The polymer solution was slowly added to the Pt-precursor solution with magnetic stirring for 12 h, and the NaOH solution was added to maintain the solution pH between 9–10. Subsequently, the solution was slowly heated to 110 ☌ with magnetic stirring, and this temperature was maintained for 4 h. The NaOH solution was slowly added to the Pt-precursor solution with constant magnetic stirring until the pH of the solution reached 9–10. Briefly, three different solutions were prepared, (i) a precursor solution prepared from 1 mmol of Pt precursor in 15 mL of TEG in a 100 mL three-necked round-bottom flask via magnetic stirring at 60 ☌ under atmospheric conditions (to maintain a constant temperature, the three-necked round-bottom flask was suspended in a silicone oil bath on a hot plate) (ii) an NaOH solution prepared from 9 mmol of NaOH in 20 mL of TEG in a 100 mL beaker via magnetic stirring at 60 ☌ under atmospheric conditions and (iii) a polymer solution comprising 0.5 mmol of PAA (or 0.4 mmol of PAAMA or 4.5 × 10 −3 mmol of PMVEMA) in 15 mL of TEG in a 100 mL beaker via magnetic stirring at room temperature under atmospheric conditions. Ultrasmall Pt-NPs coated with hydrophilic and biocompatible polymers (i.e., PAA, PAAMA, and PMVEMA) were synthesized using a one-pot polyol method ( Figure 1). Yet, despite the above-mentioned advantages, studies on Pt-NP contrast agents, as well as other heavy metal-based NP contrast agents, remain limited. They can also serve as drug delivery vehicles after conjugation with antibodies or disease-specific ligands on their surfaces, allowing disease-specific diagnosis and therapy. They can provide much longer blood retention times than iodine contrast agents owing to their considerably higher nanoparticle mass, allowing longer imaging times after intravenous injection. In addition, they can provide a lower osmolality than iodine contrast agents owing to their lower number density at the same atomic concentration. Conversely, Pt-NP contrast agents, owing to a higher X-ray attenuation coefficient of Pt and a high density of Pt atoms per nanoparticle, can yield considerably higher contrasts compared with those of iodine contrast agents. Moreover, their disease-specific imaging via conjugation with antibodies or targeting ligands is poor.
They exhibit rapid renal excretion owing to their low molecular mass, allowing for only short imaging times.
Iodine contrast agents with three or six iodine atoms per molecule generally possess high osmolality, which can cause side effects.
Pt-NP contrast agents in particular have several additional advantages with respect to iodine contrast agents.
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