Savka I. Stoeva

Nanoparticle-based bio-barcode assay redefines “undetectable” PSA and biochemical recurrence after radical prostatectomy

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 bio-barcode PSA assay is ≈300 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.

A microfluidic detection system based upon a surface immobilized biobarcode assay

The biobarcode assay (BCA) is capable of achieving low detection limits and high specificity for both protein and DNA targets. The realization of a BCA in a microfluidic format presents unique opportunities and challenges. In this work, we describe a modified form of the BCA called the surface immobilized biobarcode assay (SI-BCA). The SI-BCA employs microchannel walls functionalized with antibodies that bind with the intended targets. Compared with the conventional BCA, it reduces the system complexity and results in shortened process time, which is attributed to significantly reduced diffusion times in the micro-scale channels. Raw serum samples, without any pretreatment, were evaluated with this technique. Prostate specific antigen in the samples was detected at concentrations ranging from 40 pM to 40 fM. The detection limit of the assay using buffer samples is 10 fM. The entire assay, from sample injection to final data analysis was completed in 80 min.

Nanocrystal Superlattices of Copper, Silver and Gold, by Nanomachining

Synthesis of metallic nanoparticles has captured the attention of scientists for decades, especially for their application in the area of catalysis, but more recently due to their unusual properties, different from those of the atomic or bulk metal. In addition, ordered structures of metallic nanoparticles display properties that lie between those of the isolated particles and the bulk material. Nanoparticles can act as building blocks to form well-organized structures, known as nanocrystal superlattices (NCSL). A narrow particle size distribution is required to obtain long-range superlattice ordering. The collective properties of metallic NCSL can be engineered by controlling the particle size and the type of ligand used to stabilize the colloidal system. The most widely studied metallic systems have been the ones prepared using gold nanoparticles [1,2,3], but there are other studies where silver [4,5,6,7], and cobalt [8] have been used to prepare NCSL. In this paper, we present for the first time the synthesis of NCSL by selfassembly of thiol stabilized copper nanoparticles, which have been prepared using the solvated metal atom dispersion (SMAD) method. The main advantage of the SMAD technique is that it allows us to prepare large quantities of the metal colloid, free of impurities. This is in great contrast to other techniques such as chemical reduction. A novel method discovered in our laboratories [9,10,11], called “digestive ripening” (i.e. allowing sufficient time and temperature (usually at the solvent’s boiling point) to attain a structural equilibrium.), has been used to attain a narrow particle size distribution. The same procedure as described here has previously been used to prepare NCSL from gold and silver colloids. Herein, it is shown to be applicable for copper as well.

Nanocrystal superlattice imaging by atomic force microscopy

Applicability of Atomic Force Microscopy (AFM) for structural characterization of nanocrystal superlattices is demonstrated on high-resolution imaging of superlattices formed by thiol stabilized gold nanoparticles on carbon coated and hydrophobic supports. Thin (<1nm) uniform coating of the samples with metal film before imaging was found to eliminate the undesirable effects of tip-sample interaction. Size and interparticle spacing are in excellent agreement with transmission electron microscopy results. AFM can be used as a complementary technique for nanocrystal superlattice structural characterization providing possibilities for crystal growth investigation on a variety of supports of practical interest and high resolution of the surface structure of superlattice structures.