Microfluidic Platform for the Evaluation of Multi-Glycan Expressions on Living Cells using Electrochemical Impedance Spectroscopy and Optical Microscope

Microfluidic Gradient Culture Arrays for Cell Pro-oxidation Analysis Using Bipolar Electrochemiluminescence

A microfluidic gradient array is a widely used screening and analysis device, which has characteristics of high efficiency, high automation, and low consumption. Bipolar electrode electrochemiluminescence (BPE-ECL) has special value in microfluidic array chips. The combination of the microfluidic gradient and BPE arrays has potential for high-throughput screening. In this article, a microfluidic BPE array chip for gradient culture and conditional screening of cancer cells was designed. The generation of concentration gradients, continuous culture of cancer cells with high throughput, and drug screening through BPE-ECL of the Ru(bpy)₃²⁺/TPrA system can be performed in one chip. We tested gradient pro-oxidation of MCF-7 by ascorbic acid and the synergistic effect of pro-oxidation on doxorubicin. The method achieves high analysis efficiency through a BPE array while simplifying the tedious procedures required by cell culture methods.

Concepts, electrode configuration, characterization, and data analytics of electric and electrochemical microfluidic platforms: a review

Microfluidic cytometry (MC) and electrical impedance spectroscopy (EIS) are two important techniques in biomedical engineering. Microfluidic cytometry has been utilized in various fields such as stem cell differentiation and cancer metastasis studies, and provides a simple, label-free, real-time method for characterizing and monitoring cellular fates. The impedance microdevice, including impedance flow cytometry (IFC) and electrical impedance spectroscopy (EIS), is integrated into MC systems. IFC measures the impedance of individual cells as they flow through a microfluidic device, while EIS measures impedance changes during binding events on electrode regions. There have been significant efforts to improve and optimize these devices for both basic research and clinical applications, based on the concepts, electrode configurations, and cell fates. This review outlines the theoretical concepts, electrode engineering, and data analytics of these devices, and highlights future directions for development.

A dynamic reversible phenylboronic acid sensor for real-time determination of protein-carbohydrate interactions on living cancer cells

Real-time detection of glycosylation on label-free cancer cell surfaces is of significance for the diagnosis and treatment of cancer. In this work, we have successfully developed a novel dynamic reversible sensor based on pH-sensitive phenylboronic esters to determine in real-time the binding kinetics of protein-carbohydrate interactions on suspension cancer cell surfaces using a quartz crystal microbalance (QCM) technique.

Microfluidic platform for the real time measurement and observation of endothelial barrier function under shear stress

Electric cell-substrate impedance sensing (ECIS) is a quickly advancing field to measure the barrier function of endothelial cells. Most ECIS systems that are commercially available use gold electrodes, which are opaque and do not allow for real-time imaging of cellular responses. In addition, most ECIS systems have a traditional tissue culture Petri-dish set up. This conventional set-up does not allow the introduction of physiologically relevant shear stress, which is crucial for the endothelial cell barrier function. Here, we created a new ECIS micro-bioreactor (MBR) that incorporates a clear electrode made of indium tin oxide in a microfluidic device. Using this device, we demonstrate the ability to monitor the barrier function along culture of cells under varying flow rates. We show that while two cell types align in the direction of flow in responses to high shear stress, they differ in the barrier function. Additionally, we observe a change in the barrier function in response to chemical perturbation. Following exposure to EDTA that disrupts cell-to-cell junctions, we could not observe distinct morphological changes but measured a loss of impedance that could be recovered with EDTA washout. High magnification imaging further demonstrates the loss and recovery of the barrier structure. Overall, we establish an ECIS MBR capable of real-time monitoring of the barrier function and cell morphology under shear stress and allowing high-resolution analysis of the barrier structure.

Iron Phthalocyanine Decorated Nitrogen-Doped Graphene Biosensing Platform for Real-Time Detection of Nitric Oxide Released from Living Cells

Nitric oxide (NO) is a transcellular messenger involved in many physiological and pathological processes, but the real-time detection of NO in biological systems is still challenging due to its rapid diffusion, low concentration, and short half-life. A novel electrochemical sensing platform based on iron phthalocyanine (FePc) functionalized nitrogen-doped graphene (N-G) nanocomposites was constructed to achieve in situ monitoring of NO released from living cells on the sensing layer. By taking advantage of the synergetic effect of N-G and FePc nanocomposites, the N-G/FePc sensor displays excellent electrocatalytic activity toward NO with a high sensitivity of 0.21 μA μM^-1 cm^-2 and a low detection limit of 180 nmol L^-1. The following layer-by-layer assembly of poly-l-lysine (PLL) and Nafion further improved the capacity of resisting disturbance as well as the biocompatibility of the sensing interface. The flexible design of the ITO substrate based electrode provides a more controlled cellular biosensing system which could capture molecular signals immediately after NO released from human umbilical vein endothelial cells (HUVECs). The exhibited additional features of high sensitivity, rapid response, and ease of operation implies that the proposed N-G/FePc/Nafion/PLL ITO biosensor is a promising powerful platform in various complex biological systems.

