Integrated 3D conducting polymer-based bioelectronics for capture and release of circulating tumor cells

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.

Two-photon polymerization lithography enabling the fabrication of PEDOT:PSS 3D structures for bioelectronic applications

Conductive 3D platforms have gained increasing attention in bioelectronics thanks to the improvement in the cell-chip coupling. PEDOT:PSS is nowadays widely employed in bioelectronic applications thanks to its electrical and mechanical properties. In this work, an innovative fabrication method for the realization of PEDOT:PSS-based conductive micropillars and 3D cage-like structures is presented, combining two-photon lithography and electrodeposition techniques.

Conducting Polymer-Coated Carbon Cloth Captures and Releases Extracellular Vesicles by a Rapid and Controlled Redox Process

Electrochemical techniques offer great opportunities for the capture of chemical and biological entities from complex mixtures and their subsequent release into clean buffers for analysis. Such methods are clean, robust, rapid, and compatible with a wide range of biological fluids. Here, we designed an electrochemically addressable system, based on a conducting terpolymer [P(EDOT-co-EDOTSAc-co-EDOTEG)] coated onto a carbon cloth substrate, to selectively capture and release biological entities using a simple electrochemical redox process. The conducting terpolymer composition was optimized and the terpolymer-coated carbon cloth was extensively characterized using electrochemical analysis, Raman and Fourier transform-infrared spectroscopy, water contact angle analysis, and scanning electron microscopy. The conductive terpolymer possesses a derivative of EDOT with an acetylthiomethyl moiety (EDOTSAc), which is converted into a "free" thiol that then undergoes reversible oxidation/reduction cycles at +1.0 V and -0.8 V (vs Ag/AgCl), respectively. That redox process enables electrochemical capture and on-demand release. We first demonstrated the successful electrochemical capture/release of a fluorescently labeled IgG antibody. The same capture/release procedure was then applied to release extracellular vesicles (EVs), originating from both MCF7 and SKBR3 breast cancer cell line bioreactors. EVs were captured using the substrate-conjugated HER2 antibody which was purified from commercially available trastuzumab. Capture and release of breast cancer EVs using a trastuzumab-derived HER2 antibody has not been reported before (to the best of our knowledge). A rapid (2 min) release at a low potential (-0.8 V) achieved a high release efficiency (>70%) of the captured, HER2+ve, SKBR3 EVs. The developed system and the electrochemical method are efficient and straightforward and have vast potential for the isolation and concentration of various biological targets from large volumes of biological and other (e.g., environmental) samples.

Interfacial Electrofabrication of Freestanding Biopolymer Membranes with Distal Electrodes

Using electrical signals to guide materials' deposition has a long-standing history in metal coating, microchip fabrication, and the integration of organics with devices. In electrodeposition, however, the conductive materials can be deposited only onto the electrode surfaces. Here, an innovative process is presented to electrofabricate freestanding biopolymer membranes at the interface of electrolytes without any supporting electrodes at the fabrication site. Chitosan, a derivative from the naturally abundant biopolymer chitin, has been broadly explored in electrodeposition for integrating biological entities onto microfabricated devices. It is widely believed that the pH gradients generated at the cathode deprotonate the positively charged chitosan chains into a film on the cathode surface. The interfacial electrofabrication with pH indicators, however, demonstrated that the membrane growth was driven by the instantaneous flow of hydroxyl ions from the ambient alginate solution, rather than the slow propagation of pH gradients from the cathode surface. This interfacial electrofabrication produces freestanding membrane structures and can be expanded to other materials, which presents a new direction in using electrical signals for manufacturing.

