arXiv subjects

Snigdhadev Chakraborty

Publications and source records attributed to Snigdhadev Chakraborty.

5 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 $μ$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

Intracellular phagosome shell is rigid enough to transfer outside torque to the inner spherical particle

Intracellular phagosomes have a lipid bilayer encapsulated fluidic shell outside the particle, on the outer side of which, molecular motors are attached. An optically trapped spherical birefringent particle phagosome provides an ideal platform to probe fluidity of the shell, as the inner particle is optically confined both in translation and in rotation. Using a recently reported method to calibrate the translation and pitch rotations - yielding a spatial resolution of about 2 nm and angular resolution of 0.1 degrees - we report novel roto-translational coupled dynamics. We also suggest a new technique where we explore the correlation between the translation and pitch rotation to study extent of activity. Given that a spherical birefringent particle phagosome is almost a sphere, the fact that it turns due to the activity of the motors is not obvious, even implying high rigidity of shell. Applying a minimal model for the roto-translational coupling, we further show that this coupling manifests itself as sustained fluxes in phase space, a signature of broken detailed balance.

physics.bio-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↗

arXiv2023

Towards Stirling engine using an optically confined particle subjected to asymmetric temperature profile

The realization of microscopic heat engines has gained a surge of research interest in statistical physics, soft matter, and biological physics. A typical microscopic heat engine employs a colloidal particle trapped in a confining potential, which is modulated in time to mimic the cycle operations. Here, we use a lanthanide-doped upconverting particle (UCP) suspended in a passive aqueous bath, which is highly absorptive at 975 nm and converts NIR photons to visible, as the working substance of the engine. When a single UCP is optically trapped with a 975 nm laser, it behaves like an active particle by executing motion subjected to an asymmetric temperature profile along the direction of propagation of the laser. The strong absorption of 975 nm light by the particle introduces a temperature gradient and results in significant thermophoretic diffusion along the temperature gradient. However, the activity of the particle vanishes when the trapping wavelength is switched to 1064 nm. We carefully regulate the wavelength-dependent activity of the particle to engineer all four cycles of a Stirling engine by using a combination of 1064 nm and 975 nm wavelengths. Since the motion of the particle is stochastic, the work done on the particle due to the stiffness modulation per cycle is random. We provide statistical estimation for this work averaged over 5 cycles which can be extended towards several cycles to make a Stirling engine. Our experiment proposes a robust set-up to systematically harness temperature which is a crucial factor behind building microscopic engines.

cond-mat.stat-mech↗