Guar gum-enhanced emission of gold nanoclusters for α-glucosidase activity detection and anti-diabetic agents screening in plant extracts.

The development of efficient fluorescent methods for α-glucosidase (α-Glu) detection and α-Glu inhibitor screening plays a critical role in the therapy of type 2 diabetes (T2D). Herein, guar gum (GG), a high-abundant and non-toxic natural polymer originated from the seeds of a drought-tolerant plant, Cyamposis tetragonolobus, was found to be able to enhance the fluorescence emission of gold nanoclusters (AuNCs) probe. The emission enhancement effect was achieved by using GG at very low concentrations (<1.0 wt%) and presented in a viscosity-dependent manner through increasing solvent reorientation time and inhibiting intramolecular motions of AuNCs. Furthermore, the enhanced emission of the AuNCs was quenched by Fe3+via dynamic quenching and then restored by α-Glu. Accordingly, a fluorimetric method was proposed for the determination of α-Glu. Owing to the fluorescence enhancement effect of GG on the AuNCs probe, the detection limit of the approach was 0.13 U L-1 and the detection range was up to 5 orders of magnitude from 0.2 to 4000 U L-1, which was much better than most current α-Glu detection methods. The approach was further applied to α-Glu inhibitors screening from natural plant extracts, providing great prospects for the prevention and treatment of T2D.

Synergistic effect of silver nanoclusters and graphene oxide on visible light-driven oxidase-like activity: Construction of a sustainable nanozyme for total antioxidant capacity detection.

The high cost and low reusability of natural enzymes greatly limit their application in biosensing. In this work, a sustainable nanozyme with light-driven oxidase-like activity was fabricated by integrating protein-capped silver nanoclusters (AgNCs) with graphene oxide (GO) through multiple non-covalent interactions. The prepared AgNCs/GO nanozyme could effectively catalyze the oxidation of various chromogenic substrates by activating dissolved O2 to reactive oxygen species under visible light irradiation. Moreover, the oxidase-like activity of AgNCs/GO could be well controlled by switching on and off the visible light source. Compared with natural peroxidase and most of other oxidase-mimicking nanozymes, AgNCs/GO possessed improved catalytic activity owing to the synergistic effect between AgNCs and GO. More importantly, AgNCs/GO showed outstanding stability against precipitation, pH (2.0-8.0), temperature (10-80 °C), and storage and could be reused at least 6 cycles without obvious loss in catalytic activity. On this basis, AgNCs/GO nanozyme was used to develop a colorimetric assay for the determination of total antioxidant capacity in human serum, which had the merits of high sensitivity, low cost, and good safety. This work holds a promising prospect in developing sustainable nanozymes for biosensing and clinical diagnosis.

Confining copper nanoclusters in three dimensional mesoporous silica particles: Fabrication of an enhanced emission platform for "turn off-on" detection of acid phosphatase activity.

The incorporation of fluorescent nanoprobes into three dimensional (3D) matrixes is capable of enhancing the fluorescence properties of nanoprobes and greatly benefiting sensing application. In this work, N-acetyl-l-cysteine capped-copper nanoclusters (NAC-CuNCs) were incorporated into 3D mesoporous silica particles (M-SiO2) through electrostatic assembly. The assembly process takes only 2 min, and the fluorescence emission and quantum yield of NAC-CuNCs were significantly improved owing to the electrostatic confinement effect of M-SiO2. The prepared M-SiO2@NAC-CuNCs was further integrated with MnO2 nanosheets, a newly-emerged fluorescence nanoquencher with broad absorption spectrum. The emission intensity of M-SiO2@NAC-CuNCs was significantly decreased in the presence of MnO2 nanosheets by inner filter effect (IFE), and then recovered by ascorbic acid generated by the enzymolysis of l-ascorbic acid-2-phosphate (AAP) in the presence of acid phosphatase (ACP). On this basis, an enhanced emission platform was developed for "turn off-on" detection of ACP, a key indicator for diagnosis of prostate cancer. The detection limit for ACP activity was 0.47 U/L. Moreover, the approach was used to monitor ACP level in real serum samples with high accuracy, providing an attractive approach for clinical diagnosis of prostate cancer and other ACP-related diseases.