arXiv subjects

Qifei Ma

Publications and source records attributed to Qifei Ma.

8 recordsLinked to original sources

arXiv2026

Hydrogel microwells with light-controlled reversible closure

We present a light-responsive hydrogel nanocomposite engineered into arrays of micrometer-scale wells that can be selectively and sequentially closed and re-opened via laser illumination. Polarization-controlled light exposure induces anisotropic surface deformations, leading to the formation of protrusive flaps sealing the wells. Owing to the intrinsic elasticity and anti-adhesive properties of the hydrogel matrix, the deformation process is partially reversible, allowing flap retraction and restoration of the original well geometry. This platform facilitates contactless, on-demand trapping and release of microscale objects using a standard optical microscopy configuration. As a proof of concept, we demonstrate the controlled manipulation of a single polystyrene microbead using optical tweezers, including bead positioning within a well, light-triggered closure, and subsequent reopening to release the particle into the surrounding aqueous environment.

physics.app-ph↗

arXiv2025

Plasmonic nanopore to monitor in-pore chemistry

In solid-state nanopores, achieving reliable control over pore aperture opening and closing (gating) remains a major challenge. Gating can be driven by the applied voltage involving electrically tunable chemical reactions, achieved by selecting appropriate compounds within the nanopore volume. In particular, cyclic precipitation and dissolution of metal phosphates can be triggered by regulating cation transport through an applied transmembrane voltage, thereby enabling reversible pore gating. Under negative bias, metal phosphate precipitates form inside the pore, obstructing ion flow and reducing current. Switching the polarity dissolves the precipitates, restoring ionic conductance. This process effectively produces a nanofluidic diode characterized by a remarkably high rectification ratio. To probe these localized chemical reactions more directly, we employed a plasmonic nanopore that generates strong confined fields, enabling surface-enhanced Raman scattering (SERS) measurements within the nanopore volume during cyclic gating. These measurements not only validate the proposed in-pore chemistry but also highlight the potential of plasmonic nanopores as powerful tools for monitoring nanoscale chemical processes with high spatial resolution.

physics.app-ph↗

arXiv2025

UV-SERS monitoring of plasmons photodegradation of biomolecules on Aluminum platforms decorated with Rhodium nanoparticles

In the search for novel nanostructured materials for UV plasmonics a limited number of choices can be done. Materials such as aluminum, rhodium, gallium and few others can be used. One of the most interesting application for UV plasmonics is Surface Enhanced Raman Spectroscopy. It can be extended to this spectral range to explore spectral properties of biomolecules that have only a small cross section in the visible spectral range. We have recently reported on a functional substrates based on nanoporous aluminum decorated with rhodium nanoparticles. This system showed an interesting behavior for UV excitation at 266 nm, with an unexpected decreasing Raman intensity for increasing rhodium nanoparticles concentrations. We proposed that this effect can be due to the difficult access to the hot spots for the molecules deposited via thermal evaporation. Here we extend this study exploring the performance of the system at another UV excitation wavelengths (325 nm) reporting on experimental results obtained using a deposition process that can bring the molecules at the hot-spots in a more efficient way. Extensive spectroscopic acquisitions, combined with 3D maps, allow to shade a more clear view on the performance of this plasmonic platform. In particular, the photodegration and the potential oxidation of biomolecules driven by the hot-electron/hot-holes produced by the rhodium nanoparticles will be reported.

physics.app-ph↗

arXiv2025

Plasmonic Janus particles: A perspective on optical manipulation and biomedical applications

The compositional asymmetry of Janus micro- and nanoparticles gives unprecedented opportunities to manipulate such composite particles with different stimuli to achieve enhanced optical, magnetic and photothermal responses, which can be exploited for sensing, phototherapy, and nanoscale robotic applications. This perspective overviews recent advances in optical manipulation of plasmonic Janus particles and their implications for biomedical applications. In particular, a brief summary of optical, plasmonic, and magnetic manipulation of Janus particles of various compositions are presented. Moreover, the potentials of plasmonic and magnetic Janus particles for targeted drug delivery, photothermal therapy, hyperthermia, bio-imaging, bio-detection, and neuromodulation are briefly discussed. Finally, a perspective on the rational design and applications of this particular family of asymmetric particles is forwarded.

