Fluorescence/colorimetry/smartphone triple-mode sensing platform based on carbon dots and Co, Fe-layered double hydroxides for citrate determination

The cheap, simple, but reliable non-invasive detection means and mature early warning mechanism are beneficial for male population in underdeveloped regions to get rid of the physical and mental pain caused by prostate cancer (PCa). Citrate is presently regarded as a potential biomarker for early non-invasive diagnosis of PCa due to significant changes of citrate levels in urine during the development of PCa, even in the early stages. In this work, the Co, Fe doped layered double hydroxide (CoFe-LDH) can significantly quench the fluorescence of carbon dots (CDs) via inner filter effect (IFE) and catalyze the oxidation of colorless TMB to generate blue TMBox because of excellent oxidase-mimetic activity. However, the introduction of citrate can form a stable complex with CoFe-LDH via intercalation effect, thereby restoring the fluorescence of CDs and inhibition of oxidase-like activity of CoFe-LDH. Based on this, a triple-mode sensing platform (fluorescence, colorimetry, and smartphone) based on CDs + CoFe-LDH system has been fabricated for citrate analysis with correlative detection limits of 0.35, 0.42, and 0.60 μM. Furthermore, these three modes are applied to citrate analysis in male urine samples with ideal recoveries ranging from 94.4 to 107.4%, demonstrate the reliability and stability of these triple-mode sensing platform in practical applications.