Controllable crRNA Self-Transcription Aided Dual-Amplified CRISPR-Cas12a Strategy for Highly Sensitive Biosensing of FEN1 Activity

Colorimetric and photothermal dual readout biosensor for flap endonuclease 1 based on target-prevented gold nanoparticles aggregation

A colorimetric and photothermal dual readout biosensor for Flap endonuclease 1 (FEN1) quantification was developed on the basis of target-prevented gold nanoparticles (AuNPs) aggregation. The exposed 5'-flap of double-flap DNA substrate modified on SAMBs was firstly cleaved by FEN1. Large amount of cleaved 5'-flap remained in the supernatant after simple magnetic separation, which can adsorb on the surface of AuNPs and effectively prevent the dispersed AuNPs from aggregation under high ionic concentration, accompanied with the color changing of the system, which can be recognized by nake eyes easily. The absorption intensity at 528 nm shows a good linear relationship with the increasing FEN1 concentration from 5.0 × 10-3 to 3.1 × 10-2 U μL-1 with a LOD of 1.6 × 10-3 U μL-1 (S/N = 3). Given the aggregated AuNPs have higher photothermal effect than that of the dispersed AuNPs, the target-prevented AuNPs aggregation avoids a sharp increase of temperature for the system under the laser radiation. The temperature change is linearly correlated with the FEN1 concentration in the range of 3.1 × 10-3-6.1 × 10-2 U μL-1 with a LOD of 1.1 × 10-3 U μL-1. The whole detection process can be completed within 1 h. The proposed system had been applied to detect FEN1 concentration in serum samples with satisfied results, which can be applied in resource-limited area easily and quickly.

Label-free and low-background FEN1 sensing based on cleavage-induced ligation of bifunctional dumbbell DNA and in-situ signal readout

Flap endonuclease 1 (FEN1) is overexpressed in various types of human tumor cells and has been recognized as a promising biomarker for cancer diagnosis in recent years. In this work, a label-free fluorescent nanosensor for FEN1 detection was developed based on cleavage-induced ligation of bifunctional dumbbell DNA and in-situ signal readout by copper nanoparticles (CuNPs). The dumbbell DNA was rationally designed with a FEN1 cleavable 5' flap for target recognition and AT-riched stem-loop template for CuNPs formation. In the presence of FEN1, 5' overhanging DNA flap of dumbbell DNA was effectively removed to form a linkable nick site. After the ligation by T4 DNA ligase, the dumbbell DNA changed to exonuclease-resisted closed structure which enabled in-situ generation of fluorescent CuNPs that served as signal source for target quantification. The low background attributed to synergic digestion by exonucleases facilitated the highly sensitive detection of FEN1 with limit of detection of 0.007 U/mL. Additionally, the sensor was extended to the assay of FEN1 inhibitor (aurintricarboxylic acid) with reasonable results. Last but not least, the normal cells and tumor cells were distinguished unambiguously by this sensor according to the detected concentration difference of cellular FEN1, which indicates the robustness and practicability of this nanosensor.