Patterned Au/poly(dimethylsiloxane) substrate fabricated by chemical plating coupled with electrochemical etching for cell patterning

A Novel Approach for the Creation of Electrically Controlled LC:PDMS Microstructures

This work presents research on unique optofluidic systems in the form of air channels fabricated in PDMS and infiltrated with liquid crystalline material. The proposed LC:PDMS structures represent an innovative solution due to the use of microchannel electrodes filled with a liquid metal alloy. The latter allows for the easy and dynamic reconfiguration of the system and eliminates technological issues experienced by other research groups. The paper discusses the design, fabrication, and testing methods for tunable LC:PDMS structures. Particular emphasis was placed on determining their properties after applying an external electric field, depending on the geometrical parameters of the system. The conclusions of the performed investigations may contribute to the definition of guidelines for both LC:PDMS devices and a new class of potential sensing elements utilizing polymers and liquid crystals in their structures.

A highly flexible Ni-Co MOF nanosheet coated Au/PDMS film based wearable electrochemical sensor for continuous human sweat glucose monitoring

The development of flexible substrate materials and nanomaterials with high electrochemical performance is of great significance for constructing efficient wearable electrochemical sensors for real-time health monitoring. Herein, a wearable electrochemical sweat sensor based on a Ni-Co MOF nanosheet coated Au/polydimethylsiloxane (PDMS) film was prepared for continuous monitoring of the glucose level in sweat with high sensitivity. First, a stretchable Au/PDMS film based three-electrode system was prepared by chemical deposition of a gold layer on the hydrophilic treated PDMS. Then, Ni-Co MOF nanosheets with high electrocatalytic activity were synthesized by a facile solvothermal method and modified on the Au/PDMS electrode. The electrocatalytic activity of the Ni-Co MOF nanosheets synthesized under different Ni : Co ratios was investigated. The Ni-Co MOF/Au/PDMS (NCAP) film electrode showed excellent electrochemical performance for glucose detection with a wide linear range of 20 μM to 790 μM and a high sensitivity of 205.1 μA mM^-1 cm^-2. In addition, the flexible sensor shows high stability and a good electrochemical response to glucose when stretched and bent to different levels. Moreover, it maintained long-term stability and high selectivity for glucose monitoring. Lastly, a sweat-absorbent cloth was used to cover the working area of the sensor and was fixed with a needle and thread to form a wearable sweat glucose sensor. The sensor can be attached to the skin for stable, accurate and continuous monitoring of glucose levels in human sweat for one day. This work validates the potential of our high-performance wearable sensor for out-of-clinic health monitoring.

Simultaneous mapping of nanoscale topography and surface potential of charged surfaces by scanning ion conductance microscopy

Scanning ion conductance microscopy (SICM) offers the ability to obtain nanoscale resolution images of the membranes of living cells. Here, we show that a dual-barrel nanopipette probe based potentiometric SICM (P-SICM) can simultaneously map the topography and surface potential of soft, rough and heterogeneously charged surfaces under physiological conditions. This technique was validated and tested by systematic studies on model samples, and the finite element method (FEM) based simulations confirmed its surface potential sensing capability. Using the P-SICM method, we compared both the topography and extracellular potential distributions of the membranes of normal (Mela-A) and cancerous (B16) skin cells. We further monitored the structural and electrical changes of the membranes of both types of cells after exposing them to the elevated potassium ion concentration in extracellular solution, known to depolarize and damage the cell. From surface potential imaging, we revealed the dynamic appearance of heterogeneity of the surface potential of the individual cell membrane. This P-SICM method provides new opportunities to study the structural and electrical properties of cell membrane at the nanoscale.

Hierarchical Nanoparticle Assemblies Formed via One-Step Catalytic Stamp Pattern Transfer

The one-step catalytic stamp pattern transfer process is described for producing arrays of hierarchical nanoparticle assemblies. The method simply combines in situ nanoparticle synthesis triggered by free residual Si-H groups on PDMS stamps and the lift-off pattern transfer technique. No additional nanoparticle synthesis procedure is required before the pattern transfer process. Exquisitely uniform and precisely spaced hierarchical nanoparticle assemblies with designed geometry can be rapidly produced using the catalytic stamp pattern transfer process. Sequential catalytic stamp pattern transfer also is described to generate multilayered, hierarchical nanoparticle assemblies with various geometries. The hierarchical nanoparticle assemblies catalytically transferred onto the surface are not just nanoparticles but nanoparticle-polydimethylsiloxane residue composites. The in situ-synthesized nanoparticles retain optical properties. The hierarchical nanoparticle assemblies with precisely controlled geometry further show potential in the application of surface-enhanced Raman scattering. The capability of one-step catalytic stamp pattern transfer allows the scalable and reproducible fabrication of well-defined hierarchical nanoparticle assemblies.

