A novel label-free electrochemical DNA biosensor was constructed for the determination of Escherichia coli bacteria in environmental water samples. The aminated DNA probe was immobilized onto hollow silica microspheres (HSMs) functionalized with 3-aminopropyltriethoxysilane and deposited onto a screen-printed electrode (SPE) carbon paste with supported gold nanoparticles (AuNPs). The biosensor was optimized for higher specificity and sensitivity. The label-free E. coli DNA biosensor exhibited a dynamic linear response range of 1 × 10-10 µM to 1 × 10-5 µM (R2 = 0.982), with a limit of detection at 1.95 × 10-15 µM, without a redox mediator. The sensitivity of the developed DNA biosensor was comparable to the non-complementary and single-base mismatched DNA. The DNA biosensor demonstrated a stable response up to 21 days of storage at 4 ℃ and pH 7. The DNA biosensor response was regenerable over three successive regeneration and rehybridization cycles.
A novel rapid and sensitive optical sensor for Cu2+ ion detection based on 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-7,14-dienium dibromide (TL) immobilized on Santa Barbara Amorphous (SBA-15) has been successfully developed. The inner and outer space of SBA15 allowed a high capacity of TL compound to immobilize onto it. FESEM (Field Emission Scanning Electron Microscopy) analysis was performed to confirm the morphology of TL-SBA15, while FTIR (Fourier Transform Infrared Spectroscopy) was utilized to confirm the interaction of TL−SBA15. A binding study of TL compound towards Cu2+ ion was performed via UV-vis solution study and binding titration. The stoichiometric binding ratio and binding constant value Kb of TL towards Cu2+ ion was 1:1 and 2.33 × 103 M−1, respectively. The optical reflectance sensor based on the TL compound is selective to Cu2+ ion and demonstrated a linear response over a Cu2+ ion concentration range of 1 × 10−7 M to 2 × 10−5 M, with a detection limit (LOD) of 1.02 × 10−7 M (R2 = 0.99) and fast response time of < 1 min. It showed high reproducibility, with a relative standard deviation (RSD) obtained at 0.47%. This optical sensor is reusable up to five consecutive times on Cu2+ ion by using 0.1 M EDTA with a pH of 6 as a regeneration solution, with a reversibility RSD value of 0.79%. The developed optical sensor provides a rapid and sensitive tool for Cu2+ ion detection in teabag samples, and the results align with those obtained by the ICP-MS standard method.