Amplification-free CRISPR/Cas based dual-enzymatic colorimetric nucleic acid biosensing device

Nucleic acid testing (NAT) is widely considered the gold standard in analytical fields, with applications spanning environmental monitoring, forensic science and clinical diagnostics, among others. However, its widespread use is often constrained by complicated assay procedures, the need for specialized equipment, and the complexity of reagent handling. In this study, we demonstrate a fully integrated 3D-printed biosensensing device employing a CRISPR/Cas12a-based dual-enzymatic mechanism for highly sensitive and user-friendly nucleic acid detection. A plastic probe stick was designed to host small-sized gold nanoparticles, enhancing enzyme labeling density. Alkaline phosphatase (ALP) was then conjugated via single-stranded DNA, requiring only a single enzyme substrate addition to generate a simple visual signal change. This approach eliminates the need for amplification or centrifugation steps, achieving a limit of detection (LOD) as low as 10 pM - among the highest sensitivities reported for amplification-free colorimetric nucleic acid detection. Furthermore, we developed a device that incorporates this probe stick, integrates all necessary reagents, and features a smartphone-compatible accessory for quantitative analysis. This allows end-users to perform visual or quantitative DNA analysis with simple operations, achieving a visual detection limit of approximately 100 pM, comparable to other CRISPR-based non-amplified nucleic acid detection methods. Additionally, the system successfully distinguished perfectly matched from mismatched nucleic acid sequences, demonstrating its specificity and versatility. Although certain design limitations affected the sensitivity of the integrated device compared to the probe stick alone, the simplicity and portability of this device make it a promising tool for rapid nucleic acid screening in clinical diagnostics, environmental monitoring, and food safety control. This study paves the way for the development of practical biosensors for point-of-care testing (POCT) applications.