Cetyltrimethyl ammonium mediated enhancement of the red emission of carbon dots and an advanced method for fluorometric determination of iron(III)

Red-emissive carbon dots (CDs) were synthesized by one-step hydrothermal technique using citric acid (CA), and urea in N,N-dimethylformamide (DMF) solution. The CDs has an average diameter of 2.3 nm, excitation/emission maxima at 553/606 nm, and a low photoluminescence quantum yield (4%). Fluorescence is weakly quenched by the ions Fe³⁺, Hg²⁺, Cu²⁺, Co²⁺, Zn²⁺, Ca²⁺, Ni²⁺, and Pb²⁺. After addition of cetyltrimethyl ammonium ion (CTAB), electrostatic interaction between negatively charged CDs and CTAB causes the CDs to self-aggregate. The formation of CD/CTAB increases the average particle diameter to around 13 nm and enhances the quantum yield to 24%. The hydrophobic segments of CTAB twined into a network structure can selectively trap Fe³⁺ and then interact with surface groups of the CDs to cause quenching. The CD/CTAB nanoprobe enables fluorometric determination of Fe³⁺ with a linear response in the 0.10–10 μM concentration range and a 0.03 μM limit of detection. The probe was utilized for determination of Fe³⁺ in human serum samples, and satisfactory results were obtained.

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