Detection of membrane-bound and soluble antigens by magnetic levitation

Advanced density-based methods for the characterization of materials, binding events, and kinetics

Investigations of the densities of chemicals and materials bring valuable insights into the fundamental understanding of matter and processes. Recently, advanced density-based methods have been developed with wide measurement ranges (i.e. 0-23 g cm^-3), high resolutions (i.e. 10^-6 g cm^-3), compatibility with different types of samples and the requirement of extremely low volumes of sample (as low as a single cell). Certain methods, such as magnetic levitation, are inexpensive, portable and user-friendly. Advanced density-based methods are, therefore, beneficially used to obtain absolute density values, composition of mixtures, characteristics of binding events, and kinetics of chemical and biological processes. Herein, the principles and applications of magnetic levitation, acoustic levitation, electrodynamic balance, aqueous multiphase systems, and suspended microchannel resonators for materials science are discussed.

Pump-free microfluidic magnetic levitation approach for density-based cell characterization

Magnetic levitation (MagLev) provides a simple but promising method for density-based analysis and detection down to the individual cell level. However, each existing MagLev configuration for the single-cell density measurement, mainly consisting of a capillary (∼50 mm) placed between two magnets, yields a fairly low sample utilization because of no knowledge about the sample cells in the regions other than the limited microscope vision. Moreover, the quantitative analysis may be affected due to the unclearly defined measurement area, which is specifically associated with the uneven magnetization of magnets, cell size, degree of aggregation. In this work, we explore a pump-free microfluidic magnetic levitation approach for density-based cell characterization, enabling sensitive and effective cellular density measurement on small sample volumes. The microfluidic MagLev comprises a pump-free microfluidic chip placed between two ring magnets with like poles facing. With no external pumps, connectors or control facility, much smaller amounts of fluids (∼4 μL) could be driven automatically in the entire microchannel in 16 s. Based on the pump-free mechanism, unique density signatures of cells from different lineages (ARPE-19, HCT116, HeLa, HT1080, Huh7) are characterized by monitoring the levitation profiles. Furthermore, variation in density of A549 lung cancer cells subjected to a drug treatment are observed in our platform, allowing evaluation of the efficacy of the drug treatment at the individual cell level. Thereby, the proposed pump-free microfluidic MagLev platform, a low-cost, fully automatic and portable design for label-free density-based cell characterization, provides a universal detection tool that operates efficiently within small-volume environments.

Magnetic Levitation in Chemistry, Materials Science, and Biochemistry

All matter has density. The recorded uses of density to characterize matter date back to as early as ca. 250 BC, when Archimedes was believed to have solved "The Puzzle of The King's Crown" using density.^[1] Today, measurements of density are used to separate and characterize a range of materials (including cells and organisms), and their chemical and/or physical changes in time and space. This Review describes a density-based technique-magnetic levitation (which we call "MagLev" for simplicity)-developed and used to solve problems in the fields of chemistry, materials science, and biochemistry. MagLev has two principal characteristics-simplicity, and applicability to a wide range of materials-that make it useful for a number of applications (for example, characterization of materials, quality control of manufactured plastic parts, self-assembly of objects in 3D, separation of different types of biological cells, and bioanalyses). Its simplicity and breadth of applications also enable its use in low-resource settings (for example-in economically developing regions-in evaluating water/food quality, and in diagnosing disease).

A Novel Implementation of Magnetic Levitation to Quantify Leukocyte Size, Morphology, and Magnetic Properties to Identify Patients With Sepsis

BACKGROUND

We have developed a novel, easily implementable methodology using magnetic levitation to quantify circulating leukocyte size, morphology, and magnetic properties, which may help in rapid, bedside screening for sepsis.

OBJECTIVE

Our objectives were to describe our methodological approach to leukocyte assessment, and to perform a pilot investigation to test the ability of magnetic levitation to identify and quantify changes in leukocyte size, shape, density, and/or paramagnetic properties in healthy controls and septic patients.

METHODS

This prospective, observational cohort study was performed in a 56,000/y visit emergency department (ED) and affiliated outpatient phlebotomy laboratory. Inclusion criteria were admittance to the hospital with suspected or confirmed infection for the septic group, and we enrolled the controls from ED/outpatient patients without infection or acute illness. The bench-top experiments were performed using magnetic levitation to visualize the leukocytes. We primary sought to compare septic patients with noninfected controls and secondary to assess the association with sepsis severity. Our covariates were area, length, width, roundness, and standard deviation (SD) of levitation height. We used unpaired t test and area under the curve (AUC) for the assessment of accuracy in distinguishing between septic and control patients.

RESULTS

We enrolled 39 noninfected controls and 22 septic patients. Our analyses of septic patients compared with controls showed: mean cell area in pixels (px) 562 ± 111 vs. 410 ± 45, P < 0.0001, AUC = 0.89 (0.80-0.98); length (px), 29 ± 2.5 vs. 25 ± 1.9, P < 0.0001, AUC = 0.90 (0.83-0.98); and width (px), 27 ± 2.4 vs. 23 ± 1.5, P < 0.0001, AUC = 0.92 (0.84-0.99). Cell roundness: 2.1 ± 1.0 vs. 2.2 ± 1.2, P = 0.8, AUC = 0.51. SD of the levitation height (px) was 72 ± 25 vs. 47 ± 16, P < 0.001, AUC = 0.80 (0.67-0.93).

CONCLUSIONS

Septic patients had circulating leukocytes with especially increased size parameters, which distinguished sepsis from noninfected patients with promising high accuracy. This portal-device compatible technology shows promise as a potential bedside diagnostic.

Mapping the heterogeneity of protein corona by ex vivo magnetic levitation

In the past decade, we witnessed limited success in the clinical translation of therapeutic nanoparticles (NPs). One of the main reasons for this limited success is our poor understanding of the biological identity of NPs. Herein, we report magnetic levitation (MagLev) as a complementary analytical tool to investigate the homogeneity of the created protein corona (PC) coated NPs through an ex vivo model. Our results demonstrate that the MagLev system not only has the capacity to separate corona coated NPs, but also enables us to study the homogeneity/heterogeneity of the PC. Our findings suggest that current ex vivo isolation methods cause a heterogeneous coverage of PC profiles at the surface of NPs. The MagLev technique, therefore, would be instrumental in identifying and separating fully PC coated NPs which, in turn, enables us to achieve more accurate information on protein corona composition. Ultimately, we believe that the MagLev technique can be used for the fast screening of the homogeneity of corona coated NPs before quantitative analysis of the corona profile/composition, hence definitely improving our fundamental understanding of nano-bio interfaces.

Shape oscillations of single blood drops: applications to human blood and sickle cell disease

Sickle cell disease (SCD) is an inherited blood disorder associated with severe anemia, vessel occlusion, poor oxygen transport and organ failure. The presence of stiff and often sickle-shaped red blood cells is the hallmark of SCD and is believed to contribute to impaired blood rheology and organ damage. Most existing measurement techniques of blood and red blood cell physical properties require sample contact and/or large sample volume, which is problematic for pediatric patients. Acoustic levitation allows rheological measurements in a single drop of blood, simultaneously eliminating the need for both contact containment and manipulation of samples. The technique shows that the shape oscillation of blood drops is able to assess blood viscosity in normal and SCD blood and demonstrates an abnormally increased viscosity in SCD when compared with normal controls. Furthermore, the technique is sensitive enough to detect viscosity changes induced by hydroxyurea treatment, and their dependence on the total fetal hemoglobin content of the sample. Thus this technique may hold promise as a monitoring tool for assessing changes in blood rheology in sickle cell and other hematological diseases.