The precise and non-invasive integration of biological molecules into engineered surfaces remains a critical challenge in the development of advanced biointerfaces for biophotonics applications. Traditional fabrication techniques often rely on harsh chemical processes or photolithographic steps that risk compromising biomolecular function and lack microscale spatial selectivity. In this context, Microbubble Lithography (MBL) has established itself as an optical tweezers driven microbubble-based mask-free route toward patterning of biointerfaces in order to fabricate three-layer biointerfaces entirely in situ. This work reinforces this technology further and provides important advances in the form of quantitative understanding of the controlled patterning of fluorescent reporters on a heterostructured interface enhanced by an absorbing substrate and a cross-linker to improve interfacial stability and signal-to-noise ratios. We address important questions regarding adherence, reporter and cross-linker concentrations, while also studying the science behind the formation of such heterostructures. Thus, we explain the observed twin-peak, edge-dominated fluorescence via a phenomenological model using central thermophoretic depletion and peripheral enrichment at the three-phase contact line (TPCL), and a 3D fluorescence surface visualizing peripheral enrichment. Together, these results establish MBL as a mask-free, chemically gentle, and highly controllable route to construct an optical biochip platform to fabricate biomolecular architectures for biophotonics and biosensing applications.

We explore the physics behind the conductivity enhancement of PEDOT:PSS patterns fabricated using Microbubble Lithography, describing the complex interplay between phase separation, densification of PEDOT domains, and improved percolation pathways.

The pursuit of green methodologies for fabricating optoelectronic devices necessitates the adoption of self-assembly-based strategies to engineer efficient and sustainable platforms. Microbubble lithography (MBL) stands out as a directed self-assembly technique, enabling real-time micropatterning of conductive structures. Notably, this approach achieves significant enhancements in the conductivity of patterned polymers without requiring external dopants. However, the underlying mechanisms driving this enhancement remain poorly understood. In this study, we address this knowledge gap through a combined theoretical and experimental investigation of a binary polymer system. Molecular dynamics simulations and percolation theory reveal structural transformations that underpin improved charge transport. Furthermore, we demonstrate that phase separation at the interfaces of interacting polymers plays a pivotal role in enhancing conductivity. This separation optimizes the conformational states of the polymers, facilitating more efficient charge carrier transport and ultimately leading to higher conductivity. Our findings establish MBL-induced self-assembly as a robust and sustainable technique for fabricating conductive patterns, paving the way for its integration into next-generation optoelectronic devices.

Mesoscopic active systems exhibit various unique behaviors-absent in passive systems-due to the forces generated by the corresponding constituents by converting their available free energies. However, estimating these forces-which are also stochastic and remain intertwined with the thermal noise-is especially nontrivial. Here, we introduce a technique to extract such fluctuating active forces acting on a passive particle immersed in an active bath with high statistical accuracy by filtering out the related thermal noise. We first test the efficacy of our method under numerical scenarios with different types of activity, and then apply it to the experimental trajectories of a microscopic particle (optically) trapped inside an active bath consisting of motile E. coli bacteria. We believe that our simple yet powerful approach, which appears agnostic to the nature of the active force, should enable accurate measurement of force dynamics in living matter and potentially allow direct but reliable estimation of key thermodynamic parameters, such as heat, work, and entropy production.

Microbubble-based micro-lithographic techniques have developed rapidly over the last ten years and are capable of reproducibly patterning a wide variety of soft materials and colloids, including polymers, metals, and proteins. Zeolitic imidazolate framework (ZIF) materials have attracted a great deal of research and application interest in the field of materials science because of their chemical and thermal stabilities. Furthermore, ZIF-67 has demonstrated significant potential for applications in gas adsorption, molecule separation, electrochemistry, and catalysis, which when converted into "lab-on-a-chip" platforms might produce remarkable and diverse application-oriented outcomes. This is due to their highly adjustable nanostructures. Using Co(OAc)2.4H2O and Co(NO3)2.6H2O as the metal ion sources and 2-methylimidazole as the ligand, To design ZIF-67 (composed of Co2+ ions and imidazolate ligands) is attempted. Inspired by previous results, the Micro-Bubble Lithography (MBL) approach is used to successfully demonstrate an instantaneous in situ green synthesis and micro-patterning of ZIF-67 MOFs in this work. With reasonable stability and an over-potential of 440 mV, these micro-patterns are used as microelectrodes for the electrocatalytic oxygen evolution reaction (OER) in media having different pH.

We present a laser-assisted bottom-up fabrication method to deterministically assemble metal nanoparticles into continuous, uniform plasmonic microtracks on glass by coordinating surface chemistry, power modulation, and vertical confinement.

