text: The effectiveness of methods such as chemotherapy to treat cancer tends to plateau after some initial time as the cells undergo molecular changes that render them insensitive to the effect of anticancer drugs. Hence, it is imperative to detect the presence of cancerous cells early. An important biomarker, microRNA (miRNA), is crucial in this detection via its expression patterns. Zhang et al. have demonstrated an INHIBIT-OR gate cascade for the purpose, Yue and co. used an AND gate to construct a system with two miRNA inputs and a quantum dot photoluminescence output, and Peng et al. also constructed an AND gate-based dual-input system for the simultaneous detection of miRNAs from tumor cells.
  Akkaya et al. illustrated the application of a logic gate for photodynamic therapy in their work. A bodipy dye attached to a crown-ether and two pyridyl groups separated by spacers works according to an AND logic gate. The molecule works as a photodynamic agent upon irradiation at 660 nm under conditions of relatively high sodium and proton ion concentrations by converting triplet oxygen to cytotoxic singlet oxygen. This prototypical example would take advantage of the higher sodium levels and lower pH in tumor tissue compared to the levels in normal cells. When these two cancer-related cellular parameters are satisfied, a change is observed in the absorbance spectrum. This technique could be useful for the treatment of malignant tumors as it is non-invasive and specific.