Blue luminescent carbon dots (CDs) with a high photoluminescence (PL) quantum yield (48.3 ± 5.3%) were prepared by the one-pot hydrothermal reaction of citric acid with poly(ethylenimine) (PEI). The CDs display bright PL, narrow emission spectra, pH-dependent PL intensity, high photostability, and up-converted luminescence. The CDs exhibit a quenching of both down- and up-conversion PL in the presence of morin and thus serve as useful probes for morin detection. Both down- and up-conversion measurements allow the quantification of concentrations from 0 to 300 μmol/L with a detection limit of 0.6 μmol/L, and this dual-mode detection increases the reliability of the measurement. The proposed method of determination is simple, sensitive, and cost-effective, with potential applications in clinical and biochemical assays.

•A simple and rapid RLS method for the determination of PFOA has been developed.•The method is highly sensitive and the limit of detection is nanomole level.•The method is rapid, simple and cost-effective.•The interferences of SDS and SDBS were eliminated successfully by Ba2 + treatment.A simple, highly sensitive resonance light scattering (RLS) method for the detection of perfluorooctanoic acid (PFOA) has been developed based on the interaction with crystal violet (CV). It was found that PFOA can form complexes with CV in acid medium resulting in remarkable enhancement of the RLS intensity of the system. And the enhanced RLS intensities are in proportion to the concentration of PFOA in the range of 0.1–25.0 μmol/L (R2 = 0.9998), with a detection limit of 11.0 nmol/L (S/N = 3). In this work, the optimum reaction conditions and the interferences of foreign substances were investigated. The reaction mechanism between CV and PFOA was also studied by the absorption spectrum and scanning electron microscope (SEM). This method is successfully applied to the determination of PFOA in tap water and Jialing river water samples with RSD ≤ 4.04%.The system exhibits weak RLS peaks in the absence of PFOA, but when PFOA existed in the solution, obvious enhanced RLS peaks are observed due to the interaction between crystal violet (CV) and PFOA. Thus, a rapid and simple RLS method for sensitive detection of PFOA has been developed.

•It was a dual-readout assay for PaH.•PaH caused the aggregation of poly(A)-stabilized AuNPs for the strong affinity between poly(A) and PaH.•Poly(A) and gold nanoparticles were exploited to detect PaH with great sensitivity.•This RLS method was simple and fast without complicated labeling and separation.•PaH was detected with naked eyes for the first time.This report presents a highly sensitive, poly(A)-stabilized gold nanoparticle-based assay with dual readouts (resonance light scattering and colorimetric) for detecting palmatine hydrochloride (PaH) in real samples. The detection mechanism is based on the fact that palmatine hydrochloride has strong affinity to poly(A), which can stabilize gold nanoparticles at high ionic strength, and cause the aggregation of poly(A)-stabilized AuNPs, resulting in the enhanced resonance light scattering (RLS). At the same time, the color change of poly(A)-stabilized AuNPs solution is from red to blue via purple. Thus a highly sensitive RLS assay for PaH has been developed with a linear range of 0.023–2.5 μg/mL. The limit of detection (LOD, 3σ) is 2.3 ng/mL. In this work, the reaction mechanism of this system was investigated by scanning electron microscope (SEM), dark-field light scattering images (DLSI), dynamic light scattering (DLS) and circular dichroism (CD). This proposed method was also applied successfully for the determination of PaH in pharmaceutical preparations and urine samples with RSD ⩽ 4.0%. The results are in good agreement with those from the official method.