<span class="paragraphSection"><div class="boxTitle">Abstract</div>The CRISPR/Cas system is a powerful tool for molecular diagnostics, but its reliance on linear amplification constrains sensitivity, particularly for <span style="font-style: italic;">in situ</span> imaging. Here, we discovered that phosphorothioate (PS)-modified activators can modulate Cas enzyme conformation via hydrophobic anchoring. By adjusting the PS modification sites, we achieved precise control over Cas activation and trans-cleavage resistance. Guided by this mechanism, we proposed a tailored design strategy featuring a “scattered” PS modification to engineer a linear “Coordinator” probe. This design effectively decouples Cas enzyme activation from substrate trans-cleavage resistance, enabling the construction of a Scattered PS Nucleic Acid-driven Cas Autocatalytic system (SACA). SACA achieves exponential amplification without external enzymes, enhancing Cas12a and Cas13a sensitivity by 50 000-fold and 10 000-fold, respectively. Furthermore, the superior biostability and structural simplicity of these linear probes endow SACA with excellent compatibility, facilitating precise <span style="font-style: italic;">in situ</span> imaging of HPV16 and HPV18 mRNA in cervical cancer cells. This study not only advances the understanding of Cas enzyme regulation by chemically modified nucleic acids but also establishes a new paradigm for precise and efficient molecular diagnostics.</span>