Nanotechnology-Assisted Isolation and Analysis of Circulating Tumor Cells on Microfluidic Devices

Circulating tumor cells (CTCs), a type of cancer cell that spreads from primary tumors into human peripheral blood and are considered as a new biomarker of cancer liquid biopsy. It provides the direction for understanding the biology of cancer metastasis and progression. Isolation and analysis of CTCs offer the possibility for early cancer detection and dynamic prognosis monitoring. The extremely low quantity and high heterogeneity of CTCs are the major challenges for the application of CTCs in liquid biopsy. There have been significant research endeavors to develop efficient and reliable approaches to CTC isolation and analysis in the past few decades. With the advancement of microfabrication and nanomaterials, a variety of approaches have now emerged for CTC isolation and analysis on microfluidic platforms combined with nanotechnology. These new approaches show advantages in terms of cell capture efficiency, purity, detection sensitivity and specificity. This review focuses on recent progress in the field of nanotechnology-assisted microfluidics for CTC isolation and detection. Firstly, CTC isolation approaches using nanomaterial-based microfluidic devices are summarized and discussed. The different strategies for CTC release from the devices are specifically outlined. In addition, existing nanotechnology-assisted methods for CTC downstream analysis are summarized. Some perspectives are discussed on the challenges of current methods for CTC studies and promising research directions.

Anti-Escherichia coli Functionalized Silver-Doped Carbon Nanofibers for Capture of E. coli in Microfluidic Systems

Silver-doped carbon nanofibers (SDCNF) are used as the base material for the selective capture of Escherichia coli in microfluidic systems. Fibers were spun in a glovebox with dry atmosphere maintained by forced dry air pumped through the closed environment. This affected the evaporation rate of the solvent during the electrospinning process and the distribution of silver particles within the fiber. Antibodies are immobilized on the surface of the silver-doped polyacrylonitrile (PAN) based carbon nanofibers via a three-step process. The negatively charged silver particles present on the surface of the nanofibers provide suitable sites for positively charged biotinylated poly-(L)-lysine-graft-poly-ethylene-glycol (PLL-g-PEG biotin) conjugate attachment. Streptavidin and a biotinylated anti-E. coli antibody were then added to create anti-E. coli surface functionalized (AESF) nanofibers. Functionalized fibers were able to immobilize up to 130 times the amount of E. coli on the fiber surface compared to neat silver doped fibers. Confocal images show E. coli remains immobilized on fiber mat surface after extensive rinsing showing the bacteria is not simply a result of non-specific binding. To demonstrate selectivity and functionalization with both gram negative and gram-positive antibodies, anti-Staphylococcus aureus surface functionalized (ASSF) nanofibers were also prepared. Experiments with AESF performed with Staphylococcus aureus (S. aureus) and ASSF with E. coli show negligible binding to the fiber surface showing the selectivity of the functionalized membranes. This surface functionalization can be done with a variety of antibodies for tunable selective pathogen capture.

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.

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.

Carbon Nanotube/Conducting Polymer Hybrid Nanofibers as Novel Organic Bioelectronic Interfaces for Efficient Removal of Protein-Bound Uremic Toxins

Protein-bound uremic toxins (PBUTs) can cause noxious effects in patients suffering from renal failure as a result of inhibiting the transport of proteins and inducing their structural modification. They are difficult to remove through standard hemodialysis (HD) treatment. Herein, we report an organic bioelectronic HD device system for the effective removal of PBUTs through electrically triggered dissociation of protein-toxin complexes. To prepare this system, we employed electrospinning to fabricate electrically conductive quaternary composite nanofiber mats-comprising multiwalled carbon nanotubes (MWCNTs), poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), poly(ethylene oxide) (PEO), and (3-glycidyloxypropyl)trimethoxysilane (GOPS)-on conventional polyethersulfone (PES) dialysis membranes. These composite nanofiber platforms exhibited (i) long-term water resistance (due to cross-linking among PSS, PEO, and GOPS), (ii) high adhesion strength on the PES membrane (due to GOPS functioning as an adhesion promoter), (iii) enhanced electrical properties [due to the MWCNTs and PEDOT:PSS promoting effective electrical stimulation (ES) operation in devices containing bioelectronic interfaces (BEI)], and (iv) good anticoagulant ability and negligible hemolysis of red blood cells. We employed this organic BEI electronic system as a novel single-membrane HD device to study the removal efficiency of four kinds of uremic toxins [p-cresol (PC), indoxyl sulfate, and hippuric acid as PBUTs; creatinine as a non-PBUT] as well as the effects of ES on lowering the protein binding ratio. Our organic BEI devices provided a high rate of removal of PC with low protein loss after 4 h of a simulated dialysis process. It also functioned with low complement activation, low contact activation levels, and lower amounts of platelet adsorption, suggesting great suitability for use in developing next-generation bioelectronic medicines for HD.