High-throughput approaches for screening and analysis of cell behaviors

The rapid development of new biomaterials and techniques to modify them challenge our capability to characterize them using conventional methods. In response, numerous high-throughput (HT) strategies are being developed to analyze biomaterials and their interactions with cells using combinatorial approaches. Moreover, these systematic analyses have the power to uncover effects of delivered soluble bioactive molecules on cell responses. In this review, we describe the recent developments in HT approaches that help identify cellular microenvironments affecting cell behaviors and highlight HT screening of biochemical libraries for gene delivery, drug discovery, and toxicological studies. We also discuss HT techniques for the analyses of cell secreted biomolecules and provide perspectives on the future utility of HT approaches in biomedical engineering.

Plant Lectins as Medical Tools against Digestive System Cancers

Digestive system cancers-those of the esophagus, stomach, small intestine, colon-rectum, liver, and pancreas-are highly related to genetics and lifestyle. Most are considered highly mortal due to the frequency of late diagnosis, usually in advanced stages, caused by the absence of symptoms or masked by other pathologies. Different tools are being investigated in the search of a more precise diagnosis and treatment. Plant lectins have been studied because of their ability to recognize and bind to carbohydrates, exerting a variety of biological activities on animal cells, including anticancer activities. The present report integrates existing information on the activity of plant lectins on various types of digestive system cancers, and surveys the current state of research into their properties for diagnosis and selective treatment.

Versatile aptasensor for electrochemical quantification of cell surface glycan and naked-eye tracking glycolytic inhibition in living cells

Quantifying the glycan expression status on cell surfaces is of vital importance for insight into the glycan function in biological processes and related diseases. Here we developed a versatile aptasensor for electrochemical quantification of cell surface glycan by taking advantage of the cell-specific aptamer, and the lectin-functionalized gold nanoparticles acting as both a glycan recognition unit and a signal amplification probe. To construct the aptasensor, amine-functionalized mucin 1 protein (MUC1) aptamer was first covalently conjugated to carboxylated-magnetic beads (MBs) using the succinimide coupling (EDC-NHS) method. On the basis of the specific recognition between aptamer and MUC1 protein that overexpressed on the surface of MCF-7 cells, the aptamer conjugated MBs showed a predominant capability for cell capture with high selectivity. Moreover, a lectin-based nanoprobe was designed by noncovalent assembly of concanavalin A (ConA) on gold nanoparticles (AuNPs). This nanoprobe incorporated the abilities of both the specific carbohydrate recognition and the signal amplification based on the gold-promoted reduction of silver ions. By coupling with electrochemical stripping analysis, the proposed sandwich-type cytosensor showed an excellent analytical performance for the ultrasensitive detection of MCF-7 cells and quantification of cell surface glycan. More importantly, taking advantage of Con A-gold nanoprobe catalyzed silver enhancement, the proposed method was further used for naked-eye tracking glycolytic inhibition in living cells. This aptasensor holds great promise as a new point-of-care diagnostic tool for analyzing glycan expression on living cells and further helps cancer diagnosis and treatment.

Microfluidics in the selection of affinity reagents for the detection of cancer: paving a way towards future diagnostics

Microfluidic technologies have miniaturized a variety of biomedical applications, and these chip-based systems have several significant advantages over their large-scale counterparts. Recently, this technology has been used for automating labor-intensive and time-consuming screening processes, whereby affinity reagents, including aptamers, peptides, antibodies, polysaccharides, glycoproteins, and a variety of small molecules, are used to probe for molecular biomarkers. When compared to conventional methods, the microfluidic approaches are faster, more compact, require considerably smaller quantities of samples and reagents, and can be automated. Furthermore, they allow for more precise control of reaction conditions (e.g., pH, temperature, and shearing forces) such that more efficient screening can be performed. A variety of affinity reagents for targeting cancer cells or cancer biomarkers are now available and will likely replace conventional antibodies. In this review article, the selection of affinity reagents for cancer cells or cancer biomarkers on microfluidic platforms is reviewed with the aim of highlighting the utility of such approaches in cancer diagnostics.

