Bacteria sorting by field-flow fractionation. Application to whole-cell Escherichia coil vaccine strains

Comparison of a thickness-tapered channel in flow field-flow fractionation with a conventional channel with flow rate programming

The thickness-tapered channel structure in flow field-flow fractionation (FlFFF), recently introduced by constructing a channel with a linear decrease in thickness along its length, demonstrated effectiveness in steric/hyperlayer separation of supramicron particles with improvements in separation speed, elution recovery, and an expanded dynamic size range of separation. In this study, we conducted a comparative analysis of the performance between the impact of field (or crossflow rate) programming or outflow rate programming for the separation of polystyrene latex standards (50 ∼ 800 nm) with a conventional channel having uniform thickness and a thickness-tapered channel without programming. Outlet flow rate and crossflow rate conditions were also varied. Although the particle size resolution of the tapered channel does not surpass that of field programming in uniform thickness channel, it achieves higher-speed separation without a significant loss of resolution and without the need for a complex flow controller system even at a low outflow rate condition. Furthermore, it yielded an improved resolution for particles close to the steric transition regime (400 ∼ 600 nm) in the normal mode of separation. Due to the continuous increase in mean flow velocity down the channel, the tapered channel exhibits flexibility in separating submicron-sized particles at high crossflow rate conditions or low outflow rate conditions, of which the latter can be advantageous when coupled with mass spectrometry in a miniaturized setup.

Field-flow fractionation - an excellent tool for fractionation, isolation and/or purification of biomacromolecules

Field-flow fractionation (FFF) with its several variants, has developed into a mature methodology. The scope of the FFF investigations has expanded, covering both a wide range of basic studies and especially a wide range of analytical applications. Special attention of this review is given to the achievements of FFF with reference to recent applications in the fractionation, isolation, and purification of biomacromolecules, and from which especially those of (in alphabetical order) bacteria, cells, extracellular vesicles, liposomes, lipoproteins, nucleic acids, and viruses and virus-like particles. In evaluating the major approaches and trends demonstrated since 2012, the most significant biomacromolecule applications are compiled in tables. It is also evident that asymmetrical flow field-flow fractionation is by far the most dominant technique in the studies. The industry has also shown current interest in FFF and adopted it in some sophisticated fields. FFF, in combination with appropriate detectors, handles biomacromolecules in open channel in a gentle way due to the lack of shear forces and unwanted interactions caused by the stationary phase present in chromatography. In addition, in isolation and purification of biomacromolecules quite high yields can be achieved under optimal conditions.

Determination of Pathogens by Electrophoretic and Spectrometric Techniques

In modern medical diagnostics, where analytical chemistry plays a key role, fast and accurate identification of pathogens is becoming increasingly important. Infectious diseases pose a growing threat to public health due to population growth, international air travel, bacterial resistance to antibiotics, and other factors. For instance, the detection of SARS-CoV-2 in patient samples is a key tool to monitor the spread of the disease. While there are several techniques for identifying pathogens by their genetic code, most of these methods are too expensive or slow to effectively analyze clinical and environmental samples that may contain hundreds or even thousands of different microbes. Standard approaches (e.g., culture media and biochemical assays) are known to be very time- and labor-intensive. The purpose of this review paper is to highlight the problems associated with the analysis and identification of pathogens that cause many serious infections. Special attention was paid to the description of mechanisms and the explanation of the phenomena and processes occurring on the surface of pathogens as biocolloids (charge distribution). This review also highlights the importance of electromigration techniques and demonstrates their potential for pathogen pre-separation and fractionation and demonstrates the use of spectrometric methods, such as MALDI-TOF MS, for their detection and identification.

Flow Field-Flow Fractionation with a Thickness-Tapered Channel

This study introduces the thickness-tapered channel design for flow field-flow fractionation (FlFFF) for the first time. In this design, the channel thickness linearly decreases along the channel axis such that the flow velocity increases down the channel. Channel thickness is an important variable for controlling retention time and resolution in field-flow fractionation. Especially, in the steric/hyperlayer mode of FlFFF, in which particles (>1 μm) migrate at elevated heights above the channel wall owing to hydrodynamic lift forces, the migration of long-retaining smaller-sized particles can be enhanced in a relatively thin channel or by increasing the migration flow rate; however, an upper size limit that can be resolved is simultaneously sacrificed. A thickness-tapered channel was constructed without a channel spacer by carving the surface of a channel block such that the channel inlet was deeper than the outlet (w = 400 → 200 μm). The performance of a thickness-tapered channel was evaluated using polystyrene standards and compared to that of a channel of uniform thickness (w = 300 μm) with a similar effective channel volume in terms of sample recovery, dynamic size range of separation, and steric transition under different flow rate conditions. The thickness-tapered channel can be an alternative to maintain the resolving power for particles with an upper large-diameter limit, faster separation of particles with a lower limit, and higher elution recovery without implementing the additional field-programming option.