Light serves as a tool to generate laser-induced microbubbles that enable precise biomolecule patterning, sensitive biosensing, and bio-interface engineering. This real-time approach advances the fabrication of diagnostic platforms, overcoming the limitations of the slow, random assembly typical of conventional bottom-up methods

The fabrication of multilayered heterostructures is essential for advancing microelectronic and biosensing technologies. Conventional top-down manufacturing techniques are often cost-prohibitive and unsuitable for biomedical applications. Here, we present a bottom-up fabrication method, termed microbubble lithography, which enables the in situ construction of multilayered microstructures through layer-by-layer self-assembly. This technique allows diverse materials to be integrated into coherent heterostructures. We demonstrate the platform's utility by successfully patterning a biomarker and a reporter protein, highlighting its potential for cost-effective and environmentally sustainable sensing applications.

In situ patterning of biomolecules and living organisms while retaining their biological activity is extremely challenging, primarily because such patterning typically involves thermal stresses that could be substantially higher than the physiological thermal or stress tolerance level. Top-down patterning approaches are especially prone to these issues, while bottom-up approaches suffer from a lack of control in developing defined structures and the time required for patterning. A microbubble generated and manipulated by optical tweezers (microbubble lithography) is used to self-assemble and pattern living organisms in continuous microscopic structures in real-time, where the material thus patterned remains biologically active due to their ability to withstand elevated temperatures for short exposures. Successful patterns of microorganisms (Escherichia coli, Lactococcus. lactis and the Type A influenza virus) are demonstrated, as well as reporter proteins such as green fluorescent protein (GFP) on functionalized substrates with high signal-to-noise ratio and selectivity. Together, the data presented herein may open up fascinating possibilities in rapid in situ parallelized diagnostics of multiple pathogens and bioelectronics. A microbubble generated and manipulated by optical tweezers (microbubble lithography) is used to self-assemble and microscopically pattern Escherichia coli and the Type A influenza virus, as well as reporter proteins such as GFP, on functionalized substrates with high signal-to-noise ratio and selectivity. The entities remain biologically active, thus opening up fascinating possibilities in in situ parallelized diagnostics of multiple pathogens. image

Spin-orbit interaction (SOI) due to the tight focusing of light in optical tweezers has led to exciting and exotic avenues towards inducing rotation in microscopic particles. However, instances where the back action of the particles influences and modifies SOI effects so as to induce rotational motion are rarely known. Here we tightly focus a vector beam having radial/azimuthal polarization carrying no intrinsic angular momentum into a refractive index stratified medium and observe the orbital rotation of birefringent particles around the beam propagation axis. In order to validate our experimental findings, we perform numerical simulations of the governing equations. Our simulations reveal that the interaction of light with a birefringent particle gives rise to inhomogeneous spin currents near the focus, resulting in a finite spin momentum. This spin momentum combines with the canonical momentum to finally generate an origin-dependent orbital angular momentum, which is manifested in the rotation of the birefringent particles around the beam axis. Our study describes a unique modulation of the SOI of light due to its interaction with anisotropic particles that can open up new avenues for exotic and complex particle manipulation in optical tweezers.

Developing diagnostic tools necessitates patterning biologically active biomolecules. We present a technique for patterning biospecimens using self-assembly mediated by plasmonic microbubbles. We also successfully demonstrate a protocol for immobilising diverse biospecimens on transparent substrates for potential biosensing applications.

We provide direct evidence of the effects of interface engineering of various substrates by Microbubble lithography (MBL). We choose a model organic plastic (or polymer) poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), with conductivity of 140 S/cm, as a representative organic system to showcase our technique. Thus, we fabricate permanent patterns of PEDOT:PSS on glass, followed by a flexible PDMS substrate, and observe conductivity enhancement of 5 times on the former (694 S/cm), and 20 times (2844 S/cm) on the latter, without the use of external doping agents or invasive chemical treatment. Probing the patterned interface, we observe that MBL is able to tune the conformational states of PEDOT:PSS from coils in the pristine form, to extended coils on glass, and almost linear structures in PDMS due to its more malleable liquid-like interface. This results in higher ordering and vanishing grain boundaries leading to the highest conductivity of PEDOT:PSS on PDMS substrates.

