微生物学报  2021, Vol. 61 Issue (3): 740-749   DOI: 10.13343/j.cnki.wsxb.20200475.
http://dx.doi.org/10.13343/j.cnki.wsxb.20200475
中国科学院微生物研究所,中国微生物学会,中国菌物学会
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文章信息

田野, 娄虎, 姬彦飞, 董欣欣, 赵熙明, 张杰. 2021
Ye Tian, Hu Lou, Yanfei Ji, Xinxin Dong, Ximing Zhao, Jie Zhang. 2021
荧光银纳米团簇的生物合成及其在痕量六价铬检测中的应用
Synthesis of fluorescent silver nanoclusters for trace Cr (Ⅵ) detection
微生物学报, 61(3): 740-749
Acta Microbiologica Sinica, 61(3): 740-749

文章历史

收稿日期:2020-07-21
修回日期:2020-11-12
网络出版日期:2021-01-28
荧光银纳米团簇的生物合成及其在痕量六价铬检测中的应用
田野1 , 娄虎2 , 姬彦飞1 , 董欣欣1 , 赵熙明1 , 张杰1     
1. 东北林业大学生命科学学院, 东北盐碱植被恢复与重建教育部重点实验室, 黑龙江 哈尔滨 150040;
2. 东北林业大学林学院, 黑龙江 哈尔滨 150040
摘要[目的] 利用季也蒙毕赤酵母ZJC-1合成银纳米团簇并用于痕量Cr(Ⅵ)的检测。[方法] 使用经耐银驯化的季也蒙毕赤酵母ZJC-1生物合成荧光银纳米团簇,并对其结构和荧光性能进行了表征,探究Cr(Ⅵ)对银纳米团簇荧光的选择性猝灭作用,建立了银纳米团簇荧光强度与Cr(Ⅵ)浓度的线性关系。同时还考察了体系pH和其他金属离子对Cr(Ⅵ)检测的影响。[结果] Cr(Ⅵ)浓度在一定的范围内(1-80 μmol/L)与银纳米团簇荧光强度(F0-F)/F0有着良好的线性关系(R2=0.9821),线性方程为(F0-F)/F0=0.0054×Ccr(Ⅵ)+0.1876,检测限为184 nmol/L(信噪比为3)。利用该方法检测实际水样(松花江、马家沟河)中的Cr(Ⅵ),回收率介于97.73%-102.88%之间。[结论] 以季也蒙毕赤酵母ZJC-1为还原剂和稳定剂,制备了具有较好荧光性能的水溶性银纳米团簇,基于Cr(Ⅵ)对银纳米团簇荧光的选择性猝灭作用,建立了一种快速且灵敏检测痕量Cr(Ⅵ)的新方法,并成功地应用于松花江、马家沟河水样中Cr(Ⅵ)的测定,在分析检测领域中具有良好的应用前景。
关键词银纳米团簇    生物合成    荧光猝灭    Cr (Ⅵ)    
Synthesis of fluorescent silver nanoclusters for trace Cr (Ⅵ) detection
Ye Tian1 , Hu Lou2 , Yanfei Ji1 , Xinxin Dong1 , Ximing Zhao1 , Jie Zhang1     
1. Key Laboratory of Saline-alkali Vegetation Ecology Restoration, Ministry of Education, College of Life Sciences, Northeast Forestry University, Harbin 150040, Heilongjiang Province, China;
2. School of Forestry, Northeast Forestry University, Harbin 150040, Heilongjiang Province, China
Abstract: [Objective] Silver nanoclusters were prepared using Pichia guilliermondii ZJC-1 for the detection of trace Cr(Ⅵ). [Methods] Fluorescent silver nanoclusters were synthesized using Pichia guilliermondii ZJC-1 that was acclimated to silver. The structures and fluorescence properties of silver nanoclusters were characterized. Then we explored the selective quenching effect of Cr(Ⅵ) on the silver nanoclusters fluorescence. We also established a linear relationship between silver nanoclusters fluorescence intensity and the concentration of Cr(Ⅵ). The effect of pH and other metal ions on the detection of Cr(Ⅵ) was also examined. [Results] There was a good linear relationship between Cr(Ⅵ) and the fluorescence intensity of silver nanoclusters (R2=0.9821). The detection limit was 184 μmol/L and the signal to noise ratio (SNR) was 3. Using this method to detect Cr(Ⅵ) in actual water samples (Songhua River, Majiagou River) the recovery rate was between 97.73% and 102.88%. [Conclusion] Silver nanoclusters with good fluorescence properties can detect trace concentrations of Cr(Ⅵ) simply and rapidly.
Keywords: silver nanoclusters    biosynthesis    fluorescence quenching    Cr(Ⅵ)    