Patterning of supported gold monolayers via chemical lift-off lithography

The supported monolayer of Au that accompanies alkanethiolate molecules removed by polymer stamps during chemical lift-off lithography is a scarcely studied hybrid material. We show that these Au-alkanethiolate layers on poly(dimethylsiloxane) (PDMS) are transparent, functional, hybrid interfaces that can be patterned over nanometer, micrometer, and millimeter length scales. Unlike other ultrathin Au films and nanoparticles, lifted-off Au-alkanethiolate thin films lack a measurable optical signature. We therefore devised fabrication, characterization, and simulation strategies by which to interrogate the nanoscale structure, chemical functionality, stoichiometry, and spectral signature of the supported Au-thiolate layers. The patterning of these layers laterally encodes their functionality, as demonstrated by a fluorescence-based approach that relies on dye-labeled complementary DNA hybridization. Supported thin Au films can be patterned via features on PDMS stamps (controlled contact), using patterned Au substrates prior to lift-off (e.g., selective wet etching), or by patterning alkanethiols on Au substrates to be reactive in selected regions but not others (controlled reactivity). In all cases, the regions containing Au-alkanethiolate layers have a sub-nanometer apparent height, which was found to be consistent with molecular dynamics simulations that predicted the removal of no more than 1.5 Au atoms per thiol, thus presenting a monolayer-like structure.

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.

Inkjet-printed microelectrodes on PDMS as biosensors for functionalized microfluidic systems

Microfluidic systems based on polydimethylsiloxane (PDMS) have gained popularity in recent years. However, microelectrode patterning on PDMS to form biosensors in microchannels remains a worldwide technical issue due to the hydrophobicity of PDMS and its weak adhesion to metals. In this study, an additive technique using inkjet-printed silver nanoparticles to form microelectrodes on PDMS is presented. (3-Mercaptopropyl)trimethoxysilane (MPTMS) was used to modify the surface of PDMS to improve its surface wettability and its adhesion to silver. The modified surface of PDMS is rendered relatively hydrophilic, which is beneficial for the silver droplets to disperse and thus effectively avoids the coalescence of adjacent droplets. Additionally, a multilevel matrix deposition (MMD) method is used to further avoid the coalescence and yield a homogeneous pattern on the MPTMS-modified PDMS. A surface wettability comparison and an adhesion test were conducted. The resulting silver pattern exhibited good uniformity, conductivity and excellent adhesion to PDMS. A three-electrode electrochemical biosensor was fabricated successfully using this method and sealed in a PDMS microchannel, forming a lab-on-a-chip glucose biosensing system.

Development and calibration of a microfluidic biofilm growth cell with flow-templating and multi-modal characterization

We report the development of a microfluidic flow-templating platform with multi-modal characterization for studies of biofilms and their precursor materials. A key feature is a special three inlet flow-template compartment, which confines and controls the location of biofilm growth against a template wall. Characterization compartments include Raman imaging to study the localization of the nutrient solutions, optical microscopy to quantify biofilm biomass and localization, and cyclic voltammetry for flow velocity measurements. Each compartment is tested and then utilized to make preliminary measurements.

Self-assembled monolayers of enantiomerically functionalized periodic mesoporous organosilicas and the effect of surface chirality on cell adhesion behaviour

Enantioselective functionalization of fluorescent dye loaded periodic mesoporous organosilicas withd(l)-mannose and the preparation of their self-assembled monolayers are described. Stereoselective interactions of these monolayers with different cell types are demonstrated.

Automated chemiluminescence immunoassay for a nonionic surfactant using a recycled spinning-pausing controlled washing procedure on a compact disc-type microfluidic platform

A fully automated and integrated chemiluminescence immunoassay, carried out on a compact disc (CD)-type microfluidic platform, for the detection of alkylphenol polyethoxylates (APnEOs) is described. The pattern of the CD-type microchip was designed so as to permit the sequential solution delivery of the sample solution, the washing solution and the luminol solution, which are required in the chemiluminescence immunoassay process, along with a designed rotation program for spinning the CD-type microchip. The procedure for flowing the washing solution, the volume of which was limited on the CD-type microchip, was optimized by using a recycled spinning-pausing rotation program to overcome the non-specific adsorption of the horseradish peroxidase labeled APnEOs at the detection area. The detection limit of the immunoassay is about 10 ppb.

