Europium(III)-Modified Silver Nanoparticles as Ratiometric Colorimetric and Fluorescent Dual-Mode Probes for Selective Detection of Dipicolinic Acid in Bacterial Spores and Lake Waters

Abstract

Detection of Bacillus anthracis spores is of great importance for biosecurity and prevention of disease outbreaks. In this paper, a ratiometric colorimetric and fluorescent dual-mode platform for rapid, sensitive, and visual detection of dipicolinic acid (DPA), a biomarker of anthrax spores, was developed based on Eu 3+ -modified silver nanoparticles (AgNPs). Eu 3+ -modified AgNPs can induce the aggregation of AgNPs, its localized surface plasmon resonance (LSPR) absorption at 392 nm is decreased, and a new absorption peak at 524 nm emerged. Interestingly, upon the addition of DPA, it can effectively inhibit the aggregation of AgNPs−Eu 3+ , and the solution color changes from pink to yellow, while the red characteristic fluorescence of Eu 3+ is turned on owing to the energy transfer from DPA to Eu 3+ by the antenna effect. A new insight that AgNPs can also enhance the fluorescence of Eu 3+ was found. Eu 3+ -modified AgNPs as a dual-mode platform for ratiometric colorimetric and fluorescence detection of DPA were thus fabricated. The good linearity is in the range of 1.0−25 μM with a LOD of 0.31 μM for the ratiometric colorimetric assay and 0.25−45 μM with a LOD of 17 nM for the fluorescent assay, which is greatly lower than the dose of DPA (60 μM) released by the contagious number of spores to cause anthrax. The ratiometric colorimetric and fluorescent probes were successfully applied for the detection of DPA in lake waters and Bacillus subtilis, and as low as 1.8 × 10 4 spores were detected.

Contactless and robust dielectric microspheres-assisted surface-enhanced Raman scattering sensitivity improvement for anthrax biomarker detection

“…Dipicolinic acid (DPA), one of the main ingredients of anthrax spores (accounts for 5–15% of the dry mass of spores), has been adopted as a significant biomarker for the detection of anthrax ( Yin and Tong 2021 ). Various DPA detection methods have been reported over the past decade.…”

Detection of Bacillus cereus Spore Biomarkers Using SERS-Based Cuttlebone-Derived Organic Matrix/Silver Nanoparticles

“…In the previous study, the extraction rates of 34 and 11% were obtained, respectively, due to the differences in the preparation conditions of spore samples. At present, there are two ways to obtain DPA from spores: one is that DPA is extracted from spores by HNO 3 solution, , and the other is to add l -alanine solution , to promote germination of spores and release DPA. A better minimum detection limit for the SERS substrate spore detection will be obtained if new extraction techniques are developed in the future.…”

Recent advances in airborne pathogen detection using optical and electrochemical biosensors

“…DPA has excellent coordination ability with Eu 3+ , which helps disperse AgNPs from the Ag–Eu 3+ complex and retains their original yellow color. Using this SPR phenomenon, the limit of detection (LOD) of B. anthracis in the real sample was measured as 0.31 μM [ 43 ]. Significantly, this process has detected the DPA using colorimetry as well as fluorescence methods.…”

“…B. anthracis spores have been mostly detected through its biomarker (DPA) in optical biosensors [ 43 , 48 ]. However, this infectious bacterium is directly detected using electrochemical biosensors [ 111 ].…”