Synthesis of colistin-modified carbon nano dots (CDs-colistin) using microwave and pyrolysis methods for Escherichia coli detection

This research reports the synthesis of carbon nanodots (CDs) and colistin-modified CDs (CDs-colistin) using ammonium citrate as a precursor for the detection of Escherichia coli (E. coli). The objective was to evaluate the effect of colistin mass on fluorescence intensity and its effectiveness in detecting E. coli. The synthesis was carried out using conventional pyrolysis and microwave-assisted techniques. For the synthesis of CDs-colistin, 20 mg of ammonium citrate was mixed with various amounts of colistin (2.5; 5; 10; and 20 mg). The mixture was irradiated with microwaves at 750 W for 30 min. In addition, the same precursor mixture was subjected to thermal treatment in an oven at 180°C for 2 h under minimal oxygen conditions. The materials were characterized using FTIR to identify the formation of functional groups, and TEM was used to analyze the morphology and size of CDs-colistin. Absorbance was measured using a UV-Vis spectrophotometer (200-500 nm) to determine electronic transitions, while fluorescence properties were assessed with a spectrofluorometer (300-600 nm). CDs-colistin synthesized via microwave and pyrolysis methods exhibited spherical morphology with particle sizes of 8 nm and 9 nm, respectively. The CDs-colistin synthesized by both methods exhibited maximum fluorescence intensity at a colistin mass of 10 mg, with strong emission under excitation at 347 nm. The limit of detection (LOD) for E. coli using CDs-colistin synthesized via the microwave method was 1.497 cfu mL-1, whereas for the pyrolysis method, it was 1.813 cfu mL-1