Carbon Quantum Dots (CQDs)-Diphenyl Carbazone (DPCO) loaded thin film sensors for fluorescent and colorimetric dual mode detection of mercury in various water resources

Abstract

Mitigation of the environmental pollution has attracted huge attention in recent years owing to the caused health hazards. Mercury ions are one of the toxic heavy metals as pollutants that cause severe damage to health and the environment. Fluorometric and colorimetric-based detection of mercury in water resources is gaining popularity globally due to ease of measurement and the possibility of onsite measurement. We herein report a fluorescent and colorimetric dual-mode Diphenyl carbazone (DPCO) and Carbon quantum dots (CQDs) thin film sensor for specific detection of mercury ions. The thin film sensors were characterized using various techniques like XPS, XRD, TEM, and CLSM. The colorimetric detection is based on the specific binding of DPCO with mercury ions forming a violet-colored complex with simultaneous production of protons. The intensity of color formation was quantified with a smartphone camera and the images using ImageJ software yielding a limit of detection (LOD) of 290 ppb. Fluorometric estimation was performed at an excitation wavelength of 365 nm and an emission wavelength of 505 nm which was possible due to the pH sensitive nature of CQDs in the thin film. Mercury (Hg2+) detection to an extent of 1.8 ppb was made possible in the linear range of 0–100 μM using fluorometric method with a response time of 2 min. Accuracy of estimation of Hg2+ detection was evaluated by spiking different water samples like Tap water, and two river water samples and resulted in the range of 100–103 %. Current investigation shows that DPCO-CQDs loaded thin films coupled with a fiber-optic device and smartphone imaging could be used for accurate dual mode sensing of Hg2+ in real water resource samples.