•The luminescence of [Ru(bpy)2(dppz)]2 +-DNA is quenched by TiO2 NPs.•The quenching level is dependent on calcinations temperature and incubation pH.•Anatase TiO2 has the stronger ability to quench the luminescence than rutile TiO2.•Strong adsorption of DNA on anatase drives [Ru(bpy)2(dppz)]2 +-DNA unbinding.•Sol-gel silica matrices quench the luminescence by capturing [Ru(bpy)2(dppz)]2 +.The intercalation of [Ru(bpy)2(dppz)]2 + labeled as Ru(II) (bpy = 2,2′-bipyridine and dppz = dipyrido[3,2,-a:2′,3′-c]phenazine) into herring sperm DNA leads to the formation of emissive Ru(II)-DNA dyads, which can be quenched by TiO2 nanoparticles (NPs) and sol-gel silica matrices at heterogeneous interfaces. The calcinations temperature exhibits a remarkable influence on the luminescence quenching of the Ru(II)-DNA dyads by TiO2 NPs. With increasing calcinations temperature in the range from 200 to 850 °C, the anatase-to-rutile TiO2 crystal structure transformation increases the average particle size and hydrodynamic diameter of TiO2 and DNA@TiO2. The anatase TiO2 has the stronger ability to unbind the Ru(II)-DNA dyads than the rutile TiO2 at room temperature. The TiO2 NPs and sol-gel silica matrices can quench the luminescence of the Ru(II) complex intercalated into DNA by selectively capturing the negatively DNA and positively charged Ru(II) complex to unbind the dyads, respectively. This present results provide new insights into the luminescence quenching and competitive binding of dye-labeled DNA dyads by inorganic NPs.Download high-res image (210KB)Download full-size image

•SWCNTs@PBPA arrays are prepared using visible light-assisted voltammetry.•SWCNTs@PBPA electrode exhibits a pair of well-defined redox peaks at − 0.165 V.•SWCNTs@PBPA has photo-induced specific capacitance of 420 F g− 1 at 1.0 A g− 1.•SWCNTs@PBPA acts as photoanode and cathode catalysts for AA oxidation by O2.•The photoelectrochemical AA fuel cell shows remarkably enhanced performances.An array of single-walled carbon nanotubes (SWCNTs) coated with photoelectro-polymerized bisphenol A (PBPA) films is first fabricated using visible light-assisted multiple voltammetry. The PBPA layers endow the highly ordered SWCNTs@PBPA with unique photoelectrochemical and photoelectrocatalytic properties. A pair of well-defined redox peaks appears at the formal potential of − 0.165 V (vs. SCE) for the SWCNTs@PBPA-based electrode, which shows a linearly increasing photocurrent response with increasing BPA concentration. Furthermore, the presence of PBPA on SWCNTs leads to a negative shift of 0.158 V for the oxidative peak potential of 0.05 mM ascorbate under light irradiation, and a positive shift of 0.468 V or 0.412 V for the reduction peak potential of O2 or H2O2, respectively. The SWCNTs@PBPA arrays show good catalytic activities towards the oxidation of ascorbate and the reduction of O2. While simultaneously employing SWCNTs@PBPA as photoanode and cathode catalysts, the assembled ascorbate/O2 fuel cell exhibits remarkably enhanced performances. The proposed fuel cell indicates open-circuit photovoltage of 0.693 V, short-circuit photocurrent density of 0.29 mA cm− 2 and maximum power density of 14.05 μW cm− 2 upon light illumination of 0.18 mW cm− 2 visible light.Download high-res image (227KB)Download full-size image

•A diphenyl-as-triazine-containing Ru(II) complex is assembled on CdS and Cu2O.•Ru(II) shows tunable spectral properties by binding H2O with Kb = 0.042 L mol−1.•Ru(II) can bind AA with k = 0.12 mol L−1 s−1 and simultaneously release DHAA.•Ru(II) shows photoelectrocatalytic activity towards AA oxidation and O2 reduction.A novel ruthenium(II) complex [Ru(dppt)2]2+ (dppt = bis[3-(1,10-phenanthroline-2-yl)-5,6-diphenyl-as-triazines) labeled as Ru(II) is assembled on CdS and Cu2O electrode to prepare Ru(II)/CdS photoanode and Ru(II)/Cu2O photocathode for the oxidation of ascorbate (AA) and the reduction of dioxygen (O2), respectively. The Ru(II) complex possesses two diphenyl-as-triazine-containing polypyridyl ligands to bind H2O (Kb = 0.042 L mol−1) or AA (k = 0.12 mol L−1 s−1) through cooperative hydrogen bond, electrostatic attraction, and anion-π interactions, leading to an increase in the light-harvesting efficiency. The photoelectrocatalytic oxidation response of AA on Ru(II)/CdS electrode exhibits an enhancement upon increasing incubation time with AA in aqueous buffer solutions, in which the Ru(II) frame has ability to bind AA and simultaneously release dehydroascorbic acid (DHAA). Meanwhile, the Ru(II) complex on Cu2O photocathode acts as an appropriate binding agent to promote the photoelectrocatalytic reduction of O2 and H2O2. While employing Ru(II)/CdS anode and Ru(II)/Cu2O cathode to assemble an AA/O2 fuel cell irradiated with visible light of 0.18 mW cm−2, the proposed cell shows Ru(II)-enhanced performances with open-circuit photovoltage of 0.626 V, short-circuit current density of 49.1 μA cm−2 and maximum power density of 10.3 μW cm−2 at 0.32 V.Download high-res image (168KB)Download full-size image

