Abstract
Most iron oxide nanoparticles applications, and in special biomedical applications, require the accurate determination of iron content as the determination of particle properties from measurements in dispersions is strongly dependent on it. Inductively coupled plasma (ICP) and spectrophotometry are two typical worldwide used analytical methods for iron concentration determination. In both techniques, precise determination of iron is not straightforward and nanoparticle digestion and dilution procedures are needed prior to analysis. The sample preparation protocol has been shown to be as important as the analytical method when accuracy is aimed as many puzzling reported results in magnetic, colloidal, and structural properties are simply attributable to inadequate dissolution procedures. Therefore, a standard sample preparation protocol is needed to ensure the adequate and complete iron oxide nanoparticle dissolution and to harmonize this procedure. In this work, an interlaboratory evaluation of an optimized iron oxide nanoparticle digestion/dilution protocol was carried out. The presented protocol is simple, inexpensive, and does not involve any special device (as microwave, ultrasound, or other high-priced digestion devices). Then, iron concentration was measured by ICP-OES (performed in ICMM/CSIC-Spain) and spectrophotometry (NanoPET-Germany) and the obtained concentration values were analyzed to determine the most probable error causes. Uncertainty values as low as 1.5% were achieved after the optimized method was applied. Moreover, this article provides a list of recommendations to significantly reduce uncertainty in both sample preparation and analysis procedures.Graphical abstract
Highlights
Iron oxide nanoparticles are widely used in ex-vivo bioassays for the detection and separation of small molecules, biomarkers, DNA, and bacteria [1], and in-vivo medicalPublished in the topical collection Nanoparticles for Bioanalysis with guest editors María Carmen Blanco-López and Montserrat Rivas.saturation magnetization in Am2/Kg Fe, the specific absorption rate (SAR) in W/g Fe, or the concentration of functional groups on the particle surface in μmol/g Fe, respectively.Up to our knowledge,there is only one published protocol for the determination of iron in magnetic nanoparticles for biomedical applications using spectrophotometry [7]
The uncertainties arising from the equipment were obtained from the calibration certificate given by the supplier (Table 3)
In principle, we did not expect that the equipment employed in the preparation of the sample prior to the analysis could influence the uncertainty of the measurements
Summary
Iron oxide nanoparticles are widely used in ex-vivo bioassays for the detection and separation of small molecules, biomarkers, DNA, and bacteria [1], and in-vivo medicalPublished in the topical collection Nanoparticles for Bioanalysis with guest editors María Carmen Blanco-López and Montserrat Rivas.saturation magnetization in Am2/Kg Fe, the specific absorption rate (SAR) in W/g Fe, or the concentration of functional groups on the particle surface in μmol/g Fe, respectively.Up to our knowledge,there is only one published protocol for the determination of iron in magnetic nanoparticles for biomedical applications using spectrophotometry [7]. In the case of iron oxide nanoparticle suspensions, the sample preparation procedure poses some Bpitfalls^ for example incorrect pipetting of viscous colloids or incomplete digestion of coated nanoparticles, and contributes significantly to the uncertainty of the obtained concentration values [14]. This might be one reason why our personal experience as well as many discussion with colleagues who work with magnetic nanoparticles show us that concentration values provided for iron oxide nanoparticle suspensions are not reliable in case of both, research samples as well as commercially available iron oxide nanoparticle suspensions, and was the motivation of our study. The quantification of the iron concentration of various iron oxide nanoparticle suspensions was performed in two different labs with two different established methods with the aim to explore and minimize the uncertainty of the obtained results
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