Partha Pratim Mondal

Markov random field aided Bayesian approach for image reconstruction in confocal microscopy

The inverse problem associated with microscopic image reconstruction has attracted much attention and initiated a lot of interest in microscopic image processing. The inverse problem of image reconstruction from noisy and incomplete data is still one of the key factors for realizing the full potential of optical microscopy. We propose to address the inverse problem using Markov random field in the Bayesian domain. This approach has the potential advantage of incorporation of prior knowledge in the reconstruction process through the prior function, thus making the problem well-posed and computationally efficient for three-dimensional (3D) image reconstruction. Image reconstruction on 3D phantom and microscopic specimens shows comparatively noise-free and better-resolved images. The edges and minute features such as islets are well reconstructed. We believe that the proposed image reconstruction methodology will find applications in microscopy and imaging.

Spatial Filter Based Bessel-Like Beam for Improved Penetration Depth Imaging in Fluorescence Microscopy

Monitoring and visualizing specimens at a large penetration depth is a challenge. At depths of hundreds of microns, several physical effects (such as, scattering, PSF distortion and noise) deteriorate the image quality and prohibit a detailed study of key biological phenomena. In this study, we use a Bessel-like beam in-conjugation with an orthogonal detection system to achieve depth imaging. A Bessel-like penetrating diffractionless beam is generated by engineering the back-aperture of the excitation objective. The proposed excitation scheme allows continuous scanning by simply translating the detection PSF. This type of imaging system is beneficial for obtaining depth information from any desired specimen layer, including nano-particle tracking in thick tissue. As demonstrated by imaging the fluorescent polymer-tagged-CaCO3 particles and yeast cells in a tissue-like gel-matrix, the system offers a penetration depth that extends up to 650 µm. This achievement will advance the field of fluorescence imaging and deep nano-particle tracking.

Image reconstruction for multiphoton fluorescence microscopy

We present a general image reconstruction methodology for multiphoton fluorescence microscopy. The method is primarily based on Markov random field modeling of the detected image data. Evaluation on two-photon-excitation-(TPE) and two-photon-excited-4PI-microscopy images shows high quality artifact-free reconstruction. Image reconstruction for multiphoton imaging modalities such as TPE and 4PI may find potential application in nano-bioimaging and optical imaging.

Planar junctionless transistor with non-uniform channel doping

We propose a planar junctionless transistor (JLT) in silicon-on-insulator (SOI) with non-uniform channel doping in vertical direction to improve the ON to OFF drain current ratio. In single gate JLT in SOI, a thin device layer is depleted in the off-state from the top of the layer and the leakage current flows through bottom of the device layer, and the leakage current depends on the device layer thickness. We show that the decrease of doping in vertical direction suppresses the leakage current flowing through the bottom of the device by decreasing conductivity at the bottom of the device layer.

Simultaneous multilayer scanning and detection for multiphoton fluorescence microscopy

Fast three-(3D) imaging requires parallel optical slicing of a specimen with an efficient detection scheme. The generation of multiple localized dot-like excitation structures solves the problem of simultaneous slicing multiple specimen layers, but an efficient detection scheme is necessary. Confocal theta detection (detection at 90° to the optical axis) provides a suitable detection platform that is capable of cross-talk-free fluorescence detection from each nanodot (axial dimension ≈ 150 nm). Additionally, this technique has the unique feature of imaging a specimen at a large working distance with super-resolution capabilities. Polarization studies show distinct field structures for fixed and fluid samples, indicating a non-negligible field-dipole interaction. The realization of the proposed imaging technique will advance and diversify multiphoton fluorescence microscopy for numerous applications in nanobioimaging and optical engineering.

Fuzzy logic and maximum a posteriori-based image restoration for confocal microscopy.