•Photocatalytic oxidation of AA and GLU occurs on CdS/ITO electrode.•Photocatalytic oxidation of AA can be enhanced by GLU.•Photocatalytic oxidation of AA and GLU promotes hydrogen generation.•Solar-to-hydrogen and fuel-to-hydrogen conversion efficiencies are determined.Photocatalytic oxidation of ascorbate (AA) and glucose (GLU) on a visible light-sensitive cadmium sulfide nanoparticle modified indium-tin oxide (CdS/ITO) electrode has been successfully used to synergistically promote the photoelectrochemical generation of hydrogen on a porous nickel cathode. In a neutral medium, the photocatalytic oxidation of AA is found to drive the oxidation of GLU on the visible light-excited CdS/ITO anode, which yields the photovoltaic effect to improve the hydrogen evolution reactions. The optimized monopolar photocatalytic fuel cell using 0.1 mol L−1 AA and 0.1 mol L−1 GLU as fuel shows open-circuit photovoltage of 0.571 V (vs. SCE) upon visible light irradiation of 0.18 mW cm−2, short-circuit photocurrent density of 166.67 μA cm−2, maximum power density of 23.34 μW cm−2 at 0.275 V. The simultaneous presence of AA and GLU leads to a 22.1-fold increase of photoenergy conversion efficiency in contrast to that without fuel. Furthermore, the photocatalytic responses of the CdS/ITO electrode towards the oxidation of AA and GLU are found to remarkably promote the photoelectrochemical generation of hydrogen, which is evaluated with solar-to-hydrogen and fuel-to-hydrogen conversion efficiencies. This present study provides a new approach for better utilizing renewable energy sources to promote the hydrogen generation.

•Ru(II)PTPP/CdS shows two Ru(II)-based oxidation peaks at 0.296 V and 0.830 V.•Photoelectrocatalytic oxidation of UA exhibits good linear responses.•The butoxy chain endows Ru(II)PTPP with multifunctional catalytic properties.•Ru(II)PTPP on CF electrode can remarkably promote the reduction of oxygen.•The assembled cell has ISC of 0.136 mA cm−2 and Pmax of 31.50 μW cm−2.This paper reports the photoelectrocatalytic activities of a ruthenated porphyrin [Ru(phen)2(IP-C4O-TPP)]2+ (denoted as Ru(II)PTPP, phen = 1,10-phenanthroline, IP = imidazo[4,5-f][1,10]phenanthroline and TPP = 5,10,15,20-tetraphenylporphyrin) containing a covalently-linked butoxy chain (-C4O-) between IP and TPP moieties by means of various electrochemical techniques in combination with absorption spectroscopy and scanning electronic microscopy. Ru(II)PTPP is assembled on the surface of CdS nanoparticles, showing two Ru(II)-based peaks at 0.296 V and 0.830 V, where uric acid (UA) can be photoelectrocatalytically oxidized in a linear range of 0.01-10.0 mmol L−1. The −C4O- chain endows the Ru(II)PTPP/carbon felt (CF) electrode with favorable dioxygen (O2) binding sites to achieve a couple of new redox peaks at −0.213 V, where O2 involves electrocatalytic reduction reactions. While employing 5.0 mmol L−1 UA as fuel, and 60 mL min−1 O2 as oxidant, the proposed photoelectrochemical fuel cell shows open-circuit photovoltage of 0.656 V, short-circuit photocurrent density of 0.136 mA cm−2, and maximum power density of 31.50 μW cm−2 at 0.497 V under visible-light illumination of 0.18 mW cm−2. The present study provides an interesting platform for the utilization of renewable energy sources.

•[Ru(bpy)2(atatp)]2 +-bound DNA film is prepared by a self-standing cast method.•The stabilized DNA shows anti-oxidative activity against reactive oxygen species.•Photoluminescence of the cast film is quenched by H2O, O2, [Fe(CN)6]4 − and Cu2 +.•The proposed oxygen sensor has a wide linear range and high reproducibility.A novel [Ru(bpy)2(atatp)]2 + (bpy = 2,2′-bipyridine and atatp = acenaphtheno[1,2-b]-1,4,8,9-tetraazatriphenylene) can induce the condensation of herring sperm DNA to form an orange-red cast film via intercalation and electrostatic attraction. The thus-prepared cast film shows microsecond emission lifetimes and reversible luminescence tuning characteristics by oxygen and nitrogen with an on–off emission intensity ratio of 4.3. The photoluminescence of [Ru(bpy)2(atatp)]2 + bound to a DNA condensed matrix can be quenched by water, dissolved oxygen, copper(II) and ferrocyanide ions. The DNA binding is found to hardly alter the dynamic quenching of [Ru(bpy)2(atatp)]2 + by oxygen at a low DNA-to-Ru(II) molar ratio (r = 0.83), allowing [Ru(bpy)2(atatp)]2 + to keep a basically unchanged oxygen quenching constant, as well as endow the photo-induced electron transfer between [Ru(bpy)2(atatp)]2 + and copper(II) cations, and weaken the electrostatic attraction of [Ru(bpy)2(atatp)]2 + with ferrocyanide anions. In addition, the DNA condensation induced by [Ru(bpy)2(atatp)]2 + can protect the DNA oxidative damage against superoxide anion and hydroxyl radical toxicity. The present results could provide a versatile platform for better fabrication of optoelectronic devices.An acenaphthene-containing Ru(II) complex can induce the condensation of DNA to cast a uniform orange-red film, which shows reversible luminescence tuning characteristics by dissolved oxygen.

•PANI shows good linear spectral absorbance and/or photovoltaic responses to AA.•PANI/CF exhibits a good linear potentiometric response to O2 flux rate.•Visible light-driven AA/O2 fuel cell possesses high performance.A honeycomb-structured polyaniline (PANI) film is used to simultaneously promote the photoelectrocatalytic oxidation of ascorbic acid (AA) and electrocatalytic reduction of dioxygen (O2). The in situ spectroelectrochemical evidences suggest that the PANI film controlled between − 0.20 and 0.70 V shows four transformable redox forms, among which emeraldine base (EB) and leucoemeraldine base (LEB) can mediate the oxidation of AA and the reduction of O2, respectively. The EB-based electrode exhibits good linear spectral absorbance and/or photovoltaic responses to AA between 0.01 and 1.0 mmol L− 1 with high sensitivity and good reproducibility. The LEB-based electrode shows a good linear potentiometric response to O2 permeation flux rate between 10 and 60 mL min− 1. Furthermore, the CdS nanoparticles and carbon felt (CF) are used to support the PANI film for the preparation of PANI/CdS anode and PANI/CF cathode. The assembled photoelectrochemical fuel cell driven by visible light shows an open-circuit photovoltage of 0.614 V, short-circuit photocurrent density of 125.55 μA cm− 2, maximum power density of 19.05 μW cm− 2 at 0.492 V, fill factor of 0.24 and photoenergy conversion efficiency of 10.58%. The present study provides a new approach for the utilization of renewable energy sources.

