Tailoring Carbon Quantum Dots via Precursor Engineering for Fluorescence-Based Biosensing of E. coli

Rapid and accurate bacteria identification, particularly Escherichia coli (E. coli), is essential in the monitoring of health, environment, and food safety. E. coli, a prevalent pathogenic bacterium, serves as a key indicator of food and water contamination. Carbon quantum dots (CQDs) have appeared as promising fluorescent probes because of their small size, ease of synthesis, low toxicity, and tunable fluorescence using different carbon-rich precursors. Advances in both bottom-up and top-down synthesis procedures have enabled precise control over CQD properties and surface functionalities, enhancing their capabilities in biosensing. Among the critical factors influencing CQD performance is the strategic selection of precursors, which determines the surface chemistry and recognition potential of the resulting nanodots. The integration with other nanomaterials and the surface modification of CQDs with specific functional groups or recognition elements further improves their sensitivity and selectivity toward E. coli. This review summarizes recent progress in the modification of CQDs for the fluorescent detection of E. coli, highlighting relevant sensing mechanisms and the influence of different precursors, such as antibiotics and sugars, as well as various functionalization and surface modification strategies. The aim is to provide insight into the rational design of efficient, selective, and cost-effective CQD-based biosensors for bacterial detection.