Rong-Na Ma

A novel sandwiched electrochemiluminescence immunosensor for the detection of carcinoembryonic antigen based on carbon quantum dots and signal amplification

In this study, a novel sandwiched electrochemiluminescence (ECL) immunosensor for the detection of carcinoembryonic antigen (CEA) was developed. The nanocomposite of polydopamine and Ag nanoparticles (PDA-AgNPs) was prepared by the redox reaction between Ag+ and dopamine. This nanocomposite not only provided an effective matrix for the immobilization of primary antibody (Ab1) but also enhanced the conductivity of the electrode. Carbon quantum dots (CQDs) were immobilized on the poly(ethylenimine) functionalized graphene oxide (PEI-GO) through amido-bond. Then Au nanoparticles were decorated on the CQDs modified PEI-GO matrix, and the resulted complex AuNPs/CQDs-PEI-GO was introduced to link secondary antibody (Ab2). The CQDs can be connected to the electrode surface through the combination of CEA with Ab1 and Ab2, and then the amplified electrochemiluminescence signal of CQDs was obtained with the synergistic effect of AgNPs, polydopamine, AuNPs and PEI-GO. Under the optimal conditions, the ECL intensity was proportional to the logarithm value of CEA concentration in the linear range from 5pgmL-1 to 500ngmL-1 with a detection limit of 1.67pgmL-1 for CEA detection. The immunosensor was applied for the CEA detection in real samples with satisfactory results. The proposed ECL immunosensor showed good performance with high sensitivity, specificity, reproducibility, stability and will be potential in clinical detection.

Electrodeposition of PtNPs on the LBL assembled multilayer films of (PDDA-GS/PEDOT:PSS)n and their electrocatalytic activity toward methanol oxidation

In the present work, PDDA-functionalized graphene sheets (PDDA-GS) were prepared by reduction with hydrazine hydrate in situ in the presence of poly(diallyldimethylammonium chloride) (PDDA). The (PDDA-GS/PEDOT:PSS)n multilayer films were fabricated by a layer-by-layer self-assembly technique based on the electrostatic interaction between positively charged PDDA-GS and negatively charged poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The self-assembly process was characterized by ultraviolet-visible spectroscopy (UV-vis). Pt nanoparticles were electrodeposited in situ on the multilayer films. X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FE-SEM) were used to characterize the properties of Pt/[(PDDA-GS/PEDOT:PSS)n] multilayer films. Cyclic voltammetry and chronoamperometry were used to study the electrocatalytic activity of Pt/[(PDDA-GS/PEDOT:PSS)n] multilayer films towards methanol oxidation. The results indicated that Pt/[(PDDA-GS/PEDOT:PSS)n] showed high electrocatalytic activity toward methanol oxidation and good tolerance toward carbon monoxide (CO) poisoning. This novel support for Pt nanoparticle catalysts will be promising in the fabrication of fuel cell electrodes and other catalytic devices.

A colorimetric assay for Hg2+ detection based on Hg2+-induced hybridization chain reactions

A simple colorimetric sensing method for the detection of Hg2+ was developed by combining enzymatic catalysis with DNA-based hybridization chain reactions (HCRs). Firstly, thymine (T)-rich capture DNA (cDNA) was immobilized on a gold electrode via Au–S bonding. In the presence of Hg2+, thymine (T)-rich probe DNA (pDNA) hybridized with cDNA via T–Hg2+–T base pairs. Then the HCRs were realized using pDNA as an initiator and two biotin-labeled hairpin DNAs (H1 and H2) as fuel strands. Finally, numerous avidin-labeled horseradish peroxidase (HRP) enzymes were immobilized on long nicked ds-DNA strands, which can catalyze the H2O2-mediated oxidation of 3,3,5,5-tetramethylbenzidine dihydrochloride hydrate (TMB) to cause a dramatic color change. Under optimal conditions, the absorbance of TMB was linear with the logarithm of Hg2+ concentrations in the range of 1 fM to 1 pM, with a detection limit of 0.33 fM. This strategy exhibited good selectivity and high sensitivity, which might be a potential tool for the practical detection of Hg2+ in environmental monitoring.

Aptamer based electrochemical assay for protein kinase activity by coupling hybridization chain reaction

The present work reported a simple, lable-free and sensitive electrochemical method for the detection of protein kinase A (PKA) activity. This method was based on the specific recognition of aptamer and the aptamer-induced hybridization chain reaction (HCR) amplification strategy. The aptasensor was constructed by immobilizing capture probe on a gold electrode via an Au-S bond. When adenosine triphosphate (ATP) aptamer was introduced, its one terminus hybridized with capture probe and the other hybridized with the complementary region of an auxiliary probe, which other region triggered HCR between two hairpin DNA (H1 and H2) to form a long DNA concatamer. At last a large number of electroactive methyle blue (MB) molecules were assembled on the dsDNA concatamer, which generated a significantly amplified electrochemical signal. In the presence of ATP, the HCR would not be performed because the aptamer specifically bond to ATP and the electrochemical response would decrease. However, when ATP and PKA coexisted, the electrochemical response would recovery because that ATP had been translated into ADP by PKA. So the activity of PKA could be effectively monitored according to the change of electrochemical signal. Based on the HCR amplification strategy, the aptasensor showed a wide linear range (4 - 4 ×105 U L-1) and a low detection limit (1.5 U L-1) for the detection of PKA. Furthermore, the method was applied to study the inhibitory effect of H-89 on PKA activity. The developed aptasensor was also used to the analysis of drug-induced PKA activity in cell lysates, indicating the potential application of the developed method in the fields of clinical diagnostics and discovery of new targeted drugs.

A versatile label-free electrochemical biosensor for circulating tumor DNA based on dual enzyme assisted multiple amplification strategy

A versatile label-free electrochemical biosensor based on dual enzyme assisted multiple amplification strategy was developed for ultrasensitive detection of circulating tumor DNA (ctDNA). The biosensor consists of a triple-helix molecular switch (THMS) as molecular recognition and signal transduction probe, ribonuclease HII (RNase HII) and terminal deoxynucleotidyl transferase (TdT) as dual enzyme assisted multiple amplification accelerator. The presence of target ctDNA could open THMS and trigger RNase HII-assisted homogenous target recycling amplification to produce substantial signal transduction probe (STP). The released STP hybridized with the capture probe immobilized on a gold electrode, then TdT and assistant probe were further employed to fulfill TdT-mediated cascade extension and generate stable DNA dendritic nanostructures. The electroactive methyl blue (MB) was finally used as the signal reporter to realize the multiple electrochemical amplification ctDNA detection as the amount of MB is positively correlated with the target ctDNA. Combined with the efficient recognition capacity of the designed THMS and the excellent multiple amplification ability of RNase HII and TdT, the constructed sensing platform could detect KRAS G12DM with a wide detection range from 0.01 fM to 1 pM, and the limit of detection as low as 2.4 aM. Besides, the platform is capable of detecting ctDNA in biological fluid such as plasma. More importantly, by substituting the loop of THMS with different sequences, this strategy could be conveniently expanded into the detection of other ctDNA, showing promising potential applications in clinical cancer screening and prognosis.