The oxygen-sensing performance of [Ru(IP)2(HNAIP)]2+ (Ru1, IP = imidazo[4,5-f][1,10]phenanthroline and HNAIP = 2-(2-hydroxy-1-naphthyl)imidazo [4,5-f][1,10]phenanthroline) in the presence of DNA conformational transition has been investigated by means of absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopies, and circular dichroism spectroscopy. Ru1 shows a good linear response toward oxygen between pure nitrogen and pure oxygen with an on–off emission intensity ratio (I0/I100) of up to 9.3 via a dynamic quenching mechanism. Compared with [Ru(IP)2(DHPIP)]2+ (Ru2, DHPIP = 2-(2,4-dihydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline, I0/I100 = 5.8), the HNAIP ligand endows Ru1 with favorable oxygen binding sites to achieve larger energy and electron transfer rates. Simultaneously, Ru1 can induce the B-to-Z DNA conformational transition via a groove interaction with an intrinsic binding constant (Kb) of 7.9 × 104 M–1, whereas there is no same phenomenon for Ru2 intercalated into DNA (Kb = 3.3 × 105 M–1). Furthermore, the B-to-Z DNA conformational transition is interestingly found to decrease the Ru1-based oxygen-sensing rate by about 33%.

•[Co(phen)3]3+ has assembled on purine ring of 6-MP on MWCNTs surface.•[Co(phen)3]3+ is immobilized on Hx/MWCNTs/C electrode by p–π interactions.•S–Au bond hinders presence of characteristic redox peaks of 6-MP-[Co(phen)3]3+.•An effective approach is proposed to achieve the binding constant (8.4 × 103 M−1).Voltammetric response of [Co(phen)3]3+ (phen = 1,10-phenanthroline) and gold nanoparticles/multi-walled carbon nanotubes (GNPs/MWCNTs) to 6-mercaptopurine (6-MP) and hypoxanthine (Hx) is comparatively investigated by means of cyclic voltammetry in combination with scanning electron microscopy. The presence of 6-MP and Hx is found to influence the electrochemical assembly of [Co(phen)3]3+ on GNPs/MWCNTs modified graphite (C) electrodes. [Co(phen)3]3+ is electrochemically assembled on the 6-MP/GNPs/C and Hx/MWCNTs/C electrodes by S–Au bond and p–π interactions, showing only a pair of well-defined redox peaks. The addition of MWCNTs to the GNPs/C electrode leads to the presence of a new pair of characteristic redox peaks via π–π stacking interactions of [Co(phen)3]3+/MWCNTs with 6-MP. On basis of the voltammetric response of [Co(phen)3]3+/MWCNTs/C electrode to 6-MP, a new approach has been proposed to achieve the binding constant of 8.4 × 103 M−1. Taken together, [Co(phen)3]3+ and GNPs/MWCNTs have shown interesting voltammetric responses, which can be used to discriminate between two C-6 substituted purine analogues.

•Ru(II) complex-intercalated DNA film is assembled on CdS/ITO electrode.•Hybrid electrode shows tunable luminescence by external electric field and Cu2+.•Photoluminescence and photovoltaic response are synchronously decreased by Cu2+.•Synergistic effects of luminescence quenching and photovoltage shift are discussed.A [Ru(bpy)2(dppz)]2+-intercalated DNA film (bpy = 2,2′-bipyridine and dppz = dipyrido[3,2-a:2′,3′-c]phenazine) is successfully assembled on an indium-tin oxide (ITO) electrode modified with CdS nanoparticles, designated as Ru(II)-DNA/CdS/ITO electrode. In the present protocol, [Ru(bpy)2(dppz)]2+ intercalated in the DNA film has contributed characteristic photoluminescence properties to the Ru(II)-DNA/CdS/ITO electrode, in which CdS nanoparticles can bestow the tunable photovoltaic response. The as-prepared electrode shows a very consistent luminescence quenching by both applied anodic potentials and Cu(II) ions, which can extract the electrons from Ru(II)-based excited states (λEx = 450 nm). The photo-sensitive Ru(II)-DNA/CdS/ITO electrode is able to gain a maximum negative shift of ca. 0.467 V (open-circuit photovoltage vs. Ag/AgCl, 0.05 M NaCl) upon irradiation with UV–vis light between 350 and 700 nm. Additionally, the photovoltaic response including open-circuit photovoltage and short-circuit photocurrent for Ru(II)-DNA/CdS/ITO electrode (vs. Ag/AgCl) is also weakened by Cu(II) ions, indicating a synergistic effect with photoluminescence quenching. The preliminary results show a new approach to synchronically control the photoluminescence and photovoltaic response of DNA-metallointercalators and nanoconductor particles through the introduction of chemical agents, as well as open the way for optoelectronic switches.

•Ru(II)–BSA film exhibits the luminescence enhanced by BSA (Kb = 1.9 × 102 M−1).•Ru(II)-based luminescence mediated by BSA is dynamically quenched by Co(III).•SWCNTs promote PET between Ru(II) and Co(III).•PET mediated by BSA–SWCNTs shows detectable photovoltaic response.Photoluminescence properties of [Ru(bpy)2(tatp)]2+ (bpy = 2,2′-bipyridine and tatp = 1,4,8,9-tetra-aza-triphenylene) bound to a BSA–SWCNTs film (BSA = bovine serum albumin and SWCNTs = single-walled carbon nanotubes) upon incorporation of [Co(phen)3]3+ (phen = 1,10-phenanthroline) are first investigated by means of steady-state and time-resolved fluorescence spectroscopy. The BSA-bound [Ru(bpy)2(tatp)]2+ shows tunable luminescence properties by [Co(phen)3]3+, where an increasing amount of BSA is found to increase the emission intensity of [Ru(bpy)2(tatp)]2+–BSA dyad with binding constant of 1.9 × 102 M−1, and however decrease the luminescence of [Ru(bpy)2(tatp)]2+–BSA–[Co(phen)3]3+ triad with quenching constant of 2.4 × 103 M−1. Moreover, BSA is combined with SWCNTs to construct BSA–SWCNTs bio-nanohybrids, which mediate the photo-induced electron transfer (PET) between [Ru(bpy)2(tatp)]2+ and [Co(phen)3]3+, representing a dynamic luminescence quenching process. On basis of such a PET, [Ru(bpy)2(tatp)]2+ and [Co(phen)3]3+ are assembled on the surfaces of BSA–SWCNTs to fabricate a photoanode and a cathode, respectively, showing detectable photovoltaic response. The present study could provide a versatile platform for the fabrication and evaluation of nanoscale optoelectronic devices.