Affinity-Mediated Homogeneous Electrochemical Aptasensor on a Graphene Platform for Ultrasensitive Biomolecule Detection via Exonuclease-Assisted Target-Analog Recycling Amplification

As is well-known, graphene shows a remarkable difference in affinity toward nonstructured single-stranded (ss) DNA and double-stranded (ds) DNA. This property makes it popular to prepare DNA-based optical sensors. In this work, taking this unique property of graphene in combination with the sensitive electrochemical transducer, we report a novel affinity-mediated homogeneous electrochemical aptasensor using graphene modified glassy carbon electrode (GCE) as the sensing platform. In this approach, the specific aptamer-target recognition is converted into an ultrasensitive electrochemical signal output with the aid of a novel T7 exonuclease (T7Exo)-assisted target-analog recycling amplification strategy, in which the ingeniously designed methylene blue (MB)-labeled hairpin DNA reporters are digested in the presence of target and, then, converted to numerous MB-labeled long ssDNAs. The distinct difference in differential pulse voltammetry response between the designed hairpin reporters and the generated long ssDNAs on the graphene/GCE allows ultrasensitive detection of target biomolecules. Herein, the design and working principle of this homogeneous electrochemical aptasensor were elucidated, and the working conditions were optimized. The gel electrophoresis results further demonstrate that the designed T7Exo-assisted target-analog recycling amplification strategy can work well. This electrochemical aptasensor realizes the detection of biomolecule in a homogeneous solution without immobilization of any bioprobe on electrode surface. Moreover, this versatile homogeneous electrochemical sensing system was used for the determination of biomolecules in real serum samples with satisfying results.

Graphene-Assisted Label-Free Homogeneous Electrochemical Biosensing Strategy based on Aptamer-Switched Bidirectional DNA Polymerization

In this contribution, taking the discrimination ability of graphene over single-stranded (ss) DNA/double-stranded (ds) DNA in combination with the electrochemical impedance transducer, we developed a novel label-free homogeneous electrochemical biosensor using graphene-modified glassy carbon electrode (GCE) as the sensing platform. To convert the specific aptamer-target recognition into ultrasensitive electrochemical signal output, a novel aptamer-switched bidirectional DNA polymerization (BDP) strategy, capable of both target recycling and exponential signal amplification, was compatibly developed in this study. In this strategy, all the designed DNA structures could be adsorbed on the graphene/GCE and, thus, serve as the electrochemical impedance signal reporter, while the target acts as a trigger of this BDP reaction, in which these designed DNA structures are bound together and, then, converted to long dsDNA duplex. The distinct difference in electrochemical impedance spectroscopy between the designed structures and generated long dsDNA duplex on the graphene/GCE allows label-free and homogeneous detection of target down to femto-gram level. The target can be displaced from aptamer through the polymerization to initiate the next recognition-polymerization cycle. Herein, the design and signaling principle of aptamer-switched BDP amplification system were elucidated, and the working conditions were optimized. This method not only provides a universal platform for electrochemical biosensing but also shows great potential in biological process researches and clinic diagnostics.

Affinity biosensors for tumor-marker analysis

The use of cancer biomarkers is emerging as one of the most promising strategies for early detection and management of cancer. Biosensors can provide advanced platforms for biomarker analysis with the advantages of being easy to use, inexpensive, rapid and offering multi-analyte testing capability. The intention of this article is to discuss recent advances and trends in affinity biosensors for cancer diagnosis, prognosis and even theragnosis. The different types of affinity biosensors will be reviewed in terms of molecular recognition element. Current challenges and trends for this technology will be also discussed, with a particular emphasis on recent developments in miRNA detection.