Raman Spectroscopy-A Novel Method for Identification and Characterization of Microbes on a Single-Cell Level in Clinical Settings

Rapid and accurate identification of pathogens causing infections is one of the biggest challenges in medicine. Timely identification of causative agents and their antimicrobial resistance profile can significantly improve the management of infection, lower costs for healthcare, mitigate ever-growing antimicrobial resistance and in many cases, save lives. Raman spectroscopy was shown to be a useful-quick, non-invasive, and non-destructive -tool for identifying microbes from solid and liquid media. Modifications of Raman spectroscopy and/or pretreatment of samples allow single-cell analyses and identification of microbes from various samples. It was shown that those non-culture-based approaches could also detect antimicrobial resistance. Moreover, recent studies suggest that a combination of Raman spectroscopy with optical tweezers has the potential to identify microbes directly from human body fluids. This review aims to summarize recent advances in non-culture-based approaches of identification of microbes and their virulence factors, including antimicrobial resistance, using methods based on Raman spectroscopy in the context of possible use in the future point-of-care diagnostic process.

A New Predictive Technology for Perinatal Stem Cell Isolation Suited for Cell Therapy Approaches

The use of stem cells for regenerative applications and immunomodulatory effect is increasing. Amniotic epithelial cells (AECs) possess embryonic-like proliferation ability and multipotent differentiation potential. Despite the simple isolation procedure, inter-individual variability and different isolation steps can cause differences in isolation yield and cell proliferation ability, compromising reproducibility observations among centers and further applications. We investigated the use of a new technology as a diagnostic tool for quality control on stem cell isolation. The instrument label-free separates cells based on their physical characteristics and, thanks to a micro-camera, generates a live fractogram, the fingerprint of the sample. Eight amniotic membranes were processed by trypsin enzymatic treatment and immediately analysed. Two types of profile were generated: a monomodal and a bimodal curve. The first one represented the unsuccessful isolation with all recovered cell not attaching to the plate; while for the second type, the isolation process was successful, but we discovered that only cells in the second peak were alive and resulted adherent. We optimized a Quality Control (QC) method to define the success of AEC isolation using the fractogram generated. This predictive outcome is an interesting tool for laboratories and cell banks that isolate and cryopreserve fetal annex stem cells for research and future clinical applications.

Analysis of lipoprotein-specific lipids in patients with acute coronary syndrome by asymmetrical flow field-flow fractionation and nanoflow liquid chromatography-tandem mass spectrometry

A comprehensive lipid analysis was performed at the plasma lipoprotein level in patients with acute coronary syndrome (ACS) and stable coronary artery disease (CAD). Because the lipids in lipoproteins are related to the pathology of the cardiovascular system, lipoprotein-specific lipid analysis can be useful for understanding the mechanism of lipid-associated cardiovascular diseases. Lipoproteins were size-sorted into high density lipoproteins (HDL) and low density lipoproteins (LDL) using asymmetrical flow field-flow fractionation, then lipids of each lipoprotein were analysed using nanoflow ultrahigh performance liquid chromatography-electrospray ionization-tandem mass spectrometry. A total of 365 lipids were structurally identified and quantified by selected reaction monitoring method. Two high abundance lysophosphatidylcholines (16:0 and 18:0) were significantly increased only in the HDL of the ACS group (vs. the stable CAD group). Phosphatidylethanolamines (38:5 and 40:5) significantly increased in ACS by >2-fold in both lipoproteins. (18:0, 22:6)-diacylglycerol increased in ACS by 3.5-fold only in LDL; however, most high abundance triacylglycerols decreased 2-fold in both lipoproteins. The present study revealed the usefulness of lipoprotein-specific analysis of lipids in distinguishing ACS from stable CAD, and the selected lipids analysed in this study may be useful in the development of lipid markers for the early detection of ACS.

