A comparison of carbon dot and CdTe quantum dot toxicity in Drosophila melanogaster†

Carbon dots (CDs) are carbon nanoparticles that are typically ∼10 nm in size and feature many properties similar to quantum dots (QDs). Cadmium telluride QDs (CdTeQDs) are a frequently studied QD since their size, and therefore fluorescence spectra, can be easily controlled. However, cadmium is known to be toxic, making its use in consumer goods limited or outright banned in many jurisdictions. While many studies have examined the toxicity of CDs and CdTeQDs, few have directly compared both nanoparticles under the same conditions. Herein, we provide a direct comparison of the toxicity of nitrogen-doped CDs (NCDs), nitrogen, sulfur co-doped CDs (SCDs), and CdTeQDs in the model organism Drosophila melanogaster (fruit fly). No impact on the development of larvae into adult flies from NCDs or SCDs in the 10 – 100 mg kg⁻¹ food range was observed, whereas an EC₅₀ of 46 mg kg⁻¹ CdTeQDs in food was observed. A strong positive correlation was found between the concentration of CdTeQDs in food and the mean pupation and eclosion time, indicating severe developmental delays as CdTeQD concentration increased. Further experiments at sublethal concentrations revealed no significant difference between any of the treatments when evaluating reproductive performance, larval crawling, and fly climbing ability. Gut tube anatomy did differ between control and treatment flies, with all treatment individuals expressing lengthened, and in some cases, distended midguts. This work demonstrates that both NCDs and SCDs are considerably less toxic than CdTeQDs in the 10–100 mg kg⁻¹ food range, further enabling the former's potential applications for biocompatible QD-like nanomaterials.