Functionalised Nanopores: Chemical and Biological Modifications

Nanopore technology has established itself as a powerful tool for single-molecule studies. By analysing changes in the ion current flowing through a single transmembrane channel, a wealth of molecular information can be elucidated. Early studies utilised nanopore technology for sensing applications, and subsequent developments have diversified its remit. Nanopores can be synthetic, solid-state, or biological in origin, but recent work has seen these boundaries blurred as hybrid functionalised pores emerge. The modification of existing pores and the construction of novel synthetic pores has been an enticing goal for creating systems with tailored properties and functionality. Here, we explore chemically functionalised biological pores and the bio-inspired functionalisation of solid-state pores, highlighting how the convergence of these domains provides enhanced functionality

Protein nanopores as a platform for transmembrane nanodevices

Nanopore sensing has seen vast development over the past four decades. The technique originally looked to use electrophysiological methods to study native protein channels. However, it is now possible to exploit these proteins for sensing applications. Herein, we explore methods for covalent and non-covalent modification of a biological nanopore to achieve new functionality. Chapter 1 summarises the history of nanopore technology; from its inception as a method for studying native channels, to its deployment in nanopore sensing. To achieve effective sensing, native proteins have undergone a broad range of chemical modification to achieve enhanced functionality. This chapter explores the amalgamation of biological and solid-state nanopores. Chapter 2 seeks to the monitor the binding and catalytic turnover of substrates within a single cucurbituril molecule captured within a protein nanopore. Previous work has shown that cucurbiturils and cyclodextrins can transiently interact with an α-hemolysin channel. Capture of a single cucurbituril within a protein nanopore was achieved, and the dwell time of the binding events was optimised. Following this, it was demonstrated that observations of the catalysed Diels-Alder could be made at the single-molecule level. However, further optimisation of the resolution would be required to elucidate mechanistic information. Chapter 3 presents methods for in situ chemical functionalisation of a biological nanopore. Here, the focus is upon the chemical modification of a wild-type protein thereby to circumventing the need for mutagenesis. Three target residues are discussed: lysine, methionine and tyrosine. Successful modification was achieved at both the lysine and methionine sites of α-hemolysin. While some provisional success was recorded with tyrosine, the modifications were not reproducible. Chapter 4 introduces preliminary work towards the development of transmembrane molecular machines. This utilises the lysine modification discussed in Chapter 2 to covalently attach established synthetic molecular machines to the channel. Molecular switches, motors and pumps were all explored. Some success was achieved attaching the molecular machines to a protein channel. However, issues with pore stability limited the progress and true machine-like behaviour was not observed

Synthetically Diversified Protein Nanopores: Resolving Click Reaction Mechanisms

Nanopores are emerging as a powerful tool for the investigation of nanoscale processes at the single-molecule level. Here, we demonstrate the methionine-selective synthetic diversification of α-hemolysin (α-HL) protein nanopores and their exploitation as a platform for investigating reaction mechanisms. A wide range of functionalities, including azides, alkynes, nucleotides, and single-stranded DNA, were incorporated into individual pores in a divergent fashion. The ion currents flowing through the modified pores were used to observe the trajectory of a range of azide–alkyne click reactions and revealed several short-lived intermediates in Cu­(I)-catalyzed azide–alkyne [3 + 2] cycloadditions (CuAAC) at the single-molecule level. Analysis of ion-current fluctuations enabled the populations of species involved in rapidly exchanging equilibria to be determined, facilitating the resolution of several transient intermediates in the CuAAC reaction mechanism. The versatile pore-modification chemistry offers a useful approach for enabling future physical organic investigations of reaction mechanisms at the single-molecule level

Increase in the use of inhaled nitric oxide in neonatal intensive care units in England: a retrospective population study

Objective To describe temporal changes in inhaled nitric oxide (iNO) use in English neonatal units between 2010 and 2015.Design Retrospective analysis using data extracted from the National Neonatal Research Database.Setting All National Health Service neonatal units in England.Patients Infants of all gestational ages born 2010–2015 admitted to a neonatal unit and received intensive care.Main outcome measures Proportion of infants who received iNO; age at initiation and duration of iNO use.Results 4.9% (6346/129 883) of infants received iNO; 31% (1959/6346) were born <29 weeks, 18% (1152/6346) 29–33 weeks and 51% (3235/6346)>34 weeks of gestation. Between epoch 1 (2010–2011) and epoch 3 (2014–2015), there was (1) an increase in the proportion of infants receiving iNO: <29 weeks (4.9% vs 15.9%); 29–33 weeks (1.1% vs 4.8%); >34 weeks (4.5% vs 5.0%), (2) increase in postnatal age at iNO initiation: <29 weeks 10 days vs 18 days; 29–33 weeks 2 days vs 10 days, (iii) reduction in iNO duration: <29 weeks (3 days vs 2 days); 29–33 weeks (2 days vs 1 day).Conclusions Between 2010 and 2015, there was an increase in the use of iNO among infants admitted to English neonatal units. This was most notable among the most premature infants with an almost fourfold increase. Given the cost of iNO therapy, limited evidence of efficacy in preterm infants and potential for harm, we suggest that exposure to iNO should be limited, ideally to infants included in research studies (either observational or randomised placebo-controlled trial) or within a protocolised pathway. Development of consensus guidelines may also help standardise practice