Cellphone camera imaging of a periodically patterned chip as a potential method for point-of-care diagnostics

In this study, we demonstrate that a disposable chip periodically patterned with suitable ligands, an ordinary cellphone camera, and a simple pattern recognition software, can potentially be used for quantitative diagnostics. A key factor in this demonstration is the design of a calibration grid around the chip that, through a contrast transfer process, enables reliable analysis of the images collected under variable ambient lighting conditions. After exposure to a dispersion of amine terminated silica beads used as analyte mimicking pathogens, an epoxy-terminated glass substrate microcontact printed with octadecyltrichlorosilane (250 μm periodicity) developed a characteristic pattern of beads which could be easily imaged with a cellphone camera of 3.2 MP pixels. A simple pattern recognition algorithm using fast Fourier transform produced a quantitative estimate of the analyte concentration present in the test solution. In this method importantly, neither the chip fabrication process nor the fill-factor of the periodic pattern need be perfect to arrive at a conclusive diagnosis. The method suggests a viable platform that may potentially find use in fault-tolerant and robust point-of-care diagnostic applications.

Nonplanar conductive surfaces via "bottom-up" nanostructured gold coating

Development of technologies for the construction of bent, curved, and flexible conductive surfaces is among the most important albeit challenging goals in the promising field of "flexible electronics". We present a generic solution-based "bottom-up" approach for assembling conductive gold nanostructured layers on nonplanar polymer surfaces. The simple two-step experimental scheme is based upon incubation of an amine-displaying polymer [the abundantly used poly(dimethylsiloxane) (PDMS), selected here as a proof of concept] with Au(SCN)4(-), followed by a brief treatment with a conductive polymer [poly(3,4-thylenedioxythiophene)/poly(styrenesulfonate)] solution. Importantly, no reducing agent is co-added to the gold complex solution. The resultant surfaces are conductive and exhibit a unique "nanoribbon" gold morphology. The scheme yields conductive layers upon PDMS in varied configurations: planar, "wrinkled", and mechanically bent surfaces. The technology is simple, inexpensive, and easy to implement for varied polymer surfaces (and other substances), opening the way for practical applications in flexible electronics and related fields.

Combining surface topography with polymer chemistry: exploring new interfacial biological phenomena

This review focuses on combining surface topography and surface chemical modification by the grafting of polymers to develop optimal material interfaces with synergistic properties and functions for biological and biomedical applications.

Are carbon nanotubes a natural solution? Applications in biology and medicine

Carbon nanotubes and materials based on carbon nanotubes have many perceived applications in the field of biomedicine. Several highly promising examples have been highlighted in the literature, ranging from their use as growth substrates or tissue scaffolds to acting as intracellular transporters for various therapeutic and diagnostic agents. In addition, carbon nanotubes have a strong optical absorption in the near-infrared region (in which tissue is transparent), which enables their use for biological imaging applications and photothermal ablation of tumors. Although these advances are potentially game-changing, excitement must be tempered somewhat as several bottlenecks exist. Carbon nanotube-based technologies ultimately have to compete with and out-perform existing technologies in terms of performance and price. Moreover, issues have been highlighted relating to toxicity, which presents an obstacle for the transition from preclinical to clinical use. Although many studies have suggested that well-functionalized carbon nanotubes appear to be safe to the treated animals, mainly rodents, long-term toxicity issues remains to be elucidated. In this report, we systematically highlight some of the most promising biomedical application areas of carbon nanotubes and review the interaction of carbon nanotubes with cultured cells and living organisms with a particular focus on in vivo biodistribution and potential adverse health effects. To conclude, future challenges and prospects of carbon nanotubes for biomedical applications will be addressed.