We propose a maximum a posteriori image restoration approach to 3D confocal microscopy. The image field is suitably modeled as a Markov random field, resulting in a Gibbs distributed image. A fuzzy-logic-based potential is employed in the Gibbs prior. Unlike other potentials, the fuzzy potential distinguishes intensity variation due to genuine edges and noise. The proposed approach has generated artifact-free restored confocal microscopy images.

Three Dimensional Fluorescence Imaging Using Multiple Light-Sheet Microscopy

We developed a multiple light-sheet microscopy (MLSM) system capable of 3D fluorescence imaging. Employing spatial filter in the excitation arm of a SPIM system, we successfully generated multiple light-sheets. This improves upon the existing SPIM system and is capable of 3D volume imaging by simultaneously illuminating multiple planes in the sample. Theta detection geometry is employed for data acquisition from multiple specimen layers. This detection scheme inherits many advantages including, background reduction, cross-talk free fluorescence detection and high-resolution at long working distance. Using this technique, we generated equi-intense light-sheets of thickness approximately with an inter-sheet separation of . Moreover, the light-sheets generated by MLSM is found to be 2 times thinner than the state-of-art SPIM system. Imaging of fluorescently coated yeast cells of size (encaged in Agarose gel-matrix) is achieved. Proposed imaging technique may accelerate the field of fluorescence microscopy, cell biology and biophotonics.

Determination of electric field at and near the focus of a cylindrical lens for applications in fluorescence microscopy

We present an explicit computable integral solution of the electric field generated at the focal region of a cylindrical lens. This representation is based on vectorial diffraction theory and further enables the computation of the system point spread function of a cylindrical lens. It is assumed that there is no back-scattering and the contribution from the evanescent field is negligible. Stationary phase approximation along with the Fresnel transmission coefficients are employed for evaluating the polarization dependent electric field components. Studies were carried out to determine the polarization effects and to calculate the system resolution. The effect of s −, p − and randomly polarized light is studied on the fixed sample (electric dipole is fixed in space). Proposed approach allows better understanding of electric field effects at the focus of a cylindrical aplanatic system. This opens up future developments in the field of fluorescence microscopy and optical imaging.

Overview of nano-drugs characteristics for clinical application: the journey from the entry to the exit point

The ever-increasing number of diseases worldwide requires comprehensive, efficient, and cost-effective modes of treatments. Among various strategies, nanomaterials fulfill most of these criteria. The unique physicochemical properties of nanoparticles have made them a premier choice as a drug or a drug delivery system for the purpose of treatment, and as bio-detectors for disease prognosis. However, the main challenge is the proper consideration of the physical properties of these nanomaterials, while developing them as potential tools for therapeutics and/or diagnostics. In this review, we focus mainly on the characteristics of nanoparticles to develop an effective and sensitive system for clinical purposes. This review will present an overview of the important properties of nanoparticles, through their journey from its route of administration until disposal from the human body after accomplishing targeted functionality. We have chosen cancer as our model disease to explain the potentiality of nano-systems for therapeutics and diagnostics in relation to several organs (intestine, lung, brain, etc.). Furthermore, we have discussed their biodegradability and accumulation probability which can cause unfavorable side effects in healthy human subjects.

Minimizing photobleaching in fluorescence microscopy by depleting triplet states

A technique for minimizing photobleaching in fluorescence microscopy is proposed. One of the prominent reason for photobleaching is the involvement of metastable triplet states during the excitation-emission process. Photobleaching minimization is achieved by depleting triplet states (T1→S0) employing a depletion pulse just after the excitation pulse thereby resulting in highly populated singlet ground state S0. Thus, the next excitation pulse can cause rapid population inversion (S0→S1) due to the availability of electrons in the ground state. This increases the fraction of population that is undergoing fluorescence (S1→S0), whereas the depletion pulse continuously depletes the triplet states. An interesting phase transition from occupied to unoccupied triplet state is observed. The excitation-depletion cycle is continued throughout the imaging process. The performance of such a system is examined through theoretical calculation and computational study of population dynamics. Substantial reduction in pho...