A sensitive ratiometric fluorescence sensor for Pb(II) and Cr(VI) simultaneous detection based on microfluidic chip...

Pb(II) and Cr(VI) are persistent environmental pollutants. Their high toxicity and bioaccumulative potential endanger ecosystem stability and human health, raising significant concern in environmental research and regulation. Herein, dual-channel carbon dots (DC-CDs) are prepared by employing a one-step hydrothermal method with tris(hydroxymethyl)aminomethane and m-dihydroxybenzene as precursors. Optical analysis indicates the DC-CDs possess dual emission centers, with emission maxima at 425 nm and 525 nm, which are observable under corresponding excitation wavelengths. Both emission peaks are quenched by Pb(II) and Cr(VI) to different extents through distinct processes. The quenching by Pb(II) occurs via static quenching (SQE) paired with photoinduced electron transfer (PET), whereas the quenching by Cr(VI) is attributed to an inner filter effect (IFE) and fluorescence resonance energy transfer (FRET). The designed ratiometric probe demonstrates low detection limits (LODs) of 83 nM and 47 nM, and limit of quantifications (LOQs) of 276 nM and 156 nM for Pb(II) and Cr(VI), respectively, with wide linear ranges from 0.276 to 80 μM and 0.156 to 40 μM. Multivariate analysis, specifically linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA), facilitates the successful discrimination of samples containing mixed Pb(II) and Cr(VI). Furthermore, an inexpensive microfluidic platform integrated with the DC-CDs has been designed for point-of-care visual detection, thereby facilitating swift, precise and instrument-free assays. The reliability of the platform has been validated through testing with authentic aqueous specimens, demonstrating acceptable recovery values. Collectively, the present investigation enhances the scope of the deployment of CDs in environmental analysis. Moreover, it furnishes a dependable and transportable apparatus for the ongoing assessment of toxic metallic species, thereby fortifying water quality assurance.