Polymer Pen Research Articles

From Heterostructures to Solid-Solutions: Structural Tunability in Mixed Halide Perovskites.

The stability, reliability, and performance of halide-perovskite-based devices depend upon the structure, composition, and particle size of the device-enabling materials. Indeed, the degree of ion mixing in multicomponent perovskite crystals, although challenging to control, is a key factor in determining properties. Herein, an emerging method termed evaporation-crystallization polymer pen lithography is used to synthesize and systematically study the degree of ionic mixing of Cs0.5 FA0.5 PbX3 (FA = formamidinium; X = halide anion, ABX3 ) crystals, as a function of size, temperature, and composition. These experiments have led to the discovery of a heterostructure morphology where the A-site cations, Cs and FA, are segregated into the core and edge layers, respectively. Simulation and experimental results indicate that the heterostructures form as a consequence of a combination of both differences in solubility of the two ions in solution and the enthalpic preference for Cs-FA ion segregation. This preference for segregation can be overcome to form a solid-solution by decreasing crystal size (<60nm) or increasing temperature. Finally, these tools are utilized to identify and synthesize solid-solution nanocrystals of Cs0.5 FA0.5 Pb(Br/I)3 that significantly suppress photoinduced anion migration compared to their bulk counterparts, offering a route to deliberately designed photostable optoelectronic materials.

Patterning-mediated supramolecular assembly of lipids into nanopalms

At nanoconfined interfaces, a micellar ink of lipids was programmed to transform into various secondary structures such as discs, sheets, or sheet and discs via patterning-mediated self-assembly facilitated by polymer pen lithography. Nanoconfinement with printing force, humidity, temperature, pattern size, and total printing time all governed the intramolecular assembly of lipids and determined their structural shape and size. For example, disc or sheet architectures self-organized to produce cochleates or discotic liquid crystals, respectively. In contrast, the combined structure of sheet and discs produced a novel supramolecular output referred to as "nanopalms". The mechanism of nanopalms formation and the origin of their stability were investigated and discussed. Post patterning treatment helped to transform the patterned discs into ribbons and sheets into cochleates that could facilitate the curling of ribbons along their folding direction in a programmed manner via intermolecular self-organization producing the nanopalms.

Luminescent nanoparticle-arrays synthesized via polymer pen lithography

Luminescent nanoparticle-arrays synthesized via polymer pen lithography

Controlling Intracellular Machinery via Polymer Pen Lithography Molecular Patterning.

The plasma membrane and the actomyosin cytoskeleton play key roles in controlling how cells sense and interact with their surrounding environment. Myosin, a force-generating actin network-associated protein, is a major regulator of plasma membrane tension, which helps control endocytosis. Despite the important link between plasma membranes and actomyosin (the actin–myosin complex), little is known about how the actomyosin arrangement regulates endocytosis. Here, nanoscopic ligand arrangements defined by polymer pen lithography (PPL) are used to control actomyosin contractility and examine cell uptake. Confocal microscopy, atomic force microscopy, and flow cytometry suggest that the cytoskeletal tension imposed by the nanoscopic ligand arrangement can actively regulate cellular uptake through clathrin- and caveolin-mediated pathways. Specifically, ligand arrangements that increase cytoskeletal tension tend to reduce the cellular uptakes of cholera toxin (CTX) and spherical nucleic acids (SNAs) by regulating endocytic budding and limiting the formation of clathrin- and caveolae-coated pits. Collectively, this work demonstrates how the cell endocytic fate is regulated by actomyosin mechanical forces, which can be tuned by subcellular cues defined by PPL.

Combinatorial Synthesis and Screening of Mixed Halide Perovskite Megalibraries.

A significant bottleneck in the discovery of new mixed halide perovskite (MHP) compositions and structures is the time-consuming and low-throughput nature of current synthesis and screening methods. Here, a high-throughput strategy is presented that can be used to synthesize combinatorial libraries of MHPs with deliberate control over the halide mixing ratio and particle size (for example, CsPb(Br1-xClx)3 (0 < x < 1) with sizes between ∼100 and 400 nm). This strategy combines evaporation-crystallization polymer pen lithography (EC-PPL) and defect-engineered anion exchange to spatially encode particle size and composition, respectively. Laser exposure is used to selectively modify the defect concentration of individual particles, and thus the degree of subsequent anion exchange, allowing the preparation for ultra-high-density arrays of distinct compositions (>1 unique particle/μm2). This method was utilized to rapidly generate a library of ∼4000 CsPb(Br1-xClx)3 particles that was then screened for high-efficiency blue photoemission, which yielded CsPb(Br0.6Cl0.4)3 as the composition with the highest photoluminescence intensity. The combinatorial synthesis and screening strategy provided here, and the mechanistic understanding of the defect-engineering process gleaned from it, will enable the rapid discovery of exceptional MHP optoelectronic materials.

