To overcome the insufficient sensitivity due to distortion
of the
fluorescent images by mobile devices, we first developed a novel dual-mode
strategy for undistorted visual fluorescent sensing on μPAD
by technically manipulating the coffee-ring effect of the fluid sample.
Based on the manipulating coffee-ring effect, we divided the horizontal
direction of the resulting fluorescence image into 600 pixels and
obtained more accurate quantitative information to avoid image distortion.
The bovine serum albumin–stabilized gold nanoclusters–copper
ion complex was used as the fluorescent probe, combined with a small
imaging box and a smartphone, to achieve a rapid testing of histidine
in human urine. The output image was analyzed in dual mode: RGB numerical
analysis in pixel units and the direct measurement of the fluorescent
strips length (limit of detection (LOD) is 0.021 and 0.5 mM, respectively),
and improved antidistortion for visual fluorescent sensing. This strategy
can overcome the distortion of a smartphone-visualized fluorescent
image and shows great potential for rapid and convenient analysis.