Self-Assembled Monolayers of Oligonucleotides as Receptor Layers for Mercury Ion Sensor Ł. Górski a , R. Ziółkowski a , E. Malinowska a a Faculty of Chemistry, Department of Microbioanalytics Warsaw University of Technology, Warsaw, Poland The feasibility of using gold electrodes modified with short-chain, thymine-rich, ss-DNA oligonucleotides for determination of mercury cation is examined. The methylene blue was used as a redox marker for analytical signal generation. Biosensor response was based on the difference in electrochemical signal before and after subjecting it to sample containing Hg 2+ ion. The lower detection limit of 3 nmol L -1 for Hg 2+ was observed, together with good selectivity against common metal cations. Introduction Sensors show many advantages over other analytical methods, including low cost, fast response, ability to perform continuous measurements directly in a sample matrix, and ease of miniaturization (1). As a consequence, numerous sensor types were employed for environmental analysis, industrial quality control and clinical diagnostics (2). Among various types of sensors, electrochemical transduction methods offer some important advantages, including lower detection limit, ease of miniaturization in terms of size and power consumption, low operational costs, good reproducibility and fast response (3). In recent years, electrochemical biosensors came to a special prominence. The receptor layers of these devices are fabricated of recognition elements of biological origin, such as enzymes, nucleic acids, antibodies or whole cells (4). DNA-based biosensors are important for the detection of specific nucleic acid sequences, which could be important for diagnosis of certain genetic and infectious diseases or for tracing genetically modified foods (5). However, the scope of analytes that can be detected using DNA sensors is much broader, including metal ions, simple organic compounds, oligosaccharides, peptides, proteins and even cells or bacteria (6). For the determination of such analytes, functional nucleic acids, including aptamers and DNAzymes, are usually employed (7). The interactions of metal ions with nucleic acids have been studied for many years, mainly due to the possible toxicity and cancerogenicity of certain heavy metal ions, depending to some extent on their affinity to DNA in living organisms (8). Metal ion binding to DNA is usually based on the Coulomb interactions between metal cations and negatively charged DNA residues. However, specific metal binding is also possible via the phosphate groups of the DNA backbone and the electron donor atoms of the bases. Recently, the binding of metal ions to nucleic acids was employed for the construction of sensors for the determination of metal ions. In some of these devices, random DNA sequences are used in the receptor layer. In this case, the selectivity of resulting sensor depends mainly on electrostatic metal ion - DNA interactions. However, some specific oligonucleotide sequences show high selectivity towards certain metal ion. 10.1149/05012.0333ecst ©The Electrochemical Society ECS Transactions, 50 (12) 333-338 (2012) 333