Nucleic acid triplexes are formed when a DNA or RNA oligonucleotide binds to a polypurine-polypyrimidine-rich sequence. Triplexes have wide therapeutic applications such as gene silencing or site-specific mutagenesis. In addition, protocols based on triplex-affinity capture have been used for detecting nucleic acids in biosensing platforms. In this article, the design, synthesis, and use of parallel clamps and polypurine-reversed hairpins (PPRH) to bind to target polypyrimidine targets are described. The combination of the polypurine Watson-Crick strand with the triplex-forming strand in a single molecule produces highly stable triplexes allowing targeting of single- and double-stranded nucleic acid sequences. On the other hand, PPRHs are easily prepared and work at nanomolar range, like siRNAs, and at a lower concentration than that needed for antisense ODNs or TFOs. However, the stability of PPRHs is higher than that of siRNAs. In addition, PPRHs circumvent off-target effects and are non-immunogenic. © 2019 by John Wiley & Sons, Inc.