Fully Printed μ-Needle Electrode Array from Conductive Polymer Ink for Bioelectronic Applications

Microelectrode arrays (MEAs) are widely used platforms in bioelectronics to study electrogenic cells. In recent years, the processing of conductive polymers for the fabrication of three-dimensional electrode arrays has gained increasing interest for the development of novel sensor designs. Here, additive manufacturing techniques are promising tools for the production of MEAs with three-dimensional electrodes. In this work, a facile additive manufacturing process for the fabrication of MEAs that feature needle-like electrode tips, so-called μ-needles, is presented. To this end, an aerosol-jet compatible PEDOT:PSS and multiwalled carbon nanotube composite ink with a conductivity of 323 ± 75 S m^-1 is developed and used in a combined inkjet and aerosol-jet printing process to produce the μ-needle electrode features. The μ-needles are fabricated with a diameter of 10 ± 2 μm and a height of 33 ± 4 μm. They penetrate an inkjet-printed dielectric layer to a height of 12 ± 3 μm. After successful printing, the electrochemical properties of the devices are assessed via cyclic voltammetry and impedance spectroscopy. The μ-needles show a capacitance of 242 ± 70 nF at a scan rate of 5 mV s^-1 and an impedance of 128 ± 22 kΩ at 1 kHz frequency. The stability of the μ-needle MEAs in aqueous electrolyte is demonstrated and the devices are used to record extracellular signals from cardiomyocyte-like HL-1 cells. This proof-of-principle experiment shows the μ-needle MEAs' cell-culture compatibility and functional integrity to investigate electrophysiological signals from living cells.

Random and aligned electrospun PLGA nanofibers embedded in microfluidic chips for cancer cell isolation and integration with air foam technology for cell release

BACKGROUND

Circulating tumor cells (CTCs) comprise the high metastatic potential population of cancer cells in the blood circulation of humans; they have become the established biomarkers for cancer diagnosis, individualized cancer therapy, and cancer development. Technologies for the isolation and recovery of CTCs can be powerful cancer diagnostic tools for liquid biopsies, allowing the identification of malignancies and guiding cancer treatments for precision medicine.

METHODS

We have used an electrospinning process to prepare poly(lactic-co-glycolic acid) (PLGA) nanofibrous arrays in random or aligned orientations on glass slips. We then fabricated poly(methyl methacrylate) (PMMA)-based microfluidic chips embedding the PLGA nanofiber arrays and modified their surfaces through sequential coating with using biotin-(PEG)7-amine through EDC/NHS activation, streptavidin (SA), and biotinylated epithelial-cell adhesion-molecule antibody (biotin-anti-EpCAM) to achieve highly efficient CTC capture. When combined with an air foam technology that induced a high shear stress and, thereby, nondestructive release of the captured cells from the PLGA surfaces, the proposed device system operated with a high cell recovery rate.

RESULTS

The morphologies and average diameters of the electrospun PLGA nanofibers were characterized using scanning electron microscopy (SEM) and confocal Raman imaging. The surface chemistry of the PLGA nanofibers conjugated with the biotin-(PEG)7-amine was confirmed through time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging. The chip system was studied for the effects of the surface modification density of biotin-(PEG)7-amine, the flow rates, and the diameters of the PLGA nanofibers on the capture efficiency of EpCAM-positive HCT116 cells from the spiked liquid samples. To assess their CTC capture efficiencies in whole blood samples, the aligned and random PLGA nanofiber arrays were tested for their abilities to capture HCT116 cells, providing cancer cell capture efficiencies of 66 and 80%, respectively. With the continuous injection of air foam into the microfluidic devices, the cell release efficiency on the aligned PLGA fibers was 74% (recovery rate: 49%), while it was 90% (recovery rate: 73%) on the random PLGA fibers, from tests of 200 spiked cells in 2 mL of whole blood from healthy individuals. Our study suggests that integrated PMMA microfluidic chips embedding random PLGA nanofiber arrays may be suitable devices for the efficient capture and recovery of CTCs from whole blood samples.

