Sequential fluorescence modulation in an aptamer-functionalized bimetallic Ni/Fe-MOF for smartphone-assisted...

Fluorescence modulation through enhancement and spectral tuning is important for improving the analytical performance of luminescence-based sensing platforms. In this study, a label-free fluorescent aptasensor was developed by functionalizing a bimetallic nickel-iron metal-organic framework (Ni/Fe-MOF) with a specific single-stranded DNA aptamer for the detection of Staphylococcus aureus (S. aureus). The measured quantum yields of the monometallic Fe-MOF and Ni-MOF were 15% and 11%, respectively, whereas the Ni/Fe-MOF exhibited a quantum yield of 26%. Following the aptamer functionalization step, the quantum yield increased to 31%, indicating a change in the fluorescence properties of the sensing material. Upon exposure to S. aureus, further modulation of the fluorescence response was observed, including an increased contribution of the green emission component around 520 nm relative to the blue emission around 420 nm. This sequential fluorescence modulation enabled ratiometric detection of S. aureus, with limits of detection of 1.1 CFU·mL⁻¹ using conventional fluorometric measurements and 1.33 CFU·mL⁻¹ using smartphone-assisted analysis. The sensing platform demonstrated selectivity and rapid response under the optimized experimental conditions. In spiked wastewater samples, recoveries ranged from 94.5% to 97.9%, with RSD values below 0.63%. These results demonstrate the potential of the developed aptasensor as a portable platform for bacterial detection in aqueous and wastewater samples, while its application to more complex matrices, including food samples and biofilm-associated bacteria, will require appropriate sample pretreatment and further experimental validation.