Lithographic Patterning of Nanoscale Arrays of the Oxidase Enzyme CotA: Effects on Activity and Stability

AbstractThis study compares the enzymatic activity of nanoscale arrays bearing the oxidase CotA that are produced by two lithographic methods: polymer pen lithography (PPL), a scanning probe lithography for small‐area fabrication (≈1 cm2); and stepper photolithography, a large‐scale method (&gt;300 cm2) used in the microelectronics sector. In both cases, arrays of 600 nm gold features are produced and functionalized with CotA through a bioconjugation method that gives uniform protein orientation. The enzyme activity of these arrays is then quantified over 100 days. The enzyme arrays produced by photolithography give higher oxidation activities immediately after fabrication but degrade more rapidly when compared to those produced by PPL. This result is due to the poorer passivation on the bulk surface of photolithographically produced arrays, resulting in a greater amount of non‐specifically adsorbed enzymes. However, once the results are adjusted to account for the differences in passivation and surface area, it is found that the enzymes immobilized on the gold features give essentially the same activity regardless of the lithographic method used. Thus, these results suggest PPL is a suitable method for prototyping biodevices prior to scale‐up, provided that due consideration is given to the design of the fabricated features.

Plasma-Assisted Microcontact Printing.

Microcontact printing, polymer pen lithography, and their variations have attracted interests from a broad spectrum of research fields as a result of the feasibility of defining patterns in micro- and nanoscales. In this work, we have proposed and demonstrated a novel lithography method, named plasma-assisted microcontact printing (PA-μCP). Unlike the previous printing methods, where a direct contact is normally required for the transport of liquid-phase inks, plasma-deposited fluorocarbon (FC) has been employed in PA-μCP as the ink material, which can be transferred from the stamp to substrates through a thermal evaporation process. The geometry of the patterns can be modified by adjusting the design of stamp patterns and the contact time, and transferred FC patterns can be used directly as an etch mask to create microstructures in the substrate materials. We have demonstrated the possibility of performing multi-patterning with PA-μCP, where FC patterns can be generated conformally on structured substrates. Because the height of FC patterns is closely related to the local pattern designs, PA-μCP can be used for grayscale patterning. As a proof of concept, Fabry-Perot planar cavities are fabricated with grayscale PA-μCP for structure color printing. We believe PA-μCP is distinguished from conventional techniques by its printing mechanism, which can pave the way for convenient fabrication of photonic, electronic, and biological devices.

Electrochemical Polymer Pen Lithography.

The development of a massively parallel lithographic technique called electrochemical polymer pen lithography is reported. Pyramidal pen arrays, consisting of more than 10000 hydrogel pens loaded with metal salts, are integrated into a three-electrode cell and used to locally reduce ions at each pen tip. This system enables high-throughput patterning of a variety of metallic inks (e.g., Ni2+ , Pt2+ , Ag+ ) on the nanometer to micrometer length scale. By incorporating a z-direction piezo actuator, the extension length and dwell time can be used to precisely define feature dimensions (210 to 10µm in width, and up to 900nm in height, thus far). Furthermore, by controlling the potential and precursor concentrations, more than one element can be simultaneously deposited, creating a new tool for the synthesis of alloy features, such as NiCo, which are relevant for catalysis. Importantly, this methodology enables fine control over feature size and composition in a single pattern, which may make it ultimately useful for rapid, high-throughput combinatorial screening of metallic features.

