Cascade i-motifs-dependent reversible electrochemical impedance strategy-oriented pH and terminal deoxynucleotidyl transferase biosensing

One-pot isothermal amplification permits recycled activation of CRISPR/Cas12a for sensing terminal deoxynucleotidyl transferase activity

This study introduces a one-pot isothermal amplification assay for ultrasensitive analysis of terminal deoxynucleotidyl transferase (TdT) activity. The system realizes recycled activation of CRISPR/Cas12a, enabling exceptional signal amplification. This approach maximizes the simplicity of the detection method, offering a promising avenue for molecular disease diagnosis.

Dual Self-Amplification Homogeneous Electrochemiluminescence Biosensor for Terminal Deoxynucleotidyl Transferase Activity Based on Controlling the Surface Morphology and Charge of Reporter Nanoparticles

Terminal deoxynucleotidyl transferase (TdT) is upregulated in several types of leukemia and is considered a disease biomarker and a potential therapeutic target for leukemia. In this research, a homogeneous electrochemiluminescence (ECL) method based on the control of surface charge and morphology of tris (2,2'-bipyridine) ruthenium(II) chloride hexahydrate-doped silica nanoparticles (Ru@SiO2 NPs) has been designed for TdT activity detection. A small amount of short single-stranded DNA (ssDNA) was modified onto the surface of Ru@SiO2 NPs, and the nanoparticles with a slight positive charge experienced electrostatic attraction with the indium tin oxide (ITO) electrode with a negative charge, so relatively high ECL signals had been detected. Under the action of TdT, the ssDNA was significantly elongated, carrying numerous negative charges on its phosphate backbone, so the overall negative charge of the reporter nanoparticles was enhanced, resulting in a strong electrostatic repulsion with the ITO electrode. Simultaneously, the long ssDNA wrapped around the nanoparticles hindered the approach of the coreactant. Due to the dual effects, the ECL response of the system decreased. The constructed biosensor exhibited excellent sensitivity toward TdT over a range spanning from 1 to 100 U/L. The limit of detection is as low as 1.78 U/L. The developed approach was effectively applied to detect TdT activity in leukemic patients' leukocyte extracts.

Modification of polyacrylonitrile-derived carbon nanofibers and bacteriophages on screen-printed electrodes: A portable electrochemical biosensor for rapid detection of Escherichia coli

A facile method was developed for fabricating a disposable phage-based electrochemical biosensor for the detection of Escherichia coli. Bare screen-printed electrodes (SPEs) were modified using a two-step drop-casting method, in which polyacrylonitrile-derived electrospun carbon nanofibers (CNFs) were deposited, followed by E. coli bacteriophage immobilization. The deposition of CNFs increased the surface area for bacteriophage immobilization while maintaining a conductive link for ferro/ferricyanide redox transitions. Cyclic voltammetry and electrochemical impedance spectroscopy confirmed that the CNF modification increased the electron-transfer rate, whereas bacteriophages and E. coli blocked electron transfer at the electrode. The biosensor achieved a response within 10 min and a linear response in the E. coli concentration range of 10²-10⁶ CFU/mL. A limit of detection (LOD) of 36 CFU/mL in phosphate-buffered saline was achieved, which is the lowest LOD reported thus far for phage-based disposable SPE sensors. The biosensor exhibited recovery rates between 106 % and 119 % for E. coli detection in apple juice. The proposed fabrication method allowed electrodes to be obtained from different production batches with remarkable consistency and reproducibility, and they remained stable at room temperature for one month. Thus, a phage-based disposable SPE that can be used for bacterial detection was developed for the first time.