Highly sensitive crumpled 2D material-based plasmonic biosensors.

Mechanical properties are a crucial factor for the application of two-dimensional (2D) materials in flexible electronic and optoelectronic devices. Until now, mechanical properties of 2D materials have been primarily investigated from the load–deformation relationship of freely suspended 2D nanofilms by in-situ atomic force microscope probe nanoindentation measurements. Herein, we acquired the mechanical behavior of monolayer and few-layer molybdenum disulfide (MoS2) via applying a point load on 2D MoS2 on a soft poly-dimethylsiloxane (PDMS) substrate. The primary objective of this work is to study the elastic behavior of 2D MoS2 based on the indentation deformation of the 2D MoS2/PDMS substrate. Nanoindentation behavior of 2D MoS2 mounted on PDMS substrate is also simulated by finite element method. Combining nanoindentation experiments with theoretical simulations, we can understand the mechanical behavior of 2D materials on flexible substrates perfectly well. This work provides a new method to characterize the mechanical response of atomically ultrathin 2D nanofilms with substrate-binding effect, which is essential to promote flexible devices based on functional 2D materials.

The effects of substrate stiffness on the development of cardiomyocytes have been investigated extensively. Polydimethylsiloxane (PDMS) elastomer is one of biomaterials that are commonly used to explore the effects of substrate compliance on stem cell differentiation. Although the effects of substrate stiffness on cardiac differentiation of pluripotent stem cells, such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), have been reported, whether the stiffness of PDMS-based substrates could enhance differentiation of iPSCs toward cardiomyocyte lineage or not remains unknown. In this study, we found that a denser gelatin distribution and a higher gelatin adsorption on the stiffer PDMS. In addition, nanotopographies on PDMS substrates with different stiffness were distinct. iPSCs on the stiffer PDMS substrates showed higher pluripotency marker but lower cardiac gene expressions. In contrast, iPSCs on the softer PDMS substrates revealed lower pluripotency marker but higher cardiac gene expressions. These results indicate that stiffer PDMS substrates with gelatin coating could be used to support iPSC self-renewal and softer PDMS substrates coated with gelatin could be used for enhanced cardiac differentiation of iPSCs.

A novel method for transferring graphene onto PDMS

A lithography-free approach to create Si nanomembranes on flexible substrates

Van der Waals (vdW) materials have recently attracted a lot of attentions, because they possess a wide range of optoelectronic properties and can be applied over a wide spectral regions. For example, black phosphorus and graphene can exhibit direct and narrow band gaps, making them appeal to the mid-infrared or even far-infrared devices applications. The single layer transition metal dichalcogenides materials (TMDCs, i.e., MX2; M=Mo, W; X=S, Se, Te), have been known as direct gap semiconductors, useful in the infrared and visible spectral regimes. Additionally, due to the vdW nature, these materials can be assembled vertically to form the complex vdW heterostructures, and more importantly, can be easily transferred onto different device substrates without stringent constraints on lattice matching at the interfaces. Notably, such features can potentially lead to the novel hybrid device platforms that simultaneously take advantage of the state-of-the-art semiconductor manufacturing technologies and exotic characteristics of vdW materials In this talk, we will demonstrate novel dielectric metalenses by exploiting the vdW molybdenum disulfide (MoS2) and hexagonal boron nitride as optical materials. By using the incomplete phase-based design approach (i.e. the maximum phase shift being less than 2π), we show the thicknesses of our created vdW metalenses can be far below the operating wavelength (∼0.1λ to 0.5λ). This circumvents the current fabrication challenges of making dielectric metalenses that require the high-aspect-ratio nanoscale scattering elements. More importantly, we demonstrate that the developed MoS2 (hexagonal boron nitride) metalenses not only can focus the near-infrared (visible) light into the diffraction limited spots, but also can be useful for creating the optical images. This could enable further downscaling of optoelectronics systems, and will significantly benefit the modern imaging, motion detection and spectroscopic applications. Furthermore, by exploiting the nature of vdW interactions, we show our proposed metalenses can be readily peeled off and then transferred onto the flexible and transparent polydimethylsiloxane (PDMS) substrate. When the mechanical strain was applied on the PDMS substrate, the axial focus length of transferred vdW metalens can be widely tuned in the range from 250 to 400 µm. This highlight the possibilities of realizing integrable and tunable dielectric metalenses based on our developed vdW nanophotonics. In addition to vdW nanophotonics, we will demonstrate that the vdW-based light emitters and photodetectors can be coupled with diverse photonic structures such as the waveguides and plasmonic resonators, and show the performed hybrid device platforms can hold great promise for the photonic circuits applications.

