Agnieszka Bala

Application of nucleic acid analogues as receptor layers for biosensors

Nucleic acid-based biosensors are typically used to detect DNA or RNA fragments of clinical importance. Moreover, these sensors can also be used to detect different analytes, including viruses, peptides, small organic molecules and metal ions. However, the lack of resistance to restriction enzymes prevents the use of these sensors in in vivo measurements. Moreover, due to their reduced stability under environmental conditions as well as non-specific interactions, the usefulness of DNA biosensors can be limited. To mitigate these problems, analogues of nucleic acids can be used. These compounds are structurally similar to natural DNA, with alternative backbones. Due to their excellent affinity and specificity toward complementary strands, the most useful and popular nucleic acid analogues are peptide nucleic acid (PNA), locked nucleic acid (LNA) and phosphorothioate oligonucleotide (PTO). Herein, we present an overview of biosensors employing nucleic acid analogues as receptor layers, published in the last few years. Their advantages and their limitations are discussed.

Peptide nucleic acid as a selective recognition element for electrochemical determination of Hg2

A novel electrochemical PNA-based biosensor for the determination of Hg2+ is described. The receptor layer, containing single strands of polythymine PNA (peptide nucleic acid), was formed at the surface of gold electrode. Due to the presence of thymine bases and peptide bonds, an interaction between Hg2+ ion and receptor layer occurs. The influence of chain modification - PNA vs. DNA - and type of redox marker - anionic AQMS-Na (sodium salt of anthraquinone-2-sulfonic acid) and FeII/III (potassium ferri/ferrocyanide) or cationic MB (methylene blue) and RuHex (hexaammineruthenium(III) chloride) - were studied. Proposed PNA-based biosensor with anionic AQMS-Na as a redox marker demonstrated significantly better analytical parameters, as compared to results obtained for other tested redox markers (for measurements at pH6.0). The linear response towards Hg2+ was in the range from 5 to 500nmol·L-1 with the detection limit of 4.5nmol·L-1. The developed sensor distinguishes itself with high selectivity towards Hg2+, even for solutions containing several interfering cations. Interactions between Hg2+ and PNA receptor layer were studied using square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS).

Design and characterization of novel all-solid-state potentiometric sensor array dedicated to physiological measurements.

A novel construction of all-solid-state potentiometric sensor array designed for physiological measurements has been presented. The planar construction and elimination of liquid phase creates broad opportunities for the modifications in the sensing part of the sensor. The designed construction is based on all-solid-state ion-selective electrodes integrated with the ionic-liquid based reference electrode. Work parameters of the sensor arrays were characterized. It has been shown that presented sensor design indicates high sensitivity (55.2±1mV/dec, 56.3±2mV/dec, 58.4±1mV/dec and 53.5±1mV/pH for sodium-, potassium-, chloride- and pH-selective electrodes, respectively in 10(-5)-10(-1.5)M range of primary ions), low response time (t95 did not exceed 10s), high potential stability (potential drift in 28-h measurement was ca. ±2mV) and potential repeatability ca. ±1mV. The system was successfully applied to the simultaneous determination of K(+), Cl(-), Na(+) and pH in the model physiological solution and for the ion flux studies in human colon epithelium Caco-2 cell line as well.