铬(chromium)是自然界中常见的元素,元素符号Cr,常见的离子价态有0、+2、+3、+6。Cr(Ⅵ)是一种毒性很强的重金属,在工业生产制造过程中特别是工业废渣、废水中都可产生[1]。Cr(Ⅵ)的排放会对生态环境造成严重的污染危害,Cr(Ⅵ)不但会污染土壤、水源[2],而且具有生理毒性和免疫毒性[3],对人类健康造成威胁,国际癌症研究机构(IARC)把它列为一级致癌物[4]。因此,Cr(Ⅵ)的快速检测技术是环境监测、食品、烟草和医药检测等相关领域的重要研究方面,同时对于污染环境的场地检测、控制工业污染源以及保护人类健康具有实际的意义。

检测Cr(Ⅵ)的方法主要有原子吸收光谱法、二苯碳酰二肼分光光度法[5]、离子色谱与电感耦合等离子体质谱联用法、高效液相色谱与电感耦合等离子体联用法[6]等。然而,这几种方法由于分析时间长、分析步骤复杂不易操作、灵敏度低、仪器昂贵等问题导致技术难以得到普遍应用。荧光探针检测技术具有极好的应用前景,银纳米团簇(silver nanoclusters,AgNCs)因其优异的性能已成为材料科学和生命科学等领域的研究和应用热点。AgNCs是由几个至几十个银原子组成的相对稳定的分子级聚集体,其尺寸接近电子的费米波长,它弥补了银原子和纳米银颗粒之间的间隙,表现出类分子的化学和光学性质[7]。荧光AgNCs不仅具有强荧光效率[8]、优异的光稳定性[9],而且具有小的物理尺寸和大的stokes位移[10-11],可以作为高灵敏荧光探针应用在生物传感方面,如对金属离子[12]、生物小分子[13]、蛋白质[14]等物质的检测。因此,制备具有较好荧光性能的AgNCs,并建立灵敏检测Cr(Ⅵ)的方法具有重要意义。

采用物理法和化学法制备荧光AgNCs的反应过程繁杂,且依赖于化学试剂[15],易对环境造成污染,因而绿色环保的生物法受到越来越多研究者的青睐[16]。Sintubin等[17]成功利用乳酸菌合成了银纳米粒子;Ahmad等[18]对成熟菌体进行特殊处理,迫使其释放出大量的还原性物质,并将Ag(Ⅰ)还原为银单质。Yin等[19]利用尖孢镰刀菌胞外超氧化合物的酶促作用在胞外将Ag(Ⅰ)还原为银纳米粒子,并首次发现超氧阴离子与NADH会影响银纳米粒子的合成。Kalimuthu等[20]使用地衣芽孢杆菌成功实现了Ag(Ⅰ)的还原,并提出该反应是经由菌体细胞膜上存在的硝酸盐还原酶通过NADH电子传递系统实现的。根据以上研究可知,生物体产生的还原型物质可作为电子供体,通过NADH电子传递系统将电子传递给Ag(Ⅰ),并在分泌的酶催化下将Ag(Ⅰ)还原成银单质。

季也蒙毕赤酵母ZJC-1[21]分离筛选自长期喂食聚乙烯塑料的印度谷螟[Plodia interpunctella (Hübener)]幼虫的肠道液中,ZJC-1作为异养的真核微生物,不仅具有微生物的一系列优点,更具有较为复杂的胞内和胞外酶系统[22]。本文建立了一种利用季也蒙毕赤酵母ZJC-1制备荧光AgNCs的新方法,制备过程不添加化学还原剂和稳定剂,具有成本低、环境友好、操作简便等优点。基于Cr(Ⅵ)对AgNCs荧光的选择性猝灭作用,建立了一种快速且灵敏检测痕量Cr(Ⅵ)的新方法,并成功地应用于松花江、马家沟河水样中Cr(Ⅵ)的测定,具有极好的应用前景。

