Optically levitated micro- and nanoparticles offer an ideal playground for investigating photon–phonon interactions over macroscopic distances. Here we report the observation of long-range optical binding of multiple levitated microparticles, mediated by intermodal scattering and interference inside the evacuated core of a hollow-core photonic crystal fibre (HC-PCF). Three polystyrene particles with a diameter of 1 µm are stably bound together with an inter-particle distance of ~40 μm, or 50 times longer than the wavelength of the trapping laser. The levitated bound-particle array can be translated to-and-fro over centimetre distances along the fibre. When evacuated to a gas pressure of 6 mbar, the collective mechanical modes of the bound-particle array are able to be observed. The measured inter-particle distance at equilibrium and mechanical eigenfrequencies are supported by a novel analytical formalism modelling the dynamics of the binding process. The HC-PCF system offers a unique platform for investigating the rich optomechanical dynamics of arrays of levitated particles in a well-isolated and protected environment.

An optically trapped single GaP nanowire is studied here. Optomechanical manipulation allows aligning the wire along its major axis and probes the linear waveguiding properties and nonlinear optical response of the standalone nanostructure.

Controllable continuous release of functional materials from capsules is one of the unmet functions of theragnosis particles; on this way, understanding cargo-fluid interactions in vitro is an essential milestone. We develop a flexible platform to investigate single particle-fluid interactions utilizing a glass micropipette as a highly localized flow source around an optically trapped particle. In proof-of-concept experiments, this microparticle is sensitive to local microflow distribution, thus serving as a probe. The very same flows are capable of the particle rotating (i.e., vaterite drug cargo) at frequencies dependent on the mutual particle-pipette position. Platform flexibility comes from different interactions of a tweezer (optical forces) and a pipette (mechanical/hydrodynamical) with a microparticle, which makes this arrangement an ideal microtool. We studied the vaterite dissolution kinetics and demonstrated that it can be controlled on demand, providing a wide cargo release dynamic rate. Our results promote the use of inorganic mesoporous nanoparticles as a nanomedicine platform.

Functional nanocoatings of hollow-core microstructured optical fibers (HC-MOFs) have extended the domain of their applications to biosensing and photochemistry. However, novel modalities typically come with increased optical losses since a significant surface roughness of functional layers gives rise to additional light scattering, restricting the performance of functionalization. Here, the technique that enables a biocompatible and removable nanocoating of HC-MOFs with low surface roughness is presented. The initial functional film is formed by a layer-by-layer assembly of bovine serum albumin (BSA) and tannic acid (TA). The alkaline etching at pH 9 results in the reduction of surface roughness from 26 nm to 3 nm and decreases fiber optical losses by three times. The nanocoating can be fully removed within 7 min of the treatment. Natural biocompatibility of BSA alongside antibacterial and antifouling properties of TA makes the presented nanocoating promising for biophotonic applications.