Bioanalytical Application of Peroxidase-Mimicking DNAzymes: Status and Challenges

DNAzymes with peroxidase-mimicking activity are a new class of catalytically active DNA molecules. This system is formed as a complex of hemin and a G-quadruplex structure created by oligonucleotides rich in guanine. Considering catalytic activity, this DNAzyme mimics horseradish peroxidase, the enzyme most commonly used for signal generation in bioassays. Because DNAzymes exhibit many advantages over protein enzymes (thermal stability, easy and cheap synthesis and purification) they can successfully replace HRP in bioanalytical applications. HRP-like DNAzymes have been applied in the detection of several DNA sequences. Many amplification techniques have been conjugated with DNAzyme systems, resulting in ultrasensitive bioassays. On the other hand, the combination of aptamers and DNAzymes has led to the development of aptazymes for specific targets. An up-to-date summary of the most interesting DNAzyme-based assays is presented here. The elaborated systems can be used in medical diagnosis or chemical and biological studies.

Detection and quantification of ATP in human blood serum

Two fluorometric sensors based on the tri-serine tri-lactone scaffold and thiourea or sulfonamide moieties serving as hydrogen bond donors allowing for anion binding are described. The sensor utilizing thiourea as a recognition moiety shows fluorescence enhancement while the sensor with sulfonamide shows quenching upon addition of phosphates. Sensor arrays composed of two sensors are able to discriminate structurally similar organic phosphates in the presence of interferents in human blood serum. The quantitative analysis of ATP in human blood serum shows high accuracy (the root mean square error of prediction, 1.65%) without requiring any sample pretreatment.

High-sensitivity detection of ATP using a localized surface plasmon resonance (LSPR) sensor and split aptamers

A highly sensitive localized surface plasmon resonance (LSPR) aptasensor for detection of adenosine triphosphate (ATP) has been developed. The sensor utilizes two split ATP aptamers, one (receptor fragment) being covalently attached to the surface of a gold nanorod (GNR) and the other labeled with a random DNA sequence and TAMRA dye (probe fragment). In the presence of both ATP and the probe fragment, a significant shift takes place in the wavelength of the LSPR band. This phenomenon is a consequence of the fact that the split fragments assemble into an intact folded structure in the presence of ATP, which brings about a decrease in the distance between the GNR surface and TAMRA dye and an associated LSPR wavelength. By using this sensor system, concentrations of ATP in the range of 10 pM-10 μM can be determined. In addition, by taking advantage of its denaturation properties, the LSPR aptasensor can be reused by simply subjecting it to quadruple salt-addition/2M NaCl washing steps. That the new method is applicable to biological systems was demonstrated by its use to measure ATP concentrations in E. coli and, thus to determine cell concentrations as low as 1.0×10(3) CFU.