基于Fluoral-P衍生物的新型甲醛探针的光谱特性研究

甲醛(HCHO)是目前室内空气主要污染物之一，长期暴露在过量甲醛环境中会对人的眼睛、皮肤、呼吸器官等产生严重危害，甚至可能导致神经系统功能的丧失1]以及耳、鼻和喉癌2]。因此，快速、高效、准确地实现甲醛气体的检测，对于保障人类健康具有重大的意义。当前有很多种方法可以用于甲醛气体的检测。例如，气相色谱法(GC)3]和高效液相色谱法(HPLC)4]，色谱仪器能够提供低至μg·m-3级别的浓度检测，但是仪器较为大型笨重，并且检测非常耗时，难以实现实时连续地对甲醛气体浓度的监测；基于气敏薄膜的半导体气体传感器具备响应时间短，稳定性高以及可连续监测等优点，然而这类传感器通常检测限较高(>300 μg·m-3)，并且选择性差5]；基于酶的生物传感器通常有较好的灵敏性和选择性，但是其热稳定性通常较差，这严重限制了其应用6]。比色法和荧光法由于响应速度快，灵敏度高，检测限低，选择性好以及传感器简单便宜等特点，被广泛地应用于甲醛气体传感器的设计中去7-9]。这种方法是利用探针分子与甲醛发生特异性结合，形成新的物质，从而引起探针吸收光谱的变化或者发出荧光，实现对甲醛的定量测量。Descamps等使用4-氨基-3-戊烯-2-酮(Fluoral-P)作为探针分子，设计了一种手提式的甲醛检测仪10]。Fluoral-P是一种烯氨酮结构的物质，能与甲醛特异性结合形成环状化合物3,5-diacetyl-1,4-dihydrolutidine(DDL)。由于Fluoral-P自身的特征吸收带与DDL的吸收带相隔较远，同时与甲醛结合后能够产生大斯托克斯位移的荧光峰，因而被广泛应用于甲醛检测。然而，Fluoral-P在空气中有水分子存在的情况下极其不稳定，容易发生水解，形成乙酰丙酮和氨气，严重限制了Fluoral-P在甲醛检测上的应用10]。采用紫外可见吸收光谱、稳态荧光光谱和气相色谱质谱(GC-MS)技术研究了Fluoral-P的一种衍生物，4-氨基-1,1,1-三氟-3-丁烯-2-酮(3F-FP)，与甲醛溶液相互作用的光学和化学特性。实验发现，Fluoral-P的水解速率为k＝1.555 9×10-5 L2·mol-2·s-1，然而，3F-FP具有非常低(接近0)的水解速率，水溶液环境下表现出了极好的稳定性。同时，3F-FP可以与甲醛反应生成一种类似DDL的环状化合物6F-DDL，使得3F-FP在430 nm处出现了一个新的吸收带，并且在峰值489 nm处的荧光强度也得到了明显增强，增强因子为12，在峰值处的荧光增长速率为k=7.881×103 h-1。下一步我们将使用多孔玻璃作为3F-FP探针的载体，不仅可以提高3F-FP分子浓度，也可以增加探针分子与甲醛的接触表面积11]，荧光增长速率还可以得到进一步的提高，因此3F-FP分子在甲醛气体检测领域具备了良好的应用前景。

Study on Spectral Characteristics of a Novel Formaldehyde Probe Based on Fluoral-P Derivatives

Formaldehyde (HCHO) is one of the main pollutants of indoor air. Exposure to excessive formaldehyde for a long time will cause serious damage to human eyes, skin and respiratory organs, and even lead to loss of the function of nervous system1], as well as ear, nose and laryngeal cancer2]. Therefore, a rapid, efficient and accurate detection of gaseous formaldehyde is of great significance to human health. So far, there have been a lot of techniques that can be used for the detection of gaseous formaldehyde, such as gas chromatography (GC)3] and high-performance liquid chromatography (HPLC)4]. Although chromatographic apparatus may provide detection limits of several μg·m-3, they are time-consuming and not suitable for real-time and continuous monitoring of formaldehyde concentration because of their weight and bulk. Semiconductor gas sensors based on gas-sensitive films provide a good alternative in indoor formaldehyde monitoring due to their advantages of high stability, short response time and continuous monitoring. However, high detection limit (>300 μg·m-3) and poor selectivity is considered to be a great limitation for such sensors5]. Enzyme-based biosensors usually have a good sensitivity and selectivity, but their thermal stability is usually poor, which seriously restricts their application6]. Colorimetric and fluorescence methods are widely applied in the design of formaldehyde gas sensors because of their fast response, high sensitivity, low detection limit, good selectivity, simplicity and low cost7-9]. These methods are based on the combination of probes and formaldehyde which can generate new substances, resulting in the change of absorption spectrum or fluorescence enhancement, so that ones may achieve quantitative detection of formaldehyde. Descamps et al developed a portable formaldehyde detector by using 4-amino-3-penten-2-one (Fluoral-P) as a probe. Fluoral-P10] is a reagent with enaminone structure which can selectively react with formaldehyde to form cyclic compound 3,5-diacetyl-1,4-dihydrolutidine (DDL). Since the absorption band of Fluoral-P is far apart from the absorption band of DDL, and a fluorescence peak with large Stokes shift can be produced after combined with formaldehyde, it is widely applied for the detection of formaldehyde. However, Fluoral-P is extremely unstable and easy to hydrolyze to form acetylacetone and ammonia under the presence of water, which severely limits its application in formaldehyde detection10].In this work, we have studied the optical and chemical properties of the interaction between 4-amino-1,1,1-trifluorobut-3-en-2-one(3F-FP), a derivative of Fluoral-P, and formaldehyde solution by UV-vis absorption steady state fluorescence spectroscopy and gas chromatography-mass spectrometry(GC-MS). We found that the hydrolysis rate of Fluoral-P is k＝1.555 9×10-5 L·mol-2·s-1, however, 3F-FP has very low hydrolysis rate(close to 0) and shows excellent stability in water environment. Meanwhile, 3F-FP can react with formaldehyde to form cyclic compound 6F-DDL, and a new absorption band appears at 430 nm and the fluorescence peak intensity at 489 nm also gets a significant enhancement and the enhancement factor is 12. The fluorescence growth rate is k＝7.881×103 h-1. In the following work, we will use porous glass as the carrier for 3F-FP11], by which the concentration of 3F-FP and contact surface area between the 3F-FP probe molecule and formaldehyde can be increased, leading to further increase of the fluorescence growth rate. In conclusion, 3F-FP has shown good application prospects in the field of gaseous formaldehyde detection.