Multifunctional hydrogel nano-probes for atomic force microscopy

Abstract

Since the invention of the atomic force microscope (AFM) three decades ago, there have been numerous advances in its measurement capabilities. Curiously, throughout these developments, the fundamental nature of the force-sensing probe—the key actuating element—has remained largely unchanged. It is produced by long-established microfabrication etching strategies and typically composed of silicon-based materials. Here, we report a new class of photopolymerizable hydrogel nano-probes that are produced by bottom-up fabrication with compressible replica moulding. The hydrogel probes demonstrate excellent capabilities for AFM imaging and force measurement applications while enabling programmable, multifunctional capabilities based on compositionally adjustable mechanical properties and facile encapsulation of various nanomaterials. Taken together, the simple, fast and affordable manufacturing route and multifunctional capabilities of hydrogel AFM nano-probes highlight the potential of soft matter mechanical transducers in nanotechnology applications. The fabrication scheme can also be readily utilized to prepare hydrogel cantilevers, including in parallel arrays, for nanomechanical sensor devices.

Hydrogel Microelectromechanical System (MEMS) Resonators: Beyond Cost‐Effective Sensing Platform

“…Besides manufacturability and stability, silicon-based materials such as single crystal silicon [6] and stress-controlled silicon nitride [7,8] also offer a high-quality factor preferred for high-resolution mass sensing applications. [11][12][13] One of the promising alternative candidate materials for MEMS resonators is polymer, a large molecule composed of many repeated subunits. [10] It is clear that material requirements for stable oscillators and sensors are quite different and even contradictory.…”

“…Later on, superior sensitivity for humidity sensing [34] and enhanced performance for high-speed dynamic mode imaging [35] have been demonstrated by using the SU-8 photoresist. Hydrogels that have recently shown promising aspects with regard to multifunctional atomic force microscopy [12] and infrared induced thermal sensing based on mechanical resonance [9] and any materials that a supporting structure can be easily made with may be ideal candidates. [36] Although aforementioned encouraging milestones make SU-8 outstand among various polymer candidates, overall fabrication cost, in turn, is higher than that for other polymer materials because the rather expensive SU-8 is used for both freestanding and supporting parts and the fabrication requires standard microfabrication facilities.…”

“…With one step taken further by pyrolyzing the SU-8 microstructures, submicrometer dimensions along with improved electrical conductivity could be exploited. However, the hydrogel materials and preparation recipe, polyethyleneglycol diacrylate (PEG-DA) MW250 (prepared by 1 wt% photoinitiator), previously used for all-hydrogel AFM cantilevers [12] and hydrogel cantilever infrared sensors, [9] would be certainly relevant since their damping and stability have been thoroughly characterized in comparison with silicon and proven to be promising. Of note, the majority of the SU-8 is used to define the supporting part just holding the suspended structure.…”

Tailored probes for atomic force microscopy fabricated by two-photon polymerization

“…Jung et al 18 added a tip to the end of an optical fiber by TPP and further decreased the tip radius to 15 nm in a subsequent step by O 2 -plasma ashing. Lee et al 19 used mold inserts to attach hydrogel probes. So far, tips written with three-dimensional lithography always resembled their conventionally fabricated counterparts.…”

Polyethyleneglycol diacrylate hydrogels with plasmonic gold nanospheres incorporated via functional group optimization

“…[11]. In this context, PEG-DA based materials had shown very promising applications by preparing highly stable hydrogels which were used as mechanical sensors, piezo actuating devices, stimuli response materials and so on [12]. Moreover, polyethyleneglycol diacrylate (PEG-DA) is non-volatile, non-toxic, environmentally benign and tailor made into various shapes, enabling to act as potential stabilizers and matrices for the formation of functional hydrogels [13].…”