This PDF file contains the front matter associated with SPIE Proceedings Volume 13112, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The Thymidylate Synthase (TS) is an enzyme widely employed as a target in the treatment of various solid cancers. Nevertheless, the clinical effectiveness of the current drugs is limited by some drawbacks, which are mainly related to the interaction of TS with its consensus RNA (TSmRNA). The most employed drugs targeting TS negatively affect its autoregulatory function, which consists of the capability of TS to bind the mRNA and inhibit the translation process, thus controlling its own concentration inside the cell. Recently, new approaches have been proposed to target TS while preserving its autoregulatory function. However, the design and development or more efficient chemotherapeutic drugs necessarily require an in-depth knowledge of both the structure of TSmRNA and the binding mechanisms involved in its interaction with TS. In this work, for the first time, we used optical tweezers to investigate at the single-molecule level the structure of the binding site 1 of TSmRNA, by applying an external mechanical stimulus. We performed out-of-equilibrium pulling experiments, where each individual molecule was stretched and released several times, while monitoring its transitions among its folded and unfolded forms. The Worm-like Chain model was employed to analyze the force-distance curves, deriving information on the number of nucleotides involved in the conformational changes of TSmRNA and its stability.

Strong field gradients in electromagnetic resonators can trap individual nanospheres. Moreover, the presence of the sphere in the resonator can give rise to self-induced back-action (SIBA), which increases the trap stiffness beyond standard dipolar force theory. In this work, we investigate SIBA in a system with a silica sphere of 16 nm in diameter in a dielectric nanocavity with a strongly localized electric field. We analyze the optical forces in a novel framework based on perturbation theory with quasi-normal modes, where modifications to the gradient and scattering forces are found to arise due to the presence of the particle, thus capturing the back-action effect. This gives closed-form expressions with clear insight into the mechanism of SIBA, and provides an efficient method of estimating optical forces when SIBA is present. We compare the results with reference calculations based on the Maxwell Stress Tensor formalism and find good agreement.

Optical trapping in nanostructures has usually been achieved utilizing the strong field gradients of plasmonics resonances. However, given the inherent optical losses in metals to heat dissipation, their use can prove detrimental to biological trapping settings and can affect other trapping properties. Dielectric nanostructures do not suffer these intrinsic losses, but it remains challenging to design dielectric structures with strong field gradients. In this work, we use inverse design by topology optimization to design a dielectric nanostructure that confines light to trap nanoparticles in air. The obtained trapping potential is deep enough – with a trapping depth below -10 k_BT – to overcome thermal fluctuations.

Active matter or self-propelled particles arise across a variety of soft matter systems such as self-motile colloids and artificial swimmers, biological systems such as bacteria, and robotic systems. Active matter exhibits a wide variety of phenomena that do not occur in its equilibrium counterparts. One of the biggest issues in active systems is how to characterize and understand whether they have distinct phases or phase transitions. Here, we use machine learning (ML) in the form of principal component analysis (PCA) to study active matter phases for a collection of interacting run-and-tumble disks. One of the most interesting phenomena exhibited by active particles is motility induced phase separation. Using ML, we find evidence of the existence of multiple regimes within the motility induced phase separated state. We discuss future directions in which ML methods could be used to characterize active matter on ordered substrates created by optical means. We also describe how ML approaches could be used as a tool to characterize more complex active matter systems, to optimize rules for motion, or to create optimal substrates for specific applications.

We investigate the behavior of optical vortex propagation and orbital angular momentum (OAM) conservation in scattering media by observing phase characteristics and mode content of scattered vortex beams. Micro-sized polystyrene particles in varying concentrations and optical path lengths provide a comprehensive understanding of the light dependence on optical properties and thickness of the scattering media.

A rigid body can have six degrees of freedom, of which three are with rotational origin. In the nomenclature of the airlines, the in-plane degree of rotational freedom can be called yaw, while the first out-of-plane degree of freedom can be called pitch, with the second one called roll. Among these, only the yaw sense has been studied extensively in the optical tweezers literature, while the pitch rotation is starting to be explored. In this paper, we show a way to detect the pitch rotation in a hexagonal-shaped particle using photonic force microscopy using the forward scattered light under crossed polarizers and making it incident on a split photodiode. In this way, the pitch angle can be detected at high resolution and bandwidth. We apply this technique to detect continuous pitch rotation and also exhibit a power spectral density for an anisotropic particle optically trapped in a linearly polarized light and exhibiting Brownian motion.

