Stabilizing TiCT MXene flakes in air by removing confined water.

MXenes have demonstrated potential for various applications owing to their tunable surface chemistry and metallic conductivity. However, high temperatures can accelerate MXene film oxidation in air. Understanding the mechanisms of MXene oxidation at elevated temperatures, which is still limited, is critical in improving their thermal stability for high-temperature applications.

Pulsed Force Kelvin Probe Force Microscopy-A New Type of Kelvin Probe Force Microscopy under Ambient Conditions.

Kelvin probe force microscopy (KPFM) is an increasingly popular scanning probe microscopy technique used for nanoscale imaging of surface potential for various materials, such as metals, semiconductors, biological samples, and photovoltaics, to reveal their surface work function and/or local accumulation of charges. This featured review outlines the operation principles and applications of KPFM, including several typical commercially available variants. We highlight the significance of surface potential measurements, present the details of the method operation, and discuss the causes of the limitation on spatial resolution.

Atomic-force-microscopy-based time-domain two-dimensional infrared nanospectroscopy.

For decades, infrared (IR) spectroscopy has advanced on two distinct frontiers: enhancing spatial resolution and broadening spectroscopic information. Although atomic force microscopy (AFM)-based IR microscopy overcomes Abbe's diffraction limit and reaches sub-10 nm spatial resolutions, time-domain two-dimensional IR spectroscopy (2DIR) provides insights into molecular structures, mode coupling and energy transfers. Here we bridge the boundary between these two techniques and develop AFM-2DIR nanospectroscopy.

What Do Different Modes of AFM-IR Mean for Measuring Soft Matter Surfaces?

In the past decade, rapidly emerging atomic force microscopy-based photothermal infrared microscopy (AFM-IR) techniques have routinely delivered surface chemical imaging with tens of nanometers spatial resolution. The commercial availability of AFM-IR instruments has accelerated their popularity among soft matter and surface science communities. Various AFM-IR modes exist with different characteristics.

Pulsed Force Kelvin Probe Force Microscopy through Integration of Lock-In Detection.

Kelvin probe force microscopy measures surface potential and delivers insights into nanoscale electronic properties, including work function, doping levels, and localized charges. Recently developed pulsed force Kelvin probe force microscopy (PF-KPFM) provides sub-10 nm spatial resolution under ambient conditions, but its original implementation is hampered by instrument complexity and limited operational speed. Here, we introduce a solution for overcoming these two limitations: a lock-in amplifier-based PF-KPFM.

Inducing trained immunity in pro-metastatic macrophages to control tumor metastasis.

Metastasis is the leading cause of cancer-related deaths and myeloid cells are critical in the metastatic microenvironment. Here, we explore the implications of reprogramming pre-metastatic niche myeloid cells by inducing trained immunity with whole beta-glucan particle (WGP). WGP-trained macrophages had increased responsiveness not only to lipopolysaccharide but also to tumor-derived factors.

Lock-in amplifier based peak force infrared microscopy.

Nanoscale infrared (nano-IR) microscopy enables label-free chemical imaging with a spatial resolution below Abbe's diffraction limit through the integration of atomic force microscopy and infrared radiation. Peak force infrared (PFIR) microscopy is one of the emerging nano-IR methods that provides non-destructive multimodal chemical and mechanical characterization capabilities using a straightforward photothermal signal generation mechanism. PFIR microscopy has been demonstrated to work for a wide range of heterogeneous samples, and it even allows operation in the fluid phase.

Fourier-Transform Atomic Force Microscope-Based Photothermal Infrared Spectroscopy with Broadband Source.

The mechanical detection of photothermal expansion from infrared (IR) absorption with an atomic force microscope (AFM) bypasses Abbe's diffraction limit, forming the chemical imaging technique of AFM-IR. Here, we develop a Fourier transform AFM-IR technique with peak force infrared microscopy and broadband femtosecond IR pulses. A Michelson interferometer creates a pair of IR pulses with controlled time delays to generate photothermal signals transduced by AFM to form an interferogram.

Principle and applications of peak force infrared microscopy.

