Patterned Polydimethylsiloxane Substrate Research Articles

Fabrication and sensing properties of a molecularly imprinted polymer on a photonic PDMS substrate for the optical detection of C-reactive protein

This work presents the development of a novel photonic-based sensor on a nanoscale patterned polydimethylsiloxane (PDMS) substrate acting as transducer, combined with a molecularly imprinted polymer for the rapid and sensitive detection of C-reactive protein (CRP). A silicon wafer was patterned using electron-beam lithography with a one-dimensional (1D) reflective grating (periodicity of about 400 nm) and then replicated using nanoimprint lithography. The latter silicon mould was used for replica moulding to generate a patterned PDMS. The unique 1D design gave PDMS photonic properties that were suitable as a substrate to assemble the biorecognition layer. The surface of the photonic PDMS was modified to become hydrophilic and additionally functionalized with vinyl silane groups to bind the imprinted polymer, resulting in a photonic molecularly imprinted polymer substrate (PMIPS). The developed method was successfully used to detect CRP in serum samples. The reflectance intensity decreased with increasing CRP concentrations, and the sensing PMIPS showed a linear response between 0.005 and 1.215 µg mL−1, a limit of detection of 0.003 µg mL−1, and a selective response to CRP when tested against serum calprotectin. Overall, this novel optical sensor can be used to detect CRP, a serum biomarker of inflammation, particularly in inflammatory bowel diseases.

High‐Stability Flexible Patterned Perovskite Optoelectronic Structures Fabricated by a Laser Pyrolysis Assisted Process

AbstractFlexible patterned metal halide perovskites (MHPs) are promising to improve the perovskite‐based optoelectronic devices for applications in healthcare monitoring, flexible displays, solar cells, etc. However, their poor environmental stability and device robustness are the main obstacles for commercialization. Herein, a laser pyrolysis assisted process is developed to fabricate flexible patterned CsPbBr3 structures with high stability and flexibility. A CO2 laser is applied to micromachine the designed patterns on the flexible polydimethylsiloxane (PDMS) substrates by inducing the pyrolysis of PDMS. The CsPbBr3 quantum dots (QDs) solution is precisely filled into the patterned PDMS substrates, and subsequently sealed by another layer of PDMS on the top. To ensure the surface smoothness of the patterned PDMS for CsPbBr3 QDs embedment, the mechanism of the laser pyrolysis process is investigated by characterizing the PDMS pyrolysis products obtained at different laser energy densities. To demonstrate the high stability of the fabricated flexible patterned CsPbBr3 structures, the photoluminescent (PL) spectra of the samples are monitored for 60 days both in air and in the water. The flexibility of the fabricated structures is estimated by monitoring their PL emission under applied tension and bending. These flexible patterned CsPbBr3 structures are promising for applications in flexible optical/optoelectronic devices.

Tunable and reversible thermo-plasmonic hot spot imaging for temperature confinement

In the present study, a novel tunable two-dimensional thermo-plasmonic grating based on gold nanorods was demonstrated by combining the plasmonic properties of the gold nanostructure and the applied external voltage. In this structure, a thin layer of the gold grating was typically deposited on a patterned polydimethylsiloxane substrate using the nanoimprint lithography method. The surface plasmon resonance of the fabricated plasmonic structure was excited by the surface plasmon imaging system based on a high numerical aperture objective lens and the charged coupled device camera. Based on the results, the number of the plasmonic hot spots due to the thermo-plasmonic effect increased by the external voltage, leading to an increase in this effect. Therefore, this reversible and tunable temperature confinement can be used as the controller of each element including cells in a defined micro-position.

