Preparation of boronic acid-modified polymer dots under mild conditions and their applications in pH and glucose detection

Glucose and pH responsive fluorescence detection system based on simple synthesis of silicon-coated perovskite quantum dots

Perovskite quantum dots (PQDs) are extremely unstable in ambient air due to their inherent structural instability, which limits the wide application of PQDs. In this work, silicon-coated CsPbBr₃ PQDs (CsPbBr₃@SiO₂) was synthesized via a simple method. The SiO₂ coating effectively isolated PQDs from water and oxygen in the environment, which were the main elements that destroyed the structure stability of PQDs. The synthesized CsPbBr₃@SiO₂ can be stored in water for more than 2 months and posessed wonderful dispersibility in aqueous solution. The fluorescence intensity remained unchanged within 7 days and only decreased by 11.9 % within 2 months. We found that CsPbBr₃@SiO₂ was extremely sensitive to environmental pH, and the fluorescence intensity decreased with the reduction of pH. In addition, an excellent linear relationship with pH value in the range of 1.0 ∼ 5.0 was achieved. As we all known that glucose can be catalyzed by glucose oxidase to produce gluconic acid and hydrogen peroxide, in which a good deal of protons were produced and the pH was gradually lowered. Since CsPbBr₃@SiO₂ was stable to water and oxygen, and sensitive to ambient pH, we applied CsPbBr₃@SiO₂ to the detection of glucose. CsPbBr₃@SiO₂ showed fantastic selectivity and sensitivity to glucose, and the detection limit can even reach 18.5 μM. Furthermore, CsPbBr₃@SiO₂ was successfully applied to the detection of glucose in the human serum with satisfactory performance.

Preparation of fluorescein-modified polymer dots and their application in chiral discrimination of lysine enantiomers

Fluorescein-functionalized fluorescent polymer dots (F-PDs) were prepared by a facile one-pot method by magnetic stirring under mild conditions based on carboxymethylcellulose (CMC) and fluorescein as the precursors. The obtained F-PDs exhibited a nanoscale size of 3.2 ± 1.1 nm, excellent water solubility, and bright yellow fluorescence emission with a fluorescence quantum yield of 12.0%. The fluorescent probe displays rapid and sensitive chiral discrimination for lysine focused on different complexation abilities between lysine enantiomers and Cu²⁺. The concentration of L-lysine in the range 4 to 14 mM (R² = 0.997) was measured by the fluorescence intensity ratio (I₅₁₃/I₄₂₉); the exitation wavelength was set to λ_ex = 365 nm. The detection limit was 0.28 mM (3σ/slope). Importantly, this sensor accurately predicted the enantiomeric excess (ee) of lysine enantiomers at the designed concentration (lysine: 20 mM; Cu²⁺: 10 mM) ranges. The proposed sensor was successfully applied to determine L-lys (recovery: 95.8-101%; RSD: 0.465-3.34%) and ee values (recovery: 98.5-102%; RSD: 2.61-3.21%) in human urine samples using the standard addition method.