Internship Report from the year 2014 in the subject Chemistry - Bio-chemistry, grade: 1,0, Free University of Berlin (Institut f r Chemie und Biochemie), course: Methodenmodul Nukleins uren, language: English, abstract: Aptamers can be considered as nucleic acid based analogues of monoclonar antibodies. These DNA or RNA molecules are characterized by a high affinity and selectivity to the target as well as a huge variety of possible targets, but feature significant advantages compared to antibodies such as the lack of immunogenicity and economic in vitro generation. The preparation of aptamers is based on systematic evolution (see figure 1). Cycles of selection and replication are conducted to narrow down a huge library to aptamers with the best binding properties to the target. In this experiment, an RNA aptamer to the rPrPc protein is selected in vitro. Since a whole SELEX procedures takes several weeks, only one selection cycle is done examplarily.