Selective photoelectrochemical oxidation of DNA was achieved by ruthenium tris(bipyridine) immobilized on a tin oxide nanoparticle electrode. The metal complex was covalently attached to a protein, avidin, which adsorbed strongly on the tin oxide electrode by electrostatic interaction. Upon irradiation with 473-nm light, anodic photocurrent was generated in a blank electrolyte and was enhanced significantly after addition of poly(guanadylic acid) (poly-G) into the electrolyte. The current increased progressively with the nucleotide concentration, suggesting the enhancement effect was related to poly-G. The action spectrum indicates that the photocurrent was initiated by light absorption of the ruthenium compound immobilized on the electrode. Among the various polynucleotides examined, poly-G produced the largest photocurrent increase, followed by poly-A, single-stranded DNA, chemically damaged DNA, and double-stranded DNA, whereas poly-C and poly-U showed little effect. The combined experimental data support the hypothesis that the photoexcited Ru 2+ * species injects an electron into the semiconductor and produces Ru 3+ , which is then reduced back to Ru 2+ by guanine and adenine bases in DNA, resulting in the recycling of the metal complex and enhanced photocurrent. The photoelectrochemical reaction can be employed as a new method for the detection of DNA damage.Oxidation of DNA bases has been studied extensively in the last two decades due to the important role of DNA in aging and metabolism. 1-4 Electrochemistry provides a simple but powerful technique for obtaining both kinetic and thermodynamic information on DNA oxidation reactions. Using metal polypyridine complexes as electron mediators, electrocatalytic oxidation of DNA bases was investigated in detail. 5,6 The same strategy was also employed in the detection of DNA oxidative damage. 7 In addition, electrochemiluminescence was used to detect DNA damage on films containing metal polypyridine complexes. 8,9 We report here the first observation of DNA oxidation catalyzed photoelectrochemically by ruthenium tris(bipyridine) immobilized on a tin oxide nanoparticle electrode.Photoelectrochemistry has been utilized extensively in the construction of solar cells. In one of the most successful photoelectrochemical solar cells developed by O'Regan and Gratzel, 10 a thick, porous film of nanocrystalline TiO 2 particles was sensitized by surface-adsorbed ruthenium polypyridyl complex. Other wide bandgap semiconductors and sensitizers have also been investigated. [11][12][13] In a few reports, the technique was also employed in chemical and biological analysis, using organic, metal chelate and nanoparticle photoelectrochemical indicators and conducting electrodes. [14][15][16][17][18][19] Recently, we reported the first case of quantitative detection of a biological affinity reaction, 20 using a ruthenium polypyridine complex as a photoelectrochemical label, oxalate as the sacrificial electron donor, and nanoparticle SnO 2 as electrode material. The analytical s...

In this work we first introduced a recently developed high-resolution, deep-tissue imaging technique, ultrasound-switchable fluorescence (USF). The imaging principles based on two types of USF contrast agents were reviewed. To improve USF imaging techniques further, excellent USF contrast agents were developed based on high-performance thermoresponsive polymers and environment-sensitive fluorophores. Herein, such contrast agents were synthesized and characterized with five key parameters: (1) peak excitation and emission wavelengths (λex and λem), (2) the fluorescence intensity ratio between on and off states (IOn/IOff), (3) the fluorescence lifetime ratio between on and off states (τOn/τOff), (4) the temperature threshold to switch on fluorophores (Tth), and (5) the temperature transition bandwidth (TBW). We mainly investigated fluorescence intensity and lifetime changes of four environment-sensitive dyes [7-(2-Aminoethylamino)-N,N-dimethyl-4-benzofurazansulfonamide (DBD-ED), St633, Sq660, and St700] as a function of temperature, while the dye was attached to poly(N-isopropylacrylamide) linear polymers or encapsulated in nanoparticles. Six fluorescence resonance energy transfer systems were invented in which both the donor (DBD-ED or ST425) and the acceptor (Sq660) were adopted. Our results indicate that three Förster resonance energy transfer systems, where both IOn/IOff and τOn/τOff are larger than 2.5, are promising for application in future surface tissue bioimaging by USF technique.

Cytotoxicity of nanomaterials on living systems is known to be affected by their size, shape, surface chemistry, and other physicochemical properties. Exposure to a well-characterized subpopulation of specific nanomaterials is therefore desired to reveal more detailed mechanisms. This study develops scalable density gradient ultracentrifugation sorting of highly dispersed single-walled carbon nanotubes (SWNTs) into four distinct bands based on diameter, aggregation, and structural integrity, with greatly improved efficiency, yield, and reproducibility. With guarantee of high yield and stability of four SWNT fractions, it is possible for the first time, to investigate the structure-dependent bioeffects of four SWNT fractions. it is possible Among these, singly-dispersed integral SWNTs show no significant effects on the mitochondrial functions and hypoxia. The aggregated integral SWNTs show more significant effects on the mitochondrial dysfunction and hypoxia compared to the aggregated SWNTs with poor structure integrity. Then, it is found that the aggregated integral SWNTs induced the irregular mitochondria respiratory and pro-apoptotic proteins activation, while aggregated SWNTs with poor structure integrity greatly enhanced reactive oxygen species (ROS) levels. This work supports the view that control of the distinct structure characteristics of SWNTs helps establish clearer structure-bioeffect correlation and health risk assessment. It is also hoped that these results can help in the design of nanomaterials with higher efficiency and accuracy in subcellular translocation.

Abstract. DNA films immobilized on an indium tin oxide (ITO) electrode surface were detected and determined employing a high-affinity intercalator, Ru(bpy) 2 (dppz) 2þ (bpy ¼ 2,2 0 -bipyridine, dppz ¼ dipyrido[3,2-a:2 0 ,3 0 -c]phenazine), as a redox indicator, and oxalate as a sacrificial electron donor in solution to chemically amplify the voltammetric signal of the indicator. Nucleic acids were immobilized on ITO by layer-by-layer electrostatic adsorption, using avidin as the first layer and nucleic acid as the second layer. In quartz crystal microbalance (QCM) measurements on an avidin-coated gold surface, the amount of adsorption from a 200 mg mL À1 nucleic acid solution was found to be 3.2 ng mm À2 for both double-stranded (ds-) and single-stranded (ss-) calf-thymus DNA as well as polycytidylic acid (Poly-C). After binding with Ru(bpy) 2 (dppz) 2þ (Ru-dppz), voltammetry of the ds-DNA film on ITO was carried out in an indicator-free phosphate buffer. An anodic peak at about 1.15 V was observed, and it was assigned to Ru-dppz oxidation. When measured in an oxalate buffer, however, a catalytic current was observed due to the oxidation of oxalate by electrochemically generated Ru(bpy) 2 (dppz) 3þ , resulting in a 120-fold increase in the signal. Since oxalate itself produces a very low oxidation current on ITO, catalytic voltammetry produces about a 14-fold improvement in the signal-to-blank ratio over the nonamplified determination. As a result, ds-DNA adsorbed from 20 ng mL À1 solution could be detected, which was estimated by QCM to be 160 pg mm À2 on the surface. The catalytic current of ds-DNA was substantially higher than that of ss-DNA and poly-C, indicative of selective binding of the redox indicator to ds-DNA. The results serve as a basis for the catalytic voltammetric detection of DNA hybridization in future work.