Enhancing size based size separation through vertical focus microfluidics using secondary flow in a ridged microchannel

High throughput size based separation and sorting of bioparticles and cells is critical to a variety of biomedical processing steps for medical diagnostics and pharmaceutical purification. Improving microfluidic size-based particle/cell sorting is a challenge to better address the need for generating more homogeneous subpopulations for study and use. We propose a novel advance to microfluidic sorting devices that uses three-dimensional focusing of the sample to optimally position particles to amplify the size-dependent differences in trajectories caused by differential secondary flows. The result is an increase in the purity of small particles by 35- fold and large particles by 8-fold in comparison to unfocused flow. Our simulated and experimental data reveal for the first time that positioning particles in three-dimensional space can be used to better leverage the differential lateral movement of particles with different sizes as they flow in microchannel with transverse secondary flows. The focusing approach may also be useful to improve positioning of particles with inertial channels with multiple equilibrium positions. This technique performs continuous-flow, high throughput size based sorting of millions of particles and cells in a minute without any pre and post-processing. We have also demonstrated improved enrichment and recovery of white blood cells from human blood.

A new analytical platform based on field-flow fractionation and olfactory sensor to improve the detection of viable and non-viable bacteria in food

An integrated sensing system is presented for the first time, where a metal oxide semiconductor sensor-based electronic olfactory system (MOS array), employed for pathogen bacteria identification based on their volatile organic compound (VOC) characterisation, is assisted by a preliminary separative technique based on gravitational field-flow fractionation (GrFFF). In the integrated system, a preliminary step using GrFFF fractionation of a complex sample provided bacteria-enriched fractions readily available for subsequent MOS array analysis. The MOS array signals were then analysed employing a chemometric approach using principal components analysis (PCA) for a first-data exploration, followed by linear discriminant analysis (LDA) as a classification tool, using the PCA scores as input variables. The ability of the GrFFF-MOS system to distinguish between viable and non-viable cells of the same strain was demonstrated for the first time, yielding 100 % ability of correct prediction. The integrated system was also applied as a proof of concept for multianalyte purposes, for the detection of two bacterial strains (Escherichia coli O157:H7 and Yersinia enterocolitica) simultaneously present in artificially contaminated milk samples, obtaining a 100 % ability of correct prediction. Acquired results show that GrFFF band slicing before MOS array analysis can significantly increase reliability and reproducibility of pathogen bacteria identification based on their VOC production, simplifying the analytical procedure and largely eliminating sample matrix effects. The developed GrFFF-MOS integrated system can be considered a simple straightforward approach for pathogen bacteria identification directly from their food matrix. Graphical abstract An integrated sensing system is presented for pathogen bacteria identification in food, in which field-flow fractionation is exploited to prepare enriched cell fractions prior to their analysis by electronic olfactory system analysis.

Impact of carrier fluid composition on recovery of nanoparticles and proteins in flow field flow fractionation

Flow field flow fractionation (F4) is an invaluable separation tool for large analytes, including nanoparticles and biomolecule complexes. However, sample loss due to analyte-channel membrane interaction limits extensive usage of F4 at present, which could be strongly affected by the carrier fluid composition. This work studied the impacts of carrier fluid (CF) composition on nanoparticle (NP) recovery in F4, with focus on high ionic strength conditions. Successful analysis of NPs in a biomolecules-friendly environment could expand the applicability of F4 to the developing field of nanobiotechnology. Recovery of the unfunctionalized polystyrene NPs of 199, 102, and 45 nm in CFs with various pH (6.2, 7.4 and 8.2), increasing ionic strength (0-0.1M), and different types of co- and counter-ions, were investigated. Additionally, elution of the 85 nm carboxylate NPs and two proteins, human serum albumin (HSA) and immunoglobulin (IgG), at high ionic strengths (0-0.15M) was investigated. Our results suggested that (1) electrostatic repulsion between the negatively charged NPs and the regenerated cellulose membrane was the main force to avoid particle adsorption on the membrane; (2) larger particles experienced higher attractive force and thus were influenced more by variation in CF composition; and (3) buffers containing weak anions or NPs with weak anion as the surface functional groups provided higher tolerance to the increase in ionic strength, owing to more anions being trapped inside the NP porous structure. Protein adsorption onto the membrane was also briefly investigated in salted CFs, using HSA and IgG. We believe our findings could help to identify the basic carrier fluid composition for higher sample recovery in F4 analysis of nanoparticles in a protein-friendly environment, which will be useful for applying F4 in bioassays and in nanotoxicology studies.

