光谱学与光谱分析, 2019, 39 (12): 3749, 网络出版: 2020-01-07  

基于耦合微流控芯片的可逆式铵检测及其影响因素研究

The Reversible Ammonium Detection Based on the Coupled Microfluidic Chipand the Investigation of the Impact Factors
作者单位
浙江大学能源清洁利用国家重点实验室, 浙江 杭州 310027
摘要
铵(NH+4)的光谱检测有着重要的意义, 随着微流控领域的发展, 以快速性、 便携性以及多组分检测为目标的微流控光谱分析成效卓著。 但是分析中存在的指示剂浪费问题一直没有得到解决。 锌卟啉作为一种天然的自发光分子, 能够实现NH+4的可逆性检测, 解决这一问题, 但却存在选择性低的缺点。 针对这些问题, 实验设计了一种耦合微流控芯片, 由反应芯片、 气体扩散芯片和检测芯片组成。 其中反应芯片用于将NH+4转化为NH3, 由聚二甲基硅氧烷制成; 气体扩散芯片使NH3扩散进入待测溶液, 由上下两片玻璃芯片及夹在中间的一层PDMS材质的气体透过膜制成; 而检测芯片则通过多层结构将指示剂固定在其中。 指示剂是通过将锌卟啉永久染色在离子交换树脂上制作而成的, 在遇到NH3分子时会产生由绿到紫的变化, 而当周围变成纯水环境时, 又能够实现从紫到绿的逆向变化。 以此耦合芯片为分析平台, 搭建了一套小型化的光谱检测系统, 以便携式光谱仪为分析器件, 通过测量450 nm处的透射光谱强度变化, 实现了NH+4的定量检测, 同时研究了影响检测结果的三个参数: 气体透过膜厚度, 流速和指示剂用量。 首先通过光谱强度随时间的变化, 我们证明了指示过程的可逆性, 因而解决了指示剂浪费的问题, 时间响应也说明了指示过程的快速性; 接着通过与对照实验的对比, 说明检测过程具有很高的选择性, 能够排除干扰物的影响, 光谱变化仅仅是因为NH3的存在; 通过改变气体扩散芯片中气体透过膜的厚度, 得到了膜厚和光谱强度变化之间的关系, 膜的厚度增加使得检测效果变差, 但当膜厚小于10 μm时效果基本不变, 考虑到机械强度, 选择了10 μm作为膜的最佳厚度; 随即研究了耦合芯片中流速对于光谱强度变化的影响, 发现流速的增加会使得光谱强度变化减小, 但流速小于5 μL·min-1时效果基本不变; 最后又研究了指示剂用量对于光谱强度变化的影响, 证明指示剂过多和过少都会影响检测效果, 以5 mg为最佳。 这套以耦合芯片为平台的光谱分析系统具有体积小, 经济性高, 响应迅速的特点, 能够实现NH+4高选择性、 可逆性的定量测量。
Abstract
The spectroscopic detection of ammonium (NH+4) has great significance. With the development of microfluidics, microfluidic spectroscopic analysis aiming at rapid, portable and multi-component detection has realized tremendous achievements. However, the excessive consumption of the indicating material which exists all the time has not been settled yet. Zinc porphyrin, being a natural chromophore, can reversibly detect NH+4 and settle the problem. But it suffers from the lack of selectivity. In allusion to these issues, a coupled microfluidic chip which consists of a reaction chip, a gas-diffusion chip and a detection chip is fabricated in our experiments. The reaction chip made of polydimethylsiloxane can convert NH+4 into NH3. The gas-diffusion chip which is made of two glass chips and a piece of polydimethylsiloxane gas-diffusion membrane allows NH3 diffuses into the detection solution. The detection chip immobilizes the indicating material tightly through the multi-layer structure. The indicating material fabricated by dying zinc porphyrin on the surface of the cation exchange resin permanently will turn from green to purple when it meets NH3 and will turn reversely into green when pure water is around. Using the coupled chip as the analytical platform, we set up a miniaturized spectroscopic detection system. With a portable spectrometer being the analytical instrument, we detect NH+4 by the transmission spectrum intensity change at the wavelength of 450 nm and study three factors that could affect the detection performance: the thickness of the gas-diffusion membrane, the flow rate and the dosage of the indicating material. First, we confirm the reversibility of the indicating process and settle the issue of indicating material consumption by the spectrum change intensity. The time responses show the rapidity of the indicating process. Then through the comparison to the contrast experiment, the high selectivity of the indicating process is demonstrated because the interference has no influence and the spectrum change is attributed merely to NH3. The relationship between the membrane thickness and the spectrum intensity change is obtained by changing the thickness of the gas-diffusion membrane in the gas-diffusion chip. Results show that the increase of the membrane thickness leads to a worse detection performance, but the outcome remains stable when the thickness is less than 10 μm. So 10 μm is selected as the optimal thickness in consideration of the mechanical strength. The impact of the flow rate is investigated afterwards. The results exhibit that the increase of the flow rate will decrease the spectrum intensity change, but the performance becomes unchanged when flow rate is less than 5 μL·min-1. Last, how the dosage of the indicating material impacts the results is studied. It is demonstrated that both excessive and inadequate indicating material will deteriorate the performance. So 5 mg is selected as the optimal amount. The spectroscopic detection system which uses the coupled chip as the analytical platform has the advantages of small volume, high economy, rapid response and realizes highly selective and reversible NH+4 detection.

周昊, 杨正. 基于耦合微流控芯片的可逆式铵检测及其影响因素研究[J]. 光谱学与光谱分析, 2019, 39(12): 3749. ZHOU Hao, YANG Zheng. The Reversible Ammonium Detection Based on the Coupled Microfluidic Chipand the Investigation of the Impact Factors[J]. Spectroscopy and Spectral Analysis, 2019, 39(12): 3749.

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