arXiv subjects

Atanu Ghosh

Publications and source records attributed to Atanu Ghosh.

4 recordsLinked to original sources

arXiv2026

NaBiF$_4$: Er$^{3+}$, Yb$^{3+}$ upconversion particle as a multi-functional bio-marker

Lanthanide-doped upconversion particles (UCPs) have revolutionized optical bioimaging platforms because of their excellent photostability, non-toxicity, and utilization of near-infrared excitation, which facilitates deep tissue penetration with negligible autofluorescence. However, it remains a challenge to achieve high-contrast and sub-diffraction imaging in noisy biological media, without using a high-power laser. Here, we report various protocols applied to bismuth-doped UCPs address some of these challenges. Compared to the photoluminescence (PL) emission of the regular Yttrium doped UCPs, we observe a three-fold increment in the quantum yield of the overall emission of bismuth-UCPs, and a four-fold increment, specifically, in red emission. Leveraging this advantage, we devise a protocol employing two infrared wavelengths, 975 nm and 1064 nm, to selectively control the PL emission. Interestingly, our results reveal two distinct regimes in which PL can be systematically quenched or enhanced, by adjusting the 975 nm laser power. We model the overall dynamics as a simplified stimulated emission depletion process involving three energy levels. In addition, the particle has a thickness under sub-diffraction, shows optical trapping ability, and potential of surface functionalization to enable specific conjugation with diverse biospecimens. These studies establish bismuth doped UCPs as an excellent candidate in accomplishing advanced biomarker operating with enhanced signal-to-noise ratio and sub-diffraction imaging capabilities.

physics.optics↗

arXiv2025

In-vivo femtonewton-sensing nanotribology of Tradescantia zebrina leaf cell inner surface using roll rotation detection

Accessing the properties of a plant cell interior non-invasively is difficult due to the presence of a cell wall. Nanoparticles larger than 5 nm cannot be readily phagocytosed inside the cell like animal cells. It is here that we realise that Tradescantia zebrina plant cells have prismatic forms of calcium oxalate crystals present inside them naturally. These crystals make a ready choice to study properties of the inner cell surface with the application of optical tweezers. Moreover, out-of-plane rotations in optical tweezers have begun to be explored only recently. The pitch rotation has been detected with high resolution and several applications are explored. In this work, we first study the stable configuration while trapped in linearly polarized optical tweezers and then explore the other out-of-plane configurations to detect the roll rotation at high resolution. Then a micro-rheological analysis is performed to obtain the frictional properties of the inner surface of the plasma membrane of the leaf cell. The size of the particle is about 5 $\mu$m along the diagonal, so that the contact length with the surface is about 200 nm. We measure a frictional force of 18.5 pN at a sensitivity of about 200 fN without averaging.

physics.bio-ph↗

arXiv2025

Imaging of microwave magnetic field orientation using continuous-wave experiments on nitrogen-vacancy centers in diamond

Imaging of microwave magnetic fields with nano-scale resolution has interesting applications. Specifically, detecting the orientation of the microwave fields is useful in condensed matter physics and quantum control. However, most of the existing methods for microwave field imaging are limited to detecting the magnitude of the fields. Due to their small sensor size and favorable optical and spin properties, nitrogen-vacancy (NV) centers in diamond are highly suitable for imaging dc and ac magnetic fields. The reported methods for detecting the orientation of microwave magnetic fields use pulsed Rabi frequency measurements. Here, we demonstrate imaging of the orientation of microwave magnetic fields by only using continuous-wave experiments on NV centers. This simplifies the sensor apparatus and is particularly advantageous in applications where pulsing of the target microwave field is not possible. The method requires static bias magnetic field oriented perpendicular to the quantization axis of NV centers. We detect the direction of an arbitrary microwave magnetic field using NV centers of two different orientations. Moreover, we demonstrate that the projection of the microwave fields onto a plane can be imaged using NV centers of single orientation. It can be straightforwardly implemented using a single NV center.

quant-ph↗

arXiv2025

A label-free sub-diffractive technique for 3D intracellular tomography using thermally induced convection currents

Conventionally, 3-dimensional cellular tomography can be done with light sheet or multi-angle observations. Recently, a new technique was introduced where the cell was rotated using convection currents to visualize the outer periphery (Liu et al., Nano Lett., 2023, 23, 5148). However, the work falls short of actually observing intracellular objects like organelles etc. In this manuscript, we modify the technique by relying on computer vision algorithm called Contrast Limited Adaptive Histogram Equalisation (CLAHE) to improve the contrast for better detection of intra-cellular points, and then use optical flow detection technique to extract the in-plane speed of the point. This then is used to extract the vertical location, knowing that at the bottom part of the sphere, the point would be moving in one direction, close to the center there would be much less motion, while in the top portion of the sphere, the point would be moving in the reverse direction than the bottom. The velocity allows the exact localisation of the point in the vertical direction. This process allows for sub-diffractive intracellular tomography. This technique can further allow high-resolution detection of fluorescent molecules inside the cell also, when combined with convective flows.

physics.optics↗