Fig. 4.

In vivo biodistribution of βCas AuNPs in zebrafish larvae. a βCas AuNPs were conjugated with neutral red and injected to zebrafish larvae (5 day old) via the intracardiac route in a dose equivalent to 3 ng Au per 4.5 ng βCas. b Labeled βCas AuNPs were traced for in vivo distribution at 0.5, 6, and 12 h in dorsal and lateral positions (c). Bright fluorescence was observed from the brain 0.5 h after AuNP administration. However, fluorescence was eliminated from the cerebral region in 6 h, while it took 12 h to eliminate from the body (scale bars: 200 µM). d Tissue microtome of zebrafish brain was subjected to HSI imaging. Spectral angular mapping (SAM) images were built from HSI by scanning against the βCas AuNPs spectral library. SAM and Rule images colored the pixels as red and black, respectively, that have matching spectra of βCas AuNPs. Zebrafish larvae with βCas AuNPs in the brain presented black spots in Rule images and red pixels in SAM images. SPR spectra with peak ~530 nm were observed in the brain of βCas AuNPs treated larvae. No such spectra were recorded for control larva (scale bars: darkfield 200 µM; HSI, SAM, HSI + SAM, Rule: 10 µM; inset scale bar: 2 µM; scale bar for βCas AuNPs: 10 µM, inset scale bar: 0.5 µM). e ICP MS analysis, where the AuNP concentration was the highest in the larval brain at 0.5 h, i.e., equivalent to 0.6 ± 0.1 ng of Au, and dropped to 0.05 ± 0.01 and 0.02 ± 0.008 ng at 6 and 12 h, respectively (n = 10). f Dose–response relationship between the amount of AuNPs injected vs. the amount of AuNPs delivered across the brain (n = 10). Significantly (p < 0.05) increased amount of Au was delivered when intracardiac dose of AuNPs was increased from 1.5 to 3 ng equivalent. However, increasing the dose from 3 to 6 ng did not improve AuNP delivery across the BBB, indicating a dose saturation. Error bars represent the standard deviation. Source data are provided as a Source Data file