A new rhodamine B-based fluorescent probe RL for Cu2+ has been designed, synthesized, and characterized. It exhibits a very high selectivity and sensitivity for the detection of Cu2+ in CH3CN:H2O = 1:9 (v/v) buffered with Britton–Robinson (pH = 7.02), the detection limit can reach 0.739 nM, which is the lowest reported. Furthermore, the probe RL can be made into test papers to detect the cupric ions in drinking water by the naked eye. RL can also be used for imaging Cu2+ in living cells and is almost non-toxic.

A dual emission of two hererodinuclear Os–Ru labels with a linear calibration curve between the ECL intensity ratio (I731/I618) and tripropylamine (TPA) concentration was first established.

A series of heterodinuclear complexes [(bpy)2Ru(bpy)(CH2)n(bpy)Ir(df-ppy)2]3+ (1, where bpy is 2,2′-bipyridyl, df-ppy is 2-(2,4-difluorophenyl)pyridine, and n = 10, 12, 14) have been designed and synthesized. Both red (from the Ru moiety) and green (from the Ir moiety) electrochemiluminescence (ECL) can be acquired simultaneously thorough alternation of the scanning potentials; especially, a good linear calibration curve between the ECL intensity ratio (IRu/IIr) and the scanning potential can be reached over a potential range from 0.55 to 1.6 V. All of this provides a general methodology for developing electrochemistry induced light-emitting devices and a ratiometric ECL detection method.

A novel dual luminescence (523 nm and 615 nm) heterodinuclear RuIr complex for RNA detection was developed, which was successfully used to image rRNA in living cells.

A naphthylamine–rhodamine hybrid ratiometric and colorimetric fluorescent probe (RN) was designed and synthesized. RN can identify Pd2+ ions with high selectivity and sensitivity. Furthermore, the probe can be used to monitor Pd2+ ions in live mice by fluorescence imaging.

The fluorescence of propidium iodide (PI) can be effectively quenched with the addition of graphene oxide (GO) in aqueous solution, due to the formation of a physical adsorption material named GO–PI. A fluorescence enhancement of approximately 80 times can be observed after addition of a certain amount of DNA/RNA into the above-mentioned solution. Meanwhile, it is found that the GO–PI can enter into the nuclei and stain the DNA/RNA of living human breast cancer cells MCF-7, while PI alone cannot cross the cellular membrane in the control experiment, demonstrating GO can be employed to be an efficient PI delivery nanomaterial for live cell staining.

An aniline–rhodamine-based ratiometric fluorescent probe (RI) was designed and synthesized. RI, the metal coordinating chromophoric ligand, exhibited high selectivity and sensitivity for Pd2+ ions with a detection limit of 73.8 nM. This method of Pd2+ detection had a 10 min response time.

A rapid and highly selective luminescent probe has been developed to determine the in vitro and in vivo ClO−/H2S redox cycle using a ruthenium tris-bipyridyl complex covalently linked with phenothiazine. The luminescence intensity was considerably enhanced upon the addition of ClO− due to the oxidation of the probe to its sulfoxide derivative, which quickly returned to the original level by the reaction with H2S due to the reconstitution of the probe. The redox cycle can be repeated at least 12 times. Under optimal conditions, the luminescence intensities are linear over the concentration range of 1 × 10−9 to 1 × 10−4 mol L−1 for ClO− and 1 × 10−9 to 1 × 10−4 mol L−1 for H2S, and the detection limits are 1.8 × 10−11 mol L−1 for ClO− and 1.2 × 10−11 mol L−1 for H2S, which are much lower than those obtained with other detection methods. The proposed method is simple in design and fast in operation, and is suitable for the reversible determination of ClO− and H2S in vitro and in vivo with high selectivity.

A near infrared dye was synthesized to form an inclusion complex with cucurbit[8]uril (CB[8]) in aqueous solution which disrupted the aggregation of the dye, leading to a 30-fold fluorescence increase. This inclusion complex exhibited ultrastable photostability with good mitochondria-staining capability.

The host–guest interaction of trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (DSMI) with cucurbit[7]uril (CB[7]) was investigated through fluorescence, absorption, 1H NMR and mass spectrometry. DSMI can be included by CB[7] with 1:2 stoichiometry to form the DSMI/CB[7] complex, exhibiting a larger binding affinity than that of DNA. To make a comparison with DSMI, another pyridium vinyl group was introduced into the aniline ring of DSMI to get a hemicyanine derivative D2, and a ternary complex among D2, CB[7] and DNA was formed. All these provide new insights to investigate the interaction of organic dyes, CB[7] and DNA.

