Highly sensitive colorimetric paper-based analytical device for the determination of tetracycline using green fluorescent carbon nitride nanoparticles

A novel colorimetric assay for tetracycline (TC) using a paper-based analytical device (PAD) coupled with fluorescent carbon nitride nanoparticles (CNNPs) is proposed. The fluorescent intensity of CNNPs which were prepared from Ginkgo leaves using a one-step hydrothermal approach without any surfactant was quenched in the presence of TC. The color change of the TC colorimetric PAD, which is visually observable, was captured by a smartphone. A smartphone application was then used to assess the color images by extracting the red, green, and blue (RGB) values. The TC-PAD was confirmed to exhibit a good linearity (R2 = 0.9963) in the range of 0.8–400 µM and the detection limit was calculated to be 120 nM. Additionally, the TC-PAD exhibits acceptable repeatability (RSD < 2.9%) on real samples to give a potential for practical applications. The developed CNNPs were characterized by X-ray diffraction, UV–vis spectrometry, spectrofluorometry, X-ray photoelectron spectroscopy, and elemental analysis.