Performance of electrokinetic stacking enhanced paper-based analytical device with smartphone for fast detection of fluorescent whitening agent

Highlights: • The sensitivity of aportable PAD for fluorescent whitening agent (FWA) was 160 times enhanced by electrokinetic stacking. • A LOD comparable to the fluorescent spectrophotometer was achieved with smartphone fluorescent imaging detection. • Fast determination of FWA in napkin was successfully demonstrated with high recovery rate and reasonable reproducibility. - Abstract: Quantification is a fundamental aspect of performance of an analytical system. Paper-based analytical device (PAD) as an on-site detection platform has drawn wide attention mainly due to its portability and cost effectiveness. In this work, a portable and low-cost PAD for online preconcentration and sensitive determination of fluorescent whitening agent (FWA) was demonstrated, which was consisted of ultra violet light-emitting diode (UV LED), macro-focusing lens, smartphone and miniaturized DC voltage source. Taking a widely used FWA component VBL as the analyte, the performance of the PAD enhanced with electrokinetic stacking (ES) and fluorescence imaging detection was systematically investigated. With ES, the sensitivity of the PAD system was 160-fold enhanced, and a limit of detection (LOD) of 0.06 μg mL⁻¹ was achieved. The dynamic range was 0.1–10.0 μg mL⁻¹ (linear in 0.1–0.7 μg mL⁻¹, R² = 0.99). With manual operation, the relative standard deviation (RSD) of intra-day and inter-day were all below 15%. Eventually, VBL from different napkin samples and toilet paper was determined with average recovery rates in the range of 90%–95% (RSD = 8.0%–12.0%). This work shows that with ES, the sensitivity of PAD can be greatly improved, and a LOD close to a desktop fluorescent spectrophotometer can be achieved as demonstrated by the detection of FWA component.