Zipper-Confined DNA Nanoframe for High-Efficient and High-Contrast Imaging of Heterogeneous Tumor Cell.

Current study in the heterogeneity and physiological behavior of tumor cells is limited by the fluorescence in situ hybridization technology in terms of probe assembly efficiency, background suppression capability, and target compatibility. In a typically well-designed assay, hybridization probes are constructed in a confined nanostructure to achieve a rapid assembly for efficient signal response, while the excessively high local concentration between different probes inevitably leads to nonspecific background leakage. Inspired by the fabric zipper, we propose a novel confinement reaction pattern in a zipper-confined DNA nanoframe (ZCDN), where two kinds of hairpin probes are independently anchored respective tracks. The metastable states of the dual tracks can well avoid signal leakage caused by the nonspecific probe configuration change. Biomarker-mediated proximity ligation reduces the local distance of dual tracks, kinetically triggering an efficient allosteric chain reaction between the hairpin probes. This method circumvents nonspecific background leakage while maintaining a high efficiency in responding to targets. ZCDN is employed to track different cancer biomarkers located in both the cytoplasm and cytomembrane, of which the expression level and oligomerization behavior can provide crucial information regarding intratumoral heterogeneity. ZCDN exhibits high target response efficiency and strong background suppression capabilities and is compatible with various types of biological targets, thus providing a desirable tool for advanced molecular diagnostics.

Exploration of new ways for CRISPR/Cas12a activation: DNA hairpins without PAM and toehold and single strands containing DNA and RNA bases.

The CRISPR/Cas12a system is emerging as a promising candidate for next-generation diagnostic biosensing platforms, with the discovery of new activation modes greatly expanding its applications. Here, we have identified two novel CRISPR/Cas12a system activation modes: PAM- and toehold-free DNA hairpins, and DNA-RNA hybrid strands. Utilizing a well-established real-time fluorescence method, we have demonstrated a strong correlation between DNA hairpin structures and Cas12a activation. Compared with previously reported activation modes involving single-stranded DNA and PAM-contained double-stranded DNA, the DNA hairpin activation way exhibits similar specificity and generality. Moreover, our findings indicate that increasing the number of RNA bases in DNA-RNA hybrid strands can decelerate the kinetics of Cas12a-triggered trans-cleavage of reporter probes. These newly discovered CRISPR/Cas12a activation ways hold significant potential for the development of high-performance biosensing strategies.

Split activator of CRISPR/Cas12a for direct and sensitive detection of microRNA.

CRISPR/Cas12a-based nucleic acid assays have been increasingly used for molecular diagnostics. However, most current CRISPR/Cas12a-based RNA assays require the conversion of RNA into DNA by preamplification strategies, which increases the complexity of detection. Here, we found certain chimeric DNA-RNA hybrid single strands could activate the trans-cleavage activity of Cas12a, and then discovered the activating effect of split ssDNA and RNA when they are present simultaneously. As proof of concept, split nucleic acid-activated Cas12a (SNA-Cas12a) strategy was developed for direct detection of miR-155. By adding a short ssDNA to the proximal end of the crRNA spacer sequence, we realized the direct detection of RNA targets using Cas12a. With the assistance of ssDNA, we extended the limitation that CRISPR/Cas12a cannot be activated by RNA targets. In addition, by taking advantage of the programmability of crRNA, the length of its binding to DNA and RNA was optimized to achieve the optimal efficiency in activating Cas12a. The SNA-Cas12a method enabled sensitive miR-155 detection at pM level. This method was simple, rapid, and specific. Thus, we proposed a new Cas12a-based RNA detection strategy that expanded the application of CRISPR/Cas12a.

Multiple RNA Rapid In Situ Imaging Based on Cas9 Code Key System.

Existing RNA in situ imaging strategies mostly utilize parallel repetitive nucleic acid self-assembly to achieve multiple analysis, with limitations of complicated systems and cumbersome steps. Here, a Cas9 code key system with key probe (KP) encoder and CRISPR/Cas9 signal exporter is developed. This system triggers T-protospacer adjacent motif (T-PAM structural transitions of multiple KP encoders to form coding products with uniform single-guide RNA (sgRNA) target sequences as tandem nodes. Only single sgRNA/Cas9 complex is required to cleave multiple coding products, enabling efficient "many-to-one" tandem signaling, and non-collateral cleavage activity-dependent automatic signaling output through active introduction of mismatched bases. Compared with conventional parallel multiple signaling analysis model, the proposed system greatly simplifies reaction process and enhances detection efficiency. Further, a rapid multiple RNA in situ imaging system is developed by combining the Cas9 code key system with a T-strand displacement amplification (T-SDA) signal amplifier. The constructed system is applied to tumor cells and clinicopathology slices, generating clear multi-mRNA imaging profiles in less than an hour with just one step. Therefore, this work provides reliable technical support for clinical tumor typing and molecular mechanism investigation.