(118e) Automated Fe Quantification Assay to Accelerate Magnetic Nanoparticle Studies

Iron concentration is an important parameter used in determining many characteristics of iron oxide nanoparticles. This includes characteristics that require a known mass of iron oxide to determine, such as nanoparticle concentration or saturation magnetization, and measurements that need to be normalized for consistency, such as signal intensity in magnetic particle imaging and in hyperthermia. Iron quantification assays are commonly performed using UV-vis spectroscopy. Typically, nanoparticle samples are mixed with various reagents in series to digest the iron to an aqueous salt before forming a colored complex in solution that allows absorbance measurement. These assays tend to be time-consuming, typically taking several hours and requiring significant manual effort as many repetitive pipetting steps are involved, especially when processing many samples at once. This study aims to evaluate the performance of a liquid handling robot as a replacement to manually performed assays with the goal of reducing time spent performing menial labor without sacrificing accuracy or precision of results.

A two-step protocol was designed to be used with the Opentrons OT2 liquid handler. Early procedures using nitric acid to digest the samples in the robot resulted in undesirable rapid corrosion of many parts which may reduce equipment longevity and introduce contamination. To prevent this and to address problems beyond the capability of the robot, such as particle sedimentation and phase separation during mixing, the first step of overnight particle digestion in acid was performed manually. Following the transfer of digested samples to a quartz 96 well plate, the robot performed all subsequent pipetting and mixing steps required using a multichannel pipette for increased throughput. 3D printing was also utilized to allow for rapid design and prototyping of custom equipment such as tube racks and reservoirs. This has reduced the person-hours required to complete the assay significantly without any appreciable loss in accuracy. One test with 16 identical samples of commercial particle Ferucarbotran resulted in a measured iron concentration close to the value measured in a manual assay with a standard error of 5%. The protocol has been validated with aqueous and organic solvents and particles of various coatings including oleic acid, polyethylene glycol, and poly (maleic anhydride-alt-1-octadecene). Future work will focus on improving the efficiency of the protocol by minimizing the human interaction required and expanding the liquid handler to other procedures.

Figure 1: Liquid handling robot with equipment for iron concentration assay.