Selectivity Enhancement for Uric Acid Detection via In Situ Preparation of Blue Emissive Carbon Dots Entrapped in Chromium Metal–Organic Frameworks

In the present work, for the first time, the in situ formation of blue emissive carbon dots (bCDs) and encapsulation into the pores of chromium-based metal-organic frameworks (Cr-MOFs) are described. The luminescent bCDs via in situ process are formed and entrapped inside the pores of Cr-MOFs to form a nanocomposite of bCDs@Cr-MOFs. The bCDs@Cr-MOFs showed a strong broad blue emission at 420 nm (excited at 310 nm), which corresponds to both, the ligand (2-aminoterephthalic acid) in the Cr-MOF and the entrapped bCDs. This is assigned for the entrapping of bCDs in the pores of the MOFs. Additionally, transmission electron microscopy (TEM) images showed two types of particles, 150 rod-like shapes for Cr-MOF and 5-10 nm spherical shapes assigned for the presence of bCDs. The bCDs alone (without Cr-MOF) showed no selectivity, and their emission was quenched by different biomolecules and ions, such as ascorbic acid, uric acid, Fe3+, Cu2+, and Hg2+. The selectivity of bCDs toward uric acid was increased dramatically when they were encapsulated in the Cr-MOF. The linear range for uric acid was 20-50 μM, and the LOD was measured as 1.3 μM. Spike recoveries for the detection of uric acid in serum samples were between 94 and 108%. The relative standard deviation (RSD, n = 3) at each concentration value was less than 2%. The results showed high ruggedness and robustness of the assay due to its high shelf-life stability of probe (four weeks), water stability, and long working pH range. Validation experiments showed that the established MOF-based sensing system is appropriate for uric acid detection in real samples.