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http://www.nature.com/nchina/200 ... china.2008.125.html http://www.nature.com/nchina/200 ... china.2008.113.html Cell-surface analysis: Competing carbohydrates Anne Pichon AbstractCompetitive recognition between cell-surface carbohydrates and a biomimetic self-assembled monolayer provides convenient in situ analysis of cell-surface patterns Original article citation Ding, L., Cheng, W., Wang, X., Ding, S. & Ju, H. Carbohydrate monolayer strategy for electrochemical assay of cell surface carbohydrate. J. Am. Chem. Soc. doi: 10.1021/ja801468b (2008). Introduction © (2008) ACS Cell surfaces are covered with carbohydrate molecules, which take part in various biological processes, such as cell growth, immune responses and cell–cell communication. Previous approaches to analysing these carbohydrates and better understanding their role, however, have met with limitations because living cells are destroyed in the process. Huangxian Ju at Nanjing University and co-workers1 have prepared an assay that provides convenient in situ evaluation of cell-surface carbohydrates without destroying the living cells. The researchers mimicked the composition of a cell surface by attaching carbohydrates onto a gold substrate. Mannan — a polymer consisting of sugar residues found in cell walls — was bound to the substrate and attached to the carbohydrate through a linker. The resulting biomimetic carbohydrates then self-assembled into a monolayer that effectively competed with the surfaces of living cells in binding to lectins — a class of proteins known to connect to carbohydrates with high selectivity — conjugated with quantum dots (QD). The QDs captured on the gold surface were then analysed by electrochemistry, which revealed the composition of the cell-surface carbohydrates. Self-assembled monolayers present a wide range of functionalities with high precision, and the QD–lectin conjugates are stable and easily labelled. This convenient, sensitive strategy therefore enables the profiling of a wide range of cell surfaces. The authors of this work are from: Key Laboratory of Analytical Chemistry for Life Science, Ministry of Education, Department of Chemistry, Nanjing University, Nanjing, China; Key Laboratory of Laboratory Medical Diagnostics, Ministry of Education, Department of Laboratory Medicine, Chongqing Medical University, Chongqing, China. Reference Ding, L., Cheng, W., Wang, X., Ding, S. & Ju, H. Carbohydrate monolayer strategy for electrochemical assay of cell surface carbohydrate. J. Am. Chem. Soc. doi: 10.1021/ja801468b (2008). | Article | Electrochemical DNA sensors: Turn on the signal Anne Pichon AbstractHairpin-shaped DNA fragments and enzymes together make a highly sensitive and selective electrochemical DNA sensor Original article citation Liu, G. et al. An enzyme-based E-DNA sensor for sequence-specific detection of femtomolar DNA targets. J. Am. Chem. Soc. doi: 10.1021/ja800554t (2008). Introduction © (2008) ACS Electrochemical DNA (E-DNA) sensors are simple, efficient and inexpensive devices for genetic screening and detection. They work on the principle that the chemical interaction (hybridization) between DNA targets in solution and the probe layer — a layer of DNA fragments attached to an electrode — produces signal currents for electronic readout. Most E-DNA sensors today have limited sensitivity because of their 'signal-off' design, in which the hybridization produces low signal strengths. Chunhai Fan at the Chinese Academy of Sciences in Shanghai and co-workers1 have prepared an enzyme-based, 'signal-on' E-DNA sensor with amplified signal currents, which can detect DNA targets at extremely low concentrations. In the design, a probe layer of hairpin-shaped 'stem–loop' DNA fragments was used (see image). The researchers labelled one end of the DNA fragment with the vitamin biotin, and the other end with the steroid digoxigenin (DIG). The biotin end was attached to the electrode by a protein bridge. The DIG end was inaccessible to the solution when the DNA fragment was in the 'loop' structure. On hybridization, the DNA fragment formed a duplex 'stem', which forced the DIG end away from the electrode. Antibody-linked horseradish-peroxidase (HRP) enzymes were added to the solution of target DNA, which also contained some hydrogen peroxide. The antibody-linked HRP enzyme attached itself to the DIG-end, catalysed the reduction of hydrogen peroxide, and sent redox currents to the electrode. One HRP enzyme could catalyse thousands of reduction reactions, greatly amplifying signal currents. The resulting E-DNA sensor had femtomolar sensitivity — excelling existing sensors by several orders of magnitude. It also displayed high differentiation ability and enabled the simultaneous detection of 16 different DNA targets in one array. The authors of this work are from: Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, China; GeneFluidics, Monterey Park, California, USA. Reference Liu, G. et al. An enzyme-based E-DNA sensor for sequence-specific detection of femtomolar DNA targets. J. Am. Chem. Soc. doi: 10.1021/ja800554t (2008). | Article | |
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