The heterodinuclear metal complex OsIr has been designed and synthesized. Upon irradiation with visible light, OsIr exhibits dual luminescence (534 and 721 nm) due to the coexistence of the iridium and osmium activating centers. The cellular uptake of OsIr examined by laser scanning confocal microscopy revealed an apparent nucleolar staining. The iridium moiety interacts with proteins and RNA to trigger a significant luminescence enhancement, whereas the osmium moiety displays a near-infrared luminescence; a ratiometric luminescence response between the two moieties was observed upon protein addition.

The fluorescence of Ru(phen)3Cl2 (tris(1,10-phenanthroline)ruthenium(II) dichloride) can be effectively quenched with the addition of graphene oxide in aqueous solution, due to the formation of a GO–Ru hybrid. A fluorescence enhancement of approximately 50 times can be observed after the addition of a certain amount of DNA into the above-mentioned solution. The fluorescence increase is linearly proportional to the amount of DNA added in the concentration range of 0–70 μM and the DNA detection limit is down to 3.3 × 10−8 M. Meanwhile, it is found that the GO–Ru hybrid can enter into the nuclei and stain the DNA of living human breast cancer cells MCF-7, while Ru(phen)3Cl2 alone cannot cross the cellular membrane in the control experiment. This method can be employed to detect DNA both in vitro and in vivo.

Chemically converted graphene (CCG) was found to effectively quench the fluorescence emission of Cy3 dye 1 (the intensity is down to 1/38 of 1 alone) in aqueous solution, due to the formation of a CCG–1 hybrid. After the addition of a certain amount of bovine serum albumin (BSA) into the above-mentioned system, about 60 times fluorescence enhancement was observed for the hybrid CCG–1. This was employed to discriminate BSA: the fluorescence intensity was found to be proportional to the BSA added in the concentration range from 0 to 8 × 10−6 M, and the BSA detection limit was down to 5 × 10−8 M.

In order to find the ideal carbon chain linkage number n for achieving the highest ECL in bimetallic ruthenium tris-bipyridyl complexes, a series of novel complexes [(bpy)2Ru(bpy′)(CH2)n(bpy′)Ru(bpy)2]4+ (1, where bpy is 2,2′-bipyridyl, n = 10, 12, 14) for a coreactant electrochemiluminescence (ECL) system have been synthesized. Their ECL properties at a Au electrode have been studied in 0.1 M phosphate buffer by using tripropylamine (TPrA), 2-(dibutylamino)ethanol (DBAE) and melamine as the coreactant, to compare with that of the previously reported bimetallic ruthenium analogous complex [(bpy)2Ru(bpy′)(CH2)8(bpy′)Ru(bpy)2]4+. The results demonstrate that the ECL intensity depends largely on the length of the saturated carbon chain linkage number n. The highest ECL is reached when n = 10, suggesting that a synergistic effect on ECL enhancement co-exists between the two intramolecular linked ruthenium activating centers. Density functional theory (DFT) calculation demonstrated that the optimized bond distances between Ru and N(bpy′) are the longest both in the ground and the excited triplet states in the case of n = 10, while those for Ru and N(bpy) are the shortest in the excited triplet states. All these factors may be responsible for the above mentioned results. This study provided a methodology to further improve and tune ECL efficiency by using bimetallic ruthenium complexes linked by a flexible saturated carbon chain.

About 270 times fluorescence enhancement was observed when the hemicyanine dye, trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (DSMI), was included by cucurbit[6]uril (CB[6]). The 1:1 stoichiometry of DSMI/CB[6] complex was determined through optical spectra and 1H NMR measurement. The large fluorescence enhancement was achieved by prohibiting the twisted intramolecular charge transfer (TICT) process of DSMI inside the distorted cavity of CB[6], together with the ion-dipole interaction between DSMI and CB[6]. The distortion of the CB[6] cavity, being as the major reason for the great fluorescence enhancement, was further confirmed in the calculation results. A resettable and reconfigurable logic gate was also constructed with DSMI and CB[6] under different pH situations. This study lays a solid foundation for the design of molecular logic gates by a supramolecular interaction mode.Highlights► Suparmolecular interaction bewteen hemicyanine DSMI and cucurbit[6]uril was studied. ► About 270 times fluorescence enhancement can be achieved for the system. ► A resettable and reconfigurable logic gate was constructed with DSMI and CB[6].

