Long-lived ratiometric phosphorescence probe and portable device for cholesterol sensing in serum without background fluorescence

Visual detection using phosphorescence emission can effectively overcome the background fluorescence interference of complex samples, providing higher sensitivity and accuracy. However, the acquisition of phosphorescence photographs requires the recording of luminescence information immediately after ceasing the excitation source, which poses challenges for portable platforms. In this work, we demonstrated the quantitative analysis of cholesterol in serum by utilizing a homemade portable device combined with long-lived phosphorescent N and P doped carbon dots (NPCDs). The green emissive NPCDs were coated with silica and modified with β-cyclodextrin, resulting in an extremely long lifetime of 1.3 s and a special surface recognition function. By employing Rhodamine B as an energy acceptor, a triplet to singlet Förster resonance energy transfer system was established, leading to the transformation of green phosphorescence into orange-red phosphorescence. When cholesterol is present in the system, it disrupts the energy transfer process, resulting in the recovery of green phosphorescence. This unique color evolution without background fluorescence interference can be easily recorded using a portable device. Combined with RGB color analysis, this method enables the quantitative detection of cholesterol. This study provides a promising solution for the development of low-background nanoprobes and portable detection techniques.