Filter-Assisted Separation of Multiple Nanomaterials: Mechanism and Application in Atomic/Mass Spectrometry/Fluorescence Label-Free Multimode Bioassays.

Atomic spectrometry (AS) has been widely used in bioassay, but it requires steps to immobilize or separate the signal molecules. In this work, based on the phenomenon that the filter membrane can selectively separate multiple nanomaterials (nanoparticles (NPs) and quantum dots (QDs)) and its related ions, including poly(thymine)-templated Cu NPs and free Cu2+, Ag NPs and free Ag+, CdTe QDs and Cd2+, we constructed multimode and label-free biosensors by chemical vapor generation-atomic fluorescence spectrometry (CVG-AFS), inductively coupled plasma mass spectrometry (ICP-MS), and fluorescence. In this strategy, terminal deoxynucleotidyl transferase (TdT) and polynucleotide kinase (PNK), H2O2, and mucin 1 can be sensitively detected using Cu2+, Ag+, and Cd2+ as the signal probe, respectively. As a result, TdT and T4 PNK in single cells level can be accurately quantified. In addition, the possible separation mechanism of filter membrane was proposed, both Donnan repulsion by charged functional layer and entrapment effect by nanomaterials size contributed to the outstanding separation performance. Subsequently, on the basis that CdTe QDs can selectively identify Cu NPs/Cu2+, Ag NPs/Ag+, and C-Ag+-C/Ag+, cation-exchange reaction (CER) was introduced in this platform due to its unique advantages, including improving the sensitivity of the above system (an order of magnitude), converting the non-CVG metal elements into CVG elements, and using low-cost AFS to substitute the high-cost ICP-MS. In addition, we performed theoretical calculations of the selective CER using density functional theory (DFT). Therefore, this label-free and simple separation AS/ICP-MS sensing platform shows great potential for biomarker analysis.