Preparation of carbon nanodots capped by polyethylene glycol as a multifunctional sensor for temperature and paracetamol

In this paper, a simple and green preparative strategy for synthesizing carbon nanodots (CNDs) is developed by a one-pot hydrothermal method, using ascorbic acid (AA) as the carbon source and polyethylene glycol (PEG) with a molecular weight of 1500 as the surface modification agent. Through changing the amount ratio of PEG-1500 to AA in the synthesis, we can obtain PEG-CNDs with different functions. For example, due to the thermosensitivity of PEG-1500, the as-prepared PEG1-CNDs exhibit unique temperature sensitivity when the mass ratio of PEG-1500 to AA is 24 : 1. A reversible change of PEG1-CNDs from the solid state to transparent solution with increasing temperature can be repeated several times. The optical transmittance signal of PEG1-CNDs linearly responds to temperature in the range of 20–65 °C. Besides, while the amount ratio of PEG-1500 to AA is 12 : 1, the obtained PEG2-CNDs lose thermal sensitivity and form a stable and fluorescent solution at room temperature. The emission of PEG2-CNDs can be quenched by Fe3+, while with the addition of paracetamol (PAR), the fluorescence is recovered because of forming chelates between Fe3+ and PAR. Under the optimized conditions, the linear range of PAR obtained is 0.03–30 μM with a detection limit of 13 nM. Finally, the proposed method is successfully applied to detect PAR in human serum and urine samples with satisfactory recoveries.