Evolution from dip-pen nanolithography to mechanochemical printing

&lt;sec&gt;As a unique nanomanipulation and nanofabrication tool, dip-pen nanolithography (DPN) has enjoyed great success in the past two decades. The DPN can be used to create molecular patterns with nanoscale precision on a variety of substrates with different chemistry properties. Since its advent, the DPN has been steadily improved in the sense of applicable inks, fabrication throughput, and new printing chemistry. Among these developments, mechanical force induced mechanochemistry is of special interest.&lt;/sec&gt;&lt;sec&gt;In this review, we introduce the physical principles behind the DPN technique. We highlight the development of DPN for writing with various types of “inks”, including small molecules, viscous polymer solutions, lipids, and biomolecules, especially, the development of thermal-DPN allowing printing with inks that are usually in solid phase at room temperature. Next, we introduce the parallel-DPN and polymer pen nanolithography. These techniques greatly speed up the fabrication speed without sacrificing the precision. We also summarize the advances in chemical reaction based DPN technologies, including electrochemical DPN, metal tip-induced catalytical DPN, and mechanochemical DPN (or mechanochemical printing). To further elaborate the mechanism behind the mechanochemical printing, we briefly review the development of mechanochemistry, including the reaction mechanism, various experimental approaches to realizing mechanochemistry, and recent development in this field. We highlight the advantages of using atomic force microscopy to study mechanochemistry at a single molecule level and indicate the potential of combining this technique with DPN to realize mechanochemical printing. We envision that with the further discovery of novel mechanophores that are suitable for mechanochemical printing, this technique can be broadly applied to nanotechnology and atomic fabrication.&lt;/sec&gt;

Scanner‐Based Capillary Stamping

AbstractClassical microcontact printing and polymer pen lithography (PPL) involve ink transfer to substrates using solid elastomeric stamps. Ink depletion thus limits the number of successive stamping steps without reinking. Porous stamps developed to overcome this limitation are used only for manual proof‐of‐principle experiments. Here, porous composite stamps for scanner‐based capillary stamping (SCS) that can be mounted on automated printing devices designed for PPL are developed. Porous SCS composite stamps consist of a rigid controlled porous silica glass (CPG) layer and a porous polymeric stamping layer. The latter can be topographically structured with contact elements by replication molding. The mechanical stabilization by the CPG layer ensures that the contact elements are coplanar. SCS allows automated, continuous, high‐throughput patterning enabled by ink supply through the porous SCS composite stamps. Even after more than 800 consecutive stamp–substrate contacts without reinking (the porous SCS composite stamps themselves are used as ink reservoirs), ink microdroplets are deposited without deterioration of the pattern quality. However, SCS also allows supply of additional ink during ongoing stamping operations through the pore systems of the porous SCS composite stamps. SCS can easily be adapted for multi‐ink patterning and may pave the way for further upscaling of contact lithography.

Evolution of Dip-Pen Nanolithography (DPN): From Molecular Patterning to Materials Discovery.

Dip-pen nanolithography (DPN) is a nanofabrication technique that can be used to directly write molecular patterns on substrates with high resolution and registration. Over the past two decades, DPN has evolved in its ability to transport molecular and material "inks" (e.g., alkanethiols, biological molecules like DNA, viruses, and proteins, polymers, and nanoparticles) to many surfaces in a high-throughput fashion, enabling the synthesis and study of complex chemical and biological structures. In addition, DPN has laid the foundation for a series of related scanning probe methodologies, for example, polymer pen lithography (PPL), scanning probe block copolymer lithography (SPBCL), and beam-pen lithography (BPL), which do not rely on cantilever tips. Structures prepared with these methodologies have been used to understand the consequences of miniaturization and open a door to new capabilities in catalysis, optics, biomedicine, and chemical synthesis, where, in sum, a process originally intended to compete with tools used by the semiconductor industry for rapid prototyping has transcended that application to advanced materials discovery. This review outlines the major DPN advances, the subsequent methods based on the technique, and the opportunities for future fundamental and technological exploration. Most importantly, it commemorates the 20th anniversary of the discovery of DPN.

Subcellular Control over Focal Adhesion Anisotropy, Independent of Cell Morphology, Dictates Stem Cell Fate.

