Multiplex detection platform for tumor markers and glucose in serum based on a microfluidic microparticle array

Multiplexed microarrays based on optically encoded microbeads

In recent years, there has been growing interest in optically-encoded or tagged functionalized microbeads as a solid support platform to capture proteins or nucleotides which may serve as biomarkers of various diseases. Multiplexing technologies (suspension array or planar array) based on optically encoded microspheres have made possible the observation of relatively minor changes in biomarkers related to specific diseases. The ability to identify these changes at an early stage may allow the diagnosis of serious diseases (e.g. cancer) at a time-point when curative treatment may still be possible. As the overall accuracy of current diagnostic methods for some diseases is often disappointing, multiplexed assays based on optically encoded microbeads could play an important role to detect biomarkers of diseases in a non-invasive and accurate manner. However, detection systems based on functionalized encoded microbeads are still an emerging technology, and more research needs to be done in the future. This review paper is a preliminary attempt to summarize the state-of-the-art concerning diagnostic microbeads; including microsphere composition, synthesis, encoding technology, detection systems, and applications.

Microfluidic implementation of functional cytometric microbeads for improved multiplexed cytokine quantification

Functional microbeads have been widely applied in molecular identification and other biochemical applications in the past decade, owing to the compatibility with flow cytometry and the commercially available microbeads for a wide range of molecular identification. Nevertheless, there is still a technical hurdle caused by the significant sample volume required (∼50 μl), limited molecular detection limit (∼20 pg/ml), complicated liquid/microbead handling procedures, and the long reaction time (>2 h). In this work, we optimize the operation of an automated microbead-based microfluidic device for the reagent mixing and the dynamic cytokine detection. In particular, we adopt fluorescence microscopy for quantification of multiple microbeads in each microchamber instead of flow cytometry for a lower detection limit. The operation parameters are then configured for improved measurement performance. As demonstrated, we consider the cytokine secretion of human macrophage-differentiating lymphocytes stimulated by lipopolysaccharides. We examine requirements on the mixing duration, minimal sample volume, and the image analysis scheme for the smaller biosample volume (<5 μl), the lower cytokine detection limit (∼5 pg/ml), and shorter process time (∼30 min). Importantly, this microfluidic strategy can be further extended in the molecular profiling using other functional microbeads for a broad range of biomedical applications.

Current status and future developments in preparation and application of nonspherical polymer particles

Nonspherical polymer particles (NPPs) are nano/micro-particulates of macromolecules that are anisotropic in shape, and can be designed anisotropic in chemistry. Due to shape and surface anisotropies, NPPs bear many unique structures and fascinating properties which are distinctly different from those of spherical polymer particles (SPPs). In recent years, the research on NPPs has surprisingly blossomed in recent years, and many practical materials based on NPPs with potential applications in photonic device, material science and biomedical engineering have been generated. In this review, we give a systematic, balanced and comprehensive summary of the main aspects of NPPs related to their preparation and application, and propose perspectives for the future developments of NPPs.

Series of In Situ Photoinduced Polymer Graftings for Sensitive Detection of Protein Biomarkers via Cascade Amplification of Liquid Crystal Signals

Developing of new polymeric materials for the sensitive and rapid detection of trace protein biomarkers has attracted increasing attention in biomedical fields. Herein, series of in situ photoinduced polymer graftings were developed for sensitive detection of protein biomarkers by using featured cascade amplification of liquid crystal (LC) signals. The limit-of-detection (LOD) for native bovine serum albumin (BSA) molecules is around 10 μg/mL in a LC biosensor before signal amplification. Upon the cascade amplification using surface-grafted polymers, poly[poly(ethylene glycol) methacrylate] grafting ( s-P(PEGMA)) exhibits superior amplification ability (10⁴-fold lower than native BSA) than the other two graftings of poly(2-hydroxyethyl methacrylate) ( s-PHEMA) and poly(methacrylic acid) ( s-PMAA; 10²-fold lower than native BSA). The contact angles of water and LC on the s-P(PEGMA) grafting show significant difference in comparison with s-PHEMA and s-PMAA graftings ( p < 0.05), implying interfacial energies of the grafted polymers may dictate the orientational transition of LCs. The clinical urine samples collected from the patients with proteinuria were also used to confirm the feasibility of the polymer-amplified LC sensors for practical protein assays. The present work reveals that in situ photoinduced polymer grafting is one promising method to amplify the signals of LC biosensors for the rapid and sensitive detection of trace protein biomarkers.

