Condensed-Phase Photochemistry in the Absence of Radiation Chemistry

We report post-irradiation photochemistry studies of condensed ammonia using photons of energies below condensed ammonia’s ionization threshold of ~ 9 eV. Hydrazine (N2H4), diazene (also known as diimide and diimine) (N2H2), triazane (N3H5), and one or more isomers of N3H3 are detected as photochemistry products during temperature-programmed desorption. Product yields increase monotonically with (1) photon fluence and (2) film thickness. In the studies reported herein, the energies of photons responsible for product formation are constrained to less than 7.4 eV. Previous post-irradiation photochemistry studies of condensed ammonia employed photons sufficiently energetic to ionize condensed ammonia and initiate radiation chemistry. Such studies typically involve ion-molecule reactions and electron-induced reactions in addition to photochemistry. Although photochemistry is cited as a dominant mechanism for the synthesis of prebiotic molecules in interstellar ices, to the best of our knowledge, ours is one of the first astrochemically-relevant studies that has found unambiguous evidence for condensed-phase chemical synthesis induced by photons in the absence of ionization

Paper-based diagnostics in the antigen-depletion regime: High-density immobilization of rcSso7d-cellulose-binding domain fusion proteins for efficient target capture

© 2017 Elsevier B.V. In this work, we report the development of a general strategy for enhancing the efficiency of target capture in immunoassays, using a bifunctional fusion protein construct which incorporates a substrate-anchoring moiety for the high-abundance immobilization of an antigen-binding domain. This approach was informed by the development of a pseudo first-order rate constant model, and tested in a paper-based assay format using a fusion construct consisting of an rcSso7d binding module and a cellulose-binding domain. These rcSso7d-CBD fusion proteins were solubly expressed and purified from bacteria in high molar yields, and enable oriented, high-density adsorption of the rcSso7d binding species to unmodified cellulose within a 30-second incubation period. These findings were validated using two distinct, antigen-specific rcSso7d variants, which were isolated from a yeast surface display library via flow cytometry. Up to 1.6 micromoles of rcSso7d-CBD was found to adsorb per gram of cellulose, yielding a volume-averaged binder concentration of up to 760 μM within the resulting active material. At this molar abundance, the target antigen is captured from solution with nearly 100% efficiency, maximizing the attainable sensitivity for any given diagnostic system

Beyond Epitope Binning: Directed in Vitro Selection of Complementary Pairs of Binding Proteins

© 2019 American Chemical Society. Many biotechnological applications require the simultaneous binding of affinity reagents to nonoverlapping target epitopes, the most prominent example being sandwich immunoassays. Typically, affinity pairs are identified via post facto functional analysis of clones that were not selected for complementarity. Here, we developed the Rapid Affinity Pair Identification via Directed Selection (RAPIDS) process, which enables the efficient identification of affinity reagents that function together as complementary pairs, from in vitro libraries of â¼109 variants. We used RAPIDS to develop highly specific affinity pairs against biomarkers of tuberculosis, Zika virus, and sepsis. Without additional trial-and-error screening, these affinity pairs exhibited utility in multiple assay formats. The RAPIDS process applies selective pressure to hundreds of thousands of potential affinity pairs to efficiently identify complementary pairs that bind to separate epitopes without binding to one another or nontargets, yielding diagnostic assays that are sensitive and specific by design