Although microscale patterning techniques have been used to control cell morphology and shape, they only provide indirect control over the formation of the subcellular cytoskeletal elements that determine contractility. This paper addresses the hypotheses that nanoscale anisotropic features of a patterned matrix can direct the alignment of internal cytoskeletal actin fibers within a confined shape with an unbiased aspect ratio, and that this enhanced control over cytoskeletal architecture directs programmed cell behaviors. Here, large-area polymer pen lithography is used to pattern substrates with nanoscale extracellular matrix protein features and to identify cues that can be used to direct cytoskeletal organization in human mesenchymal stem cells. This nanopatterning approach is used to identify how anisotropic focal adhesions around the periphery of symmetric patterns yield an organized and contractile actin cytoskeleton. This work reports the important finding that anisotropic cues that increase cell contractility within a circular shape redirect cell differentiation from an adipogenic to an osteogenic fate. Together, these experiments introduce a programmable approach for using subcellular spatial cues to control cell behavior within defined geometries.

Do-It-Yourself Pyramidal Mold for Nanotechnology.

The handcrafted fabrication of a pyramidal mold on a silicon wafer for nanopatterning was investigated. This process started with the manual delivery of an aqueous glycerol solution onto the SiO2/Si wafer using a micropipette and subsequent drying to form a hemisphere whose diameter is in the range of hundreds of micrometers. A coating of polystyrene (PS) onto this wafer generates a circular hole caused by dewetting. Subsequently, anisotropic wet-etching with the PS film as a mask produces a pyramidal trench, whose apex approaches hundreds of nanometers. Various elastomeric materials were casted into this pyramidal mold. A pyramidal tip mounted on a simple micropositioner was used for electrochemistry and patterning of a protein. First, an agarose hydrogel was cast with a hydrogel pen for the electrochemical reaction (HYPER). The redox reaction at the HYPER–electrode interface demonstrated the characteristics of an ultramicroelectrode or bulk electrode based on the contact area. Second, the pyramidal polydimethylsiloxane served as a polymer pen for the contact printing of silane on a glass substrate. After the successive immobilization of biotin and avidin with fluorescence labeling, the resulting fluorescence image demonstrated the successful patterning of the protein. This new process for the creation of a pyramidal mold, referred to as a “do-it-yourself” process, offers advantages to nonspecialists in nanotechnology compared to conventional lithography, specifically simplicity, rapidity, and low cost.

Writing Behavior of Phospholipids in Polymer Pen Lithography (PPL) for Bioactive Micropatterns.

Lipid-based membranes play crucial roles in regulating the interface between cells and their external environment, the communication within cells, and cellular sensing. To study these important processes, various lipid-based artificial membrane models have been developed in recent years and, indeed, large-area arrays of supported lipid bilayers suit the needs of many of these studies remarkably well. Here, the direct-write scanning probe lithography technique called polymer pen lithography (PPL) was used as a tool for the creation of lipid micropatterns over large areas via polymer-stamp-mediated transfer of lipid-containing inks onto glass substrates. In order to better understand and control the lipid transfer in PPL, we conducted a systematic study of the influence of dwell time (i.e., duration of contact between tip and sample), humidity, and printing pressure on the outcome of PPL with phospholipids and discuss results in comparison to the more often studied dip-pen nanolithography with phospholipids. This is the first systematic study in phospholipid printing with PPL. Biocompatibility of the obtained substrates with up to two different ink compositions was demonstrated. The patterns are suitable to serve as a platform for mast cell activation experiments.

Development of Dip-Pen Nanolithography (DPN) and Its Derivatives.

Dip-pen nanolithography (DPN) is a unique nanofabrication tool that can directly write a variety of molecular patterns on a surface with high resolution and excellent registration. Over the past 20 years, DPN has experienced a tremendous evolution in terms of applicable inks, a remarkable improvement in fabrication throughput, and the development of various derivative technologies. Among these developments, polymer pen lithography (PPL) is the most prominent one that provides a large-scale, high-throughput, low-cost tool for nanofabrication, which significantly extends DPN and beyond. These developments not only expand the scope of the wide field of scanning probe lithography, but also enable DPN and PPL as general approaches for the fabrication or study of nanostructures and nanomaterials. In this review, a focused summary and historical perspective of the technological development of DPN and its derivatives, with a focus on PPL, in one timeline, are provided and future opportunities for technological exploration in this field are proposed.

Polymer Pen Lithography-Fabricated DNA Arrays for Highly Sensitive and Selective Detection of Unamplified Ganoderma Boninense DNA.

