Particle Sampling by TEM Grid Filtration

Abstract

Transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX) offers a very comprehensive tool for individual particle analysis allowing the determination of size, morphology, specific surface, and elemental composition. This information is needed in aerosol studies, especially in the field of nanomaterials. However, observations with TEM require a controlled sampling on an adapted analysis support, namely TEM grid. Techniques allowing sampling on TEM grids are of great interest to aerosol analysis. Indeed, sample preparation is not required, thereby gaining time and avoiding a risk for the sample to be altered. The present study evaluates the efficiency of a new particle collection technique based on filtration through one class of TEM-dedicated supports, namely TEM porous grids. Two types of porous grids, considered as the best on the market for this application, have been put to the test: the 'Quantifoil' type porous grid, which has a regular structure, and the 'Holey' type (Agar Scientific, Stansted, Essex, England). A filter holder has been developed specifically for this application, the MPS (Mini-Particle Sampler , Ecomesure, Janvry, France). Experimental tests have been carried out with a flow rate of 0.3 L min-1. They show that the collection is operational in the 5-nm to 150-nm size range, with a minimum efficiency of 15-18% around 30 nm. Simulation confirms these results and shows an increased efficiency even below 5 nm and beyond 150 nm. The filter holder MPS designed in this study is a low-cost, portable, versatile, and easy-to-use tool.