Continuous hydrophoretic separation and sizing of microparticles using slanted obstacles in a microchannel

We report a microfluidic separation and sizing method of microparticles with hydrophoresis--the movement of suspended particles under the influence of a microstructure-induced pressure field. By exploiting slanted obstacles in a microchannel, we can generate a lateral pressure gradient so that microparticles can be deflected and arranged along the lateral flows induced by the gradient. Using such movements of particles, we completely separated polystyrene microbeads with 9 and 12 microm diameters. Also, we discriminated polystyrene microbeads with diameter differences of approximately 7.3%. Additionally, we measured the diameter of 10.4 microm beads with high coefficient of variation and compared the result with a conventional laser diffraction method. The slanted obstacle as a microfluidic control element in a microchannel is analogous to the electric, magnetic, optical, or acoustic counterparts in that their function is to generate a field gradient. Since our method is based on intrinsic pressure fields, we could eliminate the need for external potential fields to induce the movement of particles. Therefore, our hydrophoretic method will offer a new opportunity for power-free and biocompatible particle control within integrated microfluidic devices.

Zeta-potential Analyses using Micro Electrical Field Flow Fractionation with Fluorescent Nanoparticles

Increasingly growing application of nanoparticles in biotechnology requires fast and accessible tools for their manipulation and for characterization of their colloidal properties. In this work we determine the zeta-potentials for polystyrene nanoparticles using micro electrical field flow fractionation (mu-EFFF) which is an efficient method for sorting of particles by size. The data obtained by mu-EFFF were compared to zeta potentials determined by standard capillary electrophoresis. For proof of concept, we used polystyrene nanoparticles of two different sizes, impregnated with two different fluorescent dyes. Fluorescent emission spectra were used to evaluate the particle separation in both systems. Using the theory of electrophoresis, we estimated the zeta-potentials as a function of size, dielectric permittivity, viscosity and electrophoretic mobility. The results obtained by the mu-EFFF technique were confirmed by the conventional capillary electrophoresis measurements. These results demonstrate the applicability of the mu-EFFF method not only for particle size separation but also as a simple and inexpensive tool for measurements of nanoparticles zeta potentials.

Micro-thermal field-flow fractionation of bacteria

The retention of Staphylococcus epidermidis bacteria cells, achieved with the use of micro-thermal field-flow fractionation and described in this paper, represents the first experimental proof that the separation and characterization of the bio-macromolecules and biological particles is possible by exploiting Ludwig-Soret effect of thermal diffusion. The experiments were carried out under gentle experimental conditions preventing the denaturation of the bacteria. Lift forces, appearing at high linear velocities of the carrier liquid, generated the focusing mechanism of the retention which resulted in high-speed and high-performance separation performed in less than 10 min.

Miniaturized asymmetrical flow field-flow fractionation: Application to biological vesicles

Asymmetrical flow field-flow fractionation (AFlFFF) has been carried out in a miniaturized channel by reducing the channel dimensions. Performance of the miniaturized AFlFFF (mAFlFFF) channel was evaluated with standard proteins and polystyrene latex spheres from nanometer to micrometer size. By reducing the channel dimension, proteins or particulate materials can be separated within a few minutes without a significant loss in resolution. The mAFlFFF channel was applied for the separation of exosomes harvested from immortalized human mesenchymal stem cell line. It shows a potential to fractionate exosome vesicles according to sizes which can be useful for proteomic studies in relation to immunotherapeutic applications.

Characterization of functionalized styrene–butadiene rubber by flow field-flow fractionation/light scattering in organic solvent

Flow field-flow fractionation (FlFFF) using an organic solvent as mobile phase has been effectively utilized for the separation and characterization of functionalized styrene-butadiene rubbers (SBR) that are polymerized and followed by coupling reaction in solution. Separation of broad molecular weight SBR was accomplished by an asymmetrical FlFFF channel in THF under field programming and the molecular weight distribution (MWD) of the SBR sample was determined by on-line measurement of light scattering. In this study, FlFFF has been utilized to characterize high-MW functionalized SBR from the low-MW non-functionalized molecules which were used for coupling reaction to produce high-MW functionalized SBRs, and to determine the coupling number of the functionalized SBRs depending on the type of the coupling reagents. The resulting MWD of the SBR samples prepared by the different coupling reagents (SnCl(4) and a polydimethylsiloxane compound) were compared.

