Exploring Masses and Internal Mass Distributions of Single Carboxysomes in Free Solution Using Fluorescence and Interferometric Scattering in an Anti-Brownian Trap

Atmospheric-Pressure Mass Spectrometry by Single-Mode Nanoelectromechanical Systems

Weighing particles above the megadalton mass range has been a persistent challenge in commercial mass spectrometry. Recently, nanoelectromechanical systems-based mass spectrometry (NEMS-MS) has shown remarkable performance in this mass range, especially with the advance of performing mass spectrometry under entirely atmospheric conditions. This advance reduces the overall complexity and cost while increasing the limit of detection. However, this technique required the tracking of two mechanical modes and the accurate knowledge of mode shapes that may deviate from their ideal values, especially due to air damping. Here, we used a NEMS architecture with a central platform, which enables the calculation of mass by single-mode measurements. Experiments were conducted using polystyrene and gold nanoparticles to demonstrate the successful acquisition of mass spectra using a single mode with an improved areal capture efficiency. This advance represents a step forward in NEMS-MS, bringing it closer to becoming a practical application for the mass sensing of nanoparticles.

Determining the Local Refractive Index of Single Particles by Optical Imaging Technique

The refractive index points to the interplay between light and objects, which is rarely studied down to micronano scale. Herein, we demonstrated a conventional bright-field imaging technique to determine the local refractive index of single particles combined with a series of refractive index standard solutions. This intrinsic optical property is independent with the particle size and surface roughness with a single chemical component. Furthermore, we accurately tuned refractive index of homemade core-shell nanoparticles by adjusting the ratio of core-to-shell geometry. This simple and effective strategy reveals extensive applications in exploring, designing and optimizing the physical and optical characterizations of composite photonic crystals with high precision. It also indicates potentials in the field of reflective displays, optical identification, and encryption.