Optical sectioning by two-pinhole confocal fluorescence microscopy

All Fiber Vector Magnetometer Based on Nitrogen-Vacancy Center

Magnetometers based on nitrogen-vacancy (NV) centers in diamonds have promising applications in fields of living systems biology, condensed matter physics, and industry. This paper proposes a portable and flexible all-fiber NV center vector magnetometer by using fibers to substitute all conventional spatial optical elements, realizing laser excitation and fluorescence collection of micro-diamond with multi-mode fibers simultaneously and efficiently. An optical model is established to investigate multi-mode fiber interrogation of micro-diamond to estimate the optical performance of NV center system. A new analysis method is proposed to extract the magnitude and direction of the magnetic field, combining the morphology of the micro-diamond, thus realizing μm-scale vector magnetic field detection at the tip of the fiber probe. Experimental testing shows our fabricated magnetometer has a sensitivity of 0.73 nT/Hz^1/2, demonstrating its feasibility and performance in comparison with conventional confocal NV center magnetometers. This research presents a robust and compact magnetic endoscopy and remote-magnetic measurement approach, which will substantially promote the practical application of magnetometers based on NV centers.

SPLIT-PIN software enabling confocal and super-resolution imaging with a virtually closed pinhole

In point-scanning microscopy, optical sectioning is achieved using a small aperture placed in front of the detector, i.e. the detection pinhole, which rejects the out-of-focus background. The maximum level of optical sectioning is theoretically obtained for the minimum size of the pinhole aperture, but this is normally prevented by the dramatic reduction of the detected signal when the pinhole is closed, leading to a compromise between axial resolution and signal-to-noise ratio. We have recently demonstrated that, instead of closing the pinhole, one can reach a similar level of optical sectioning by tuning the pinhole size in a confocal microscope and by analyzing the resulting image series. The method, consisting in the application of the separation of photons by lifetime tuning (SPLIT) algorithm to series of images acquired with tunable pinhole size, is called SPLIT-pinhole (SPLIT-PIN). Here, we share and describe a SPLIT-PIN software for the processing of series of images acquired at tunable pinhole size, which generates images with reduced out-of-focus background. The software can be used on series of at least two images acquired on available commercial microscopes equipped with a tunable pinhole, including confocal and stimulated emission depletion (STED) microscopes. We demonstrate applicability on different types of imaging modalities: (1) confocal imaging of DNA in a non-adherent cell line; (2) removal of out-of-focus background in super-resolved STED microscopy; (3) imaging of live intestinal organoids stained with a membrane dye.

A phasor-based approach to improve optical sectioning in any confocal microscope with a tunable pinhole

Confocal fluorescence microscopy is a well‐established imaging technique capable of generating thin optical sections of biological specimens. Optical sectioning in confocal microscopy is mainly determined by the size of the pinhole, a small aperture placed in front of a point detector. In principle, imaging with a closed pinhole provides the highest degree of optical sectioning. In practice, the dramatic reduction of signal‐to‐noise ratio (SNR) at smaller pinhole sizes makes challenging the use of pinhole sizes significantly smaller than 1 Airy Unit (AU). Here, we introduce a simple method to “virtually” perform confocal imaging at smaller pinhole sizes without the dramatic reduction of SNR. The method is based on the sequential acquisition of multiple confocal images acquired at different pinhole aperture sizes and image processing based on a phasor analysis. The implementation is conceptually similar to separation of photons by lifetime tuning (SPLIT), a technique that exploits the phasor analysis to achieve super‐resolution, and for this reason we call this method SPLIT‐pinhole (SPLIT‐PIN). We show with simulated data that the SPLIT‐PIN image can provide improved optical sectioning (i.e., virtually smaller pinhole size) but better SNR with respect to an image obtained with closed pinhole. For instance, two images acquired at 2 and 1 AU can be combined to obtain a SPLIT‐PIN image with a virtual pinhole size of 0.2 AU but with better SNR. As an example of application to biological imaging, we show that SPLIT‐PIN improves confocal imaging of the apical membrane in an in vitro model of the intestinal epithelium.

Realization of noncontact confocal optical microsphere imaging microscope

A novel noncontact confocal optical microsphere imaging microscope (COMIM) is proposed to achieve high contrast optical nano-imaging at a high scanning speed. The developed setup obtains images with significantly higher contrast when compared with conventional bright-field microsphere nano-imaging, as well as with a commercial confocal laser scanning microscope (CLSM). With the image-by-image scanning scheme, COMIM takes only 11% time to complete a three-dimensional (3D) scanning image than using a commercial CLSM, while still offers an outstanding resolving power for the nano-features on the sample.

Subtractive imaging in confocal scanning microscopy using a CCD camera as a detector

We report a scheme for the detector system of confocal microscopes in which the pinhole and a large-area detector are substituted by a CCD camera. The numerical integration of the intensities acquired by the active pixels emulates the signal passing through the pinhole. We demonstrate the imaging capability and the optical sectioning of the system. Subtractive-imaging confocal microscopy can be implemented in a simple manner, providing superresolution and improving optical sectioning.

Lateral resolution enhancement in confocal microscopy by vectorial aperture engineering

This article reports the design and implementation of a lateral resolution-enhancement technique in confocal microscopy that can work, in principle, either in the reflection mode or in the fluorescence mode. Taking the difference between two images corresponding to two different vectorially (involving amplitude, phase, and polarization of light) engineered illumination pupils or apertures of a confocal microscope, high spatial frequency contents in the resultant image can be significantly enhanced. This can be realized by incorporating an extra vectorial beam-forming element into the illumination beam path of a conventional confocal microscope. The method of the proposed technique has been explained by giving it an analytical treatment supported by numerical simulation results. The technique has been implemented in a reflection mode confocal microscope and results obtained are presented.