Electrochemical response and separation in cyclic electric field-flow fractionation

Electric field-flow fractionation (EFFF) is a separation technique that couples a lateral electric field with axial Poiseuille flow to separate particles on the basis of size and/or mobility. In unidirectional EFFF, the field rapidly decreases in time due to charging of the double layer. The field strength could be increased by performing EFFF with cyclic electric fields. In cyclic electric field-flow fractionation (CEFFF), a periodic voltage, which can be either sinusoidal or square-wave, is applied in the lateral direction. In this paper, we measure the electrochemical response of CEFFF, i.e., the current-time response for a given time-dependent voltage and then utilize this electrochemical response in a transport model to predict separation. The CEFFF device studied here comprises two gold-coated glass plates separated by a spacer. The transient current profiles are measured for a step change and cyclic square-shaped voltage. The current profile is compared with the equivalent circuit model, and is fitted to a sum of two decaying exponentials. The dependence of the electrochemical response on voltage, frequency, channel thickness, and salt concentration is studied. Next, the electrochemical data are utilized in the convection-diffusion equation to develop a model for separation by CEFFF. The equations are solved by using a combination of analytical and numerical techniques to determine the mean velocity and the dispersion coefficient of molecules, and to determine the effect of various parameters on the separation efficiency of the EFFF device. Also, the model predictions are compared with experimental data available in the literature.

Field-flow fractionation of proteins, polysaccharides, synthetic polymers, and supramolecular assemblies

This review summarizes developments and applications of flow and thermal field-flow fractionation (FFF) in the areas of macromolecules and supramolecular assemblies. In the past 10 years, the use of these FFF techniques has extended beyond determining diffusion coefficients, hydrodynamic diameters, and molecular weights of standards. Complex samples as diverse as polysaccharides, prion particles, and block copolymers have been characterized and processes such as aggregation, stability, and infectivity have been monitored. The open channel design used in FFF makes it a gentle separation technique for high- and ultrahigh-molecular weight macromolecules, aggregates, and self-assembled complexes. Coupling FFF with other techniques such as multiangle light scattering and MS provides additional invaluable information about conformation, branching, and identity.

Different elution modes and field programming in gravitational field-flow fractionation: field programming using density and viscosity gradients

In previous papers, several approaches to programming of the resulting force field in GFFF were described and investigated. The experiments were dealing with flow-velocity and channel thickness, i.e. factors influencing hydrodynamic lift forces (HLF). The potential of density and viscosity of carrier liquid for field programming was predicted and demonstrated by preliminary experiments. This work is devoted to experimental verification of the influence of carrier liquid density and viscosity. Several carrier liquid density and simultaneously viscosity gradients using water-methanol mixtures are in this work implemented in the separation of a model silica mixture. Working with the water-methanol gradients, one is not able to separate the influence of density from the contribution of viscosity. However, we found experimental conditions to show the isolated effect of carrier liquid density (two water-methanol mixtures of equal viscosity differing in their densities). In order to demonstrate the isolated effect of viscosity, we implemented in this work a new system of (hydroxypropyl)methyl cellulose (HPMC) carrier liquids. Three different HPMC compositions enabled to vary the viscosity more than two times at almost constant density. With increasing carrier liquid viscosity, the focusing and elevating trend was clearly pronounced for 5 and 10 microm silica particles. By the isolated effect of increased viscosity, the centre of the 10 microm particle zone was elevated to the streamline at 16% of the channel height. These experiments have shown that the influence of carrier liquid viscosity on HLF should be taken into account even at higher levels above the channel bottom, i.e. beyond the near-wall region. Further, it is shown that higher value of carrier liquid viscosity improves the separation of the model mixture in terms of time and resolution.

Field-flow fractionation and biotechnology

The gentle separation mechanism has made field-flow fractionation particularly suited to samples of biotechnological interest, from proteins and nucleic acids to viruses, subcellular units and whole cells. Recent progress in field-flow fractionation technology, as well as the development of coupled techniques combining field-flow fractionation capabilities with the specificity and sensitivity of well-established analytical methods, opens up new biotechnological applications for field-flow fractionation. The most recent appealing applications include: sorting and fingerprinting of bacteria for whole-cell vaccine production; noninvasive and tagless sorting of immature and stem cells; separation of intact proteins and enzymes in top-down proteomics; and the development of flow-assisted, multianalyte immunoassays using nano- and micron-sized particles with immobilized biomolecules.