Nanodiamonds with color centers are to an increasing degree investigated as intracellular biosensors for magnetic fields, electrical fields, or temperature changes, as well as for abundance of free radicals or pH inside live cells. A common color-center is the nitrogen-vacancy (NV) center, where a substitutional nitrogen atom is positioned next to a vacancy within the diamond host crystal. The nanodiamond with negatively charged NV− center is particularly versatile due to its biocompatibility and its purely optical addressability. Our work aims to use NV-center nanodiamonds both as intracellular biosensors and as probe particles within an optical trap to determine the viscoelastic properties of the intracellular environment in single-cell studies. For this to be successful, several prior steps are needed: 1) The uptake of nanodiamonds within the cells should be characterized, including studies of subcellular localization, and a controllable protocol developed; 2) Any effect of the trapping laser on the NV-center sensing should be characterized and understood, and a protocol for stable trapping along with accurate biosensing should be developed. In this work we summarize the preliminary findings of our ongoing investigations to address these points. We show results of T1-relaxometry with and without CW NIR laser irradiation in a suspension cell model, analyze optical trapping of nanodiamonds with CW light in an adhesion cell model, and investigate implications of the presence of the optical trapping laser on T1-relaxometry measurements.

Accurate optical sensing and micromanipulation requires sensitive measurements of the position, orientation, and dynamics of small particles—and sometimes even large objects—under consideration. The signals acquired in the process, including those needed for the feedback control of these particles and objects, are inevitably contaminated by quantum fluctuations and noise that accompany the physical processes of optical interference and photodetection (or photon counting). This paper explores the origins of signal fluctuation and quantum noise that are inevitably associated with such sensitive measurements.

Freely propagating, purely optical skyrmions may be generated from combinations of vector beams with orthogonal polarisation states. Through this approach it is possible to create skyrmions of both Néel (hedgehog) and Bloch (spiral) types, using both paraxial [Gao et al. Phys. Rev. A, 102, 053513 (2020)] and focussed Laguerre-Gaussian beams [Gutiérrez-Cuevas and Pisanty, J. Opt. 23, 024004 (2021)]. In this computational study we construct skyrmionic beams with different skyrmion numbers and types with a view to analysing the spin and orbital angular momentum fluxes carried by the beams. The optical forces and torques experienced by dielectric and absorbing particles are calculated and their dynamic behaviour assessed.

There is a large class of particle like systems, including cold atoms, colloidal particles, magnetic particles, and active matter, that can be coupled to a periodic substrate. Such substrates may be effectively one- or two-dimensional and can be created by optical means. A variety of commensuration effects can occur when the spacing between particles matches the periodicity of the substrate. In addition, a number of interesting dynamic effects arise under dc and ac driving, where the nature of the particle flow depends on the commensuration conditions. Here, we consider particles with competing long-range repulsive and short-range attractive interactions driven over a quasi-one-dimensional periodic substrate. In the absence of the substrate, the particles adopt crystalline, stripe, or bubble orderings; however, in the presence of the substrate, a wide variety of novel static and dynamic phases can arise.

For a fluorescence microscopy system, a set-up often costs upwards of one hundred thousand dollars, if not multiple hundreds. This makes research inaccessible to any institutions except those with the highest level of funding. Our research addresses the challenges of high-magnification fluorescence microscopy by using low-cost off-the-shelf components to create a fluorescence imaging system. We use a cost-effective widefield system for neuroimaging using an OLED array via an Arduino microcontroller and a custom-made image processing algorithm. The OLEDs enable fluorescence microscopy with their green and blue emissions having significant overlap with the absorption spectrums for the Alexa Fluor 532 and FITC fluorescent probes. We use this system for Fourier ptychography and leverage image processing algorithms to achieve high-resolution images by combining low-resolution images within the Fourier plane. A phase retrieval algorithm and a regression model are utilized to find optimal coefficients for our transform matrices. This project is promising to democratize neuroimaging, especially in resource-constrained settings with affordable costs and portability. It is small-scale, 6’x8’x12’, and compatible with any MATLAB system, thereby allowing even further reach into under-served areas.