Cells are cultured on platforms made of a variety of materials with selected topographies during studies of cell response and behavior. Understanding the effects of substrates is essential for such applications as developing effective interfaces between body cells and implanted materials and devices. In this study, the effects of substrate surface properties on cell differentiation and alignment on C2C12 myoblasts cultured on conventional or fabricated polymeric cell culture substrates were investigated. Comparisons were made between cells cultured on tissue culture grade polystyrene (TCPS), glass, Permanox, and cured polydimethylsiloxane (PDMS) substrates. Fluorescent immunohistochemistry of cell markers was used to analyse the extent of differentiation. Alignment and guidance of cell growth and spread were studied using patterned platforms. Gratings were made on polystyrene (PS) and PDMS and differentiation was facilitated after 5 days by media exchange. Differences in cell morphology were observed between cells cultured on TCPS and PDMS substrates. Fully differentiated myotubes were observed in highest numbers on TCPS substrates and were non-detectable on PDMS substrates in the time frame of 144 h. Muscle cell alignment and their differentiation followed along the grating patterns on PS and elongated along the pattern length. On the other hand, on PDMS cells formed sheets of tissue and peeled from the substrate. We have revealed the potential for the combinations of surface materials and topography on cell behavior to induce accelerated differentiation and coordinated alignment. The results demonstrate that culture environment can be designed or engineered to modify or regulate muscle cell functions. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1638-1645, 2016.

The interparticle gap manipulation of Au-Ag nanoparticle arrays deposited on flexible and atmospheric plasma-treated PDMS substrate for SERS detection

Facile fabrication of micro/nano-structured wrinkles by controlling elastic properties of polydimethylsiloxane substrates