Versatile Microfluidic Platform for the Assessment of Sialic Acid Expression on Cancer Cells Using Quantum Dots with Phenylboronic Acid Tags

This work describes a versatile microfluidic platform for evaluation of cell-surface glycan expression at the single-cell level using quantum dots (QDs) tagged with phenylboronic acid. The platform was integrated with dual microwell arrays, allowing the introduction of cells in two states using the same cell culture chamber. The simultaneous analysis of cells in the same environment minimized errors resulting from different culture conditions. As proof-of-concept, the expressions of sialic acid (SA) groups on K562 cells, with or without 3'-azido-3'-deoxythymidine (AZT) treatment, were evaluated in the same chamber. 3-Aminophenylboronic acid functionalized CdSeTe@ZnS-SiO2 QDs (APBA-QDs) were prepared as probes to recognize SA groups on K562 cells with only one-step labeling. The results showed that the expression of SA moieties on K562 cells was increased by 18% and 31% after treatment with 20 and 40 μM AZT, respectively. Performing the drug treatment and control experiments simultaneously in the same chamber significantly improved the robustness and effectiveness of the assay. The strategy presented here provides an alternative tool for glycan analysis in a sensitive, high-throughput, and effective manner.

Glycan-based diagnostic devices: current progress, challenges and perspectives

The development of glycan-based diagnostic devices is illustrated with recent examples from both carbohydrate recognition and device design aspects.

Glycoprofiling of cancer biomarkers: Label-free electrochemical lectin-based biosensors

Glycosylation of biomolecules is one of the most prevalent post- and co-translational modification in a human body, with more than half of all human proteins being glycosylated. Malignant transformation of cells influences glycosylation machinery resulting in subtle changes of the glycosylation pattern within the cell populations as a result of cancer. Thus, an altered terminal glycan motif on glycoproteins could provide a warning signal about disease development and progression and could be applied as a reliable biomarker in cancer diagnostics. Among all highly effective glycoprofiling tools, label-free electrochemical impedance spectroscopy (EIS)-based biosensors have emerged as especially suitable tool for point-of-care early-stage cancer detection. Herein, we highlight the current challenges in glycoprofiling of various cancer biomarkers by ultrasensitive impedimetric-based biosensors with low sample consumption, low cost fabrication and simple miniaturization. Additionally, this review provides a short introduction to the field of glycomics and lectinomics and gives a brief overview of glycan alterations in different types of cancer.

Biophysical characterization of lectin–glycan interactions for therapeutics, vaccines and targeted drug-delivery

Lectin–glycan interactions play a role in biological processes, host–pathogen interactions and in disease. A more detailed understanding of these interactions is not only useful for the elucidation of their biological function but can also be applied in immunology, drug development and delivery and diagnostics. We review some commonly used biophysical techniques for studying lectin–glycan interactions; namely: frontal affinity chromatography, glycan/lectin microarray, surface plasmon resonance, electrochemical impedance spectroscopy, isothermal titration calorimetry, fluorescent assays, enzyme linked lectin sorbent assay and saturation transfer difference nuclear magnetic resonance spectroscopy. Each method is evaluated on efficiency, cost and throughput. We also consider the advantages and limitations of each technique and provide examples of their application in biology, drug discovery and delivery, immunology, glycoprofiling and biosensing.

Paper-based electrochemiluminescence origami cyto-device for multiple cancer cells detection using porous AuPd alloy as catalytically promoted nanolabels

The detection of cancer cells is important and fundamental for cancer diagnosis and therapy, which has attracted considerable interest recently. Although traditional cyto-sensors have been widely explored due to their high sensitivity and selectivity, it is still a challenge to develop a low-cost, portable, disposable, fast, and easy-to-use cancer cell detection method for applying in the field of cancer diagnosis and therapy. Herein, to address these challenges, we developed a microfluidic paper-based electrochemiluminescence origami cyto-device (μ-PECLOC), in which aptamers modified 3D macroporous Au-paper electrodes were employed as the working electrodes and efficient platforms for the specific cancer cells capture. Owing to the effective disproportionation of hydrogen peroxide and specific recognition of mannose on cell surface, concanavalin-A conjugated porous AuPd alloy nanoparticles were introduced into this μ-PECLOC as the catalytically promoted nanolabels for peroxydisulfate ECL system. Under the optimal conditions, the proposed μ-PECLOC exhibited excellent analytical performance with good stability, reproducibility, and accuracy, towards the cyto-sensing of four types of cancer cells indicating the potential applications to facilitate effective and multiple early cancer diagnosis and clinical treatment.

Nanoscale controlled architecture for development of ultrasensitive lectin biosensors applicable in glycomics

In this Minireview the most advanced patterning protocols and transducing schemes for development of ultrasensitive label-free and label-based lectin biosensors for glycoprofiling of disease markers and some cancerous cells are described. Performance of such lectin biosensors with interfacial properties tuned at a nanoscale are critically compared to the most sensitive immunoassay format of analysis and challenges ahead in the field are discussed. Moreover, key elements for future advances of such devices on the way to enhance robustness and practical applicability of lectin biosensors are revealed.

