Electrochemical Polymer Pen Lithography

Mechanochemistry: Fundamental Principles and Applications

Mechanochemistry is an emerging research field at the interface of physics, mechanics, materials science, and chemistry. Complementary to traditional activation methods in chemistry, such as heat, electricity, and light, mechanochemistry focuses on the activation of chemical reactions by directly or indirectly applying mechanical forces. It has evolved as a powerful tool for controlling chemical reactions in solid state systems, sensing and responding to stresses in polymer materials, regulating interfacial adhesions, and stimulating biological processes. By combining theoretical approaches, simulations and experimental techniques, researchers have gained intricate insights into the mechanisms underlying mechanochemistry. In this review, the physical chemistry principles underpinning mechanochemistry are elucidated and a comprehensive overview of recent significant achievements in the discovery of mechanically responsive chemical processes is provided, with a particular emphasis on their applications in materials science. Additionally, The perspectives and insights into potential future directions for this exciting research field are offered.

Nanotechnology-Based Wearable Electrochemical Biosensor for Disease Diagnosis

Recently, flexible electronics have significantly transformed information and communications technology (ICT). In particular, wearable devices, via integration with attachable biosensors, have driven the development of new types of biosensors and diagnostic devices for point-of-care testing (POCT). Moreover, wearable electrochemical biosensors can be applied to diagnose diseases in real time based on the synergistic effect generated from the incorporation of the electrochemical technique. Besides, to improve the sensitivity of electrochemical biosensors while retaining their wearability, novel nanomaterials and nanotechnologies have been introduced. In this review, recent studies on nanotechnology-based wearable electrochemical biosensors for accurate disease diagnosis are discussed. First, widely used techniques for developing flexible electrodes, including nanolithography- and nano/microneedle-based patches, are presented. Next, the latest studies on developing wearable electrochemical biosensors for the diagnosis of diseases such as diabetes and dermatitis are discussed by categorizing the biosensors into nanolithography- and nano/microneedle-based categories. Finally, this review explores the latest research trends on the application of nanotechnology-enabled nanopatterning and nano/microneedle technologies to electrochemical wearable biosensors. This review suggests novel approaches and methods for developing wearable electrochemical biosensors for real-time disease diagnosis under POCT applications.

Scanning Electrochemical Probe Lithography for Ultra-Precision Machining of Micro-Optical Elements with Freeform Curved Surface

Two challenges should be overcome for the ultra-precision machining of micro-optical element with freeform curved surface: one is the intricate geometry, the other is the hard-to-machining optical materials due to their hardness, brittleness or flexibility. Here scanning electrochemical probe lithography (SECPL) is developed, not only to meet the machining need of intricate geometry by 3D direct writing, but also to overcome the above mentioned mechanical properties by an electrochemical material removal mode. Through the electrochemical probe a localized anodic voltage is applied to drive the localized corrosion of GaAs. The material removal rate is obtained as a function of applied voltage, motion rate, scan segment, etc. Based on the material removal function, an arbitrary geometry can be converted to a spatially distributed voltage. Thus, a series of micro-optical element are fabricated with a machining accuracy in the scale of 100 s of nanometers. Notably, the spiral phase plate shows an excellent performance to transfer parallel light to vortex beam. SECPL demonstrates its excellent controllability and accuracy for the ultra-precision machining of micro-optical devices with freeform curved surface, providing an alternative chemical approach besides the physical and mechanical techniques.

Architected Poly(ionic liquid) Composites with Spatially Programmable Mechanical Properties and Mixed Conductivity

Structural electrolytes present advantages over liquid varieties, which are critical to myriad applications. In particular, structural electrolytes based on polymerized ionic liquids or poly(ionic liquids) (pILs) provide wide electrochemical windows, high thermal stability, nonvolatility, and modular chemistry. However, current methods of fabricating structural electrolytes from pILs and their composites present limitations. Recent advances have been made in 3D printing pIL electrolytes, but current printing techniques limit the complexity of forms that can be achieved, as well as the ability to control mechanical properties or conductivity. We introduce a method for fabricating architected pIL composites as structural electrolytes via embedded 3D (EMB3D) printing. We present a modular design for formulating ionic liquid (IL) monomer composite inks that can be printed into sparse, lightweight, free-standing lattices with different functionalities. In addition to characterizing the rheological and mechanical behaviors of IL monomer inks and pIL lattices, we demonstrate the self-sensing capabilities of our printed structural electrolytes during cyclic compression. Finally, we use our inks and printing method to spatially program self-sensing capabilities in pIL lattices through heterogeneous architectures as well as ink compositions that provide mixed ionic-electronic conductivity. Our free-form approach to fabricating structural electrolytes in complex, 3D forms with programmable, anisotropic properties has broad potential use in next-generation sensors, soft robotics, bioelectronics, energy storage devices, and more.

Variable Nanoelectrode at the Air/Water Interface by Hydrogel-Integrated Atomic Force Microscopy Electrochemical Platform

A nanoelectrode with a controllable area was developed using commercial atomic force microscopy and a hydrogel. Although tremendous advantages of small electrodes from micrometer scale down to nanometer scale have been previously reported for a wide range of applications, precise and high-throughput fabrication remains an obstacle. In this work, the set-point feedback current in a modified scanning ionic conductance microscopy system controlled the formation of electrodes with a nanometer-sized area by contact between the boron-doped diamond (BDD) tip and the agarose hydrogel. The modulation of the electroactive area of the BDD-coated nanoelectrode in the hydrogel was successively investigated by the finite element method and cyclic voltammetry with the use of a redox-contained hydrogel. Moreover, this nanoelectrode enables the simultaneous imaging of both the topography and electrochemical activity of a polymeric microparticle embedded in a hydrogel.

Mechanochemical Lithography

Surfaces with patterned biomolecules have wide applications in biochips and biomedical diagnostics. However, most patterning methods are inapplicable to physiological conditions and incapable of creating complex structures. Here, we develop a mechanochemical lithography (MCL) method based on compressive force-triggered reactions. In this method, biomolecules containing a bioaffinity ligand and a mechanoactive group are used as mechanochemical inks (MCIs). The bioaffinity ligand facilitates concentrating MCIs from surrounding solutions to a molded surface, enabling direct and continuous printing in an aqueous environment. The mechanoactive group facilitates covalent immobilization of MCIs through force-triggered reactions, thus avoiding the broadening of printed features due to the diffusion of inks. We discovered that the ubiquitously presented amino groups in biomolecules can react with maleimide through a force-triggered Michael addition. The resulting covalent linkage is mechanically and chemically stable. As a proof-of-concept, we fabricate patterned surfaces of biotin and His-tagged proteins at nanoscale spatial resolution by MCL and verify the resulting patterns by fluorescence imaging. We further demonstrated the creation of multiplex protein patterns using this technique.