Recognition and ratiometric visual sensing of long-chain unsaturated fatty acids by a white-light-emitting quantum-dot complex

Abstract

Herein we report the twin advantages of a white-light-emitting quantum-dot complex (WLE-QDC), comprising Mn²⁺-doped ZnS quantum dots (Qdots) and a zinc quinolato (ZnQ₂) complex, towards the selective recognition of long-chain unsaturated fatty acids (LCUFAs; e.g., Na-salt of oleic acid) from their corresponding saturated forms (e.g., Na-salt of stearic acid). Importantly, the WLE-QDC provided the unique ratiometric visual detection of LCUFAs with a detection limit of 0.127 μM in the linear range of 4.2–16.6 μM. This was pursued by monitoring alterations in the photoluminescence color from white to cyan, the hue, the chromaticity and the emission intensity ratio (I₄₈₀/I₅₉₀) of WLE-QDC upon interaction with LCUFAs. The concurrent hydrophobic and π–π interactions between the ZnQ₂ complex (present in WLE-QDC) and LCUFAs might play an important role in this regard. Remarkably, the high selectivity of WLE-QDC towards LCUFAs led to their practical utilization in the quantification of LCUFAs in commercial vegetable oils.