Jason J. Davis

Protein electrochemistry at carbon nanotube electrodes

Abstract The application of the carbon nanotube as an electrode material is demonstrated. Redox proteins on and within these tubes give reproducible, well-behaved voltammetric responses.

The immobilisation of proteins in carbon nanotubes

Carbon nanotubes, fullerene-related structures, have been used for the immobilisation of proteins and enzymes. We have been able to demonstrate, for the first time, direct imaging by high resolution transmission electron microscopy of Zn2Cd5-metallothionein, cytochromes c, c, and β-lactamase 1. This was achieved, without modification, because the biomolecules encapsulated within nanotubes appear to be shielded from the consequences of exposure to the intense electron beam. The results indicate that the internal surface of the nanotubes interacts strongly with the enzymes resulting in their immobilisation. In some cases, the proteines are seen to be distorted giving a concave meniscus inside the tubes. Single protein molecules, their dimers, tetramers and higher oligomers are observed inside the central cavity. Comparison of the catalytic activities of immobilised β-lactamase 1 on or in nanotubes with the free enzyme in the hydrolysis of penicillin, however, showed a significant amount of the immobilised enzyme remained catalytically active, implying that no drastic conformational change had taken place. The carbon nanotube appears to act as a benign host in its ability to encapsulate protein molecules within an environment which offers some protection.

Reversible Luminescence Switching of a Redox-Active Ferrocene–Europium Dyad

The copper-catalyzed cycloaddition reaction between a propargyl-appended europium complex and azidomethylferrocene yields a d-f dyad whose photophysical properties can be reversibly switched by varying the oxidation state of the ferrocene chromophore.

An optimised electrochemical biosensor for the label-free detection of C-reactive protein in blood.

C-reactive protein (CRP) is an acute phase protein whose levels are increased in many disorders. There exists, in particular, a great deal of interest in the correlation between blood serum levels and the severity of risk for cardiovascular disease. A sensitive, label-free, non-amplified and reusable electrochemical impedimetric biosensor for the detection of CRP in blood serum was developed herein based on controlled and coverage optimised antibody immobilization on standard polycrystalline gold electrodes. Charge transfer resistance changes were highly target specific, linear with log CRP concentration across a 0.5-50nM range and associated with a limit of detection of 176pM. Significantly, the detection limits are better than those of current CRP clinical methods and the assays are potentially cheap, relatively automated, reusable, multiplexed and highly portable. The generated interfaces were capable not only of comfortably quantifying CRP across a clinically relevant range of concentrations but also of doing this in whole blood serum with interfaces that were, subsequently, reusable. The importance of optimising receptor layer resistance in maximising assay sensitivity is also detailed.

Zinc metalloporphyrin-functionalised nanoparticle anion sensorsElectronic supplementary information (ESI) available: synthetic procedure for 1 and 2, titration experimental protocol and nanoparticle TEM. See http://www.rsc.org/suppdata/cc/b3/b313658b/

Disulfide-functionalised zinc metalloporphyrins self-assembled on gold nanoparticles exhibit remarkable, surface-enhanced, anion binding affinities as compared to the free metalloporphyrin.

The label free picomolar detection of insulin in blood serum.

Insulin, a polypeptide hormone secreted by pancreatic cells, is a key regulator in glucose homeostasis. Its deficiency leads to insulin-dependent (type I) diabetes whereas resistance to insulin is common in type II diabetes, obesity and a range of endocrine disorders. Its determination is of considerable value, particularly in the clinical diagnosis of diabetes mellitus and the doping control of athletes. It has, additionally, been noted as a potential breast cancer marker (serum insulin levels being found to be raised in comparison to control patients). Electrochemical assays are potentially very cheap, highly sensitive, and very readily transposed to a point of care. Though there exist numerous examples of label free impedimetric or capacitative assaying of biomolecules, these are rarely demonstrated to be effective in complex biological mixtures or to be applicable to low molecular weight targets (since they operate through the interfacial displacement of water/ions and/or the steric blocking of a redox probe). We report herein an ultrasensitive electrochemical and label-free biosensor for insulin in blood serum with a clinically relevant linear range and detection limit of 1.2pM. The transducing surfaces, based on readily prepared, antibody modified, polyethylene glycol monolayer modified polycrystalline gold surfaces, respond in a highly specific and re-useable manner to the target in up to 50% blood serum.

Environmentally responsive MRI contrast agents.

Biomedical imaging techniques can provide a vast amount of anatomical information, enabling diagnosis and the monitoring of disease and treatment profile. MRI uniquely offers convenient, non-invasive, high resolution tomographic imaging. A considerable amount of effort has been invested, across several decades, in the design of non toxic paramagnetic contrast agents capable of enhancing positive MRI signal contrast. Recently, focus has shifted towards the development of agents capable of specifically reporting on their local biochemical environment, where a switch in image contrast is triggered by a specific stimulus/biochemical variable. Such an ability would not only strengthen diagnosis but also provide unique disease-specific biochemical insight. This feature article focuses on recent progress in the development of MRI contrast switching with molecular, macromolecular and nanoparticle-based agents.

One-step synthesis and AFM imaging of hydrophobic LDH monolayers

Hydrophobic layered double hydroxide particles with a single layer structure have been successfully synthesised in a reverse microemulsion system; atomic force microscopy has proven a powerful tool for the study of these delicate nanoparticles.

Sulfate anion templation of a neutral pseudorotaxane assembly using an indolocarbazole threading component.

The first example of anion templated pseudorotaxane formation between two neutral components in solution and in surface assembled monolayers is described.

Label-free sub-picomolar protein detection with field-effect transistors

Proteins mediate the bulk of biological activity and are powerfully assayed in the diagnosis of diseases. Protein detection relies largely on antibodies, which have significant technical limitations especially when immobilized on two-dimensional surfaces. Here, we report the integration of peptide aptamers with extended gate metal-oxide-semiconductor field-effect transistors (MOSFETs) to achieve label-free sub-picomolar target protein detection. Specifically, peptide aptamers that recognize highly related protein partners of the cyclin-dependent kinase (CDK) family are immobilized on the transistor gate to enable human CDK2 to be detected at 100 fM or 5 pg/mL, well within the clinically relevant range. The target specificity, ease of fabrication, and scalability of these FET arrays further demonstrate the potential application of the multiplexable field effect format to protein sensing.