Functionalized conducting polymer nanodots for enhanced cell capturing: the synergistic effect of capture agents and nanostructures

Chemically-Modified Sepharose 6B Beads for Collection of Circulating Tumor Cells

The isolation and quantitative characterization of circulating tumor cells (CTCs) are of great importance in cancer diagnosis and prognosis. However, isolating and detecting CTCs in whole blood presents a significant challenge due to the low numbers of CTCs (often ranging from one to five) in samples containing billions of erythrocytes. Recently, point-of-care devices that use antibody trapping coupled with remote immunofluorescence analyses have been described to identify the number and type of CTCs in blood. In this study, we propose a novel method for trapping and quantifying CTCs using Sepharose 6B beads of 45-160 μm size that are engineered with capture antibodies. Specifically, we employed CD44 antibody conjugates (bearing a maleimide group) that are specific to the CTCs of breast cancer to thiol-Sepharose beads 6B. These beads, when mixed with MDAMB231 and Jurkat cells and filtered through a 40 μm filter, can capture ~80% of MDAMB231 cells. Furthermore, the antibody-modified Sepharose 6B can be stored at four degrees Celsius for a period exceeding six months.

Conducting Polymers as Versatile Tools for the Electrochemical Detection of Cancer Biomarkers

The detection of cancer biomarkers has recently become an established method for the early diagnosis of cancer. The sensitive analysis of specific biomarkers can also be clinically applied for the determination of response to treatment and monitoring of disease progression. Because of the ultra-low concentration of cancer biomarkers in body fluids, diagnostic tools need to be highly sensitive and specific. Conducting polymers (CPs) are particularly known to exhibit numerous features that enable them to serve as excellent materials for the immobilization of biomolecules and the facilitation of electron transfer. Their large surface area, porosity, and the presence of functional groups provide CPs with binding sites suitable for capturing biomarkers, in addition to their sensitive and easy detection. The aim of this review is to present a comprehensive summary of the available electrochemical biosensors based on CPs and their composites for the ultrasensitive detection of selected cancer biomarkers. We have categorized the study based on different types of targeted biomarkers such as DNAs, miRNAs, proteins, enzymes, neurotransmitters and whole cancer cells. The sensitivity of their detection is enhanced by the presence of CPs, providing a limit of detection as low as 0.5 fM (for miRNA) and 10 cells (for the detection of cancer cells). The methods of multiplex biomarker detection and cell capture are indicated as the most promising category, since they furnish more accurate and reliable results. Ultimately, we discuss the available CP-based electrochemical sensors and promising approaches for facilitating cancer diagnosis and treatment.

Recent advances in micro-/nanostructure array integrated microfluidic devices for efficient separation of circulating tumor cells

Circulating tumor cells (CTCs) released from the primary tumor to peripheral blood are promising targets for liquid biopsies. Their biological information is vital for early cancer detection, efficacy assessment, and prognostic monitoring. Despite the tremendous clinical applications of CTCs, development of effective separation techniques are still demanding. Traditional separation methods usually use batch processing for enrichment, which inevitably destroy cell integrity and affect the complete information acquisition. Considering the rarity and heterogeneity of CTCs, it is urgent to develop effective separation methods. Microfluidic chips with precise fluid control at the micron level are promising devices for CTC separation. Their further combination with micro-/nanostructure arrays adds more biomolecule binding sites and exhibit unique fluid barrier effect, which significantly improve the CTC capture efficiency, purity, and sensitivity. This review summarized the recent advances in micro-/nanostructure array integrated microfluidic devices for CTC separation, including microrods, nanowires, and 3D micro-/nanostructures. The mechanisms by which these structures contribute to improved capture efficiency are discussed. Two major categories of separation methods, based on the physical and biological properties of CTCs, are discussed separately. Physical separation includes the design and preparation of micro-/nanostructure arrays, while chemical separation additionally involves the selection and modification of specific capture probes. These emerging technologies are expected to become powerful tools for disease diagnosis in the future.

Discovery and characterization of circulating tumor cell clusters in neuroendocrine tumor patients using nanosubstrate-embedded microchips

Circulating tumor cell (CTC) clusters are present in cancer patients with severe metastasis, resulting in poor clinical outcomes. However, CTC clusters have not been studied as extensively as single CTCs, and the clinical utility of CTC clusters remains largely unknown. In this study, we aim sought to explore the feasibility of NanoVelcro Chips to simultaneously detect both single CTCs and CTC clusters with negligible perturbation to their intrinsic properties in neuroendocrine tumors (NETs). We discovered frequent CTC clusters in patients with advanced NETs and examined their potential roles, together with single NET CTCs, as novel biomarkers of patient response following peptide receptor radionuclide therapy (PRRT). We observed dynamic changes in both total NET CTCs and NET CTC cluster counts in NET patients undergoing PRRT which correlated with clinical outcome. These preliminary findings suggest that CTC clusters, along with single CTCs, offer a potential non-invasive option to monitor the treatment response in NET patients undergoing PRRT.

