Due to its unique structure and properties, human breast milk lactoferrin (hLF) has many nutritional and health-promoting functions in infants, including protection against inflammation and bacterial infections. The lack of LF in breastmilk or formula can result in the weakening of the infant’s immune system. Noncompetitive polarization fluorescence immunoassay (FPIA) is a promising method for hLF quantification in milk and dairy products, which does not require the separation of the bound and free protein and allows to avoid time-consuming sample preparation. The use of fluorescently labeled single-domain camelid antibodies (nanobodies) for protein recognition in FPIA makes it possible to quantify relatively large antigens, in particular, hLF. In this work, we used previously obtained fluorescein isothiocyanate (FITC)-conjugated anti-hLF5 and anti-hLF16 nanobodies, which selectively recognized two different human lactoferrin epitopes, but did not bind to goat lactoferrin. The kinetics of hLF interaction with the FITC-labeled nanobodies was studied. The dissociation constant (KD) for the anti-LF5 and anti-LF16 nanobodies was 3.2 ± 0.3 and 4.9 ± 0.4 nM, respectively, indicating the high-affinity binding of these nanobodies to hLF. We developed the FPIA protocol and determined the concentration of FITC-labeled anti-hLF5 and anti-hLF16 nanobodies that provided the optimal fluorescence signal and stable fluorescence polarization value. We also studied the dependence of fluorescence polarization on the hLF concentration in the noncompetitive FPIA with FITC-anti-hLF5 nanobody. The detection limit for hLF was 2.1 ± 0.2 µg/ml and the linear range for determining the hLF concentration was 3-10 µg/ml. FPIA is commonly used to assay low-molecular-weight substances; however, the use of fluorescently labeled nanobodies allows quantification of high-molecular-weight proteins. Here, we demonstrated that FPIA with fluorescently labeled nanobodies can be used for hLF quantification in milk.

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Abstract—The round-the-world Antarctic expedition of the Russian Navy that took place from December 2019 to June 2020 on board the Russian Navy oceanographic research vessel (ORV) Admiral Vladimirsky was supported by the Russian Geographical Society and was dedicated to the 200th anniversary of the discovery of Antarctica and the 250th birthday anniversary of Admiral Ivan Kruzenshtern. One of the expedition’s main objectives was to instrumentally determine the position of the South Magnetic Pole (SMP) whose latest location had been measured more than twenty years before. Planning of magnetometric research, its monitoring and processing of obtained data were carried out by members of the Chair of Geophysical Methods of the Earth’s Crust Study of the MSU Department of Geology and the Fedorov Institute of Applied Geophysics. Based on a set of instrumental determinations (modular proton-precession differential magnetometers, vector three-component flux-gate magnetometers, the ship compass), the SMP position was measured to a precision of ±5 km. Proceeding from the 1980 and 2000 instrumental SMP determinations, it is proven that over the past 40 years, the SMP has been shifting at a consistent velocity in the same direction.