Effect of ammonium citrate concentration variation on the carbon dots colistin modification for Escherichia coli detection

World Health Organization (WHO) mentioned that diarrhea is one of the main causes of under-five mortality in developing countries due to Escherichia coli (E. coli) bacteria. Synthesis of colistin-conjugated-carbon dots using ammonium citrate as a precursor for E. coli detection has been carried out to study its application for detection in water samples from urban population wells. Synthesis of carbon dots (CDs) was carrried out using conventional pyrolisis method. Ammonium citrate with mass variation of 10; 15; 20; and 25 mg were added to 2.5 g colistin and heated at 180 C for 1 h. Brown residue was yielded; more over the functional groups and morphology were characterized by FT-IR and TEM. The brown residue is further diluted by distilled water, centrifuged at 8000 rpm for 10 min. The absorbances were analyzed using spectrophotometer UV-Vis. Carbon dots colistin with different concentration of ammonium citrate variations were analyzed using spectrophotometer fluorescence at 310-450 nm and the highest intensity would be used for E. coli detection. From the experimental part, it was found that CDs colistin has spherical morphology with diameter around 3-10 nm. The highest intensity was achieved at excitation wavelength of 360 nm from CDs colistin with 20 mg ammonium citrate. In the detection process of three household urban wells water in Yogyakarta-Indonesia, it was concluded that one sample was found to contain E. coli whose concentration was higher than the permitted limit of 235 cfu per 100 mL set by Ministry of Health-Republic of Indonesia