Bessel Beams in Ophthalmology: A Review.

The achievable resolution of a conventional imaging system is inevitably limited due to diffraction. Dealing with precise imaging in scattering media, such as in the case of biomedical imaging, is even more difficult owing to the weak signal-to-noise ratios. Recent developments in non-diffractive beams such as Bessel beams, Airy beams, vortex beams, and Mathieu beams have paved the way to tackle some of these challenges. This review specifically focuses on non-diffractive Bessel beams for ophthalmological applications. The theoretical foundation of the non-diffractive Bessel beam is discussed first followed by a review of various ophthalmological applications utilizing Bessel beams. The advantages and disadvantages of these techniques in comparison to those of existing state-of-the-art ophthalmological systems are discussed. The review concludes with an overview of the current developments and the future perspectives of non-diffractive beams in ophthalmology.

Bifunctional Fluorescent/Raman Nanoprobe for the Early Detection of Amyloid.

One of the pathological hallmarks of Alzheimer's disease (AD) is the abnormal aggregation of amyloid beta (Aß) peptides. Therefore the detection of Aß peptides and imaging of amyloid plaques are considered as promising diagnostic methods for AD. Here we report a bifunctional nanoprobe prepared by conjugating gold nanoparticles (AuNPs) with Rose Bengal (RB) dye. RB is chosen due to its unique Raman fingerprints and affinity with Aß peptides. After the conjugation, Raman signals of RB were significantly enhanced due to the surface-enhanced Raman scattering (SERS) effect. Upon binding with Aß42 peptides, a spectrum change was detected, and the magnitude of the spectrum changes can be correlated with the concentration of target peptides. The peptide/probe interaction also induced a remarkable enhancement in the probes' fluorescence emission. This fluorescence enhancement was further utilized to image amyloid plaques in the brain slices from transgenic mice. In this study, the RB-AuNPs were used for both SERS-based detection of Aß42 peptides and fluorescence-based imaging of amyloid plaques. Compared to monofunctional probes, the multifunctional probe is capable to provide more comprehensive pathophysiological information, and therefore, the implementation of such multifunctional amyloid probes is expected to help the investigation of amyloid aggregation and the early diagnosis of AD.

Gold nanocages entering into the realm of high-contrast photoacoustic ocular imaging.

Bioinert gold nanoparticles of various shapes and functionalities are widely accepted as contrast agents (CAs) for several modalities of imaging, viz., electron microscopy, computerized tomography (CT), X-ray and photoacoustic (PA) imaging. However, testing of novel compact-imaging probes for ocular diagnostic imaging is always challenging. Here, ultra-fast microwave oven synthesized gold nanocages (AuNcgs) were successfully demonstrated for high-contrast PA ocular imaging for the first time. Methods are described for the synthesis, characterization and application of quickly synthesized AuNcgs in diagnostic ocular imaging. PA and ultrasound (US) images were acquired using a commercial US imaging scanner integrated with a tunable nanosecond pulsed laser. This integrated hybrid-modality system is a combined PA and US platform for imaging which enabled acquiring of complementary structural and optical absorption-based information simultaneously. Initial experiments were conducted using tubings filled with solutions of different concentrations of quickly synthesized AuNcgs. Biological PA and US imagings were demonstrated using enucleated porcine eye samples. Based on the acquired results, it is envisaged that AuNcgs can be employed as a high strength PA CA to potentially diagnose ocular disease like uveal melanoma in the near future.

Red, green, and blue gray-value shift-based approach to whole-field imaging for tissue diagnostics.

Identification of abnormal pathology in situ remains one of the challenges of medicine. The interpretation of tissue conditions relies mainly on optical assessment, which can be difficult due to inadequate visual differences or poor color delineation. We propose a methodology to identify regions of abnormal tissue in a targeted area based on red, green, blue (RGB) shift analysis employing a simple CCD color camera and light-emitting diode illumination in a whole-field-imaging scheme. The concept involves analysis of RGB components in an image with respect to a reference set of RGB values under different illumination wavelengths. The magnitude of the gray value shift is estimated by calculating the Euclidean distance between their normalized RGB coordinates. The shift values obtained using these concepts are thereafter used to construct pseudo-colored images with high contrast, enabling easy identification of abnormal areas in the tissue. Images processed from experiments conducted with excised Wistar rat colon sample (lightly doped with Alexafluor 488) and with simulated tumor (cancer cell pellet placed on colon) showed clear localization of tumor region. This proposed approach and methodology is expected to find potential applications for the in vivo diagnosis of disease.