps Abstract: Dusty water-ice snowpacks on Mars may provide a habitable zone for DNA based photosynthetic life. Previous work has over estimated the depths and thicknesses of such photohabitable zones by not considering the effect of red dust within the snowpack. For the summer solar solstice, at 80[degrees]N and a surface albedo of 0.45, there is a calculated photohabitable zone in the snowpack between depths of 5.5 and 7.5cm. For an albedo of 0.62, there is a calculated photohabitable zone in the snowpack between depths of 8 and 11cm. A coupled atmosphere-snow radiative-transfer model was set to model the Photosynthetic Active Radiation and DNA dose rates through water-ice snow at the north polar region of Mars. The optical properties of the polar caps were determined by creating a laboratory analogue to the Mars north polar deposits, and directly measuring light penetration and albedo. It is important for future exobiology missions to the polar regions of Mars to consider the implications of these findings, as drilling to depths of [approximately equal to]11cm should be sufficient to determine whether life exists within the martian snows, whether it is photosynthetic or otherwise, as at this depth the snow cover will provide a permanent protection from DNA damaging UV radiation. Author Affiliation: (a) Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom (b) NERC Field Spectroscopy Facility, Grant Institute, School of GeoSciences, University of Edinburgh, Edinburgh EH9 3JW, United Kingdom Article History: Received 7 July 2009; Revised 29 October 2009; Accepted 20 November 2009

By making use of the aggregation-induced emission feature of silole, compound 1 with an ammonium group is designed and synthesized with a view to developing a new optical probe for fluorescence turn-on detection of DNA and label-free fluorescence nuclease assay. The fluorescence of 1 increases largely upon mixing with DNA, in particular for long DNA, indicating that I can be used for fluorescence turn-on detection of DNA. More interestingly, 1 can be employed to follow the DNA cleavage process by nuclease. Therefore, a label-free fluorescence nuclease assay method is successfully established with 1. Furthermore, this label-free fluorescence assay can also be used for inhibitor screening of nucleases. Given its simplicity, easy operation, sensitivity and cost-effectiveness, this method can be extended to other nuclease assays and high-throughput screening of nuclease inhibitors.

Thin solid films of salmon deoxyribonucleic acid (DNA) have been fabricated by treatment with a surfactant and used as host for the laser dye sulforhodamine (SRh). The DNA films have an absorption peak at ~260 nm owing to absorption by the nitrogenous aromatic bases. The SRh molecules in the DNA films have absorption and emission peaks at 578 and 602 nm, respectively. The maximum emission was obtained at ~1 wt. % SRh in DNA, equivalent to ~100 DNA base pairs per SRh molecule. A distributed feedback grating structure was fabricated on a Si[O.sub.2]--Si substrate using interference lithography. The grating period of 437 nm was selected, corresponding to second-order emission at the amplified spontaneous emission wavelength of 650 nm. Lasing was obtained by pumping with a doubled Nd:YAG laser at 532 nm. The lasing threshold was 3 [micro]J, corresponding to ~30 [micro]J/[cm.sup.2] or 4 kW/[cm.sup.2]. The emission linewidth decreased from ~30 nm in the amplified spontaneous emission mode to OCIS codes: 050.2770, 140.2050, 140.3580, 160.2540, 160.5470.

We observe surface stress changes in response to thermal dehybridization, or melting, of double-stranded DNA (dsDNA) oligonucleotides that are grafted on one side of a microcantilever beam. Changes in surface stress occur when one complementary DNA strand melts and diffuses away from the other, resulting in alterations of the electrostatic, counterionic, and hydration interaction forces between the remaining neighboring surface-grafted DNA molecules. We have been able to distinguish changes in the melting temperature of dsDNA as a function of salt concentration and oligomer length. This technique also highlights differences between surface immobilized and solution DNA melting dynamics, which allows us to better understand the stability of DNA on surfaces. The transduction of phase transitions into a mechanical signal is ubiquitous for DNA, making cantilever-based detection a widely useful and complementary alternative to calorimetric and fluorescence measurements.

Hypocrellin A (HA), an efficient phototherapeutic agent, can chelate with lanthanum ion to form a 1:1 complex, which exhibits enhanced (super 1)O2 generation yield, a red-shifted absorption window greatly improved water solubility, a much lengthened triplet excited state lifetime, and an increased affinity to DNA with respect to HA. The effects in turn lead to a more potent photodamage ability on calf thymus DNA for La(super 3+)-HA in both aerobic and anaerobic conditions, indicating the potential application of La(super 3+) HA in the field of photodynamic therapy.

The fundamental photophysical properties of tC are investigated. The lowest energy absorption is well separated from the absorption of the nucleobases and has a transition moment polarized at an angle of ~35degree to the long axis of the tC chromosphere.

The flavin cofactor of Escherchia coli DNA photolyase in its neutral radical form, FADH., is investigated by high-frequency/high-field continuous-wave electron paramagnetic resonance at 360 GHz. Accurate g-tensor principal values are determined for a protein-associated neutral flavin radical.

A study was done on the structural polymorphism of DNA/lipopolyamine (multi-cationic lipid) complexes by using X-ray diffraction and cryo-electron microscopy. The series of experiments reported show that the polymorphism of the DNA lipid complexes is driven by the initial state of the cationic lipid.

Fluorescent tag can be affixed to proteins or genetic structures of interest. Fluorescent tag can be affixed to proteins or genetic structures of interest., Author Affiliations: DNA tags could help scientists to study ion channels (yellow), which allow specific ions to pass through the membrane of nerve cells (green). [see PDF for image] Credit: [...]

Forster resonance energy transfer (FRET) assay is used for monitoring the state of DNA (double- vs single-stranded) at a specific region within a DNA fragment, at both the ensemble level and the single-molecule level. The results have shown that ' quenchable' FRET can be applied in many processes involving DNA opening and closing, as well as in the development of new antibacterial therapies involving transcription.