Cell adhesion on a POEGMA-modified topographical surface

It is well known that adsorbed proteins play a major role in cell adhesion. However, it has also been reported that cells can adhere to a protein-resistant surface. In this work, the behavior of L02 and BEL-7402 cells on a protein-resistant, 3D topographical surface was investigated. The topographical gold nanoparticle layer (GNPL) surfaces were prepared by chemical gold plating, and the topography was described by roughness parameters acquired from a multiscale analysis. Both smooth Au and GNPL surfaces were modified with POEGMA polymer brushes using surface-initiated ATRP. The dry and hydrated thicknesses of POEGMA brushes on both smooth and rough surfaces were measured by AFM using a nanoindentation method. Protein adsorption experiments using (125)I radiolabeling revealed similarly low levels of protein adsorption on smooth and GNPL surfaces modified with POEGMA, thus allowing an investigation of the effects of topography on cell behavior under conditions of minimal protein adsorption. The roles of VN and FN adsorption in both L02 cells and BEL-7402 cells adhesion were investigated using cell culturing with and without a serum supplement. It was found that initial cell adhesion occurred via proteins adsorbed from the cell culture medium, whereas subsequent durable cell adhesion could be attributed to the topographical structure of the surface. Although cell spreading on protein-resistant surfaces was constrained because of the lack of adsorbed proteins, we found that cells adherent to topographical surfaces were more firmly attached and thus were more durable compared to those on smooth surfaces. In general, however, we conclude that topography is more important for cell adhesion on a protein-resistant surface.

Surface coating as a key parameter in engineering neuronal network structures in vitro

By quantitatively comparing a variety of macromolecular surface coating agents, we discovered that surface coating strongly modulates the adhesion and morphogenesis of primary hippocampal neurons and serves as a switch of somata clustering and neurite fasciculation in vitro. The kinetics of neuronal adhesion on poly-lysine-coated surfaces is much faster than that on laminin and Matrigel-coated surfaces, and the distribution of adhesion is more homogenous on poly-lysine. Matrigel and laminin, on the other hand, facilitate neuritogenesis more than poly-lysine does. Eventually, on Matrigel-coated surfaces of self-assembled monolayers, neurons tend to undergo somata clustering and neurite fasciculation. By replacing coating proteins with cerebral astrocytes, and patterning neurons on astrocytes through self-assembled monolayers, microfluidics and micro-contact printing, we found that astrocyte promotes soma adhesion and astrocyte processes guide neurites. There, astrocytes could be a versatile substrate in engineering neuronal networks in vitro. Besides, quantitative measurements of cellular responses on various coatings would be valuable information for the neurobiology community in the choice of the most appropriate coating strategy.

Gold nanoparticle layer: a promising platform for ultra-sensitive cancer detection

Developing new technologies applicable to the sensitive detection of cancer in its early stages has always been attractive in diagnosis. A stable gold nanoparticle layer (GNPL)-modified high-binding ELISA plate was obtained via chemical plating and was proven to be more efficient in binding proteins while maintaining their activity. GNPL-based ELISA for the representative biomarker carcinoembryonic antigen (CEA) demonstrated that GNPL markedly amplified the ELISA signal and significantly improved the limit of detection (LOD). Antithrombin detection further confirms the effectiveness and universality of this GNPL-based platform. The entire assay procedure is simple and low in cost and does not require special facilities. All these virtues indicate that this GNPL platform holds great promise in clinical applications for the early diagnosis of cancer.

Electric detection of DNA with PDMS microgap electrodes and silver nanoparticles

In this work a novel microdevice sensor has been developed by plating gold on the PDMS surface to generate a sandwich-type gap electrode for DNA detection. The microdevice utilizes a gold band electrode-PDMS-gold band electrode configuration and the minimum detectable volume could be as low as 5 μL. The 20 μm PDMS-based gap was chemically modified with DNA capture probes and DNA sandwich hybrids were formed with the addition of DNA target and silver nanoparticle probes. To increase detection sensitivity, parallel detection zones have been developed in which the relevant resistances decrease substantially upon hybridyzation. By measuring the change in electrical conductivity, the DNA target in the concentration range of 1000-0.1 nM can be assayed and the limit of lowest detectable concentration was achieved at 0.01 nM.

Air plasma assisting microcontact deprinting and printing for gold thin film and PDMS patterns

In this paper, we present a simple method to fabricate gold film patterns and PDMS patterns by air plasma assisting microcontact deprinting and printing transfer approaches. Chemical gold plating is employed instead of conventional metal evaporation or sputtering to obtain perfect gold film both on flat and topographic PDMS chips, and complicated SAM precoating is replaced by simple air plasma treatment to activate both the surface of gold film and PDMS. In this way, large area patterns of conductive gold film and PDMS patterns could be easily obtained on the elastomeric PDMS substrate. Both the chemical plating gold film and transferred gold film were of good electrochemical properties and similar hydrophilicity with smooth and conductive surface, which made it potentially useful in microfluidic devices and electronics. The gold transfer mechanism is discussed in detail. For typical applications, a cell patterning chip based on the gold pattern was developed to imply the interfacial property, and dielectrophoresis control of live cells was carried out with the patterned gold as interdigital electrodes to show the conductivity.