In recent years, there has been considerable interest and research activity in using gold nanoparticle materials for biomedical applications including biomolecular detection, bioimaging, drug delivery, and photothermal therapy. In order to apply gold nanoparticles in the real biological world, we need to have a better understanding of the potential interactions between gold nanoparticle materials and biomolecules in vivo and in vitro. Here, we report the use of dynamic light scattering (DLS) for gold nanorods characterization and nanorod-protein interaction study. In the size distribution diagram, gold nanorods with certain aspect ratios exhibit two size distribution peaks, one with an average hydrodynamic diameter at 5-7 nm, and one at 70-80 nm. The small size peak is attributed to the rotational diffusion of the nanorods instead of an actual dimension of the nanorods. When proteins are adsorbed to the gold nanorods, the average particle size of the nanorods increases and the rotational diffusion-related size distribution peak also changes dramatically. We examined the interaction between four different proteins, bovine serum albumin, human serum albumin, immunoglobulin G, and immunoglobulin A (IgA) with four gold nanorods that have the same diameter but different aspect ratios. From this study, we found that protein adsorption to gold nanorods is strongly dependent on the aspect ratio of the nanorods, and varies significantly from protein to protein. The two serum albumin proteins caused nanorod aggregation upon interaction with the nanorods, while the two immunoglobulin proteins formed a stable protein corona on the nanorod surface without causing significant nanorod aggregation. This study demonstrates that DLS is a valuable tool for nanorod characterization. It reveals information complementary to molecular spectroscopic techniques on gold nanorod-protein interactions.

When citrate ligands-capped gold nanoparticles are mixed with blood sera, a protein corona is formed on the nanoparticle surface due to the adsorption of various proteins in the blood to the nanoparticles. Using a two-step gold nanoparticle-enabled dynamic light scattering assay, we discovered that the amount of human immunoglobulin G (IgG) in the gold nanoparticle protein corona is increased in prostate cancer patients compared to noncancer controls. Two pilot studies conducted on blood serum samples collected at Florida Hospital and obtained from Prostate Cancer Biorespository Network (PCBN) revealed that the test has a 90-95% specificity and 50% sensitivity in detecting early stage prostate cancer, representing a significant improvement over the current PSA test. The increased amount of human IgG found in the protein corona is believed to be associated with the autoantibodies produced in cancer patients as part of the immunodefense against tumor. Proteomic analysis of the nanoparticle protein corona revealed molecular profile differences between cancer and noncancer serum samples. Autoantibodies and natural antibodies produced in cancer patients in response to tumorigenesis have been found and detected in the blood of many cancer types. The test may be applicable for early detection and risk assessment of a broad spectrum of cancer. This new blood test is simple, low cost, requires only a few drops of blood sample, and the results are obtained within minutes. The test is well suited for screening purpose. More extensive studies are being conducted to further evaluate and validate the clinical potential of the new test.

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