Sensitive detection of polycyclic aromatic hydrocarbons using CdTe quantum dot-modified TiO₂ nanotube array through fluorescence resonance energy transfer.

CdTe quantum dots (QDs) are prepared on TiO(2) nanotubes (TiO(2) NTs), for the first time, with pulse electrodeposition. A novel single-drop optical sensor is prepared with the CdTe QDs-modified TiO(2) NTs, and applied for the detection of polycyclic aromatic hydrocarbons (PAHs) based on fluorescence resonance energy transfer (FRET). Excited at 270 nm, the sensor shows fluorescence emission at around 370 nm. As PAHs are with absorption/fluorescence emission at around 364/410 nm, FRET happens between the CdTe QDs and PAHs with the CdTe QDs as donors and PAHs as receptors. The sensitivity is dependent on the number of rings of the PAHs, with the highest sensitivity observed in the response to benzo(a)pyrene (BaP). Using FRET, the sensitivity to BaP is enhanced by about 2 orders with respect to the direct fluorescent spectrometry. The proposed sensor shows a linear response to the logarithm of BaP concentration in the range of 400 nM to 40 pM, with a detection limit of 15 pM, which is much close to the quality criteria (15.1 pM) in drinking water set by U.S. Environment Protection, suggesting that the proposed sensor can be used for quick scanning of PAHs. The achieved sensitivity is much higher than that of the published sensor-based methods. As PAHs are quantified based on the relative fluorescence intensity at 410-370 nm, the sensor need no calibration with a standard sensor, avoiding the influence from the sensor-to-sensor difference. The practicability of the sensor is tested by analyzing PAHs in Xiangjiang River water, the PAHs contents ranges from 0.045 to 2.847 ng/L based on the sampling spots.