-
此节利用第2节建立的红外量子点荧光探测系统对PbS胶质量子点薄膜的荧光回波进行远距离探测。为对比分析,定制两种尺寸相同(5 cm×5 cm),厚度分别为0.5 mm与1.1 mm、PbS量子点浓度分别为3 wt%与6 wt%的薄膜样品,并在后续分析中简称样品A与样品B。
为减少自然光干扰与环境变化扰动,实验选择在夜间空旷的户外环境中进行。实验中,将红外量子点薄膜待测样品置于较大尺寸的金属背板中心制成标靶,垂直放置于与激光器和探测系统基本等高的一定距离之外,并测试背景噪声。随后,再由可见的氦氖激光作为980 nm激光脉冲的导引光对样品进行瞄准激发。固定激光器的出射功率,改变激光器/探测器与样品之间的距离
$ L $ ,从而调节样品表面的激发光功率密度$ {I}_{exc} $ 在0~16.5 mW/cm2之间变化,并将探测系统光学接收单元的性能调整到最优状态,分别记录荧光信号经系统多级放大后的电压峰峰值$ {V}_{PP} $ 以及经相敏检波电路输出的直流电压值$ {V}_{DC} $ 。图7为系统分别对两种量子点薄膜样品A、B进行探测时,红外荧光经系统检波处理后的输出直流电压$ {V}_{DC} $ 随探测距离$ L $ 的变化曲线。图 7 量子点荧光检波输出直流电压变化图
Figure 7. Variation of output DC voltage of the detection system for quantum dot fluorescence
图7表明,当红外量子点样品A与样品B受到激发产生荧光回波时,探测系统输出的直流电压随探测距离的增大(
$ {I}_{exc} $ 减小)而降低,并分别在56.2 m和65.2 m处达到极限,此时的直流电压值接近于量子点样品未激发时系统的输出直流电压${V}_{DC}^{0}\approx 130\;\rm{m}\rm{V}$ 。当探测距离再继续增大时,有、无激发光时的系统输出没有明显差别,量子点荧光无法探测。图8以样品B为例,给出了在较近和较远两处位置探测时系统输出的已调放大波形(图8(a)、图8(c))和解调后的直流波形(图8(b)、图8(d))。
图 8 样品B荧光检测信号波形(相敏检波前后)
Figure 8. Fluorescence detection signal waveforms of sample B (before and after phase sensitive detection)
从图8所示的荧光检测信号波形可以看到,在较近(32.7 m)和较远(65.2 m)两个距离处系统均能实现荧光回波的有效探测(
$ {V}_{DC} $ ),但探测距离的增大已经导致荧光检测信号放大后波形的明显劣化与失真。相敏检波电路在一定程度上弥补了这一失真,由噪声中提取出真正的荧光信号,有效地增加了系统对荧光回波的可探测距离。然而,随着探测距离的进一步增大,已调放大波形失真加剧,相敏检波电路的补偿作用达到极限。此时,系统对荧光回波的探测几乎失效,探测距离达到极大值${L}^{Max}$ ,相敏检波电路输出直流电压值${V}_{{DC}}\approx 140\;\rm{m}\rm{V}$ 。由于待测样品在较远距离发射荧光并传输,可近似为点光源发光。因此,根据照度定律,系统接收端光电探测器表面接收到的荧光功率密度
$ {I}_{R} $ 与探测距离$ L $ 以及激发光功率密度$ {I}_{exc} $ 和量子点材料的荧光转换效率$ \eta $ 之间存在如下关系:$$ {I}_{R}=\frac{{I}_{exc}\cdot \eta \cdot M}{{L}^{2}} $$ (1) 式中:
$ M $ 为等效的荧光传输透过率参数,包含系统光学接收孔径、环境与滤光片等造成的能量衰减,测试条件相同时,其值基本不变。改写公式(1),得到:$$ L={\left(\frac{M\eta }{{I}_{R}}\right)}^{\frac{1}{2}}\cdot {\left({I}_{exc}\right)}^{\frac{1}{2}} $$ (2) 这表明,系统对材料荧光的探测距离
$ L $ 随激发光强与材料荧光转换效率的增大而增大,且与探测器表面的荧光功率密度$ {I}_{R} $ 成反比。因此,当激发光强与待测材料不变时,探测系统对量子点材料的受激荧光存在最大可探测距离$ {L}^{Max} $ ,其值由光电探测器光强响应的最小阈值$ {I}_{R}^{th} $ 决定。$$ {L}^{Max}={\left(\frac{M\eta }{{I}_{R}^{th}}\right)}^{\frac{1}{2}}\cdot {\left({I}_{exc}\right)}^{\frac{1}{2}} $$ (3) 图9给出调节照射样品表面的激发光强度大小时,系统随着红外量子点材料样品A与样品B最大可探测距离的变化情况。图9(a)和图9(b)分别对应两种不同的光电探测器的响应阈值。
图 9 量子点样品荧光最大可探测距离随激发光功率密度的变化关系
Figure 9. The maximum detectable distance of fluorescence for quantum dot sample varies with the power density of excitation light
图中散点数据及其拟合曲线规律表明,被测PbS量子点薄膜样品的荧光最大可探测距离随其表面激发光功率密度的增大而呈抛物线型增长,在激发光功率密度为
$ 45 \;{\rm{mW/{cm}}}^{2} $ 时达百米量级;增大系统光电探测器孔径后,这一距离进一步增大到120 m (样品A)和160 m (样品B),若进一步优化实验条件,甚至可以达到134 m (样品A)和210 m (样品B)。并且,数据变化趋势显示被测红外量子点材料的荧光发光能力与远距离传输能力尚未饱和,若样品表面的激发光强度继续增加,荧光回波脉冲的可探测距离也将继续按曲线规律进一步增大。这意味着前述荧光探测系统能够在百米甚至两百米之外成功检测到红外量子点样品的受激荧光,进而可以通过样品的有无判断如何实现红外量子点材料的远距离识别。当激发光功率密度较低时(
