葉酸對於人體的生理上有著至關的重要性。而亞鐵離子在環境和人體中亦扮演著一定的角色。因此，開發一款簡單、靈敏且準確的系統檢測生物系統中葉酸和亞鐵離子是非常有意義的。近年，石墨烯量子點因其量子限制以及邊緣效應，使其光學性能被廣泛應用在光學傳感應用中。儘管現今有許多種方法能夠製備石墨烯量子點，但仍有些許的缺點，如操作複雜、高溫的製程環境以及冗長的反應時間等。需要開發一種簡便且環保的大氣常壓微電漿合成石墨烯量子點或感測器。而基於光致發光的石墨烯量子點感測器展現了它的便利性、快速的回應、高靈敏及選擇性。
本研究將分享，檸檬酸在缺少化學還原劑下透過大氣常壓微電漿系統合成石墨烯量子點。並將合成的石墨烯量子點作為光致發光探針去感測葉酸和亞鐵離子。此外，可以通過簡單地調整氫氧化鈉的比例和反應溫度來調節石墨烯量子點的光致發光熒光強度。在這，我們探索了石墨烯量子點、葉酸和亞鐵離子的選擇性與能量轉移和碳官能基團之間的關係。根據XPS和FTIR研究結果，可簡單證實石墨烯量子點與葉酸形成的奈米共軛物，並可以進一步用作熒光探針進行亞鐵離子感測。本研究提供了一種合成石墨烯量子點的新方法，可同時檢測葉酸和亞鐵離子，且具有良好的選擇性、靈敏度和檢測極限。

Folic acid (FA) is essential for the physiological processes in human body. Ferrous iron (Fe2+ ion) also plays a critical role in the areas of environmental systems and human body. Therefore, it is important to develop simple, sensitive and accurate methods for detection of FA and Fe2+ ions in biological systems. Recently graphene quantum dots (GQDs) have been shown with strong quantum confinement and edge effects, leading them exhibit unique optical properties for optical sensing applications. While several methods can be used to prepare GQDs, they are disadvantaged with limiting of reactants, complicated operation, time consuming inefficiency and high temperature required. It is needed to develop a facile and green microplasma-assisted synthesis of GQDs or sensing applications. Furthermore, photoluminescence sensing performance of GQDs is a simplicity, rapid response, superior sensitivity and selectivity detection.
Here, we report a study to synthesis GQDs from citric acid without chemical reducing agents using microplasma under ambient conditions. The PL spectroscopic study indicates the synthesized GQDs could be used as a PL probe for FA and Fe2+ ion sensing. In addition, the PL fluorescence intensity of GQDs could be tuned by simply adjusting the ratio of NaOH and the reaction temperature. Moreover, we explored that the selectivity of GQDs, FA and Fe2+ ion relationship between the energy transfer and carbon functionalities. Systematic XPS and FTIR study suggest that the GQDs/FA nanoconjugates could be further applied as the fluorescence probe for Fe2+ ion sensing. Our work provides a new method to synthesis GQDs for dual sensing of FA and Fe2+ ion with good selectivity, sensitivity and limit of detection (LOD).

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