1 仪器和试剂 1.1 实验仪器

本实验所用仪器设备见表 1

表 1. 主要仪器设备 Table 1. Major instruments and equipment
Sequence number Instrument Model Manufacturer
1 Constant temperature shock incubator HZQ-F160A Shanghai Yiheng Technology Instrument Co., LTD
2 High speed bench centrifuge TG16-WS Hunan Xiangxin Instrument and Meter Co. LTD
3 Transmission electron microscopy JEM-2100 Japan Electronic Company
4 Vacuum drying oven DZF-6050 Shanghai Boxun Medical Bio-instrument Co., LTD
5 Super-clean worktable SW-CJ Suzhou Antai Air Technology Co. LTD
6 Electronic balance CPJ1003 Auhaus Instruments Co., LTD
7 Fluorescence spectrometer 970CRT Shanghai Jingke Instrument Co., LTD
8 Uv-vis spectrophotometer uv-vis8453 Agilent Corporation
9 High pressure steam sterilizer MLS-3781L-PC Matsushita Health Medical Equipment Co. LTD

1.2 实验试剂

硝酸银、硝酸铬、硝酸钠、硝酸镁、硝酸钙、硝酸镉、硝酸铜、硝酸钾、硝酸铁、硝酸汞、硝酸铅、重铬酸钾、盐酸、氢氧化钠,以上试剂均为分析纯,购于天津市科密欧化学试剂有限公司;葡萄糖、酵母提取物、胰蛋白胨、琼脂粉均购于北京奥博星生物技术有限公司;实验用水均为超纯水。

1.3 溶液的配制

YPD液体培养基(100 mL):称量2 g葡萄糖、1 g酵母提取物、2 g胰蛋白胨,用蒸馏水定容至100 mL,搅拌均匀,经高压蒸汽灭菌器115 ℃灭菌20 min后使用。

YPD固体培养基(100 mL):称量2 g葡萄糖、1 g酵母提取物、2 g胰蛋白胨、2 g琼脂粉,用蒸馏水定容至100 mL,加热溶解,经高压蒸汽灭菌器115 ℃灭菌20 min后使用。

1.4 菌株ZJC-1的去银纯化筛选

刮取保存在4 ℃ YPD斜面培养基上的季也蒙毕赤酵母ZJC-1,接种到含有0.2 mmol/L硝酸银的YPD液体培养基中,于140 r/min、28 ℃下培养24 h。然后取2 mL菌液接种到硝酸银浓度为0.4 mmol/L的YPD液体培养基中,相同条件下培养24 h,依次提高硝酸银的浓度至1.0 mmol/L。最终得到耐银的ZJC-1活化菌株。

将菌株ZJC-1接种到无银离子的YPD固体斜面培养基,脱银纯化3次后,可排除筛选菌株过程中银的影响。

1.5 AgNCs的合成与表征

向300 mL YPD液体培养基中加入硝酸银,使其终浓度为1.0 mmol/L,接种5 mL活化的菌株ZJC-1,体系于28 ℃、140 r/min恒温振荡培养48 h。将培养液5000 r/min离心5 min,上清液经0.22 μm滤膜过滤,滤液置于70 ℃真空干燥箱中烘干。制备的AgNCs经由透射电子显微镜(TEM)、紫外可见吸收光谱、荧光光谱进行表征。所制备的AgNCs可长期放置在4 ℃冰箱中储存待用。

1.6 Cr(Ⅵ) 的检测

AgNCs粉末用蒸馏水配制成0.2 mg/mL的溶液,放入石英四通光比色皿中。使用电压700 V氙灯为光源,激发狭缝宽度为10 nm,发射狭缝宽度为10 nm,扫描间隔为1 nm,扫描速度为500 nm/min。扫描范围为200–800 nm,确定AgNCs激发波长。

取4.5 mL上述AgNCs样品,分别向其中加入500 μL不同的金属离子[Cr(Ⅵ)、Fe(Ⅲ)、Hg(Ⅱ)、Pb(Ⅱ)、Mg(Ⅱ)、Cu(Ⅱ)、Cd(Ⅱ)、Ca(Ⅱ)、Na(Ⅰ)、K(Ⅰ)、Cr(Ⅲ)],金属离子终浓度为500 μmol/L,在最大激发波长下得到体系的荧光发射光谱。AgNCs溶液对Cr(Ⅵ)的选择性采用Stern-Volmer方程进行分析[23],即F0/F=1+Ksv[Q]。F0F分别为不加金属离子和加入金属离子时AgNCs的荧光强度。Ksv为Stern-Volmer常数,[Q]为金属离子浓度。

为了评价AgNCs对Cr(Ⅵ)的检测范围,向4.5 mL AgNCs溶液中加入500 μL不同浓度的Cr(Ⅵ)储备液,浓度范围为0–500 μmol/L,混合均匀后,所有样品在最大激发波长处测荧光光谱,重复3次。