Traumatic Brain Injury (TBI) is the result of external forces impacting the brain. Despite scientific progress, TBI remains a significant cause of impairment and mortality. Recently, laser-induced shockwave (LIS) has emerged as an effective method for TBI simulation. LIS generates shockwaves through pulsed laser-induced plasma formation, allowing for the controlled study of TBI at the cellular level. This study introduces a novel approach to examine cellular morphological changes in response to shear stress, focusing on astrocyte cell type AST-1, by combining LIS with quantitative phase microscopy (QPM). QPM is a label-free technique that allows for real-time cellular dynamics observation through 3D imaging. Integrating LIS and QPM assesses astrocyte responses to shear stress caused by LIS, revealing both immediate and sustained morphological changes. Post-LIS exposure analysis shows significant alterations in astrocyte circularity, volume, surface area, and other features. Statistical tests confirm these observed trends, providing valuable insights into astrocyte responses to mechanical forces. These findings enhance our understanding of how mechanical stimuli affect astrocyte morphology, which may offer the potential for identifying and developing therapeutic strategies in TBI and related neurological disorders.

Fungal infections in humans have significantly increased, primarily due to various Candida species such as Candida albicans, Candida tropicalis, and Candida auris, along with a rise in antifungal resistance. In response to these challenges, new strategies like antimicrobial photodynamic therapy (APDT) have been explored. However, understanding the specific cellular responses to these treatments remains a challenge. In this context, microscopic manipulation with optical tweezers (OT) emerges as a valuable tool for investigating these responses.

A novel method combining OT and APDT is presented to monitor the effects of treatments on individual fungal cells, focusing on C. tropicalis. Cells were placed in a 96-well microplate with Sabouraud dextrose broth to create biofilms and promote the formation of opaque cells by phenotypic switching. Methylene blue with a 10 μM concentration was added to the cells and irradiated with a lethal light dose of 60 J cm^-². Subsequently, an intracellular lipid body was captured using an OT system and the stiffness of the trap over time was determined by analyzing its Brownian motion. The results revealed an increase in the intracellular viscosity during cell death processes activated by the application of APDT. This multifaceted methodology lays the foundation for formulating more effective therapeutic strategies against fungal infections.

Optical tweezers represent a versatile means of trapping and manipulating micro and nano-objects without physical contact, leveraging the unique properties of focused laser beams to exert forces on microparticles. However, optical trapping of traditional metallic and magnetic particles faces challenges due to their large refractive index, absorption characteristics, and plasmonic effects. In response to these challenges, we present Fe-doped upconversion particles. These particles exhibit strong ferromagnetic properties while maintaining adequate refractive index values, making them ideal candidates for opto-magnetic manipulation. Through our work, we demonstrate the simultaneous trapping and magnetic manipulation of these Fe-doped upconverting particles using optical tweezers, enabling precise control over six degrees of freedom of a rigid body, including the three rotational senses. Moreover, we rely on photonic force microscopy to accurately detect the motion of these optically trapped particles exposed to external magnetic fields.

Optical tweezers provide a non-contact method to trap, move, and manipulate micro- and nano-sized objects. Using properly designed dielectric and plasmonic nanostructure configurations, optical tweezers have been tailored to create stable and precise trapping for nanoscale objects. Recent advances in numerical optimization techniques allow further enhancement in nanoscale optical traps through inverse optimization of such configurations. One of the main challenges in such optimization approaches is the time-consuming nature of full-wave simulation of nanostructures and postprocessing steps to extract optical forces. To address this challenge, we introduce a surrogate solver based on residual neural networks that can accurately predict the forces exerted on a nanoparticle. Our results illustrate the possibility of capturing the highly nonlinear dynamics of local optical forces using moderate-sized datasets, particularly appealing to the inverse design of optical tweezers.