A sharp and selective fluorescence paper-based sensor based on inner filter effect for ratiometric detection of four Sudan dyes in food matrix

•A ratiometric fluorescent strip is designed based on IFE for detecting Sudan I-IV.•The fluorescent spectrum of Tm@Er has more overlap with the absorption of Sudan I-IV.•Single Tm@Er with core–shell structure provides a more stable ratiometric signal.•UiO-66 improve the adsorption and DMIPs realize the selective detection of Sudan I-IV.•Sensitive and portable application is realized in chilli powder with complex matrix. The addition of Sudan dyes with carcinogenic effects to food threatens human health. Herein, a ratiometric fluorescence strip consisting of core–shell upconversion particles (NaYF4:Yb,Tm@NaYF4:Yb,Er), metal–organic frameworks and dual-template molecularly imprinted polymers was developed to selectively and sensitively detect four Sudan dyes based on inner filter effect (detection time only takes 8 min). The high adsorption capacity of metal–organic frameworks and the greater overlap between the emission of NaYF4:Yb,Tm@NaYF4:Yb,Er and the absorbance of four Sudan dyes enable the signal responses to be more sensitive. The limits of detection in chilli powder samples are as low as 29.87 ng/g, 37.55 ng/g, 47.89 ng/g and 51.02 ng/g, with satisfactory recovery (93.32–103.4%) and minor relative standard deviations (≤4.3%). This method broadens the idea for low-cost and portable detection of multiple illegal additives in complex substrates with high selectivity and sensitivity based on one kind of fluorescent strip.