Refining of Particulates at Stimuli-Responsive Interfaces: Label-Free Sorting and Isolation

The mechanism of separation methods, for example, liquid chromatography, is realized through rapid multiple adsorption-desorption steps leading to the dynamic equilibrium state in a mixture of molecules with different partition coefficients. Sorting of colloidal particles, including protein complexes, cells, and viruses, is limited due to a high energy barrier, up to millions kT, required to detach particles from the interface, which is in dramatic contrast to a few kT for small molecules. Such a strong interaction renders particle adsorption quasi-irreversible. The dynamic adsorption-desorption equilibrium is approached very slowly, if ever attainable. This limitation is alleviated with a local oscillating repulsive mechanical force generated at the microstructured stimuli-responsive polymer interface to switch between adsorption and mechanical-force-facilitated desorption of the particles. Such a dynamic regime enables the separation of colloidal mixtures based on the particle-polymer interface affinity, and it could find use in research, diagnostics, and industrial-scale label-free sorting of highly asymmetric mixtures of colloids and cells.

A review of enrichment methods for circulating tumor cells: from single modality to hybrid modality

Circulating tumor cell (CTC) analysis as a liquid biopsy can be used for early diagnosis of cancer, evaluating cancer progression, and assessing treatment efficacy. The enrichment of CTCs from patient blood is important for CTC analysis due to the extreme rarity of CTCs. This paper updates recent advances in CTC enrichment methods. We first review single-modality methods, including biophysical and biochemical methods. Hybrid-modality methods, combining at least two single-modality methods, are gaining increasing popularity for their improved performance. Then this paper reviews hybrid-modality methods, which are categorized into integrated and sequenced hybrid-modality methods. The state of the art indicates that the CTC capture efficiencies of integrated hybrid-modality methods can reach 85% or higher by taking advantage of the superimposed and enhanced capture effects from multiple single-modality methods. Moreover, a hybrid method integrating biophysical with biochemical methods is characterized by both high processing rate and high specificity.

Functionalization Strategies of PEDOT and PEDOT:PSS Films for Organic Bioelectronics Applications

Organic bioelectronics involves the connection of organic semiconductors with living organisms, organs, tissues, cells, membranes, proteins, and even small molecules. In recent years, this field has received great interest due to the development of all kinds of devices architectures, enabling the detection of several relevant biomarkers, the stimulation and sensing of cells and tissues, and the recording of electrophysiological signals, among others. In this review, we discuss recent functionalization approaches for PEDOT and PEDOT:PSS films with the aim of integrating biomolecules for the fabrication of bioelectronics platforms. As the choice of the strategy is determined by the conducting polymer synthesis method, initially PEDOT and PEDOT:PSS films preparation methods are presented. Later, a wide variety of PEDOT functionalization approaches are discussed, together with bioconjugation techniques to develop efficient organic-biological interfaces. Finally, and by making use of these approaches, the fabrication of different platforms towards organic bioelectronics devices is reviewed.

Well-Defined Nanostructured Biointerfaces: Strengthened Cellular Interaction for Circulating Tumor Cells Isolation

The topographic features at the cell-material biointerface are critical for cellular sensing of the extracellular environment (ECM) and have gradually been recognized as key factors that regulate cell adhesion behavior. Herein, a well-defined nanostructured biointerface is fabricated via a new generation of mussel-inspired polymer coating to mimic the native ECM structures. Upon the bioinert background presence and biospecific ligands conjugation, the affinity of cancer cells to the resulting biofunctional surfaces, which integrate topographic features and biochemical cues, is greatly strengthened. Both the conjugated bioligand density, filopodia formation, and focal adhesion expression are significantly enhanced by the surficial nano-features with an optimized size-scale. Thus, this nanostructured biointerface exhibits high capture efficiency for circulating tumor cells (CTCs) with high sensitivity, high biospecificity, and high purity. Benefiting from the unique bioligands conjugation chemistry herein, the captured cancer cells can be responsively detached from the biointerfaces without damage for downstream analysis. The present biofunctional nanostructured interfaces offer a good solution to address current challenges to efficiently isolate rare CTCs from blood samples for earlier cancer diagnosis.

Penetration mechanism of cells by vertical nanostructures

Cell penetration by high aspect-ratio vertical nanostructures such as nanowires and nanopillars provides a powerful method for accessing the cell interior for delivery and sensing. However, there is a lack of studies on the understanding of the mechanism of cell membrane penetration and how design nanostructures to optimize the efficiency of penetration remains unclear. Here, we propose an analytical model to elucidate the mechanism of cells penetration by analyzing the free-energy change of cells adhered to the nanostructures surface. Furthermore, we provide a simple method to evaluate the crossover radius or density for cell membrane penetration. By introducing a dimensionless parameter, i.e., adhesion area factor, we investigated the effects of the radius and distribution densities of nanostructures on cell membrane penetration which is determined by the competition between adhesion energy and deformation energy. Besides, a diagram of the distribution of cell penetration and no penetration is obtained. From the cell penetration diagram, one can determine easily and intuitively the relations of cell penetration state with the radius and distribution densities of nanostructures. Our theoretical results seem to show broad agreement with experimental observations, which implies that these studies would provide useful guidance to the design of nanopatterned surfaces for biomedical applications.