The fluorescence of acridine orange (AO) can be quenched significantly with addition of the single-wall carbon nanotubes (SWCNTs) solution, due to the formation of a hybrid complex between AO and SWCNTs. A fluorescence enhancement of approximately 18× can be observed after the addition of certain amount of DNA into the above mentioned solution. The fluorescence increase was linearly proportional to the amount of DNA added in the concentration range of 0–50.75 μM, and the DNA detection limit was down to 8.56 × 10−8 M. This method can be used to detect DNA in vitro.Highlights► Hybrid complex of AO–SWCNTs has been utilized for DNA detection. ► The detection sensitivity can be improved due to the diminished autofluorescence. ► No more procedures have to be employed to remove free AO left in the system.

The electrochemiluminescence (ECL) of Ru(bpy)32+ at bare and single-wall carbon nanotube (SWNT) modified glassy carbon (GC) electrodes has been employed for the determination of melamine for the first time, giving a linear response (R2 = 0.99682) for melamine concentration from 1.0 × 10−10 to 1.0 × 10−5 M at a bare GC electrode in pH 10 borate buffer, and the detection limit is 1.0 × 10−10 M. However, the detection limit can be reduced further to 1.0 × 10−13 M after modification of the GC electrode by SWNTs. This is much lower compared to other detection methods. The proposed method was applied to the determination of melamine added to a commercial milk sample; the recovery is quite satisfactory with good reproducibility and stability. All of these results provide the possibility of developing a novel ECL detection method for melamine.

A series of 1-ethyl-1′-arylmethyl-4,4′-bipyridinium compounds is synthesized, where the aryl is phenyl (BEV), 2-naphthyl (NEV), 2-anthracenyl (AEV) or 1-pyrenyl (PEV). Among them, PEV and AEV can bind with calf thymus DNA mainly through intercalation and groove-binding modes, and both of them can be observed to photocleave plasmid pBR 322 DNA significantly under irradiation with a xenon arc lamp. After inclusion of cucurbit[8]uril (CB[8]), all of the aromatic donor–viologen acceptor compounds exhibit efficient DNA photocleavage ability. The reason is that CB[8] can inhibit the intramolecular backwards electron transfer in the aromatic donor–viologen acceptor molecule, prolonging the lifetime of the charge separated excited state to some extent. These studies bring a new subject in DNA photocleavage research and a potential application of the host–guest supramolecular system.

A redox-induced radical Ru(bpy)32+–(CH2)n–MV+˙ (n = 4, 7) and its dimerization in cucurbit[8]uril (CB[8]) have been observed concomitantly in aqueous solution, which depends heavily on the length of the carbon chain linkage, in the case of n = 4, the characteristic pattern for the radical dimer is predominating, while that for the radical becomes dominated for n = 7.

A stable 1:1:1 ternary inclusion donor–acceptor dyad complex PTZ–MV2+–CB[8] with NIR absorption (500–1100 nm, λmax = 756 nm) can easily be obtained by use of a supramolecular method. It exhibits photocleavage ability on supercoiled plasmid DNA (pBR322), suggesting a potential application in photodynamic therapy.

Three ruthenium complexes 1a, 1b and 1c were synthesized, in which the phenothiazine moiety was covalently linked to the ruthenium complex through a 4 carbon chain and amide bond, respectively. The results demonstrate that one PTZ moiety is preferred to reach a good ECL performance, and the 4 carbon chain linked complex 1a exhibits the highest ECL enhancement (up to about 9 times), in comparison with the commonly utilized parent Ru(bpy)32+, permitting a lower detection limit of 1.0 × 10−14 M with signal to noise of 3 for 20 mM DBAE at Au electrode.

A novel rhenium(I) bipyridyl complex 1a, [(4,4’-di-COOEt-bpy)Re(CO)3(py-NHCO-PTZ)PF6] and a model 1b, [(4,4’-di-COOEt-bpy)Re(CO)3(py-PTZ)PF6] (bpy is 2, 2’-bipyridine, py-NHCO-PTZ is phenothiazine-(10-carbonyl amide) pyridine and py-PTZ is 10-(4-picolyl) phenothiazine) were synthesized. Their photo-induced electron transfer (ET) reaction with electron acceptor methyl viologen (MV2+) in acetonitrile was studied by nanosecond laser flash photolysis at room temperature. Photoexcitation of 1 in the presence of MV2+ led to ET from the Re moiety to MV2+ generating Re(II) and methyl viologen radical (MV·+). Then Re(II) was reduced either by the charge recombination with MV·+ or by intramolecular ET from the attached PTZ, regenerating the photosensitizer Re(I) and forming the PTZ radical at 510 nm. In the case of 1b, the absorption for PTZ radical can be observed distinctly accompanied intermolecular ET, whereas not much difference at 510 nm can be detected for 1a on the time scale of the experiments. This demonstrates that the linking bridge plays a key role on the intramolecular ET in complex 1.