physics.optics↗

arXiv2025

Dynamics of DNA-Templated Ultrafine Silver Nanowires Formation

Recent research on silver nanowires prepared on DNA templates has focused on two fundamental applications: nano-scale circuits and sensors. Despite its broad potential, the formation kinetics of DNA-templated silver nanowires remains unclear. Here, we present an experimental demonstration of the formation of silver nanowires with a diameter of 2.2+0.4 nm at the single-molecule level through chemical reduction. We conducted equilibrium and perturbation kinetic experiments to measure force spectroscopy during the formation of Ag+ -DNA complexes and Ag-DNA complexes, using optical tweezers combined with microfluidics. The addition of AgNO3 resulted in an increase in force of 5.5-7.5 pN within 2 minutes, indicating that Ag+ compacts the DNA structure. In contrast, the addition of hydroquinone caused the force to decrease by 4-5 pN. Morphological characterization confirmed the presence of a dense structure formed by silver atoms bridging the DNA strands, and revealed conformational differences before and after metallization. We compare our experimental data with Brownian dynamics simulations using a coarse-grained double-stranded DNA (dsDNA) model that provides insights on the dependency of the force on the persistence length.

physics.app-ph↗

arXiv2024

Application of Optical Tweezers in the Study of Emulsions for Multiple Applications

Emulsions are ubiquitous in everyday life and find applications in various industries. Optical tweezers (OTs) have emerged as the preferred method for studying emulsion dynamics. In this review, we first introduce the theory of optical trapping and emulsion stability. We then survey applications in the manipulation of emulsions, stability mechanism, the processes of aggregation and coalescence, and important responsive and switchable behaviors. And we overview the instrumentation framework of various OT setups, and evaluate their complexity and cost with a view towards the democratization of this technology. Following this, we delve into basic experimentation methods, the challenges associated with using OTs in emulsion applications. Additionally, we present a promising research outlook, including studies on stability mechanism of emulsions stabilized by compound or mixed emulsifiers or rigid or soft particles, as well as dynamic processes of responsive or functional emulsions.

physics.optics↗

arXiv2024

Advances and Applications of Dynamic Surface-Enhanced Raman Spectroscopy (SERS) for Single Molecule Studies

Dynamic surface-enhanced Raman spectroscopy (SERS) is nowadays one of the most interesting applications of SERS, in particular for single molecule studies. In fact, it enables the study of real-time processes at the molecular level. This review summarizes the latest developments in dynamic SERS techniques and their applications, focusing on new instrumentation, data analysis methods, temporal resolution and sensitivity improvements, and novel substrates. We highlight the progress and applications of single-molecule dynamic SERS in monitoring chemical reactions, catalysis, biomolecular interactions, conformational dynamics, and real-time sensing and detection. We aim to provide a comprehensive review on its advancements, applications as well as its current challenges and development frontiers.

physics.app-ph↗

arXiv2024

Porous aluminium decorated with rhodium nanoparticles, preparation and use as platform for UV plasmonics

There is a high current interest for novel plasmonic platforms and materials able to extend their applicability into the ultraviolet (UV) region of the electromagnetic spectrum. In the UV it is possible to explore spectral properties of biomolecules with small cross section in the visible spectral range. However, most used metals in plasmonics have their resonances at wavelengths > 350 nm. Aluminum and rhodium are two interesting candidate materials for UV plasmonics, and in this work we developed a simple and low-cost preparation of functional substrates based on nanoporous aluminum decorated with rhodium nanoparticles. We demonstrate that these functionalized nanoporous metal films can be exploited as plasmonic materials suitable for enhanced UV Raman spectroscopy

physics.app-ph↗