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近年来,汞(Hg)作为最危险的有毒重金属之一,已引起了人们的广泛关注[1]。汞离子(Hg2+)具有生物聚集性,在自然界中,Hg2+能通过放大作用,在食物链之间不断传递,自下而上积累,营养级越高,Hg2+的浓度就越大。Hg2+还具有强毒性,进入人体以后,会破环肾脏,影响人体的呼吸系统和神经系统[2]。因此,急需开发一种有效的Hg2+选择性检测技术,并将其应用于生物科学和环境科学。
光学检测(通过荧光变化或比色变化)是最方便的测量技术。因此,近年来荧光探针因其操作简单、灵敏度高、对生物系统无损伤等特点而备受关注[3-4]。在过去的几十年里,大多数测定Hg2+的荧光探针都是基于螯合反应的荧光猝灭型探针,Hg2+充当荧光猝灭剂,然而它们往往会受到其他具有相似配位性能的金属离子的影响[5-6]。相比之下,基于Hg2+促进脱硫反应释放荧光团从而增强荧光强度的方法,就具有更好的专一性。目前,科研工作者开发了大量荧光增强型探针,并将它们用于Hg2+的选择性检测[7-12]。然而,它们有些激发/发射波长较短,有些则需要大量有机试剂作为助溶剂。因此,亟待发展发射波长长、水溶性好、灵敏度和选择性高的新型荧光增强型探针,并将其用于环境中Hg2+浓度的特异性检测。
半花菁席夫碱染料具有良好的光物理和光化学性质,如理想的激发/发射波长,大的摩尔吸收系数,其在水溶液中存在席夫碱(SB)和质子化席夫碱(PSB)两种形式,SB形式的吸收波长较短,没有荧光,而PSB形式的吸收波长较长,并且有荧光,SB形式转换为PSB形式之后,会造成体系荧光信号的增加,这非常有利于构建以半花菁席夫碱染料为荧光团的荧光探针[13-14]。基于此,本文报道了一种新型的以半花菁席夫碱染料为荧光团,与Hg2+有较高的亲和力的硫代碳酸酯基团为识别受体的荧光探针(MC-Hg)。由于硫代碳酸酯基团强的吸电子能力,探针MC-Hg的pKa值较低,在弱酸和中性条件下,主要以SB形式存在,没有荧光,当与Hg2+反应后,硫代碳酸酯离去,释放出半花菁荧光团MCF,pKa值升高,在弱酸和中性条件下,主要以PSB形式存在,有荧光,从而实现对Hg2+的选择性检测(机理示意图如图1所示)。
荧光恢复型半花菁荧光探针的构建及其在水样中汞离子检测中的应用
Construction of a merocyanine-based turn-on fluorescent probe and its application in the detection of mercury ion in water sample
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摘要: 汞离子(Hg2+)对人体有很大的危害,对Hg2+的检测具有重要意义。本文构建了一种荧光恢复型半花菁荧光探针MC-Hg,该探针以半花菁席夫碱类染料为荧光团,硫代碳酸酯为识别基团,可实现水溶液中的Hg2+的测定。含有硫代碳酸酯基团的MC-Hg具有较低的pKa值,在弱酸和中性条件下,主要以席夫碱(SB)形式存在,没有荧光。然而,当与Hg2+反应后,硫代碳酸酯离去后,释放出半花菁荧光团,pKa值升高,在弱酸和中性条件下,主要以质子化席夫碱(PSB)形式存在,荧光增强,从而实现对Hg2+的检测。实验研究了探针对Hg2+的响应性能,考察了pH和干扰离子对探针MC-Hg与Hg2+响应性能的影响。结果表明,探针MC-Hg具有良好的稳定性和水溶性,对Hg2+的检测具有响应速度快、选择性高的特点。在pH值为6.4时,荧光探针MC-Hg对Hg2+的响应效果最佳。随着Hg2+的加入,检测体系在645 nm处的荧光强度逐渐增强,与Hg2+浓度呈良好的线性关系,线性范围为0.0—7.0×10−6 mol·L−1,且检测体系在612 nm处形成新的吸收峰,并逐渐增强。此外,探针MC-Hg具有潜在的应用价值,已成功应用于实际水样中Hg2+的测定。Abstract: Mercury ion (Hg2+) is very harmful to human health, so it is of great significance to detect Hg2+. In this paper, a new merocyanine-based fluorescent turn-on probe MC-Hg was developed, which used merocyanine Schiff base dye as fluorophore and thiocarbonate as recognition group for the determination of Hg2+ in aqueous solution. MC-Hg with thiocarbonate has a low pKa value, and it mainly exists in the form of Schiff base (SB) without fluorescence under weak acid and neutral conditions. After reacting with Hg2+, its thiocarbonate group was removed to afford a merocyanine dye as the final product, whose pKa value increased, and was present mainly as the fluorescent protonated Schiff base (PSB) form under weak acid and neutral conditions, which can be utilized for the detection of Hg2+. The response of the probe to Hg2+ was studied, and the effects of pH and interference ions on the response of the probe MC-Hg to mercury ions were investigated. The results showed that the probe MC-Hg had good stability and water solubility, and show fast response and high selectivity toward Hg2+. Furthermore, the fluorescence probe MC-Hg showed the best response to mercury ions at pH 6.4. With the addition of Hg2+, the fluorescence intensity of the detection system at 645 nm gradually increased linearly with Hg2+ concentration in the range of 0.0—7.0× 10−6 mol·L−1, and the UV absorption value formed a new peak at 612 nm, and also gradually increased. In addition, the probe MC-Hg has potential application and has been successfully applied to the determination of Hg2+ in real water samples.
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Key words:
- mercury ion /
- fluorescent probe /
- merocyanine /
- high selectivity /
- water samples
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图 5 加入Hg2+前后的MC-Hg溶液荧光强度的差值随pH值的变化图(a);探针MC-Hg和加入Hg2+的MC-Hg溶液的荧光强度随时间的变化图(b);
Figure 5. (a) Fluorescence intensity of MC-Hg solution added with Hg2+ varied with pH value where F0 and F are the fluorescence intensity of the probe before and after adding Hg2+; (b) Time-coursed fluorescence responses of probe MC-Hg to Hg2+;
表 1 实际水样中Hg2+浓度的检测
Table 1. Analysis of Hg2+ concentrations in real water samples
水样
Water samples加入Hg2+(×10−6)/(mol·L−1)
Hg2+ spikeda回收Hg2+(×10−6)/(mol·L−1)
Hg2+ recovered回收率/%
Recovery汉江水
Hanjiang River0.0 未检出 1.0 1.02 102 2.0 1.96 98.0 4.0 3.93 98.3 自来水
Tap water0.0 未检出 1.0 0.96 96.0 2.0 2.01 101 4.0 3.97 99.3 a3次测量结果的平均值. aMean of three determinations. 表 2 检测Hg2+的荧光分析方法对比
Table 2. A comparison of fluorescent methods for detection of Hg2+
材料
Materials线性范围/
(μmol·L−1)
Linear range检出限/
(nmol·L−1)
Detection limit响应时间/
min
Response time激发/发射
波长/nm
λex/λem溶剂
Solvent文献
References基于花菁染料的荧光探针 1.5—7.5 7.3 5.0 600/790 乙醇/水
(5/95,V/V)[25] 基于半花菁染料的荧光探针 2.0—10.0 320 5.0 630/710 乙腈/水
(1/99,V/V)[26] 基于半花菁染料的荧光探针 3.0—5.5 180 5.0 587/708 二甲基亚砜/水(2/8,V/V) [27] 基于罗丹明B染料的荧光探针 1.0—20.0 330 15.0 530/583 乙醇/水
(2/8,V/V)[28] 基于苯并噻唑染料的荧光探针 5.0—100.0 310 30.0 405/525 乙腈/水
(1/1,V/V)[29] 基于半花菁染料的荧光探针 0.0—7.0 270 3 580/645 丙酮/水
(1/99,V/V)本工作 -
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