The effect of steric hindrance on FRET efficiency in carbon dots for fluorescence regulation and stability enhancement

Surface modification can influence the optical properties of nanomaterials. In this study, we synthesized tunable dual-emissive carbon dots (CDs) by changing the amount of methyl in the starting materials. With higher methyl content, the spatial resistance increase, which in turn diminished Förster Resonance Energy Transfer (FRET) efficiency between the core states and surface states of the CDs. This results in a decrease in green fluorescence intensity and a relative dominance of blue fluorescence. The FRET effect was systematically investigated through characterizations and calculations. Beneficial from high steric hindrance, CDs derived from 2-amino-2-methyl-1-propanol (CDs-AMP) with multi-branches exhibited high stability under various conditions, including prolonged storage, UV exposure, extreme pH levels, and high-concentration salt solutions. Based on this, a probe for detecting Fe 3+ ions was constructed and applied in real samples including mineral, tap, and lake waters. The fluorescence intensity was linear with the concentration of Fe 3+ ions in the range of 0–40 μM, with the detection limit of 0.2 μM.