Abstract：
Functional nucleic acids (FNAs) have attracted a lot of attention for the rapid detection of metal ions. Cr3+ is one of the major heavy metal ions in natural waters. Due to the slow ligand exchange rate of Cr3+, the FNA-based Cr3+ sensors require long assay times, limiting the on-site applications. In this study, we report that the good\'s buffers containing amino and polyhydroxy groups greatly increase the ligand exchange rate of Cr3+. Using EDTA as a model coordinate ligand, the Tris buffer (100 mM, pH 7.0) showed the best acceleration effect among the eight buffers. It improved the rate constant ∼20-fold, shorten the half-time 19-fold, and lowered the activation energy ∼70% at 40 °C. The Tris buffer was then applied for sensor based on the Cr3+-binding induced fluorescence quenching of fluorescein (FAM)-labeled and single-stranded DNA (ssDNA), which shortened the assay time from 1 h to 1 min. The Tris buffer also ∼100% enhanced the fluorescence intensity of FAM, achieving the 11.4-fold lower limit of detection (LOD = 6.97 nM, S/N = 3). By the combination use of the Tris buffer and ascorbic acid, the strong interference from Cu2+, Pb2+, and Fe3+ suffered in many previous reported Cr3+ sensors was avoided. The practical application of the sensor for the detection of Cr3+ spiked in the real water samples were demonstrated with high recovery percentages. The Tris buffer could be applied for other metal ions with slow ligand exchange rate (such as V2+, Co3+ and Fe2+) to solve diverse issues such as long assay time and low synthesis yield of metal complexes, without the need of heating treatment.
摘要：
功能核酸(FNA)在快速检测金属离子方面受到了广泛的关注。Cr3+是天然水体中主要的重金属离子之一。由于Cr3+的配体交换速率较慢，基于FNA的Cr3+传感器需要较长的测定时间，限制现场应用。在这项研究中,我们报道，含有氨基和多羟基的良好的缓冲液大大提高了Cr3+的配体交换速率。使用EDTA作为模型配位配体，Tris缓冲液(100mM,pH7.0）在八种缓冲液中显示出最佳的加速效果。它提高了速率常数~20倍，将半场时间缩短19倍，并在40°C时降低活化能~70%。然后将Tris缓冲液用于基于荧光素（FAM）标记的和单链DNA（ssDNA）的Cr3结合诱导的荧光猝灭的传感器，将测定时间从1小时缩短至1分钟。Tris缓冲液也100%增强了FAM的荧光强度，达到11.4倍的检测下限(LOD=6.97nM，S/N=3)。通过结合使用Tris缓冲液和抗坏血酸，Cu2+的强烈干扰，Pb2+,在许多以前报道的Cr3+传感器中，Fe3+受到了影响。证明了该传感器在实际水样中加标Cr3+检测中的实际应用，回收率很高。Tris缓冲液可用于其他具有慢配体交换速率的金属离子（例如V2+，Co3+和Fe2+）解决了多种问题，如分析时间长，金属配合物合成产率低，不需要加热处理。
