Background: Magnetic nanoparticles (MNPs) generate heat when exposed to an alternating magnetic field. Consequently, MNPs are used for magnetic fluid hyperthermia (MFH) for cancer treatment, and have been shown to increase the efficacy of chemotherapy and/or radiation treatment in clinical trials. A downfall of current MFH treatment is the inability to deliver sufficient heat to the tumor due to: insufficient amounts of MNPs, unequal distribution of MNPs throughout the tumor, or heat loss to the surrounding environment. Objective: In this study, the objective was to identify MNPs with high heating efficiencies quantified by their specific absorption rate (SAR). Methods: A panel of 31 commercially available MNPs were evaluated for SAR in two different AMFs. Additionally, particle properties including iron content, hydrodynamic diameter, core diameter, magnetic diameter, magnetically dead layer thickness, and saturation mass magnetization were investigated. Results: High SAR MNPs were identified. For SAR calculations, the initial slope, corrected slope, and Box-Lucas methods were used and validated using a graphical residual analysis, and the Box-Lucas method was shown to be the most accurate. Other particle properties were identified and examined for correlations with SAR values. Positive correlations of particle properties with SAR were found, including a strong correlation for the magnetically dead layer thickness. Conclusions: This work identified high SAR MNPs for hyperthermia, and provides insight into properties which correlate with SAR which will be valuable for synthesis of next-generation MNPs. SAR calculation methods must be standardized, and this work provides an in-depth analysis of common calculation methods.

Laser microsurgery is a powerful tool for neurobiology, used to ablate cells and sever neurites in-vivo. We compare a relatively new laser source to two well-established designs. Rare-earth-doped modelocked fibre lasers that produce high power pulses recently gained popularity for industrial uses. Such systems are manufactured to high standards of robustness and low maintenance requirements typical of solid-state lasers. We demonstrate that an Ytterbium-doped fibre femtosecond laser is comparable in precision to a Ti:Sapphire femtosecond laser (1-2 micrometres), but with added operational reliability. Due to the lower pulse energy required to ablate, it is more precise than a solid-state nanosecond laser. Due to reduced scattering of near infrared light, it can lesion deeper (more than 100 micrometres) in tissue. These advantages are not specific to the model system ablated for our demonstration, namely neurites in the nematode C. elegans, but are applicable to other systems and transparent tissue where a precise micron-resolution dissection is required.

Confocal microscopes can reject out-of-focus and scattered light; however, widefield microscopes are far more common in biological laboratories due to their accessibility and lower cost. We report confocal imaging capacity on a widefield microscope by adding a spatial light modulator (SLM) and utilizing custom illumination and acquisition methods. We discuss our illumination strategy and compare several procedures for postprocessing the acquired image data. We assessed the performance of this system for rejecting out-of-focus light by comparing images taken at 1.4 NA using our widefield microscope, our SLM-enhanced setup, and a commercial confocal microscope. The optical sectioning capability, assessed on thin fluorescent film, was 0.85 ± 0.04 μm for our SLM-enhanced setup and 0.68 ± 0.04 μm for a confocal microscope, while a widefield microscope exhibited no sectioning capability. We demonstrate our setup by imaging the same set of neurons in C. elegans on widefield, SLM, and confocal microscopes. SLM enhancement greatly reduces background from the cell body, allowing visualization of dim fibers nearby. Our SLM-enhanced setup identified 96% of the dim neuronal fibers seen in confocal images while a widefield microscope only identified 50% of the same fibers. Our microscope add-on represents a very simple (2-component) and inexpensive (<$600) approach to enable widefield microscopes to optically section thick samples.

Imaging, visual screens, and optical surgery are frequently applied to the nematode Caenorhabditis elegans at subcellular resolution for in vivo biological research. However, these approaches remain low-throughput and require significant manual effort. To improve throughput and enable automation in these techniques, we implement a novel cooling method to immobilize C. elegans directly on their cultivation plate. Previous studies cooled animals in microfluidics or flooded wells to 1-4 C. Counterintuitively, we find that cooling to 5-7 C immobilizes animals more effectively than lower temperatures. At 6 C, animal movement consists of bouts of submicron nose tip movement occurring at a sufficiently low magnitude and frequency to permit clear imaging. We demonstrate the ability to perform subcellular-resolution fluorescence imaging, including 64x magnification 3D image stacks and 2-min long timelapse recordings of the ASJ neuron without blurring from animal motion. We also observe no long-term side effects from cooling immobilization on animal lifespan or fecundity. We believe our cooling method enables high-throughput and high-resolution microscopy with no chemical or mechanical interventions.