Mpeg sh5k

i-colloid™ Au 15 nm (optical density 1 [OD1]) and 20 nm (OD1) from IMRA America, Inc., were used to take advantage of its novel surface properties allowing sequential surface modification.26 –28 (link) Methoxy-PEG-thiol, MW 5k (methoxy-PEG-thiol, MW 5,345, substitution purity: >90%, abbreviated as “mPEG-SH5k”), was purchased from Creative PEGWorks (Chapel Hill, NC, USA). Fluorescein isothiocyanate-PEG-thiol, MW 5k (FITC-PEG-SH, substitution purity: >80%, “FITC-PEG-SH5k”), was purchased from Nanocs, Inc (New York, NY, USA). Cysteine-modified (RGD)₄ peptide (MW: 1,845.98, purity: >95%, abbreviated as “RGD peptide”) with amino acid sequence RGDRGDRGDRGDPGC was purchased from RS synthesis, LLC (Louisville, KY, USA). Methoxy-PEG-SH5k, FITC-PEG-SH5k and RGD peptide were in powder form and dissolved in deionized (DI) water having an electric conductivity of <0.1 μS/cm without further purification. All solutions were freshly made as needed and used within 12 h. Dynamic light scattering (DLS) measurement with Zetasizer Nano ZS90 (Malvern Instruments, Malvern, Worcestershire, UK) was employed to measure an increase in hydrodynamic diameter of AuNPs with surface modification. UV-2700 UV-Vis Spectrophotometer (Shimadzu Corporation, Kyoto, Japan) was used for optical density (OD) or absorbance measurement of the colloidal suspension.