Using Magnetic Ions to Probe and Induce Magnetism of Pyrophosphates, Bacteria, and Mammalian Cells

Abstract

Magnetic isolation using magnetic nanoparticles (MNPs) as trapping probes have been widely used in sample pretreatment to shorten analysis time. Nevertheless, to generate MNPs is time-consuming. Furthermore, the generated MNPs have to be further functionalized to gain the capability of recognizing their target species. Thus, an alternative approach that can impose magnetism to nonmagnetic species by simply using magnetic ions as the probes is developed in this study. That is, we employ magnetic ions (Fe, Co, and Ni) that can interact with nonmagnetic species containing oxygen-containing functional groups as the probes. Pyrophosphate (PPi), bacteria, and mammalian cells were selected as the model samples. Our results show that the as-prepared magnetic ion-PPi conjugates gain sufficient magnetism and can be readily aggregated by applying an external magnetic field. Moreover, the magnetic trapping is reversible. The PPi-containing conjugates can lose their magnetic property simply using ethylenediaminetetraacetic acid or aluminum ions as competing agents to remove or to replace, respectively, the conjugated magnetic ions. In addition, bacteria and mammalian cells that possess abundant oxygen-containing functional groups on their cell surfaces can be selectively probed by magnetic ions and gain sufficient magnetism for magnetic isolation from complex serum samples.

Magnetic Graphene Oxide-Based Affinity Surface-Assisted Laser Desorption/Ionization Mass Spectrometry for Screening of Aflatoxin B1 from Complex Samples

“…To eliminate the centrifugation step and further shorten the preparation time, magnetic GO nanoprobes were prepared. According to our previous studies, , it is possible to impose magnetism to nonmagnetic species by immobilizing magnetic metal ions, e.g., Fe 3+ , Co 2+ , and Ni 2+ , onto nonmagnetic species through chelation. Thus, it should also be possible to impose magnetism to nonmagnetism nanomaterials such as GO.…”

“…Magnetic isolation can be easily conducted and only a small magnet is sufficient for conducting magnetic isolation of the conjugates of magnetic nanoprobe–target species. We previously have demonstrated that nonmagnetic species, such as bacterial and cells, can gain apparent magnetism by simply mixing with magnetic metal ions, such as Fe 3+ and Gd 3+ . The binding mechanism is based on the hard–soft acid–base (HSAB) theory .…”

Europium Ion-Based Magnetic-Trapping and Fluorescence-Sensing Method for Detection of Pathogenic Bacteria

“…26 The resulting magnetic metal ion−bacteria conjugates have a high density of magnetic metal ions in a small space, i.e., a bacterial cell, and can be easily isolated by simply placing an external magnet. 24,25 Eu 3+ has been utilized as a biosensing probe for various target analytes due to its fluorescence capabilities. 27−30 In addition to its fluorescence property, Eu 3+ also exhibits paramagnetic properties owing to its electron configuration ([Xe]4f 6 ), which makes it a potential candidate for use as a magnetic probe.…”

“…Generation of such probes was usually time-consuming. Thus, a simple and rapid approach for magnetic isolation of bacteria from sample solution has been demonstrated. , That is, magnetic metal ions, including Fe 3+ , Co 2+ , Ni 2+ , and Gd 3+ have been shown to effectively confer magnetism to both Gram-positive and Gram-negative bacteria by anchoring on the bacterial surface. This interaction occurs due to the presence of oxygen-containing functional groups such as phosphates, which act as hard Lewis bases, on the bacterial surface, and the above-mentioned magnetic metal ions, acting as either borderline or hard Lewis acids, according to the Hard Soft Acid Base (HSAB) theory .…”

“…This interaction occurs due to the presence of oxygen-containing functional groups such as phosphates, which act as hard Lewis bases, on the bacterial surface, and the above-mentioned magnetic metal ions, acting as either borderline or hard Lewis acids, according to the Hard Soft Acid Base (HSAB) theory . The resulting magnetic metal ion–bacteria conjugates have a high density of magnetic metal ions in a small space, i.e., a bacterial cell, and can be easily isolated by simply placing an external magnet. , …”