CRISPR-based non-nucleic acid detection

Characterization of clustered regularly interspaced short palindromic repeat (CRISPR)-associated (Cas) trans-cleavage activities has initiated the era of next-generation CRISPR diagnostics. By using the trans-cleavage reaction for signal output, CRISPR systems have been engineered to detect non-nucleic acids (NNAs), including ions, inorganic small molecules, organic compounds, proteins, and bacteria. Diverse strategies are being used to specifically recognize NNAs and regulate Cas trans-cleavage activities, via generation or depletion of output signals. In this review, we introduce the principles and advantages of CRISPR-based NNA detection. We then classify CRISPR-based NNA detection strategies into three classes: the generation or depletion of free activators, synthesis of crRNAs, and reconstruction of active Cas effectors. Finally, we discuss the challenges and potential strategies to advance both clinical and nonclinical applications of CRISPR-based NNA detection.