Xue-Wen Liu

Background eliminated signal-on electrochemical aptasensing platform for highly sensitive detection of protein

Using platelet-derived growth factor B chain dimer (PDGF-BB) as the model target, a background current eliminated electrochemical aptameric sensing platform for highly sensitive and signal-on detection of protein is proposed in this paper. Successful fabrication of the biosensor depends on ingenious design of aptamer probe, which contains the aptamer sequence for PDGF-BB and the recognition sequence for EcoRI endonuclease. In the absence of PDGF-BB, the ferrocene labeled aptamer probe folds into a hairpin structure and forms a recognition site for EcoRI. By treatment with endonuclease, the specific and cleavable double-stranded region is cut off and redox-active ferrocene molecule is removed from the electrode surface, and almost no peak current is observed. When binding with target protein, the designed aptamer probe changes its conformation and dissociates the recognition double strand. The integrated aptamer probe is maintained when exposing to EcoRI endonuclease, resulting in obvious peak current. Therefore, a signal-on and sensitive sensing strategy for PDGF-BB detection is fabricated with eliminated background current. Under the optimized experimental conditions, a wide linear response range of 4 orders of magnitude from 20pgmL(-1) to 200ngmL(-1) is achieved with a detection limit of 10pgmL(-1). Moreover, the present aptameric platform is universal for the analysis of a broad range of target molecules of interest by changing and designing the sequence of aptamer probe.

Study on DNA binding behavior and light switch effect of new coumarin-derived Ru(II) complexes

A new ligand mhcip (mhcip=2-(4-methyl-7-hydroxyl-8-coumarinyl)imidazo[4,5-f]-[1,10]phenanthroline) and its ruthenium complexes, [Ru(L)2mhcip](2+) (L=bpy (2,2-bipyridine), phen (1,10-phenanthroline)), have been synthesized and characterized. The introduction of coumarin ring may play an important role in the strong fluorescence of the complexes. Intercalative binding mode between both complexes and CT-DNA was determined by UV-visible spectroscopy, fluorescence spectroscopy and viscosity measurements. The two complexes show efficient DNA photocleavage under irradiation at 365 nm. The cycling of light switch off and on has been achieved for both complexes through the introduction of Cu(2+) and EDTA in the absence or presence of DNA.

DNA binding, photocleavage behavior, and topoisomerase I inhibitory activity of Ru(II) complexes incorporating an asymmetric phenazine-type ligand

Two ruthenium complexes incorporating an asymmetric ligand, [Ru(L)2pipz]2+ (L = bpy (2,2′-bipyridine), phen (1,10-phenanthroline), pipz = 2-pyridine-1H-imidazo[4,5-b]phenazine), have been synthesized and characterized. The interactions of the two complexes with DNA have been investigated by UV–visible spectroscopy, fluorescence spectroscopy, and viscosity measurements. Both complexes bind to DNA by intercalation and efficiently cleave pBR322 DNA under irradiation. Singlet oxygen () was the main reactive oxygen species involved in DNA photocleavage. Topoisomerase inhibition and DNA strand passage assay demonstrated that both complexes can act as efficient catalytic inhibitors of DNA topoisomerase I. Graphical abstract

A novel, label-free fluorescent aptasensor for cocaine detection based on a G-quadruplex and ruthenium polypyridyl complex molecular light switch

In this report, a novel, label-free fluorescence aptasensor for cocaine was developed based on a G-quadruplex and ruthenium(II) complex molecular light switch. A Ru[(bpy)2(bqdppz)]2+ ligand with high selectivity towards G-quadruplex was synthesized and introduced to serve as a prominent molecular light switch via specifically recognizing a cocaine aptamer G-quadruplex. The one-step detection strategy was simply achieved by target-binding-triggered structural dissociation of G-quadruplex accompanied by the sufficient release of Ru-ligand and significant decrease of fluorescent signal. A linear response was obtained over the range of 12–1300 nM, with a low detection limit of 5 nM. The proposed aptasensing method possesses the advantages of speed, easy preparation, being label-free, high sensitivity and low cost.

