S ince they were first reported by two independent research groups 1,2 in 1990, aptamers have been widely used in analytical detection, separation, diagnostics, imaging, and therapeutics. Aptamers are synthetic single-stranded DNA or RNA molecules. They are shorter than 100 nucleotides (nt) in length, and they generally have high binding affinity and selectivity for specific targets, ranging from macromolecules (e.g., proteins) to small molecules (e.g., metal ions). A number of recent reviews have summarized applications of aptamers to diagnostics, 3,4 molecular imaging, 5 therapeutics, 6 and sensing. 7,8 Our present Review is unique in that our focus is on recent

a b s t r a c tThe detection and quantification of disease-related proteins play critical roles in clinical practice and diagnostic assays. We present an affinity probe capillary electrophoresis/laser-induced fluorescence polarization (APCE/LIFP) assay for detection of human thrombin using a specific aptamer as probe. In the APCE/LIFP assay, the mobility and fluorescence polarization of complex are measured simultaneously during CE analysis. The affinity complex of human thrombin can be well separated from unbound aptamer on CE and clearly identified on the basis of its fluorescence polarization and migration. Because of the binding favorable G-quartet conformation potentially involved in the specific aptamer, it was assumed that monovalent and bivalent cations promoting the formation of a stable G quadruplex conformation in the aptamer may enhance the binding of the aptamer and thrombin. Therefore, we investigated the effects of various metal cations on the binding of human thrombin and the aptamer. Our results show that cations like K + and Mg 2+ could not stabilize the affinity complex. Without the use of typical cations, a highly sensitive assay of human thrombin was developed with the corresponding detection limits of 4.38 × 10 −19 and 2.94 × 10 −19 mol in mass for standard solution and human serum, respectively.

The separation of metallothionein (ML) isoforms using capillary electrophoresis (CE) has been improved by applying surface-modified capillaries, and the metal composition of MTs has been characterized by subsequent inductively coupled plasma sector field mass spectrometry (ICPSFMS). Nine MT complexes in a commercial preparation from rabbit liver were successfully separated on an anionic polymer-coated column, prepared by immobilizing poly(2-acrylamido-2-methyl-1-propanesulfonic acid) on the fused-silica surface via a linking agent. On uncoated capillaries or those coated dynamically with cationic materials, only three complexes could be separated. Online isotope dilution analysis combined with CE/ICPSFMS indicated the stoichiometric molar metal contents in the MT complexes.

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