Thiol-modified Aptamer Research Articles

Fractal gold modified electrode for ultrasensitive thrombin detection

We report a label-free and ultrasensitive aptasensor based on a fractal gold modified (FracAu) electrode for thrombin detection with a femtomolar detection limit. The FracAu electrode was prepared by electrodeposition of hydrogen tetrachloroaurate (HAuCl(4)) onto a bare indium tin oxide (ITO) electrode surface. After this process the electrode was characterized by SEM. A thiol-modified aptamer against thrombin was immobilized on the FracAu electrode through a self-assembling process. Upon thrombin binding, the interfacial electron transfer of the FracAu electrode was perturbed by the formation of an aptamer-thrombin complex. The concentration of thrombin in the sample solution was determined by measuring the change in the oxidation peak current of hydroxymethyl ferrocene (C(11)H(12)FeO) with differential pulse voltammetry (DPV). The current response (reduced peak current) had a linear relationship with the logarithm of thrombin concentrations in the range of 10(-15) to 10(-10) M with a detection limit of 5.7 fM. Furthermore, the as-prepared FracAu electrode exhibited high selectivity. The application of FracAu electrodes may be extended to prepare other types of biosensors, such as immunosensors, enzyme biosensors and DNA biosensors. These results show that FracAu electrodes have great promise for clinical diagnosis of disease-related biomarkers.

End-to-End Assembly of Gold Nanorods on the Basis of Aptamer−Protein Recognition

The specific binding between aptamers and proteins has drawn much attention recently both in molecular biochemistry and sensing field since aptamers have the advantage of binding specificity and generality, so that the aptamer−protein recognition has now been developed as a model for biorecognition. The work presented herein illustrates a novel method for the end-to-end assembly of gold nanorods (AuNRs) based on the specific aptamer−protein recognition. Owing to the capping reagent of cetyltrimethylammonium bromide (CTAB) on the longitudinal side surface of AuNRs, the thiol-modified aptamer of thrombin preferentially binds onto the edges of AuNRs by the formation of a thiol−gold covalent bond. The addition of thrombin, which has two binding sites for its aptamer, initiated the end-to-end assembly of AuNRs, which could be confirmed with scanning electronic microscopic (SEM) imaging. The structures of the assembled AuNRs were determined by the concentrations of thrombin and the assembly procedures. All of t...

Specific detection of oxytetracycline using DNA aptamer-immobilized interdigitated array electrode chip

An electrochemical sensing system for oxytetracycline (OTC) detection was developed using ssDNA aptamer immobilized on gold interdigitated array (IDA) electrode chip. A highly specific ssDNA aptamer that bind to OTC with high affinity was employed to discriminate other tetracyclines (TCs), such as doxycycline (DOX) and tetracycline (TET). The immobilized thiol-modified aptamer on gold electrode chip served as a biorecognition element for the target molecules and the electrochemical signals generated from interactions between the aptamers and the target molecules was evaluated by cyclic voltammetry (CV) and square wave voltammetry (SWV). The current decrease due to the interference of bound OTC, DOX or TET was analyzed with the electron flow produced by a redox reaction between ferro- and ferricyanide. The specificity of developed EC-biosensor for OTC was highly distinguishable from the structurally similar antibiotics (DOX and TET). The dynamic range was determined to be 1–100 nM of OTC concentration in semi-logarithmic coordinates.

A simple and direct electrochemical detection of interferon-γ using its RNA and DNA aptamers

Tuberculosis is the most frequent cause of infection-related death worldwide. We constructed a simple and direct electrochemical sensor to detect interferon (IFN)-γ, a selective marker for tuberculosis pleurisy, using its RNA and DNA aptamers. IFN-γ was detected by its 5′-thiol-modified aptamer probe immobilized on the gold electrode. Interaction between IFN-γ and the aptamer was recorded using electrochemical impedance spectroscopy and quartz crystal microbalance (QCM) with high sensitivity. The RNA-aptamer-based sensor showed a low detection limit of 100 fM, and the DNA-aptamer-based sensor detected IFN-γ to 1 pM in sodium phosphate buffer. With QCM analysis, the aptamer immobilized on the electrode and IFN-γ bound to the aptamer probe was quantified. This QCM result shows that IFN-γ exists in multimeric forms to interact with the aptamers, and the RNA aptamer prefers the high multimeric state of IFN-γ. Such a preference may describe the low detection limit of the RNA aptamer shown by impedance analysis. In addition, IFN-γ was detected to 10 pM by the DNA aptamer in fetal bovine serum, a mimicked biological system, which has similar components to pleural fluid.