•Ru(II)/TiO2/ITO anode shows good photoelectrocatalysis for sulfite oxidation.•Cu(II)/SWCNTs/C cathode shows excellent electrocatalytic reduction response to H2O2.•Photoanode is evaluated by using in situ spectroelectrochemical monitoring.•The photo-stimulated SO32−/H2O2 fuel cell exhibits attractive performance.An anisomerous ruthenated porphyrin [Ru(bpy)2(MPyTMPP)Cl]+ (designated as Rub2P, bpy = 2,2′-bipyridine and MPyTMPP = 5-(4-pyridyl)-10,15,20-tris(4-metylphenyl)porphyrin) is first applied to the photoelectrocatalytic oxidation of sulfite on a nano-TiO2 modified indium-tin oxide (ITO) electrode. The Rub2P/TiO2/ITO electrode shows a pair of well-defined redox peaks and good linear electrocatalytic response toward the oxidation of sulfite between 0.02 and 10.0 mM. Both absorption and emission of Rub2P depleted by an anode potential (+0.9 V vs. Ag–AgCl/0.05 M NaCl) are found to be effectively restored by the electrocatalytic oxidation of sulfite. A [Cu(phen)2Cl]+/SWCNTs/C electrode (phen = 1,10-phenanthrothine, SWCNTs = single-walled nanotubes and C = graphite) is also fabricated, showing an excellent linear electrocatalytic reduction response to H2O2 between 0.05 and 1.0 mM. On the basis of photoelectrocatalysis of Rub2P and electrocatalysis of [Cu(phen)2Cl]+, a photo-stimulated SO32−/H2O2 fuel cell with a saturated KCl salt-bridge is elaborately assembled. The proposed hybrid fuel cell upon 0.1 mW cm−2 UV light has attractive performances, which indicate open-circuit photovoltage (Voc) of 0.612 V, short-circuit photocurrent (Isc) of 153.96 μA cm−2 and maximum power density (Pmax) of 33.55 μW cm−2 at 0.46 V, fill factor (ff) of 0.36 and photoenergy conversion efficiency (η) of 35.6%, respectively. The results from this study provide an effective method for better designing and building photo-stimulated enzyme-free fuel cells.

•V-shaped di-Ru(II) complex binds to DNA groove-surfaces with high binding affinity.•Luminescent di-Ru(II) complex can effectively induce condensation of DNA.•Herring sperm DNA is condensed into long chain particle clusters.•High salt concentration facilitates decondensation of DNA-based adducts.This paper first reports on the condensation of DNA to a tightly packed state induced by a V-shaped di-ruthenium(II) complex [Ru2(bpy)4(mbpibH2)]Cl4 (bpy = 2,2′-bipyridine and mbpibH2 = 1,3-bis([1,10]phenanthroline[5,6-d]imidazol-2-yl)benzene), which binds to the groove of herring sperm DNA (hsDNA) with the binding constant of 2.0 × 107 M− 1 (0.05 M NaCl, pH 7.2). The di-Ru(II) complex is found to induce the condensation of both hsDNA to long chain-like particle clusters and originally circular plasmid pBR322 DNA to particulate structure under neutral conditions. More interestingly, the presence of NaCl has a significant impact on the condensation and decondensation of DNA upon incorporation of [Ru2(bpy)4(mbpibH2)]4 +, representing tunable luminescence characteristics by NaCl. High salt concentration facilitates the decondensation of DNA-[Ru2(bpy)4(mbpibH2)]4 + adducts. The results from this study offer an effective method to control the condensation and decondensation of DNA upon incorporation of luminescent concentrators.A V-shaped luminescent di-Ru(II) complex bound in DNA grooves can induce the formation of DNA-based adducts, which are released by varying NaCl concentration.

•Electrochemical oxidation of Ru(II)-based unit deactivates characteristic spectral response.•Ru(III)-based species are generated from electrochemical oxidation and visible light excitation.•Electrocatalytic response of ruthenated porphyrin shows a linear dependence on guanine.•Electrocatalytic oxidation of guanine indicates an EC′ mechanism.An in situ spectroelectrochemical method has been successfully used to study the electrocatalytic oxidation of guanine on an anisomerous ruthenated porphyrin [Ru(bpy)2(MPyTMPP)Cl]+ (bpy = 2, 2′-bipyridine and MPyTMPP = 5-(4-pyridyl)-10,15,20-tris(4-metylphenyl)porphyrin) modified indium-tin oxide (ITO) electrode. The [Ru(bpy)2(MPyTMPP)Cl]+/ITO electrode shows a pair of well-defined redox peaks at the formal potential of 0.79 V (vs. Ag–AgCl/0.05 M NaCl) and an intense emission peak at 654 nm. The evidences from photo-induced potentiometric measurement and electrochemically induced emission spectra under the excitation of visible light suggest the formation of Ru(III)-based species, which quenches the luminescence of Ru(II)-based excited states by an analogous Stern–Volmer model. The [Ru(bpy)2(MPyTMPP)Cl]+/ITO electrode exhibits a good linear electrocatalytic response for guanine oxidation between 0.05 and 0.4 mM. The electrocatalytic oxidation of guanine is found to fully restore the characteristic spectral response weakened by Ru(III)-based species. Taken together, the results from this study provide a powerful basis for better understanding the electrocatalytic and photo-induced oxidation of analytes by dye-redox mediators.Graphical abstract

