Optically sizing single atmospheric particulates with a 10-nm resolution using a strong evanescent field

Although an accurate evaluation of the distribution of ultrafine particulate matter in air is of utmost significance to public health,the usually used PM2.5 index fails to provide size distribution information.Here we demonstrate a low-profile and cavity-free size spectrometer for probing fine and ultrafine particulate matter by using the enhanced particle-perturbed scattering in strong optical evanescent fields of a nanofiber array.The unprecedented size resolution reaches 10 nm for detecting single 100-nm-diameter nanoparticles by employing uniform nanofibers and controlling the polarizations of the probe light.This size spectrometry was tested and used to retrieve the size distribution of particulate matter in the air of Beijing,yielding mass concentrations of nanoparticles,as a secondary exercise,consistent with the officially released data.This nanofiber-array probe shows potential for the full monitoring of air pollution and for studying early-stage haze evolution and can be further extended to explore nanoparticle interactions.

Operando monitoring transition dynamics of responsive polymer using optofluidic microcavities

Optical microcavities have become an attractive platform for precision measurement with merits of ultrahigh sensitivity,miniature footprint and fast response.Despite the achievements of ultrasensitive detection,optical microcavities still face significant challenges in the measurement of biochemical and physical processes with complex dynamics,especially when multiple effects are present.Here we demonstrate operando monitoring of the transition dynamics of a phase-change material via a self-referencing optofluidic microcavity.We use a pair of cavity modes to precisely decouple the refractive index and temperature information of the analyte during the phase-transition process.Through real-time measurements,we reveal the detailed hysteresis behaviors of refractive index during the irreversible phase transitions between hydrophilic and hydrophobic states.We further extract the phase-transition threshold by analyzing the steady-state refractive index change at various power levels.Our technology could be further extended to other materials and provide great opportunities for exploring on-demand dynamic biochemical processes.

Real-time monitoring of hydrogel phase transition in an ultrahigh Q microbubble resonator

The ability to sense dynamic biochemical reactions and material processes is particularly crucial for a wide range of applications,such as early-stage disease diagnosis and biomedicine development.Optical microcavities-based label-free biosensors are renowned for ultrahigh sensitivities,and the detection limit has reached a single nanoparticle/molecule level.In particular,a microbubble resonator combined with an ultrahigh quality factor(Q)and inherent microfluidic channel is an intriguing platform for optical biosensing in an aqueous environment.In this work,an ultrahigh Q microbubble resonator-based sensor is used to characterize dynamic phase transition of a thermosensitive hydrogel.Experimentally,by monitoring resonance wavelength shift and linewidth broadening,we(for the first time to our knowledge)reveal that the refractive index is increased and light scattering is enhanced simultaneously during the hydrogel hydrophobic transition process.The platform demonstrated here paves the way to microfluidical biochemical dynamic detection and can be further adapted to investigating single-molecule kinetics.