Portable visual assay for anthrax biomarker based on lanthanide coordination polymer nanoparticles and smartphone-integrated mini-device

Abstract

The development of highly selective and sensitive assays for dipicolinic acid (DPA), a biomarker of Bacillus anthracis, is of great importance for biosecurity and maintaining public health. Herein, lanthanide coordination polymer nanoparticles (LML-Tb³⁺-AMP NPs) were fabricated as a ratiometric fluorescence sensor for real-time and visual detection of DPA. The LML-Tb³⁺-AMP NPs were prepared by spontaneous self-assembly of Tb³⁺, luminol (LML) and adenosine 3′-monophosphate (AMP) at room temperature, and only emitted blue fluorescence dominated by LML, with no green fluorescence from Tb³⁺ being observed. Upon the addition of DPA, the green characteristic fluorescence of Tb³⁺ is turned on immediately owing to the energy transfer from DPA to Tb³⁺ by the antenna effect. As the concentration of DPA was increased, the emission intensity of LML remained constant, acting as a stable internal reference, while the fluorescence of Tb³⁺ was obviously enhanced. Good linearity in the range of 0.01 to 10 μM was observed with a detection limit of 3.4 nM, which is much lower than the lowest infectious dose of anthrax (60 μM). In conjunction with a custom-built device, a portable visual assay based on nano-staining of a hydrogel sensor was further fabricated, and the fluorescence images could be transduced into data information for the quantification of DPA. The practical application of the hydrogel sensor was further demonstrated by monitoring the DPA release upon spore germination. This strategy offers a prompt, simple and sensitive method for the visual and on-site sensing of DPA, and holds great promise for environmental monitoring.