A bubble-mediated intelligent microscale electrochemical device for single-step quantitative bioassays

An intelligent microscale electrochemical device (iMED) for one-step, quantitative and multiplexed electrochemical detection of biomarkers for infectious diseases and tumors is developed. A "plug-in-cartridge" technology is introduced and adapted for use in screen-printed electrodes (SPEs) in electrochemical devices. Using this iMED, biomarkers for two types of tumors and one infectious disease are detected at sub-ng/mL levels in less than 30 min.

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.

On-chip selective capture of cancer cells and ultrasensitive fluorescence detection of survivin mRNA in a single living cell

The rapid recognition of cancer cells and detection of tumor biomarker survivin mRNA plays a critical role in the early diagnosis of many cancers. Based on the integration of specific cancer cell capture and intracellular survivin mRNA detection, this work presents a novel and sensitive on-chip approach for the bioanalysis of survivin mRNA in a single living cell. The microchannel surface was firstly modified with a prostate stem cell antigen (PSCA) monoclonal antibody as the recognition element for prostate cancer cells (PC-3). As a result of the antigen-antibody specific affinity interactions, PC-3 cells could be selectively captured on the microchannel surface. After cell capture, nano-sized graphene oxide-poly(ethylene glycol) bis(amine) (NGO-PEG) was employed as a quencher and carrier of a signal tag, fluorescein isothiocyanate (FITC)-labeled antisense oligonucleotide (F-S1), which is complementary to part of survivin mRNA (target survivin mRNA), to transfect into the captured PC-3 cells. Upon the selective binding of S1 to intracellular survivin mRNA, F-S1 will be released from the NGO-PEG, inducing the fluorescence recovery of FITC. This antibody-based microfluidic device enables simple and inexpensive monitoring of the amount of survivin mRNA in single captured cell without the need for sample pretreatment. The survivin mRNA content in each PC-3 cell was estimated to be (4.8 ± 1.8) × 10(6) copies. This strategy opens a different perspective for ultrasensitive survivin mRNA detection, which may facilitate the early screening for malignancy.

Lectin-functionalized poly(glycidyl methacrylate)-block-poly(vinyldimethyl azlactone) surface scaffolds for high avidity microbial capture

Microbial exopolysaccharides (EPS) play a critical and dynamic role in shaping the interactions between microbial community members and their local environment. The capture of targeted microbes using surface immobilized lectins that recognize specific extracellular oligosaccharide moieties offers a nondestructive method for functional characterization of EPS content. In this report, we evaluate the use of the block copolymer, poly(glycidyl methacrylate)-block-4,4-dimethyl-2-vinylazlactone (PGMA-b-PVDMA), as a surface scaffold for lectin-specific microbial capture. Three-dimensional polymer films were patterned on silicon substrates to provide discrete, covalent coupling sites for Triticum vulgare and Lens culinaris lectins. This material increased the number of Pseudomonas fluorescens microbes captured by up to 43% compared to control scaffolds that did not contain the copolymer. These results demonstrate that PGMA-b-PVDMA scaffolds provide a platform for improved microbe capture and screening of EPS content by combining high avidity lectin surfaces with three-dimensional surface topography.

A disposable electrochemiluminescence device for ultrasensitive monitoring of K562 leukemia cells based on aptamers and ZnO@carbon quantum dots

We developed a new electrochemiluminescence (ECL) platform for ultrasensitive and selective detection of leukemia cells. In order to construct the platform, the nonporous gold with controllable three-dimensional porosity and good conductivity was used to modify the screen-printed carbon electrode. The carbon quantum dots (CQDs) coated ZnO nanosphere (ZnO@CQDs) were used as good ECL label with low cytotoxicity and good biocompatibility. Structure characterization was obtained by means of transmission electron microscopy and scanning electron microscopy images. The aptamer was used for cell capture and the concanavalin A conjugated ZnO@CQDs was used for selective recognition of the cell surface carbohydrate. The proposed method showed a good analytical performance for the detection of K562 cells ranging from 1.0 × 10(2) to 2.0 × 10(7) cells mL(-1) with a detection limit of 46 cells mL(-1). The as-proposed device has the advantages of high sensitivity, nice specificity and good stability and could offer great promise for sensitive detection of leukemia cells in response to therapy.