Facile synthesis of long-wavelength dual-emissive carbon dots for multifunctional use in pH sensing, vitamin B detection, and bioimaging.

A facile one-step hydrothermal synthesis of dual-emission fluorescent carbon dots (D-CDs) is presented using giemsa stain and malic acid as precursors. The resulting D-CDs exhibit unique long-wavelength dual-emission properties with exceptional pH sensitivity across a broad range (3.0-10.0), showing particularly strong linear correlation (R = 0.9927) in the physiologically relevant pH window (5.0-9.0). This pH-dependent behavior, combined with their excellent photostability, makes them ideal probes for biological imaging applications. The D-CDs also demonstrate selective detection capability for vitamin B (VB) through inner filter effect-mediated quenching of the green emission channel (520 nm), achieving a wide linear detection range (2-120 μM) with a low detection limit (0.96 μM). Comprehensive biocompatibility assessments confirmed low cytotoxicity (> 86% cell viability at 60 μg·mL⁻) and successful application in both cellular systems and zebrafish models. Their unique combination of dual-emission properties, pH sensitivity, selective molecular recognition, and excellent biosafety establishes D-CDs as a versatile platform for physiological monitoring and biomedical imaging applications.