Real-time in vivo imaging of subpopulations of circulating tumor cells using antibody conjugated quantum dots

INTRODUCTION

The detection of circulating tumor cells (CTCs) is very important for cancer diagnosis. CTCs can travel from primary tumors through the circulation to form secondary tumor colonies via bloodstream extravasation. The number of CTCs has been used as an indicator of cancer progress. However, the population of CTCs is very heterogeneous. It is very challenging to identify CTC subpopulations such as cancer stem cells (CSCs) with high metastatic potential, which are very important for cancer diagnostic management.

RESULTS

We report a study of real-time CTC and CSC imaging in the bloodstreams of living animals using multi-photon microscopy and antibody conjugated quantum dots. We have developed a cancer model for noninvasive imaging wherein pancreatic cancer cells expressing fluorescent proteins were subcutaneously injected into the earlobes of mice and then formed solid tumors. When the cancer cells broke away from the solid tumor, CTCs with fluorescent proteins in the bloodstream at different stages of development could be monitored noninvasively in real time. The number of CTCs observed in the blood vessels could be correlated to the tumor size in the first month and reached a maximum value of approximately 100 CTCs/min after 5 weeks of tumor inoculation. To observe CTC subpopulations, conjugated quantum dots were used. It was found that cluster of differentiation (CD)24+ CTCs can move along the blood vessel walls and migrate to peripheral tissues. CD24+ cell accumulation on the solid tumors' sides was observed, which may provide valuable insight for designing new drugs to target cancer subpopulations with high metastatic potential. We also demonstrated that our system is capable of imaging a minor population of cancer stem cells, CD133+ CTCs, which are found in 0.7% of pancreatic cancer cells and 1%-3% of solid tumors in patients.

CONCLUSIONS

With the help of quantum dots, CTCs with higher metastatic potential, such as CD24+ and CD133+ CTCs, have been identified in living animals. Using our approach, it may be possible to investigate detailed metastatic mechanism such as tumor cell extravasation to the blood vessels. In addition, the number of observed CTCs in the blood stream could be correlated with tumor stage in the early stage of cancer.

An Inertia-Deformability Hybrid Circulating Tumor Cell Chip: Design, Clinical Test, and Numerical Analysis

Detection and capture of circulating tumor cells (CTCs) with microfluidic chips hold significance in cancer prognosis, diagnosis, and anti-cancer treatment. The counting of CTCs provides potential tools to evaluate cancer stages as well as treatment progress. However, facing the challenge of rareness in blood, the precise enumeration of CTCs is challenging. In the present research, we designed an inertial-deformability hybrid microfluidic chip using a long spiral channel with trapezoid-circular pillars and a capture zone. To clinically validate the device, the microfluidic chip has been tested for the whole blood and lysed blood with a small number of CTCs (colorectal and nonsmall-cell lung cancer) spiked in. The capture efficiency reaches over 90% for three types of cancer cell lines at the flow rate of 1.5 mL/h. Following numerical modeling was conducted to explain the working principle and working condition (Reynolds number below 10 and Dean number around 1). This design extended the effective capture length, improved the capture efficiency, and made the CTC enumeration much easier. We believe that this hybrid chip is promising clinically in the CTCs enumeration, evaluation of cancer therapy, and pharmacological responses.

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.

Poly(3,4-ethylenedioxythiophene)-Based Nanofiber Mats as an Organic Bioelectronic Platform for Programming Multiple Capture/Release Cycles of Circulating Tumor Cells