DNA Interaction, Photocleavage and Topoisomerase I Inhibition by Ru(II) Complex with a New Ligand Possessing Phenazine Unit

A new ruthenium complex with a dppz-like ligand pyidppz, [Ru(bpy)2(pyidppz)]2+ (pyidppz = 2-(pyridine-2-yl)imidazo-[4,5-b]dipyrido-[3,2-a:2′,3′-c]phenazine) has been synthesized and characterized by ES-MS, elemental analysis, 1H NMR. Intercalative mode of the complex bound to calf thymus DNA has been supported by different spectroscopic methods and viscosity measurements. The introduction of phenazine unit may be one of the main reasons for the weak emission of Ru(II) complex in aqueous solution. Under irradiation, this complex can efficiently cleave DNA. And the photocleavage reaction of the complex is found to be inhibited in the presence of singlet oxygen scavenger. Topoisomerase inhibition and DNA strand passage assay demonstrated that [Ru(bpy)2(pyidppz)]2+ and its parent complex [Ru(bpy)2(pyip)]2+ (pyip = 2-(pyridine-2-yl)imidazo[4,5-f][1,10]phenanthroline) can act as efficient catalytic inhibitor of DNA topoisomerase I.

Highly Sensitive Fluorescent Aptasensor for Thrombin Detection Based on Competition Triggered Rolling Circle Amplification

Abstract Based on the competition reaction of target protein, aptamer probe, padlock probe and the complementary sequence, a highly sensitive fluorescent aptasensor was developed in this study in combination with rolling circle amplification. In the absence of target protein, the ligation-rolling circle amplification reaction was repressed because the complementary sequence hybridized with aptamer probe to form double-stranded duplex. On the contrary, in the presence of target protein, the target molecules bond specifically with its aptamer probe, inducing the displacement of the complementary sequence and hybridization with padlock probe. The padlock probe was circularized with the assistance of Escherichia coli DNA ligase, and the rolling circle amplification process could be accomplished by Phi29 DNA polymerase. The amplification product contained thousands of repeated sequences which could hybridize with the loop of molecular beacons (the detection probes), resulting in a significant fluorescence signal. The effects of length of complementary DNA (CDNA) sequence and concentration of padlock probe were investigated. Under the optimized experimental conditions, the model target protein of thrombin was highly sensitively detected by the proposed aptasensing system in a linear range of 0.067–32.4 nM with a detection limit of 0.03 nM (approximately 90 amol target molecules). Moreover, the present sensing method was universal for other target analysis by skillful design of the sequence of aptamer probe and related oligonucleotides.

DNA Interaction and Photocleavage Properties of Ru (II) Complexes [Ru(bpy)2(pibi)]2+ and [Ru(phen)2(pibi)]2+

A new asymmetry ligand pibi (pibi = 2-(pyridine-2-yl)-1-H-imidazo[4,5-f]benzo[d]imidazolone) and its ruthenium complexes with [Ru(L)2(pibi)]2+ (L = bpy (2, 2′-bipyridine), phen (1, 10-phenanthroline)), have been synthesized and characterized. The binding of two complexes with calf thymus DNA has been investigated by spectroscopic and viscosity measurement. The results indicate that both complexes can bind to CT-DNA through intercalative mode. Under irradiation at 365 nm, both complexes can partly promote the photocleavage of plasmid pBR322DNA. The low singlet oxygen generation abilities of the two complexes may be the factor for the low DNA photocleavage abilities.

A lysosome targetable fluorescent probe for palladium species detection base on an ESIPT phthalimide derivative

A novel lysosome-targetable phthalimide fluorescent probe was designed for detecting palladium based on ESIPT for signal transduction. The fluorescent probe conjugating with allylcarbamate displayed weak fluorescent due to the ESIPT process hinder by allylcarbamate. But with the addition of palladium, the ESIPT emission was recovery though the palladium-catalyzed deallylation reaction and the fluorescence intensity exhibited 40-fold enhancement at 511u202fnm. In addition, the probe showed excellent selectivity, high sensitivity, fast responds and low limit detection for palladium with a larger Stoke-shift. Moreover, the targetable probe was also successfully applied for detecting palladium in lysosomes of living cells. Hence, the probe though ESIPT modulation is a promising for monitoring palladium in practical samples.

Selective and Sensitive Detection of Silver(I) Ion Based on Tetracationic Complex and TGA/GSH Co-capped Quantum Dots as an Effective Fluorescent Sensing Platform

CdTe quantum dots capped with glutathione (GSH) and thioglycolic acid (TGA) were synthesized and the interaction between QDs and tetracationic Fe complex was investigated. Based on the specific interaction between Ag+ and cytosine bases (C), we designed a label-free DNA sensor for the detection of Ag+ in aqueous solution. Furthermore, tetracationic Fe complex with a higher positive charge is demonstrated to improve the sensitivity of the sensor. A detection limit of 3.3 nmol dm-3 was obtained, which was lower than in previous reports. This sensor also exhibits promising potential for real sample analysis.