The results from an integrated experimental and theoretical study of thymine-thymine photodimerization in short single-strand and duplex DNA structures possessing a single locked nucleic acid TT step is reported. Controlling the ground-state conformation by the locked nucleic acids is found to result in a remarkable increase in both the quantum yield and the selectivity of photoproduct formation.

Application of electrostatic complexes containing a cationic conjugated oligoelectrolyte (COE) and fluorescein (FAM)-labeled single-stranded DNA (ssDNA) as the basis for identifying various bacteria is demonstrated. The quantified changes in the PL spectra upon addition of the bacteria and the differential response from the five ssDNAs gave rise to a multicomponent array response to facilitate identification of the microorganism.

A combination of the steady-state and time-resolved spectroscopy techniques is employed to explain the mechanisms involved in the fluorescence of natural DNA.

Hydrolysis of TA photoproduct has led to two derivatives displaying different formation kinetic profiles depending on the oligomer content. The formation efficiency of TA photoproducts in UV-C-irradiated DNA has exceeded the formation of the trans,syn cyclobutane pyrimidine dimer at TT sites.

Single-molecule spectroscopy is used for studying water-soluble perylene dicarboximide fluorophores (PDI), which are immobilized in aqueous buffer by attaching the fluorophore to DNA. The studies have evaluated how the fluorescence control of PDIs is used for superresolution 'Blink-Microscopy' in aqueous or organic media and for single-molecule spectroscopy.

Several spectroscopic studies are conducted to explain the dynamics of the various freely diffusing fluorescence-labeled double-stranded [gamma]-phage DNA molecules. The various problems faced with the previous studies regarding the distinction between Rouse and Zimm models are also discussed.

The development of an electronic DNA sensor probe assembly by using barium strontium titanate (BST) applied by pulsed laser deposition in conjugation with optical spectroscopy and impedance spectroscopy methods is described. The design has the advantages of label-free detection and large detectable capacitance changes upon hybridization and does not need the application of a gold electrode layer.

A photoreactive analogue of cisplatin, Pt[BP.sub.6] was used to construct a DNA duplex containing a site-specific platinum interstrand cross-link (ICL) to gain insight into detailed mechanism by which cellular protein recognize and process cisplatin-DNA damage. The studies identified proteins that recognize the platinum ICL in cisplatin-resistant cells that halted at various phases of the cell cycle, and in different carcinoma cells and the difference in the nuclear proteins that bind to the plantinum ICL from those to binding to intrastrand cross-links indicated the different mechanisms for disruption of cellular functions.

The creation of gold surfaces modified by single- or double-stranded DNA self-assembled monolayers (SAMs) has produced heterogeneous surface packing densities by using electrochemical studies coupled with fluorescence imaging. The modification in the method used for producing the DNA SAMs has resulted in different surface with much fewer aggregates and more electromodulation of the fluorescence intensity, though at much lower DNA surface density.

The identification of a multicolor set of water-soluble oligodeoxyfluoroside (ODF) dyes that exhibit emission colors across the visible spectrum and all of which can be simultaneously excited by long-wavelength ultraviolet (UV) light is described. The results have shown that ODF dyes are useful as labels in biological systems, which has allowed the simultaneous tracking of multiple species by color and the visualization in moving systems where classical fluorophores have failed.

Vertical electronic excitations in model systems representing single- and double-stranded B-DNA are characterized by using electronic structure theory and are compared to the optically bright [super 1][pi][pi]* states. The studies have shown that a single Watson-Crick base pair is an inadequate model of the photophysics of B-DNA.

A label-free, multiplexed DNA assay using fluorescent conjugated polymers as a detection probe for illustrating hybridization on metallic striped nanorods is described. The results have shown attomole detection sensitivity and single-mutation specificity that are comparable to those of single-element assays but with much improved throughput.

The trapping and conversion of visible light energy into chemical energy is examined by using a supramolecular assembly. The results have shown the suitability of the system as a prototype for DNA-based light-harvesting devices, in which energy transfer from the aqueous phase to the interior of the lipid membrane is followed by charge separation.

The DNA conjugates, [beta]-cyclodextrin ([beta]-CyD)-modified oligodeoxyribonucleotide (CyD-ODN), and the nucleobase-specific fluorescent DNA ligand (MNDS) are described and simultaneously used them for single nucleotide polymorphism (SNP) analysis in aqueous solution. The combined use of 3'- or 5'-modified CyD-ODNs with dansyl-tethered ligands is a general and flexible method for fluorescent SNP analysis in a homogeneous solution.

Spectroelectrochemical titrations of cryptochrome I from Arabidopsis thaliana (A.t) and cyclobutane pyrimidine dimers (CPD) photolyases from both Escherichia coli (E.c) and Anacystis nidulans (A.n) that allow comparison of their redox transitions are described. The studies have shown that down-shift of both flavin redox transitions is required in the evolution from photolyases (PL) to cryptochrome I (CRY).

The structure of a spore photoproduct of the dinucleoside TpT (SPTpT) is reexamined to determine the absolute configuration of the natural SP by combining NMR measurements and density functional theory calculations. The results have shown that this natural SPTpT compound is the dinucleotide 5'->3' with an R configuration at the carbon [C.sub.5a].

Steady-state fluorescence and fluorescence correlation spectroscopy (FCS) are used for examining the thermodynamics and dynamics of DNA hybridization/dehybridization at a terminal of a DNA duplex. The dynamic parameters of the activation energy of single base-pair reaction derived from the two fluorescence resonance energy (FRET) pairs are consistent and the enthalpy change and entropy change of single base-pair formation have agreed well with the theoretical prediction.