A method of preparing a crystalline zwitterionic zinc(II)-carboxylate compound includes the steps of preparing a mixture of zinc(II) ions and a first pyridyl ligand having three carboxylic acid moieties; subjecting the mixture to conditions under which a precipitate is formed; separating the precipitate; adding a solvent and optionally a second pyridyl ligand to the separated precipitate; subjecting the obtained mixture to conditions under which crystals of the zwitterionic zinc(II)-carboxylate compound are formed; and separating the crystals of the zwitterionic zinc(II)-carboxylate compound. Preferably but not exclusively, the crystalline zwitterionic zinc(II)-carboxylate compound essentially consists of at least one 1D coordination polymer. The compounds are suitable for providing a sensing platform for detecting the presence or amount of target nucleic acid, particularly HIV-1 ds-DNA, with specificity, and, thus, a method of detecting a target nucleic acid sequence in a sample and a kit including the compounds and an oligonucleotide probe are also provided.