Plasmonics and polarotonics of two dimensional (2D) materials have attracted significant attention due to their desirable dispersion relation. Regarding plasmons, according to the 2D dispersion equation, the cutoff frequency limit can be eliminated. Additionally, their large tuneability, high doping (ultradoping) range, and the existence of favorable depolarization factors allow for their better control. Among 2D materials, molybdenum disulfides and molybdenum oxides have recently received increased attention.1-5 The polariton propagation has also been recently shown in atomically smooth molybdenum oxides. For plasmonic propagatrions, tunable plasmon resonances in suspended 2D molybdenum oxide and molybdenum sulfide flakes are demonstrated. The 2D configuration generates a large depolarization factor and the presence of ultra-doping produces visible-light plasmon resonances. The ultra-doping process is conducted by reducing the semiconducting 2D molybdenum trioxide flakes using simulated solar irradiation. The generated plasmon resonances are controlled by the doping levels and the flakes’ lateral dimensions, as well as by exposure to model proteins and enzymes. It is also possible to reach ultradoping levels. Alternatively, by electrochemically intercalating lithium into 2D molybdenum disulfide nanoflakes, plasmon resonances in the visible and near UV wavelength ranges are achieved. These plasmon resonances are controlled by the high doping level of the nanoflakes after the intercalation, producing two distinct resonance peak areas based on the crystal arrangements. The system is also benchmarked for biosensing using bovine serum albumin. The talk will provide the foundation for developing future 2D molybdenum sulphide and oxide based biological and optical units. Polaronic propagation in full stoichiometric molybdenum oxides will also be discussed.6 References 1 Zhang, B. Y.; Zavabeti, A.; Chrimes, A. F.; Haque, F.; O'Dell, L. A.; Khan, H.; Syed, N.; Datta, R.; Wang, Y.; Chesman, A. S. R.; Daeneke, T.; Kalantar-zadeh, K.; Ou, J. Z.,. Advanced Functional Materials 2018, 28, 1706006. 2 Wang, Y.; Ou, J. Z.; Chrimes, A. F.; Carey, B. J.; Daeneke, T.; Alsaif, M. M. Y. A.; Mortazavi, M.; Zhuiykov, S.; Medhekar, N.; Bhaskaran, M.; Friend, J. R.; Strano, M. S.; Kalantar-Zadeh, K., Nano Letters 2015, 15, 883-890. 3 Ma, W.; Alonso-González, P.; Li, S.; Nikitin, A. Y.; Yuan, J.; Martín-Sánchez, J.; Taboada-Gutiérrez, J.; Amenabar, I.; Li, P.; Vélez, S.; Tollan, C.; Dai, Z.; Zhang, Y.; Sriram, S.; Kalantar-Zadeh, K.; Lee, S. T.; Hillenbrand, R.; Bao, Q., Nature 2018, 562, 557-562. 4 de Castro, I. A.; Datta, R. S.; Ou, J. Z.; Castellanos-Gomez, A.; Sriram, S.; Daeneke, T.; Kalantar-zadeh, K., Advanced Materials 2017, 29, 1701619. 5 Alsaif, M. M. Y. A.; Latham, K.; Field, M. R.; Yao, D. D.; Medhekar, N. V.; Beane, G. A.; Kaner, R. B.; Russo, S. P.; Ou, J. Z.; Kalantar-Zadeh, K., Advanced Materials 2014, 26, 3931-3937. 6 Ma W.; Alonso-González, P.; Li, S.; Nikitin, A.W.; Yuan, J.; Martín-Sánchez, J.; Taboada-Gutiérrez, J.; Amenabar, I.; Li, P., Vélez, S.; Tollan, C.; Dai, Z.; Zhang, Y.; Sriram, S.; Kalantar-Zadeh, K.; Lee. S-T., Hillenbrand, R.; Bao, Q. Nature 2018, 562, 557-562.

Three samples of strain sensors have been fabricated and presented in this paper with different methods. First sample was made by spray coating of MWCNTs on poly-dimethylsiloxane (PDMS) substrate; second sample was by depositing of 0.3 wt% of MWCNTs powder on PDMS substrate at 100°C and third sample was fabricated by CVD method to grow MWCNTs array on SiO 2 substrate. It revealed from experiment results that strain sensor fabricated by spray coating method showed high sensitivity with tunability from 3.25–19.17 %, high stretchability of 60 %, good linearity and excellent long time stability.

Distinct physical factors originating from the cellular microenvironment are crucial to the biological homeostasis of stem cells. While substrate stiffness and orientation are known to regulate the mechanical remodeling and fate decision of mesenchymal stem cells (MSCs) separately, it remains unclear how the two factors are combined to manipulate their mechanical stability under gravity vector. Here we quantified these combined effects by placing rat MSCs onto stiffness-varied poly-dimethylsiloxane (PDMS) substrates in upward (180°), downward (0°), or edge-on (90°) orientation. Compared with those values onto glass coverslip, the nuclear longitudinal translocation, due to the density difference between the nucleus and the cytosol, was found to be lower at 0° for 24 h and higher at 90° for 24 and 72 h onto 2.5 MPa PDMS substrate. At 0°, the cell was mechanically supported by remarkably reduced actin and dramatically enhanced vimentin expression. At 90°, both enhanced actin and vimentin expression worked cooperatively to maintain cell stability. Specifically, perinuclear actin stress fibers with a large number, low anisotropy, and visible perinuclear vimentin cords were formed onto 2.5 MPa PDMS at 90° for 72 h, supporting the orientation difference in nuclear translocation and global cytoskeleton expression. This orientation dependence tended to disappear onto softer PDMS, presenting distinctive features in nuclear translocation and cytoskeletal structures. Moreover, cellular morphology and focal adhesion were mainly affected by substrate stiffness, yielding a time course of increased spreading area at 24 h but decreased area at 72 h with a decrease of stiffness. Mechanistically, the cell tended to be stabilized onto these PDMS substrates via β1 integrin–focal adhesion complexes–actin mechanosensitive axis. These results provided an insight in understanding the combination of substrate stiffness and orientation in defining the mechanical stability of rMSCs.

