Many cations such as sodium ions have strong influence on anchoring behaviors of liquid crystals (LC). Since DNA is negatively charged and forms complex with metal ions, it is possible to form DNA/metal ions complex on surfaces to disrupt orientations of LC. This phenomenon is used to establish a principle for detecting surface immobilized DNA by using LC. In contrast, peptide nucleic acid (PNA) is electroneutral. It does not complex with metal ions or affect the orientations of LC. Therefore, PNA can be used as a probe to hybridize with specific DNA with a unique sequence, and the principle mentioned above can be used to detect the DNA target by using metal ions and LC. Based on this method, a 600 bp DNA target in buffer can be detected with a limit of detection at 10 fM. Unlike other fluorescence-based DNA assays, this LC-based detection method does not require labeling of DNA, and the test result can be viewed with the naked eye under a polarized microscope. (C) 2014 Elsevier Inc. All rights reserved.