This invention is related to the immobilization of peptide nucleic acids (PNAs) onto solid surfaces for use in hybridization, purification, biosensing, and other biochemical applications. Specifically, their use to increase the thermal stability, specificity, and lifetime of devices based on in situ hybridization is disclosed. A method is disclosed by which peptide nucleic acids replace oligonucleotides as probes in the detection of specific DNA and RNA sequences.