Biocompatible channels for field-flow fractionation of biological samples: correlation between surface composition and operating performance

Biocompatible methods capable of rapid purification and fractionation of analytes from complex natural matrices are increasingly in demand, particularly at the forefront of biotechnological applications. Field-flow fractionation is a separation technique suitable for nano-sized and micro-sized analytes among which bioanalytes are an important family. The objective of this preliminary study is to start a more general approach to field-flow fractionation for bio-samples by investigation of the correlation between channel surface composition and biosample adhesion. For the first time we report on the use of X-ray photoelectron spectroscopy (XPS) to study the surface properties of channels of known performance. By XPS, a polar hydrophobic environment was found on PVC material commonly used as accumulation wall in gravitational field-flow fractionation (GrFFF), which explains the low recovery obtained when GrFFF was used to fractionate a biological sample such as Staphylococcus aureus. An increase in separation performance was obtained first by conditioning the accumulation wall with bovine serum albumin and then by using the ion-beam sputtering technique to cover the GrFFF channel surface with a controlled inert film. XPS analysis was also employed to determine the composition of membranes used in hollow-fiber flow field-flow fractionation (HF FlFFF). The results obtained revealed homogeneous composition along the HF FlFFF channel both before and after its use for fractionation of an intact protein such as ferritin.

Separation of charged colloids by a combination of pulsating lateral electric fields and poiseuille flow in a 2D channel

Separation of colloidal particles of different sizes is becoming increasingly important due to rapid developments in the area of proteomics, genetic engineering, drug discovery, etc. In particular, there is a need to accomplish these separations on a microscale in 'lab-on-a-chip' devices. In this paper, we propose a new method for accomplishing separation of charged colloids of different sizes in a microchannel. This method involves a combination of pulses of lateral electric fields and Poiseuille flow in the axial direction. We develop a model for this separation technique and obtain closed form solutions for the mean velocity and the dispersion coefficient for a pulse of molecules introduced into the channel. These expressions are then utilized to determine the channel length and the separation time. For reasonable value of design constants, the proposed technique can separate molecules of different sizes that have diffusivities of 10(-10) and 0.5 x 10(-10) m2/s in 15.7 s in a 3.7 mm long channel. The length and the time increase to 5.45 cm and 231 s if the ratio of the diffusivities is reduced from 2 to 1.2, i.e., the latter diffusivity is increased to 0.835 x 10(-10) m2/s, while keeping all the other parameters the same. If the diffusivities are about 10(-9) m(2)/s, the length and the time for separation are 1 cm and 17.5 s for D1/D2=2, and 16 cm and 269 s for D1/D2=1.2.

Application of Flow Field Flow Fractionation-ICPMS for the Study of Uranium Binding in Bacterial Cell Suspensions

Field flow fractionation (FFF) is a size-based separation technique applicable to biomolecules, colloids, and bacteria in solution. When interfaced with ICPMS on-line, elemental data can be collected concurrent with size distribution. We employed hyperlayer flow FFF (Fl FFF) methodology to separate cells of Shewanella oneidensis strain MR-1 from exopolymers present in washed cell suspensions. With a channel flow of 4 mL min-1 and a cross-flow of 0.4 mL min-1 cells eluted with a retention time of 4.7 min corresponding to an approximate equivalent spherical cell diameter of 0.8 microm. Cell suspensions were amended with increasing concentrations of U to establish an adsorption isotherm and with fixed U concentrations at varying pH to establish the pH dependence of sorption. A linear sorption isotherm was determined for U solution concentrations of 0.2-16 microM, maximum U sorption occurred at pH 5. A high molecular weight compound, presumably a cell exudate, was identified by Fl FFF-ICPMS. This cell exudate complexed U, and at elevated pH, the exudate appeared to have a greater affinity for U than cell surfaces. Thus, Fl FFF interfaced with ICPMS detection is a powerful analytical technique for metal sorption studies with bacteria; analysis can be carried out on small sample volumes (25 microL) and additional speciation information can be gained because of the versatile Fl FFF separation range and multielement detection capabilities of ICPMS.

