Yuqin Li

An electrochemiluminescence biosensor for sensitive and selective detection of Hg2+ based on π–π interaction between nucleotides and ferrocene–graphene nanosheets

A solid-state electrochemiluminescence (ECL) biosensor based on a DNA-modified electrode platform that depends on the variation of π-π interaction before and after the binding of target analytes is put forward. The single-stranded DNA (ssDNA) probe was successfully assembled on the surface of a glassy carbon electrode (GCE), which was pre-modified with Ru(bpy)3 2+ complex and gold nanoparticles (GNPs). The ssDNA probe could strongly adsorb graphene due to the strong π-π interaction between nucleotides and graphene (GN), while in the presence of Hg2+, the conformational transformation of DNA from a single-stranded to a double-stranded structure resulted in inhibited adsorption of GN. With thymine (T)-rich ssDNA as a Hg2+ probe, we prepared the ECL biosensor by using ferrocene-graphene (Fc-GN) as a quenching unit to quench the ECL emission of Ru(bpy)3 2+, and the Hg2+ can be detected by quenching efficiency transformation when the Fc-GN gets away from Ru(bpy)3 2+. The biosensor exhibited a sensitive response to various ranges of concentration of Hg2+ with a detection limit of 18 pM. The ECL biosensor held great promise in the highly sensitive and selective detection of Hg2+ in natural water.

Separation and determination of aloperine, sophoridine, matrine and oxymatrine by combination of flow injection with microfluidic capillary electrophoresis

A novel, rapid and accurate method for the separation and determination of aloperine (ALP), sophoridine (SRI), matrine (MT) and oxymatrine (OMT) has been developed by combination of flow injection (FI) with microfluidic capillary electrophoresis (CE) for the first time. In the present paper, a continuous sample introduction interface was described. The interface with an H-channel structure was produced using a non-lithographic approach. The H-channel structure was fixed on a planar plastic base utilizing a horizontal 6.5cm-long separation capillary with two vertical sidearm tubes on each end that served as inlet and outlet flow-through electrode reservoirs. The inlet reservoir also functioned as interface for coupling to the FI system. The buffer solution used was a 50mmoll(-1) borate solution with the pH adjusted to 8.80 with 2moll(-1) HCl. The performance of the system was demonstrated in the separation and determination of ALP, SRI, MT and OMT with UV detection at 215nm, achieving baseline separation within 2min. A series of samples was injected repeatedly without current interruption and subsequent rinsing, and the contents of these four bio-alkaloids in two marketed drugs were determined with satisfactory recovery by this proposed method.

Separation and determination of the anthraquinones in Xanthophytum attopvensis pierre by nonaqueous capillary electrophoresis

A nonaqueous capillary electrophoresis (NACE) method with direct on-column UV detection has been developed for the separation of the pharmaceutically important anthraquinones from the total grass of Xanthophytum attopvensis pierre extract. The separation of three main anthraquinones (1-hydroxy-2-methoxy-3-hydroxymethyl-9, 10-anthraquinone-1-O-beta-d-glucoside (1), rubiadin- 1-methylether (2) and 1-methoxy-2-formyl-3-hydroxy-9, 10-anthraquinone (3)) was optimized with respect to concentration of sodium cholate (SC) and acetic acid, addition of acetonitrile (ACN), and applied voltage. Baseline separation was obtained for the three analytes within 5min using a running buffer containing 50mM sodium cholate (SC), 1.0% acetic acid and 40% ACN in methanol. The method of NACE for the separation and determination of bioactive ingredient in traditional Chinese medicines was discussed.

Combining a loop-stem aptamer sequence with methylene blue: a simple assay for thrombin detection by resonance light scattering technique

An ingenious sensing strategy for detecting thrombin in human serum has been developed on the basis of a hairpin DNA sequence and resonance light scattering (RLS) technique. A thrombin aptamer sequence was embedded inside the hairpin DNA strand (H-eTBA), which was designed to be the loop-stem structure. Moreover, methylene blue (MB) was utilized as the RLS signal indicator according to its different affinity to single or double stranded DNA. Upon the addition of thrombin, the thrombin aptamer inside H-eTBA interacted specifically with thrombin. Thus the conformation of H-eTBA would change. After the introduction of the DNA strand (CTBA), which was complementary to H-eTBA, the amount of double stranded DNA would decrease as a consequence. Later when MB solution was added, the RLS signal would present various response values based on different amounts of thrombin. The determination of thrombin in human serum could be obtained with a detection limit of 0.32 nM and this specific sensor could be applied to detect thrombin practically. Furthermore, this aptasensor showed quite good selectivity and simplicity toward thrombin. Finally, the proposed sensing method showed its superiority with selectivity and practicability, which could be used as a simple platform for thrombin detection.

A novel glutathione-stabilized silver–gold nano-alloy/Cu2+ combination as a fluorescent switch probe for L-histidine

A new and environmentally friendly approach for the preparation of glutathione-stabilized silver–gold nano-alloys (GSH-AgAuNAs) with high fluorescence was proposed in this work. The as-prepared GSH-AgAuNAs were characterized with various methods and coupled with copper ions (Cu2+) to form a fluorescent switch probe (GSH-AgAuNAs/Cu2+ combination) for the detection of L-histidine. The fluorescence of the GSH-AgAuNAs was first quenched by adding an appropriate amount of Cu2+ solution. Then, in the presence of L-histidine, the GSH-AgAuNAs/Cu2+ combination solution exhibited an obvious fluorescence enhancement due to the specific interaction between the imidazole group of L-histidine and Cu2+. The strong chelation between L-histidine and Cu2+ illustrated the feasibility of constructing a selective “switch on” probe for the detection of L-histidine over other amino acids. Different from other methods for detecting L-histidine based on fluorescent nanomaterials, our work promises high selectivity, simplicity and the avoidance of organic solvents. Under the optimal conditions, the newly constructed GSH-AgAuNAs/Cu2+ fluorescent probe showed a satisfactory linear detection range of 2 to 40 μM, with a detection limit of 1.19 μM. The practical use of the GSH-AgAuNAs/Cu2+ combination in real human serum samples was tested, illustrating its potential application in L-histidine detection.