Efficient Capture and Raman Analysis of Circulating Tumor Cells by Nano-Undulated AgNPs-rGO Composite SERS Substrates

The analysis of circulating tumor cells (CTCs) in the peripheral blood of cancer patients is critical in clinical research for further investigation of tumor progression and metastasis. In this study, we present a novel surface-enhanced Raman scattering (SERS) substrate for the efficient capture and characterization of cancer cells using silver nanoparticles-reduced graphene oxide (AgNPs-rGO) composites. A pulsed laser reduction of silver nanowire-graphene oxide (AgNW-GO) mixture films induces hot-spot formations among AgNPs and artificial biointerfaces consisting of rGOs. We also use in situ electric field-assisted fabrication methods to enhance the roughness of the SERS substrate. The AgNW-GO mixture films, well suited for the proposed process due to its inherent electrophoretic motion, is adjusted between indium tin oxide (ITO) transparent electrodes and the nano-undulated surface is generated by applying direct-current (DC) electric fields during the laser process. As a result, MCF7 breast cancer cells are efficiently captured on the AgNPs-rGO substrates, about four times higher than the AgNWs-GO films, and the captured living cells are successfully analyzed by SERS spectroscopy. Our newly designed bifunctional substrate can be applied as an effective system for the capture and characterization of CTCs.

Functionalized reduced graphene oxide with aptamer macroarray for cancer cell capture and fluorescence detection

An integrated aptamer macroarray functionalized with reduced graphene oxide (rGO) to specifically capture and sensitively detect cancer cells is reported. The capture for cancer cells is based on effective recognition of the modified rGO surface through the aptamer against epithelial cell adhesion molecule (EpCAM). The rough structure of rGO enhances morphologic interactions between rGO film interface and the cancer cells, while super-hydrophilicity of modified rGO hinders nonspecific cell capture. The synergistic interactions offer the aptamer macroarray high efficiency of cancer cell capture. By means of a turn-on fluorescence strategy based on the conformation change of the aptamer induced by the target recognition, the enriched cancer cells can be directly read out at excitation/emission wavelengths of 550/680 nm without washing, separation, and dying steps. The working range is 1 × 10² to 2 × 10⁴ cells per mL with a detection limit of 22 cells per mL. The results indicate that the aptamer macroarray has a considerable foreground for early diagnosis, therapy, and monitoring of cancer. Graphical abstract.

Tunable Control of the Hydrophilicity and Wettability of Conjugated Polymers by a Postpolymerization Modification Approach

A facile method to prepare hydrophilic polymers by a postpolymerization nucleophillic aromatic substitution reaction of fluoride on an emissive conjugated polymer (CP) backbone is reported. Quantitative functionalization by a series of monofunctionalized ethylene glycol oligomers, from dimer to hexamer, as well as with high molecular weight polyethylene glycol is demonstrated. The length of the ethylene glycol sidechains is shown to have a direct impact on the surface wettability of the polymer, as well as its solubility in polar solvents. However, the energetics and band gap of the CPs remain essentially constant. This method therefore allows an easy way to modulate the wettability and solubility of CP materials for a diverse series of applications.

On the Interaction between 1D Materials and Living Cells

One-dimensional (1D) materials allow for cutting-edge applications in biology, such as single-cell bioelectronics investigations, stimulation of the cellular membrane or the cytosol, cellular capture, tissue regeneration, antibacterial action, traction force investigation, and cellular lysis among others. The extraordinary development of this research field in the last ten years has been promoted by the possibility to engineer new classes of biointerfaces that integrate 1D materials as tools to trigger reconfigurable stimuli/probes at the sub-cellular resolution, mimicking the in vivo protein fibres organization of the extracellular matrix. After a brief overview of the theoretical models relevant for a quantitative description of the 1D material/cell interface, this work offers an unprecedented review of 1D nano- and microscale materials (inorganic, organic, biomolecular) explored so far in this vibrant research field, highlighting their emerging biological applications. The correlation between each 1D material chemistry and the resulting biological response is investigated, allowing to emphasize the advantages and the issues that each class presents. Finally, current challenges and future perspectives are discussed.

A Review on Microdevices for Isolating Circulating Tumor Cells

Cancer metastasis is the primary cause of high mortality of cancer patients. Enumeration of circulating tumor cells (CTCs) in the bloodstream is a very important indicator to estimate the therapeutic outcome in various metastatic cancers. The aim of this article is to review recent developments on the CTC isolation technologies in microdevices. Based on the categories of biochemical and biophysical isolation approaches, a literature review and in-depth discussion will be included to provide an overview of this challenging topic. The current excellent developments suggest promising CTC isolation methods in order to establish a precise indicator of the therapeutic outcome of cancer patients.

Mechanotactic Activation of TGF-β by PEDOT Artificial Microenvironments Triggers Epithelial to Mesenchymal Transition

Epithelial to mesenchymal transition (EMT) is integral for cells to acquire metastatic properties, and ample evidence links it to bioorganic framework of the tumor microenvironment (TME). Hydroxymethyl-functionalized 3,4-ethylenedioxythiophene polymer (PEDOT-OH) enables construction of diverse nanotopography size and morphologies and is therefore exploited to engineer organic artificial microenvironments bearing nanodots from 300 to 1000 nm in diameter to understand spatiotemporal EMT regulation by biophysical components of the TME. MCF-7 breast cancer cells are cultured on these artificial microenvironments, and temporal regulation of cellular morphology and EMT markers is investigated. The results show that upon physical stimulation, cells on 300 nm artificial microenvironments advance to EMT and display a decreased extracellular matrix (ECM) protein secretion. In contrast, cells on 500 nm artificial microenvironments are trapped in EMT-imbalance. Interestingly, cells on 1000 nm artificial microenvironments resemble those on control surfaces. Upon further investigation, it is found that EMT induction is triggered via transforming growth factor β (TGF-β) and ECM cleaving protein, matrix metalloproteinease-9. Immunostaining EMT proteins highlighted that EMT induction is achieved through attenuation of cell-cell and cell-microenvironment adhesions. The physical stimulation-induced TGF-β perturbation can have a profound impact on the understanding of tumor-promoting signaling cascades originated by cellular microenvironment.