$ <2\;{\rm{mW/{cm}}}^{2} $ ),图中荧光最大可探测距离的实测值明显小于曲线拟合值。这说明当激发光较弱时,其照射量子点薄膜样品产生荧光的功率转换效率达不到拟合曲线系数所等效的荧光效率值,即样品中的量子点可能尚未充分激发。只有当激发光功率密度增大到一定程度时,PbS量子点薄膜样品的荧光激发效率才能达到稳定。这在一定程度上说明,红外量子点薄膜样品受激辐射远距离传输荧光的过程存在阈值性。此外,由于每幅图中两组数据的测试系统参数与环境参数均相同,其拟合系数
$ q $ 之比与样品荧光效率之比存在如下关系:$$ \frac{{\eta }_{A}}{{\eta }_{B}}={\left(\frac{{q}_{A}}{{q}_{B}}\right)}^{2} $$ (4) 将曲线拟合系数
$ {q}_{A} $ 、$ {q}_{B} $ 的值代入公式(4),可以得到两种样品的荧光功率效率之比为:$$ \frac{{\eta }_{A}}{{\eta }_{B}}\approx \frac{1}{1.8} $$ (5) 即激发光功率密度相同时,样品B受激辐射的荧光强度是样品A的1.8倍,这也是图中样品B比样品A能够达到更大的探测距离极限的原因,产生这一差异主要是由于两种量子点薄膜样品的厚度和量子点分散浓度都不相同。显然,量子点浓度越高、薄膜厚度越大,单位激光功率激发时产生的有效荧光越强。后续结合材料样品的具体制备过程,可以进一步定量分析量子点浓度、薄膜厚度等参数对荧光效率的影响。同时,若能够定量测算环境及系统的光学衰减,上述过程还可用于估算和对比不同形态红外量子点材料的荧光功率效率,并由此指导防伪与识别应用中红外量子点样品的制备工艺。
Long-distance recognition of infrared quantum dot materials
-
摘要: 量子点分立的能级结构使其具有独特的光电性质,因而在激光能源、光电检测等领域应用广泛。其尺寸调谐的受激辐射特性与灵活多变的应用形态也使其成为一种理想的荧光标记材料,在生物医学、微观物质检测以及防伪与目标识别等领域备受关注。对于应用场景多为宏观自然环境的防伪与目标识别领域,不可避免地需要对红外波段的量子点荧光进行较远距离的检测与分析。因此,文中基于微弱信号检测技术设计构建了一套红外量子点荧光的远距离探测系统,并用其对PbS胶质量子点薄膜荧光进行了检测实验。实验结果及分析表明,波长~1300 nm的红外量子点荧光辐射可以在100~200 m距离之外被系统有效提取,从而实现红外量子点材料的远距离识别。系统对荧光特性的检测结果用于分析和指导不同红外量子点材料的制备过程,也将推动其远距离识别应用的多样性发展。Abstract: Quantum dots are widely used in laser energy, photoelectric detection and other fields due to its unique photoelectric properties. Its size-dependent stimulated emission and flexible application form also make it an ideal fluorescent labeling material, which has attracted much attention in the fields of biomedicine, micromaterial detection, anti-counterfeiting and target recognition. In the field of anti-counterfeiting and target recognition where the application scenes are mostly macro natural environments, it is inevitable to detect and analyze the infrared fluorescence of quantum dots at a relatively long distance. Therefore, a long-distance detection system of infrared fluorescence for quantum dot was established based on weak signal detection technology and used to detect the fluorescence of PbS colloidal quantum dot films. The effective detection range of the fluorescence at 1300 nm for the samples was over 100-200 meters and may increase further. This meant that long-distance recognition of infrared quantum dot materials was realized. The detection results can be used to analyze and guide the preparation process of different infrared quantum dot materials, which will also promote the diversified development of their remote recognition applications.
