After a BS and MS in Chemistry from the Freie Universität Berlin, Germany, I used my expertise in physical and analytical Chemistry to received a PhD from the Department of Food Technology, Engineering and Nutrition at Lund's University in Sweden. I specialized within the Field-Flow Fractionation family, a very versatile and gentle separation technique able to separate large size ranges, from nanometer up to several micrometer. My thesis was titled "On the Aggregation of Cereal β-Glucan and its Association with other Biomolecules: A Study using Asymmetric Flow Field-Flow Fractionation (AF4)". After a postdoctoral position at Santa Clara University, CA, USA, I am now setting up an Asymmetric Flow Field-Flow Fractionation system with several detectors in the Barron Lab, BioE, here at Stanford.
Postdoctoral Scholar, Santa Clara University, Santa Clara, CA, USA, Chemistry & Biochemistry (Physical and Analytical Chemistry, Microfluidics) (2021)
Doctor of Philosophy, Lund's University, Lund, Sweden, Food Technology, Engineering & Nutrition (Analytical Chemistry) (2018)
Master of Science, Freie Universität Berlin, Berlin, Germany, Chemistry (Physical and Analytical Chemistry) (2012)
Bachelor of Science, Freie Universität Berlin, Berlin, Germany, Chemistry (2009)
Annelise Barron, Postdoctoral Faculty Sponsor
Method for Passive Droplet Sorting after Photo-Tagging
2020; 11 (11)
We present a method to photo-tag individual microfluidic droplets for latter selection by passive sorting. The use of a specific surfactant leads to the interfacial tension to be very sensitive to droplet pH. The photoexcitation of droplets containing a photoacid, pyranine, leads to a decrease in droplet pH. The concurrent increase in droplet interfacial tension enables the passive selection of irradiated droplets. The technique is used to select individual droplets within a droplet array as illuminated droplets remain in the wells while other droplets are eluted by the flow of the external oil. This method was used to select droplets in an array containing cells at a specific stage of apoptosis. The technique is also adaptable to continuous-flow sorting. By passing confined droplets over a microfabricated trench positioned diagonally in relation to the direction of flow, photo-tagged droplets were directed toward a different chip exit based on their lateral movement. The technique can be performed on a conventional fluorescence microscope and uncouples the observation and selection of droplets, thus enabling the selection on a large variety of signals, or based on qualitative user-defined features.
View details for DOI 10.3390/mi11110964
View details for Web of Science ID 000593216200001
View details for PubMedID 33126559
View details for PubMedCentralID PMC7692103
Microfluidic Platform for the Isolation of Cancer-Cell Subpopulations Based on Single-Cell Glycolysis
2020; 92 (10): 6949-6957
High rates of glycolysis in tumors have been associated with cancer metastasis, tumor recurrence, and poor outcomes. In this light, single cells that exhibit high glycolysis are specific targets for therapy. However, the study of these cells requires efficient tools for their isolation. We use a droplet microfluidic technique developed in our lab, Sorting by Interfacial Tension (SIFT), to isolate cancer cell subpopulations based on glycolysis without the use of labels or active sorting components. By controlling the flow conditions on chip, the threshold of selection can be modified, enabling the isolation of cells with different levels of glycolysis. Hypoxia in tumors, that can be simulated with treatment with CoCl2, leads to an increase in glycolysis, and more dangerous tumors. The device was used to enrich CoCl2 treated MDA-MB 231 breast cancer cells from an untreated population. It is also used to sort K562 human chronic myelogenous leukemia cells that have either been treated or untreated with 2-deoxy-d-glucose (2DG), a pharmaceutical that targets cell metabolism. The technique provides a facile and robust way of separating cells based on elevated glycolytic activity; a biomarker associated with cancer cell malignancy.
