We report the development of a previously undescribed gold nanoparticle bio-barcode assay probe for the detection of prostate specific antigen (PSA) at 330 fg/mL, automation of the assay, and the results of a clinical pilot study designed to assess the ability of the assay to detect PSA in the serum of 18 men who have undergone radical prostatectomy for prostate cancer. Due to a lack of sensitivity, available PSA immunoassays are often not capable of detecting PSA in the serum of men after radical prostatectomy. This new biobarcode PSA assay is Ϸ300 times more sensitive than commercial immunoassays. Significantly, with the barcode assay, every patient in this cohort had a measurable serum PSA level after radical prostatectomy. Patients were separated into categories based on PSA levels as a function of time. One group of patients showed low levels of PSA with no significant increase with time and did not recur. Others showed, at some point postprostatectomy, rising PSA levels. The majority recurred. Therefore, this new ultrasensitive assay points to significant possible outcomes: (i) The ability to tell patients, who have undetectable PSA levels with conventional assays, but detectable and nonrising levels with the barcode assay, that their cancer will not recur. (ii) The ability to assign recurrence earlier because of the ability to measure increasing levels of PSA before conventional tools can make such assignments. (iii) The ability to use PSA levels that are not detectable with conventional assays to follow the response of patients to adjuvant or salvage therapies.carcinoma of prostate ͉ prostate specific antigen

We report the synthesis of high density lipoprotein (HDL) bio-mimetic nanoparticles capable of binding cholesterol. These structures use a gold nanoparticle core to template the assembly of a mixed phospholipid layer and the adsorption of apolipoprotein A-I. These synthesized structures have the general size and surface composition of natural HDL, and importantly, bind free cholesterol (K d = 4 nM). The determination of the K d for these particles, with respect to cholesterol complexation, provides a key starting and comparison point for measuring and evaluating the properties of subsequently developed synthetic versions of HDL.High density lipoprotein (HDL) is a dynamic serum nanostructure protective against the development of atherosclerosis and resultant illnesses such as heart disease and stroke.1 Increasing circulating serum HDL levels provides a promising therapeutic approach to preventing and, potentially, reversing atherosclerosis by augmenting reverse cholesterol transport.2 -4 However, a facile route to synthetic HDL remains a challenge, as methods to control and mimic the size, surface chemistry, and activity of HDL in vitro diagnostic probes.9 -11 Herein, we report a new Au NP core-shell structure, where the Au NP core serves as a size-and shape-controllable scaffold 12 for constructing an HDL-like particle from phospholipids and apolipoprotein A-I (APOA1). Importantly, the proof-ofconcept HDL-Au NP structure we report is designed to be within the size range of HDL and to mimic the general surface composition of HDL. Furthermore, we demonstrate that, like HDL, HDL-Au NPs are capable of binding cholesterol.In a typical synthesis, an aqueous suspension of citrate-stabilized gold nanoparticles (5 ± 0.75 nm) is mixed with an aqueous solution of purified APOA1 and stirred overnight (Scheme 1).APOA1, comprised of 10 amphipathic alpha helices each with a hydrophobic domain and a negatively charged hydrophilic domain, is the main protein component of HDL and defines the structure and physiology of HDL in vivo. [13][14][15][16] Next, a 1:1 solution of disulfidefunctionalized lipid, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[3-(2-pyridyldithio)propionate], and amine functionalized lipid, 1-2-dipalmitoyl-sn-glycero-3-phosphocholine, was mixed in CHCl 3 and added to the aqueous suspension of particles in 100-fold excess with respect to the Au NPs. While several ratios were tried, these ratios were found to give loadings of lipid and protein similar to that of natural HDL (vide infra). The disulfide lipid was selected since the disulfide functionality allows for chemisorption to the surface of the Au NP. The amine-modified lipid is a naturally occurring phospholipid known to electrostatically and hydrophobically associate with APOA1. [13][14][15][16] This addition results in a two-phase mixture. Upon gradual heating, CHCl 3 is evaporated and the lipids are transferred to the aqueous phase containing the dispersed Au NPs with APOA1. Note that if the disulfide lipid is added alone and without pri...

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