Development of multi-environment dual-probe atomic force microscopy system using optical beam deflection sensors with vertically incident laser beams

An integrated hinged dual-probe for co-target fast switching imaging

The diversity of functional applications of atomic force microscopes is the key to the development of nanotechnology. However, the single probe configuration of the traditional atomic force microscope restricts the realization of different application requirements for the same target area of a single sample, and the replacement of the working probe will lead to the loss of the target area. Here, the design, simulation, fabrication, and application of a unique atomic force microscope dual-probe are presented, which consists of a pair of parallel cantilevers with a narrow gap and a U-shaped hinged probe base. The Integrated Hinged Dual-Probe (IHDP) is developed specifically for fast switching of probes working in limited space and independent and precise manipulation of each probe. The deflection signal sensing of two cantilevers is achieved simultaneously by a single laser beam, and the decoupled independent cantilever deflection signals do not interfere with each other. The switching of the working probe is achieved by a piezoelectric ceramic with a 2 µm stroke and U-shaped hinge structure, which is fast and does not require tedious and repetitive spatial position calibration. By measuring standard grid samples, IHDP exhibits excellent measurement and characterization capabilities. Finally, a working probe switching imaging experiment was conducted on solidified rat cardiomyocytes, and the experimental process and imaging results demonstrated the superiority of IHDP in switching probe scanning imaging of the same target area of a single sample. The two probes of IHDP can undergo arbitrary functionalization modifications, which helps achieve multidimensional information acquisition for a single target.

Development of a multi-functional multi-probe atomic force microscope system with optical beam deflection method

We developed a multi-probe atomic force microscope (MP-AFM) system with up to four probes and realized various functions such as topography mapping, probing electrical property, and local temperature measurement. Each probe mounted on the corresponding probe scanner was controlled independently, and the system employed the optical beam deflection method to measure the deflection of each cantilever. A high-performance MP-AFM system with a compact optical design and rigid actuators was finally established. We demonstrated AFM high-resolution imaging in air and performed four-probe imaging in parallel and multi-functional characterization with the MP-AFM system.

Dual-Probe Atomic Force Microscopy based on tuning fork probes for critical dimension metrology

Atomic force microscopy (AFM) is widely used for nano-dimensional metrology in semiconductor manufacturing and metrological system. However, the conventional AFM can't provide accurate CD characterization of nanostructures, due to its top-down configuration and probe-size effect. In this paper, we develop a dual-probe atomic force microscopy (DPAFM). Compared to conventional optical-lever based AFM, the DPAFM exploits two tuning fork probes that simplifies significantly the setup and can be controlled based on frequency-modulation (FM) mode. The developed DPFAM is implemented that builds a zero-reference point by dual-probe alignment firstly, following which, characterizes nanostructures from two sides independently with the two probes. The final CD feature is determined by matching profiles from the two probes based on the zero-reference point. The capability of the DPAFM is validated by experiments on a CD-standard structure, that achieves the true CD assessment with good accuracy and repeatability.

Ascent of atomic force microscopy as a nanoanalytical tool for exosomes and other extracellular vesicles

Over the last 30 years, atomic force microscopy (AFM) has made several significant contributions to the field of biology and medicine. In this review, we draw our attention to the recent applications and promise of AFM as a high-resolution imaging and force sensing technology for probing subcellular vesicles: exosomes and other extracellular vesicles. Exosomes are naturally occurring nanoparticles found in several body fluids such as blood, saliva, cerebrospinal fluid, amniotic fluid and urine. Exosomes mediate cell-cell communication, transport proteins and genetic content between distant cells, and are now known to play important roles in progression of diseases such as cancers, neurodegenerative disorders and infectious diseases. Because exosomes are smaller than 100 nm (about 30-120 nm), the structural and molecular characterization of these vesicles at the individual level has been challenging. AFM has revealed a new degree of complexity in these nanosized vesicles and generated growing interest as a nanoscale tool for characterizing the abundance, morphology, biomechanics, and biomolecular make-up of exosomes. With the recent interest in exosomes for diagnostic and therapeutic applications, AFM-based characterization promises to contribute towards improved understanding of these particles at the single vesicle and sub-vesicular levels. When coupled with complementary methods like optical super resolution STED and Raman, AFM could further unlock the potential of exosomes as disease biomarkers and as therapeutic agents.