The use of asymmetrical flow field-flow fractionation in pharmaceutics and biopharmaceutics

Field-flow fractionation (FFF) is a family of flexible analytical fractionating techniques which have the advantage that the separation of analytes is achieved, solely through the interaction of the sample with an external, perpendicular physical field, rather than by the interaction with a stationary phase. The rapid progress in pharmaceutical biotechnology goes along with an increasing demand in potent, high-efficient analytical methods. Thus, FFF techniques are gaining increasing attention for their ability to separate and characterize populations of polymers, colloids and particles of up to about 100 microm in size. It is the intention of this review to provide an overview on common FFF techniques, to summarize inherent advantages and limitations and to introduce both established and challenging applications in the (bio)pharmaceutical field. Thereby, asymmetrical flow FFF is addressed predominantly, since it is the most versatile applicable FFF technique.

Hollow-Fiber Flow Field-Flow Fractionation for Whole Bacteria Analysis by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

This work proposes for the first time the use of hollow-fiber flow field-flow fractionation (HF FlFFF) for improved matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOFMS) of whole bacteria. HF FlFFF has proved to be able to prepurify or fractionate different species of whole bacteria. Sample preparation by HF FlFFF gives improved spectra quality because noncellular components possibly present in the sample can be separated from the cells. When a mixture of two bacteria (Bacillus subtilis and Escherichia coli) is fractionated through HF FlFFF, MALDI/TOFMS analysis of each separated bacterial species preserves the most characteristic ion signals of the species without the presence of characteristic signals of the other species. The main advantages of HF FlFFF for MALDI/TOFMS analysis of whole bacteria are miniaturization, simplicity, and low cost of the fractionator components. This low cost makes disposable usage of the fractionator possible, thus eliminating the risk of run-to-run contamination of spectra due to sample carryover. The low fractionator volume yields bacterial fractionation on the order of a few minutes, which is comparable to MALDI/TOFMS analysis time. The small fractionation volume makes sample dilution low enough so that additional sample concentration steps are not strictly required to preserve MALDI/TOFMS detection.

Turbidimetric Detection Method in Flow-Assisted Separation of Dispersed Samples

Characterization of dispersed samples is an outstanding trend in analytical science. Among flow-assisted separation techniques for dispersed samples, size exclusion chromatography, hydrodynamic chromatography, and field-flow fractionation are the most widely applied. With dispersed analytes separated by these techniques, the UV/vis spectrophotometric detectors work as turbidimeters. To directly convert the analytical signal for quantitative analysis, the extinction properties of the dispersed analyte must be known. A new method is proposed to experimentally obtain-by single-run, flow-assisted separation with UV/vis diode-array detectors-the mass-size (or number-size) distribution function of the analytes when a retention-to-size relationship is either theoretically or empirically available for the chosen separation technique. This approach needs neither standards nor reliance on a method to predict the optical properties of the analytes. Theory and original algorithms are presented. Algorithms are then tested to optimize the numerical routines. Accuracy and robustness of the method are evaluated by simulation, and limitations for the application to experimental data are described. Finally, first application to field-flow fractionation shows validity of the method when applied to a few real cases.

Analysis of whole bacterial cells by flow field-flow fractionation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The purpose of this study is to develop a novel bacterial analysis method by coupling the flow field-flow fractionation (flow FFF) separation technique with detection by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The composition of carrier liquid used for flow FFF was selected based on retention of bacterial cells and compatibility with the MALDI process. The coupling of flow FFF and MALDI-TOF MS was demonstrated for P. putida and E. coli. Fractions of the whole cells were collected after separation by FFF and further analyzed by MALDI-MS. Each fraction, collected over different time intervals, corresponded to different sizes and possibly different growth stages of bacteria. The bacterial analysis by flow FFF/MALDI-TOF MS was completed within 1 h with only preliminary optimization of the process.

Hyperlayer hollow-fiber flow field-flow fractionation of cells

Interest in low-cost, analytical-scale, highly efficient and sensitive separation methods for cells, among which bacteria, is increasing. Particle separation in hollow-fiber flow field-flow fractionation (HF FlFFF) has been recently improved by the optimization of the HF FIFFF channel design. The intrinsic simplicity and low cost of this HF FlFFF channel allows for its disposable usage. which is particularly appealing for analytical bio-applications. Here, for the first time, we present a feasibility study on high-performance, hyperlayer HF FIFFF of micrometer-sized bacteria (Escherichia coli) and of different types of cells (human red blood cells, wine-making yeast from Saccharomyces cerevisiae). Fractionation performance is shown to be at least comparable to that obtained with conventional, flat-channel hyperlayer FIFFF of cells, at superior size-based selectivity and reduced analysis time.