Folic acid, due to its high affinity toward folate receptors (FR), is recognized as one of the most promising cancer targeting vectors. However, the inherent defects of low water solubility (1.6 µg mL⁻¹), high sensitivity toward photo‐bleaching, low fluorescent quantum yields (QYs, <0.5%) seriously limit its practical application. Herein, ultrastable, highly luminescent graphene quantum dots (GQDs) that selectively target diverse cancer cells are prepared and tested. The new GQDs present step changes compared to common folic acid through an ≈6250 times increase in water solubility (to ≈10 mg mL⁻¹), more than 150 times in QYs (up to ≈77%), while maintaining luminescence stability up to 98% when subjected to UV, visible light, and heating over 360 min. It is shown that the suppression of nonradiative transitions by amino groups pyrolyzed from pterin plays a key role in the mechanism of high QYs and excellent stability. The functional groups that are likely responsible for the selective targeting of cancer cells with different levels of folate receptor expression on the surface are identified. Collectively with these promising properties, the new functional graphene quantum dots may open a new avenue for cancer diagnosis, drug delivery, and therapies.

中文翻译：

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靶向癌症的石墨烯量子点：荧光量子产率，稳定性和细胞选择性。

叶酸由于对叶酸受体（FR）的高度亲和力，被认为是最有前途的癌症靶向载体之一。然而，低水溶性（1.6 µg mL ^-1），对光致漂白的高敏感性，低荧光量子产率（QYs，<0.5％）的固有缺陷严重限制了其实际应用。本文中，制备并测试了选择性靶向多种癌细胞的超稳定，高度发光的石墨烯量子点（GQD）。与普通叶酸相比，新GQD的阶跃变化是水溶性增加了≈6250倍（达到≈10mg mL ^-1）），在QYs中超过150倍（高达≈77％），同时在紫外线，可见光和360分钟以上的加热下保持高达98％的发光稳定性。结果表明，从蝶呤裂解而来的氨基对非辐射跃迁的抑制作用在高QYs和极好的稳定性的机制中起着关键作用。确定了可能负责选择性靶向表面具有不同水平叶酸受体表达的癌细胞的官能团。具有这些有希望的特性，新的功能性石墨烯量子点可以为癌症诊断，药物输送和治疗开辟新的途径。