Near-infrared plasmonic assemblies of gold nanoparticles with multimodal function for targeted cancer theragnosis

Here we report a novel assembly structure of near-infrared plasmonic gold nanoparticles (AuNPs), possessing both photoacoustic (PA) and photothermal (PT) properties. The template for the plasmonic AuNP assembly is a bioconjugate between short double-strand DNA (sh-dsDNA) and human methyl binding domain protein 1 (MBD1). MBD1 binds to methylated cytosine-guanine dinucleotides (mCGs) within the sequence of sh-dsDNA. Hexahistidine peptides on the engineered MBD1 function as a nucleation site for AuNP synthesis, allowing the construction of hybrid conjugates, sh-dsDNA-MBD1-AuNPs (named DMAs). By varying the length of sh-dsDNA backbone and the spacer between two adjacent mCGs, we synthesized three different DMAs (DMA_5mCG, DMA_9mCG, and DMA_21mCG), among which DMA_21mCG exhibited a comparable photothermal and surprisingly a higher photoacoustic signals, compared to a plasmonic gold nanorod. Further, epidermal growth factor receptor I (EGFR)-binding peptides are genetically attached to the MBD1 of DMA_21mCG, enabling its efficient endocytosis into EGFR-overexpressing cancer cells. Notably, the denaturation of MBD1 disassembled the DMA and accordingly released the individual small AuNPs (<5 nm) that can be easily cleared from the body through renal excretion without causing accumulation/toxicity problems. This DMA-based novel approach offers a promising platform for targeted cancer theragnosis based on simultaneous PA imaging and PT therapy.