View details for DOI 10.1021/acs.analchem.9b05738
View details for Web of Science ID 000537144800023
View details for PubMedID 32297730
View details for PubMedCentralID PMC7473507
Comparison between conventional and frit-inlet channels in separation of biopolymers by asymmetric flow field-flow fractionation
2019; 144 (15): 4559-4568
Asymmetric flow field-flow fractionation (AF4) is a separation technique in which a focusing/relaxation step is used after the sample is injected onto the separation channel. During the focusing/relaxation step, the sample is focused by two counter-directed flows. This allows sample components to establish a diffusion-dependent equilibrium concentration profile. The focusing step may, in some cases, cause a loss of sample due to adsorption into the accumulation wall (i.e. the membrane) or due to aggregation of the sample. In addition, the increase in sample concentration during the focusing step may prevent complete relaxation and cause overloading effects. In this study, a modified AF4 channel equipped with a frit inlet (FI-AF4) is utilized, where the sample is relaxed hydrodynamically as it enters to the channel through the frit. The main advantage of the FI-AF4 channel is to omit the focusing step. The FI-AF4 channel could also allow higher injection mass than in a conventional channel while still avoiding overloading. The purpose of the present study is to compare two channels (conventional and FI-AF4 channels) in terms of the plate height (H), resolution (Rs) and the mass recovery for analysis of a mixture of glycogen and pullulan. In addition, waxy maize (WM) starch was used to compare the mass overloading of the two channels. The results show that the type of relaxation method (i.e. focusing or hydrodynamic relaxation) had no significant effect on mass recovery. The resolution (Rs), was higher in the conventional AF4 channel than in the FI-AF4 channel for the separation of glycogen and pullulan. The results also show that it was possible to inject a higher mass of WM starch (i.e. twice the mass) onto the FI-AF4 channel, compared to a conventional AF4 channel, without observing an overloading effect.
View details for DOI 10.1039/c9an00466a
View details for Web of Science ID 000476812000012
View details for PubMedID 31225551
- Aggregation and microstructure of cereal beta-glucan and its association with other biomolecules COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 2019; 560: 402-409
- Characterization of cereal beta-glucan extracts: Conformation and structural aspects FOOD HYDROCOLLOIDS 2018; 79: 218-227
- The effect of in vitro gastrointestinal conditions on the structure and conformation of oat beta-glucan FOOD HYDROCOLLOIDS 2018; 77: 659-668
Interaction between cereal beta-glucan and proteins in solution and at interfaces
COLLOIDS AND SURFACES B-BIOINTERFACES
2018; 162: 256-264
Cereal β-glucan is well known for its beneficial health effects, such as lowering of blood cholesterol values and a reduced risk of coronary heart disease. These effects are often discussed in relation to the dissolution and aggregation behavior of the β-glucan during human digestion. Furthermore, potential proteinaceous material present is believed to have an important impact on the formation of viscous slurries during digestion and might influence the aggregation behavior of the β-glucan. Therefore, the interaction and aggregation behavior of a β-glucan isolate (OBC90) with two different proteins (gliadin and whey protein) was investigated in solution at different pH with regards to kinetics of aggregation and protein/β-glucan ratio and at interfaces. Aggregates were found at low pH and the aggregation and composition of aggregates seems to depend on the type of protein. Furthermore, phosphate was found at low concentrations in the β-glucan, most likely being the reason for the net negative charge at pH≤4. Therefore, electrostatic interaction is suggested to play an important role for the aggregation between β-glucan and proteins.