Peak force infrared (PFIR) microscopy is an emerging atomic force microscopy (AFM)-based infrared microscopy that bypasses Abbe's diffraction limit on spatial resolution. The PFIR microscopy utilizes a nanoscopically sharp AFM tip to mechanically detect the tip-enhanced infrared photothermal response of the sample in the time domain. The time-gated mechanical signals of cantilever deflections transduce the infrared absorption of the sample, delivering infrared imaging and spectroscopy capability at sub 10 nm spatial resolution.

Dual-Color Peak Force Infrared Microscopy.

Peak force infrared (PFIR) microscopy achieves nanoscale infrared imaging at sub-10 nm spatial resolution through photothermal mechanical detection of atomic force microscopy (AFM). However, it suffers from a major limitation that only one infrared frequency can be scanned for an AFM frame at a time. To overcome this limitation, we report here dual-color PFIR microscopy that enables simultaneous imaging at two infrared frequencies.

Super-resolution mid-infrared spectro-microscopy of biological applications through tapping mode and peak force tapping mode atomic force microscope.

Small biomolecules at the subcellular level are building blocks for the manifestation of complex biological activities. However, non-intrusive in situ investigation of biological systems has been long daunted by the low spatial resolution and poor sensitivity of conventional light microscopies. Traditional infrared (IR) spectro-microscopy can enable label-free visualization of chemical bonds without extrinsic labeling but is still bound by Abbe's diffraction limit.

Nano-Chemical and Mechanical Mapping of Fine and Ultrafine Indoor Aerosols with Peak Force Infrared Microscopy.

Indoor aerosols can adversely affect human health as we increasingly spend more time indoors. One of the aerosol research challenges is measuring fine and ultrafine aerosol particles with nanoscale dimensions. Spectroscopic tools, often diffraction-limited, cannot access the intra-particle heterogeneity.

Liquid medium annealing for fabricating durable perovskite solar cells with improved reproducibility.

Solution processing of semiconductors is highly promising for the high-throughput production of cost-effective electronics and optoelectronics. Although hybrid perovskites have potential in various device applications, challenges remain in the development of high-quality materials with simultaneously improved processing reproducibility and scalability. Here, we report a liquid medium annealing (LMA) technology that creates a robust chemical environment and constant heating field to modulate crystal growth over the entire film.

Integrated Tapping Mode Kelvin Probe Force Microscopy with Photoinduced Force Microscopy for Correlative Chemical and Surface Potential Mapping.

Kelvin probe force microscopy (KPFM) is a popular technique for mapping the surface potential at the nanoscale through measurement of the Coulombic force between an atomic force microscopy (AFM) tip and sample. The lateral resolution of conventional KPFM variants is limited to between ≈35 and 100 nm in ambient conditions due to the long-range nature of the Coulombic force. In this article, a novel way of generating the Coulombic force in tapping mode KPFM without the need for an external AC driving voltage is presented.

Differences in surface chemistry of regenerated lignocellulose fibers determined by chemically sensitive scanning probe microscopy.

Tuning the composition of regenerated lignocellulosic fibers in the production process enables targeting of specific material properties. In composite materials, such properties could be manipulated by controlled heterogeneous distribution of chemical components of regenerated fibers. This attribute requires a visualization method to show their inherent chemical characteristics.

Vibrational Spectroscopic Detection of a Single Virus by Mid-Infrared Photothermal Microscopy.

We report a confocal interferometric mid-infrared photothermal (MIP) microscope for ultra-sensitive and spatially resolved chemical imaging of individual viruses. The interferometric scattering principle is applied to detect the very weak photothermal signal induced by infrared absorption of chemical bonds. Spectroscopic MIP detection of single vesicular stomatitis viruses (VSVs) and poxviruses is demonstrated.

Liquid-Phase Peak Force Infrared Microscopy for Chemical Nanoimaging and Spectroscopy.

Peak force infrared (PFIR) microscopy is an emerging atomic force microscopy that bypasses Abbe's diffraction limit in achieving chemical nanoimaging and spectroscopy. The PFIR microscopy mechanically detects the infrared photothermal responses in the dynamic tip-sample contact of peak force tapping mode and has been applied for a variety of samples, ranging from soft matters, photovoltaic heterojunctions, to polaritonic materials under the air conditions. In this article, we develop and demonstrate the PFIR microscopy in the liquid phase for soft matters and biological samples.