A redox-active [Ru(bpy)2(tatp)]2+–BSA–SWCNTs (bpy=2,2′-bipyridine, tatp=1,4,8,9-tetra-aza-triphenylene, BSA=bovine serum albumin, SWCNTs=single-walled carbon nanotubes) hybrid film is fabricated on an indium–tin oxide (ITO) electrode via one-step electrochemical co-assembly approach. BSA is inherently dispersive and therefore served as the linking mediator of SWCNTs, which facilitate the redox reactions of [Ru(bpy)2(tatp)]2+ employed as a reporter of BSA. The evidences from differential pulse voltammetry, cyclic voltammetry, scanning electron microscope, emission spectroscopy and fluorescence microscope reveal that the [Ru(bpy)2(tatp)]2+–BSA–SWCNTs hybrid can be electrochemically co-assembled on the ITO electrode, showing two pairs of well-defined Ru(II)-based redox waves. Furthermore, the electrochemical co-assembly of the [Ru(bpy)2(tatp)]2+–BSA–SWCNTs hybrid is found to be strongly dependent on the simultaneous presence of BSA and SWCNTs, indicating a good linear response to BSA in the range from 6 to 50 mg L−1. The results from this study provide an electrochemical co-assembly method for the development of non-redox protein biosensors.Graphical abstractHighlights► A [Ru(bpy)2(tatp)]2+–BSA–SWCNTs film is co-assembled on ITO electrodes. ► The hybrid film shows two pairs of well-defined Ru(II)-based redox waves. ► The presence of BSA-linked SWCNTs promotes electrochemical assembly of [Ru(bpy)2(tatp)]2+. ► The BSA sensor shows a good linear response between 6 and 50 mg L−1.

A multiple sweep voltammetry is effectively applied to the electrochemical assembly of polypyridyl cobalt(III) complexes [Co(phen)2(tatp)]3+ and [Co(phen)3]3+ (where phen = 1,10-phenanthroline and tatp = 1,4,8,9-tetra-aza-triphenylene) on a glassy carbon electrode modified with DNA or sodium dodecyl sulfate (SDS)-dispersed multi-walled carbon nanotubes (MWCNTs). The DNA-MWCNTs and SDS-MWCNTs are found to impact redox reactions of [Co(phen)2L]3+ (L = phen or tatp) adsorbed on the electrode surfaces. The anionic surfactant (SDS) facilitates the adsorption of [Co(phen)2L]3+ on the MWCNT surfaces via a fully-packed π–π stacking mode. An excess amount of DNA as the dispersant attached to the surface of MWCNTs interferes with the π–π stacking between MWCNTs and [Co(phen)2L]3+, representing a DNA-bridged binding mode. Moreover, the DNA-MWCNT or SDS-MWCNT modified electrodes are suitable for the detection of 6-mercaptopurine (6-MP) using [Co(phen)2(tatp)]3+ as voltammetric probes. The proposed sensor exhibits a high selectivity to 6-MP (detection limit = 0.05 μM) and a good linear response in the range from 0.2 μM to 0.2 mM.Graphical abstractHighlights► Electrochemical assembly of [Co(phen)2L]3+ on MWCNT surfaces. ► SDS facilitates adsorption of [Co(phen)2L]3+ by fully-packed π–π stacking. ► Adsorption of [Co(phen)2L]3+ on DNA-MWCNT surfaces is via DNA-bridged binding mode. ► A 6-mercaptopurine sensor shows a good linear response between 0.2 μM and 0.2 mM.

An imidazophenanthroline-containing ruthenium(II) complex [Ru(bpy)2(mbpibH2)]2+ (bpy = 2,2′-bipyridine, mbpibH2 = 1,3-bis([1,10]phenanthroline[5,6-d]imidazol-2-yl)benzene) can bind DNA through groove-binding and/or non-classical intercalation modes, revealed by spectrophotometric methods, viscosity measurements and variable ionic strength experiments. On the basis of binding interactions between cationic [Ru(bpy)2(mbpibH2)]2+ and anionic DNA at a molar ratio of 1:1, a yellow transparent cast film has been assembled on an indium-tin oxide (ITO) surface using a solution-based self-standing method. The prepared DNA-[Ru(bpy)2(mbpibH2)]2+ film shows a bi-exponential luminescence decay with τ1 = 62.1 ns (8.0%) and τ2 = 594.5 ns (92.0%), whose lifetimes become much shorter than those of DNA-bound [Ru(bpy)2(mbpibH2)]2+ in buffer solutions. The Ru(II) complex with a free bi-dentate coordination site in the DNA cast film shows tunable luminescence, quenched dynamically by Cu2+ and restored by using EDTA to eliminate two modes of Cu2+-binding. The results from this study provide a significant foundation for better understanding the fabrication and modulation of a DNA-based solid luminescence device using the Ru(II) complexes as DNA-concentrating and signal-sensing agents.Graphical abstractHighlights► Ru(II) complexes can bind DNA via groove-binding and/or non-classical intercalation modes. ► Luminescent Ru(II)-based DNA films are assembled on ITO surfaces. ► Ru(II)-based DNA films show two-mode tunable photoluminescence by Cu2+ and EDTA.

The quenching and recovery kinetics of photoluminescence of [Ru(bpy)2(tatp)]2+ (Ru1) and [Ru(bpy)2(dmtatp)]2+ (Ru2) intercalated within DNA (where bpy = 2,2′-bipyridine, tatp = 1,4,8,9-tetra-aza-triphenylene and dmtatp = 2,3-dimethyl-1,4,8,9-tetra-aza-triphenylene) have been investigated by steady-state and time-resolved methods performed at various temperatures (293–333 K). Two complexes Ru1 and Ru2 show a single-exponential luminescence decay with τRu1 = 246.0 ns and τRu2 = 513.5 ns, whose luminescence upon intercalating into DNA exhibits very consistent bi-exponential decay changes. The addition of Cu2+ ions is found to dynamically quench the luminescence of both DNA-bound Ru(II) complexes, involving a spontaneous exothermic process. The sequential addition of EDTA can partially recover the luminescence quenched by Cu2+, however depending on methyl substituents of the intercalative ligand. The chemical conversion and luminescence control mechanism of the two DNA-bound Ru(II) complexes is discussed in detail. The present results should be of value for better understanding chemical modulation of DNA-bound Ru(II) complexes as luminescence probes.Graphical abstractHighlights► Cu2+ addition quenches dynamically luminescence of DNA-bound Ru(II) complexes. ► Luminescence quenching involves a spontaneous exothermic process. ► EDTA addition recovers partially the quenched luminescence. ► Luminescence tuning depends on structure-based intercalative ligands.