In this paper, we reported a theoretical study of a novel Surface plasmon resonance (SPR) biosensor composed of BK7 prism, gold (Au)/silver (Ag) bimetallic layer, silicon and two-dimensional (2D) materials. The bimetallic layer combines the advantages of Au and Ag and the high refractive index silicon layer enhances the electric field on the surface of the sensor, so that the sensor has a better overall performance in terms of sensitivity and figure of merit (FOM). Compared with ordinary dielectrics, 2D materials have excellent photoelectric properties, such as larger specific surface area, higher carrier density and stronger adsorption capacity, which improve the detection ability of the sensor. The sensitivity of the optimized sensor achieves 297.2°/RIU, 274°/RIU and 246°/RIU when the silicon layer is covered with graphene, MXene (Ti3T2Cx) and MoS2, respectively. Compared with the traditional SPR sensor, the sensitivity of the structure has been significantly improved, and its excellent performance has broad application prospects in biosensing and other fields.

This paper reports a simple and high-productive fabrication method of flexible piezoelectric substrate. To achieve a low-cost fabrication process of the substrate, we developed a novel transfer technique of piezoelectric thin films which were formed on temporary stainless-steel substrate to target PDMS (Poly-dimethylsiloxane) substrate by using wet etching process. We experimentally clarified that Pb(Zr,Ti)O 3 (PZT) thin films transferred on PDMS substrate, which is developed flexible piezoelectric substrate, have piezoelectric properties by evaluating crystal structures and an inverse piezoelectric effect. This fabrication method might allow us to efficiently develop novel MEMS (micro-electro-mechanical systems) devices such as wearable sensors and artificial muscle in large quantities at a low cost.

Localized bimodal response of neurite extensions and structural proteins in dorsal-root ganglion neurons with controlled polydimethylsiloxane substrate stiffness

Diabetes has become a global health challenge, driving the demand for innovative, non-invasive diagnostic technologies to improve glucose monitoring. Urinary glucose concentration, a reliable indicator of metabolic changes, provides a practical alternative for frequent monitoring without the discomfort of invasive methods. In this simulation-based study, we propose a novel asymmetric photonic structure that integrates Tamm plasmon polariton (TPP) modes and a cavity mode for high-precision refractive index sensing, with a conceptual focus on the potential detection of urinary glucose. The structure supports three distinct resonance modes, each with unique field localization. Both the TPP modes, confined at the metallic–dielectric interfaces, serve as stable references whose wavelengths are unaffected by refractive-index variations in human urine, whereas the cavity mode exhibits a redshift with increasing refractive index, enabling high responsiveness to analyte changes. The evaluation of sensing performance employs a sensitivity formulation that leverages either TPP mode as a reference and the cavity mode as a probe, thereby achieving dependable measurement and spectral stability. The optimized design achieves a sensitivity of 693 nm·RIU−1 and a maximum figure of merit of 935 RIU−1, indicating high detection resolution and spectral sharpness. The device allows both reflectance and transmittance measurements to ensure enhanced versatility. Moreover, the coupling between TPP and cavity modes demonstrates hybrid resonance, empowering applications such as polarization-sensitive or angle-dependent filtering. The figure of merit is analyzed further, considering resonance wavelength shifts and spectral sharpness, thus manifesting the structure’s robustness. Although this study does not provide experimental data such as calibration curves, recovery rates, or specificity validation, the proposed structure offers a promising conceptual framework for refractive index-based biosensing in human urine. The findings position the structure as a versatile platform for advanced photonic systems, offering precision, tunability, and multifunctionality beyond the demonstrated optical sensing capabilities.