Immobilization of fibrinogen antibody on self-assembled gold monolayers for immunosensor applications

Voltammetric-based immunosensing of Newcastle disease virus on polyethylene glycol-containing self-assembled monolayer modified gold electrode

A voltammetric immunosensor for the detection of Newcastle disease virus (NDV) has been developed by employing polyclonal antibody targeting NDV (anti-NDV) as a bioreceptor. Anti-NDV was immobilized on polyethylene glycol (PEG)-containing self-assembled monolayer (SAM) which was activated with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimidehydrochloride (EDC) and N-hydroxy succinimide (NHS) coupling on screen-printed gold electrode (SPGE). The introduction of PEG-containing SAM on the SPGE allowed the bioreceptor to covalently bound to the electrode surface whilst still providing a hydrophilic layer on the electrode which is important to greatly reduce non-specific bindings. The bioreceptor functionalized electrode was then allowed to be incubated with NDV-spiked samples. The electrode surface modification with PEG-containing SAM, immobilization of anti-NDV as bioreceptor, up to the detection of NDV were characterized electrochemically through differential pulse voltammetry (DPV) analysis in [Fe(CN)6]3- as the redox probe. Decrement of anodic current peak (Ipa) of [Fe(CN)6]3- was seen as the concentration of NDV increased from 0.156 to 20 HA μL-1 with the limit of detection (LoD) of 1.50 HA μL-1 at 3σ m-1. The detection of NDV in HA μL-1 unit in this study would ease interlaboratory interpretation as it was the same unit used in hemagglutination (HA) assay of conventional NDV diagnosis. The specificity of anti-NDV used as bioreceptor towards NDV was confirmed through western blot analysis, whilst the selectivity of the bioreceptor-functionalized electrode has been tested with allantoic fluid as the negative control in which no apparent changes of anodic peak (Ipa) has been seen. This simple, fast, and less laborious electrochemical detection method could become an alternative to the conventional method for NDV detection.

Differences in perchlorate adsorption to azobenzene monolayers on gold formed from thioacetate and thiol precursors

Modification of metal surfaces with complex molecules opens interesting opportunities to build additional functionality into these surfaces. In this work, self assembled monolayers (SAMs) based on the same photoswitchable azobenzene motif but with different head groups have been synthesized and their SAMs on Au(111)/Si substrates have been characterized. 3-[(4-phenylazo)phenoxy]propyl thiol (PAPT) and its acetyl group protected analog, 3-[(4-phenylazo)phenoxy]propyl thioacetate (PAPA), have been synthesized. SAMs from PAPT and PAPA have been characterized by infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ellipsometry and cyclic voltammetry (CV). The SAM-forming units of both SAMs are the same, as confirmed by IR and XPS, and the SAMs have similar surface coverage, as evidenced by analysis of the reductive desorption peaks in CVs. The tilt angle of the azobenzene moiety was ca. 75° with respect to the surface normal as determined by IR spectroscopy, i.e., the molecules are lying quite flat on the gold surface. Despite similar surface coverages, the CVs for PAPT in aqueous perchlorate solution show a typical perchlorate adsorption peak to gold, whereas the corresponding experiments with PAPA show no perchlorate adsorption at all. In conclusion, SAM formation can lead to an increase in the number of electrochemically accessible surface sites on the final, SAM covered surface. Whether the amount of such sites increases or decreases, depends on the precursor. The precursor most likely affects the adsorption mechanism and thus the atomic surface structure of the metal at the metal/SAM interface. Thus, details of the SAM formation mechanism, which is affected by the precursor used, can have quite strong effects on the electrochemical properties, and likely also electrocatalytic properties, of the resulting modified surface.