Evaluation of Medipix2 detector for recording electron diffraction data in low dose conditions

Abstract

The drive for elucidation of important macromolecular structures to high resolution in their 3D native or near-native state places continuously higher demands on the quality of the experimental data. For instance, recording of diffraction patterns good enough for structural studies from cryo-preserved bio-macromolecules at low dose conditions remains challenging and highly desirable. The emergence of hybrid pixel detectors opens up new possibilities for direct electron detection and superior detector performance. Here, we report on the characteristics of the Medipix2 detector in diffraction studies, with a special focus on the reliability of the intensities acquired in very low dose conditions. Diffraction data recorded on a Medipix2 detector were assessed in refinement analysis. R-factors lower than 10% were obtained from data recorded at electron dose of 0.05 el/Å 2 . The reproducibility of the data was also shown to be high, given the correlation coefficient of the intensities being higher than 0.9970. The contrast that could be achieved at very low dose conditions was at least an order of magnitude better than that of image plates, based on a direct comparison.

A Medipix quantum area detector allows rotation electron diffraction data collection from submicrometre three-dimensional protein crystals

“…In this fashion its noise is almost exclusively determined by the counting statistics of the electrons. This gives a significant improvement over conventional CCD cameras in electron microscopes (Faruqi & McMullan, 2011;Georgieva et al, 2011).…”

Protein structure determination by electron diffraction using a single three-dimensional nanocrystal

“…We could improve the SNR substantially with a more accurate and sensitive detector. Previously, we measured three-dimensional nanocrystals similar to the polymorph presented here using CCD detectors and image plates (Georgieva et al, 2007(Georgieva et al, , 2011. For protein crystals that had a similar diffracting volume to that reported here, we could never measure more than a few diffraction patterns of high-resolution data with a CCD detector or image plate before radiation damage became too severe.…”

“…For protein crystals that had a similar diffracting volume to that reported here, we could never measure more than a few diffraction patterns of high-resolution data with a CCD detector or image plate before radiation damage became too severe. A quantitative comparison between image plates and a Medipix hybrid pixel detector indicated a substantial improvement to be offered by the latter (Georgieva et al, 2011;Nederlof et al, 2013). Hybrid pixel detectors such as Medipix, Timepix and EIGER (Llopart et al, 2002Johnson et al, 2012) are well suited for measuring high-energy electrons (McMullan et al, 2007), and can overcome difficulties in detecting weak peaks, for example for CCD and CMOS detectors (Hattne et al, 2016;Rodriguez & Gonen, 2016).…”

“…Previously, we used a single quad Medipix detector (Georgieva et al, 2011;Nederlof et al, 2013) and a Timepix detector (van Genderen et al, 2016) of 512 Â 512 pixels (55 Â 55 mm pixel size). For very well ordered crystals this detector size is sufficient for resolving up to 50 orders of diffraction.…”

“…Detector features that are of particular interest for electron diffraction are the absence of readout noise, a high dynamic range and the ability to distinguish between the signal from diffracted electrons and that from the high X-ray background that is inherently present in any TEM (Georgieva et al, 2011;Nederlof et al, 2013;van Genderen et al, 2016). These features require a counting detector, a concept that has recently also been introduced in monolithic and CMOS detectors.…”