Multiplex localization of sequential peptide epitopes by use of a planar microbead chip

Epitope mapping is crucial for the characterization of protein-specific antibodies. Commonly, small overlapping peptides are chemically synthesized and immobilized to determine the specific peptide sequence. In this study, we report the use of a fast and inexpensive planar microbead chip for epitope mapping. We developed a generic strategy for expressing recombinant peptide libraries instead of using expensive synthetic peptide libraries. A biotin moiety was introduced in vivo at a defined peptide position using biotin ligase. Peptides in crude Escherichia coli lysate were coupled onto streptavidin-coated microbeads by incubation, thereby avoiding tedious purification procedures. For read-out we used a multiplex planar microbead chip with size- and fluorescence-encoded microbead populations. For epitope mapping, up to 18 populations of peptide-loaded microbeads (at least 20 microbeads per peptide) displaying the primary sequence of a protein were analyzed simultaneously. If an epitope was recognized by an antibody, a secondary fluorescence-labeled antibody generated a signal that was quantified, and the mean value of all microbeads in the population was calculated. We mapped the epitopes for rabbit anti-PA28γ (proteasome activator 28γ) polyclonal serum, for a murine monoclonal antibody against PA28γ, and for a murine monoclonal antibody against the hamster polyoma virus major capsid protein VP1 as models. In each case, the identification of one distinct peptide sequence out of up to 18 sequences was possible. Using this approach, an epitope can be mapped multiparametrically within three weeks.

Hydrogel microparticles for biosensing

Due to their hydrophilic, biocompatible, and highly tunable nature, hydrogel materials have attracted strong interest in the recent years for numerous biotechnological applications. In particular, their solution-like environment and non-fouling nature in complex biological samples render hydrogels as ideal substrates for biosensing applications. Hydrogel coatings, and later, gel dot surface microarrays, were successfully used in sensitive nucleic acid assays and immunoassays. More recently, new microfabrication techniques for synthesizing encoded particles from hydrogel materials have enabled the development of hydrogel-based suspension arrays. Lithography processes and droplet-based microfluidic techniques enable generation of libraries of particles with unique spectral or graphical codes, for multiplexed sensing in biological samples. In this review, we discuss the key questions arising when designing hydrogel particles dedicated to biosensing. How can the hydrogel material be engineered in order to tune its properties and immobilize bioprobes inside? What are the strategies to fabricate and encode gel particles, and how can particles be processed and decoded after the assay? Finally, we review the bioassays reported so far in the literature that have used hydrogel particle arrays and give an outlook of further developments of the field.

Rapid prototyping of microchannels with surface patterns for fabrication of polymer fibers

Microfluidic technology has provided innovative solutions to numerous problems, but the cost of fabricating microfluidic channels is impeding its expansion. We created multilayer microchannels significantly quicker and cheaper than current methods.

Gel pad array chip for high throughput and multi-analyte microbead-based immunoassays

We present here a gel pad array chip for high-throughput and multi-analyte microbead-based immunoassays. The chip is fabricated by photo-patterning of two polymeric gels, polyacrylamide gel and polyethylene glycol (PEG) gel, on a glass slide. The resulting chip consists of 40 polyacrylamide gel pad array units for the immobilization of microbeads and each gel pad array is surrounded with a PEG micropillar ring to confine the samples within the microarray. As a proof of concept, this chip was tested for quantitative immunoassays for two model cancer markers, human chorionic gonadotropin (hCG) and prostate specific antigen (PSA), in serum samples. Detection limits below the physiological threshold level for cancer diagnosis were achieved with good inter- and intra-chip reproducibility. Moreover, by using spatial encoded microbeads, simultaneous detection of both hCG and PSA on each gel pad array is achieved with single filter fluorescence imaging. This gel pad array chip is easy to use, easy to fabricate with low cost materials and minimal equipment and reusable. It could be a useful tool for common biolabs to customize their own microbead array for multi-analyte immunoassays.

Microfluidic platforms for biomarker analysis

Biomarkers have been described as characteristics, most often molecular, that provide information about biological states, whether normal, pathological, or therapeutically modified. They hold great potential to assist diagnosis and prognosis, monitor disease, and assess therapeutic effectiveness. While a few biomarkers are routinely utilised clinically, these only reflect a very small percentage of all biomarkers discovered. Numerous factors contribute to the slow uptake of these new biomarkers, with challenges faced throughout the biomarker development pipeline. Microfluidics offers two important opportunities to the field of biomarkers: firstly, it can address some of these developmental obstacles, and secondly, it can provide the precise and complex platform required to bridge the gap between biomarker research and the biomarker-based analytical device market. Indeed, adoption of microfluidics has provided a new avenue for advancement, promoting clinical utilisation of both biomarkers and their analytical platforms. This review will discuss biomarkers and outline microfluidic platforms developed for biomarker analysis.

Micro-scale blood plasma separation: from acoustophoresis to egg-beaters

Plasma is a rich mine of various biomarkers including proteins, metabolites and circulating nucleic acids. The diagnostic and therapeutic potential of these analytes has been quite recently uncovered, and the number of plasma biomarkers will still be growing in the coming years. A significant part of the blood plasma preparation is still handled manually, off-chip, via centrifugation or filtration. These batch methods have variable waiting times, and are often performed under non-reproducible conditions that may impair the collection of analytes of interest, with variable degradation. The development of miniaturised modules capable of automated and reproducible blood plasma separation would aid in the translation of lab-on-a-chip devices to the clinical market. Here we propose a systematic review of major plasma analytes and target applications, alongside existing solutions for micro-scale blood plasma extraction, focusing on the approaches that have been biologically validated for specific applications.