This technology includes a new class of oligomeric molecules called thyclotides for diagnostic and therapeutic development. Thyclotides is described where chiral tetrahydrofuran (THF) diamine units are linked together with alternating glycines, and nucleobases are attached to this backbone as sidechains. The thyclotide sequence consists of a series of nucleobases similar to that of a nucleic acid sequence. Thyclotides are easily synthesized and purified with excellent solubility in water. Thyclotide sequences bind to complementary DNA and RNA sequences with very strong affinity. Thyclotides can be used to inhibit PCR amplification, which is useful for application where PCR clamping is needed to suppress amplification of native DNA when trying to detect low levels of mutant DNA. Thyclotides are surprisingly cell-permeable, and can be used to suppress microRNA in cells and therefore effect important biological responses.