Total Internal Reflection Peak Force Infrared Microscopy.

Total internal reflection (TIR) infrared spectroscopy is a convenient measurement tool for collecting spectra for chemical identification. However, TIR infrared microscopy lacks high spatial resolution due to the optical diffraction limit and difficulty to preserve a high-quality wave front for focus. In this article, we present the peak force infrared microscopy in the TIR geometry to achieve a 10 nm spatial resolution.

Macrophage activation on "phagocytic synapse" arrays: Spacing of nanoclustered ligands directs TLR1/2 signaling with an intrinsic limit.

The activation of Toll-like receptor heterodimer 1/2 (TLR1/2) by microbial components plays a critical role in host immune responses against pathogens. TLR1/2 signaling is sensitive to the chemical structure of ligands, but its dependence on the spatial distribution of ligands on microbial surfaces remains unexplored. Here, we reveal the quantitative relationship between TLR1/2-triggered immune responses and the spacing of ligand clusters by designing an artificial "phagocytic synapse" nanoarray platform to mimic the cell-microbe interface.

Nanoscale Chemical Features of the Natural Fibrous Material Wood.

Peak force infrared (PFIR) microscopy is a recently developed approach to acquire multiple chemical and physical material properties simultaneously and with nanometer resolution: topographical features, infrared (IR)-sensitive maps, adhesion, stiffness, and locally resolved IR spectra. This multifunctional mapping is enabled by the ability of an atomic force microscope tip in the peak force tapping mode to detect photothermal expansion of the sample. We report the use of the PFIR to characterize the chemical modification of bio-based native and intact wooden matrices, which has evolved into an increasingly active research field.

Peak force visible microscopy.

The optical responses of molecules and materials provide a basis for chemical measurement and imaging. The optical diffraction limit in conventional light microscopy is exceeded by mechanically probing optical absorption through the photothermal effect with atomic force microscopy (AFM). However, the spatial resolution of AFM-based photothermal optical microscopy is still limited, and the sample surface is prone to damage from scratching due to tip contact, particularly for measurements on soft matter.

Peak Force Infrared-Kelvin Probe Force Microscopy.

Correlative scanning probe microscopy of chemical identity, surface potential, and mechanical properties provide insight into the structure-function relationships of nanomaterials. However, simultaneous measurement with comparable and high resolution is a challenge. We seamlessly integrated nanoscale photothermal infrared imaging with Coulomb force detection to form peak force infrared-Kelvin probe force microscopy (PFIR-KPFM), which enables simultaneous nanomapping of infrared absorption, surface potential, and mechanical properties with approximately 10 nm spatial resolution in a single-pass scan.

Simultaneous Nanoscale Imaging of Chemical and Architectural Heterogeneity on Yeast Cell Wall Particles.

Particles extracted from yeast cell walls are naturally occurring immunomodulators with significant therapeutic applications. Their biological function has been thought to be a consequence of the overall chemical composition. In contrast, here we achieve direct nanoscale visualization of the compositional and structural heterogeneity of yeast cell wall particles and demonstrate that such nanoscale heterogeneity directly influences the receptor function of immune cells.

Probing Mid-Infrared Phonon Polaritons in the Aqueous Phase.

Phonon polaritons (PhPs) are collective phonon oscillations with hybridized electromagnetic fields, which concentrate mid-infrared optical fields that can match molecular vibrations. The utilization of PhPs holds the promise for chemical sensing tools and polariton-enhanced nanospectroscopy. However, investigations and innovations on PhPs in the aqueous phase remain stagnant because of the lack of mid-infrared nanoimaging methods in water.

Pulsed Force Kelvin Probe Force Microscopy.

Measurement of the contact potential difference (CPD) and work functions of materials are important in analyzing their electronic structures and surface residual charges. Kelvin probe force microscopy (KPFM), an imaging technique of atomic force microscopy, has been widely used for surface potential and work function mapping at the nanoscale. However, the conventional KPFM variants are often limited in their spatial resolution to 30-100 nm under ambient conditions.