Ratiometric fluorescence detection of anthrax biomarker based on terbium (III) functionalized graphitic carbon nitride nanosheets.

Detection of anthrax biomarker dipicolinic acid (DPA) is of great importance upon the crisis of bioterrorism. Development of fluorescent materials for DPA detection, particularly one that fully depends on single luminescent response, faces the challenge of being susceptible to interferences. The accompanying accuracy problems offer great opportunities for the establishment of more reliable ratiometric analysis method. Herein, a ratiometric fluorescent probe based on terbium functionalized graphitic carbon nitride nanosheets (Tb-g-C3N4NS) is attempted for quantitative detection of DPA to address the distinct function of g-C3N4NS as both carrier and reference fluorophore, which is a so-far unexplored option in fluorescent detection approaches. We achieve the incorporation of Tb3+ into framework of g-C3N4NS by using a simple synthetic strategy comprised of thermal pyrolysis and ultrasonic exfoliation. Combining the reference signal over g-C3N4NS at 440 nm (I440) with the response signal of Tb3+ at 546 nm (I546), concentration of DPA can be easily calculated via its linear correlation with the intensity ratio (I546/I440), giving a precise measurement towards DPA with a detection limit as low as 9.9 nM. Besides enabling an excellent self-calibrating detection of DPA, this work also inspires broader use of g-C3N4NS for relevant process.

Visual Luminescent Probes Constructed by Eu3+ Complex-Functionalized Silica Nanocomposites and Their Langmuir-Blodgett Films at Interfaces.

The trivalent europium ion (Eu3+) has garnered a great deal of interest for the design of luminescent materials possessing compound-independent emission bands, strong luminescent intensity, and long emission lifetimes. We herein introduce a synthetic methodology capable of constructing visual luminescent probes from Eu3+ complex-functionalized silica nanocomposites and their Langmuir-Blodgett (LB) films at interfaces. In order to facilitate the coordinative stabilization of Eu3+ over carrier surfaces, silica nanoparticles (nanoSiO2) were pregrafted with terpyridyl (TPy) to make nanoSiO2TPy linkers. Then, a well-designed coordination reaction of nanoSiO2TPy with EuCl3 and 2,6-pyridinedicarboxylic acid (DPA) was carried out at solid-liquid and air-water interfaces, where our desired material (denoted as nanoSiO2TPy@EuDPA) and its corresponding LB film are obtained. The presence of TPy and DPA interacting with Eu3+ plays a key role in regulating the chemical nature of the particle surface, hence giving rise to closely packed nanocomposite arrays in the film. As a result, the improvement in uniformity and stability is achieved alongside the enhancement in emission intensity and lifetime. With such advantageous optical properties, we find them workable as facile, green, and affordable luminescent sensors, by which a range of common toxic anions (Cr2O72-, MnO4-, and PO43-) can be visually and quantitatively recognized. Notably, the LB film-based material could afford a higher Ksv value (1.53 × 105 M-1), a lower detection limit (0.157 µM), and better recyclability than its original powder analogue, showcasing its utility as a more promising candidate for practical use.