Fig. 1: Characterization of synthesized chain-like gold nanoparticle clusters conjugated with RGD peptide (CGNP clusters-RGD) and quantification of the photoacoustic (PA) and optical coherence tomography (OCT) properties.

a Illustration of synthesis of CGNP clusters-RGD. Ultra-pure colloidal gold nanoparticles (GNPs) were first fabricated by physical method (using femtosecond laser). Then, discrete GNPs were self-assembled using pentapeptide Cys-Ala-Leu-Asn-Asn (CALNN) and cysteamine in order to create CGNP clusters. b Transmission electron microscopy (TEM) image of CGNP clusters-RGD, ×2000, 20 kV; bar = 200 nm. c Region of CGNP clusters-RGD at high magnification, indicated by red square box in b. The CGNPs surrounded with a gray shell representing CALNN-PEG-RGD layer. d Comparisons of hydrodynamic size between GNPs and CGNP clusters-RGD measured in water by using dynamic light scattering (DLS). e UV-Vis absorption spectra of GNPs and CGNP clusters-RGD. f Quantitative characterization of the colloidal stability of CGNP clusters-RGD over time for up to 8 weeks by using UV-Vis absorption spectroscopy analysis. g In vitro photostability of CGNP clusters-RGD during nanosecond pulsed laser irradiation (65 s) at various pulse fluences (0.005, 0.01, 0.02, and 0.04 mJ/cm²). h Confocal fluorescent microscope image of single HeLa cell treated with FITC-labeled CGNP clusters-RGD at concentration of 50 µg/mL for 24 h. Blue fluorescent color indicates the cell’s nuclei stained with Hoechst 33342. Green color shows the position of CGNP clusters-RGD accumulated around the cell nuclei. i and j dark field images of HeLa cells after incubated with conventional GNPs-RGD with diameter of 20 nm and CGNP clusters-RGD, respectively. Note that the internalized CGNP clusters-RGD appeared indicating that CGNP clusters-RGD were stable in biological tissue. Source data are provided as a Source Data file.