A series of bimetallic ruthenium complexes [(bpy)2Ru(bpy)(CH2)n(bpy)Ru(bpy)2]4+ (1, where bpy is 2,2′-bipyridinyl, n = 3, 5, 8) for the coreactant electrochemiluminescence (ECL) system have been synthesized. Their ECL property at different working electrode has been studied in 0.1 M phosphate buffer by using tripropylamine (TPrA) and 2-(dibutylamino) ethanol (DBAE) as the coreactant. The results demonstrate that the ECL intensity depends largely on the length of the saturated carbon chain linkage: the longer is the carbon chain, the higher is the ECL intensity. A remarkable ECL enhancement (up to about 25 times), in comparison with the commonly used metallic [Ru(bpy)3]2+, has been observed from 1c (n = 8) at Pt electrode. With 20 mM TPrA, the log of the ECL intensity increases linearly with the log of complex 1c concentrations over the concentration range of 1.0 × 10−16 to 1.0 × 10−6 M at glassy carbon electrode. The detection limit is 1.0 × 10−16 M at a signal-to-noise ratio of 3. This is the highest ECL detection limit for bimetallic system reported until now. The study provides a general methodology to further improve and tune the ECL efficiency by using multimetallic ruthenium complexes.

N-(4-Hydroxy-phenoxyethyl)-N′-ethyl-4,4′-bipyridium (1) can form a stable 1:1 inclusion complex with CB[8] in aqueous solution, in which the hydroxyphenol (HP) moiety is back-folded and inserted together with the viologen moiety into the cavity of CB[8]. When the ethyl viologen dication (EV2+) in 1 is reduced, chemically or electrochemically, an intramolecular partner radical (EV+˙-HP)/CB[8] can be detected, meanwhile, a dynamic balance between the partner radical and the intermolecular radical dimer (EV+˙-HP)2/CB[8] can be observed.

A novel dual luminescence (523 nm and 615 nm) heterodinuclear RuIr complex for RNA detection was developed, which was successfully used to image rRNA in living cells.

A dual emission of two hererodinuclear Os–Ru labels with a linear calibration curve between the ECL intensity ratio (I731/I618) and tripropylamine (TPA) concentration was first established.

A stable 1:1:1 ternary inclusion donor–acceptor dyad complex PTZ–MV2+–CB[8] with NIR absorption (500–1100 nm, λmax = 756 nm) can easily be obtained by use of a supramolecular method. It exhibits photocleavage ability on supercoiled plasmid DNA (pBR322), suggesting a potential application in photodynamic therapy.

A redox-induced radical Ru(bpy)32+–(CH2)n–MV+˙ (n = 4, 7) and its dimerization in cucurbit[8]uril (CB[8]) have been observed concomitantly in aqueous solution, which depends heavily on the length of the carbon chain linkage, in the case of n = 4, the characteristic pattern for the radical dimer is predominating, while that for the radical becomes dominated for n = 7.

N-(4-Hydroxy-phenoxyethyl)-N′-ethyl-4,4′-bipyridium (1) can form a stable 1:1 inclusion complex with CB[8] in aqueous solution, in which the hydroxyphenol (HP) moiety is back-folded and inserted together with the viologen moiety into the cavity of CB[8]. When the ethyl viologen dication (EV2+) in 1 is reduced, chemically or electrochemically, an intramolecular partner radical (EV+˙-HP)/CB[8] can be detected, meanwhile, a dynamic balance between the partner radical and the intermolecular radical dimer (EV+˙-HP)2/CB[8] can be observed.

A series of 1-ethyl-1′-arylmethyl-4,4′-bipyridinium compounds is synthesized, where the aryl is phenyl (BEV), 2-naphthyl (NEV), 2-anthracenyl (AEV) or 1-pyrenyl (PEV). Among them, PEV and AEV can bind with calf thymus DNA mainly through intercalation and groove-binding modes, and both of them can be observed to photocleave plasmid pBR 322 DNA significantly under irradiation with a xenon arc lamp. After inclusion of cucurbit[8]uril (CB[8]), all of the aromatic donor–viologen acceptor compounds exhibit efficient DNA photocleavage ability. The reason is that CB[8] can inhibit the intramolecular backwards electron transfer in the aromatic donor–viologen acceptor molecule, prolonging the lifetime of the charge separated excited state to some extent. These studies bring a new subject in DNA photocleavage research and a potential application of the host–guest supramolecular system.