In this investigation, we employed a novel one-step electrospinning process to fabricate poly(ethylene oxide) (PEO)/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) core/shell nanofiber structures with improved water resistance and good electrochemical properties and characterized them using scanning electron microscopy, transmission electron microscopy, and time-of-flight secondary ion mass spectrometry imaging. We then integrated a biotinylated poly-(l-lysine-graft-ethylene glycol) (PLL-g-PEG-biotin) coating with three-dimensional (3D) PEDOT-based nanofiber devices for dynamic control over the capture/release performance of rare circulating tumor cells (CTCs) on-chip. The detailed capture/release behavior of the circulating tumor cells was studied using an organic bioelectronic platform comprising PEO/PEDOT:PSS nanofiber mats with 3 wt % (3-glycidyloxypropyl)trimethoxysilane as an additive. We have demonstrated that these nanofiber mats deposited on five-patterned indium tin oxide finger electrodes are excellent candidates for use as functional bioelectronic interfaces for the isolation, detection, sequential collection, and enrichment of rare CTCs through electrical activation of each single electrode. This combination behaved as an ideal model system displaying a high cell-capture yield for antibody-positive cells while resisting the adhesion of antibody-negative cells. Taking advantage of the electrochemical doping/dedoping characteristics of PEDOT:PSS materials, the captured rare cells could be electrically triggered release through the desorption phenomena of PLL-g-PEG-biotin on device surface. More than 90% of the targeted cancer cells were captured on the 3D PEDOT-based nanofiber microfluidic device; over 87% of captured cancer cells were subsequently released for collection; approximately 80% of spiked cancer cells could be collected in a 96-well plate. Therefore, this 3D PEDOT-based nanofiber approach appears to be an economical route for the large-scale preparation of systems for enhancing the downstream characterization of rare CTCs.

Multifunctional Nanofibers for Specific Purification and Release of CTCs

Recovering pure and viable circulating tumor cells (CTCs) from blood has been a challenging task for molecular characterization and functional analysis, which has attracted wide attention these days. Herein, we fabricate a thermoresponsive chitosan nanofiber substrate to effectively capture, purify, and release the target cancer cells, assisted by PNIPAAm brushes and DNA hybridization. The PNIPAAm brushes are designed to enable WBCs to detach from aptamer-PNIPAAm-chitosan-nanofiber (aptamer-P-CNFs) surfaces during the conformational transition. Meanwhile these specific captured CTCs are retained at a high purity. Moreover, effective and intact release of CTCs from the substrates without any foreign agents is realized by complementary sequences efficiently hybridizing with aptamers, and the specific cell release makes CTCs further purified. The present work provides a new strategy in the design of biointerface for recovering target CTCs from whole blood samples with high purity.

Self-assembled coronene nanofiber arrays: toward integrated organic bioelectronics for efficient isolation, detection, and recovery of cancer cells

Integrated coronene-based nanofiber array devices for circulating tumor cell isolation, detection, and recovery through electrical stimulation.

Rhipsalis (Cactaceae)-like Hierarchical Structure Based Microfluidic Chip for Highly Efficient Isolation of Rare Cancer Cells

The circulating tumor cells (CTCs), originating from the primary tumor, play a vital role in cancer diagnosis, prognosis, disease monitoring, and precise therapy. However, the CTCs are extremely rare in the peripheral bloodstream and hard to be isolated. To overcome current limitations associated with CTC capture and analysis, the strategy incorporating nanostructures with microfluidic devices receives wide attention. Here, we demonstrated a three-dimensional microfluidic device (Rm-chip) for capturing cancer cells with high efficiency by integrating a novel hierarchical structure, the "Rhipsalis (Cactaceae)"-like micropillar array, into the Rm-chip. The PDMS micropillar array was fabricated by soft-lithography and rapid prototyping method, which was then conformally plated with a thin gold layer through electroless plating. EpCAM antibody was modified onto the surface of the micropillars through the thiol-oligonucleotide linkers in order to release captured cancer cells by DNase I treatment. The antibody-functionalized device achieved an average capture efficiency of 88% in PBS and 83.7% in whole blood samples. We believe the Rm-chip provided a convenient, economical, and versatile approach for cell analysis with wide potential applications.