We report a light-driven interface engineering of a microcatalytic chip comprising a PV3W9O40 type component, MWCNTs and polypyrrole that enables unusual facile para nitration with high selectivity (95%). The chip is designed by simultaneously synthesizing the soft-oxometalate (SOM) pre-catalyst components and patterning them on a glass surface using microbubble lithography. The design reported involves interface engineering such that the exposure of the oxo-sites (of patterned SOMs) enables aromatic substrate anchoring. Such an anchoring silences the site-directing electronic effects of the functional groups in aromatics. This leads to unusual site selectivity leading to facile para-nitration with high selectivity (95%). The generality of this light driven catalyst design is demonstrated with a set of substrates that unequivocally demonstrate the silencing effect of the functional groups in aromatics. This technique can lead to an unprecedented methodology for the synthesis of any aromatic di-/tri-/multi-substitution otherwise difficult to achieve with high selectivity and atom economy, and that is sustainable in design. We report a light-driven interface engineering of a microcatalytic chip comprising a PV3W9O40 type component, MWCNTs and polypyrrole that enables unusual facile para nitration with high selectivity (95%).

We pattern PEDOT:PSS using microbubble lithography on glass and PDMS, and obtain more than twenty-fold conductivity increase on the latter due to melting of PSS shells by laser absorption and reorganization of the polymers into linear conformations.

A microbubble nucleated due to the absorption of a tightly focused laser at the interface of a liquid-solid substrate enables directed and irreversible self-assembly of mesoscopic particles dispersed in the liquid at the bubble base. This phenomenon has facilitated a new microlithography technique which has grown rapidly over the past decade and can now reliably pattern a vast range of soft materials and colloids, ranging from polymers to metals to proteins. In this review, we discuss the science behind this technology and the present state-of-the-art. Thus, we describe the physics of the self-assembly driven by the bubble, the techniques for generating complex mesoarchitectures, both discrete and continuous, and their properties, and the various applications demonstrated in plastic electronics, site-specific catalysis, and biosensing. Finally, we describe a roadmap for the technique to achieve its potential of successfully patterning "everything" mesoscopic and the challenges that lie therein.

Rotational optical tweezers uses circularly polarized light to rotate birefringent microparticles. Normally, if the particle is trapped far away from a surface, the rotation rate only goes to zero when the tweezers laser power is turned to zero. However, we find that if one traps close to a surface, the rotation rate goes to zero even at finite tweezers laser powers for some type of substrates. We suspect this to be due to binding between the substrate and the birefringent particle, keeping in mind that the hydrodynamic drag for this mode of rotation cannot increase beyond 1.2 times the drag away from the surface. We use this to probe some surfaces and find that there is no binding for hydrophilic ones but hydrophilic ones particularly tend to show a power threshold beyond which the birefringent particle starts rotating. We also place the particle on the threshold and observe ”stick-slip” kind of rotational behaviour.

Optical tweezers are powerful tools for high resolution study of surface properties. Such experiments are traditionally performed by studying the active or the brownian fluctuation of trapped particles in the X, Y, Z direction. Here we find that employing the fourth dimension, rotation, allows for sensitive and fast probing of the surface. Optical tweezers are capable of rotating trapped birefringent microparticles when applied with circularly polarized light, thus called the Rotational Optical Tweezers. When the trapped birefringent microparticle is far enough away from the surface, the rotation rate is dependent only on the laser power. However, we find that if one traps close to a surface, the rotation rate goes to zero even at finite tweezers laser powers for some specific type of substrates. We suspect this to be due to interaction between the substrate and the birefringent particle, keeping in mind that the hydrodynamic drag for this mode of rotation cannot increase beyond 1.2 times the drag away from the surface. We use this to probe some surfaces and find that there is no binding for hydrophobic ones but hydrophilic ones particularly tend to show a power threshold beyond which the birefringent particle starts rotating. We calculate that the threshold energy of the tweezers is consistent with the Van der Waals potential energy, when the mode of interaction with the surface is purely physical. We also find that for chitosan, the mode of interaction is possibly different from Van der Waals. We place the particle on the threshold and observe stick-slip kind of rotational behaviour.

Evaporating sessile droplets have been known to exhibit oscillations on the air-liquid interface. These are generally over millimeter scales. Using a novel approach, we are able to measure surface height changes of 500 nm amplitude using optical trapping of a set of microscopic particles at the interface, particularly when the vertical thickness of the droplet reduces to less than 50 μm. We find that at the later stages of the droplet evaporation, particularly when the convection currents become large, the top air-water interface starts to spontaneously oscillate vertically as a function of time in consistency with predictions. We also detect travelling wave trains moving in the azimuthal direction of the drop surface which are consistent with hydrothermal waves at a different combination of Reynolds, Prandtl and Evaporation numbers than previously observed. This is the first time that wave-trains have been observed in water, being extremely challenging to detect both interferometrically and with infra-red cameras. We also find that such waves apply a force parallel to the interface along the propagation direction.