1：Experimental Design and Method Selection:

Hydrothermal synthesis method was used for preparing carbon dots and nanocomposites. The rationale is to create a green, cost-effective sensor with photoluminescent and magnetic properties.

2：Sample Selection and Data Sources:

Almond soot was used as a green precursor for carbon templates. Pseudomonas aeruginosa bacteria, Pb(II), and Hg(II) ions were used for sensing applications.

3：List of Experimental Equipment and Materials:

Materials include Ni(CH3COO)2·4H2O, Fe(NO3)3·9H2O, NaOH, ethylene diamine, citric acid, distilled water from Merck Company. Equipment includes X-ray diffractometer (Philips with CuKα radiation), SEM (MIRA3 TESCAN), TEM, FT-IR spectrometer, UV-Vis spectrometer, PL spectrometer, VSM (Meghnatis Danesh Pajouh Co., Iran), ultrasonic set-up (Bandeline MS 73 with Ti transducer, 20 kHz, 100 W power).

4：Experimental Procedures and Operational Workflow:

- Preparation of carbon dots: Mix ethylene diamine and citric acid in water, hydrothermal treatment at 180°C for 6h. - Preparation of hollow NiFe2O4 nanoparticles: Dissolve soot, Ni and Fe salts in water, adjust pH to 9 with NaOH, hydrothermal treatment at 180°C for 6h, centrifugation, washing, calcination at 500°C for 2h. - Preparation of NiFe2O4-carbon dot nanocomposite: Disperse hollow NiFe2O4 in water, add citric acid and ethylene diamine, hydrothermal treatment at 180°C for 6h, washing. Characterization using XRD, SEM, TEM, FT-IR, UV-Vis, PL, VSM. Sensing experiments by adding bacteria and ions to measure PL quenching. Antibacterial tests by degrading bacteria with nanocomposite.

5：6h. - Preparation of hollow NiFe2O4 nanoparticles:

5. Data Analysis Methods: XRD for phase identification, SEM and TEM for morphology and size analysis, FT-IR for functional groups, UV-Vis and PL for optical properties, VSM for magnetic properties. Quantum yield calculated using Rhodamin B as reference.