Fractionating Polymer Microspheres as Highly Accurate Density Standards

This paper describes a method of isolating small, highly accurate density-standard beads and characterizing their densities using accurate and experimentally traceable techniques. Density standards have a variety of applications, including the characterization of density gradients, which are used to separate objects in a variety of fields. Glass density-standard beads can be very accurate (±0.0001 g cm^–3) but are too large (3–7 mm in diameter) for many applications. When smaller density standards are needed, commercial polymer microspheres are often used. These microspheres have standard deviations in density ranging from 0.006 to 0.021 g cm^–3; these distributions in density make these microspheres impractical for applications demanding small steps in density. In this paper, commercial microspheres are fractionated using aqueous multiphase systems (AMPS), aqueous mixture of polymers and salts that spontaneously separate into phases having molecularly sharp steps in density, to isolate microspheres having much narrower distributions in density (standard deviations from 0.0003 to 0.0008 g cm^–3) than the original microspheres. By reducing the heterogeneity in densities, this method reduces the uncertainty in the density of any specific bead and, therefore, improves the accuracy within the limits of the calibration standards used to characterize the distributions in density

Separation of Nanoparticles in Aqueous Multiphase Systems through Centrifugation

This paper demonstrates the use of aqueous multiphase systems (MuPSs) as media for rate-zonal centrifugation to separate nanoparticles of different shapes and sizes. The properties of MuPSs do not change with time or during centrifugation; this stability facilitates sample collection after separation. A three-phase system demonstrates the separation of the reaction products (nanorods, nanospheres, and large particles) of a synthesis of gold nanorods, and enriches the nanorods from 48 to 99% in less than ten minutes using a benchtop centrifuge

Aqueous Multiphase Systems of Polymers and Surfactants Provide Self-Assembling Step-Gradients in Density

This Communication demonstrates the generation of over 300 phase-separated systemsranging from two to six phasesfrom mixtures of aqueous solutions of polymers and surfactants. These aqueous multiphase systems (MuPSs) form self-assembling, thermodynamically stable step-gradients in density using a common solvent, water. The steps in density between phases of a MuPS can be very small (Δρ ≈ 0.001 g/cm³), do not change over time, and can be tuned by the addition of co-solutes. We use two sets of similar objects, glass beads and pellets of different formulations of Nylon, to demonstrate the ability of MuPSs to separate mixtures of objects by differences in density. The stable interfaces between phases facilitate the convenient collection of species after separation. These results suggest that the stable, sharp step-gradients in density provided by MuPSs can enable new classes of fractionations and separations based on density

Schematic of the density-based tests to identify SCD.

<p>Both versions of the SCD-AMPS are designed to separate dense red blood cells present in SCD from whole blood. Blood passes through the phases—top (T) and bottom (B) for SCD-AMPS-2 and top (T), middle (M), and bottom (B) for SCD-AMPS-3—upon centrifugation. If sickled cells are present, they collect at the interface between the bottom phase and the seal (<i>B/S</i>), and provide a visual readout for the presence of SCD. In SCD-AMPS-3, the additional phase allows the discrimination of Hb SS from Hb SC by evaluating the distribution of red cells at the upper interfaces (between the top and middle phases (<i>T/M</i>) and the middle and bottom phases (<i>M/B</i>).</p

Tabulation of Results of SCD-AMPS Tests Compared to Reference Test Results by Hemoglobin Electrophoresis.

<p>*Samples found to have>50% Hb S but non-zero levels of Hb A, potentially a result of Hb S with β-thalassemia or a transfused Hb SS subject.</p><p>Tabulation of Results of SCD-AMPS Tests Compared to Reference Test Results by Hemoglobin Electrophoresis.</p

Equipment for the SCD-AMPS rapid test.

<p>All the equipment necessary to run the rapid test in a rural clinic fits inside a backpack and were evaluated at rural health centers in Zambia.</p

Inclusion and Exclusion Criteria for Study.

<p>Inclusion and Exclusion Criteria for Study.</p

Basic Characteristics of the Study Population.

<p>Basic Characteristics of the Study Population.</p

The sensitivity and specificity of SCD-AMPS as a function of the amount of time between collecting samples and running tests.

<p>The specificity shows a decline over each 24 hour increment, with a significant decline over 48 hours (p-value <0.0005). The sensitivity increased between the first and second time interval, but then decreased between the second and third interval (p-values <0.01). The sample size used for each time interval is provided below each bar.</p

Barriers and potential solutions to advancing POC diagnostics research.

<p>Barriers and potential solutions to advancing POC diagnostics research.</p