Tunable 3D nanofibrous and bio-functionalised PEDOT network explored as a conducting polymer-based biosensor

Conducting polymers that possess good electrochemical properties, nanostructured morphology and functionality for bioconjugation are essential to realise the concept of all-polymer-based biosensors that do not depend on traditional nanocatalysts such as carbon materials, metal, metal oxides or dyes. In this research, we demonstrated a facile approach for the simultaneous preparation of a bi-functional PEDOT interface with a tunable 3D nanofibrous network and carboxylic acid groups (i.e. Nano-PEDOT-COOH) via controlled co-polymerisation of EDOT and EDOT-COOH monomers, using tetrabutylammonium perchlorate as a soft-template. By tuning the ratio between EDOT and EDOT-COOH monomer, the nanofibrous structure and carboxylic acid functionalisation of Nano-PEDOT-COOH were varied over a fibre diameter range of 15.6 ± 3.7 to 70.0 ± 9.5 nm and a carboxylic acid group density from 0.03 to 0.18 μmol cm^-2. The nanofibres assembled into a three-dimensional network with a high specific surface area, which contributed to low charge transfer resistance and high transduction activity towards the co-enzyme NADH, delivering a wide linear range of 20-960 μM and a high sensitivity of 0.224 μA μM^-1 cm^-2 at the Nano-PEDOT-COOH50% interface. Furthermore, the carboxylic acid groups provide an anchoring site for the stable immobilisation of an NADH-dependent dehydrogenase (i.e. lactate dehydrogenase), via EDC/S-NHS chemistry, for the fabrication of a Bio-Nano-PEDOT-based biosensor for lactate detection which had a response time of less than 10 s over the range of 0.05-1.8 mM. Our developed bio-Nano-PEDOT interface shows future potential for coupling with multi-biorecognition molecules via carboxylic acid groups for the development of a range of advanced all-polymer biosensors.

Nanostructured Substrates for Detection and Characterization of Circulating Rare Cells: From Materials Research to Clinical Applications

Circulating rare cells in the blood are of great significance for both materials research and clinical applications. For example, circulating tumor cells (CTCs) have been demonstrated as useful biomarkers for "liquid biopsy" of the tumor. Circulating fetal nucleated cells (CFNCs) have shown potential in noninvasive prenatal diagnostics. However, it is technically challenging to detect and isolate circulating rare cells due to their extremely low abundance compared to hematologic cells. Nanostructured substrates offer a unique solution to address these challenges by providing local topographic interactions to strengthen cell adhesion and large surface areas for grafting capture agents, resulting in improved cell capture efficiency, purity, sensitivity, and reproducibility. In addition, rare-cell retrieval strategies, including stimulus-responsiveness and additive reagent-triggered release on different nanostructured substrates, allow for on-demand retrieval of the captured CTCs/CFNCs with high cell viability and molecular integrity. Several nanostructured substrate-enabled CTC/CFNC assays are observed maturing from enumeration and subclassification to molecular analyses. These can one day become powerful tools in disease diagnosis, prognostic prediction, and dynamic monitoring of therapeutic response-paving the way for personalized medical care.

The prognostic role of circulating tumor cells in colorectal cancer

Introduction: Metastasis is the main cause of cancer-associated death in colorectal cancer (CRC). The presence of circulating tumor cells (CTC) in the blood is associated with an increased risk of recurrence and poor prognosis. The clinical significance of CTCs as a novel biomarker has been extensively studied in the last decade. It has been shown that CTC detection applies to early cancer detection. The presence of CTCs is associated with metastatic spread and poor survival and is also useful as a marker for therapy response.Areas covered: We summarize the role of CTC in CRC, their clinical significance, current methods for CTC detection and challenges as well as future perspectives of CTC research.Expert commentary: The clinical significance of CTC in CRC patients is well established. Although insightful, the available marker-based approaches hampered our understanding of the CTCs and their biology, as such approaches do not take into account the heterogeneity of these cell populations. New technologies should expand the marker-based detection to multi biomarker-based approaches together with recent technological advances in microfluidics for single cell enrichment and analysis.

