ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Dual-mode visual and fluorescent detection of tetracycline using green carbon dots integrated with smartphone-based on-site analysis

Hemn A. Qader, Sameera Sh. Mohammed Ameen, Idrees B. Qader, and Khalid M. Omer

Department of Pharmaceutical Chemistry, College of Pharmacy, Hawler Medical University, Erbil, Iraq

E-mail: sameera.m.ameen@uoz.edu.krd

Received: 7 September 2025  Accepted: 2 April 2026

Abstract:

Point-of-care testing demands analytical platforms that are not only sensitive and reliable but also facile, cost-effective, and suitable for decentralized use. In this study, we report the development of a novel ratiometric fluorescent nanosensor based on green-synthesized blue-emissive carbon quantum dots (CQDs) for the quantification of tetracycline (TC) in pharmaceutical formulations. The dual-emission system exhibits a distinct fluorescence response upon interaction with TC, characterized by quenching of the native blue emission and simultaneous enhancement of green-yellow fluorescence. This modulation arises from competitive absorption between TC and CQDs, as well as aggregation-induced emission (AIE), which significantly improves the signal-to-noise ratio by minimizing background interference. The probe’s performance was evaluated using both conventional spectrofluorometry and a smartphone-assisted visual detection platform, enabling portable and user-friendly on-site analysis. The method demonstrated excellent linearity over a concentration range of 18.0–550.0 µM (R² = 0.9926), with a detection limit as low as 8.0 µM, indicating high sensitivity and reliability. Practical applicability was validated through accurate and precise detection of TC in pharmaceutical formulations such as commercial capsules and ointments. Furthermore, the environmental sustainability and applicability of the proposed method were rigorously assessed using the Analytical GREEnness (AGREE), the Green Analytical Procedure Index (GAPI), modified complex GAPI, Click Analytical Chemistry Index (CACI) metrics, blue applicability grade index (BAGI), Carbon footprint reduction index (CaFRI), and the Analytical Eco-Scale, all of which confirmed its strong alignment with green analytical chemistry principles and applicability. Overall, this work introduces a sustainable, dual-emission CQD-based sensing platform integrated with smartphone technology as a promising tool for rapid, accessible, and eco-friendly pharmaceutical analysis.

Graphical abstract

Keywords: Carbon quantum dots; Ratiometric fluorescence; Greenness evaluation; Smartphone-assisted visual detection; Tetracycline

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04872-9

Chemical Papers 80 (7) 8041–8055 (2026)