There is an increasing demand for lithography methods to enable the fabrication of diagnostic devices for the biomedical and agri-food sectors. In this regard, scanning probe lithography methods have emerged as a possible approach for this purpose, as they are not only convenient, robust and accessible, but also enable the deposition of “soft” materials such as complex organic molecules and biomolecules. In this report, the use of polymer pen lithography for the fabrication of DNA oligonucleotide arrays is described, together with the application of the arrays for the sensitive and selective detection of Ganoderma boninense, a fungal pathogen of the oil palm. When used in a sandwich assay format with DNA-conjugated gold nanoparticles, this system is able to generate a visually observable result in the presence of the target DNA. This assay is able to detect as little as 30 ng of Ganoderma-derived DNA without any pre-amplification and without the need for specialist laboratory equipment or training.

Design of Elastomer-CNT Film Photoactuators for Nanolithography.

Polymer pen lithography (PPL) is an approach to multiplexing scanning probe lithography, in which an array of probes on a compliant film-coated rigid substrate are used to write patterns on a surface. Recently, it was shown that these nominally passive pen arrays can be rendered photo-active by making them out of a polydimethylsiloxane (PDMS)–carbon nanotube (CNT) composite. While such photoactuated pens in principle represent a rapid, maskless, and versatile nanomanufacturing strategy, a key challenge that remains is learning how to effectively control the writing of each pen, individually. In this research, we studied the design of PDMS–CNT thin-film photoactuators and experimentally explored the role of illumination radius, film thickness, and CNT concentration. Additionally, we have proposed a model that predicts actuation efficiency, actuation time, and the crosstalk between pens. Based upon these results, we have generated a map of working efficiency to elucidate the ideal choice for specific actuation requirements. This work lays the foundation for studying further photoactuatable composite films as actuators in applications beyond lithography including soft robotics and adaptive optics.

Catalyst discovery through megalibraries of nanomaterials

The nanomaterial landscape is so vast that a high-throughput combinatorial approach is required to understand structure-function relationships. To address this challenge, an approach for the synthesis and screening of megalibraries of unique nanoscale features (>10,000,000) with tailorable location, size, and composition has been developed. Polymer pen lithography, a parallel lithographic technique, is combined with an ink spray-coating method to create pen arrays, where each pen has a different but deliberately chosen quantity and composition of ink. With this technique, gradients of Au-Cu bimetallic nanoparticles have been synthesized and then screened for activity by in situ Raman spectroscopy with respect to single-walled carbon nanotube (SWNT) growth. Au3Cu, a composition not previously known to catalyze SWNT growth, has been identified as the most active composition.

Large-area Scanning Probe Nanolithography Facilitated by Automated Alignment and Its Application to Substrate Fabrication for Cell Culture Studies

Scanning probe microscopy has enabled the creation of a variety of methods for the constructive ('additive') top-down fabrication of nanometer-scale features. Historically, a major drawback of scanning probe lithography has been the intrinsically low throughput of single probe systems. This has been tackled by the use of arrays of multiple probes to enable increased nanolithography throughput. In order to implement such parallelized nanolithography, the accurate alignment of probe arrays with the substrate surface is vital, so that all probes make contact with the surface simultaneously when lithographic patterning begins. This protocol describes the utilization of polymer pen lithography to produce nanometer-scale features over centimeter-sized areas, facilitated by the use of an algorithm for the rapid, accurate, and automated alignment of probe arrays. Here, nanolithography of thiols on gold substrates demonstrates the generation of features with high uniformity. These patterns are then functionalized with fibronectin for use in the context of surface-directed cell morphology studies.

Large-area Scanning Probe Nanolithography Facilitated by Automated Alignment and Its Application to Substrate Fabrication for Cell Culture Studies.

Scanning probe microscopy has enabled the creation of a variety of methods for the constructive ('additive') top-down fabrication of nanometer-scale features. Historically, a major drawback of scanning probe lithography has been the intrinsically low throughput of single probe systems. This has been tackled by the use of arrays of multiple probes to enable increased nanolithography throughput. In order to implement such parallelized nanolithography, the accurate alignment of probe arrays with the substrate surface is vital, so that all probes make contact with the surface simultaneously when lithographic patterning begins. This protocol describes the utilization of polymer pen lithography to produce nanometer-scale features over centimeter-sized areas, facilitated by the use of an algorithm for the rapid, accurate, and automated alignment of probe arrays. Here, nanolithography of thiols on gold substrates demonstrates the generation of features with high uniformity. These patterns are then functionalized with fibronectin for use in the context of surface-directed cell morphology studies.