A phenazine-containing Ru(II) complex [Ru(bpy)2(tatp)]2+ (bpy = 2,2′-bipyridine and tatp = 1,4,8,9-tetra-aza-triphenylene) is first applied to a modification of the nano-TiO2/indium-tin oxide (ITO) electrode by the method of repetitive voltammetric sweeping. The resulting [Ru(bpy)2(tatp)]2+-modified TiO2 electrode shows two pairs of well-defined redox waves and excellent electrocatalytic activity for the oxidation of guanine. [Ru(bpy)2(tatp)]2+ on TiO2 surfaces exhibits intense absorbance and photoluminescence in visible region, revealed by absorption spectra, emission spectra and fluorescence microscope. While [Ru(bpy)2(tatp)]2+-sensitized TiO2 is functionalized as an anode to combine with a continuous wave green laser via an optical microscope, the luminescence of Ru(II)-based excited states can be enhanced by the oxidation of guanine. Furthermore, the [Ru(bpy)2(tatp)]2+-sensitized TiO2 electrode is used as photoanode and hemoglobin-modified single-walled carbon nanotubes (SWCNTs) as cathode for the elaboration of a photo-stimulated guanine/H2O2 fuel cell with a saturated KCl salt-bridge. It becomes evident that the photo-stimulated fuel cell performance depends strongly on the excited states of Ru(II) complex-sensitized anodes as well as the electrocatalytic oxidation of guanine. This study provides an electrochemically-tuned luminescence method for better evaluating contributions of the sensitizer excited states to photo-stimulated fuel cells.Graphical abstractHighlights► The Ru(II) complexes adsorbed on TiO2 surfaces can catalyze the oxidation of guanine in the absence and presence of light irradiation. ► The photosensitizers possessing the luminescence quenched by anodic electrode potentials are suitable for use as the anodes of photo-stimulated fuel cells. ► On the basis of the electrochemically-tuned photoluminescence of Ru(II) complexes-sensitized TiO2 anodes, a photo-stimulated guanine/H2O2 fuel cell is fabricated.

In this correspondence, we report on the first preparation of [Ru(bpy)2(dppz)]2+-intercalated (bpy = 2,2'-bipyridine; dppz = dipyrido[3,2-a:2',3'-c]phenazine) DNA films on an indium−tin oxide surface via a solution-based self-standing strategy, carried out by the direct mixing of aqueous solutions of both anionic DNA and cationic metallointercalator at a molar ratio of 5:6. The luminescence of a [Ru(bpy)2(dppz)]2+-intercalated DNA cast film is studied and found to show excellent tunable characteristics by Cu2+ ions and ethylenediaminetetraacetic acid addition.

The electrochemical oxidation of DNA mediated by [Ru(bpy)2tatp]2+ (bpy = 2,2′-bipyridine, tatp = 1,4,8,9-tetra-aza-triphenylene) upon incorporation of [Co(phen)3]3+ (phen = 1,10-phenanthroline) has been investigated. The results from emission spectra and fluorescence microscope images suggest the formation of an aggregate containing [Ru(bpy)2tatp]2+, DNA and [Co(phen)3]3+ based on the strong interactions. The evidences from repetitive differential pulse voltammograms and cyclic voltammogams reveal that the presence of [Co(phen)3]3+ can promote the oxidation of DNA mediated by [Ru(bpy)2tatp]2+ on an indium tin oxide (ITO) electrode. The oxidative response of DNA shows a cumulative enhancement with increasing the voltammetric sweeping number, and a stable linear response to DNA is found between 0.001 mM and 0.1 mM. Furthermore, the oxidative mechanism of DNA mediated by [Ru(bpy)2tatp]2+ upon incorporation of [Co(phen)3]3+ becomes evident, depending on the concentration of DNA and mediators, the structure of mediators and scan rate. The results from this study provide a significant basis for better understanding the oxidative damage of DNA mediated by DNA-binding agents.Graphical abstractHighlights► Co(III) complexes weaken DNA-promoted assembly of [Ru(bpy)2tatp]2+ on ITO electrodes. ► Co(III) complexes promote Ru(II)-mediated oxidation of DNA. ► Oxidative response of DNA shows a linear range from 0.001 to 0.1 mM.

A classical ruthenium(II) complex [Ru(bpy)2(dppz)]2+ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a:2′,3′-c]phenazine) was combined with guanine and single-walled carbon nanotubes dispersed with DNA (SWCNTs-DNA) to prepare electrochemically tunable photoluminescence materials. These multi-component aggregates were found to show enhanced luminescence by the electrocatalytic oxidation of guanine under the excitation of a continuous wave green laser at a constant anodic potential via an electrode-solution interface. The results from this study provide a significant foundation for better understanding of DNA-based luminescent devices.

A polymer-based pH electrode has been successfully fabricated via a simple electropolymerization of bisphenol A (BPA) on an indium tin oxide (ITO) electrode using repetitive voltammetric sweeping. A combination of voltammetry, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy revealed that polybisphenol A (PBPA) films with benzoquinonyl and hydroquinonyl groups not only showed basically reversible redox activities, but also exhibited the mixed ionic–electronic conductivity. The redox peak potential and open circuit potential using the PBPA/ITO electrode as a pH sensor presented response slopes of −58.6 ± 1.4 mV/pH and −56.7 ± 1.6 mV/pH, respectively. The potentiometric signals were stable in electrolyte solutions and displayed a wide response range for the detection of pH. Compared with the commercial glass pH electrode, the PBPA-based electrode showed several advantages including easy fabrication, low cost, high stability and selectivity.

The homogeneous and mediated oxidation of guanine by [Ru(bpy)3]2+ (2,2′-bipypyridine) in the presence of surfactants and single-walled carbon nanotubes (SWCNTs) has been investigated using cyclic voltammetry, repetitive differential pulse voltammetry and rotating electrode method. In acidic medium, the oxidation of guanine was controlled by mass transport process of [Ru(bpy)3]2+ in solution, leading to a homogeneous electrocatalysis. In neutral medium, the result from emission spectroscopy suggested the formation of the aggregates containing [Ru(bpy)3]2+, dihexadecyl phosphate (DHP) and guanine. The electrocatalysis of [Ru(bpy)3]2+ toward guanine oxidation was promoted by anionic surfactant DHP and, however, hindered by an excess amount of hexadecyl trismethyl ammonium chloride (HTAC) or SWCNTs added to solutions. The electrocatalytic mechanism of [Ru(bpy)3]2+ for guanine oxidation becomes evident, strongly depending on the presence of anionic or cationic surfactants and SWCNTs.