The fluorescence of Ru(phen)3Cl2 (tris(1,10-phenanthroline)ruthenium(II) dichloride) can be effectively quenched with the addition of graphene oxide in aqueous solution, due to the formation of a GO–Ru hybrid. A fluorescence enhancement of approximately 50 times can be observed after the addition of a certain amount of DNA into the above-mentioned solution. The fluorescence increase is linearly proportional to the amount of DNA added in the concentration range of 0–70 μM and the DNA detection limit is down to 3.3 × 10−8 M. Meanwhile, it is found that the GO–Ru hybrid can enter into the nuclei and stain the DNA of living human breast cancer cells MCF-7, while Ru(phen)3Cl2 alone cannot cross the cellular membrane in the control experiment. This method can be employed to detect DNA both in vitro and in vivo.

Chemically converted graphene (CCG) was found to effectively quench the fluorescence emission of Cy3 dye 1 (the intensity is down to 1/38 of 1 alone) in aqueous solution, due to the formation of a CCG–1 hybrid. After the addition of a certain amount of bovine serum albumin (BSA) into the above-mentioned system, about 60 times fluorescence enhancement was observed for the hybrid CCG–1. This was employed to discriminate BSA: the fluorescence intensity was found to be proportional to the BSA added in the concentration range from 0 to 8 × 10−6 M, and the BSA detection limit was down to 5 × 10−8 M.

A new rhodamine B-based fluorescent probe RL for Cu2+ has been designed, synthesized, and characterized. It exhibits a very high selectivity and sensitivity for the detection of Cu2+ in CH3CN:H2O = 1:9 (v/v) buffered with Britton–Robinson (pH = 7.02), the detection limit can reach 0.739 nM, which is the lowest reported. Furthermore, the probe RL can be made into test papers to detect the cupric ions in drinking water by the naked eye. RL can also be used for imaging Cu2+ in living cells and is almost non-toxic.

Three ruthenium complexes 1a, 1b and 1c were synthesized, in which the phenothiazine moiety was covalently linked to the ruthenium complex through a 4 carbon chain and amide bond, respectively. The results demonstrate that one PTZ moiety is preferred to reach a good ECL performance, and the 4 carbon chain linked complex 1a exhibits the highest ECL enhancement (up to about 9 times), in comparison with the commonly utilized parent Ru(bpy)32+, permitting a lower detection limit of 1.0 × 10−14 M with signal to noise of 3 for 20 mM DBAE at Au electrode.

In order to find the ideal carbon chain linkage number n for achieving the highest ECL in bimetallic ruthenium tris-bipyridyl complexes, a series of novel complexes [(bpy)2Ru(bpy′)(CH2)n(bpy′)Ru(bpy)2]4+ (1, where bpy is 2,2′-bipyridyl, n = 10, 12, 14) for a coreactant electrochemiluminescence (ECL) system have been synthesized. Their ECL properties at a Au electrode have been studied in 0.1 M phosphate buffer by using tripropylamine (TPrA), 2-(dibutylamino)ethanol (DBAE) and melamine as the coreactant, to compare with that of the previously reported bimetallic ruthenium analogous complex [(bpy)2Ru(bpy′)(CH2)8(bpy′)Ru(bpy)2]4+. The results demonstrate that the ECL intensity depends largely on the length of the saturated carbon chain linkage number n. The highest ECL is reached when n = 10, suggesting that a synergistic effect on ECL enhancement co-exists between the two intramolecular linked ruthenium activating centers. Density functional theory (DFT) calculation demonstrated that the optimized bond distances between Ru and N(bpy′) are the longest both in the ground and the excited triplet states in the case of n = 10, while those for Ru and N(bpy) are the shortest in the excited triplet states. All these factors may be responsible for the above mentioned results. This study provided a methodology to further improve and tune ECL efficiency by using bimetallic ruthenium complexes linked by a flexible saturated carbon chain.

An aniline–rhodamine-based ratiometric fluorescent probe (RI) was designed and synthesized. RI, the metal coordinating chromophoric ligand, exhibited high selectivity and sensitivity for Pd2+ ions with a detection limit of 73.8 nM. This method of Pd2+ detection had a 10 min response time.