Magneto-Fluorescent Microbeads for Bacteria Detection Constructed from Superparamagnetic Fe₃O₄ Nanoparticles and AIS/ZnS Quantum Dots

Abstract

The efficient and sensitive detection of pathogenic microorganisms in aqueous environments, such as water used in medical applications, drinking water, and cooling water of industrial plants, requires simple and fast methods suitable for multiplexed detection such as flow cytometry (FCM) with optically encoded carrier beads. For this purpose, we combine fluorescent Cd-free Ag–In–S ternary quantum dots (t-QDs) with fluorescence lifetimes (LTs) of several hundred nanoseconds and superparamagnetic Fe3O4 nanoparticles (SPIONs) with mesoporous CaCO3 microbeads to a magneto-fluorescent bead platform that can be surface-functionalized with bioligands, such as antibodies. This inorganic bead platform enables immuno-magnetic separation, target enrichment, and target quantification with optical readout. The beads can be detected with steady-state and time-resolved fluorescence microscopy and flow cytometry (FCM). Moreover, they are suited for readout by time gated emission. In the following, the preparation of these magneto-fluorescent CaCO3 beads, their spectroscopic and analytic characterization, and their conjugation with bacteria-specific antibodies are presented as well as proof-of-concept measurements with Legionella pneumophila including cell cultivation and plating experiments for bacteria quantification. Additionally, the possibility to discriminate between the long-lived emission of the LT-encoded capture and carrier CaCO3 beads and the short-lived emission of the dye-stained bacteria with time-resolved fluorescence techniques and single wavelength excitation is demonstrated.

Spectral-Time Multiplexing in FRET Complexes of AgInS2/ZnS Quantum Dot and Organic Dyes

“…To increase and vary the LTs of organic dyes served as luminescent labels, it was proposed to utilize time-resolved Förster resonance energy transfer (TR-FRET) between organic dyes (energy acceptor) and inorganic lanthanide complexes with long LTs (energy donors) [ 18 , 19 , 20 , 21 , 22 ]. In this case, FRET-induced long-lived sensitized luminescence of the labels was analyzed allowing the discrimination of the autoluminescence [ 23 , 24 , 25 ]. This scheme with long-lived Eu (III) and Tb (III) complexes as energy donors has been realized using the time-gating technique in [ 23 , 24 , 25 ] where FRET-induced long-lived sensitized luminescence of labels was demonstrated.…”

“…In this case, FRET-induced long-lived sensitized luminescence of the labels was analyzed allowing the discrimination of the autoluminescence [ 23 , 24 , 25 ]. This scheme with long-lived Eu (III) and Tb (III) complexes as energy donors has been realized using the time-gating technique in [ 23 , 24 , 25 ] where FRET-induced long-lived sensitized luminescence of labels was demonstrated. The FRET-induced prolongation of luminescence LT of acceptor dyes to submicrosecond times has been also shown by an example of donor/acceptor complex with Mn-doped CdS/ZnS QDs as a donor [ 14 ].…”

Magneto-Fluorescent Hybrid Sensor CaCO3-Fe3O4-AgInS2/ZnS for the Detection of Heavy Metal Ions in Aqueous Media

“…The next step was the formation of polyelectrolyte multilayers and the deposition of the QDs layer on a surface of the microspheres by LbL method. Oppositely charged electrostatically interacting polymers and QDs have deposited alternately on the surface of microspheres [ 43 , 44 , 45 ]. In this work, we used PAH and PSS polymers and QDs AgInS 2 /ZnS core/shell capped with the hydrophilic ligand TGA.…”

Immunomagnetic separation: An effective pretreatment technology for isolation and enrichment in food microorganisms detection

“…The results indicated that up to 50% of L. pneumophila cells with the concentration of 100 CFU/mL could be isolated by IMPs. Compared with those only aminated MPs, the CE of the newly synthesized material was improved about 100 times, which was beneficial for improving the detection performance (Martynenko et al., 2019). Similarly, based on the fluorescence and separation properties, Au‐shell‐coated MPs provide new techniques for highly sensitive detection of target bacteria.…”