Browsing by Author "Nabok, Alexei"

Now showing 1 - 4 of 4
  • Thumbnail Image
    ItemOpen Access
    Detection of β-amyloid peptide (1–16) and amyloid precursor protein (APP770) using spectroscopic ellipsometry and QCM techniques: A step forward towards Alzheimers disease diagnostics
    (Elsevier, 2010-12-15) Mustafa, M. K.; Nabok, Alexei; Parkinson, D.; Tothill, Ibtisam E.; Salam, Faridah; Tsargorodskaya, A.
    A highly sensitive method of spectroscopic ellipsometry in total internal reflection mode (TIRE) was exploited for detecting β-amyloid peptide (Aβ1–16) in the direct immune reaction with monoclonal DE2 antibodies (raised against Aβ1–16) electrostatically immobilised on the surface of gold. A rapid detection of Aβ1–16 in a wide range of concentrations from 5 μg/ml down to 0.05 ng/ml was achieved using a cost-effective and label-free direct immunoassay format. TIRE dynamic spectral measurements proved that the immune reaction between DE2 monoclonal antibodies and Aβ1–16 is highly specific with the affinity constant KD = 1.46 × 10−8 mol/l. The same DE2 antibodies were utilised for detection of amyloid precursor protein APP770, a larger protein containing Aβ1–16 domain, using the quartz crystal microbalance (QCM) measurements in liquid. A combination of QCM and TIRE kinetics results allowed the evaluation of the originally unknown concentration of APP770 in complete medium solution containing other proteins, salts, and amino acids.
  • Thumbnail Image
    ItemOpen Access
    Optical and AFM study of electrostatically assembled films of CdS and ZnS colloid nanoparticles.
    (Elsevier Science B.V., Amsterdam., 2008-05-30T00:00:00Z) Suryajaya, S.; Nabok, Alexei; Davis, Frank; Hassan, A.; Higson, Seamus P. J.; Evans-Freeman, J.
    CdS and ZnS semiconducting colloid nanoparticles coated with the organic shell, containing either SO3− or NH2+ groups, were prepared using the aqueous phase synthesis. The multilayer films of CdS (or ZnS) were deposited onto glass, quartz and silicon substrates using the technique of electrostatic self- assembly. The films produced were characterized with UV–vis spectroscopy, spectroscopic ellipsometry and atomic force microscopy. A substantial blue shift of the main absorption band with respect to the bulk materials was found for both CdS and ZnS films. The Efros equation in the effective mass approximation (EMA) theoretical model allowed the evaluation of the nanoparticle radius of 1.8 nm, which corresponds well to the ellipsometry results. AFM shows the formation of larger aggregates of nanoparticles on solid surfa
  • Thumbnail Image
    ItemOpen Access
    Species differentiation by DNA-modified carbon electrodes using an ac impedimetric approach.
    (Elsevier Science B.V., Amsterdam., 2005-02-15T00:00:00Z) Davis, Frank; Nabok, Alexei; Higson, Seamus P. J.
    A simple and novel electrochemical biosensor based approach is described for differentiating between differing species of fish on the basis of DNA hybridisation events. Screen-printed carbon electrodes modified with a variety of polymers were used to immobilise commercially available DNA in a single- stranded form. AC impedimetric measurements were firstly carried out on these systems and then upon exposure to single-stranded DNA solutions. When the electrode and solution DNA were complementary, a large drop in impedance was measured; this did not occur for non-matching DNA exposures. DNA hybridisation sensors for closely related species of fish were in the first instance developed as a demonstration for this approach. Species of fish such as herrings and salmon could be differentiated by this method. This sensor format offers great promise for many DNA hybridisation applications and lends itself to mass fabrication due to the simplicity and inexpensiveness of the materials and methods used. The hybridisation results were confirmed by use of ellipsometry to measure the characteristics of similar films deposited on silicon substrates.
  • Thumbnail Image
    ItemOpen Access
    The study of genomic DNA adsorption and subsequent interactions using total internal reflection ellipsometry.
    (Elsevier Science B.V., Amsterdam., 2007-10-31T00:00:00Z) Nabok, Alexei; Tsargorodskaya, Anna; Davis, Frank; Higson, Seamus P. J.
    The adsorption of genomic DNA and subsequent interactions between adsorbed and solvated DNA was studied using a novel sensitive optical method of total internal reflection ellipsometry (TIRE), which combines spectroscopic ellipsometry with surface plasmon resonance (SPR). Single strands of DNA of two species of fish (herring and salmon) were electrostatically adsorbed on top of polyethylenimine films deposited upon gold coated glass slides. The ellipsometric spectra were recorded and data fitting utilized to extract optical parameters (thickness and refractive index) of adsorbed DNA layers. The further adsorption of single stranded DNA from an identical source, i.e. herring ss-DNA on herring ss-DNA or salmon ss-DNA on salmon ss-DNA, on the surface was observed to give rise to substantial film thickness increases at the surface of about 20–21 nm. Conversely adsorption of DNA from alternate species, i.e. salmon ss- DNA on herring ss-DNA or herring ss-DNA on salmon ss-DNA, yielded much smaller changes in thickness of 3–5 nm. AFM studies of the surface roughness of adsorbed layers were in line with the TIRE d