Adam Hollerbach

On‐Demand Ambient Ionization of Picoliter Samples Using Charge Pulses

Relay electrospray ionization (rESI) from a capillary containing a sample solution (or from an array of such capillaries) is triggered by charge deposition onto the capillary. Suitable sources of primary ions, besides electrosprays, are plasma ion and piezoelectric discharge plasma sources. With no requirement for physical contact, high-throughput sample screening is enabled by rapidly addressing individual secondary (sample) capillaries. Sub-pL sample volumes can be loaded and sprayed. Polar analytes, including neurotransmitters, phosphopeptides, oligonucleotides, illicit drugs, and pharmaceutical compounds are successfully ionized by rESI with concentration sensitivities (0.1 ppb for acetylcholine) which are similar to nanoESI but absolute sensitivities are orders of magnitude better. Nonpolar analytes (steroids, alkynes) are ionized by rESI using an open-tube secondary capillary and injecting electrolytically generated metal cations from the primary electrospray.

Structure of faustovirus, a large dsDNA virus.

Significance Since the discovery of Mimivirus in 2003, many new giant viruses have been isolated and characterized, now that the definition of viruses excludes their ability to pass through the finest available filters. At least one of these viruses can cause serious infections. Here we describe the structure of faustovirus, the prototypic member of a new family of large double-stranded DNA viruses that are homologs of the Asfarviridae. Contrary to other large viruses, faustovirus has a double-protein shell surrounding the genomic material, something never described before for a DNA virus. In addition, the gene that encodes the major capsid protein shows an unusual organization, stretching over 17,000 bp in the genome while encoding for only 652 amino acids. Many viruses protect their genome with a combination of a protein shell with or without a membrane layer. Here we describe the structure of faustovirus, the first DNA virus (to our knowledge) that has been found to use two protein shells to encapsidate and protect its genome. The crystal structure of the major capsid protein, in combination with cryo-electron microscopy structures of two different maturation stages of the virus, shows that the outer virus shell is composed of a double jelly-roll protein that can be found in many double-stranded DNA viruses. The structure of the repeating hexameric unit of the inner shell is different from all other known capsid proteins. In addition to the unique architecture, the region of the genome that encodes the major capsid protein stretches over 17,000 bp and contains a large number of introns and exons. This complexity might help the virus to rapidly adapt to new environments or hosts.

Ion Separation in Air Using a Three-Dimensional Printed Ion Mobility Spectrometer

The performance of a small, plastic drift tube ion mobility spectrometer (DT-IMS) is described. The IMS was manufactured using three-dimensional (3D) printing techniques and operates in the open air at ambient pressure, temperature, and humidity. The IMS housing and electrodes were printed from nonconductive polylactic acid (PLA, housing) and conductive polyethylene terephthalate glycol-modified polymer containing multiwalled carbon nanotubes (PETG-CNT, electrodes). Ring electrodes consisting of both an inner disk and an outer ring were used to prevent neutral transmission while maximizing ion transmission. As a stand-alone instrument, the 3D printed IMS is shown to achieve resolving powers of between 24 and 50 in positive ion mode using tetraalkylammonium bromide salts (TAA), benzylamines (mono-, di-, and tri-), and illicit drugs (MA, MDEA, and haloperidol). Resolving powers of between 29 and 42 were achieved in negative ion mode using sodium alkyl sulfates (C8, C12, C16, and C18). Reduced ion mobilities of TAA cations (C2-C8) were calculated at 14% relative humidity in air to be 1.36, 1.18, 1.03, 0.90, 0.80, 0.73, and 0.67, respectively. The effect of humidity on reduced ion mobilities of TAA cations is discussed. 3D printing is shown to be a quick and cost-effective way to produce small IMS instruments that can compete in performance with conventionally manufactured IMS instruments that also operate in the open air. An important difference between this IMS and other instruments is the absence of a counter gas flow.

Ion Mobility-Mass Spectrometry using a Dual-Gated 3D printed Ion Mobility Spectrometer

Described herein is the development of a 3D-printed drift-tube ion mobility spectrometer (IMS) which operates in the open air and is capable of being coupled to any mass spectrometer. The IMS possesses one electrospray focusing electrode, 31 drift electrodes with 7 mm inner diameters, and 2 ion gates at opposite ends of the IMS, totaling 109 mm in length. The second ion gate was timed with respect to the first ion gate to transmit portions of the separating ion packets to the MS at specified time intervals. By scanning the second ion gate and acquiring mass spectra during each time interval, we reconstructed ion mobility chronograms using mass spectra. Resolving powers of up to 45 were acquired using tetraalkylammonium cations. Separation is also demonstrated for solutions of amphetamines, opioids (fentanyls/fentanils), and bradykinin and angiotensin II. The highest mobility resolving powers were obtained when the injection times of the first and second ion gates were 0.3 and 1.0 ms, respectively. Experiments were performed on both an ion trap and triple quadruple mass analyzer to showcase the adaptability of the plastic IMS. Insights were gained into how ions separate in the open air compared to vacuum conditions with pure gas.

Desorption Electrospray Ionization: Methodology and Applications

Desorption electrospray ionization (DESI) is a widely used ionization technique for determining the chemical nature of surfaces by mass spectrometry. The ability to perform experiments in air with minimal to no sample preparation makes DESI an attractive technique in academic, industrial, and medical laboratories. A wide range of compounds can be analyzed directly from surfaces, from hydrocarbons to proteins. The fundamental principles and applications of DESI, both mature and developing, are discussed in this article along with a detailed explanation of the experimental design.

Tumor Cell Detection by Mass Spectrometry Using Signal Ion Emission Reactive Release Amplification.

A method is presented for the detection of circulating tumor cells (CTC) using mass spectrometry (MS), through reporter-ion amplification. Particles functionalized with short-chain peptides are bound to cells through antibody-antigen interactions. Selective release and MS detection of peptides is shown to detect as few as 690 cells isolated from a 10 mL blood sample. Here we present proof-of-concept results that pave the way for further investigations.