1.7 AgNCs在实际水样中的应用

为了评价AgNCs在实际水样中对Cr(Ⅵ)的检测性能,以黑龙江省哈尔滨市松花江江水样品和黑龙江省哈尔滨市马家沟河河水样品为研究对象,对该传感器的性能进行了测试[24]。实际水样经过12000 r/min离心15 min,收集上清液用0.22 μm的超滤膜进行过滤。取加入不同浓度Cr(Ⅵ)的水样500 μL,加入1.5 mL AgNCs溶液中,测定其最大激发波长下的荧光强度。分别测定3次并取其平均值。

2 结果和讨论 2.1 AgNCs的表征

图 1-A为AgNCs的TEM图像,内嵌图表明AgNCs颗粒分布均匀,大小均一,形状近似球形;图 1-B为AgNCs的粒径大小分布图,使用Image J软件计算出AgNCs的平均粒径为2.48 nm[25]

图 1 AgNCs的透射电子显微镜图像(A)与粒径分布(B) Figure 1 TEM image (A) and the particle size distribution of AgNCs (B). Inset figure shows AgNCs distribution at 5 nm.

AgNCs的紫外可见吸收光谱和荧光光谱如图 2所示。曲线a为AgNCs的紫外可见吸收光谱,银纳米颗粒的大小决定了吸收峰的位置,尺寸越小,吸收峰越向紫外区移动。谱线在400–500 nm处没有特征的表面等离子体共振峰,说明合成的是纳米团簇[26];曲线b为AgNCs的荧光光谱,在激发波长为372 nm条件下,AgNCs溶液在474 nm处有明显的荧光发射峰。此外,图 2的内嵌图显示,AgNCs溶液在日光下呈黄色(图左),在紫外灯照射下呈现出蓝色(图右)。

图 2 AgNCs的紫外可见-荧光光谱图 Figure 2 UV-vis and fluorescence spectra of AgNCs. a: UV-visible absorption spectrogram of AgNCs; b: Fluorescence spectrum of AgNCs at excitation wavelength of 372 nm. Inset figure shows AgNCs in daylight (left) and uv light (right).

2.2 AgNCs对Cr(Ⅵ) 的特异性检测

分析了环境水样中可能存在的金属离子对AgNCs荧光强度的影响,如图 3所示,只有当体系中加入Cr(Ⅵ)时会引起AgNCs的荧光猝灭,而其他金属离子的加入对AgNCs荧光强度影响不大,表明AgNCs对Cr(Ⅵ)具有特异选择性。基于此可建立灵敏快速测定Cr(Ⅵ)的分析方法。

图 3 加入不同金属离子的AgNCs体系的荧光光谱图 Figure 3 Fluorescence spectra of AgNCs system with different metal ions added.

2.3 Cr(Ⅵ) 检测的线性范围

基于AgNCs对Cr(Ⅵ)的特异性荧光猝灭,本实验进一步探讨AgNCs对Cr(Ⅵ)的线性检测范围。如图 4所示,当Cr(Ⅵ)的浓度在0–100 μmol/L时,AgNCs的荧光强度随Cr(Ⅵ)浓度的增加而减弱,当Cr(Ⅵ)浓度达到100 μmol/L时,AgNCs溶液的荧光猝灭程度达到99.8%。

图 4 加入Cr(Ⅵ)的AgNCs体系的荧光光谱图,Cr(Ⅵ)浓度范围为0– 100 μ mol/L Figure 4 The fluorescence spectra of AgNCs with Cr(Ⅵ) were measured in the concentration range of 0–100 μmol/L.

图 4波长为474 nm (峰值)处的荧光强度值,利用Stern-Volmer方程[23]得到(F0–F)/F0值,线性拟合结果如图 5所示,在AgNCs溶液加入不同浓度的Cr(Ⅵ)后,体系的荧光猝灭程度(F0–F)/F0与Cr(Ⅵ)浓度(1–80 μmol/L)呈良好的线性关系(R2=0.9821)。线性方程为(F0–F)/F0=0.0054×Ccr(Ⅵ)+0.1876,其中Cr(Ⅵ)的单位为μmol/L,检测限为184 nmol/L (信噪比为3)。

图 5 AgNCs体系的荧光(F0F)/F0值与Cr(Ⅵ)浓度的线性关系图 Figure 5 The linear relationship between concentration of Cr(Ⅵ) and (F0–F)/F0.