Emerging Nanotechnologies for Liquid Biopsy: The Detection of Circulating Tumor Cells and Extracellular Vesicles

Liquid biopsy enables noninvasive and dynamic analysis of molecular or cellular biomarkers, and therefore holds great potential for the diagnosis, prognosis, monitoring of disease progress and treatment efficacy, understanding of disease mechanisms, and identification of therapeutic targets for drug development. In this review, the recent progress in nanomaterials, nanostructures, nanodevices, and nanosensors for liquid biopsy is summarized, with a focus on the detection and molecular characterization of circulating tumor cells (CTCs) and extracellular vesicles (EVs). The developments and advances of nanomaterials and nanostructures in enhancing the sensitivity, specificity, and purity for the detection of CTCs and EVs are discussed. Sensing techniques for signal transduction and amplification as well as visualization strategies are also discussed. New technologies for the reversible release of the isolated CTCs and EVs and for single-CTC/EV analysis are summarized. Emerging microfluidic platforms for the integral on-chip isolation, detection, and molecular analysis are also included. The opportunities, challenges, and prospects of these innovative materials and technologies, especially with regard to their feasibility in clinical applications, are discussed. The applications of nanotechnology-based liquid biopsy will bring new insight into the clinical practice in monitoring and treatment of tumor and other significant diseases.

Modulating Electrode Kinetics for Discrimination of Dopamine by a PEDOT:COOH Interface Doped with Negatively Charged Tricarboxylate

The rapidly developing field of conducting polymers in organic electronics has many implications for bioelectronics. For biosensing applications, tailoring the functionalities of the conducting polymer's surface is an efficient approach to improve both sensitivity and selectivity. Here, we demonstrated a facile and economic approach for the fabrication of a high-density, negatively charged carboxylic-acid-group-functionalized PEDOT (PEDOT:COOH) using an inexpensive ternary carboxylic acid, citrate, as a dopant. The polymerization efficiency was significantly improved by the addition of LiClO₄ as a supporting electrolyte yielding a dense PEDOT:COOH sensing interface. The resulting PEDOT:COOH interface had a high surface density of carboxylic acid groups of 0.129 μmol/cm² as quantified by the toluidine blue O (TBO) staining technique. The dopamine response measured with the PEDOT:COOH sensing interface was characterized by cyclic voltammetry with a significantly reduced ΔE_p of 90 mV and a 3-fold increase in the I_pa value compared with those of the nonfunctionalized PEDOT sensing interface. Moreover, the cyclic voltammetry and electrochemical impedance spectroscopy results demonstrated the increased electrode kinetics and highly selective discrimination of dopamine (DA) in the presence of the interferents ascorbic acid (AA) and uric acid (UA), which resulted from the introduction of negatively charged carboxylic acid groups. The negatively charged carboxylic acid groups could favor the transfer, preconcentration, and permeation of positively charged DA to deliver improved sensing performance while repelling the negatively charged AA and UA interferents. The PEDOT:COOH interface facilitated measurement of dopamine over the range of 1-85 μM, with a sensitivity of 0.228 μA μM^-1, which is 4.1 times higher than that of a nonfunctionalized PEDOT electrode (0.055 μA μM^-1). Our results demonstrate the feasibility of a simple and economic fabrication of a high-density PEDOT:COOH interface for chemical sensing, which also has the potential for coupling with other biorecognition molecules via carboxylic acid moieties for the development of a range of advanced PEDOT-based biosensors.

Dual-function nanostructured platform for isolation of nasopharyngeal carcinoma circulating tumor cells and EBV DNA detection

Circulating tumor cells (CTCs) and plasma levels of Epstein-Barr virus (EBV) DNA are sensitive prognostic tools for monitoring disease status in nasopharyngeal carcinoma (NPC) patients. Herein, we introduce a novel and low-cost platform for capturing CTCs, the Si nanowires/microscale pyramids (NWs/MPs) hierarchical substrate, which could capture NPC cells in vitro and also detect EBV DNA at very low concentrations. In this study, Si NWs/MPs hierarchical substrates with varying wire length were fabricated using a metal-assisted chemical etching method. Anti-EpCAM antibodies were further conjugated on the substrate for capturing NPC CTCs in vitro. Capture efficiency was evaluated using immunofluorescence and scanning electronic microscopy (SEM) was utilized to understand cell morphology. The Si NWs/MPs substrate was also transformed into a Surface enhanced Raman scattering (SERS) substrate by coating with Ag nanoparticles (AgNPs) for detection of EBV DNA by Raman spectroscopy. The results demonstrated that Si NWs/MPs with 20 min of etch time had the best capturing performance. Additionally, SEM observations revealed good contact of CTCs with Si NWs/MPs substrates. Moreover, the AgNPs-coated NWs/MPs substrate was shown to be a sensitive EBV DNA detector, by which the DNA detection limit can reach up to 10^-13M. In conclusion, the Si NWs/MPs platform not only exhibits superior cell capturing ability, but also can sensitively detect EBV DNA at very low concentrations. This platform has great potential to become a promising diagnostic tool for monitoring disease status and prognostication of NPC patients.