Peptide-Mediated Platelet Capture at Gold Micropore Arrays

Ordered spherical cap gold cavity arrays with 5.4, 1.6, and 0.98 μm diameter apertures were explored as capture surfaces for human blood platelets to investigate the impact of surface geometry and chemical modification on platelet capture efficiency and their potential as platforms for surface enhanced Raman spectroscopy of single platelets. The substrates were chemically modified with single-constituent self-assembled monolayers (SAM) or mixed SAMs comprised of thiol-functionalized arginine-glycine-aspartic acid (RGD, a platelet integrin target) with or without 1-octanethiol (adhesion inhibitor). As expected, platelet adhesion was promoted and inhibited at RGD and alkanethiol modified surfaces, respectively. Platelet adhesion was reversible, and binding efficiency at the peptide modified substrates correlated inversely with pore diameter. Captured platelets underwent morphological change on capture, the extent of which depended on the topology of the underlying substrate. Regioselective capture of the platelets enabled study for the first time of the surface enhanced Raman spectroscopy of single blood platelets, yielding high quality Raman spectroscopy of individual platelets at 1.6 μm diameter pore arrays. Given the medical importance of blood platelets across a range of diseases from cancer to psychiatric illness, such approaches to platelet capture may provide a useful route to Raman spectroscopy for platelet related diagnostics.

Chitosan Nanofibers for Specific Capture and Nondestructive Release of CTCs Assisted by pCBMA Brushes

Over the last decade, significant progress has been made to develop sensitive devices for the capture of circulating tumor cells (CTCs) from blood of cancer patients. However, simple capture and counting of CTCs cannot provide effective information for understanding the biology of them. In this work, a functional biointerface is fabricated for specific capture and nondestructive release of CTCs from blood samples. A nanostrucure of porous network based on chitosan nanofibers is fabricated by electrospinning, to mimic the function of extracellular matrices, and then the poly(carboxybetaine methacrylate) (pCBMA) brushes integrating onto nanofiber interface provide the effect of interfacial properties to control nonspecific cell adhesion and the multivalent immobilization of aptamers to induce high efficient and specific CTC capture. Furthermore, a complementary sequence is used to efficiently hybridize with the aptamer to achieve nondestructive release of the captured target cells, assisted by the flexible space provided by pCBMA brushes. This work also shows how nanostructure and the interface molecules regulate the morphology of the captured CTCs, and reveals the importance of the controllable cell morphology on biointerface for an effective nondestructive release of the captured CTCs.

Organic Photovoltaics and Bioelectrodes Providing Electrical Stimulation for PC12 Cell Differentiation and Neurite Outgrowth

Current bioelectronic medicines for neurological therapies generally involve treatment with a bioelectronic system comprising a power supply unit and a bioelectrode device. Further integration of wireless and self-powered units is of practical importance for implantable bioelectronics. In this study, we developed biocompatible organic photovoltaics (OPVs) for serving as wireless electrical power supply units that can be operated under illumination with near-infrared (NIR) light, and organic bioelectronic interface (OBEI) electrode devices as neural stimulation electrodes. The OPV/OBEI integrated system is capable to provide electrical stimulation (ES) as a means of enhancing neuron-like PC12 cell differentiation and neurite outgrowth. For the OPV design, we prepared devices incorporating two photoactive material systems--β-carotene/N,N'-dioctyl-3,4,9,10-perylenedicarboximide (β-carotene/PTCDI-C8) and poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM)--that exhibited open circuit voltages of 0.11 and 0.49 V, respectively, under NIR light LED (NLED) illumination. Then, we connected OBEI devices with different electrode gaps, incorporating biocompatible poly(hydroxymethylated-3,4-ethylenedioxythiophene), to OPVs to precisely tailor the direct current electric field conditions during the culturing of PC12 cells. This NIR light-driven OPV/OBEI system could be engineered to provide tunable control over the electric field (from 220 to 980 mV mm(-1)) to promote 64% enhancement in the neurite length, direct the neurite orientation on chips, or both. The OPV/OBEI integrated systems under NIR illumination appear to function as effective power delivery platforms that should meet the requirements for wirelessly offering medical ES to a portion of the nervous system; they might also be a key technology for the development of next-generation implantable bioelectronics.

Size-controllable ultrathin carboxylated polypyrrole nanotube transducer for extremely sensitive 17β-estradiol FET-type biosensors

Size-controllable aptamer conjugated ultrathin carboxylated polypyrrole nanotubes (A-UCPPyNTs) were successfully fabricated as transducers in 17β-estradiol field-effect transistor (FET)-type biosensors which has extremely high sensitivity (∼1 fM) and unique selectivity.