Figure 3.
(A) FTIR analysis of citric acid (CA), carbon quantum dots (CQDs), peptide (HSER), and peptide-coated CQDs (HSER-CQDs) in the range 2000–1000 cm−1. The amide I region shows an increased peak at 1625 cm−1 as a result of HSER interaction with CQDs; shouldered with a lower peak at 1650 cm−1. The former peak in amides indicates short-range hydrogen bond interactions, while the latter indicates long range hydrogen bond interactions. (B) Complete FTIR spectra for the range 4000–400 cm−1. A clear and broad band around 3000 cm−1 correlates with the hydroxyl group. The overall decrease of CQDs vibrations (red line) confirms successful coating by HSER peptide in the complex HSER-CQDs (purple line). (C) The zeta potential of HSER, CQDs and HSER–CQDs, and (D) the zeta size of the CQDs is marked as 1 and HSER–CQDs is marked as 2. Data represent the mean ±SD, n = 5.