Recent advances in microfluidic methods in cancer liquid biopsy

Early cancer detection, its monitoring, and therapeutical prediction are highly valuable, though extremely challenging targets in oncology. Significant progress has been made recently, resulting in a group of devices and techniques that are now capable of successfully detecting, interpreting, and monitoring cancer biomarkers in body fluids. Precise information about malignancies can be obtained from liquid biopsies by isolating and analyzing circulating tumor cells (CTCs) or nucleic acids, tumor-derived vesicles or proteins, and metabolites. The current work provides a general overview of the latest on-chip technological developments for cancer liquid biopsy. Current challenges for their translation and their application in various clinical settings are discussed. Microfluidic solutions for each set of biomarkers are compared, and a global overview of the major trends and ongoing research challenges is given. A detailed analysis of the microfluidic isolation of CTCs with recent efforts that aimed at increasing purity and capture efficiency is provided as well. Although CTCs have been the focus of a vast microfluidic research effort as the key element for obtaining relevant information, important clinical insights can also be achieved from alternative biomarkers, such as classical protein biomarkers, exosomes, or circulating-free nucleic acids. Finally, while most work has been devoted to the analysis of blood-based biomarkers, we highlight the less explored potential of urine as an ideal source of molecular cancer biomarkers for point-of-care lab-on-chip devices.

Engineering Antifouling Conducting Polymers for Modern Biomedical Applications

Conducting polymers are considered to be favorable electrode materials for implanted biosensors and bioelectronics, because their mechanical properties are similar to those of biological tissues such as nerve and brain tissues. However, one of the primary challenges for implanted devices is to prevent the unwanted protein adhesion or cell binding within biological fluids. The nonspecific adsorption generally causes the malfunction of implanted devices, which is problematic for long-term applications. When responding to the requirements of solving the problems caused by nonspecific adsorption, an increasing number of studies on antifouling conducting polymers has been recently published. In this review, synthetic strategies for preparing antifouling conducting polymers, including direct synthesis of functional monomers and post-functionalization, are introduced. The applications of antifouling conducting polymers in modern biomedical applications are particularly highlighted. This paper presents focuses on the features of antifouling conducting polymers and the challenges of modern biomedical applications.

Theoretical and Experimental Study of Reversible and Stable Wetting States of a Hierarchically Wrinkled Surface Tuned by Mechanical Strain

The wetting behavior of hierarchically wrinkled surfaces has attracted great interest because of its broad application in flexible electronic, microfluidic chip, and biomedicine. However, theoretical studies concerning the relationship between the apparent contact angle and mechanical strain applied on the soft and flexible surface with a hierarchically wrinkled structure are still limited. We established a theoretical framework to describe and understand how prestrain and applied dynamic strain reversibly tune the wettability of the hierarchically wrinkled surface. More specifically, a direct relationship between the mechanical strain and contact angle was built through reversible tuning of the amplitude and the wavelength of the wrinkled structures caused by mechanical strain, which allowed for more precise adjustment of surface wettability. To verify the accuracy of the theoretical relationship between the contact angle and mechanical strain, a soft surface with a hierarchically wrinkled structure was prepared by combining wrinkled microstructures and strip ones. The results showed that the experimental contact angles were in agreement with the theoretical ones within a limited error range. This will be helpful for further investigation on the wettability of hierarchically wrinkled surfaces.

Soft and flexible material-based affinity sensors

Recent advances in biosensors and point-of-care (PoC) devices are poised to change and expand the delivery of diagnostics from conventional lateral-flow assays and test strips that dominate the market currently, to newly emerging wearable and implantable devices that can provide continuous monitoring. Soft and flexible materials are playing a key role in propelling these trends towards real-time and remote health monitoring. Affinity biosensors have the capability to provide for diagnosis and monitoring of cancerous, cardiovascular, infectious and genetic diseases by the detection of biomarkers using affinity interactions. This review tracks the evolution of affinity sensors from conventional lateral-flow test strips to wearable/implantable devices enabled by soft and flexible materials. Initially, we highlight conventional affinity sensors exploiting membrane and paper materials which have been so successfully applied in point-of-care tests, such as lateral-flow immunoassay strips and emerging microfluidic paper-based devices. We then turn our attention to the multifarious polymer designs that provide both the base materials for sensor designs, such as PDMS, and more advanced functionalised materials that are capable of both recognition and transduction, such as conducting and molecularly imprinted polymers. The subsequent content discusses wearable soft and flexible material-based affinity sensors, classified as flexible and skin-mountable, textile materials-based and contact lens-based affinity sensors. In the final sections, we explore the possibilities for implantable/injectable soft and flexible material-based affinity sensors, including hydrogels, microencapsulated sensors and optical fibers. This area is truly a work in progress and we trust that this review will help pull together the many technological streams that are contributing to the field.

Deprotonation-Induced Conductivity Shift of Polyethylenedioxythiophenes in Aqueous Solutions: The Effects of Side-Chain Length and Polymer Composition

Deprotonation-induced conductivity shift of poly(3,4-ethylenedixoythiophene)s (PEDOTs) in aqueous solutions is a promising platform for chemical or biological sensor due to its large signal output and minimum effect from material morphology. Carboxylic acid group functionalized poly(Cn-EDOT-COOH)s are synthesized and electrodeposited on microelectrodes. The microelectrodes are utilized to study the effect of carboxylic acid side-chain length on the conductivity curve profiles in aqueous buffer with different pH. The conductivity shifts due to the buffer pH are effected by the length of the carboxylic acid side-chains. The shifts can be explained by the carboxylic acid dissociation property (pKa) at the solid-liquid interface, self-doping effect, and effective conjugation length. Conductivity profiles of poly(EDOT-OH-co-C₂-EDOT-COOH) copolymers are also studied. The shifts show linear relationship with the feed monomer composition used in electrochemical polymerization.