-
Key words:
- quantum dot /
- infrared /
- recognition /
- fluorescence detection
-
-
[1] Cheng Cheng, Jiang Huilv. Research progress of CdSe/ZnS and PbSe-quantum-dot fibers and fiber amplifiers [J]. Infrared and Laser Engineering, 2011, 40(10): 1873-1880. (in Chinese) [2] Wang Zihao, Fanto Michael L, Steidle Jeffrey A, et al. Passively mode-locked InAs quantum dot lasers on a silicon substrate by Pd-GaAs wafer bonding [J]. Applied Physics Letters, 2017, 110(14): 141110. [3] Tang Jing, Sargent Edward H. Infrared colloidal quantum dots for photovoltaics: Fundamentals and recent progress [J]. Advanced Materials, 2011, 23(1): 12-29. doi: 10.1002/adma.201001491 [4] Chen Qian, Gao Fangfang, Wang Huan, et al. Synthesis and characterization of PbS quantum dots sensitized sensitized titanium dioxide nanotubes solar cells [J]. Journal of the Chinese Ceramic Society, 2018, 46(8): 1169-1172. [5] Song Xiaoxian, Zhang Yating, Zhang Haiting, et al. Graphene and PbS quantum dot hybrid vertical phototransistor [J]. Nanotechnology, 2017, 28(14): 145201. doi: 10.1088/1361-6528/aa5faf [6] Yang Qi, Shen Jun, Wei Xingzhan, et al. Recent progress on the mechanism and device structure of graphene-based infrared detectors [J]. Infrared and Laser Engineering, 2020, 49(1): 0103003. (in Chinese) doi: 0103003 [7] Zhao Shuangyi, Wang Yue, Huang Wen, et al. Developing near-infrared quantum-dot light-emitting diodes to mimic synaptic plasticity [J]. Science China Materials, 2019, 62(10): 1470-1478. [8] Wijaya Hadhi, Darwan Daryl, Zhao Xiaofei, et al. Efficient near-infrared light-emitting diodes based on ln(Zn)As-ln(Zn)P-CaP-ZnS quantum dots [J]. Advanced Functional Materials, 2020, 30(4): 1906483. [9] Medintz Igorl, Uyeda H Tetsuo, Goldman Ellen R. Quantum dot bioconjugates for imaging, labelling and sensing [J]. Nature Materials, 2005, 4: 435-446. [10] Chen Yongfen, Rosenzweig Zeev. Luminescent CdS quantum dots as selective ion probes [J]. Analytical Chemistry, 2002, 74(19): 5132-5138. doi: 10.1021/ac0258251 [11] You J Q, Yan D, He Y, et al. Polyethyleneimine-protected Ag2S quantum dots for near-infrared fluorescence-enhanced detection of trace-level Hg2+ in water [J]. Journal of Water Chemistry and Technology, 2020, 42(1): 36-44. doi: 10.3103/S1063455X20010105 [12] Xing Xiaoxue,Wang Xianwei, Qin Hongwu, et al. CH4 detection based on near-infrared luminescence of PbSe quantum dots [J]. Chinese Optics, 2018, 11(4): 662-668. (in Chinese) [13] Yu Zhuangzhuang, Kang Tianfang, Lu Liping. An electro-chemical molecularly imprinted sensor for tetracycline based on gold nanoparticles and graphene quantum dots [J]. Journal of Instrumental Analysis, 2020, 39(2): 182-189. (in Chinese) [14] Zeng Yunlong, Zhao Min, Zhang Min, et al. A novel near-infrared fluorescence aptasensor assay for ochratoxin A in traditional chinese medicine [J]. Chinese Journal of Luminescence, 2019, 40(1): 115-121. (in Chinese) [15] Rahul S Tade, Pravin O Patil. Green synthesis of fluorescent graphene quantum dots and its application in selective curcumin detection [J]. Current Applied Physics, 2020, 20(11): 1226-1236. doi: 10.1016/j.cap.2020.08.006 [16] Li Wenshuai, Huang Saipeng, Wen Huiyun et al. Fluorescent recognition and selective detection of nitrite ions with carbon quantum dots [J]. Analytical and Bioanalytical Chemistry, 2020, 412(4): 993-1002. doi: 10.1007/s00216-019-02325-9 [17] Zhang Dan, Yu Jinhai, Li Dongze, et al. Preparation of high quality Ag2S quantum dots with near-infrared emission and their applications in bioimaging [J]. Chemical Journal of Chinese