(652f) Selective Capture and Release of Biomolecules in Complex Solutions Using Gold Nanoparticles and Electromagnetic Fields

Functionalized gold nanoparticles have been studied extensively for various biological applications including drug delivery to cells and tissues, tumor therapy, and biosensing in complex biological systems. The most commonly studied particle shapes are spheres and rods of varying diameters and aspect ratios. In comparison to gold nanospheres, gold nanorods are particularly advantageous because they offer two-dimensions for tuning particle properties - the length of the nanorods determine the longitudinal surface plasmon resonance (LSPR), and the width of the nanorods determine the transverse or lateral surface plasmon resonance(TSPR). The former is particularly interesting for engineering complex functionalities into gold nanoparticles. One such example is the photothermal ablation effect studied extensively in tumor therapy. When gold nanorods are exposed to electromagnetic waves matching LSPR, the incident energy is converted into localized heat which can be deployed for killing tumor cells. We have extended the basic physics of this light-matter interaction to develop sophisticated biosensing approaches for detection of biomolecules in complex biological fluids. Our objective in this study is to demonstrate (i) the ability of peptide-functionalized gold nanorods to selectively bind to specific biomolecules such as proteins, enzymes and antibodies in a complex mixture, and (ii) the ability to trigger release of the biomolecules, on demand, under the influence of an electromagnetic field. To achieve this objective, we designed nanorods of aspect ratios varying from 2-4 that were coupled to 3 different cysteine-terminated peptides via the gold-thiol bond. The peptides employed in this study were chosen for their high affinity and high specificity of binding to three different biomolecules of varying size, charge, hydrophobicity and tertiary structures â?? an IgG antibody, human cardiac troponin I, and streptavidin. Fetal bovine serum (FBS) was used as a background for the mixture of these proteins to simulate a complex biological sample. Peptide-functionalized nanoparticles were incubated simultaneously in a mixture of the target proteins, each labeled with a different fluorophore, in FBS and were washed and centrifuged to remove unbound material. On exposure to light of specific wavelengths from 550 nm, 800 nm and 1100 nm, we demonstrate the selective release of the target biomolecules in a wavelength-dependent fashion. The amount of material released from the nanorods was quantified using UV spectrophotometry. Selectivity was quantified as the ratio of the desired biomolecule to background material released from the nanorods. The amount of material released was a strong function of the incident wavelength, intensity and time of exposure. Capture and release capabilities in FBS were compared with similar measurements performed in a low complexity background containing bovine serum albumin (0%, 1% and 10% wt/vol) in phosphate buffered saline. The results from these studies can be further extended for the detection and quantification of a large number of proteins in biological samples of clinical relevance such as human serum. These studies are also promising for the detection of protein variants for developing analytical techniques in downstream bioprocessing applications.