Size-matching hierarchical micropillar arrays for detecting circulating tumor cells in breast cancer patients' whole blood

Circulating tumor cells (CTCs) are important markers for cancer diagnosis and treatment, but it is still a challenge to recognize and isolate CTCs because they are very rare in the blood. To selectively recognize CTCs and improve the capture efficiency, micro/nanostructured substrates have been fabricated for this application; however the size of CTCs is often ignored in designing and engineering micro/nanostructured substrates. Herein, a spiky polymer micropillar array is fabricated for capturing CTCs with high efficiency. The surface of the micropillar is cactus-like, and is composed of nanospikes. This hierarchical polymer array is designed according to the size of CTCs, which allows for more interactions of the CTCs with the array by setting the size of gaps among the micropillars to match with the CTCs. This polymer array is created by molding on an ordered silicon array, and then it is coated with an antiepithelial cell adhesion molecule antibody (anti-EpCAM). After co-culture with MCF-7 cells for 45 min, the capture efficiency of this array for CTCs is up to 91% ± 2%. Moreover, the anti-EpCAM modified polymer micropillar arrays present an excellent capacity to isolate CTCs from the whole blood samples of breast cancer patients. This study may provide a new concept for capturing target cells by designing and engineering micro/nanostructured substrates according to the size of target cells.

Facile Synthesis of a 3,4-Ethylene-Dioxythiophene (EDOT) Derivative for Ease of Bio-Functionalization of the Conducting Polymer PEDOT

In the pursuit of conducting polymer based bio-functional devices, a cost-effective and high yield synthesis method for a versatile monomer is desired. We report here a new synthesis strategy for a versatile monomer 2-methylene-2,3-dihydrothieno (3,4-b) (1,4) dioxine, or 3,4-ethylenedioxythiophene with a exomethylene side group (EDOT-EM). Compared to the previously reported synthesis route, the new strategy uses less steps, with faster reaction rate, and higher yield. The presence of EM group opens up endless possibility for derivatization via either hydro-alkoxy addition or thiol-ene click chemistry. EDOT-EM could be polymerized into stable and low impedance PEDOT-EM polymer using electro-polymerization method on different conducting substrates at both macro and micro scales. Facile post-functionalization of PEDOT-EM with molecules of varying size and functionality (from small molecules to DNAs and proteins) was achieved. The new synthetic route of EDOT-EM and the ease of post-functionalization of PEDOT-EM will greatly accelerate the use of conducting polymer in a broad range of organic electronics and bioelectronics applications.

Electrodeposition of Zwitterionic PEDOT Films for Conducting and Antifouling Surfaces

Conferring antifouling properties can extend the use of conducting polymers in biosensors and bioelectronics under complex biological conditions. On the basis of the antifouling properties of a series of zwitterionic polymers, we synthesized new thiophene-based compounds bearing a phosphorylcholine, carboxybetaine, or sulfobetaine pendant group. The monomers were synthesized by a facile reaction of thiol-functionalized 3,4-ethylenedioxythiophene with zwitterionic methacrylates. Electrochemical copolymerization was performed to deposit zwitterionic poly(3,4-ethylenedioxythiophene) (PEDOT) films with tunable conducting and antifouling properties on a conducting substrate. Electrochemical impedance spectroscopy showed that the conductivity and capacitance decreased with increasing zwitterionic content in the films. Protein adsorption and cell adhesion studies showed the effects of the type and content of zwitterions on the antifouling characteristics. Optimization of the electrodeposition conditions enabled development of both conducting and antifouling polymer films. These antifouling conjugated functional polymers have promising applications in biological environments.

A blood cell repelling and tumor cell capturing surface for high-purity enrichment of circulating tumor cells

A red blood cell membrane mimetic surface decorated with FA and RGD ligands can efficiently capture tumor cells with high selectivity.

Cell-imprinted biomimetic interface for intelligent recognition and efficient capture of CTCs

Synergistically contributing to plastic and natural antibodies, a cell-imprinted biomimetic interface exhibited high sensitivity and efficiency in CTC capture, providing novel insight into cell–biointerface interactions.

Superhydrophobicity: advanced biological and biomedical applications

The biological and biomedical applications of superhydrophobic surface.

Enhanced capture and release of circulating tumor cells using hollow glass microspheres with a nanostructured surface

Self-floating hollow glass microspheres (HGMS) modified with tumor-specific antibodies have been developed for the capture of circulating tumor cells (CTCs), and have demonstrated effective cell isolation and good viability of isolated cancer cells. However, the capture efficiency decreases dramatically if the spiked cell concentration is low, possibly due to insufficient interactions between cancer cells and the HGMS surface. In order to apply HGMS-based CTC isolation to clinically relevant samples, it is desirable to create nanostructures on the surface of HGMS to enhance cell-surface interactions. Nevertheless, current microfabrication methods cannot generate nanostructured-surfaces on microspheres. The authors have developed a new HGMS with a controlled nanotopographical surface structure (NSHGMS), and demonstrated isolation and recovery of rare cancer cells. NSHGMS are achieved by applying layer-by-layer (LbL) assembly of negatively charged SiO2 nanoparticles and positively charged poly-l-arginine molecules, then sheathing the surface with an enzymatically degradable LbL film made from biotinylated alginate and poly-l-arginine, and capping with anti-EpCAM antibodies and anti-fouling PEG molecules. Compared to smooth-surfaced HGMS, NSHGMS showed shorter isolation time (20 min), enhanced capture efficiency (93.6 ± 4.9%) and lower detection limit (30 cells per mL) for commonly used cancer cell lines (MCF7, SK-BR-3, PC-3, A549 and CCRF-CEM). This NSHGMS-based CTC isolation method does not require specialized lab equipment or an external power source, and thus, can be used for the separation of targeted cells from blood or other body fluids in a resource-limited environment.

