This thesis has been divided into four projects exploring various applications of peptide nucleic acids (PNA) in library screenings and DNA detection. The first two projects used PNA to improve previously reported screening strategies: dynamic combinatorial libraries (DCLs) and DNA-encoded chemical libraries (DELs). The other two projects were motivated by the imminent need to understand, detect, and neutralize the SARS-CoV-2 during the COVID-19 pandemic. This led us to study the immunodominant linear epitopes of SARS-CoV-2 very early on in the outbreak, and to develop a dual-readout DNA-detection method for SARS-CoV-2 later on.