A method for the chemical modulation of the photoluminescence of a DNA-bound diruthenium(II) complex, [(bipy)2Ru(bpib)Ru(bipy)2]4+ (bipy = 2,2′-bipyridine, bpib = 1,4-bis([1, 10]phenanthroline [5,6-d]imidazol-2-yl) benzene) by the introduction of Cu2+ ion and EDTA has been developed. The diruthenium(II) complex showed strong photoluminescence both in buffer solutions and on an indium-tin oxide (ITO) surface, which was not modulated by Cu2+ or EDTA. The DNA-bound [(bipy)2Ru(bpib)Ru(bipy)2]4+ with a binding constant of 3.8 × 104 M−1 showed an enhancement in the luminescence based on the electrostatic interaction between the complex and DNA. The presence of Cu2+ was found to quench the luminescence of DNA-bound [(bipy)2Ru(bpib)Ru(bipy)2]4+, but the quenched luminescence was recovered by addition of an equimolar concentration of EDTA. Hence, the photoluminescence of DNA-bound [(bipy)2Ru(bpib)Ru(bipy)2]4+ depends strongly on the introduction of Cu2+ and EDTA.

The electrochemical properties of ferrocene (Fc) on a glassy carbon (GC) electrode modified by multi-walled carbon nanotubes (MWNTs) in the presence and absence of surfactants have been investigated by progressively voltammetric sweeping. Dihexadecyl phosphate (DHP) and hexadecyl trismethyl ammonium chloride (HTAC) are found to impact the redox reactions of Fc adsorbed on MWNT surfaces. An excess amount of DHP dispatches Fc from MWNTs surfaces, leading to weakly adsorbed configuration of Fc. The formal potential of the adsorbed Fc in the presence of DHP shifts to a lower potential. Cationic surfactant HTAC on MWNT surfaces depresses the redox reactions corresponding to the weakly adsorbed configuration of Fc. It becomes evident that the configuration and hence redox reactions of Fc depend strongly on the presence and concentrations of surfactants on the electrode surfaces and in the buffer solutions.

The luminescence properties of [Ru(bpy)2MDHIP]2+ (bpy = 2,2′-bipyridine, MDHIP = 2,4-dihydrophenyl-imidazo[4,5-f][1,10]phenanthroline) in the absence and presence of DNA modulated by the introduction of Cu2+ ion and EDTA have been investigated. It is found that the ruthenium(II) complex can insert and stack between the base pairs of calf thymus DNA with MDHIP ligand, and the intramolecular hydrogen bond is located inside of the DNA. The presence of DNA can enhance the luminescence intensities of [Ru(bpy)2MDHIP]2+ both in buffer solution and on an ITO surface. Moreover, the luminescence intensities of [Ru(bpy)2MDHIP]2+ and DNA-bound [Ru(bpy)2MDHIP]2+ are quenched by Cu2+, and next recovered by the addition of EDTA. The repetitive luminescence-modulations have been achieved through the introduction of equimolar Cu2+ and EDTA, respectively. In addition, it becomes evident that the number of luminescence-modulation cycles for [Ru(bpy)2MDHIP]2+ in the absence and presence of DNA is influenced by the cumulative concentrations of CuEDTA, generated successively by the strong coordination of Cu2+ to EDTA.

Electrochemical oxidation of guanine mediated by [Ru(bpy)2dpp]2+ (where bpy = 2,2′-bipyridine, dpp = 2,3-bis (2-pyridyl) pyrazine) and their electrochemical assembly at an ITO electrode prompted by guanine have been investigated with cyclic voltammetry and differential pulse voltammetry. It is found that [Ru(bpy)2dpp]2+ can serve as an excellent mediator to induce the oxidation of guanine, and the mediated peak currents increase linearly with the rise of guanine concentration in the range from 0.01 to 0.20 mmol L−1. Interestingly, with the increase of repetitive voltammetric sweeping numbers, [Ru(bpy)2dpp]3+/2+ can be assembled onto the ITO electrode and guanine has the ability to enhance the peak currents of prewaves. Also, with the rise of guanine concentration from 0.01 to 0.15 mmol L−1, the peak currents of prewaves increase gradually. Meanwhile, the mediated mechanism of guanine oxidation by [Ru(bpy)2dpp]2+ and the assembled process of [Ru(bpy)2dpp]3+/2+ on the ITO surface in the presence of guanine are discussed in detail.

Modulation of the luminescence properties of a di-ruthenium(II) complex [(bpy)2Ru(BL)Ru(bpy)2]4+ (bpy = 2,2′-bipyridine, BL = 2-hydroxyl-5-methyl-1,3-bis([1,10]phenanthroline-[5,6-d]imidazol-2-yl)benzene) by DNA and/or Cu2+ ion has been investigated. It is found that the ruthenium(II) complex can coordinate to the Cu2+ ion in both the absence and presence of DNA. Binding to DNA is through electrostatic interactions and the intramolecular hydrogen bond in the complex is located outside of the DNA. The binding constant is 1.6 × 104 M−1. Moreover, it is demonstrated that DNA has the ability to enhance the luminescence intensities of both the di-ruthenium(II) complex and the tri-metallic system generated by chelating with Cu2+. Conversely, Cu2+ ion can quench the luminescence of both the free ruthenium(II) complex and the DNA-bound ruthenium(II) complex.

The electrochemical assembly of [Ru(bpy)2tatp]2+ (where bpy = 2,2′-bipyridine, tatp = 1,4,8,9-tetra-aza-triphenylene) on the multi-walled carbon nanotubes-modified glassy carbon electrode (MWNTs/GC) in the presence of anionic and cationic surfactants has been investigated. A diffusion-controlled wave and three prewaves are exhibited on the differential pulse voltammogram of [Ru(bpy)2tatp]2+. The formal potential of the prewaves is found to be much negative than that of the diffusion-controlled wave. An appropriate amount of anionic surfactants including dihexadecyl phosphate (DHP) and deoxyribonucleic acid (DNA) can prompt the assembly of [Ru(bpy)2tatp]2+ on the MWNTs/GC electrode by using the method of repetitive voltammetric sweeping. In contrast, cationic surfactant such as hexadecyl trismethyl ammonium chrolide (HTAC) dispersed on the MWNTs surface is found to inhibit the assembly of [Ru(bpy)2tatp]2+. Meanwhile, the assembled principle of [Ru(bpy)2tatp]2+ on the MWNTs/GC electrode with the participation of surfactants is discussed in detail.

