Visual/CVG-AFS/ICP-MS multi-mode and label-free detection of target nucleic acids based on a selective cation exchange reaction and enzyme-free strand displacement amplification.

Conventional atomic spectrometry biosensors usually require labeling and separation of signaling molecules. Visual assays have direct and effective characteristics; however, they have poor accuracy. We intended to improve the analytical performance of our previous work and simplify the experimental operation while maintaining the advantages of simple operation and low cost. Herein, we describe the development of a visual, chemical vapor generation-atomic fluorescence spectrometry (CVG-AFS) and inductively coupled plasma-mass spectrometry (ICP-MS) three-mode method for the analysis of nucleic acids via CdTe quantum dot (QD)-assisted selective cation exchange reaction and enzyme-free strand displacement amplification. This work mainly utilized the ability of CdTe QDs to selectively differentiate free Hg2+ from the T-Hg2+-T complex in addition to the simple selective membrane filtration separation of Cd2+ from CdTe QDs to improve the performance of label-free bioassay methods. Due to the superior optical features of CdTe QDs, they can not only be used as a signal molecule for atomic spectroscopy, but also for direct use in visual readings. Under optimal experimental conditions, the developed strategy displayed a wide linear range along with limits of detection (LODs) of 10 fM and 3 fM (2 fM) in the linear concentration ranges of 10 fM-100 pM and 10 fM-1 nM with the naked eye and CVG-AFS (ICP-MS) assays, respectively. This method also exhibited excellent DNA sequence specificity. This assay had advantageous characteristics such as an easy operation, simple design, high sensitivity, and diversified signal readout manner, which demonstrate its great potential in medical diagnosis applications.