View details for DOI 10.1016/j.colsurfb.2017.11.059
View details for Web of Science ID 000425076500030
View details for PubMedID 29216512
Co-elution phenomena in polymer mixtures studied by asymmetric flow field-flow fractionation
JOURNAL OF CHROMATOGRAPHY A
2018; 1532: 251-256
Most polymers generally have complex characteristics. Analysis and understanding of these characteristics is crucial as they, for instance, influence functionality. Separation and analysis of samples of polymers, biopolymers in particular, is challenging since they often display broad distributions in size, structure and molar mass (M) and/or a tendency to form aggregates. Only few analytical techniques are suitable for the task. AF4-MALS-dRI is highly suited for the task, but the analysis can nevertheless be especially challenging for heterogeneous mixtures of polymers that exhibit wide size distributions or aggregation. For such systems, systematic and thorough method development is clearly a requirement. This is the purpose of the present work, where we approach the problem of heterogeneous polymer samples systematically by analyzing mixtures of two different polymers which are also characterized individually. An often observed phenomenon in AF4 of samples with a high polydispersity is a downturn in M vs. elution time, especially common at high retention. This result is often dismissed as an artifact attributed to various errors in detection and data processing. In this work, we utilize AF4-MALS-dRI to separate and analyze binary mixtures of the well-known polysaccharides pullulan and glycogen, or pullulan and poly(ethylene oxide), respectively, in solution. The results show that an observed downturn - or even an upturn - in M can be a correct result, caused by inherent properties of the analyzed polymers.
View details for DOI 10.1016/j.chroma.2017.12.028
View details for Web of Science ID 000423894500029
View details for PubMedID 29249538
Co-elution effects can influence molar mass determination of large macromolecules with asymmetric flow field-flow fractionation coupled to multiangle light scattering
JOURNAL OF CHROMATOGRAPHY A
2017; 1506: 138-141
Starch and hence, amylopectin is an important biomacromolecule in both the human diet as well as in technical applications. Therefore, accurate and reliable analytical methods for its characterization are needed. A suitable method for analyzing macromolecules with ultra-high molar mass, branched structure and high polydispersity is asymmetric flow field-flow fractionation (AF4) in combination with multiangle light scattering (MALS) detection. In this paper we illustrate how co-elution of low quantities of very large analytes in AF4 may cause disturbances in the MALS data which, in turn, causes an overestimation of the size. Furthermore, it is shown how pre-injection filtering of the sample can improve the results.
View details for DOI 10.1016/j.chroma.2017.05.029
View details for Web of Science ID 000403990300017
View details for PubMedID 28551020
Characterization of the molar mass distribution of macromolecules in beer for different mashing processes using asymmetric flow field-flow fractionation (AF4) coupled with multiple detectors
ANALYTICAL AND BIOANALYTICAL CHEMISTRY
2017; 409 (19): 4551-4558
The macromolecular composition of beer is largely determined by the brewing and the mashing process. It is known that the physico-chemical properties of proteinaceous and polysaccharide molecules are closely related to the mechanism of foam stability. Three types of "American pale ale" style beer were prepared using different mashing protocols. The foam stability of the beers was assessed using the Derek Rudin standard method. Asymmetric flow field-flow fractionation (AF4) in combination with ultraviolet (UV), multiangle light scattering (MALS) and differential refractive index (dRI) detectors was used to separate the macromolecules present in the beers and the molar mass (M) and molar mass distributions (MD) were determined. Macromolecular components were identified by enzymatic treatments with β-glucanase and proteinase K. The MD of β-glucan ranged from 106 to 108 g/mol. In addition, correlation between the beer's composition and foam stability was investigated (increased concentration of protein and β-glucan was associated with increased foam stability).
View details for DOI 10.1007/s00216-017-0393-8
View details for Web of Science ID 000404906800006
View details for PubMedID 28508088
Characterization of cereal beta-glucan extracts from oat and barley and quantification of proteinaceous matter
2017; 12 (2): e0172034
An extraction method for mixed-linkage β-glucan from oat and barley was developed in order to minimize the effect of extraction on the β-glucan structure. β-Glucan were characterized in terms of molecular size and molar mass distributions using asymmetric flow field-flow fractionation (AF4) coupled to multiangle light scattering (MALS), differential refractive index (dRI) and fluorescence (FL) detection. The carbohydrate composition of the extracts was analysed using polysaccharide analysis by carbohydrate gel electrophoresis (PACE) and high-performance anion-exchange chromatography (HPAEC). Whether there were any proteinaceous moieties linked to β-glucan was also examined. Purified extracts contained 65% and 53% β-glucan for oats and barley, respectively. The main impurities were degradation products of starch. The extracts contained high molecular weight β-glucan (105-108 g/mol) and large sizes (root-mean-square radii from 20 to 140 nm). No proteins covalently bound to β-glucan were detected; therefore, any suggested functionality of proteins regarding the health benefits of β-glucan can be discounted.
