Towards the clinical translation of a silver sulfide nanoparticle contrast agent: large scale production with a highly parallelized microfluidic chip

Abstract

Purpose: Ultrasmall silver sulfide nanoparticles (Ag₂S-NP) have been identified as promising contrast agents for a number of modalities and in particular for dual-energy mammography. These Ag₂S-NP have demonstrated marked advantages over clinically available agents with the ability to generate higher contrast with high biocompatibility. However, current synthesis methods for inorganic nanoparticles are low-throughput and highly time-intensive, limiting the possibility of large animal studies or eventual clinical use of this potential imaging agent.

Methods: We herein report the use of a scalable silicon microfluidic system (SSMS) for the large-scale synthesis of Ag₂S-NP. Ag₂S-NP produced using this system were compared to bulk synthesis and a commercially available microfluidic device through characterization, contrast generation, in vivo imaging, and clearance profiles.

Results: Using SSMS chips with 1 channel, 10 parallelized channels, and 256 parallelized channels, we determined that the Ag₂S-NP produced were of similar quality as measured by core size, concentration, UV-visible spectrometry, and in vitro contrast generation. Moreover, by combining parallelized chips with increasing reagent concentration, we were able to increase output by an overall factor of 5,100. We also found that in vivo imaging contrast generation was consistent across synthesis methods and confirmed renal clearance of the ultrasmall nanoparticles. Finally, we found best-in-class clearance of the Ag₂S-NP occurred within 24 h.

Conclusions: These studies have identified a promising method for the large-scale production of Ag₂S-NP, paving the way for eventual clinical translation.

Keywords: Contrast agents; High throughput; Large scale synthesis; Nanoparticles; Silver sulfide.

Fig. 1

Schematic, photographs, and micrographs showing microfluidic chips used for synthesis of Ag₂S-NP

Fig. 2

A) Representative images of Ag₂S-NP produced using each SSMS chip after running for one minute and B) rate of production using each device (mean ± SEM). Characterization of the Ag₂S-NP synthesized including C) representative TEM micrographs with insets showing 4 times the magnification, D) core size measurements (mean ± SEM), and E) UV–visible spectra

Fig. 3

Characterization of the Ag₂S-NP synthesized with increased concentrations including A) representative TEM micrographs, B) core size measurements (mean ± SEM), and C) product concentration as measured by ICP

Fig. 4

In vitro CT imaging. A) Representative µCT scans with iopamidol, 1X-Ag₂S-NP, 10X-Ag₂S-NP, 256X-Ag₂S-NP at concentrations ranging from 0 – 10 mg/mL and B) quantification of the CT attenuation rate for the different solutions (mean ± SD)

Fig. 5

A) Representative 3D µCT images showing 10X-Ag₂S-NP being renally cleared. Images include pre-injection and 5 min, 30 min, 60 min, 120 min, and 1440 min post-injection. Kidneys are indicated by yellow markers and bladders are indicated with green. Quantification of CT attenuation in the B) kidneys and C) bladder at each time point. n = 5 per group. Data is presented as mean ± SEM

Fig. 6

A) Biodistribution of Ag₂S-NP in mice 24 h post-injection (mean ± SEM). n = 5 per group. B) Total clearance of Ag₂S-NP in mice within 24 h (mean ± SEM)