Interactions of adsorbed albumin with underpotentially deposited copper on gold piezoelectrodes

Adsorption and Interaction of Bovine Serum Albumin and Pluronic P103 Triblock Copolymer on a Gold Electrode: Double-Layer Capacitance Measurements

The interactions of proteins and other molecules and their adsorption onto substrates is a fascinating topic that has been applied to surface technologies, biosensors, corrosion studies, biotechnologies, and other fields. The success of these applications requires a previous characterization using some analytical techniques that, ordinarily, are not electrochemical. This work proposes analyzing the variation of the double-layer capacitance obtained through impedance electrochemical spectroscopy as an alternative strategy to show evidence of the interactions between proteins and triblock copolymers. The proposal is supported through the study of the interaction and adsorption of bovine serum albumin (BSA) and a commercial triblock copolymer (P103) in phosphate buffer on a gold electrode. The double-layer capacitance and the apparent interface thickness vs polarization potential curves as well as the potential of zero charge for pure P103 (0.6 wt %, corresponding to 6 g L^-1), pure BSA (3 mg mL^-1), and P103-BSA solutions (0.6 wt % and 3 mg mL^-1, respectively) are sensitive enough to show not only the interaction and the adsorption of the species but also the polarization potential where these interactions are taking place. A qualitative and quantitative analysis concerning the double-layer capacitance behavior is given. The significance and impact of this work is also presented.

Formation of 3-Dimensional Gold, Copper and Palladium Microelectrode Arrays for Enhanced Electrochemical Sensing Applications

Microelectrodes offer higher current density and lower ohmic drop due to increased radial diffusion. They are beneficial for electroanalytical applications, particularly for the detection of analytes at trace concentrations. Microelectrodes can be fabricated as arrays to improve the current response, but are presently only commercially available with gold or platinum electrode surfaces, thus limiting the sensing of analytes that are more electroactive on other surfaces. In this work, gold (Au), copper (Cu), and palladium (Pd) are electrodeposited at two different potentials into the recessed holes of commercial microelectrode arrays to produce 3-dimensional (3D) spiky, dendritic or coral-like structures. The rough fractal structures that are produced afford enhanced electroactive surface area and increased radial diffusion due to the 3D nature, which drastically improves the sensitivity. 2,4,6-trinitrotoluene (TNT), carbon dioxide gas (CO₂), and hydrogen gas (H₂) were chosen as model analytes in room temperature ionic liquid solvents, to demonstrate improvements in the sensitivity of the modified microelectrode arrays, and, in some cases (e.g., for CO₂ and H₂), enhancements in the electrocatalytic ability. With the deposition of different materials, we have demonstrated enhanced sensitivity and electrocatalytic behaviour towards the chosen analytes.

Ratiometric fluorescent sensor for visual determination of copper ions and alkaline phosphatase based on carbon quantum dots and gold nanoclusters

In this work, a novel ratiometric fluorescent sensor, based on carbon dots (CDs) and gold nanoclusters (AuNCs), is developed for highly sensitive and selective visual colorimetric detection of Cu²⁺ and alkaline phosphatase (ALP). The ratiometric fluorescent sensor was synthesized by covalently linking 11-mercaptoundecanoic acid (11-MUA)-stabilized AuNCs to the surface of amino-functionalized CD/SiO₂ nanoparticles. The red fluorescence of the AuNCs can be quenched by Cu²⁺ owing to coordination between Cu²⁺ and 11-MUA; however, the blue emission of the CDs was insensitive to Cu²⁺ owing to the protective silica shell. The quenching of the AuNCs' fluorescence returned when PPi was added because of the higher affinity between Cu²⁺ and PPi than that between Cu²⁺ and 11-MUA. In the presence of ALP, PPi was catalytically hydrolyzed into phosphate (Pi), which showed a much weaker affinity for Cu²⁺. Thus, Cu²⁺ ions were released, and the fluorescence of the AuNCs was quenched once more. Based on this principle, Cu²⁺ and ALP could be simultaneously detected. The developed ratiometric fluorescent sensor could detect Cu²⁺ over a range from 0.025 to 4 μM with a detection limit of 0.013 μM and ALP over a range from 0.12 to 15 U/L with a detection limit of 0.05 U/L. The present method was successfully applied for the detection of Cu²⁺ and ALP in real water samples and in human serum samples, respectively. This ratiometric fluorescent approach may provide a highly sensitive and accurate platform for visual Cu²⁺ and ALP sensing in environmental monitoring and medical diagnosis.

A flexible and highly sensitive nonenzymatic glucose sensor based on DVD-laser scribed graphene substrate

Flexible and implantable glucose biosensors are emerging technologies for continuous monitoring of blood-glucose of diabetes. Developing a flexible conductive substrates with high active surface area is critical for advancing the technology. Here, we successfully fabricate a flexible and highly sensitive nonenzymatic glucose by using DVD-laser scribed graphene (LSG) as a flexible conductively substrate. Copper nanoparticles (Cu-NPs) are electrodeposited as the catalyst. The LSG/Cu-NPs sensor demonstrates excellent catalytic activity toward glucose oxidation and exhibits a linear glucose detection range from 1 μM to 4.54 mM with high sensitivity (1.518 mA mM^-1 cm^-2) and low limit of detection (0.35 μM). Moreover, the LSG/Cu-NPs sensor shows excellent reproducibility and long-term stability. It is also highly selective toward glucose oxidation under the presence of various interfering species. Excellent flexing stability is also demonstrated by the LSG/Cu-NPs sensor, which is capable of maintaining 83.9% of its initial current after being bent against a 4-mm diameter rod for 180 times. The LSG/Cu-NPs sensor shows great potential for practical application as a nonenzymatic glucose biosensor. Meanwhile, the LSG conductive substrate provides a platform for the developing next-generation flexible and potentially implantable bioelectronics and biosensors.

Piezometric biosensors for anti-apoptotic protein survivin based on buried positive-potential barrier and immobilized monoclonal antibodies

The anti-apoptotic protein survivin (Sur) plays an important role in the regulation of cell division and inducing the chemotherapeutic drug resistance. The Sur protein and its mRNA have recently been studied as cancer biomarkers and potential targets for cancer therapy. In this work, we have focused on the design of immunosensors for the detection of Sur based on buried positive-potential barrier layer structure and anti-survivin antibody. The modification of solid AuQC piezoelectrodes was monitored by recording the resonance frequency shift and electrochemical measurements during each step of the sensor preparation. Our results indicate that the immunosensor with covalently bound monoclonal anti-survivin antibody can detect Sur with the limit of detection, LOD=1.7nM (S/N=3σ). The immunosensor applicability for the analysis of real samples was assessed by testing samples of cell lysate solutions obtained from human astrocytoma (glioblastoma) U-87MG cell line, with the experiments performed using the standard addition method. The good linearity of the calibration curves for PBS and lysate solutions at low Sur concentrations confirm the high specificity of the proposed biosensor and good discrimination against nonspecific interactions with lysate components. The calculations indicate that there is still room to increase the Sur capture capacity for Sur while miniaturizing the sensor. The important advantage of the sensor is that it can be reused by a simple regeneration procedure.