View details for DOI 10.1371/journal.pone.0172034
View details for Web of Science ID 000394423900046
View details for PubMedID 28196092
View details for PubMedCentralID PMC5308836
Analysis of beta-glucan molar mass from barley malt and brewer's spent grain with asymmetric flow field-flow fractionation (AF4) and their association to proteins
2017; 157: 541-549
β-Glucan benefits are related with its molar mass and it would be of interest to better understand how this parameter can be changed by processing and variety for design of food with specific health effects. For this purpose, extracts from barley malts and brewers' spent grain, processed at different conditions, were analysed regarding β-glucan content, molar mass, and protein content. Molar mass distribution was assessed using asymmetric flow field-flow fractionation (AF4) with multiangle light scattering (MALS), differential refractive index (dRI) and fluorescence (FL) detection. β-Glucan was detected in a wide molar mass range, <2000 to approximately 6.7×106g/mol. Differences in molar masses were more noticeable between barley varieties and steeping malting conditions than by mashing of malt. Barley products processed to preserve β-glucan contained more β-glucan of high molar mass with potential to shift the fermentation site to the distal colon. Enzymatic degradation of proteins indicated presence of aggregates containing β-glucan and protein.
View details for DOI 10.1016/j.carbpol.2016.10.045
View details for Web of Science ID 000391896800061
View details for PubMedID 27987960
Role of polysaccharides in food, digestion, and health
CRITICAL REVIEWS IN FOOD SCIENCE AND NUTRITION
2017; 57 (2): 237-253
Polysaccharides derived from plant foods are major components of the human diet, with limited contributions of related components from fungal and algal sources. In particular, starch and other storage carbohydrates are the major sources of energy in all diets, while cell wall polysaccharides are the major components of dietary fiber. We review the role of these components in the human diet, including their structure and distribution, their modification during food processing and effects on functional properties, their behavior in the gastrointestinal tract, and their contribution to healthy diets.
View details for DOI 10.1080/10408398.2014.939263
View details for Web of Science ID 000387762600001
View details for PubMedID 25921546
View details for PubMedCentralID PMC5152545
The effect of baking and enzymatic treatment on the structural properties of wheat starch
2016; 213: 768-774
In this study, bread was baked with and without the addition of α-amylase. Starch was extracted from the baked bread and its molecular properties were characterized using (1)H NMR and asymmetric flow field-flow fractionation (AF4) connected to multi-angle light scattering (MALS) and other detectors. The approach allows determination of molar mass, root- mean-square radius and apparent density as well as the average degree of branching of amylopectin. The results show that starch size and structure is affected as a result of the baking process. The effect is larger when α-amylase is added. The changes include both a decrease molar mass and size as well as an increase in apparent density. Moreover, an increase in average degree of branching and the number of reducing ends H-1(β-r) and H-1(α-r) can be observed.
View details for DOI 10.1016/j.foodchem.2016.07.045
View details for Web of Science ID 000380289900099
View details for PubMedID 27451246
- Supported Mesoporous and Hierarchical Porous Pd/TiO2 Catalytic Coatings with Controlled Particle Size and Pore Structure CHEMISTRY OF MATERIALS 2012; 24 (20): 3828-3838
- Infrared spectroscopic ellipsometry (IRSE) and X-ray photoelectron spectroscopy (XPS) monitoring the preparation of maleimide-functionalized surfaces: from Au towards Si (111) SURFACE AND INTERFACE ANALYSIS 2011; 43 (9): 1203-1210