A Markedly Improved Synthetic Approach for the Preparation of Multifunctional Au-DNA Nanoparticle Conjugates Modified with Optical and MR Imaging Probes

Abstract

We describe a new, and vastly superior approach for labeling spherical nucleic acid conjugates (SNAs) with diagnostic probes. SNAs have been shown to provide the unique ability to traverse the cell membrane and deliver surface conjugated DNA into cells while preserving the DNA from nuclease degradation. Our previous work on preparing diagnostically labeled SNAs was labor intensive, relatively low yielding, and costly. Here, we describe a straightforward and facile preparation for labeling SNAs with optical and MR imaging probes with significantly improved physical properties. The synthesis of Gd(III) labeled DNA Au nanoparticle conjugates is achieved by sequential conjugation of 3′-thiol-modified oligonucleotides and cofunctionalization of the particle surface with the subsequent addition of 1,2 diothiolate modified chelates of Gd(III) (abbreviated: DNA-GdIII@AuNP). This new generation of SNA conjugates has a 2-fold increase of DNA labeling and a 1.4-fold increase in Gd(III) loading compared to published constructs. Furthermore, the relaxivity (r1) is observed to increase 4.5-fold compared to the molecular dithiolane-Gd(III) complex, and 1.4-fold increase relative to previous particle constructs where the Gd(III) complexes were conjugated to the oligonucleotides rather than directly to the Au particle. Importantly, this simplified approach (2 steps) exploits the advantages of previous Gd(III) labeled SNA platforms; however, this new approach is scalable and eliminates modification of DNA for attaching the contrast agent, and the particles exhibit improved cell labeling.

Recent Development of Gold Nanoparticles as Contrast Agents for Cancer Diagnosis

“…Gd(III) chelates have been conjugated to AuNPs, with a surprising relaxivity improvement, and intracellular and intra-tumor retention [ 82 , 83 ]. Studies by Meade and co-workers have conjugated 1,2 diothiolate modified chelates of Gd(III) to AuNPs surface and improved the relaxivity ( r 1 ) up to 4.5-fold compared to the molecular dithiolane-Gd(III) complex [ 84 , 85 ]. The dramatic r 1 relaxivity increase is because of the increased local Gd(III) concentration per particle [ 86 ].…”

Gold nanomaterials functionalised with gadolinium chelates and their application in multimodal imaging and therapy

“…More recently, cyclic disulfides, which form dithiolates on attachment to the surface ( Fig. 3G-I), [26][27][28] and dithiocarbamates ( Fig. 3J) [29][30][31] have also been employed, as they provide a more secure two-site attachment.…”

“…45 DNA strands, in particular, have enabled hundreds of gadolinium chelates to be incorporated into each gold nanoparticle assembly. 26,[46][47][48] While the presence of many gadolinium units is often an advantage, it is the overall relaxivity that remains the broader goal. Through the rational design of the nanomaterial surface units and chelates, dramatic increases can be made in the relaxivity of individual gadolinium chelates, leading to improved contrast enhancement.…”

DNA-functionalized Gold Nanorods for Targeted Triple-modal Optical Imaging and Photothermal Therapy of Triple-negative Breast Cancer

“…19 Subsequent functionalization of DNA strands with fluorophores and MRI active moieties augment additional imaging modalities. 17,[20][21] Recently, a dual-modality nanoparticle with SERS and fluorescence imaging capabilities was developed using DNA-based optimization strategy and applied for cancer imaging and therapy. 22 Herein, we have developed a generalized fabrication strategy of AuNP-based triple modal nanoprobes (TMNPs) with three complementary optical modalities: optoacoustic, fluorescence, and surface-enhanced Raman Scattering (SERS) with complementary strengths.…”

“…19 Subsequent functionalization of DNA strands with fluorophores and MRI active moieties augment additional imaging modalities. 17, 20-21 Recently, a dual-modality nanoparticle with SERS and fluorescence imaging capabilities was developed using DNA-based optimization strategy and applied for cancer imaging and therapy. 22…”