Departamento de Química Analítica e Ingeniería Química, Edificio Polivalente, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain.
Lab Chip. 2012 May 8;12(11):2006-14. doi: 10.1039/c2lc40099e. Epub 2012 Apr 24.
Single-walled carbon nanotubes (SWCNTs) should constitute an important natural step towards the improvement of the analytical performance of microfluidic electrochemical sensing. SWCNTs inherently offer lower detection potentials, higher surfaces and better stability than the existing carbon electrodes. However, pristine SWCNTs contain some carbonaceous and metallic impurities that influence their electrochemical performance. Thus, an appropriate processing method is important for obtaining high purity SWCNTs for analytical applications. In this work, a set of 0.1 mg mL(-1) SWCNT dispersions with different degrees of purity and different dispersants (SDBS; pluronic F68 and DMF) was carefully characterized by near infrared (NIR) spectroscopy giving a Purity Index (NIR-PI) ranging from 0.039 to 0.310. The highest purity was obtained when air oxidized SWCNTs were dispersed in SDBS, followed by centrifugation. The SWCNT dispersions were utilized to modify microfluidic chip electrodes for the electrochemical sensing of dopamine and catechol. In comparison with non-SWCNT-based electrodes, the sample with the highest NIR-PI (0.310) exhibited the best analytical performance in terms of improved sensitivity (3-folds higher), very good signal-to-noise ratio, high resistance-to-fouling in terms of relative standard deviation (RSD 7%; n = 15), and enhanced resolution (2-folds higher). In addition, very well-defined concentration dependence was also obtained with excellent correlation coefficients (r ≥ 0.990). Likewise, a good analytical sensitivity, suitable detection limits (LODs) and a very good precision with independence of the concentration assayed (RSDs ≤ 5%) was achieved. These valuable features indicate the suitability of this material for quantitative analysis. NIR-PI and further TEM and XRD characterization demonstrated that the analytical response was driven and controlled by the high NIR-PI of the SWCNTs used. The significance of this work is the demonstration for the first time of the sensitivity-purity relationship in SWCNT microfluidic chips. A novel and valuable analytical tool for electrochemical sensing has been developed: SWCNTs with high purity and a rich surface chemistry with functional groups, both essential for analytical purposes. Also, this work helps to better understand the analytical potency of SWCNTs coupled to microfluidic chips and it opens new gates for using these unique dispersions in real-world applications.
单壁碳纳米管（SWCNTs）应该构成朝着改善微流控电化学传感分析性能的重要自然步骤。SWCNTs 本质上提供比现有碳电极更低的检测电位、更高的表面积和更好的稳定性。然而，原始的 SWCNTs 含有一些影响其电化学性能的碳质和金属杂质。因此，对于获得用于分析应用的高纯度 SWCNTs，适当的处理方法很重要。在这项工作中，一组 0.1mg/mL 的 SWCNT 分散体具有不同程度的纯度和不同的分散剂（SDBS；聚氧乙烯 F68 和 DMF），通过近红外（NIR）光谱进行了仔细的表征，得到了从 0.039 到 0.310 的纯度指数（NIR-PI）。在空气中氧化的 SWCNTs 分散在 SDBS 中并经过离心处理，得到的纯度最高。将 SWCNT 分散体用于修饰微流控芯片电极，用于电化学检测多巴胺和儿茶酚。与非 SWCNT 基电极相比，NIR-PI 最高的（0.310）样品在灵敏度（提高 3 倍）、非常好的信噪比、相对标准偏差（RSD 为 7%；n = 15）方面的抗污染能力、以及增强的分辨率（提高 2 倍）方面表现出最佳的分析性能。此外，还获得了非常好的浓度依赖性和出色的相关系数（r≥0.990）。同样，实现了良好的分析灵敏度、合适的检测限（LOD）和与所测定浓度无关的非常好的精密度（RSDs≤5%）。这些有价值的特征表明该材料适用于定量分析。NIR-PI 以及进一步的 TEM 和 XRD 表征表明，分析响应是由所使用的 SWCNTs 的高 NIR-PI 驱动和控制的。这项工作的意义在于首次证明了 SWCNT 微流控芯片中的灵敏度-纯度关系。已经开发出一种用于电化学传感的新型有价值的分析工具：具有高纯度和丰富表面化学的 SWCNTs，两者都是分析目的所必需的。此外，这项工作有助于更好地理解与微流控芯片结合的 SWCNTs 的分析潜力，并为在实际应用中使用这些独特的分散体开辟了新的途径。
