Multi-detector Array CD-MS for Rapid Analysis of Very High Mass Analytes

Project Summary/Abstract This proposal describes key steps towards designing a high-throughput charge detection mass spectrometer that is optimized for very high mass particles in the megadalton and gigadalton mass range. Charge detection mass spectrometry (CD-MS) is an emerging technology capable of accurately measuring the mass of large and heterogeneous analytes, making it highly suitable for a wide array of applications including biopharmaceuticals including gene therapy vectors, virus particles such as adenovirus and lentivirus, liposomes, and large miomarkers such as lipoproteins and exosomes. CD-MS often employs an electrostatic ion trap containing a conductive detection cylinder connected to a charge sensitive amplifier. Trapped ions repeatedly pass through the detection cylinder, generating a square wave signal, and are individually analyzed by Fast Fourier Transform for their mass-to-charge ratio (m/z) and charge by measuring their oscillation frequency and signal magnitude, respectively. While a trap offers the highest charge resolution, and therefore the highest mass resolution, it suffers from low sensitivity and can be time-consuming. For example, routine mass spectrum acquisition takes around 15 minutes for a sample with 1012 particles/mL and the lower detection limit is approximately 1010 particles/mL. Lower concentrations also require longer to analyze. In this proposal we aim to design a detector array CD-MS instrument capable of enhancing the sensitivity and throughput by two orders of magnitude for heterogeneous samples where higher mass resolution is not necessary for accurately characterizing the mass distribution. This array will consist of ten individual detection cylinders in a linear arrangement. Ions will be flown through the array and refocused towards the central axis by electrostatic lenses. Charge sensitive amplifiers and analog to digital converters will generate and send signals from each detector to a central processing unit such as a field-programmable gate array (FPGA) for the signals to be packaged into files and then sent to a server for data processing. In this investigation, development will begin by performing ion trajectory simulations for optimizing geometric parameters of the array and focusing voltages applied to the lenses to maximize ion transmission through the array, thereby maximizing sensitivity. These trajectories will then be used to generate representative simulated signals. Following from that, code will be written to extract the ion m/z and charge from the simulated signals. Alongside code development, we will explore different amplifier configurations that give rise to the fastest analysis and best charge determination. Finally, we wish to develop an integrated circuit for CD-MS amplifiers which has the potential to significantly improve the charge measurement precision and will have a more robust and reproducible construction than the current custom amplifier design. The development of this high-throughput CD-MS array is key to meeting the need for an instrument capable of accurately and rapidly characterizing the mass distribution of very heavy biological analytes.