Universities, 2018, 39(4): 623-628. (in Chinese) [18] Zhang Yan, Wei Yong, Dai Yiwen, et al. Targeted labeling and biological toxicity of Zn3In2S6-CEA quantum dot fluorescent probe to colon cancer cell line SW480 [J]. Chinese Journal of Cancer Prevention and Treatment, 2018, 25(9): 615-621. (in Chinese) [19] Wang Juncheng, Yang Feifei, Gao Guanbin, et al. Ag doped HgS quantum dots: a pH-tunable near-infrared-II fluorescent nanoprobe [J]. Journal of Inorganic Materials, 2019, 34(11): 1156-1160. (in Chinese) [20] Kalkal Ashish, Pradhan Rangadhar, Kadian Sachin, et al. Biofunctionalized graphene quantum dots based fluorescent biosensor towards efficient detection of small cell lung cancer [J]. ACS Applied Bio Materials, 2020, 3(8): 4922-4932. doi: 10.1021/acsabm.0c00427 [21] Sarkar Suresh, Le Phuong, Geng Junlong, et al. Short-wave infrared quantum dots with compact sizes as molecular probes for fluorescence microscopy [J]. Journal of the American Chemical Society, 2020, 142(7): 3449-3462. doi: 10.1021/jacs.9b11567 [22] Morgan Nicole Y, English Sean, Chen Wei, et al. Real time in vivo non-invasive optical imaging using near-infrared fluorescent quantum dots [J]. Academic Radiology, 2005, 12(3): 313-323. doi: 10.1016/j.acra.2004.04.023 [23] Michalet X, Pinaud F F, Bentolila L A, et al. Quantum dots for live cells, in vivo imaging, and diagnostics [J]. Science, 2005, 307(5709): 538-544. doi: 10.1126/science.1104274 [24] Yao Jun, Li Pingfan, Li Lin, et al. Biochemistry and biomedicine of quantum dots: from biodetection to bioimaging, drug discovery, diagnostics, and therapy [J]. Acta Biomaterialia, 2018, 74: 36-55. doi: 10.1016/j.actbio.2018.05.004 [25] Cai Xiaoli, Luo Yanan, Zhang Weiying, et al. pH-Sensitive ZnO quantum dots–doxorubicin nanoparticles for lung cancer targeted drug delivery [J]. ACS Applied Materials & Interfaces, 2016, 8(34): 22442-22450. [26] Fakayode Olayemi J, Tsolekile Ncediwe, Songca Sandile P, et al. Applications of functionalized nanomaterials in photo-dynamic therapy [J]. Biophysical Reviews, 2018, 10: 49-67. doi: 10.1007/s12551-017-0383-2 [27] Tong Liying, Fu Hao, Jia Zhijian, et al. Quantitative detection of dual miRNAs based on enzyme-sheared quantum dot fluorescence amplification [J]. Acta Photonica Sinica, 2020, 49(5): 0516001. (in Chinese) [28] Mohamed Abdel-Salam, Basma Omran, Kathryn Whitehead, et al. Superior properties and biomedical applications of microorganism-derived fluorescent quantum dots [J]. Molecules, 2020, 25(19): 4486. doi: 10.3390/molecules25194486 [29] Xu Bo, Qian Zhiyu. Research of anti-counterfeiting technology based on near-infrared fluorescent quantum dots [J]. Computer Measurement & Control, 2010, 18(4): 878-880. (in Chinese) [30] Yan Lei, Yu Yanlin. Microwave-assisted synthesis of S, N-codoped carbon dots with strong emission and application as anti-counterfeit ink [J]. Journal of Criminal Investigation Police University of China, 2018(6): 112-116. (in Chinese) [31] Liu Yanhong, Wang Na, Yu Xiaoqi, et al. Preparation and performance analysis of invisible fluorescent ink based on carbon dots [J]. Research and Exploration in Laboratory, 2020, 39(8): 1-4, 33. (in Chinese) [32] Geng Rui, Zhang Yujiang, Chen Qingshan. Research on photoluminescence characteristics of infrared PbX quantum dots [J]. Infrared Technology, 2017, 39(2): 125-129, 135. (in Chinese) [33] Cheng Cheng, Li Jiejie. Experimental measurement and determination of photoluminescence lifetime of PbS quantum dots [J]. Acta Optica Sinica, 2017, 37(1): 0130001. (in Chinese) doi: 10.3788/AOS201737.0130001