Direct Writing and Characterization of Three-Dimensional Conducting Polymer PEDOT Arrays

Direct writing is an effective and versatile technique for three-dimensional (3D) fabrication of conducting polymer (CP) structures. It is precisely localized and highly controllable, thus providing great opportunities for incorporating CPs into microelectronic array devices. Herein we demonstrate 3D writing and characterization of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT:PSS) pillars in an array format, by using an in-house-constructed variant of scanning ion conductance microscopy (SICM). CP pillars with different aspect ratios were successfully fabricated by optimizing the writing parameters: pulling speed, pulling time, concentration of the polymer solution, and the micropipette tip diameter. Especially, super high aspect ratio pillars of around 7 μm in diameter and 5000 μm in height were fabricated, indicating a good capability of this direct writing technique. Additions of an organic solvent and a cross-linking agent contribute to a significantly enhanced water stability of the pillars, critical if the arrays were to be used in biologically relevant applications. Surface morphologies and structural analysis of CP pillars were characterized by scanning electron microscopy and Raman spectroscopy, respectively. Electrochemical properties of the individual pillars of different heights were examined by cyclic voltammetry using a double-barrel micropipette as an electrochemical cell. Exceptional mechanical properties of the pillars, such as high flexibility and robustness, were observed when bent by applying a force. The 3D pillar arrays are expected to provide versatile substrates for functionalized and integrated biological sensing and electrically addressable array devices.

Glycan Stimulation Enables Purification of Prostate Cancer Circulating Tumor Cells on PEDOT NanoVelcro Chips for RNA Biomarker Detection

A glycan-stimulated and poly(3,4-ethylene-dioxythiophene)s (PEDOT)-based nanomaterial platform is fabricated to purify circulating tumor cells (CTCs) from blood samples of prostate cancer (PCa) patients. This new platform, phenylboronic acid (PBA)-grafted PEDOT NanoVelcro, combines the 3D PEDOT nanosubstrate, which greatly enhances CTC capturing efficiency, with a poly(EDOT-PBA-co-EDOT-EG3) interfacial layer, which not only provides high specificity for CTC capture upon antibody conjugation but also enables competitive binding of sorbitol to gently release the captured cells. CTCs purified by this PEDOT NanoVelcro chip provide well-preserved RNA transcripts for the analysis of the expression level of several PCa-specific RNA biomarkers, which may provide clinical insights into the disease.

NanoVelcro rare-cell assays for detection and characterization of circulating tumor cells

Circulating tumor cells (CTCs) are cancer cells shredded from either a primary tumor or a metastatic site and circulate in the blood as the potential cellular origin of metastasis. By detecting and analyzing CTCs, we will be able to noninvasively monitor disease progression in individual cancer patients and obtain insightful information for assessing disease status, thus realizing the concept of "tumor liquid biopsy". However, it is technically challenging to identify CTCs in patient blood samples because of the extremely low abundance of CTCs among a large number of hematologic cells. In order to address this challenge, our research team at UCLA pioneered a unique concept of "NanoVelcro" cell-affinity substrates, in which CTC capture agent-coated nanostructured substrates were utilized to immobilize CTCs with remarkable efficiency. Four generations of NanoVelcro CTC assays have been developed over the past decade for a variety of clinical utilities. The 1st-gen NanoVelcro Chips, composed of a silicon nanowire substrate (SiNS) and an overlaid microfluidic chaotic mixer, were created for CTC enumeration. The 2nd-gen NanoVelcro Chips (i.e., NanoVelcro-LMD), based on polymer nanosubstrates, were developed for single-CTC isolation in conjunction with the use of the laser microdissection (LMD) technique. By grafting thermoresponsive polymer brushes onto SiNS, the 3rd-gen Thermoresponsive NanoVelcro Chips have demonstrated the capture and release of CTCs at 37 and 4 °C respectively, thereby allowing for rapid CTC purification while maintaining cell viability and molecular integrity. Fabricated with boronic acid-grafted conducting polymer-based nanomaterial on chip surface, the 4th-gen NanoVelcro Chips (Sweet chip) were able to purify CTCs with well-preserved RNA transcripts, which could be used for downstream analysis of several cancer specific RNA biomarkers. In this review article, we will summarize the development of the four generations of NanoVelcro CTC assays, and the clinical applications of each generation of devices.

The effects of surface topography of nanostructure arrays on cell adhesion

The effects of geometry and surface density distribution of nanopillars on cell adhesion studied by a quantitative thermodynamic model showed that high (low) surface distribution density and large (small) radius result in the “Top” (“Bottom”) mode.