Fluorometric biosensor based on boronic acid-functionalized ZnO-derived nanostructures for the detection of N-acetylneuraminic acid and its in vivo bio-imaging studies

Background: N-acetylneuraminic acid (Neu5Ac) is a sialic acid-based biomarker in neurological disorders like Alzheimer's disease (AD) and aging. Their abnormal concentrations in biological fluids like human serum and cerebrospinal fluid (CSF) are highly concerning. Conventional analytical methods lack time-saving, high sensi-tivity, and convenient labor options for their detection. In this study, a selectively recognizable fluorometric sensor was developed based on the boronic acid-functionalization of carbon-rich zinc oxide-derived nano-structures (ZnO NSs) for Neu5Ac detection. Methods: The ZnO NSs were synthesized using the acid-alkali-assisted hydrothermal method from anionic sur-factants like sodium dodecyl sulfate (SDS). These were functionalized with 3-(aminopropyl)-triethoxysilane (APTES): (APT-ZnO NSs), aspirin [acetylsalicylic acid (ASA)]: (ASA-APT-ZnO NSs), and quercetin: (Qu-ASA-APT-ZnO NSs). To enhance the detection capacity against Neu5Ac, Qu-ASA-APT-ZnO NSs were modified with 3-ami-nophenylboronic acid (APBA) (APBA-ZnO NSs). Their structural, functional, and optical performance were investigated using XRD and Raman, FT-IR, and UV-Vis spectroscopy. Significant findings: Flower-like ZnO NSs showed a typical ZnO plane (110) of wurtzite hexagonal crystalline phase under HRTEM analysis. The novelty of the proposed work is the development of highly sensitive and efficient APBA-ZnO NSs for Neu5Ac detection in the linear concentration range of 0 to 8 mu M with a low detection limit of 0.56 mu M. These results are comparable to the other reports, and their multicolor fluorescence properties in zebrafish larvae confirm them as magnificent fluorescent probes for in vivo bio-imaging studies. The practicality of the proposed APBA-ZnO NSs was explored in serum and CSF samples, which showed potential recovery percentage ranges of 97-104.66% and 96.33-105.37%, respectively. In the future, these fluorescent probes will have the appropriate scope for the in vitro and in vivo detection of diverse neurological biomarkers.

Automated summary

In this study, a selectively recognizable fluorometric sensor based on carbon-rich zinc oxide-derived nano-structures (ZnO NSs) was developed for detecting the biomarker Neu5Ac in neurological disorders. The sensor showed high sensitivity and efficiency, with the potential for in vitro and in vivo detection of diverse neurological biomarkers.