Nanostructured rough gold electrodes as platforms to enhance the sensitivity of electrochemical genosensors

Electrochemical detection of specific interactions between apolipoprotein E isoforms and DNA sequences related to Alzheimer's disease

Apolipoprotein E4 (ApoE4) has a key role on the onset and progression of Alzheimer's disease (AD), since it favours the deposition of toxic amyloid-beta (Aβ) aggregates in the brain. These effects might result from the interaction between ApoE4 and specific DNA promoters related to cellular autophagy pathways and to the expression of neuroprotective proteins, like sirtuin-1. Herein, we modified gold electrodes with mixed self-assembled monolayers of 6-mercapto-1-hexanol and thiolated DNA oligonucleotides related to CLEAR (associated with autophagic processes that enable the clearance of toxic species, such as Aβ) and SirT1 (related to the expression of sirtuin-1) promoter sequences. The interactions of the immobilized DNA sequences with isoforms of ApoE (ApoE4/ApoE3/ApoE2) were investigated by differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) measurements. By monitoring current and charge transfer resistance (R_ct) variations, CLEAR showed to interact specifically with ApoE4, whereas SirT1 showed a higher affinity to ApoE4 compared to ApoE3 and ApoE2. To the best of our knowledge, this is the first report about the application of electrochemical techniques to investigate the sequence-specific interaction between ApoE isoforms and CLEAR and SirT1 oligonucleotides.

Electrochemical Deposition of Nanomaterials for Electrochemical Sensing

The most commonly used methods to electrodeposit nanomaterials on conductive supports or to obtain electrosynthesis nanomaterials are described. Au, layered double hydroxides (LDHs), metal oxides, and polymers are the classes of compounds taken into account. The electrochemical approach for the synthesis allows one to obtain nanostructures with well-defined morphologies, even without the use of a template, and of variable sizes simply by controlling the experimental synthesis conditions. In fact, parameters such as current density, applied potential (constant, pulsed or ramp) and duration of the synthesis play a key role in determining the shape and size of the resulting nanostructures. This review aims to describe the most recent applications in the field of electrochemical sensors of the considered nanomaterials and special attention is devoted to the analytical figures of merit of the devices.

Au nanoparticle in situ decorated RGO nanocomposites for highly sensitive electrochemical genosensors

A novel hybrid nanocomposite formed by RGO flakes, surface functionalized by 1-pyrene carboxylic acid (PCA), densely and uniformly in situ decorated by Au NPs, is reported, for miRNA detection.

Hairpin-based DNA electrochemical sensor for selective detection of a repetitive and structured target codifying a gliadin fragment

High selectivity of genosensors is crucial for certain applications such as those involving species with high genetic variability. This is an unresolved problem when dealing with long target sequences that is further complicated when the target contains repetitive sequence domains. As a model for this situation, the problem of detecting gluten in food with identification of the source is studied. In order to discriminate the specific DNA sequence that encodes the wheat prolamin (gliadin) from rye and barley prolamins, the exquisite selectivity of a rationally designed hairpin capture probe is proposed and compared to a nonstructured capture probe. An electrochemical sandwich assay is proposed, involving capture probes chemisorbed on Au surfaces and biotinylated-signaling probes in combination with streptavidin-peroxidase labeling conjugates. As a result, a genosensor with similar sensitivity to that observed with linear probes but with complete specificity against closely related species was achieved. The surface-attached DNA stem-loop yields a device capable of accurately discriminating wheat DNA from rye and barley with a limit of detection of 1 nM.

An electrochemical sensing strategy based on a three dimensional ordered macroporous polyaniline–platinum platform and a mercury(ii) ion-mediated DNAzyme functionalized nanolabel

An Hg²⁺-switched DNA biosensor using a three dimensional ordered macroporous polyaniline–platinum platform and a G-rich sequence recognition probe was developed, with the detection limit of 8.7 × 10⁻¹⁴ M.

Sensitive pseudobienzyme electrocatalytic DNA biosensor for mercury(II) ion by using the autonomously assembled hemin/G-quadruplex DNAzyme nanowires for signal amplification

Herein, a novel sensitive pseudobienzyme electrocatalytic DNA biosensor was proposed for mercury ion (Hg(2+)) detection by using autonomously assembled hemin/G-quadruplex DNAzyme nanowires for signal amplification. Thiol functionalized capture DNA was firstly immobilized on a nano-Au modified glass carbon electrode (GCE). In presence of Hg(2+), the specific coordination between Hg(2+) and T could result in the assembly of primer DNA on the electrode, which successfully triggered the HCR to form the hemin/G-quadruplex DNAzyme nanowires with substantial redox probe thionine (Thi). In the electrolyte of PBS containing NADH, the hemin/G-quadruplex nanowires firstly acted as an NADH oxidase to assist the concomitant formation of H2O2 in the presence of dissolved O2. Then, with the redox probe Thi as electron mediator, the hemin/G-quadruplex nanowires acted as an HRP-mimicking DNAzyme that quickly bioelectrocatalyzed the reduction of produced H2O2, which finally led to a dramatically amplified electrochemical signal. This method has demonstrated a high sensitivity of Hg(2+) detection with the dynamic concentration range spanning from 1.0 ng L(-1) to 10 mg L(-1) Hg(2+) and a detection limit of 0.5 ng L(-1) (2.5 pM) at the 3Sblank level, and it also demonstrated excellent selectivity against other interferential metal ions.