High-throughput atomic force microscopes operating in parallel

Morphometric and Nanomechanical Screening of Peripheral Blood Cells with Atomic Force Microscopy for Label-Free Assessment of Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis

Neurodegenerative disorders (NDDs) are complex, multifactorial disorders with significant social and economic impact in today's society. NDDs are predicted to become the second-most common cause of death in the next few decades due to an increase in life expectancy but also to a lack of early diagnosis and mainly symptomatic treatment. Despite recent advances in diagnostic and therapeutic methods, there are yet no reliable biomarkers identifying the complex pathways contributing to these pathologies. The development of new approaches for early diagnosis and new therapies, together with the identification of non-invasive and more cost-effective diagnostic biomarkers, is one of the main trends in NDD biomedical research. Here we summarize data on peripheral biomarkers, biofluids (cerebrospinal fluid and blood plasma), and peripheral blood cells (platelets (PLTs) and red blood cells (RBCs)), reported so far for the three most common NDDs-Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). PLTs and RBCs, beyond their primary physiological functions, are increasingly recognized as valuable sources of biomarkers for NDDs. Special attention is given to the morphological and nanomechanical signatures of PLTs and RBCs as biophysical markers for the three pathologies. Modifications of the surface nanostructure and morphometric and nanomechanical signatures of PLTs and RBCs from patients with AD, PD, and ALS have been revealed by atomic force microscopy (AFM). AFM is currently experiencing rapid and widespread adoption in biomedicine and clinical medicine, in particular for early diagnostics of various medical conditions. AFM is a unique instrument without an analog, allowing the generation of three-dimensional cell images with extremely high spatial resolution at near-atomic scale, which are complemented by insights into the mechanical properties of cells and subcellular structures. Data demonstrate that AFM can distinguish between the three pathologies and the normal, healthy state. The specific PLT and RBC signatures can serve as biomarkers in combination with the currently used diagnostic tools. We highlight the strong correlation of the morphological and nanomechanical signatures between RBCs and PLTs in PD, ALS, and AD.

Binary-state scanning probe microscopy for parallel imaging

Scanning probe microscopy techniques, such as atomic force microscopy and scanning tunnelling microscopy, are harnessed to image nanoscale structures with an exquisite resolution, which has been of significant value in a variety of areas of nanotechnology. These scanning probe techniques, however, are not generally suitable for high-throughput imaging, which has, from the outset, been a primary challenge. Traditional approaches to increasing the scalability have involved developing multiple probes for imaging, but complex probe design and electronics are required to carry out the detection method. Here, we report a probe-based imaging method that utilizes scalable cantilever-free elastomeric probe design and hierarchical measurement architecture, which readily reconstructs high-resolution and high-throughput topography images. In a single scan, we demonstrate imaging with a 100-tip array to obtain 100 images over a 1-mm² area with 10⁶ pixels in less than 10 min. The potential for large-scale tip integration and the advantage of a simple probe array suggest substantial promise for our approach to high-throughput imaging far beyond what is currently possible.

High-throughput imaging has generally been challenging for scanning probe microscopy techniques. Here, the authors introduce binary-state scanning probe microscopy, which uses a cantilever-free elastomeric probes and a hierarchical measurement architecture for parallel topography imaging.

Multiprobe scanning probe microscope using a probe-array head

We have developed a microelectromechanical system (MEMS)-based multiprobe scanning probe microscope (SPM) to improve imaging efficiency. The SPM head contains seven identical MEMS probes, and each of them integrates a displacement sensor and a Z-axis actuator. Force constant mode is designed based on the force feedback strategy rather than on the position feedback strategy for this kind of SPM head. A nano-measuring machine is equipped with the lateral XY scanners, which can reach a motion range of 25 mm × 25 mm. After calibration, the measurement of one-dimensional grating has been made to demonstrate the capability of multiprobe scanning.

On the resolution of subsurface atomic force microscopy and its implications for subsurface feature sizing

Ultrasound atomic force microscopy (AFM) has received considerable interest due to its subsurface imaging capabilities, particularly for nanostructure imaging. The local contact stiffness variation due to the presence of a subsurface feature is the origin of the imaging contrast. Several research studies have demonstrated subsurface imaging capabilities with promising resolution. However, there is limited literature available about the definition of spatial resolution in subsurface AFM. The changes in contact stiffness and their link to the subsurface resolution are not well understood. We propose a quantitative approach to assess the resolution in subsurface AFM imaging. We have investigated the influences of several parameters of interest on the lateral resolution. The quantification of the subsurface feature size can be based on threshold criteria (full width at half maximum and Rayleigh criteria). Simulations and experimental measurements were compared, revealing that the optimal choice of parameter settings for surface topography AFM is suboptimal for subsurface AFM imaging.

Parallelized DNA tethered bead measurements to scrutinize DNA mechanical structure

Tethering beads to DNA offers a panel of single molecule techniques for the refined analysis of the conformational dynamics of DNA and the elucidation of the mechanisms of enzyme activity. Recent developments include the massive parallelization of these techniques achieved by the fabrication of dedicated nanoarrays by soft nanolithography. We focus here on two of these techniques: the Tethered Particle motion and Magnetic Tweezers allowing analysis of the behavior of individual DNA molecules in the absence of force and under the application of a force and/or a torque, respectively. We introduce the experimental protocols for the parallelization and discuss the benefits already gained, and to come, for these single molecule investigations.

Automated multi-sample acquisition and analysis using atomic force microscopy for biomedical applications

In the last 20 years, atomic force microscopy (AFM) has emerged as a ubiquitous technique in biological research, allowing the analysis of biological samples under near-physiological conditions from single molecules to living cells. Despite its growing use, the low process throughput remains a major drawback. Here, we propose a solution validated on a device allowing a fully automated, multi-sample analysis. Our approach is mainly designed to study samples in fluid and biological cells. As a proof of concept, we demonstrate its feasibility applied to detect and scan both fixed and living bacteria before completion of data processing. The effect of two distinct treatments (i.e. gentamicin and heating) is then evidenced on physical parameters of fixed Yersinia pseudotuberculosis bacteria. The multi-sample analysis presented allows an increase in the number of scanned samples while limiting the user's input. Importantly, cantilever cleaning and control steps are performed regularly-as part of the automated process-to ensure consistent scanning quality. We discuss how such an approach is paving the way to AFM developments in medical and clinical fields, in which statistical significance of results is a prerequisite.