Investigation of the effect of substrate morphology on MDCK cell mechanical behavior using atomic force microscopy

Living cells sense and respond to their extracellular environment. Their contact guidance is affected by the underlying substrate morphology. Previous studies of the effect of the substrate pattern on the mechanical behavior of living cells were only limited to the quantification of the cellular elasticity. However, how the length and time scales of the cellular mechanical properties are affected by the patterned substrates are yet to be studied. In this study, the effect of the substrate morphology on the biomechanical behavior of living cells was thoroughly investigated using indentation-based atomic force microscopy. The results showed that the cellular biomechanical behavior was affected by the substrate morphology significantly. The elasticity and viscosity of the cells on the patterned Polydimethylsiloxane (PDMS) substrates were much lower compared to those of the ones cultured on flat PDMS. The poroelastic diffusion coefficient of the cells was higher on the patterned PDMS substrates, specifically on the substrate with 2D pitches. In addition, fluorescence images showed that the substrate topography directly affects the cell cytoskeleton morphology. Together, the results suggested that cell mechanical behavior and morphology can be controlled using substrates with properly designed topography.

Single-Droplet Multiplex Bioassay on a Robust and Stretchable Extreme Wetting Substrate through Vacuum-Based Droplet Manipulation.

Herein, a droplet manipulation system with a superamphiphobic (SPO)-superamphiphilic (SPI) patterned polydimethylsiloxane (PDMS) substrate is developed for a multiplex bioassay from single-droplet samples. The SPO substrate is fabricated by sequential spraying of adhesive and fluorinated silica nanoparticles onto a PDMS substrate. It is subsequently subjected to oxygen plasma with a patterned mask to form SPI patterns. The SPO layer exhibits extreme liquid repellency with a high contact angle (>150°) toward low surface tension and viscous biofluidic droplets (e.g., ethylene glycol, blood, dimethyl sulfoxide, and alginate hydrogel). In contrast, the SPI exhibits liquid adhesion with a near zero contact angle. Using the droplet manipulation system, various liquid droplets can be precisely manipulated and dispensed onto the predefined SPI patterns on the SPO PDMS substrate. This system enables a multiplex colorimetric bioassay, capable of detecting multiple analytes, including glucose, uric acid, and lactate, from a single sample droplet. In addition, the detection of glucose concentrations in a plasma droplet of diabetic and healthy mice are performed to demonstrate the feasibility of the proposed system for efficient clinical diagnostic applications.

High-Performance Ultrathin BiVO4 Photoanode on Textured Polydimethylsiloxane Substrates for Solar Water Splitting

Photoelectrochemical (PEC) water splitting devices rely on light-absorbers to absorb sunlight, and the photogenerated electrons and holes further react with water to generate hydrogen and oxygen. Fabricating light-absorbers on textured substrates offers alternative routes for optimizing their PEC performance. Textured substrates would greatly enhance both light absorption and surface reactions of photoanodes and thus reduce the total amount of light-absorbers needed. Herein, we report the fabrication of ultrathin BiVO4 photoanode film on textured polydimethylsiloxane (PDMS) substrates by using a modified water-assisted transfer printing method. Significantly, a pristine BiVO4 photoanode of only 80 nm thick shows a photocurrent density of 1.37 mA/cm2 at 1.23 VRHE on patterned PDMS substrates, which is further increased to ∼2.0 mA/cm2 at 1.23 VRHE when FeOOH oxygen evolution catalyst is added. We believe that our transfer printing method can be broadly applied to integrate photoelectrodes and other thin-fil...

Ultraviolet photodetector based on ZnO nanorods grown on a flexible PDMS substrate

A flexible, reproducible, sensitive and low-cost ultraviolet (UV) detector has been fabricated based on zinc oxide (ZnO) nanorods grown on a patterned polydimethylsiloxane (PDMS) substrate. The substrate was seeded with ZnO nanoparticles synthesised via simple low-temperature hydrothermal method using pomegranate peel extract as a reducing agent. The produced ZnO-nanorods/PDMS (ZnO-NR/PDMS) samples were tested for their UV-sensing properties. Samples were characterised using scanning electron microscopy, X-ray diffraction, I–V characteristics, UV-Vis spectroscopy and photoluminescence measurements. The UV photoresponse mechanism of prototype UV detector was analysed. The detector exhibited quite high on/off ratios between photoresponse current and dark current. With the flexible PDMS substrate, the detector photoresponse was tested with and without bending and exhibited a very slight change in the photoresponse current. The detector current–time response was also tested under various UV light intensities for three test cycles to examine the detector stability, hysteresis behaviour and performance. It is anticipated that the fabrication of ZnO-NR/PDMS UV detector may have significant potential application in flexible optoelectronic devices.

