AbstractElectrode fouling is a phenomenon that can severely affect the analytical characteristics of a technique or a sensor, such as sensitivity, detection limit, reproducibility, and overall reliability. Electrode fouling generally involves the passivation of an electrode surface by a fouling agent that forms an increasingly impermeable layer on the electrode, inhibiting the direct contact of an analyte of interest with the electrode surface for electron transfer. Some potential fouling agents include proteins, phenols, amino acids, neurotransmitters, and other biological molecules. Various antifouling strategies have been reported to reduce or eliminate electrode fouling. Most antifouling strategies exploit a protective layer or barrier on an electrode substrate to prevent the fouling agent from reaching the electrode surface. Although such strategies can be quite effective, they are inappropriate for systems in which the analyte itself is also the fouling agent. In such cases, other strategies must be used, including electrode surface modification and electrochemical activation. In this review, recent strategies to minimise and efforts to overcome electrode fouling across a diverse range of analytes and fouling agents will be presented.

PACS numbers: 82.65.Dp, 82.70.Dd, 87.22.Bt.We explore the interplay of membrane curvature and nonspecific binding due to excluded-volume effects among colloidal particles inside lipid bilayer vesicles. We trapped submicron spheres of two different sizes inside a pear-shaped, multilamellar vesicle and found the larger spheres to be pinned to the vesicle's surface and pushed in the direction of increasing curvature. A simple model predicts that hard spheres can induce shape changes in flexible vesicles. The results demonstrate an important relationship between the shape of a vesicle or pore and the arrangement of particles within it.Entropic excluded-volume (depletion) effects are well known to lead to phase separation in the bulk of colloids and emulsions consisting of large and small particles with short-range repulsive interactions [1][2][3][4][5][6]. More recently, attraction of the large particles to flat, hard walls [7,8] and repulsion from step edges [9] have been demonstrated in binary hard-sphere mixtures. A key concept suggested in these papers is that the geometric features of the surface can create "entropic force fields" that trap, repel or induce drift of the larger particles. This mechanism is not limited to suspensions of micron-sized particles; it may play a role in "lock and key" steric interactions on smaller macromolecular length scales. For example, the shape of pores and liposomes inside cells is likely to affect the behavior of macromolecules confined within them [10].In this Letter, we present experimental results that demonstrate new entropic effects at surfaces. In particular, the behavior of particles confined within vesicles reveals quantitatively the striking effect of membrane curvature. We first discuss experiments probing the behavior of a microscopic sphere trapped inside a rigid, phospholipid vesicle. Adding much smaller spheres to the mixture changes the distribution of the larger sphere in a way that depends on the curvature of the vesicle wall (see Fig. 1(b) and (c)). The results are consistent with the depletion force theory and illustrate a new mechanism for the size-dependent arrangement of particles within pores. We then explore theoretically some consequences of replacing the rigid wall with a flexible one. The entropic curvature effects can overcome the membrane's stiffness, leading to a new mechanism for shape changes in vesicles.We first briefly review depletion effects in mixtures of microscopic hard spheres of two different sizes. Moving two of the larger spheres toward one another does not change their interaction energy (which is zero for hard spheres) but does increase the volume accessible to the other particles (Fig. 2). The resulting gain in entropy reduces the free energy of the system by (3/2)αφ S k B T [11,12]. Here, α is the ratio of large to small radii (R L /R S ), φ S is the small-sphere volume fraction, and k B T is Boltzmann's constant times the absolute temperature. This simple result relies on the approximation that the small spheres are a structurel...

A novel nanoparticle label capable of amplifying the electrochemical signal of DNA hybridization is fabricated by functionalizing poly(styrene‐co‐acrylic acid) microbeads with CdTe quantum dots. CdTe‐tagged polybeads are prepared by a layer‐by‐layer self‐assembly of the CdTe quantum dots (diameter = 3.07 nm) and polyelectrolyte on the polybeads (diameter = 323 nm). The self‐assembly procedure is characterized using scanning and transmission electron microscopy, and X‐ray photoelectron, infrared and photoluminescence spectroscopy. The mean quantum‐dot coverage is (9.54 ± 1.2) × 103 per polybead. The enormous coverage and the unique properties of the quantum dots make the polybeads an effective candidate as a functionalized amplification platform for labelling of DNA or protein. Herein, as an example, the CdTe‐tagged polybeads are attached to DNA probes specific to breast cancer by streptavidin–biotin binding to construct a DNA biosensor. The detection of the DNA hybridization process is achieved by the square‐wave voltammetry of Cd2+ after the dissolution of the CdTe tags with HNO3. The efficient carrier‐bead amplification platform, coupled with the highly sensitive stripping voltammetric measurement, gives rise to a detection limit of 0.52 fmol L−1 and a dynamic range spanning 5 orders of magnitude. This proposed nanoparticle label is promising, exhibits an efficient amplification performance, and opens new opportunities for ultrasensitive detection of other biorecognition events.

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This review focusses on unique material modification and signal amplification strategies reported in developing photoelectrochemical (PEC) biosensors with utmost sensitivity and selectivity. These successes have partly been achieved by applying...

In this study, our goal was to produce a self-assembled layer on a gold electrode that would enable the capture of antibodies orientated for maximum binding to their specific antigen in an immunosensor. To achieve this, the amine groups from lysine residues in protein G were initially converted to thiol groups with 2-iminothiolane. The high affinity of thiols for a gold surface facilitates the direct formation of a self-assembled protein G layer. Following this, the coated gold electrode was exposed to a solution of capture antibody (mAb1) so that these antibodies could attach to the protein G layer through their nonantigenic regions, leaving antigen binding sites available with minimal steric hindrance for binding of target analyte. A comparative study between this method and the more conventional strategy of covalently attaching a layer of nonthiolated protein G on an alkanethiol self-assembled monolayer-coated gold electrode has been performed. Based on a reduced preparation time, and an enhanced capacity for immobilized capture antibody to bind its target analyte due to a more favorable orientation, the layer of thiolated protein G was found to be a more suitable backbone for an electrochemical immunosensor.

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The development of an amperometric immunosensor for the detection of human chorionic gonadotrophin (hCG) is described. In this immunosensor, Nafion was used to immobilize an anti-hCG monoclonal antibody onto a glassy carbon electrode. A systematic study on the effects of experimental parameters such as the quantity of ethanol present in the Nafion solution, the percentage composition of Nafion, the pH of the immobilization buffer, and the concentration of antibody used for entrapment experiments on the binding between the immobilized antibody and 125I-labeled hCG has been carried out. Two immobilization methods, coimmobilization and adsorption immobilization, have then been attempted. A binding of approximately 3% was obtained in the former method, while 5.5% binding was achieved in the latter. On the basis of these results, adsorption immobilization was employed to entrap antibody on the electrode surface. A sandwich assay was then developed for hCG in which the enzyme horseradish peroxidase was conjugated to a second anti-hCG monoclonal antibody. The activity of the enzyme was determined electrochemically by the reduction of benzoquinone to hydroquinone. Binding of hCG to immobilized antibody determines the quantity of enzyme-conjugated antibody at the electrode surface, permitting the quantification of hCG. By a standard additions calibration method of hCG performed in blank human serum samples, the immunosensor exhibits a limit of linearity at 200 mIU mL-1 and a detection limit of 11.2 mIU mL-1 (based on twice the standard deviation of the blank solution).