A Simple low-cost device enables four epi-illumination techniques on standard light microscopes

Synchronized strobed phase contrast and fluorescence microscopy: the interlaced standard reimagined

We propose a simple, cost-effective method for synchronized phase contrast and fluorescence video acquisition in live samples. Counter-phased pulses of phase contrast illumination and fluorescence excitation light are synchronized with the exposure of the two fields of an interlaced camera sensor. This results in a video sequence in which each frame contains both exposure modes, each in half of its pixels. The method allows real-time acquisition and display of synchronized and spatially aligned phase contrast and fluorescence image sequences that can be separated by de-interlacing in two independent videos. The method can be implemented on any fluorescence microscope with a camera port without needing to modify the optical path.

The Future in Sensing Technologies for Malaria Surveillance: A Review of Hemozoin-Based Diagnosis

Early and effective malaria diagnosis is vital to control the disease spread and to prevent the emergence of severe cases and death. Currently, malaria diagnosis relies on optical microscopy and immuno-rapid tests; however, these require a drop of blood, are time-consuming, or are not specific and sensitive enough for reliable detection of low-level parasitaemia. Thus, there is an urge for simpler, prompt, and accurate alternative diagnostic methods. Particularly, hemozoin has been increasingly recognized as an attractive biomarker for malaria detection. As the disease proliferates, parasites digest host hemoglobin, in the process releasing toxic haem that is detoxified into an insoluble crystal, the hemozoin, which accumulates along with infection progression. Given its magnetic, optical, and acoustic unique features, hemozoin has been explored for new label-free diagnostic methods. Thereby, herein, we review the hemozoin-based malaria detection methods and critically discuss their challenges and potential for the development of an ideal diagnostic device.

Label-free Imaging and Bending Analysis of Microtubules by ROCS Microscopy and Optical Trapping

Mechanical manipulation of single cytoskeleton filaments and their monitoring over long times is difficult because of fluorescence bleaching or phototoxic protein degradation. The integration of label-free microscopy techniques, capable of imaging freely diffusing, weak scatterers such as microtubules (MTs) in real-time, and independent of their orientation, with optical trapping and tracking systems, would allow many new applications. Here, we show that rotating-coherent-scattering microscopy (ROCS) in dark-field mode can also provide strong contrast for structures far from the coverslip such as arrangements of isolated MTs and networks. We could acquire thousands of images over up to 30 min without loss in image contrast or visible photodamage. We further demonstrate the combination of ROCS imaging with fast and nanometer-precise 3D interferometric back-focal-plane tracking of multiple beads in time-shared optical traps using acoustooptic deflectors to specifically construct and microrheologically probe small microtubule networks with well-defined geometries. Thereby, we explore the frequency-dependent elastic response of single microtubule filaments between 0.5 Hz and 5 kHz, which allows for investigating their viscoelastic response up to the fourth-order bending mode. Our spectral analysis reveals constant filament stiffness at low frequencies and frequency-dependent stiffening following a power law ∼ω^p with a length-dependent exponent p(L). We find further evidence for the dependence of the MT persistence length on the contour length L, which is still controversially debated. We could also demonstrate slower stiffening at high frequencies for longer filaments, which we believe is determined by the molecular architecture of the MT. Our results shed new light on the nanomechanics of this essential, multifunctional cytoskeletal element and pose new questions about the adaptability of the cytoskeleton.

Label-Free Single-Molecule Imaging with Numerical-Aperture-Shaped Interferometric Scattering Microscopy

Our ability to optically interrogate nanoscopic objects is controlled by the difference between their extinction cross sections and the diffraction-limited area to which light can be confined in the far field. We show that a partially transmissive spatial mask placed near the back focal plane of a high numerical aperture microscope objective enhances the extinction contrast of a scatterer near an interface by approximately T^-1/2, where T is the transmissivity of the mask. Numerical-aperture-based differentiation of background from scattered light represents a general approach to increasing extinction contrast and enables routine label-free imaging down to the single-molecule level.

Ultrasensitive Label-Free Nanosensing and High-Speed Tracking of Single Proteins

Label-free detection, analysis, and rapid tracking of nanoparticles is crucial for future ultrasensitive sensing applications, ranging from understanding of biological interactions to the study of size-dependent classical-quantum transitions. Yet optical techniques to distinguish nanoparticles directly among their background remain challenging. Here we present amplified interferometric scattering microscopy (a-iSCAT) as a new all-optical method capable of detecting individual nanoparticles as small as 15 kDa proteins that is equivalent to half a GFP. By balancing scattering and reflection amplitudes the interference contrast of the nanoparticle signal is amplified 1 to 2 orders of magnitude. Beyond high sensitivity, a-iSCAT allows high-speed image acquisition exceeding several hundreds of frames-per-second. We showcase the performance of our approach by detecting single Streptavidin binding events and by tracking single Ferritin proteins at 400 frames-per-second with 12 nm localization precision over seconds. Moreover, due to its extremely simple experimental realization, this advancement finally enables a cheap and routine implementation of label-free all-optical single nanoparticle detection platforms with sensitivity operating at the single protein level.