[Co(phen)3]3+/multi-walled carbon nanotubes modified graphite electrode ([Co(phen)3]3+/MWNT/C) has been developed to monitor quantitatively 6-mercaptopurine (6-MP) concentration and to study the effect of rabbit blood as disturbance agents on the determination. Multi-walled carbon nanotubes (MWNT) are used for efficient immobilization of [Co(phen)3]3+. The prepared [Co(phen)3]3+/MWNT/C electrode exhibits an excellent redox activity. 6-MP is detected by monitoring the reductive current values of free [Co(phen)3]3+ or the [Co(phen)3]3+–6-MP complex generated by the interaction of [Co(phen)3]3+ on the MWNT modified graphite electrode with 6-MP. These electrochemical signals are found to be sensitive enough to monitor 6-MP concentration changes, and the [Co(phen)3]3+/MWNT/C electrode has also been applied to the evaluation of 6-MP in the presence of rabbit blood.

The adsorbed process of ferrocene on a glassy carbon (GC) electrode modified by multi-walled carbon nanotubes (MWNTs) and electrochemical properties of the adsorbed layers are investigated. It is found that the redox process of ferrocene in solution is controlled by diffusion and surface electrochemical steps on the MWNT/GC electrode in contrast to the diffusion-controlled process of ferrocene on the GC electrode. The adsorbed ferrocene exhibits a pair of well-defined redox waves in the potential range from − 0.2 V to 0.6 V. Interestingly, two pairs of obvious redox waves for the adsorbed ferrocene are observed at the switching potential over 0.8 V and the peak current values of redox waves in more positive potential increase with the enlarging switching potential. The electrochemical reaction model of ferrocene adsorbed on the MWNT/GC electrode is proposed.

The effects of copper ion on the interaction of [Ru(bpy)2HPIP]2+(bpy = 2,2′-bipyridine, HPIP = 2-(2-hydroxyphenyl) imidazo [4,5-f] [1, 10] phenanthroline) with DNA have been investigated by electronic absorption spectroscopy and fluorescence spectroscopy. HPIP ligand of the complex with an intramolecular hydrogen bond can bind Cu2+ in the absence of DNA, as revealed by the absorbance and fluorescence decrease for [Ru(bpy)2HPIP]2+. The resultant heterometallic complex binds to DNA via intercalation of HPIP into the DNA base pairs and its DNA-binding ability is stronger than [Ru(bpy)2HPIP]2+ itself. The DNA bound [Ru(bpy)2HPIP]2+ cannot bind Cu2+ at low Cu2+ concentration and the intramolecular hydrogen bond in HPIP is located inside the DNA helix. While the Cu2+ concentration is relative high, Cu2+ can quench the fluorescence of DNA bound [Ru(bpy)2HPIP]2+. The quenching reason is proposed.

A controllable assembly technique of [Ru(bpy)2IP]3+/2+ (where bpy = 2,2′-bipyridine and IP = imidazo[4,5,f][1,10]phenanthroline) promoted by calf thymus DNA at an ITO electrode is proposed. The stable assembled layer containing [Ru(bpy)2IP]3+/2+ and double stranded DNA is obtained on the ITO electrode using repetitive voltammetric sweeping, confirmed by ex situ voltammetry, X-ray photoelectron spectroscopy (XPS) and the inverted fluorescence microscopy. There exist two pairs of diffusion-controlled waves and two pairs of prewaves for [Ru(bpy)2IP]2+ in the voltammetric sweeping process. The half-wave potentials of the prewaves are far more negative than those of the diffusion-controlled waves. These experimental results suggest that double stranded DNA is enable to accelerate and increase the controllable assembly of Ru(bpy)2IP]3+/2+ by using the ITO surface. The fluorescence microscopy imaging reveals that [Ru(bpy)2IP]3+/2+ has the ability to bind with double strand DNA. The fluorescence intensity of [Ru(bpy)2IP]3+/2+ with DNA is stronger than that without DNA.

DNA-binding properties of novel copper(II) complex [Cu(l-Phe)(TATP)(H2O)]+, where l-Phe = l-phenylalaninate and TATP = 1,4,8,9-tetra-aza-triphenylene are investigated using electronic absorption spectroscopy, fluorescence spectroscopy, voltammetry and viscosity measurement. It is found that the presence of calf thymus DNA results in a hypochromism and red shift in the electronic absorption, a quenching effect on fluorescence nature of ethidium bromide–DNA system, an enhanced response on voltammograms of [Co(phen)3]3+/2+–DNA system, and an obvious change in viscosity of DNA. From absorption titration, fluorescence analysis and voltammetric measurement, the binding constant of the complex with DNA is calculated. The latter two methods reveal the stronger binding of [Cu(l-Phe)(TATP)(H2O)]+ complex to double strand DNA by the moderate intercalation than [Co(phen)3]3+. Such a binding induces the cleavage of plasmid pBR322 DNA in the presence of H2O2.

A polymer-based pH electrode has been successfully fabricated via a simple electropolymerization of bisphenol A (BPA) on an indium tin oxide (ITO) electrode using repetitive voltammetric sweeping. A combination of voltammetry, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy revealed that polybisphenol A (PBPA) films with benzoquinonyl and hydroquinonyl groups not only showed basically reversible redox activities, but also exhibited the mixed ionic–electronic conductivity. The redox peak potential and open circuit potential using the PBPA/ITO electrode as a pH sensor presented response slopes of −58.6 ± 1.4 mV/pH and −56.7 ± 1.6 mV/pH, respectively. The potentiometric signals were stable in electrolyte solutions and displayed a wide response range for the detection of pH. Compared with the commercial glass pH electrode, the PBPA-based electrode showed several advantages including easy fabrication, low cost, high stability and selectivity.