Evaporation of water droplets on soft patterned surfaces

The evaporation process of a sessile drop of water on soft patterned polydimethylsiloxane (PDMS) substrates is investigated in this study. Different softness of a regular pillar-like patterned PDMS substrate can be achieved by controlling the mixing ratio of a PDMS's prepolymer base and a curing agent at 10 : 1, 20 : 1 and 30 : 1. The receding contact angle is smaller for softer pillar-like patterned substrates. Consequently, the evaporation rate is faster on softer pillar-like substrates. A sessile drop on the regular pillar-like PDMS substrates, prepared at the mixing ratio of a base to a curing agent of 10 : 1 and 20 : 1, is observed to start evaporating in the constant contact radius (CCR) mode then switching to the constant contact angle (CCA) mode via stepwise jumping of the contact line, and finally shifting to the mixed mode sequentially. During the evaporation, a wetting transition from the Cassie to the Wenzel state occurs earlier for the softer substrate because softer pillars relatively cannot stand the increasingly high Laplace pressure. For the softest regular pillar-like PDMS substrate prepared at the mixing ratio of the base to the curing agent of 30 : 1 (abbreviated by PDMS-30 : 1 substrate), the pillars collapse irreversibly after the sessile drop exhibits the wetting transition into the Wenzel state. Furthermore, it is interesting to find out that the initial stage of evaporation of a sessile drop on the PDMS-30 : 1 substrate in the Cassie state is in the CCR mode followed by the CCA mode with stepwise retreatment of the contact line. Further evaporation would induce the wetting transition from the Cassie to the Wenzel state (due to the collapse of pillars) and resume the CCR mode followed by the CCA mode again sequentially.

Mechanically Tuning the Localized Surface Plasmon Resonances of Gold Nanostructure Arrays

We report the fabrication of metal nanostructures on a polydimethylsiloxane (PDMS) substrate by transferring polystyrene beads onto PDMS substrate followed by metal deposition. Experimentally tuning the plasmon resonance of the metal nanostructures was demonstrated by stretching the patterned PDMS substrate. The distance between adjacent nanodisks affects the coupling between the disks, leading to a repeatable and reversible shift in the spectrum. The device can be valuable in many applications such as bio/chemical sensing, reconfigurable optics, and the study of coupled resonances.

Alignment of skeletal muscle myoblasts and myotubes using linear micropatterned surfaces ground with abrasives

Alignment of cells plays a significant key role in skeletal muscle tissue engineering because skeletal muscle tissue in vivo has a highly organized structure consisting of long parallel multinucleated myotubes formed through differentiation and fusion of myoblasts. In the present study, we developed an easy, simple, and low-cost method for aligning skeletal muscle cells by using surfaces with linear microscale features fabricated by grinding. Iron blocks were ground in one direction with three kinds of abrasives (9 microm diamond suspension, #400 sandpaper, and #150 sandpaper) and then used as molds to make micropatterned polydimethylsiloxane (PDMS) substrates (type I, type II, and type III). Observation of the surface topography revealed that the PDMS substrates exhibited different degree of mean roughness (Ra), 0.03 microm for type I, 0.16 microm for type II, and 0.56 microm for type III, respectively. Murine skeletal muscle cell line C2C12 myoblasts were cultured and differentiated on the patterned PDMS substrates, and it was examined whether the alignment of C2C12 myoblasts and myotubes was possible. Although the cell growth and differentiation on the three types of patterned substrates were similar to those on the flat PDMS substrate as a control, the alignment of both C2C12 myoblasts and myotubes was obviously observed on types II and III, but not on type I or the control substrate. These results indicate that surfaces ground with abrasives will be useful for fabricating aligned skeletal muscle tissues.