2.4 金属离子的干扰试验

为了考察其他金属离子对AgNCs检测Cr(Ⅵ)的干扰,固定Cr(Ⅵ)浓度为100 μmol/L,分别在检测体系中加入1 mmol/L的干扰金属离子。如图 6所示,黑色柱形为只加干扰离子时,AgNCs体系在474 nm (峰值)的荧光强度值,红色柱形为同时加入Cr(Ⅵ)和干扰离子时,AgNCs体系在474 nm (峰值)的荧光强度值。结果表明,其他金属离子与Cr(Ⅵ)共存时,不影响AgNCs的荧光响应,可忽略它们的潜在性干扰,说明了基于AgNCs构建的荧光探针具有较高的选择性。

图 6 干扰离子对AgNCs检测Cr(Ⅵ)的影响 Figure 6 The effect of other metal ions on the system to check the Cr(Ⅵ).

2.5 pH对AgNCs检测Cr(Ⅵ) 的影响

为了考察pH值对AgNCs检测Cr(Ⅵ)的影响,固定AgNCs溶液的浓度为0.2 mg/mL,pH在5–11范围内,分别向体系中加入100 μmol/L Cr(Ⅵ)。结果如图 7所示,在372 nm激发波长下,pH值为5–11时,荧光强度F/F0差别不大,表明pH值变化对AgNCs检测Cr(Ⅵ)的结果影响不大。

图 7 pH对AgNCs检测Cr(Ⅵ)的影响 Figure 7 The effect of pH on the system to check the Cr(Ⅵ).

2.6 实际水样中Cr(Ⅵ) 的检测

评估了AgNCs作为Cr(Ⅵ)检测传感器的可行性。测试结果如表 2所示,实验采用多组平行测定了松花江、马家沟河中不同浓度的Cr(Ⅵ)的回收率,发现其回收率为97.73%–102.88%,说明实际水样中的有机物、矿物质等杂质对Cr(Ⅵ) 测定结果影响不大,故该探针能够应用于实际水样中Cr(Ⅵ)的检测。

表 2. 检测实际水样中Cr (Ⅵ)回收率 Table 2. Detection of Cr(Ⅵ) in actual water samples
Sample Added of Cr(Ⅵ)/(μmol/L) Detection of Cr(Ⅵ)/(μmol/L) Recovery rate/% RSD/%
Songhua River 20 19.67 98.35 2.15
Songhua River 40 39.66 99.14 2.60
Songhua River 80 79.10 98.88 3.13
Majiagou river 20 20.58 102.88 3.52
Majiagou river 40 39.78 99.45 1.94
Majiagou river 80 78.19 97.73 2.90

3 总结

荧光AgNCs常见的制备方法有化学还原法[27]、光还原法[28]、化学刻蚀法[29]、微波辅助合成法[30]、超声法[31]和模板法[32-33]等。但是这些方法通常具有反应条件苛刻、费时费力、产率低、耗费高等缺点,不适合广泛的应用。常见的AgNCs生物合成方法需要添加DNA或蛋白质作为稳定剂和保护剂[34],且合成的过程中Ag(Ⅰ)的还原仍依赖于化学还原剂如NaBH4。目前,大部分微生物被证实具有合成银纳米粒子的能力[17-20],但能合成粒径更小的AgNCs的微生物罕见报道。本研究利用季也蒙毕赤酵母ZJC-1与硝酸银共培养,反应条件为28 ℃、140 r/min恒温振荡培养48 h,将培养液离心、过滤、烘干实现了AgNCs的绿色合成。所得AgNCs平均粒径为2.48 nm,其形貌特征和荧光性能与其他报道一致[26-33]

基于Cr(Ⅵ)对该荧光AgNCs具有特异性猝灭作用建立了检测痕量Cr(Ⅵ)新方法。体系的荧光猝灭程度(F0-F)/F0与Cr(Ⅵ)浓度(1–80 μmol/L)呈良好的线性关系(R2=0.9821),线性方程为(F0F)/F0=0.0054×CCr(Ⅵ)+0.1876,其中Cr(Ⅵ)的单位为μmol/L,检测限为184 nmol/L (信噪比为3)。利用该方法检测松花江、马家沟河中的Cr(Ⅵ),回收率介于97.73%–102.88%之间。通常Cr(Ⅵ)的检测方法分为电化学分析法和光谱分析法两大类,其中分光光度法是国际上标准的Cr(Ⅵ)检测方法[35]。本文建立的检测Cr(Ⅵ)新方法与先前报道[36-40]对比具有可行性,且本方法由于其绿色环保,快速检测、灵敏度高的优点,将在分析检测领域中具有良好的应用前景。但有关于ZJC-1合成AgNCs的具体机制还有待更加深入的研究。在实验室模拟条件和环境监测的实践中,研究Cr(Ⅵ)对AgNCs荧光的特异性猝灭机理仍具有挑战性。

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